Patent Application
20220352685
The present invention relates to semiconductor photonic, discrete optic, integrated optic, and opto-electronic devices. In particular, the present invention relates to highly-integrated compact semiconductor laser on a single chip based on integrated diffraction grating.
Present semiconductor laser system based on diffraction grating typically make use of bulk optical diffraction grating and the use of discrete optical components such as lenses that are tedious to be aligned with each other optically. Such semiconductor laser systems based on diffraction grating are sometime referred to as diffraction-grating semiconductor lasers. They have the advantage of wavelength selectivity utilizing diffraction grating or utilizing grating to combined a few wavelengths together into a single output mirror. However, laser systems based on discrete optical components are mechanically fragile. They are typically very heavy and cannot be easily carried or moved around.
There is an unmet need in the art for an integrated laser system on a single integrated chip that is very compact in size, very light weight, mechanically very rugged, low in manufacturing costs, and high in wall-plugged electrical power efficiency.
It is an aim of the present invention to provide ultra-compact highly-integrated diffraction-grating semiconductor lasers on chips that are compact in size, light weight, mechanically rugged, low in manufacturing cost, and in some cases high in electrical wall-plugged power efficiency or high in optical power output, comparing to typical lasers based on discrete optical components.
Another objective of this invention is to provide an integrated semiconductor laser system on a single semiconductor chip based on the integration of a few key integrated optical components that result in an efficient laser on a single chip with multiple functional configurations.
The present invention has overcome the aforementioned limitations of the prior arts on diffraction-grating based semiconductor laser systems utilizing discrete optical components.
In one embodiment of the present invention, a laser system is integrated on a single integrated chip via the use of an integrated curved diffraction grating combined with one or more integrated Bragg-grating reflectors, that enables a fully integrated diffraction-grating based laser that do not need the use of any optical lens.
In another embodiment of the present invention, one or more photonic devices are integrated on a substrate. The photonic devices comprise one or more optical gain material areas. One or more passive photonic components are fabricated on a passive waveguiding layer. The passive photonic components contain at least a curved optical grating and at least one wavelength-channel-combined-arm Bragg reflector. The method further transfers a thin layer of material capable of providing optical power amplification.
In another embodiment of the present invention, the wavelength-channel-combined-arm Bragg reflector is fabricated into a planar waveguiding layer.
In as yet another embodiment of the present invention, the wavelength-channel-combined-arm Bragg reflector is fabricated into a planar waveguiding layer with high-refractive index contrast, resulting in a broad optical bandwidth of reflection and transmission.
In as yet another embodiment of the present invention, the planar waveguiding layer is silicon.
In as yet another embodiment of the present invention, the number of reflecting teeth in the wavelength-channel-combined-arm Bragg reflector is adjusted to provide a highly reflecting beam-power reflector or a partially-transmitting beam-power reflector.
In as yet another embodiment of the present invention, the optical beam is confined in the direction perpendicular to the substrate surface via planar or channel waveguides, and a curved diffraction grating is fabricated into a planar waveguiding area with the surfaces of the grating teeth approximately perpendicular to the substrate plane.
In as yet another embodiment of the present invention, one side of the optical beam propagating path intersects with the wavelength-channel-combined-arm Bragg reflector, and another side of the optical beam propagating path intersects with the curved diffraction grating is positioned the mouth of a channel waveguide (called wavelength-channel-separated waveguide mouth).
In as yet another embodiment of the present invention, the optical power in a wavelength of light in the optical beam propagating toward the wavelength-channel-combined-arm Bragg-grating reflector is reflected back either fully or partially by the wavelength-channel-combined-arm Brag-grating reflector toward the curved diffraction grating and is further diffracted by the curved diffraction grating to enter the said wavelength-channel-separated waveguide mouth.
In as yet another embodiment of the present invention, there are two or more of the said waveguide mouths, with each mouth receiving a wavelength of the light beam reflecting back from the wavelength-channel-combined-arm Bragg reflector towards the grating.
In as yet another embodiment of the present invention, the beam entering the mouth of a channel waveguide is guided via a linear or a curvilinear path along a channel waveguide to an optical gain region.
In as yet another embodiment of the present invention, the optical gain region is composed of an active gain material layer forming a gain channel waveguide bonded on top of a passive transparent channel waveguide.
In as yet another embodiment of the present invention, the optical beam energy in the passive transparent channel waveguide is transferred from the passive channel waveguide to the gain material layer via laterally tapering structures on at least one of the passive channel waveguiding layer or the gain channel waveguide layer.
In as yet another embodiment of the present invention, the optical beam energy in the gain channel waveguide is transferred from the gain channel waveguide to the passive channel waveguide via laterally tapering structures on at least one of the passive channel waveguiding layer or the gain channel waveguide layer.
In as yet another embodiment of the present invention, the optical beam energy propagating through the gain region from the grating-facing waveguide mouth is entered into a passive channel waveguide. The beam in the passive channel waveguide is then reflected back either fully or partially via a Bragg-grating reflector.
In yet another embodiment of the present invention, the curved diffraction grating is designed such that the beam size in direction parallel to the plane of the substrate is larger at the wavelength-channel-combined-arm Bragg-grating reflector than at the wavelength-channel-separated waveguide mouth.
In yet another embodiment of the present invention, the curved grating is designed such that the beam size in direction parallel to the plane of the substrate (called the horizontal mode size) is small at the wavelength-channel-separated waveguide mouth, but is large at the wavelength-channel-combined-arm Bragg-grating reflector. There may be one or more than one waveguide mouths with each mouth receiving a wavelength channel. This enables the intensity at the wavelength-channel-combined-arm Bragg-grating reflector that would have higher optical power (by combining the many wavelength channels) to be made low or comparable to the intensity of the light beam at each of the wavelength-channel-separated waveguide mouth that would receive light energy in only one of the wavelength channels. The lowered intensity in the relatively higher-power beam at the wavelength-channel-combined-arm Bragg-grating reflector reduces the chance of optical damage at the wavelength-channel-combined-arm Bragg reflector region.
In as yet another embodiment of the present invention, the wavelength-channel-combined-arm Bragg-grating reflector is made of Bragg grating's teeth that are curved in shape (instead of linear in shape like a straight line), so as to achieve larger horizontal beam size and hence lower beam intensity at the wavelength-channel-combined-arm Bragg-grating reflector.
In as yet another embodiment of the present invention, the optical beam energy propagating towards the wavelength-channel-combined-arm Bragg-grating reflector is partially transmitted at the reflector to an optical-fiber coupler such as a surface-grating based optical fiber coupler, or a planar (horizontal) beam-transformer based optical fiber coupler.
In as yet another embodiment of the present invention, the spatial region that brings in the optical fiber to the optical-fiber coupler is hermetically sealed.
