Patent Grant
10355451
Various embodiments of this application relate to the field of tunable lasers.
Tunable lasers are widely used in telecommunications, sensing, and test and measurement applications. Semiconductor tunable lasers are particularly useful for their small size and low power consumption. One example of a semiconductor tunable laser is a sampled grating distributed Bragg reflector laser (SGDBR) which uses Vernier tuning of two SGDBR (sampled grating distributed Bragg reflector) mirrors. In various embodiments, the sampled grating distributed Bragg reflectors can include a plurality of distributed Bragg reflectors which cumulatively produce a comb of reflections. The full width half maximum and reflection strength of the comb can be tailored by various design parameters including grating burst length, number of bursts, spacing between bursts coupling coefficient etc., Various other embodiments of tunable lasers include Y branch configurations of the above, digital supermode distributed Bragg reflectors, coupled cavity designs, and tunable grating-coupler designs.
Systems and methods that enable an optical transmitter capable of generating optical signals with various modulation formats may be beneficial in optical networks and systems. Example embodiments described herein have several features, no single one of which is indispensable or solely responsible for their desirable attributes. Without limiting the scope of the claims, some of the advantageous features will now be summarized.
Various embodiments of a tunable laser described herein comprise a laser cavity formed between a broadband mirror and a comb reflector. The laser cavity includes a gain section and an optional phase section. Such embodiments of a tunable laser can achieve a wide wavelength tuning range by utilizing a Vernier effect between cavity modes of the laser cavity and the modes of the comb reflector.
Various embodiments of a tunable laser described herein comprise a Y-branch laser comprising a first branch comprising a first reflector, a gain section and a comb reflector and a second branch comprising a second reflector, an optional phase section and a comb reflector. Wavelength tuning in the Y-branch can be achieved by using a Vernier effect between cavity modes of the laser cavity formed by the first and the second branches and the modes of the comb reflector.
Various embodiments of tunable lasers described herein comprise a laser cavity formed by a comb reflector comprising an optically active material (e.g., gain material). In various embodiments, the laser cavity can comprise lenses or other optical components within the laser cavity. In various embodiments, the laser cavity can be configured as an external cavity laser.
Various embodiments of tunable lasers comprising a comb reflector can be integrated (e.g., monolithically integrated) with additional optical components and/or devices as a photonic integrated circuit. For example, various embodiments of tunable lasers comprising a comb reflector can be monolithically integrated with a semiconductor optical amplifier and/or a modulator (e.g., an electroabsorption modulator (EAM) or a Mach-Zehnder type modulator). The modulator can be configured for direct modulation of light from the tunable laser at bit-rates greater than or equal to about 1 Gbps, greater than or equal to about 2.5 Gbps, greater than or equal to about 10 Gbps, greater than or equal to about 40 Gbps, greater than or equal to about 100 Gbps, greater than or equal to about 256 Gbps, or values in between any of these values.
One innovative aspect of the subject matter of this application includes a wavelength tunable laser comprising a gain medium; a reflective comb mirror disposed at one side of the gain medium, the reflective comb mirror having a plurality of reflection peaks; and a broadband reflector disposed at another side of the gain medium. The reflective comb mirror and the broadband reflector form a laser cavity formed having a plurality of cavity modes. The reflective comb mirror is configured to be electrically or thermally tuned such that at least one of the plurality of reflection peaks overlaps with one of the plurality of cavity modes to generate a laser signal. The reflective comb mirror can comprise additional gain material separate from said gain medium. For example, the reflective comb mirror can comprise one or more sections comprising additional gain material separate from said gain medium. In various embodiments, the gain medium can comprise the reflective comb mirror.
Another innovative aspect of the subject matter of this application is embodied in a wavelength tunable laser comprising a laser cavity formed by a reflective comb mirror and a broadband reflector. The reflective comb mirror has a plurality of reflection peaks. The laser cavity comprises a gain medium. The laser cavity has a plurality of cavity modes. The laser cavity comprises a phase section that is configured to introduce a change in optical path of an optical signal in the laser cavity. The phase section and/or the reflective comb mirror are configured to be electrically or thermally tuned such that at least one of the plurality of reflection peaks of the reflective comb mirror overlaps with one of the plurality of cavity modes to produce a laser signal.
