Patent Application
20230102430
The present disclosure relates to a light source module.
The present application claims the benefit of priority under Japanese Patent Application No. 2020-006906, filed on Jan. 20, 2020, Japanese Patent Application No. 2020-006907, filed on Jan. 20, 2020, and Japanese Patent Application No. 2020-160719, filed on Sep. 25, 2020, the contents of each of which are relied upon and incorporated herein by reference in their entireties.
Patent Document 1 discloses a technique related to an edge-emitting semiconductor laser element. This semiconductor laser element includes a lower cladding layer formed on a substrate, an upper cladding layer, an active layer interposed between the lower cladding layer and the upper cladding layer, a photonic crystal layer interposed at least between the active layer and the upper cladding layer or between the active layer and the lower cladding layer, and a first drive electrode for supplying a drive current to a first region of the active layer. A longitudinal direction of the first drive electrode is inclined with respect to a normal line of a light output end face of the semiconductor laser element when viewed from a thickness direction of the semiconductor laser element. A region corresponding to the first region of the photonic crystal layer has first and second periodic structures in which arrangement periods of different refractive index portions having refractive indexes different from surroundings are different from each other. Two or more laser beams forming a predetermined angle with respect to the longitudinal direction of the first drive electrode are generated inside the semiconductor laser element according to a difference between the reciprocals of the arrangement periods in the first and second periodic structures. Among these laser beams, a refraction angle of one laser beam directed to the light output end face with respect to the light output end face is less than 90 degrees. The other at least one laser beam directed to the light output end face meets a total reflection critical angle condition with respect to the light output end face.
Non-Patent Document 1 discloses a technique related to a computer-generated hologram (CGH). One pixel is constituted by four subpixels each having an independent reflectance, which are created by printing, and reflected laser light beams emitted to a plurality of pixels are combined. In this case, Non-Patent Document 1 describes that a light emission direction from each pixel can be arbitrarily shifted. Non-Patent Document 2 describes that, in the technique described in Non-Patent Document 1, when each pixel includes three subpixels each having an independent reflectance, the light emission direction from each pixel can be arbitrarily shifted.
As a result of studying the above-described technique of the related art, the inventors have found the following problems. That is, in the related art, a technique of changing a light traveling direction or generating an arbitrary optical image by performing spatial phase modulation have been studied. In a certain technique, a phase modulation layer including a plurality of modified refractive index regions is provided in the vicinity of an active layer of a semiconductor laser element. Then, in a virtual square lattice set on a plane perpendicular to a thickness direction of the phase modulation layer, for example, with respect to a plurality of the modified refractive index regions, the gravity center of each of the modified refractive index regions is disposed at a position away from a lattice point of the virtual square lattice, and an angle of a vector connecting the corresponding lattice point with the gravity center with respect to the virtual square lattice is individually set. Like a photonic crystal laser element, such an element can output laser light beam in a stacking direction, spatially control a phase distribution of the laser light beam, and output the laser light beam as an arbitrary optical image.
However, in the above-described element, since the arrangement of a plurality of the modified refractive index regions of the phase modulation layer is fixed, only one optical image designed in advance can be outputted. In order to dynamically change the output optical image and the light traveling direction, it is necessary to dynamically control the phase distribution of the output light.
The present disclosure has been made to solve the above-described problems, and an object of the present disclosure is to provide a light source module capable of dynamically controlling a phase distribution of light.
A light source module according to an aspect of the present disclosure includes a semiconductor stack portion, a first electrode, a second electrode, a third electrode, and a fourth electrode. The semiconductor stack portion includes a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, and a stacked body including an active layer and a photonic crystal layer. The stacked body including the active layer and the photonic crystal layer is disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer. The photonic crystal layer causes oscillation at a Γ point. The semiconductor stack portion includes a phase synchronization portion and an intensity modulation portion which are arranged in a first direction which is one of resonance directions of the photonic crystal layer. A portion of the stacked body constituting at least a part of the intensity modulation portion has M (M is an integer of two or more) pixels arranged in a second direction intersecting the first direction. Each of the M pixels includes N1 (N1 is an integer of two or more) subpixels arranged in the second direction. A length of a region including consecutive N2 (N2 is an integer of two or more and N1 or less) subpixels among the N1 subpixels, which is defined in the second direction, is smaller than an emission wavelength λ of the active layer. The first electrode is electrically connected to a portion of the first conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The second electrode is electrically connected to a portion of the second conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The third electrode is provided in one-to-one correspondence with the N1 subpixels, and is electrically connected to one of a portion of the first conductivity type semiconductor layer and a portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The fourth electrode is electrically connected to the other one of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The light source module outputs light from each of the M pixels included in the intensity modulation portion in a direction intersecting both the first direction and the second direction.
A light source module according to another aspect of the present disclosure includes a semiconductor stack portion, a first electrode, a second electrode, a third electrode, and a fourth electrode. The semiconductor stack portion includes a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, and a stacked body including an active layer and a resonance mode forming layer. The stacked body including the active layer and the resonance mode forming layer is disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer. The semiconductor stack portion includes a phase synchronization portion and an intensity modulation portion which are arranged in a first direction which is one of resonance directions of the resonance mode forming layer. A portion of the stacked body constituting at least a part of the intensity modulation portion has M (M is an integer of two or more) pixels arranged in a second direction intersecting the first direction. Each of the M pixels includes N1 (N1 is an integer of two or more) subpixels arranged in the second direction. A length of a region including consecutive N2 (N2 is an integer of two or more and N1 or less) subpixels among the N1 subpixels, which is defined in the second direction, is smaller than an emission wavelength λ of the active layer. The first electrode is electrically connected to a portion of the first conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The second electrode is electrically connected to a portion of the second conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The third electrode is provided in one-to-one correspondence with the N1 subpixels, and is electrically connected to one of a portion of the first conductivity type semiconductor layer and a portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The fourth electrode is electrically connected to the other one of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The resonance mode forming layer includes a base layer and a plurality of modified refractive index regions having a refractive index different from a refractive index of the base layer and distributed two-dimensionally on a plane perpendicular to a thickness direction of the resonance mode forming layer. The arrangement of a plurality of the modified refractive index regions satisfies a condition of M-point oscillation. In the portion of the resonance mode forming layer included in the intensity modulation portion, in the virtual square lattice set on the plane, the gravity center of each of a plurality of the modified refractive index regions is disposed in any one of a first mode and a second mode. In the first mode, the gravity center of each of a plurality of the modified refractive index regions is disposed away from the corresponding lattice point, and an angle of a vector connecting the corresponding lattice point with the gravity center with respect to the virtual square lattice is individually set. In the second mode, the gravity center of each of a plurality of the modified refractive index regions is disposed on a straight line passing through the lattice point of the virtual square lattice and inclined with respect to the square lattice, and a distance between the gravity center of each of a plurality of the modified refractive index regions and the corresponding lattice point is individually set. The distribution of the angle of the vector in the first mode or the distribution of the distance in the second mode satisfies a condition for outputting light from the intensity modulation portion in a direction intersecting both the first direction and the second direction.
According to the present disclosure, it is possible to provide a light source module capable of dynamically controlling a phase distribution of light.
First, the contents of the embodiment of the present invention will be individually listed and described.
(1) A first light source module according to an aspect of the present disclosure includes a semiconductor stack portion, a first electrode, a second electrode, a third electrode, and a fourth electrode.