In as yet another embodiment of the present invention, the surface-grating based optical fiber coupler is composed of a surface grating that emits the beam in a direction approximately perpendicular to a substrate plane and a Fresnel lens structure that further reduces a beam diameter emitted to a smaller value.
In as yet another aspect of the present invention, each of the photonic devices is sandwiched from at least one of the top or the bottom via cooling fixtures that allow water cooling of the photonic device.
The preferred embodiments of the invention will hereinafter be described in conjunction with the appended drawings provided to illustrate but not to limit the invention, wherein like designations denote like elements, and in which:
Skilled artisans will appreciate that the elements in the figures are illustrated for simplicity and clarity, and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to the other elements, to help in improving understanding of the embodiments of the present invention. Also, specific materials or dimensions shown in the figures are for illustration purposes and are not meant to limit the scopes of the present invention.
In the present description, certain terms have been used for brevity, clearness and understanding. No unnecessary limitations are to be applied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes only and are intended to be broadly construed. The different systems and methods described herein may be used alone or in combination with other systems and methods. Various equivalents, alternatives and modifications are possible within the scope of the appended claims. Each limitation in the appended claims is intended to invoke interpretation under 35 U.S.C. § 112, sixth paragraph, only if the terms “means for” or “step for” are explicitly recited in the respective limitation.
Lasers or laser systems based on discrete optical components are mechanically fragile. They are typically very heavy and cannot be easily carried or moved around. The main focus of this invention is a highly integrated laser system on a single integrated chip that is very compact in size, very light weight, mechanically very rugged, low in manufacturing costs, and high in wall-plugged electrical power efficiency, comparing to high-power lasers based on discrete optical components generally.
This invention focuses on highly-integrated compact semiconductor laser on a single chip based on integrated diffraction grating. Each laser is made as a single integrated chip using a full-wafer-level process without the need to align discrete optical components. The laser is capable of lasing at either a single wavelength or a plurality of optical wavelengths with use of a single curved diffraction grating, the use of one or more broadband integrated Bragg-grating reflectors, and other integrated optical components. The entire integrated laser can be configured to achieve various functional operations. The various functional operations include the case with a single output waveguide that combines two or more lasing wavelengths together (referred to as combined multi-wavelength single-output (CMWSO) laser), thereby achieving a higher output power. There are other functional operations that can be achieved with use of the various integrated components.
A focus of this invention is a laser system on a single integrated chip, based on the use of an integrated curved diffraction grating combined with one or more integrated Bragg-grating reflectors, that enables a fully integrated diffraction-grating based laser that do not need the use of any optical lens. Furthermore, the integrated laser system can be configured to achieved various different functional operations. The integrated laser system of the present invention is compact in size, light in weight, mechanically rugged, lower in manufacturing cost, and high in electrical wall-plugged power efficiency, comparing to lasers based on discrete optical components.
Each semiconductor integrated laser system of the present invention is made as a single integrated semiconductor chip using a full-wafer-level process without the need to align discrete optical components. This lowers the cost of production, reduces the size and weight of the lasers substantially, and makes the lasers much more rugged. In the case of the higher-power CMWSO lasers, the lasers will have superb beam focusing capability (with beam quality factor M2˜1) and high brightness B. The laser wavelength can be at near infrared (e.g., 1550 nm) or at any other wavelengths by scaling the design accordingly. The production costs of these integrated laser systems can be much lower than the production cost of laser systems based on discrete components, and the output powers of these integrated lasers can be delivered into single-mode optical fibers.
The present invention is about a method to design and realize a class of lasers on a photonic integrated circuit that is efficient and capable of integration with other photonic devices. The geometry for the lasers is based on the use of “integrated diffraction grating” as part of the laser design. The diffraction grating enables multiple lasing wavelength channels to be combined into a single output on the chip. As a result, this class of lasers is capable of a wide variety of functionalities, including high output power by combining the output powers of many lasing wavelengths into a single output waveguide. The output can be further coupled to a single optical fiber. Thus, this class of lasers would have applications ranging from efficient single-wavelength lasers made on an integrated photonic chip, lasers capable of combining with electronic integrated circuits on a single chip, multi-wavelength lasers for optical communications that need many wavelength channels to transmit optical data, to high-power lasers that can reach watts level optical power output in a single-mode optical fiber and many others.
One characteristic of the laser structure in the present invention is its use of an optical thin-film transfer (OTFT) structure combined with an integrated diffraction grating as part of the laser geometry. For the purposes of this application, the term a “thin film” will be taken to mean a film with a thickness less than 10 times the optical wavelength used in the device. The optical thin-film transfer structure enables efficient devices by providing an efficient way to combine low-optical-loss passive optical waveguides with material layers that can provide optical gain. The diffraction grating geometry enables multiple-wavelength lasing or single-wavelength lasing with high spectral purity (i.e., a narrow spectral linewidth for the lasing mode). The OTFT structure-based platform forms the three-dimensional device structure for the lasers of the present invention. The diffraction grating based geometry then enables the unique advantages and functionalities of the lasers. The class of lasers of the present invention will be referred to as Integrated Diffraction-Grating-based Optical Thin-Film-Transferred lasers, or as IDG-OTFT lasers.
To describe the IDG-OTFT lasers in detail, below the application first describes the OTFT structure based photonic integrated circuit platform, referred to as OTFT platform or as OTFTP, then describes the geometry of the laser design involving integrated diffraction grating.
Optical-Thin-Film-Transfer Based Photonic Integrated Circuit Platform
The basic three-dimensional structure of the IDG-OTFT lasers is based on an Optical Thin-Film-Transfer Structure called the OTFT platform. The OTFT platform is attractive as it enables high quality integration of passive and active optical materials on a single chip. Passive optical materials are important to make low-optical-loss optical waveguides and optical diffraction grating needed for the lasers. Active optical materials are needed for example to provide the optical gain needed (e.g., via current injection into a quantum-well structure) for achieving lasing. Before describing the geometry of the laser device, first the three-dimensional structure of the OTFT platform that it is based on is described.
As is known to those skilled in the art, there are various optically transparent materials that can be used as the passive layer material. For the purpose of illustration and not limitation, this application will describe the OTFT platform by using silicon as the exemplary passive material and will focus on 1550 nm wavelength range for which the silicon material is optically transparent. Those skilled in the art would know that other optically transparent materials and other optical wavelengths can be used and the device dimensions example used to illustrate the laser operations at 1550 nm wavelength range can be converted to equivalent dimensions when other materials and other optical wavelengths are used. Usually, the required physical dimensions of the devices involved are linearly proportional to the wavelength and linearly inversely proportional to the optical refractive index of the materials used, as is well known to those skilled in the art.