Another innovative aspect of the subject matter discussed herein is embodied in a wavelength tunable laser comprising a gain region comprising a gain medium; a comb mirror disposed at one side of the gain region, the comb mirror having a plurality of reflection peaks; and a broadband mirror disposed at another side of the gain region. A laser cavity formed by the comb mirror and the broadband mirror has a plurality of cavity modes. The comb mirror is configured to be electrically or thermally controlled such that at least one of the plurality of reflection peaks overlaps with one of the plurality of cavity modes.
In various embodiments of the tunable laser, the gain region, the comb mirror and the broadband mirror can be disposed on a substrate comprising at least one waveguide. The substrate can comprise a crystalline material. The gain region can comprise a multi-quantum well semiconductor heterojunction. Various embodiments of the tunable laser can be configured as a semiconductor laser. The comb mirror can comprise one or more regions comprising gain medium. The one or more regions comprising gain medium can be separate from the gain region. The comb mirror can comprise one or more regions that are devoid of the gain medium. In various embodiments, the gain region can comprise the comb mirror. The tunable laser can further comprise a phase section configured to introduce a change in optical path of an optical signal in the laser cavity. The phase section can be configured to be electrically or thermally controlled such that at least one of the plurality of reflection peaks overlaps with one of the plurality of cavity modes. In various embodiments of the laser, two or more reflection peaks of the comb mirror can be accommodated in a gain bandwidth of the gain region. In various embodiments, a length of the laser cavity can be configured such that a non-integer number of cavity modes are between two consecutive reflection peaks of the comb mirror. In various embodiments, the broadband mirror can comprise a cleaved facet.
Yet another innovative aspect of the subject matter discussed herein is embodied in a wavelength tunable laser comprising a crystalline substrate; a waveguide on the crystalline substrate; a first reflector at one end of the waveguide, a second reflector at another end of the waveguide, and a gain region in a cavity formed by the first and the second reflectors. The first reflector comprises a plurality of reflective regions and has a plurality of reflection peaks in a wavelength range. The second reflector has substantially uniform reflectivity for wavelengths in the wavelength range. The gain region comprises a gain medium. The gain region has a gain peak in the wavelength range, the gain peak having a maximum gain; and a gain bandwidth equal to a width of the gain peak at 50% of the maximum gain. The cavity formed by the first and the second reflectors has a plurality of cavity modes. A length of the cavity is configured such that a non-integer number of cavity modes are between consecutive reflection peaks of the first reflector. In some embodiments, the wavelength range can be between about 650 nm and about 1950 nm. In some other embodiments, the wavelength range can comprise at least one of a first range from about 1250 nm and about 1360 nm, a second range from about 1500 nm and about 1580 nm, or a third range from about 1600 nm and about 1700 nm. Various embodiments of the tunable laser can further comprise one or more electrodes configured to provide electrical current or voltage to move the reflection peaks of the first reflector with respect to the cavity modes to select a desired lasing wavelength. In some embodiments, two or more reflection peaks of the first reflector can be within the gain bandwidth. The first reflector can be a comb mirror and the second reflector can be a broadband mirror.
Various embodiments described herein comprise a laser cavity formed by a broadband reflector having a spectral reflectivity curve with a bandwidth between about 20 nm and about 300 nm, a comb mirror having a plurality of reflection peaks, the bandwidth of an individual reflection peak from the plurality of reflection peaks being less than about 10 nm. The wavelength distance between consecutive reflection peaks of the comb mirror (also referred to as free spectral range (FSR) of the comb mirror) can be less than about 50 nm. The laser cavity comprises a gain region between the broadband reflector and the comb mirror. The laser cavity has a plurality of cavity modes. The optical path length is configured adjust the spacing between cavity modes of the laser cavity such that a non-integer number of cavity modes are present between two consecutive reflection peaks of the comb mirror. In various embodiments, two or more reflection peaks of the comb mirror can occur within a gain bandwidth of the laser cavity. In various embodiments, the laser cavity can comprise a phase section which can be used to change a wavelength of a laser signal output from the laser cavity. For example, electrical voltage and/or electrical current can be applied to the phase section to change the wavelength of the laser signal output from the laser cavity. As another example, the phase section can be heated or cooled to change the wavelength of the laser signal output from the laser cavity. In some implementations, position of the plurality of reflection peaks of the comb mirror can be changed to change the wavelength of the laser signal output from the laser cavity. The position of the plurality of reflection peaks of the comb mirror can be changed by applying electrical current or electrical voltage to the comb mirror. In various embodiments, the laser cavity comprising the gain region, the broadband reflector and the comb mirror can be formed on a substrate comprising a waveguide layer. In various embodiments, the substrate can be a crystalline substrate. In various embodiments, the laser cavity comprising the gain region, the broadband reflector and the comb mirror can be monolithically integrated on a substrate comprising a waveguide layer.