The semiconductor stack portion includes a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, and a stacked body including an active layer and a photonic crystal layer. The stacked body including the active layer and the photonic crystal layer is disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer. The photonic crystal layer causes oscillation at a Γ point. The semiconductor stack portion includes a phase synchronization portion and an intensity modulation portion which are arranged in a first direction which is one of resonance directions of the photonic crystal layer. A portion of the stacked body constituting at least a part of the intensity modulation portion has M (M is an integer of two or more) pixels arranged in a second direction intersecting the first direction. Each of the M pixels includes N1 (N1 is an integer of two or more) subpixels arranged in the second direction. A length of a region including consecutive N2 (N2 is an integer of two or more and N1 or less) subpixels among the N1 subpixels, which is defined in the second direction, is smaller than an emission wavelength λ of the active layer. The first electrode is electrically connected to a portion of the first conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The second electrode is electrically connected to a portion of the second conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The third electrode is provided in one-to-one correspondence with the N1 subpixels, and is electrically connected to one of a portion of the first conductivity type semiconductor layer and a portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The fourth electrode is electrically connected to the other one of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The light source module outputs light from each of the M pixels included in the intensity modulation portion in a direction intersecting both the first direction and the second direction.
In the first light source module, when a current is supplied between the first electrode and the second electrode, and between the third electrode and the fourth electrode, the active layers included in the phase synchronization portion and the intensity modulation portion emit light. The light outputted from the active layer enters the photonic crystal layer, and resonates in two directions including the first direction, which are perpendicular to the thickness direction in the photonic crystal layer. This light becomes a phase-aligned coherent laser light beam in the photonic crystal layer of the phase synchronization portion.
Furthermore, since the photonic crystal layer included in the intensity modulation portion is arranged in the first direction with respect to the photonic crystal layer included in the phase synchronization portion, a phase of the laser light beam in the photonic crystal layer of each subpixel coincides with a phase of the laser light beam in the photonic crystal layer of the phase synchronization portion, and as a result, the phases of the laser light beams in the photonic crystal layer are aligned between the subpixels. Since the photonic crystal layer causes Γ-point oscillation, the phase-aligned laser light beam is outputted from each subpixel included in the intensity modulation portion in a direction intersecting both the first direction and the second direction (typically, the thickness direction of the intensity modulation portion).
The third electrode is provided in one-to-one correspondence with each subpixel. Therefore, the magnitude of the current supplied to the intensity modulation portion can be individually adjusted for each subpixel. That is, light intensity of the laser light beam outputted from the intensity modulation portion can be adjusted individually (independently) for each subpixel. Furthermore, in the first light source module, in each pixel, a length of the region including consecutive N2 subpixels among the N1 subpixels in the second direction (that is, the arrangement direction of the subpixels) is smaller than the emission wavelength λ, of the active layer, that is, the wavelength of the laser light beam. In a case where the subpixels that output light at the same time are limited to the consecutive N2 subpixels among the N1 subpixels constituting each pixel, each pixel can be regarded as a pixel having a single phase equivalently. In a case where the phases of the laser light beams outputted from the N1 subpixels constituting each pixel are aligned with each other, the phase of the laser light beam outputted from each pixel is determined according to an intensity distribution realized by the N1 subpixels constituting the pixel. Therefore, according to the first light source module, the phase distribution of the light can be dynamically controlled.
(2) A second light source module according to an aspect of the present disclosure includes a semiconductor stack portion, a first electrode, a second electrode, a third electrode, and a fourth electrode. The semiconductor stack portion includes a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, and a stacked body including an active layer and a resonance mode forming layer. The stacked body including the active layer and the resonance mode forming layer is disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer. The semiconductor stack portion includes a phase synchronization portion and an intensity modulation portion which are arranged in a first direction which is one of resonance directions of the resonance mode forming layer. A portion of the stacked body constituting at least a part of the intensity modulation portion has M (M is an integer of two or more) pixels arranged in a second direction intersecting the first direction. Each of the M pixels includes N1 (N1 is an integer of two or more) subpixels arranged in the second direction. A length of a region including consecutive N2 (N2 is an integer of two or more and N1 or less) subpixels among the N1 subpixels, which is defined in the second direction, is smaller than an emission wavelength λ of the active layer. The first electrode is electrically connected to a portion of the first conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The second electrode is electrically connected to a portion of the second conductivity type semiconductor layer constituting at least a part of the phase synchronization portion. The third electrode is provided in one-to-one correspondence with the N1 subpixels, and is electrically connected to one of a portion of the first conductivity type semiconductor layer and a portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The fourth electrode is electrically connected to the other one of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. The resonance mode forming layer includes a base layer and a plurality of modified refractive index regions having a refractive index different from a refractive index of the base layer and distributed two-dimensionally on a plane perpendicular to a thickness direction of the resonance mode forming layer. The arrangement of a plurality of the modified refractive index regions satisfies a condition of M-point oscillation. In the portion of the resonance mode forming layer included in the intensity modulation portion, in the virtual square lattice set on the plane, the gravity center of each of a plurality of the modified refractive index regions is disposed in any one of a first mode and a second mode. In the first mode, the gravity center of each of a plurality of the modified refractive index regions is disposed away from the corresponding lattice point, and an angle of a vector connecting the corresponding lattice point with the gravity center with respect to the virtual square lattice is individually set. In the second mode, the gravity center of each of a plurality of the modified refractive index regions is disposed on a straight line passing through the lattice point of the virtual square lattice and inclined with respect to the square lattice, and a distance between the gravity center of each of a plurality of the modified refractive index regions and the corresponding lattice point is individually set. The distribution of the angle of the vector in the first mode or the distribution of the distance in the second mode satisfies a condition for outputting light from the intensity modulation portion in a direction intersecting both the first direction and the second direction.
In the second light source module, when a current is supplied between the first electrode and the second electrode, and between the third electrode and the fourth electrode, the active layers of the phase synchronization portion and the intensity modulation portion emit light. The light outputted from the active layer enters the resonance mode forming layer, and resonates in two directions including the first direction, which are perpendicular to the thickness direction in the resonance mode forming layer. This light becomes a phase-aligned coherent laser light beam in the resonance mode forming layer of the phase synchronization portion. Furthermore, since each resonance mode forming layer of the intensity modulation portion divided into a plurality of the subpixels is arranged in the first direction with respect to the resonance mode forming layer of the phase synchronization portion, the phase of the laser light beam in the resonance mode forming layer of each subpixel coincides with the phase of the laser light beam in the resonance mode forming layer of the phase synchronization portion, and as a result, the phases of the laser light beams in the resonance mode forming layer are aligned between the subpixels.
The resonance mode forming layer of the second light source module causes the M-point oscillation, but in a portion of the resonance mode forming layer included in the intensity modulation portion, a distribution form of a plurality of the modified refractive index regions satisfies a condition for light to be outputted from the intensity modulation portion in a direction intersecting both the first direction and the second direction. Therefore, the phase-aligned laser light beam is outputted from each subpixel included in the intensity modulation portion in a direction intersecting both the first direction and the second direction.
The third electrode is provided in one-to-one correspondence with each subpixel. Therefore, the magnitude of the current supplied to the intensity modulation portion can be individually adjusted for each subpixel. That is, light intensity of the laser light beam outputted from the intensity modulation portion can be adjusted individually (independently) for each subpixel. Furthermore, also in the second light source module, in each pixel, a length of the region including consecutive N2 subpixels among the N1 subpixels in the second direction (that is, the arrangement direction of the subpixels) is smaller than the emission wavelength λ of the active layer, that is, the wavelength of the laser light beam. In a case where the subpixels that output light at the same time are limited to the consecutive N2 subpixels among the N1 subpixels constituting each pixel, each pixel can be regarded as a pixel having a single phase equivalently. In a case where the phases of the laser light beams outputted from the N1 subpixels constituting each pixel are aligned with each other, the phase of the laser light beam outputted from each pixel is determined according to an intensity distribution realized by the N1 subpixels constituting the pixel. Therefore, according to the second light source module, the phase distribution of the light can be dynamically controlled.