Furthermore, for the purpose of illustration and not limitation, the exemplary OTFT platform by using III-V semiconductor (e.g., Indium Phosphide (InP) or Indium Gallium Arsenide Phosphide (InGaAsP) as the active materials (e.g., to provide the optical gain needed to achieve lasing) will be described. Those skilled in the art would know that many other semiconductor-based materials (or optical gain materials that are not semiconductors) can also be used as the active optical materials. Thus, while the various exemplary embodiments described below use silicon, SOI, and III-V semiconductors for illustration purpose to illustrate the device structures in the embodiments, they are not meant to limit the invention, unless specifically specified. Many other materials can be used as long as they serve the same functional purposes for example, to provide the optical transparency, the optical gain, or the required refractive indices or the refractive-index differences, as is well known to those skilled in the art.
With the above in mind, an exemplary embodiment of the OTFT platform is shown in
To form an active waveguide with optical gain, the silicon layer is first etched down in direction perpendicular to the plane of the substrate 1900 to form a waveguide 1030 with waveguide width wSi 1031 and waveguide thickness (or height) tSi 1011 as shown in
For a typical OTFT-Platform device, passive silicon waveguides 1030, diffraction grating (not shown), and other passive devices (not shown) are first fabricated on the silicon layer as illustrated by
A typical epitaxial layer structure 1500 is shown in
In another embodiment, as illustrated by
As shown in
In an exemplary embodiment, after the wafer bonding and transfer of the epitaxial layer structure 1500 onto the silicon surface 1012, the structure 1500 is further patterned by photoresist and photolithography (or electron-beam (Ebeam) resists and Ebeam lithography) or the like, and then further fabricated into device structures via etching and other fabrication processes. As an exemplary embodiment,
An Exemplary Embodiment of a Device of the Present Invention Showing an Exemplary Geometry of a Laser System Integrated on a Chip
For the purpose of illustration and not limitation, an exemplary geometry for the present invention is shown in
As an exemplary embodiment of the present invention utilizing the OTFT platform of
As an exemplary embodiment, assuming the silicon layer is surrounded by silicon dioxide (n˜1.5), silicon nitride (n˜2), or aluminum nitride (AlN; n˜2.1) as the waveguide cladding materials, such waveguide would be considered a strongly-confined or high-refractive-index contrast waveguide. In addition, the use of AlN is particularly conducive for high-power laser applications as it has very high thermal conductivity close to that of metal and has been shown to be a good material for integrated optic devices at 1550 nm wavelength range.
As an exemplary embodiment, for application at the 1550 nm wavelength range, a 500 nm thick tSi 1011 for the silicon layer 1010 shown in
Thus, as discussed above, at 1550 nm wavelength range, when the silicon waveguide thickness is thicker than about 300 nm, a few vertical modes can be guided. However, it turns out that waveguide with a few modes can be made to guide mainly in the first-order mode using various techniques, including a “mode filter” to be described below that would cause high loss for the higher-order modes and hence can be used to filter out the higher-order modes. With proper mode management, the silicon waveguide thickness could even go thicker than the 1000 nm mentioned above and still make the first-order fundamental mode the dominant guided mode.
The above is exemplary aspect of the passive waveguide thickness that can be used in the present invention that would enable the achievement of higher lasing power. The description of
An optical beam called the “output beam” OB 2020 near OM 2010 is reflected back from OM 2010 and propagates towards a diffraction grating called the integrated diffraction grating IDG 2030. Note the spatial region occupied by beam OB 2020 is shown in shaded gray and this beam propagates in both directions as shown by the double arrows in the figure (it propagates towards OM 2010 and then reflected from OM 2010 and propagates towards IDG 2030). The beam at OM 2010 has a certain beam width, which would be labelled as OBW 2025 (output-mirror beam width). As an optional embodiment, an output beam aperture OBA 2040 with a width OBAW 2045 is placed just before the output mirror. The width OBAW 2045 is just large enough to pass the output beam width OBW 2025 with minimal loss.
The diffraction grating IDG 2030 then diffracts the beam reflected back from the output mirror OM 2010 towards a gain waveguide element GWE12111 if the beam is at wavelength lambda 1 (labelled as “λ1”). If the beam from the output mirror has wavelength “λ2”, then it would be diffracted towards waveguide gain element GWE22112. If the beam from the output mirror has wavelength “Xn”, then it would be diffracted towards waveguide gain element GWEn 211n, etc.
Beam propagating towards gain waveguide element 1 GWE12111 is first received by a beam-receiving silicon waveguide mouth, called the “gain-element waveguide mouth 1” labelled as GE-WM12121. The width of GE-WM12121 is labelled as GE-WMW12131.
GE-WM12121 receives the beam from the grating IDG 2030 and acts as a “slit” for the grating spectrometer. The function of the slit of an optical spectrometer to pass certain spectral bandwidth of the spectrally dispersed beam is well known to those skilled in the art. Such slit is made by an opening of a certain width for the dispersed light beam to pass through referred to as the slit width. In this case, the width GE-WMW12131 of the waveguide mouth GE-WM12121 functions as the slit width. For the purpose of discussion, GE-WM12121 may be called the “exit slit 1” of the grating spectrometer and GE-WMW12131 is then the width of exit slit 1. The output beam aperture OBA 2040 may be referred to as the “entrance slit” of the grating spectrometer and OBAW 2045 is the width of the entrance slit. Obviously for the laser cavity with bidirectional propagating beam, the labelling of which slit is the “entrance” or the “exit” slit is a matter of choice. As far as the grating IDG 2030 serving as an optical spectrometer is concerned, it is conventional to think of it as having an entrance beam with a broad optical spectrum that is diffracted to many exit directions, each direction for a particular optical wavelength range. The beam received by GE-WM12121 is then guided to a gain waveguide section GS12041 that has a bonded epitaxial layer structure like that of layer 1500 in
In summary, a general wavelength λn from the output mirror OM 2010 would be diffracted by the grating IDG 2030 towards gain waveguide element GWEn 211n with gain-element waveguide mouth GE-WMn 212n. The width of the mouth of this gain-element passive waveguide (e.g., made of silicon layer 1010, in the form of a channel waveguide 1030) is denoted as GE-WMWn 213n. The spacing between two adjacent gain element waveguide mouths, such as for element n and n+1 is denoted by WMSn(n+1) 231n(n+1). It is typical to place the waveguide mouths close to each other forming an array with almost constant adjacent element spacing and, in that case, the gain element waveguide-mouth spacings WMSn(n+1) 231n(n+1) would simply be called WMS 2310 (not shown in
More specifically, light at the waveguide mouth GE-WMn 212n is in the silicon layer (e.g., in layer 1010 of
The high reflector GE-HRn 214n reflects the beam back to VMCBn 252n, gain section GSn 204n, VMCFn 251n, and towards silicon waveguide mouth GE-WMn 212n. Before the waveguide mouth is a gain-element mode filter MFn 254n that filters out the higher order guided modes and passes basically only the lowest-order fundamental waveguide mode (in the silicon layer). This mode filter is described in detail later. After the mode filter, the beam then exits waveguide mouth GE-WMn 212n and propagates back to the IDG 2030 grating, which subsequently diffracts the beam back to the output beam aperture OBA 2040 and then the output mirror OM 2010. Part of the light at the output mirror OM 2010 is transmitted to a fiber coupler FC 2060 made of surface grating on the silicon planar waveguide. The fiber coupler couples the beam into an optical fiber OF 2070 as output, and is described in detail later. Part of the light at the output mirror OM 2010 is reflected back towards the grating IDG 2030 and forms a closed optical path. The closed path forms an optical cavity with optical gain section GSn 204n providing the needed optical gain to achieve lasing at wavelength λn.