The reflective comb mirror can comprise additional gain material separate from the gain medium in the laser cavity. The reflective comb mirror can comprise one or more sections comprising additional gain material separate from the gain medium. In various embodiments, the gain medium of the laser cavity can comprises the reflective comb mirror.
A laser comprising a SGDBR or a comb reflector at one end of the laser cavity and a broadband reflector at another end of the laser cavity. The SGDBR or comb reflector is configured to provide a reflection peak with a narrow spectral bandwidth with a higher grating coupling coefficient. The SGDBR is configured such that only a single reflection peak of the SGDBR within the gain bandwidth of the laser. The SGDBR can be configured such that other reflection peaks of the SGDBR are outside the gain bandwidth of the laser or outside of the reflection envelope of its own comb. Such a laser can have limited wavelength tunability since no Vernier effect is achieved. Lasing in such a laser can occur at a wavelength at or near the maxima of the reflection peak of the SGDBR that falls in the gain bandwidth.
A laser comprising a SGDBR or a comb reflector at one end of the laser cavity and a DBR at another end of the laser cavity. The DBR is configured to select a single reflection peak of the SGDBR while the selected reflection peak of the SGDBR selects the lasing mode. Such a laser may not be broadly tunable due to the lack of Vernier effect.
A Y-branch laser comprising a first branch comprising a broadband reflector, a second branch comprising a SGDBR and a third branch comprising a broadband reflector or a DBR.
Any of the lasers of Example 1-3 in which the SGDBR or the DBR comprise higher order gratings having order greater than the first order.
A single mode laser comprising a first SGDBR or a first comb reflector at one end of the laser cavity and a second SGDBR or a second comb reflector at another end of the laser cavity. The spacing between consecutive reflection peaks of the second SGDBR or the second comb reflector can be greater than the spacing between consecutive reflection peaks of the first SGDBR or the first comb reflector such that only one reflection peak of the first SGDBR or the first comb reflector is selected by the second SGDBR or the second comb reflector. The design of this laser is different from a widely wavelength tunable SGDBR laser in that the second SGDBR or the second comb reflector has a very different comb spacing from the first SGDBR or the first comb reflector (e.g. multiple times FSR) and therefore cannot be tuned over a wide wavelength range.
A laser comprising:
a gain region including a gain peak, the gain peak comprising:
a maximum gain; and
a gain bandwidth defined at 30% of the maximum gain;
a reflector at one end of the gain region; and
a reflective grating structure at another end of the gain region, the reflector and the reflective grating structure forming a cavity comprising the gain region, the cavity having a plurality of cavity modes spaced apart from each other,
the reflective grating structure having a plurality of reflectance peaks, wherein a spacing between the plurality of reflectance peaks is configured such that only one reflectance peak from the plurality of reflectance peaks is in the gain bandwidth, and
wherein a full width at half maximum of the reflectance peak in the gain bandwidth is greater than or equal to about 0.05 times the cavity mode spacing and less than or equal to about 7 times the cavity mode spacing.
The laser of Example 6, comprising a semiconductor material.
The laser of any of Examples 6 and 7 comprising a waveguide.
A photonic integrated circuit comprising the laser of any of Examples 6-8.
The laser of any of Examples 6-9, wherein the reflector is a broadband reflector.
The laser of any of Examples 6-10, wherein the reflective grating structure is a sampled grating distributed Bragg reflector (SGDBR).
The laser of any of Examples 6-11, wherein the spacing between the plurality of reflectance peaks is greater than or equal to about half the gain bandwidth.
The laser of any of Examples 6-12, wherein the spacing between the plurality of reflectance peaks is greater than or equal to about 15 nm and less than or equal to about 200 nm.
The laser of any of Examples 6-13, wherein a full width at half maximum of the reflectance peak in the gain bandwidth is greater than or equal to about 1 times the cavity mode spacing and less than or equal to about 5 times the cavity mode spacing.
The laser of any of Examples 6-14, wherein the reflectance peak in the gain bandwidth has a reflection magnitude that is at least 20% greater than reflection magnitude of other reflectance peaks of the plurality of reflectance peaks.
The laser of any of Examples 6-15, comprising a doped glass.
The laser of any of Examples 6-16, wherein the reflector comprises a high reflective coating or a partial reflective coating.