(3) As an aspect of the present disclosure, in the second light source module, a portion of the resonance mode forming layer included in the phase synchronization portion may have a photonic crystal structure in which a plurality of the modified refractive index regions are periodically disposed. In this case, the phase-aligned laser light beam can be supplied from the phase synchronization portion to each subpixel.
(4) As an aspect of the present disclosure, in the second light source module, a condition for light to be outputted in a direction intersecting both the first direction and the second direction from the intensity modulation portion may be that in-plane wave number vectors in four directions each including a wave number spread corresponding to angular spread of the light outputted from the intensity modulation portion are formed on an reciprocal lattice space of the resonance mode forming layer, and the magnitude of at least one in-plane wave number vector among the in-plane wave number vectors in four directions is smaller than 2π/λ.
(5) As an aspect of the present disclosure, in the first light source module, the photonic crystal layer may include a phase shift portion provided in one-to-one correspondence with the N1 subpixels, the phase shift portion being configured to cause the phases of light outputted from each pixel in the first direction to be different from each other between the N1 subpixels. Similarly, as an aspect of the present disclosure, in the second light source module, the resonance mode forming layer may include a phase shift portion provided in one-to-one correspondence with the N1 subpixels, the phase shift portion being configured to cause the phases of light outputted from each pixel in the first direction to be different from each other between the N1 subpixels. In this case, the phase of the laser light beam outputted from each pixel in the first direction is different for each subpixel. Therefore, the phase of the laser light beam outputted from each pixel in a direction intersecting both the first direction and the second direction is also different for each subpixel. The phase of the laser light beam outputted from each pixel is determined according to the intensity distribution and the phase distribution of the N1 subpixels constituting the pixel. In this case, it is possible to dynamically modulate the phase distribution of the light in an output direction intersecting both the first direction and the second direction, and the degree of freedom of controlling the phase distribution of the light is further increased.
(6) As an aspect of the present disclosure, in the first and second light source modules, the first electrode may be in contact with the first conductivity type semiconductor layer and cover the entire surface of the portion of the first conductivity type semiconductor layer included in the phase synchronization portion. Furthermore, the second electrode may be in contact with the second conductivity type semiconductor layer and cover the entire surface of the second conductivity type semiconductor layer included in the phase synchronization portion. In this case, the laser light beam outputted from the phase synchronization portion in the stacking direction is shielded by the first electrode and the second electrode. In particular, in the first light source module, the photonic crystal layer of the phase synchronization portion causes Γ-point oscillation, and thus such shielding by the first electrode and the second electrode is effective.
(7) As an aspect of the present disclosure, in the first and second light source modules, the third electrode may be in contact with one of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. Furthermore, the fourth electrode may have a frame shape surrounding an opening for allowing light to pass, and may be in contact with the other one of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute at least a part of the intensity modulation portion. In this case, while a sufficient current is supplied to the active layer of the intensity modulation portion, the laser light beam can be outputted from the intensity modulation portion in a direction intersecting both the first direction and the second direction.
(8) As an aspect of the present disclosure, in the first and second light source modules, the semiconductor stack portion may include a plurality of slits. The subpixels and a plurality of the slits are alternately arranged one by one in the second direction. In this case, the intensity modulation portion can be divided into a plurality of subpixels with a simple configuration.
(9) As an aspect of the present disclosure, in the first and second light source modules, both the number N1 and the number N2, which are described above, may be three or more. In this case, the phase of the laser light beam outputted from each pixel can be controlled in a range of 0° to 360°.
As described above, each aspect listed in the section of [Description of embodiments of present invention] is applicable to each of all the remaining aspects or to all combinations of these remaining aspects.
Hereinafter, a specific structure of the light source module according to the embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope of the invention. Furthermore, in the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description will be omitted.
The main surface 11a and the back surface 11b of the semiconductor substrate 11 are flat and parallel to each other. The semiconductor substrate 11 is used for epitaxially growing a plurality of the semiconductor layers of the semiconductor stack portion 10. In a case where a plurality of the semiconductor layers of the semiconductor stack portion 10 are GaAs-based semiconductor layers, the semiconductor substrate 11 is, for example, a GaAs substrate. In a case where a plurality of the semiconductor layers of the semiconductor stack portion 10 are InP-based semiconductor layers, the semiconductor substrate 11 is, for example, an InP substrate. In a case where a plurality of the semiconductor layers of the semiconductor stack portion 10 are GaN-based semiconductor layers, the semiconductor substrate 11 is, for example, a GaN substrate. A thickness of the semiconductor substrate 11 is, for example, in a range of 50 μm to 1000 μm. The semiconductor substrate 11 has p-type or n-type conductivity. A planar shape of the main surface 11a is, for example, a rectangular or square shape.
The first cladding layer 12 is a semiconductor layer formed on the main surface 11a of the semiconductor substrate 11 by epitaxial growth. The first cladding layer 12 has the same conductivity type as that of the semiconductor substrate 11. The semiconductor substrate 11 and the first cladding layer 12 constitute the first conductivity type semiconductor layer in the present disclosure. The first cladding layer 12 may be directly provided on the main surface 11a by epitaxial growth, or may be provided on the main surface 11a via a buffer layer provided between the main surface 11a and the first cladding layer 12. The active layer 13 is a semiconductor layer formed on the first cladding layer 12 by epitaxial growth. The active layer 13 generates light by receiving supply of a current. The photonic crystal layer 14 is a semiconductor layer formed on the active layer 13 by epitaxial growth. The second cladding layer 15 is a semiconductor layer formed on the photonic crystal layer 14 by epitaxial growth. The contact layer 16 is a semiconductor layer formed on the second cladding layer 15 by epitaxial growth. The second cladding layer 15 and the contact layer 16 have a conductivity type opposite to that of the first cladding layer 12. The second cladding layer 15 and the contact layer 16 constitute the second conductivity type semiconductor layer in the present disclosure.
A refractive index of the active layer 13 is greater than refractive indexes of the first cladding layer 12 and the second cladding layer 15, and a band gap of the active layer 13 is smaller than band gaps of the first cladding layer 12 and the second cladding layer 15. The photonic crystal layer 14 may be provided between the first cladding layer 12 and the active layer 13 or between the active layer 13 and the second cladding layer 15. Another semiconductor layer (for example, an optical confinement layer) may be further provided between the active layer 13 and photonic crystal layer 14 and the first cladding layer 12, between the active layer 13 and photonic crystal layer 14 and the second cladding layer 15, or both.
The photonic crystal layer 14 has a two-dimensional diffraction lattice. The photonic crystal layer 14 includes a base layer 14a and a plurality of modified refractive index regions 14b provided inside the base layer 14a. Refractive indexes of the modified refractive index regions 14b are different from the refractive index of the base layer 14a. The modified refractive index regions 14b are disposed at constant intervals in the X-direction and the Y-direction in the base layer 14a. Each of the modified refractive index regions 14b may be a hole, or may be configured by embedding a semiconductor having a refractive index different from that of the base layer 14a in the hole. The planar shape of each of the modified refractive index regions 14b may be various shapes such as a circular shape, a polygonal shape (triangle, quadrangle, and the like), and an elliptical shape.
The modified refractive index regions 14b are disposed at intervals so as to satisfy a condition off-point oscillation with respect to the emission wavelength of the active layer 13.