Thus, wavelength λn would lase if gain section GSn 204n is powered up (i.e., applied with electrical current or voltage to achieve optical gain). All the different wavelengths share the common output mirror OM 2010 and the output optical fiber OF 2070.
The gain waveguide elements GWE12111 . . . GWEm 211m (assuming a total of m elements) form an array with an array of entrance mouths GE-WM12121 . . . GE-WMm 212m.
In one implementation, the gain sections GS12041 . . . GSm 204m are placed close to the entrance mouths so the spacing between two adjacent gain section GSS 2320 is about equal to the spacing between adjacent gain-element waveguide mouth WMS 2310 (i.e., WMS˜GSS). This would be the “straight-waveguide connection geometry” (SWGC geometry) shown in
In an alternative implementation shown in
Note that the high-reflector GE-HRn 214n at the end of each of the gain element GWEn 211n can be made on the silicon layer 1010 in
Note that OM 2010 is also called the “wavelength-channel-combined-arm Bragg reflector” as all the different lasing wavelength channels that go through gain sections GS12041 . . . GSn 204n, are all combined at OM 2010 to give a single output beam with all the lasing wavelength channel. Note also that GE-WM12121 . . . GE-WMm 212m are also called “wavelength-channel-separated waveguide mouths”. Further also note that each of the high-reflector GE-HR12141 . . . GE-HRn 214n (at the end of the respective gain waveguide elements GWE12111 . . . GWEn 211n) is called a “wavelength-channel-separated-arm Bragg reflector”.
Integrated Diffraction Grating Design
For the purpose of illustration and not limitation, as an exemplary embodiment, herein is described in more detail the integrated diffraction grating IDG 2030. There are various designs desirable for IDG 2030, including the usual Echelle Rowland grating design, and designs that are smaller in size, higher in spectral resolution, or lower in optical loss than the Echelle Rowland grating design. There are also designs with broadband focusing aberration correction enabling high wavelength resolution, high diffraction efficiency, and compact size over a broad spectral bandwidth. Which design to use is dependent on the intended application of the specific IDG-OTFT laser involved. Thus, there is not just one single design but various designs for the grating IDG 2030.
The IDG 2030 can be made on the silicon top layer of a silicon-on-insulator (SOI) wafer such as layer 1010 in
Beside the high resolution, broad bandwidth, and compact size, there are a few key desirable properties for the various designs of grating IDG 2030 that are important specifically for high-power laser applications. To understand that, as shown in
In the IDG-OTFT laser implementation shown in
The ER-grating design for grating ERG3000 has a few difficulties for high-power integrated laser applications:
The ER-grating design has the property that the physical width of the beam BW 3500 (not shown in
The exit slits in the ER-grating design have to lie on the Rowland circle 3300. Thus, the waveguide mouths GE-WM12121 . . . GE-WMn 212n of the gain waveguide elements GWE12111 . . . GWEn 211n are not on a straight line but are on a curved line. This makes it harder to place the gain medium section GS12041 . . . GSn 204n at close to the gain-element waveguide mouths GE-WM12121 . . . GE-WMn 212n and hence harder to realize the SWGC geometry, which is preferred in some applications as it can minimize the lengths of the connecting silicon waveguides FOW 206n and hence minimize propagation loss. In addition, when the exit slit width is small compared to the optical wavelength used in the device, the large beam divergence angle from the narrow exit slit (formed by the gain-element waveguide mouth GE-WMn 212n) can result in the diverging beam being partly blocked by the adjacent waveguide mouth.
To address the above shortfall for the Echelle grating design for grating IDG 2030, an embodiment of the grating design for grating IDG 2030 uses computationally generated grating that has substantial freedom, referred to collectively as super-compact grating (SCG), to implement the placements of the exit slits formed by the waveguide mouths GE-WM12121 . . . GE-WMn 212n. Such computationally generated SCG grating designs are described in the reference patent listed in front referred to as patent: PGR1, PGR2, PGR3, PGR4, PGR5, PGR6, and PGR7, and are hereby incorporated in their entirety. In one aspect of such SCG grating,
Furthermore,
For example, for the purpose of illustration and not limitation, if the widths of the beams at the gain-element waveguide mouths GE-WM12121 . . . GE-WMn 212n are around 5 microns, the width of the output beam can be designed to be 50-400 microns wide to match the mode diameter of multi-mode fibers or it can also be designed to be about 20 microns wide to match the mode size of “large-mode-area” (LMA) single-mode fiber or 8 microns wide to match the mode size of regular single mode fiber. This flexibility makes the use of such grating design to be able to meet a wide variety of possibilities in terms of the maximum power of the laser and the type of optical fiber the output laser light is connected to.
Note that in the laser application shown by
Exemplary Gain Medium Structure
For the purpose of illustration and not limitation, two exemplary gain medium structures are illustrated for operation at the 1550 nm optical wavelength range, which is called the regular-mode-size (RMS) structure 4000 and the large-mode-size (LMS) structure 5000 as shown in
For the RMS structure 4000 shown in
For the purpose of illustration and not limitation, for the LMS structure 5000 shown in
Thus, both the RMS 4000 and LMS 5000 structures are designed so that only the lowest order mode would have low loss and would be the one to achieve lasing. In an exemplary embodiment, as an option, below the bottom N-doped layer is an array of narrow silicon structures 1099 formed by etching down the top silicon layer 1010 of the SOI wafer, each having a width narrower than 250 nm and spaced by 500 nm center-to-center. This array is to lower the effective refractive index of the silicon layer so the mode will be more pushed up into the structure 4000 or 5000 that would have higher averaged refractive index. Note that the silicon-layer etching is done before the InP epitaxial layer wafer bonding. This silicon structure has an “effective propagating refractive index” lower than the refractive index of InP and would not be penetrated much by the optical mode.