The laser of any of Examples 6-17, wherein the reflector comprises a reflective facet.
The laser of any of Examples 6-18, configured to output laser light with optical power between about 0.1 mW and 10.0 mW.
The laser of any of Examples 6-18, configured to output laser light with optical power between about 100 mW and 3 W.
The laser of any of Examples 6-18, configured to output laser light with optical power between about 1 W and 100 W.
A laser comprising:
a gain region having a gain peak, the gain peak comprising:
a first reflective grating structure at one end of the gain region, the first reflective grating structure having a reflectance peak in the gain bandwidth; and
a second reflective grating structure at another end of the gain region, the gain region, the first reflective grating structure and the second reflective grating structure forming a cavity, the cavity having a plurality of cavity modes spaced apart from each other, the second reflective grating structure having a plurality of reflectance peaks,
wherein full width at half maximum of the reflectance peak of the first reflective grating structure is greater than or equal to about 0.05 times the spacing between consecutive reflectance peaks of the plurality of reflectance peaks of the second reflective grating structure and less than or equal to about 7 times the spacing between consecutive reflectance peaks of the plurality of reflectance peaks of the second reflective grating structure, and
wherein a full width at half maximum of the plurality of reflectance peaks of the second reflective grating structure is greater than or equal to about 0.05 times the cavity mode spacing and less than or equal to about 7 times the cavity mode spacing.
The laser of Example 22, comprising a semiconductor material.
The laser of any of Examples 22 and 23 comprising a waveguide.
A photonic integrated circuit comprising the laser of any of Examples 22-24.
The laser of any of Examples 22-25, wherein the first reflective grating structure is a distributed Bragg reflector (DBR).
The laser of any of Examples 22-26, wherein the second reflective grating structure is a sampled grating distributed Bragg reflector (SGDBR).
The laser of any of Examples 22-27, wherein the full width at half maximum of the reflectance peak of the first reflective grating structure is between about 0.1 nm and about 30 nm.
The laser of any of Examples 22-28, wherein the full width at half maximum of the plurality of reflectance peaks of the second reflective grating structure is between about 0.01 nm and about 10 nm.
The laser of any of Examples 22-29, wherein the spacing between consecutive reflectance peaks of the plurality of reflectance peaks of the second reflective grating structure is between about 0.1 nm and about 20 nm.
The laser of any of Examples 22-30, comprising a doped glass.
The laser of any of Examples 22-31, wherein the first reflective grating structure or the second reflective grating structure comprises a high reflective coating or a partial reflective coating.
The laser of any of Examples 22-32, wherein the first reflective grating structure or the second reflective grating structure comprises a reflective facet.
The laser of any of Examples 22-33, configured to output laser light with optical power between about 0.1 mW and 10.0 mW.
The laser of any of Examples 22-33, configured to output laser light with optical power between about 100 mW and 3 W.
The laser of any of Examples 22-33, configured to output laser light with optical power between about 1 W and 100 W.
A laser cavity comprising:
a gain region having a gain peak, the gain peak comprising:
a first reflective grating structure at one end of the gain region, the first reflective grating structure having a first plurality of reflectance peaks spaced apart from each other; and
a second reflective grating structure at another end of the gain region, the gain region, the first reflective grating structure and the second reflective grating structure forming a cavity, the cavity having a plurality of cavity modes spaced apart from each other, the second reflective grating structure having a second plurality of reflectance peaks spaced apart from each other,
wherein the spacing between consecutive reflectance peaks of the first plurality of reflectance peaks is between about 1.5 times and about 200 times the spacing between consecutive reflectance peaks of the second plurality of reflectance peaks, such that only one reflectance peak of the first plurality of reflectance peaks is in the gain bandwidth.
The laser of Example 37, comprising a semiconductor material.
The laser of any of Examples 37 and 38 comprising a waveguide.
A photonic integrated circuit comprising the laser of any of Examples 37-39.
The laser of any of Examples 37-40, wherein the first reflective grating structure or the second reflective grating structure is a sampled grating distributed Bragg reflector (SGDBR).
The laser of any of Examples 37-41, wherein the full width at half maximum of the reflectance peak of the first reflective grating structure is between about 0.01 nm and about 10 nm.
The laser of any of Examples 37-42, wherein the full width at half maximum of the reflectance peak of the second reflective grating structure is between about 0.01 nm and 10 nm.
The laser of any of Examples 37-44, wherein the spacing between consecutive reflectance peaks of the plurality of reflectance peaks of the second reflective grating structure is between about 0.1 nm and 20 nm.