The semiconductor stack portion 10 includes the phase synchronization portion 17 and the intensity modulation portion 18. The phase synchronization portion 17 and the intensity modulation portion 18 are arranged in a Y-direction (first direction) which is one of the resonance directions of the photonic crystal layer 14. In one example, the phase synchronization portion 17 and the intensity modulation portion 18 are adjacent to each other in the Y-direction. Another portion may be interposed between the phase synchronization portion 17 and the intensity modulation portion 18. The planar shapes of the phase synchronization portion 17 and the intensity modulation portion 18 are, for example, rectangular or square. In one example, the phase synchronization portion 17 and the intensity modulation portion 18 have a pair of sides facing each other in the X-direction and a pair of sides facing each other in the Y-direction. One side of the phase synchronization portion 17 on the intensity modulation portion 18 side in the X-direction and one side of the intensity modulation portion 18 on the phase synchronization portion 17 side in the X-direction face each other while being separated from each other or coincide with each other. In the example illustrated in
As illustrated in
Each pixel Pa includes N1 (N1 is an integer of two or more) subpixels Pb arranged in the arrangement direction (for example, the X-direction) of the pixel Pa.
The semiconductor stack portion 10 further includes a plurality of the slits S. Each of the slits S is a groove formed in the semiconductor stack portion 10 and is a gap. The slits S extend in the Y-direction and in the Z-direction which is a depth direction, and the subpixels Pb and the slits S are alternately disposed one by one in the arrangement direction of the subpixels Pb (for example, the X-direction). Therefore, the slit S is located between the subpixels Pb adjacent to each other. Note that the slit S may not be a gap, and may be filled with, for example, a material having a higher resistance and a higher refractive index than the active layer 13 and the photonic crystal layer 14. The intensity modulation portion 18 is optically and electrically divided into a plurality of the subpixels Pb by the slit S. A width of each slit S defined in the arrangement direction of the subpixels Pb is less than λ/N1, and an interval between the adjacent slits S (that is, a width of each subpixel Pb in the arrangement direction) is less than λ/N1.
The first electrode 21 and the second electrode 22 are metal electrodes provided in the phase synchronization portion 17. The first electrode 21 is electrically connected to the contact layer 16 of the phase synchronization portion 17. In the present embodiment, the first electrode 21 is an ohmic electrode in contact with a surface of the contact layer 16 of the phase synchronization portion 17, and covers the entire surface of the contact layer 16 of the phase synchronization portion 17. The second electrode 22 is electrically connected to the semiconductor substrate 11 of the phase synchronization portion 17. In the present embodiment, the second electrode 22 is an ohmic electrode in contact with the back surface 11b of the semiconductor substrate 11 of the phase synchronization portion 17, and covers the entire back surface 11b of the semiconductor substrate 11 of the phase synchronization portion 17. Note that the present invention is not limited to this example, and the first electrode 21 may cover only a part of the surface of the contact layer 16 of the phase synchronization portion 17, and the second electrode 22 may cover only a part of the back surface 11b of the semiconductor substrate 11 of the phase synchronization portion 17. The second electrode 22 may be in ohmic contact with the first cladding layer 12 instead of the semiconductor substrate 11.
The third electrode 23 and the fourth electrode 24 are metal electrodes provided in the intensity modulation portion 18. The third electrode 23 is electrically connected to the contact layer 16 of the intensity modulation portion 18. In one example, the third electrode 23 is an ohmic electrode in contact with the surface of the contact layer 16 of the intensity modulation portion 18. The third electrode 23 is provided in one-to-one correspondence with each subpixel Pb. That is, M×N1 third electrodes 23 are provided on the contact layer 16 in correspondence with the respective subpixels Pb. A planar shape of each of the third electrodes 23 is similar to the planar shape of each subpixel Pb, and is, for example, a rectangular shape of which a longitudinal direction thereof coincides with the Y-direction.
The fourth electrode 24 is electrically connected to the semiconductor substrate 11 of the intensity modulation portion 18. In one example, the fourth electrode 24 is an ohmic electrode in contact with the back surface 11b of the semiconductor substrate 11 of the intensity modulation portion 18. The fourth electrode 24 has an opening 24a through which the laser light beam L outputted from the intensity modulation portion 18 passes. A planar shape of the fourth electrode 24 is a rectangular or square frame shape surrounding the opening 24a. The laser light beam L is outputted from each pixel Pa in a direction intersecting both the X-direction and the Y-direction (for example, the Z-direction).
The antireflection film 25 is provided inside the opening 24a of the fourth electrode 24 on the back surface 11b, and prevents the laser light beam L to be outputted from the semiconductor substrate 11 from being reflected by the back surface lib. The antireflection film 25 is comprised of an inorganic material such as a silicon compound.
The conductivity type of the semiconductor substrate 11 and the first cladding layer 12 is, for example, n-type. The conductivity type of the second cladding layer 15 and the contact layer 16 is, for example, p-type. A specific example of the light source module 1A will be described below.
The semiconductor substrate 11: n-type GaAs substrate (thickness of about 150 μm)
The first cladding layer 12: n-type AlGaAs (refractive index: 3.39, thickness: 0.5 μm or greater and 5 μm or less)
The active layer 13: InGaAs/AlGaAs multiple quantum well structure (thickness of InGaAs layer: 10 nm, thickness of AlGaAs layer: 10 nm, and 3 periods)
The second cladding layer 15: p-type AlGaAs (refractive index: 3.39, thickness: 0.5 μm or greater and 5 μm or less)
The contact layer 16: p-type GaAs (thickness 0.05 μm or greater and 1 μm or less)
The base layer 14a: i-type GaAs (thickness 0.1 μm or greater and 2 μm or less)
The modified refractive index region 14b: pores, arrangement period: 282 nm
The first electrode 21 and the third electrode 23: Cr/Au or Ti/Au
An arrangement pitch of the third electrode 23 (arrangement pitch of subpixels Pb): 564 nm
The total number of the third electrodes 23 (the total number M×N1 of subpixels Pb): 351
The total number M of pixels Pa: 117
The second electrode 22 and the fourth electrode 24: GeAu/Au
The antireflection film 25: for example, a silicon compound film of SiN, SiO2, or the like (thickness of 0.1 μm or greater and 0.5 μm or less)
Widths of the phase synchronization portion 17 and the intensity modulation portion 18 in the X-direction: 200 μm
A width of the phase synchronization portion 17 in the Y-direction: 150 μm
A width of the intensity modulation portion 18 in the Y-direction: 50 μm
A chip size: 700 μm on one side
Here, an example of a method for manufacturing the light source module 1A will be described with reference to
First, as illustrated in
Next, by the way, as illustrated in
Alternatively, a region having a high refractive index and a high resistance may be formed by performing ion implantation (for example, oxide ion implantation) via the etching mask instead of forming the slit S.
Subsequently, as illustrated in
Subsequently, as illustrated in
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Subsequently, as illustrated in
Thereafter, as illustrated in
As described above, operational effects obtained by the light source module 1A according to the present embodiment will be described. When a bias current is supplied between the first electrode 21 and the second electrode 22, and between the third electrode 23 and the fourth electrode 24, carriers are collected between the first cladding layer 12 and the second cladding layer 15 in each of the phase synchronization portion 17 and the intensity modulation portion 18, and light is efficiently generated in the active layer 13. The light outputted from the active layer 13 enters the photonic crystal layer 14, and resonates in the X-direction and in the Y-direction, which are perpendicular to the thickness direction in the photonic crystal layer 14. This light becomes a phase-aligned coherent laser light beam in the photonic crystal layer 14 of the phase synchronization portion 17.