Exemplary Vertical Coupler Design
As noted in
For the purpose of illustration and not limitation, a vertical mode coupler VMC 6000 is shown in
For the purpose of illustration and not limitation, a second array of 5 “down-tapering” teeth, labelled as tooth 6301, 6302, 6303, 6304, 6305, are made in the silicon layer 1010, with each tooth tapering down from about 1 micron in width at point C to below 300 nm in width at point D (It may not be very clear from the 3D figure, these teeth 6301, 6302, 6303, 6304, 6305 are actually on the silicon layer 1010 that is below the layer (layer 4100+4200 for 6301, 6302, 6303, 6304, 6305—in the figure layer 4100+4200 are made translucent). For the purpose of illustration and not limitation, the distance between point C to D shall be around 20-300 microns. In this example for the purpose of illustration and not limitation, this “down-tapering” teeth structure enables the mode to be pushed up from the silicon layer 1010 into the 700 nm-thick layer (layer 4100+4200) containing the waveguide core. The evolution of the beam mode is illustrated schematically in
For the purpose of illustration and not limitation, the 1500 nm-thick top cladding layer 4300 of structure RMS 4000 shown in
For the purpose of illustration and not limitation, the simulated modes at different points for the case of the vertical coupling from silicon waveguide to the RMS (regular core) structure 4000 of
Thus, from
For the purpose of illustration and not limitation, in the case of the LMS structure 5000 of
Exemplary High-Reflector Structure
For the purpose of illustration and not limitation, the high reflector GE-HRn 214n (see
There are various possible structures for high reflector GE-HRn 214n. Possible structures of GE-HRn 214n will be referred to as High-Reflector HR 7000 in
In general, the lengths (7301, 7302, . . . 730M, 730(M+1) . . . 730(E+1)) of the etched holes can be all different or the same. In general, the lengths (7401, 7402, . . . 740M, 740(M+1) . . . 740(E)) of the solid sections can also be all different or the same. However, it is typical in a design to choose the lengths for the holes to be all the same and the lengths for the solid sections to be all the same. In that can, one can label the length of the etched down region (i.e., the holes) to be L17300 with propagating refractive index n17350 (called the low-refractive-index grating tooth) and the length of the solid section (unetched down section) to be L27400 with propagating refractive index n27450 (called the high-refractive-index grating tooth).
For the purpose of illustration and not limitation, to minimize vertical diffraction loss in the low-refractive-index grating teeth L17300 that are etched down, L17300 can be shorter than L27400 so that: L1=λ/(8 n1) and L2=λ*3/(8 n2) where λ=1550 nm, instead of the usual quarter wave design L1=λ/(4 n1) and L2=λ/(4 n2). By doing so, the vertical diffraction loss can be kept at below 1% for the case of the 500 nm to 1,000 nm thick silicon guiding layer. In another exemplary embodiment, L17300 and L27400 can be designed as the quarter-wave grating structure with L1=λ/(4 n1) and L2=λ/(4 n2). Those skilled in the art would know that there are various ways to design the Bragg grating structures, and most of them can be used as long as they can provide the reflection and transmission required for function as GE-HRn 214n.
For the purpose of illustration and not limitation, the vertical cross-section (side view) of this high reflector HR7000 made with 12 periods of L1+L2 is shown in
For the purpose of illustration and not limitation, the laser output mirror OM 2010 in
Exemplary Mode Filter Structure
For the purpose of illustration and not limitation, there are two mode filters that can be used in cascade in some cases or each of these two filters can be used by itself: one is the horizontal mode filter Device 8000 shown in
For the purpose of illustration and not limitation, the first-order fundamental mode has the narrowest horizontal mode width and the second-order or higher modes has wider horizontal mode widths and would incur higher loss due to the Ti metal as they would have higher energy reaching to the Ti metal regions on both side of the WLG rib 8020. For the purpose of illustration and not limitation, the simulation shown by
For the purpose of illustration and not limitation, the structure of the vertical mode filter 8500 shown in
As an option, in-between layer 8510 and waveguide 1010, is inserted with an interspaced material ISM 8520 with a material reflective index nISM 8525. For illustration purpose and not limitation, an example of layer ISM 8520 is a 300 nm thick silicon nitride layer with nISM˜1.5. The design of layers ISM 8520 and MLM 8520 is to enhance mode energy in waveguide WLG 1010 to be lose to the layer MLM 8520 (by transferring energy to layer MLM 8520) in a way that is high for higher order modes and minimal to negligible for the fundamental waveguide mode in waveguide WLG 1010. This typically requires the index value for nMLM 8525 to be about equal to or higher than index nWLG 1015. Typically, the index nISM 8525 of the interspaced layer (ISM 8520) is lower than both the value of nMLM 8525 and nWLG 1015. The thickness of the interspaced layer (ISM 8520) is chosen to control the amount of loss so that the higher order modes have high loss while the loss of the fundamental mode is low or negligible.
For the purpose of illustration and not limitation, to further absorb the optical energy that has been transferred (or lost) to the mode-leaking material layer MLM 8510 from the guided mode in waveguide WLG 1010, on top of the layer MLM 8510 is deposited with highly optically absorbing metal AM 8550. As an example for illustration purpose, metal layer AM 8550 is made of Titanium (Ti) that has high optical absorption,
As the vertical first-order fundamental guided mode would have the smallest vertical mode width and the second-order or higher guided modes would have larger vertical mode widths, as is known to those skilled in the art, the second-order or higher modes in waveguide WLG 1010 would couple more energy to the top MLM 8510 layer and hence would incur higher loss of energy to MLM 8510 layer. The energy reaching MLM 8510 layer will be dispersed away in MLM 8510 layer due to propagation side way or scattering loss in MLM 8510 layer. Optionally, the energy reaching MLM 8510 can also be further absorbed by the metal AM 8550.
For the purpose of illustration and not limitation, the simulation shown in
For the purpose of illustration and not limitation, the total length of cascading the horizontal mode filter 8000 of
Exemplary Surface-Emitting Grating Fiber Coupler
For the purpose of illustration and not limitation, at the output mirror OM 2010, a part of the beam is transmitted and further propagation from the output mirror OM 2010 to an optical grating fiber coupler FC 2060.
Two main versions for fiber coupler FC 2060 are described below. The first version for FC 2060 is in the form of a surface-emitting grating SG 9600 is shown in
Serving as an example for illustration purpose but not limitation, the period of these teeth can be near an optical wavelength in the grating layer (instead of half wavelength for reflector). The period is chosen close to an optical wavelength to ensure that the light to emits out of the grating layer (e.g., layer 1010) in the vertical direction (out of the plane of the wafer substrate) towards an optical fiber, instead of reflecting the light energy back within the layer. As is known to those skilled in the art, there are other grating designs that can also emit light in the vertical direction, such example, using two or three times the optical wavelength in the grating layer, which can all be employed for the design of surface grating SG 9600 for fiber coupler FC 2060. An appropriate choice of period would enable the light to be diffracted to be propagating near vertically upward. As the fiber mode is a Gaussian shape, it is preferable that the light diffracted by the grating is also matching the Gaussian shape. For the purpose of illustration and not limitation, one way to do so is to change the duty cycle of the width of L1:L2, where L1 is the length of the etched down region and L2 is the length of the unetched region for the grating. This changing duty cycle for the grating teeth can be employed to tailor the longitudinal mode size and shape to also closely match the fiber mode. One can either follow or modify from this scheme for the grating fiber coupler.