The laser of any of Examples 37-44, comprising a doped glass.
The laser of any of Examples 37-45, wherein the first reflective grating structure or the second reflective grating structure comprises a high reflective coating or a partial reflective coating.
The laser of any of Examples 37-46, wherein the first reflective grating structure or the second reflective grating structure comprises a reflective facet.
The laser of any of Examples 37-47, configured to output laser light with optical power between about 0.1 mW and 10.0 mW.
The laser of any of Examples 37-47, configured to output laser light with optical power between about 100 mW and 3 W.
The laser of any of Examples 37-47, configured to output laser light with optical power between about 1 W and 100 W.
The laser of any of Examples 1-50, comprising antireflection coatings disposed on a side of the reflector, the reflective grating structure, first reflective grating structure or the second reflective grating structure opposite the gain region.
The laser of any of Examples 6-51, wherein the reflective grating structure, first reflective grating structure or the second reflective grating structure is configured as a comb mirror.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
In the following description of the various embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration various embodiments of the device.
It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of present invention.
These and other features will now be described with reference to the drawings summarized above. The drawings and the associated descriptions are provided to illustrate embodiments and not to limit the scope of the disclosure or claims. Throughout the drawings, reference numbers may be reused to indicate correspondence between referenced elements. In addition, where applicable, the first one or two digits of a reference numeral for an element can frequently indicate the figure number in which the element first appears.
Although certain preferred embodiments and examples are disclosed below, inventive subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and to modifications and equivalents thereof. Thus, the scope of the claims appended hereto is not limited by any of the particular embodiments described below. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, the structures, systems, and/or devices described herein may be embodied using a variety of techniques including techniques that may not be described herein but are known to a person having ordinary skill in the art. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein. It will be understood that when an element or component is referred to herein as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present therebetween. For clarity of description, “reflector” or “mirror” can be used interchangeably to refer to an optical element and/or a surface having a reflectivity greater than or equal to about 0.01% and less than or equal to 100% including any value in between.
A new innovative tunable semiconductor laser is contemplated herein that offers advantages of simpler tuning mechanism as well as lower power consumption. Various embodiments of tunable lasers described herein can be tuned with fewer controls (e.g., one or two controls). Various embodiments of the innovative tunable laser comprising a comb mirror described herein comprise a comb mirror to define a series of selectable lasing modes each of which can be continuously tuned over a short wavelength range. The tunable laser can be configured to output a laser signal having a desired wavelength by selecting a lasing mode of the comb mirror that is closest to the desired wavelength and tuning the selected mode to the desired wavelength by temperature tuning and/or electrical tuning. The tuning range of the innovative tunable laser comprising a comb mirror can be greater than or equal to about 5 nm, greater than or equal to about 10 nm, greater than or equal to about 20 nm, greater than or equal to about 50 nm, greater than or equal to about 100 nm, less than or equal to about 200 nm, less than or equal to about 300 nm, less than or equal to about 500 nm, or have any value in a range or sub-range defined by any of these values.
One possible embodiment of the innovative tunable semiconductor laser device is shown in
In various embodiments, the comb mirror 103 can be a periodically chirped reflector or a superstructure grating or mirror. In some embodiments, the comb mirror 103 can comprise a sampled grating distributed Bragg reflector. The comb mirror 103 can have a reflectivity between about 0.01% and about 99.9% for incident light having a reflective wavelength in the operating wavelength range of the tunable laser. The comb mirror 103 has a plurality of reflection peaks in the operating wavelength range of the tunable laser. Each reflection peak can have a maximum reflection at a wavelength in the operating wavelength range of the tunable laser and a bandwidth given by the spectral width of the individual reflection peak at half the maximum reflection. The wavelength at which the maximum of an individual reflection peak occurs can be tuned electrically or thermally. For example, the wavelength at which the maximum of an individual reflection peak occurs can be changed by changing the temperature of the comb mirror 103 or by providing an electrical current or electrical voltage to the comb mirror 103. The bandwidth of an individual reflection peak can be in a range between about 0.001 nm and about 10 nm, between about 0.01 nm and about 5 nm, between about 0.05 nm and about 4 nm, between about 0.1 nm and about 3 nm, between about 0.2 nm and about 2.5 nm, between about 0.5 nm and about 2.0 nm, between about 0.7 nm and about 1.0 nm, or any value in a range/sub-range formed by these values.