Since the photonic crystal layer 14 of the intensity modulation portion 18 is arranged in the Y-direction with respect to the photonic crystal layer 14 of the phase synchronization portion 17, a phase of the laser light beam in the photonic crystal layer 14 of each subpixel Pb coincides with a phase of the laser light beam in the photonic crystal layer 14 of the phase synchronization portion 17. As a result, the phases of the laser light beams in the photonic crystal layer 14 are aligned between the subpixels Pb. Since the photonic crystal layer 14 of the present embodiment causes Γ-point oscillation, the phase-aligned laser light beam L is outputted from each subpixel Pb of the intensity modulation portion 18 in a direction intersecting both the X-direction and the Y-direction (typically, the Z-direction). A part of the laser light beam L directly reaches the semiconductor substrate 11 from the photonic crystal layer 14. Furthermore, the rest of the laser light beam L reaches the third electrode 23 from the photonic crystal layer 14, is reflected by the third electrode 23, and then reaches the semiconductor substrate 11. The laser light beam L passes through the semiconductor substrate 11, and exits from the back surface 11b of semiconductor substrate 11 to the outside of the light source module 1A through the opening 24a of the fourth electrode 24.
The third electrode 23 is provided in correspondence with each subpixel Pb. Therefore, the magnitude of the bias current supplied to the intensity modulation portion 18 can be individually adjusted for each subpixel Pb. That is, light intensity of the laser light beam L outputted from the intensity modulation portion 18 can be adjusted individually (independently) for each subpixel Pb. Furthermore, in each pixel Pa, the length Da of the region including consecutive N2 subpixels Pb in the arrangement direction (X-direction) is smaller than the emission wavelength λ of the active layer 13, that is, the wavelength of the laser light beam L.
Here,
However, in the methods illustrated in
Note that as described above, even in a case where each pixel Pa includes three or more subpixels Pb, the number of subpixels Pb that simultaneously output the light is limited to two. When a length of a region including two subpixels Pb in the arrangement direction is smaller than the emission wavelength λ of the active layer 13, two subpixels Pb can be regarded as pixels including a single light emission point equivalently. Therefore, when the range of the phase distribution that can be dynamically controlled is less than 360°, the number of subpixels Pb that simultaneously output the light is limited to consecutive N2 (N2 is an integer of two or more and N1 or less), and the length Da of a region including the consecutive N2 subpixels Pb in the arrangement direction may be set to be less than the emission wavelength λ of the active layer 13. Note that as described above, in a case where both the number N1 and the number N2 are three or more, a spatial phase in the X-direction of the laser light beam L outputted from each pixel Pa can be dynamically controlled in a range of 0° to 360°.
As described above, in the light source module 1A of the present embodiment, it is possible to dynamically control the phase distribution of the laser light beam L.
As in the present embodiment, the first electrode 21 may be in contact with the contact layer 16 and cover the entire surface of the contact layer 16 of the phase synchronization portion 17, and the second electrode 22 may be in contact with the semiconductor substrate 11 and cover the entire surface of the semiconductor substrate 11 of the phase synchronization portion 17. In this case, the laser light beam outputted from the phase synchronization portion 17 in the stacking direction (Z-direction) can is shielded by the first electrode 21 and the second electrode 22. The photonic crystal layer 14 of the phase synchronization portion 17 causes Γ-point oscillation, and thus such shielding by the first electrode 21 and the second electrode 22 is effective.
As in the present embodiment, the fourth electrode 24 may have a frame shape that is in contact with the semiconductor substrate 11 and surrounds the opening 24a through which the laser light beam L passes. In this case, while a sufficient bias current is supplied to the active layer 13 of the intensity modulation portion 18, the laser light beam L can be outputted through the opening 24a from the intensity modulation portion 18 in a direction intersecting both the X-direction and the Y-direction.
As in the present embodiment, the semiconductor stack portion 10 may have the slit S. A plurality of the subpixels Pb and the slits S may have a plurality of slits S alternately arranged one by one in the arrangement direction of the subpixels Pb. In this case, the intensity modulation portion 18 can be divided into a plurality of the subpixels Pb with a simple configuration.
As described above, in the present embodiment, the third electrode 23 corresponding to each subpixel Pb is in contact with the contact layer 16, and the frame-shaped fourth electrode 24 having the opening 24a is in contact with the back surface 11b of the semiconductor substrate 11. In the present embodiment or each modification example to be described later, the third electrode corresponding to each subpixel Pb may be provided on the back surface 11b of the semiconductor substrate 11 (or the first cladding layer 12), and the frame-shaped fourth electrode having an opening may be provided on the contact layer 16. That is, the third electrode provided corresponding to each subpixel Pb is electrically connected to one portion (semiconductor layer) of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute a part of the intensity modulation portion 18, and the fourth electrode is electrically connected to the other portion (semiconductor layer) of the portion of the first conductivity type semiconductor layer and the portion of the second conductivity type semiconductor layer which constitute a part of the intensity modulation portion. According to this, it is possible to achieve the same operational effects as those of the present embodiment.
Furthermore, an arrangement pitch (center interval) of the third electrodes 23 defined in the arrangement direction of the subpixels Pb may be an integer multiple of a lattice interval a. In this case, the light intensity of the laser light beam L outputted from each subpixel Pb is brought close to a uniform state.
Here, an example of a method for manufacturing the light source module according to the present modification example will be described with reference to
First, as illustrated in
Subsequently, as illustrated in
Subsequently, as illustrated in
As in the present modification example, the slit SA may be formed so as to divide the photonic crystal layer 14 and the active layer 13 from the surface of the semiconductor stack portion 10. Even in this case, it is possible to achieve the same operational effects as those of the above-described embodiment. Furthermore, since the slit SA electrically and optically divides the second cladding layer 15 and the contact layer 16, an electrical and optical crosstalk between the subpixels Pb adjacent to each other is further decreased.
A difference between the present modification example and the above-described embodiment is a structure of the photonic crystal layer 14 in the intensity modulation portion 18. That is, in the present modification example, the photonic crystal layer 14 includes a phase shift portion 14c provided in one-to-one correspondence with the N1 subpixels Pb, and the phase shift portion 14c makes phases of the laser light beams L outputted from the pixels Pa in the Y-direction different from each other between N1 subpixels Pb.
A specific description will be made with reference to
These center intervals are set such that a phase difference between the laser light beams L outputted from the subpixels Pb becomes an integer multiple of 2π/N1. In a case of N1=3, the center intervals W1 to W3 are set such that a phase difference between the laser light beams L outputted from the subpixels Pb becomes an integer multiple of 2π/3. In one example, one of the center intervals W1 to W3 is set to be ⅔ times (or 5/3 times) the lattice interval a, another one is set be to 4/3 times the lattice interval a, and the remaining one is set to be equal to the lattice interval a. In other words, a difference between the center interval W1 and the center interval W2, and a difference between the center interval W2 and the center interval W3 are set to be ⅓ times the lattice interval a. Note that as described above, in a case where Γ-point oscillation occurs in the photonic crystal layer 14, the lattice interval a is equal to λ/n (λ: emission wavelength, n: effective refractive index of photonic crystal layer 14). An arrangement order of three subpixels Pb is determined regardless of the center interval.