For the purpose of illustration and not limitation, in order to achieve maximum power emission to the top and reduce any power scattering to the bottom part of the chip, as shown by
For the purpose of illustration and not limitation, the 1 dB optical bandwidth of the grating fiber coupler can be about as wide as 30-60 nm. For the purpose of illustration and not limitation, the 30-60 nm bandwidth can be achieved by orienting the fiber more towards the normal so that the fiber sustains an angle from the normal of less than or approximately 8 degrees. Wide optical bandwidth will enable higher beam power output for the laser (IDG-OTFT laser).
The desirable width of the output beam is dependent on the type of output fiber to be used. For the purpose of illustration and not limitation, it is typically desirable that the width of the output beam at the grating to be approximately 200 microns if a multimode fiber is used as output fiber OF 2070, as the mode diameter of a multi-mode fiber can be as large as 200 microns. On the other hand, it is desirable that the width of the output beam at the grating be about 8 microns or 20 microns if a regular single mode fiber is used or a large-mode-area (LMA) single-mode fiber is used. This is because the mode diameter of a regular single mode fiber is 8 micron and that of a large-mode-area (LMA) single-mode fiber can be around 20 microns.
The beam width at the output mirror OM 2010 is denoted by BWOUT 9900. Often, it is desirable to have a large beam width for BWOUT 9900 of approximately 200 micrometers (200 um) in diameter or larger so as to reduce the optical intensity at the output mirror OM 2010. This would be the case if the IDG-OTFT laser is high in output power (e.g., in Watts to tens of Watts level). In that case, to couple into an output optical fiber OF 2070 with a fiber mode size diameter FMD 2075 that is smaller, like FMD 2075 of 8 microns or 20 microns, would require vertical emission from then output waveguide layer 1010, also to reduce the beam width BWOUT 9900 (e.g., of 200 um) to fit the smaller fiber mode diameter FMD 2075 (of 8 um or 20 um). One way to achieve the mode size reduction is to use Fresnel lens structure FLS 9800 to focus the large vertical output beam to a smaller beam diameter to match the fiber mode size. Serving as an example for the purpose of illustration and not limitation, a Fresnel lens structure FLS 9800 can be made by deposition ˜2 microns thick nitrides (Si3N4 or AlN) on the grating surface with elliptical (or circular) grooves as shown in
For the purpose of illustration and not limitation,
For the purpose of illustration and not limitation, if a wider bandwidth is needed, a vertical taper coupler can be fabricated. For example, a graded-refractive index micro lens with super-high numerical aperture, called super-GRIN lens that can be integrated on silicon chip to couple light from silicon waveguide to optical fiber. The super-GRIN lens or vertical taper-based fiber coupler would have wide spectral bandwidth of over 300 nm and can be used if optical spectral bandwidth wider than 60 nm is needed for future expansion.
For the purpose of illustration and not limitation, for the case of a super-GRIN lens or vertical taper on the edge of the chip, one can enlarge the vertical mode size to a 20-micron mode size by using the super-GRIN lens or the vertical taper, and also use an external lens to refocus the large beam width laterally. The use of such edge-emitting mode-transforming structures would be needed only when the spectral bandwidth is expanded to larger than 60 nm.
Cooling System Design
For the purpose of illustration and not limitation, in an exemplary embodiment, the chip is cooled by a cooling system and the cooling system Device 10000 is as shown in
For the purpose of illustration and not limitation, in an exemplary embodiment, the top of the chip is covered mainly by relatively thick metal 10200. As an example for illustration purpose, metal 10200 is mainly gold (˜10-100 microns thick with TC(gold)=314 W/m-K) and some nickel, for electrical contact and comprehensive heat spreading. The chip may also have layers of dielectric materials or polymer materials as part of the chip fabrication process. The dielectric material may include silicon nitride (Si3N4 or called SiN) or aluminum nitride (AlN) or silicon dioxide (SiO2). The metal 10200 may also cover on top of these dielectric or polymer materials. Note that AlN is in general a good thermal conductor as solid and as deposited material (TC(solid-AlN) ˜285 W/m-K; CTE(AlN)=4.5×10−6/K; n˜2.1). AlN is also transparent at 1550 nm (it is a large bandgap UV material) and has been shown experimentally to be suitable for use in integrated optics at 1550 nm.
For the purpose of illustration and not limitation, in an exemplary embodiment, the top surface of the chip is mainly the N-doped InP layer that has the highest electrical resistance and hence is the main electrical heating source. This metalized P-side with metal layer 10200 on top can be soldered to the metalized “CTE-matching high-heat-conduction plate” CM 10100 with a solder layer SL 10300. The plate CM 10100 can also be metalized by depositing with nickel and gold to enable soldering. Serving as an example for illustration purpose, the soldering can be done by ultrasonic soldering equipment to remove any air void and the thickness of solder layer SL 10300 should in general be made very thin (only tens of microns) as solder has high CTE. As an example for illustration purpose, Gold-Tin solder can be used as the solder for solder layer SL 10300 as it has good heat conductance and also comparatively low CTE (CTE=16×10−6/K) comparing to that of Lead based solder (CTE=25-30×10−6/K). The solder layer SL 10300 should be thin comparing to the chip thickness of about 150 microns.