Note that in the example illustrated in
As in the present modification example, the photonic crystal layer 14 of each subpixel Pb may include the phase shift portion 14c for making the phase of the laser light beam L outputted from each pixel Pa different from each other between N1 subpixels Pb. In this case, the phase of the laser light beam L outputted from each pixel Pa in the Y-direction is different for each subpixel Pb. The phase of the laser light beam L outputted from each pixel Pa in the Y-direction is determined in accordance with the intensity distribution and the phase distribution of N1 subpixels Pb constituting the pixel Pa. In this case, the phase of the laser light beam L in the Y-direction can be dynamically modulated, but an optical wave traveling in the Y-direction is diffracted in the Z-direction due to the diffraction effect of the modified refractive index region 14b in the intensity modulation portion 18. Therefore, as a result, the phase in the Z-direction can also be dynamically modulated. That is, it is possible to dynamically modulate the phase distribution of the light in an output direction, and the degree of freedom of controlling the phase distribution of the laser light beam L is further increased. That is, as illustrated in
Furthermore, a form of the modified refractive index region 14b and a method for forming the modified refractive index region 14b are similar to those in the above-described embodiment.
The resonance mode forming layer 14A has a two-dimensional diffraction lattice. The resonance mode forming layer 14A includes a base layer 14a and a plurality of modified refractive index regions 14b provided inside the base layer 14a. Refractive indexes of the modified refractive index regions 14b are different from the refractive index of the base layer 14a. The modified refractive index regions 14b are disposed at constant intervals in a direction inclined at 45° with respect to the X-direction and inclined at 45° from the Y-direction in the base layer 14a. A configuration of each of the modified refractive index regions 14b is similar to that in the above-described embodiment.
The resonance mode forming layer 14A of the phase synchronization portion 17 has a photonic crystal structure in which a plurality of the modified refractive index regions 14b are periodically arranged. The modified refractive index regions 14b are disposed at intervals so as to satisfy a condition of M-point oscillation with respect to the emission wavelength of the active layer 13.
In the example described above, the case where the modified refractive index region 14b is located at the opening center of the lattice frame of the square lattice has been described, but the modified refractive index region 14b may be located at the opening center of the lattice frame of another lattice (for example, a triangular lattice).
The intensity modulation portion 18 of the present embodiment has a configuration as a so-called static-integrable phase modulating (S-iPM) laser. Each pixel Pa outputs the laser light beam L in a direction perpendicular to the main surface 11a of the semiconductor substrate 11 (that is, the Z-direction), a direction inclined with respect to the direction perpendicular to the main surface 11a of the semiconductor substrate 11, or a direction including both the directions. Hereinafter, the configuration of the resonance mode forming layer 14A of the intensity modulation portion 18 will be described in detail.
As illustrated in
The angle distribution a (x, y) of the modified refractive index region 14b in the resonance mode forming layer 14A is determined by, for example, the following procedure.
As a first precondition, a virtual square lattice configured by M1×N1 (M1 and N1 are integers of one or more) unit constituent regions R having a square shape is set on an X′-Y′ plane in the X′Y′Z orthogonal coordinate system defined by the Z-axis coinciding with the normal direction of the main surface 11a and the X′-Y′ plane coinciding with one surface of the resonance mode forming layer 14A including a plurality of the modified refractive index regions 14b.
As a second precondition, it is assumed that the coordinates (ξ, η, ζ) in the X′Y′Z orthogonal coordinate system satisfy the relationships represented by the following Formulas (1) to (3) with respect to the spherical coordinates (r, θrot, θtilt) defined by a radial length r, an inclination angle θtilt from the Z-axis, and a rotation angle θrot from the X′-axis specified on the X′-Y′plane as illustrated in
ξ=r sin θtilt cos θrot (1)
η=r sin θtilt sin θrot (2)
ζ=r cos θtilt (3)
When the laser light beam L outputted from the light source module 1C is a set of bright spots directed in a direction defined by angles θtilt and θrot, the angles θtilt and θrot are converted into a coordinate value kx on a KX-axis corresponding to the X′-axis, which is a normalized wave number defined by the following Formula (4), and a coordinate value ky on a KY-axis corresponding to the Y′-axis and orthogonal to the KX-axis, which is a normalized wave number defined by the following Formula (5). The normalized wave number means a wave number normalized with a wave number 2π/a corresponding to the lattice interval of the virtual square lattice as 1.0. At this time, in a wave-number space defined by the KX-axis and the KY-axis, a specific wave number range including the beam pattern corresponding to the laser light beam L includes M2×N2 (M2 and N2 are integers of one or more) image regions each having a square shape. Note that the integer M2 does not need to coincide with the integer M1. Similarly, the integer N2 does not need to coincide with the integer N1. Formulas (4) and (5) are disclosed in, for example, Non-Patent Document 3 described above.
a: Lattice constant of virtual square lattice
λ: Oscillation wavelength of light source module 1C
As a third precondition, in the wave-number space, a complex amplitude distribution F (x, y) obtained by performing two-dimensional inverse discrete Fourier transform of each of image regions FR (kx, ky) specified by a coordinate component kx (an integer of zero or more and M2-1 or less) in the KX-axis direction and a coordinate component ky (an integer of zero or more and N2-1 or less) in the KY-axis direction into a unit constituent region R (x, y) on the X′-Y′ plane specified by a coordinate component x (an integer of zero or more and M1-1 or less) in the X′-axis direction and a coordinate component y (an integer of zero or more and N1-1 or less) in the Y′-axis direction is given by the following Formula (6) with j as an imaginary unit. The complex amplitude distribution F (x, y) is defined by the following Formula (7) when the amplitude distribution is A (x, y) and the phase distribution is φ (x, y). As a fourth precondition, the unit constituent region R (x, y) is defined by an s-axis and a t-axis, which are parallel to the X′-axis and the Y′-axis, respectively and orthogonal in the lattice point O (x, y) as the center of the unit constituent region R (x, y).
Under the first to fourth preconditions, the resonance mode forming layer 14A of the intensity modulation portion 18 is configured to satisfy the following fifth condition or sixth condition. That is, the fifth condition is satisfied by disposing the gravity center G away from the lattice point O (x, y) in the unit constituent region R (x, y). The sixth condition is satisfied by disposing the corresponding modified refractive index region 14b inside the unit constituent region R (x, y) such that in a state in which a line segment length r2 (x, y) from the lattice point O (x, y) to the corresponding gravity center G is set to a common value in each of M1×N1 unit constituent regions R, an angle α (x, y) formed by a line segment connecting the lattice point O (x, y) with the corresponding gravity center G and the s-axis satisfies
α(x,y)=C×φ(x,y)+B,
where
C: Proportional constant, for example, 180°/π
B: Arbitrary constant, for example, zero.
Next, the M-point oscillation of the resonance mode forming layer 14A of the intensity modulation portion 18 will be described. As described above, for the M-point oscillation, the lattice interval a of the virtual square lattice, the emission wavelength λ of the active layer 13, and the equivalent refractive index n of the mode may satisfy the condition of λ=(20.5)n×a.
The magnitudes of the in-plane wave number vectors K1 to K4 (that is, the magnitude of a stationary wave in the in-plane direction) are smaller than the magnitude of a basic reciprocal lattice vector B1. Therefore, a vector sum of the in-plane wave number vectors K1 to K4 and the basic reciprocal lattice vector B1 does not become zero, and the wave number in the in-plane direction cannot become zero due to the diffraction, so that the diffraction does not occur in a direction perpendicular to the plane (Z-axis direction). In this state, not only zero-order light in the direction perpendicular to the plane (Z-axis direction) but also +1st-order light and −1st-order light in a direction inclined with respect to the Z-axis direction are not outputted in each pixel Pa of the M-point oscillation.