For the purpose of illustration and not limitation, in an exemplary embodiment, the main task of the CTE-matched high-heat-conduction plate CM 10100 is to transmit heat as much as possible to the cooling liquid CLQ 10400. The plate CM 10100 shall be thick enough to have the mechanical strength but otherwise as thin as possible to increase thermal conductance. For the purpose of illustration and not limitation, in an exemplary embodiment, a thickness of around 0.5-1 mm for CM 10100 can be used. A popular material choice for the CTE-matched plate CM 10100 is metal-diamond composite. For the purpose of illustration and not limitation, in an exemplary embodiment, the thermal conductivity of this CTE-matched thermal conducting plate CM 10100 is typically in the range of TC=500 W/m-K (achievable via a metal-diamond composite material), which is higher than that of metal. Diamond has very low CTE and metal has higher CTE than silicon. Such composite can be made CTE matched to that of silicon of CTE=2.6×10−6/K. The reason the CTE matching is important for this plate is because the temperature at the plate is expected to be high. At high enough cooling liquid flow rate, a heat removal rate of over 1-5 kW/cm2 can be reached. For the purpose of illustration and not limitation, in an exemplary embodiment, this could have enough “cooling power per unit area” or “cooling power density” for the laser chip. For the purpose of illustration and not limitation, in an exemplary embodiment, the other side of the CTE plate CM 10100 would be a dimension-matching metal pieces that make a closed enclosure chamber CMB 10500 with the CTE-matching plate CM 10100 to allow cooling liquid CLQ 10400 to flow through. The cooling liquid CLQ 10400 side of the “CTE-matched high-heat-conduction plate” CM 10100 labelled as CLQS 10450 may be corrugated or made with cooling fins structure to increase the heat-transfer surface area so as to reduce the required cooling liquid flow rate. See also
For the purpose of illustration and not limitation, in another exemplary embodiment, the approach involves micro-channel liquid cooling. Microchannel cooling plate has many micro-size channels that are hundreds of microns in size to circulate the cooling liquid through. In the case with micro-channel cooling, the CTE matched high-heat-conduction plate CM 10100 is still used for the soldered contact to the chip but the liquid chamber CMB 10500 is replaced with liquid microchannels LMC 10700 (not shown in
For the purpose of illustration and not limitation, assuming the cooling liquid is water, a cooling system that would provide a cooling rate of 1,000 W/cm2, would require a water flow rate at 0.15-0.4 Gallon/min or 0.6-1.5 liter/min (assuming ˜25-10° C. water temperature increase). The heated water subsequently has to be cooled at ˜1,200 W assuming a laser power of 300 W and wall plug-efficiency of 25%. This water cooling can be achieved a commercial water-recirculating chiller. As an example, for the purpose of illustration, a small (air-cooled) water refrigerating chiller available with 1,200 W cooling capacity is about 12 lbs in weight, 6″×8″×11″ in size, and ˜720 W in wall-plug power (basically using 2 units of the chiller), each unit with up to 700 W cooling power, size 6″×8″×5.3″, 2 l/min water circulating rate, weighing 6 lbs, and ˜360 W in wall-plug power). Another possibility is a thermo-electric (TE) water chiller (air cooled) that would be 48 lbs in weight, 6″×8″×30″ in size, and 1200 W in wall-plug power (basically using 6 units of the TE based chiller, each unit with size 6″×8″×5″, weighing 8 lbs, and 200 W in wall-plug power).
For the purpose of illustration and not limitation, in an exemplary embodiment, if cooling to near ambient temperature is suitable, a forced air system with 1 kW cooling to cool the heated cooling liquid may be realizable with a very compact heat exchanger with 20 cm3 volume (˜4 cm×4 cm×4 cm). The power consumption for such blast-air cooling liquid cooling system is usually about 10% of the cooling power (i.e., ˜100 W for 1 kW cooling power). The laser chip would work at higher than room temperature but would become less effective when the laser power is high.
As an option, the bottom part of the chip CP 100 can also be bonded with the CTE matched plate CM 10101 (like CM 10100 at the top), the cooling chamber CMB 10501 (like CMB 10500 at the top), cooling liquid CLQ 10401 (like CLQ 10400 at the top), and solder SL10301 (like SL 10300 at the top). These are illustrated in
Electrical Contact
For the purpose of illustration and not limitation, in an exemplary embodiment, a schematic illustrating how the electrical contacts to the chip are made is shown in
For the purpose of illustration and not limitation, in an exemplary embodiment, for the bottom contact 11200, there are two approaches to make the electrical contact to the bottom contact from an external electrical source.
The first approach is to open an access hole from the top to contact the bottom contact as shown by
The second approach is to selectively etch away the bottom chip material layers. As an example for illustration and not limitation, one of the bottom layers at the active gain area is silicon. In that case, one can use KOH to etch away the silicon layer. Above the silicon layer is the 1-micron thick buried oxide (BOX) layer. This BOX layer can be selectively etched away as well using Hydrogen Fluoride (HF) solution. The BOX layer etching would then expose the top waveguiding silicon layer just below the optical gain material area. Serving as an example for illustration purpose, after the BOX layer etching, one can deposit the area with silicon nitride or aluminum nitride (from the exposed side) as a waveguiding cladding to protect the region just below the guided optical mode so as not to cause additional optical loss to the guided mode. The two wide regions next to the guided mode can be accessed for bottom metal contact 10200 to the highly N-doped InP bottom layer, as illustrated by
Both methods are usable though the second method has the advantage of providing better heat dissipation from the bottom side, although it is estimated that less than 30% of the heat energy would travel by the bottom side simply because the top P-doped side has the main electrical heating and it is at least 4 times closer to the top metal than the bottom metal. Note that the contact metals would typically be electroplated to 10-50 microns thick to enable good heat spreading via the thick metal. This thick metal layer also serves to provide good electrical conduction to the top electrical contact.
The present invention has overcome the aforementioned limitations of the prior arts on diffraction-gratings based semiconductor laser systems utilizing discrete optical components. It is an aim of the present invention to provide ultra-compact highly-integrated diffraction-grating based integrated semiconductor lasers with a thin-film-transfer structure, called IDG-OTFT Lasers, that are compact in size, light weight, mechanically rugged, low in manufacturing cost, high in electrical wall-plugged power efficiency, and in some cases high in optical power output, comparing to typical lasers based on discrete optical components.
In one embodiment of the present invention, a laser system is integrated on a single integrated chip via the use of an integrated curved diffraction grating combined with one or more integrated Bragg-grating reflectors, that enables a fully integrated diffraction-grating based laser that do not need the use of any optical lens.
In another embodiment of the present invention, one or more photonic devices are integrated on a substrate. The photonic devices comprise one or more optical gain material areas. One or more passive photonic components are fabricated on a passive waveguiding layer. The passive photonic components contain at least a curved optical grating and at least one wavelength-channel-combined-arm Bragg reflector. The method further transfers a thin layer of material capable of providing optical power amplification.
In another embodiment of the present invention, the wavelength-channel-combined-arm Bragg reflector is fabricated into a planar waveguiding layer.
In as yet another embodiment of the present invention, the wavelength-channel-combined-arm Bragg reflector is fabricated into a planar waveguiding layer with high-refractive index contrast, resulting in a broad optical bandwidth of reflection and transmission.
In as yet another embodiment of the present invention, the planar waveguiding layer is silicon.
In as yet another embodiment of the present invention, the number of reflecting teeth in the wavelength-channel-combined-arm Bragg reflector is adjusted to provide a highly reflecting beam-power reflector or a partially-transmitting beam-power reflector.
In as yet another embodiment of the present invention, the optical beam is confined in the direction perpendicular to the substrate surface via planar or channel waveguides, and a curved diffraction grating is fabricated into a planar waveguiding area with the surfaces of the grating teeth approximately perpendicular to the substrate plane.