In the present embodiment, the following action is taken on the resonance mode forming layer 14A of the intensity modulation portion 18, and thus a part of the +1st-order light and −1st-order light is outputted from each pixel Pa. That is, as illustrated in
In
Subsequently, the size and direction of the diffraction vector V1 for accommodating at least one of the in-plane wave number vectors K1 to K4 within the light line LL will be examined. The following Formulas (8) to (11) represent the in-plane wave number vectors K1 to K4 before the diffraction vector V1 is added.
The wave number vector spreads Δkx and Δky satisfy the following Formulas (12) and (13), respectively. A maximum value Δkxmax of the spread of the in-plane wave number vector in the X′-axis direction and the maximum value Δkymax of the spread of the in-plane wave number vector in the Y′-axis direction are defined by the angular spread of the designed optical image.
−Δkxmax≤Δkx≤Δkxmax (12)
−Δkymax≤Δky≤Δkymax (13)
When the diffraction vector V1 is represented by the following Formula (14), the in-plane wave number vectors K1 to K4 to which the diffraction vector V1 is added are represented by the following formulas (15) to (18).
Considering that any of the in-plane wave number vectors K1 to K4 falls within the light line LL in the above-described Formulas (15) to (18), the relationship of the following Formula (19) is established.
That is, by adding the diffraction vector V1 that satisfies Formula (19), any of the in-plane wave number vectors K1 to K4 falls within the light line LL, and a part of the +1st-order light and −1st-order light is outputted.
The size (radius) of the light line LL is set to 2π/λ for the following reasons.
In
As an example of a specific method of adding the diffraction vector V1 to the in-plane wave number vectors K1 to K4, a method of superimposing the phase distribution φ2 (x, y) irrelevant to a desired output light shape on a phase distribution φ1 (x, y) according to the desired output light shape is considered. In this case, the phase distribution φ (x, y) of the resonance mode forming layer 14A of the intensity modulation portion 18 is represented as φ (x, y)=φ1 (x, y)+φ2 (x, y). φ1 (x, y) corresponds to a phase of complex amplitude when a desired shape of the output light is Fourier-transformed as described above. Furthermore, φ2 (x, y) is a phase distribution for adding the diffraction vector V1 satisfying the above-described Formula (19). Note that the phase distribution φ2 (x, y) of the diffraction vector V1 is represented by an inner product of a diffraction vector V1 (Vx, Vy) and a position vector r (x, y), and is given with the following Formula.
φ2(x,y)=V1·r=Vxx+Vyy
In the present modification example, in a case where the wave number spread based on the angular spread of the output light is included in a circle having a radius Δk centered on a certain point on the wave-number space, the wave number spread can be simply considered as follows. By adding the diffraction vector V1 to the in-plane wave number vectors K1 to K4 in four directions, the magnitude of at least one of the in-plane wave number vectors K1 to K4 in the four directions becomes smaller than 2π/λ (light line LL). This may be considered that by adding the diffraction vector V1 to a vector obtained by removing a wave number spread Δk from the in-plane wave number vectors K1 to K4 in the four directions, the magnitude of at least one of the in-plane wave number vectors K1 to K4 in the four directions is smaller than a value {(2π/λ)−Δk} obtained by subtracting the wave number spread Δk from 2π/λ.
In this mode, the magnitude and direction of the diffraction vector V1 for accommodating at least one of the in-plane wave number vectors K1 to K4 within the region LL2 will be explained. The following Formulas (20) to (23) represent the in-plane wave number vectors K1 to K4 before the diffraction vector V1 is added.
Here, when the diffraction vector V1 is represented by the following Formula (14), the in-plane wave number vectors K1 to K4 to which the diffraction vector V1 is added are represented by the following formulas (24) to (27).
Considering that any of the in-plane wave number vectors K1 to K4 falls within the region LL2 in the above-described Formulas (24) to (27), the relationship of the following Formula (28) is established. That is, by adding the diffraction vector V1 that satisfies Formula (28), any of the in-plane wave number vectors K1 to K4 obtained by removing the wave number spread Δk falls within the region LL2. Even in such a case, a part of the +1st-order light and −1st-order light can be outputted.
In this case, the inclination angle β is constant in the resonance mode forming layer 14B of the intensity modulation portion 18. The inclination angle β satisfies 0°<β<90°, and in one example, β=45°. Alternatively, the inclination angle β satisfies 180°<β<270°, and in one example, β=225°. In a case where the inclination angle β satisfies 0° <β<90° or 180°<β<270°, the straight line D extends from a first quadrant to a third quadrant of a coordinate plane defined by the X′-axis and the Y′-axis. The inclination angle β satisfies 90°<β<180°, and in one example, β=135°. Alternatively, the inclination angle β satisfies 270°<β<360°, and in one example, β=315°. In a case where the inclination angle β satisfies 90°<β<180° or 270°<β<360°, the straight line D extends from a second quadrant to a fourth quadrant of the coordinate plane defined by the X′-axis and the Y′-axis. As described above, the inclination angle β is an angle excluding 0°, 90°, 180°, and 270°.
Here, in the unit constituent region R (x, y) of which coordinates are defined by the s-axis parallel to the X′-axis and a t-axis parallel to the Y′-axis, a distance between the lattice point O and the gravity center G is r (x, y). x is a position of an x-th lattice point on the X′-axis, and y is a position of a y-th lattice point on the Y′-axis. In a case where the distance r (x, y) is a positive value, the gravity center G is located on the first quadrant (or the second quadrant). In a case where the distance r (x, y) is a negative value, the gravity center G is located on the third quadrant (or the fourth quadrant). In a case where the distance r (x, y) is zero, the lattice point O and the gravity center G coincide with each other. The inclination angles are preferably 45°, 135°, 225°, and 275°. At these inclination angles, only two of the four wave number vectors (for example, the in-plane wave number vector (±π/a, +π/a)) forming the stationary wave at an M point are phase-modulated, and the other two are not phase-modulated. Therefore, a stable stationary wave can be formed.
The distance r (x, y) between the gravity center G of each of the modified refractive index regions and the lattice point O corresponding to each of the unit constituent regions R is individually set for each of the modified refractive index regions 14b according to the phase distribution φ (x, y) in accordance with a desired output light shape. In the present disclosure, such an arrangement mode of the gravity center G is referred to as a second mode. The phase distribution φ (x, y) and a distance distribution r (x, y) have a specific value for each position determined by the values of x and y, but is not necessarily represented by a specific function. A distribution of the distance r (x, y) is determined by extracting the phase distribution φ (x, y) from a complex amplitude distribution obtained by inverse Fourier transforming the desired output light shape.
That is, in a case where a phase φ (x, y) at certain coordinates (x, y) is P0, the distance r (x, y) is set to zero, in a case where the phase φ (x, y) is π+P0, the distance r (x, y) is set to the maximum value R0, and in a case where the phase φ (x, y) is −n+P0, the distance r (x, y) is set to the minimum value −R0. For an intermediate phase φ (x, y), the distance r (x, y) is set such that r (x, y)={φ (x, y)−P0}× R0/π. An initial phase P0 can be arbitrarily set.
When the lattice interval of the virtual square lattice is a, the maximum value R0 of r (x, y) is, for example, within the range of the following Formula (29). When the complex amplitude distribution is obtained from a desired optical image, it is possible to improve reproducibility of the beam pattern by applying an iterative algorithm such as the GS method generally used at the time of calculation for hologram generation.