In as yet another embodiment of the present invention, one side of the optical beam propagating path intersects with the wavelength-channel-combined-arm Bragg reflector, and another side of the optical beam propagating path intersects with the curved diffraction grating is positioned the mouth of a channel waveguide (called wavelength-channel-separated waveguide mouth).
In as yet another embodiment of the present invention, the optical power in a wavelength of light in the optical beam propagating toward the wavelength-channel-combined-arm Bragg-grating reflector is reflected back either fully or partially by the wavelength-channel-combined-arm Brag-grating reflector toward the curved diffraction grating and is further diffracted by the curved diffraction grating to enter the said wavelength-channel-separated waveguide mouth.
In as yet another embodiment of the present invention, there are two or more of the said waveguide mouths, with each mouth receiving a wavelength of the light beam reflecting back from the wavelength-channel-combined-arm Bragg reflector towards the grating.
In as yet another embodiment of the present invention, the beam entering the mouth of a channel waveguide is guided via a linear or a curvilinear path along a channel waveguide to an optical gain region.
In as yet another embodiment of the present invention, the optical gain region is composed of an active gain material layer forming a gain channel waveguide bonded on top of a passive transparent channel waveguide.
In as yet another embodiment of the present invention, the optical beam energy in the passive transparent channel waveguide is transferred from the passive channel waveguide to the gain material layer via laterally tapering structures on at least one of the passive channel waveguiding layer or the gain channel waveguide layer.
In as yet another embodiment of the present invention, the optical beam energy in the gain channel waveguide is transferred from the gain channel waveguide to the passive channel waveguide via laterally tapering structures on at least one of the passive channel waveguiding layer or the gain channel waveguide layer.
In as yet another embodiment of the present invention, the optical beam energy propagating through the gain region from the grating-facing waveguide mouth is entered into a passive channel waveguide. The beam in the passive channel waveguide is then reflected back either fully or partially via a Bragg-grating reflector.
In yet another embodiment of the present invention, the curved diffraction grating is designed such that the beam size in direction parallel to the plane of the substrate is larger at the wavelength-channel-combined-arm Bragg-grating reflector than at the wavelength-channel-separated waveguide mouth.
In yet another embodiment of the present invention, the curved grating is designed such that the beam size in direction parallel to the plane of the substrate (called the horizontal mode size) is small at the wavelength-channel-separated waveguide mouth, but is large at the wavelength-channel-combined-arm Bragg-grating reflector. There may be one or more than one waveguide mouths with each mouth receiving a wavelength channel. This enables the intensity at the wavelength-channel-combined-arm Bragg-grating reflector that would have higher optical power (by combining the many wavelength channels) to be made low or comparable to the intensity of the light beam at each of the wavelength-channel-separated waveguide mouth that would receive light energy in only one of the wavelength channels. The lowered intensity in the relatively higher-power beam at the wavelength-channel-combined-arm Bragg-grating reflector reduces the chance of optical damage at the wavelength-channel-combined-arm Bragg reflector region.
In as yet another embodiment of the present invention, the wavelength-channel-combined-arm Bragg-grating reflector is made of Bragg grating's teeth that are curved in shape (instead of linear in shape like a straight line), so as to achieve larger horizontal beam size and hence lower beam intensity at the wavelength-channel-combined-arm Bragg-grating reflector.
In as yet another embodiment of the present invention, the optical beam energy propagating towards the wavelength-channel-combined-arm Bragg-grating reflector is partially transmitted at the reflector to an optical-fiber coupler such as a surface-grating based optical fiber coupler, or a planar (horizontal) beam-transformer based optical fiber coupler.
In as yet another embodiment of the present invention, the spatial region that brings in the optical fiber to the optical-fiber coupler is hermetically sealed.
In as yet another embodiment of the present invention, the surface-grating based optical fiber coupler is composed of a surface grating that emits the beam in a direction approximately perpendicular to a substrate plane and a Fresnel lens structure that further reduces a beam diameter emitted to a smaller value.
In as yet another aspect of the present invention, each of the photonic devices is sandwiched from at least one of the top or the bottom via cooling fixtures that allow water cooling of the photonic device.
In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and/or method steps described herein may be used alone or in combination with other configurations, systems and/or method steps. It is to be expected that various equivalents, alternatives and/or modifications are possible within the scope of the appended claims.
The present invention claims priority to U.S. Provisional Application No. 63/182,768, filed May 1, 2022, titled “Ultra-Compact Multi-Wavelength-Channel-Capable Integrated Semiconductor Laser”, the content of which is incorporated by reference in its entirety. The present invention incorporates by reference U.S. Provisional Applications Nos. 62/399,483, filed Sep. 25, 2016, titled “Highly Integrated Compact Diffraction Grating Based Semiconductor Laser;” in its entirety. The present invention also references the following patents: (1) (referred to as PGR1) U.S. Pat. No. 7,283,233, Issue Date: 16 Oct. 2007, titled “Curved grating spectrometer with very high wavelength resolution;” (2) (referred to as PGR2) U.S. Pat. No. 7,623,235, Issue Date: 24 Nov. 2009, “Curved grating spectrometer with very high wavelength resolution;” (3) (referred to as PGR3) U.S. Pat. No. 8,462,338, Issue Date: 11 Jun. 2013, “Curved grating spectrometer and wavelength Multiplexer or Demultiplexer with very high wavelength resolution;” (4) (referred to as PGR4) U.S. Pat. No. 9,612,155 B2, Issue Date: 4 Apr. 2017, “CURVED GRATING SPECTROMETER AND WAVELENGTH MULTIPLEXER OR DEMULTIPLEXER WITH VERY HIGH WAVELENGTH RESOLUTION;” (5) (referred to as PGR5) U.S. Pat. No. 8,854,620 B2, Issue Date: 7 Oct. 2014, “CURVED GRATING SPECTROMETER AND WAVELENGTH MULTIPLEXER OR DEMULTIPLEXER WITH VERY HIGH WAVELENGTH RESOLUTION;” (6) (referred to as PGR6) Application number PCT/US2015/049386, application Date: 10 Sep. 2015, “CURVED GRATING SPECTROMETER AND WAVELENGTH MULTIPLEXER OR DEMULTIPLEXER WITH VERY HIGH WAVELENGTH RESOLUTION;” (7) (referred to as PGR7) U.S. application Ser. No. 15/362,037 (US Application: US20170102270A1), application Date: 28 Nov. 2016, “CURVED GRATING SPECTROMETER AND WAVELENGTH MULTIPLEXER OR DEMULTIPLEXER WITH VERY HIGH WAVELENGTH RESOLUTION.”
| Number | Date | Country | |
|---|---|---|---|
| 63182768 | May 2021 | US |