In the second mode, a desired output light shape can be obtained by determining the distribution of the distance r (x, y) of the modified refractive index region 14b of the resonance mode forming layer 14B. Under the first to fourth preconditions as in the above-described first mode, the resonance mode forming layer 14B is configured to satisfy the following condition. That is, the corresponding modified refractive index region 14b is disposed in the unit constituent region R (x, y) such that the distance r (x, y) from the lattice point O (x, y) to the gravity center G of the corresponding modified refractive index region 14b satisfies
r(x,y)=C×(φ(x,y)−P0)
where
C: Proportional constant, for example, R0/π
P0: Arbitrary constant, for example, zero.
In a case where it is desired to obtain a desired output light shape, the output light shape may be inverse Fourier transformed to give the distribution of the distance r (x, y) in accordance with the phase φ (x, y) of the complex amplitude to a plurality of the modified refractive index regions 14b. The phase φ (x, y) and the distance r (x, y) may be proportional to each other.
Also in the second mode, similarly to the first mode described above, the lattice interval a of the virtual square lattice and the emission wavelength λ of the active layer 13 satisfy the condition of the M-point oscillation. Moreover, when considering the reciprocal lattice space in the resonance mode forming layer 14B, the magnitude of at least one of the in-plane wave number vectors K1 to K4 in the four directions each including the wave number spread due to the distribution of the distance r (x, y) is smaller than 2π/λ that is, the light line LL.
Also in the second mode, the following action is taken on the resonance mode forming layer 14B in the light emitting device oscillating at the M point, and thus a part of the +1st-order light and −1st-order light is outputted. Specifically, as illustrated in
Alternatively, as illustrated in
Operational effects obtained by the light source module 1C according to the present modification example, which is described above, will be described. When a bias current is supplied between the first electrode 21 and the second electrode 22, and between the third electrode 23 and the fourth electrode 24, carriers are collected between the first cladding layer 12 and the second cladding layer 15 in each of the phase synchronization portion 17 and the intensity modulation portion 18, and light is efficiently generated in the active layer 13. The light outputted from the active layer 13 enters the resonance mode forming layer 14A, and resonates in the X-direction and the Y-direction, which are perpendicular to the thickness direction in the resonance mode forming layer 14A. This light becomes a phase-aligned coherent laser light beam in the resonance mode forming layer 14A of the phase synchronization portion 17.
A portion of the resonance mode forming layer 14A constituting a part of the intensity modulation portion 18 is arranged in the Y-direction with respect to a portion of the resonance mode forming layer 14A constituting a part of the phase synchronization portion 17. Therefore, the phase of the laser light beam in the resonance mode forming layer 14A of each subpixel Pb coincides with the phase of the laser light beam in the resonance mode forming layer 14A of the phase synchronization portion 17. As a result, the phases of the laser light beams in the resonance mode forming layer 14A are aligned between the subpixels Pb.
The resonance mode forming layer 14A of the present modification example causes oscillation at the M-point, but in the resonance mode forming layer 14A of the intensity modulation portion 18, a distribution form of a plurality of the modified refractive index regions 14b satisfies a condition for the laser light beam L to be outputted from the intensity modulation portion 18 in a direction intersecting both the X-direction and the Y-direction. Therefore, the phase-aligned laser light beam L is outputted from each subpixel Pb of the intensity modulation portion 18 in a direction intersecting both the X-direction and the Y-direction (for example, a direction inclined with respect to the Z-direction). A part of the laser light beam L directly reaches the semiconductor substrate 11 from the resonance mode forming layer 14A. Furthermore, the rest of the laser light beam L reaches the third electrode 23 from the resonance mode forming layer 14A, is reflected by the third electrode 23, and then reaches the semiconductor substrate 11. The laser light beam L passes through the semiconductor substrate 11, and exits from the back surface 11b of semiconductor substrate 11 to the outside of the light source module 1C through the opening 24a of the fourth electrode 24.
Also in the present modification example, the third electrode 23 is provided in correspondence with each subpixel Pb. Therefore, the magnitude of the bias current supplied to the intensity modulation portion 18 can be individually adjusted for each subpixel Pb. That is, the light intensity of the laser light beam L outputted from the intensity modulation portion 18 can be adjusted individually (independently) for each subpixel Pb. Furthermore, in each pixel Pa, the length Da of the region including consecutive N2 subpixels Pb in the arrangement direction (X-direction) (see
As in the present modification example, the resonance mode forming layer 14A (or 14B) included in the phase synchronization portion 17 may have a photonic crystal structure in which a plurality of the modified refractive index regions 14b are periodically disposed. In this case, the phase-aligned laser light beam can be supplied from the phase synchronization portion 17 to each subpixel Pb.
As in the present modification example, a condition for the laser light beam L to be outputted in a direction intersecting both the X-direction and the Y-direction from the intensity modulation portion 18 may be that the in-plane wave number vectors K1 to K4 in the four directions each including a wave number spread corresponding to an angular spread of the laser light beam L outputted from the intensity modulation portion 18 are formed on an reciprocal lattice space of the resonance mode forming layer 14A (or 14B), and the magnitude of at least one in-plane wave number vector is smaller than 2π/λ, that is, the light line LL. As described above, normally, in a stationary wave state of the M-point oscillation, the light propagated in the resonance mode forming layer 14A (or 14B) is totally reflected, and the output of both a signal light (for example, at least one of the +1st-order light and −1st-order light) and the 0th-order light is suppressed. On the other hand, in an S-iPM laser, the in-plane wave number vectors K1 to K4 as described above can be adjusted by considering the arrangement of each modified refractive index region 14b. In a case where the magnitude of at least one in-plane wave number vector is smaller than 2π/λ, the in-plane wave number vector has a component in the thickness direction (Z-direction) of the resonance mode forming layer 14A (or 14B) and does not cause total reflection at an interface with air. As a result, a part of the signal light as the laser light beam L can be outputted from each pixel Pa.
A difference between the present modification example and the third modification example is a structure of the resonance mode forming layer 14A (or 14B) in the intensity modulation portion 18. That is, in the present modification example, similarly to the above-described second modification example, the phase shift portion 14c for making phases of the laser light beams L outputted from the pixels Pa in the Y-direction different from each other between N1 subpixels Pb is included in the resonance mode forming layer 14A (or 14B) of each subpixel Pb. Details of the phase shift portion 14c are similar to those of the second modification example.
As in the present modification example, the phase shift portion 14c for making phases of the laser light beams L outputted from the pixels Pa in the Y-direction different from each other between N1 subpixels Pb may be included in the resonance mode forming layer 14A (or 14B) of each subpixel Pb. In this case, the phase of the laser light beam L outputted from each pixel Pa is different for each subpixel Pb. The phase of the laser light beam L outputted from each pixel Pa is determined in accordance with the intensity distribution and the phase distribution of N1 subpixels Pb constituting the pixel Pa. Therefore, the degree of freedom of controlling the phase distribution of the laser light beam L can be further increased.
The light source module according to the present disclosure is not limited to the above-described embodiment, and various other modifications can be made. For example, in the above-described embodiment and each modification example, an example in which a plurality of pixels Pa are arranged one-dimensionally has been described, but a plurality of the pixels Pa may be arranged two-dimensionally. In this case, for example, a plurality of the light source modules disclosed in the above-described embodiment or each modification example may be combined. Furthermore, in the above-described embodiment, an example in which the semiconductor stack portion 10 mainly includes a GaAs-based semiconductor has been described, but the semiconductor stack portion 10 may mainly include an InP-based semiconductor or may mainly include a GaN-based semiconductor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-006906 | Jan 2020 | JP | national |
| 2020-006907 | Jan 2020 | JP | national |
| 2020-160719 | Sep 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/001315 | 1/15/2021 | WO |