The distance between consecution reflection peaks of the comb mirror 103 is referred to as free spectral range (FSR). The FSR can be between about 0.05 nm and about 50 nm, between about 0.1 nm and about 30 nm, between about 0.1 nm and about 1 nm, between about 0.2 nm and about 10 nm, between about 0.3 nm and about 15 nm, between about 0.5 nm and about 15 nm, a value in any range/sub-range formed by any of these values. The laser cavity formed by the comb mirror 103 and the broadband mirror 104 has a plurality of cavity modes. In various embodiments, the laser cavity can be configured such that a non-integer number of cavity modes may fit into a single free spectral range (distance between two consecutive reflection peaks) of the comb mirror 103. Without any loss of generality, when the laser cavity is configured such that a non-integer number of cavity modes are present between two consecutive reflection peaks of the comb mirror 103, different cavity modes would overlap with different portions of consecutive reflection peaks of the comb mirror 103. Accordingly, in many embodiments of the innovative tunable laser comprising a comb mirror, different cavity modes selected by consecutive reflection peaks of the comb mirror would not be able to simultaneously lase. Without any loss of generality, the optical path length of the laser cavity can be configured such that a non-integer number of cavity modes may fit into a single free spectral range (distance between two consecutive reflection peaks) of the comb mirror 103. In various embodiments, the comb mirror 103 can be a sampled grating distributed Bragg reflector (SGDBR).
The broadband mirror 104 can be configured as a front or a back mirror of the laser device. Similarly, the comb mirror 103 can be configured as a front or a back mirror. In various embodiments, the front mirror has a reflectivity configured to allow a portion of the laser signal to be output through the front mirror. For example, the front mirror can have a reflectivity between about 0.1% and about 99%, between about 0.1% and about 60%, between about 1% and about 80%, between about 5% and about 70%, between about 10% and about 65%, between about 20% and about 60%, or any value in a range/sub-range defined by any of these values so as to allow output a portion of the laser signal through the front mirror. Other values outside this range are also possible. Various embodiments may make use of the laser signal from either end of the laser, or in some applications from both ends simultaneously.
As discussed above, the wavelengths at which the reflectivity of the plurality of reflection peaks of comb mirror 103 have a maximum value can be tuned such as, for example by providing an electric current and/or electrical voltage through an electrical contact associated with the comb mirror 103. In this manner, the comb mirror 103 is configured to select one or more of the cavity modes to generate a laser signal at a desired wavelength. Without any loss of generality, tuning the comb mirror 103 can result in movement of at least one of the reflection peaks across the cavity modes such that at least one of the cavity modes overlaps with the at least one of the reflection peaks. In some embodiments, heater pads or liquid crystal with electrodes configured to apply voltage across the liquid crystal can be associated with the comb mirror 103 and used to tune the FSR of the comb mirror 103. Various embodiments of heater pads include disposing a resistive metallic strip over the comb mirror 103, and applying an electric current through the resistive strip resulting in local heating which ultimately results in tuning of the comb mirror. Various parameters (e.g., length of the cavity, reflectivity of the comb mirror 103 and/or the broadband mirror 104) can be adjusted such that the cavity modes are spaced wide enough apart to obtain a laser signal with a single mode having side mode suppression ratio (SMSR) greater than about 20 dB (e.g., about 30 dB, about 40 dB, about 50 dB, etc. or any range formed by any of these values). In various embodiments, the output signal from the laser can have a SMSR between about 10 dB and about 150 dB, between about 30 dB and about 140 dB, between about 40 dB and about 120 dB, between about 50 dB and about 110 dB, between about 60 dB and about 100 dB, between about 70 dB and about 90 dB or any range or a combination of ranges between any of these value.
The laser cavity formed by the broadband mirror 104 and the comb mirror 103 can include an optional phase section 101 to help manipulate the cavity mode placement. The phase section 101 can be configured to effect a change in the optical path length of the optical signal in the cavity. In various embodiments, electrical current or an electrical voltage can be applied to the phase section 101 through electrical contacts (e.g., in proximity to the phase section) to alter the optical path length of the optical signal in the laser cavity. In some embodiments, the optical path length of the optical signal in the laser cavity can be changed by effecting a temperature change in the phase section 101. A temperature change in the phase section 101 can be caused, for example, by applying an electric current through a resistive strip disposed with respect to the phase section 101.
In various embodiments, the phase section 101 can be disposed between the gain region 102 and the comb mirror 103, and in some embodiments the phase section 101 can be within the gain region 102. Other locations are also possible. The phase section 101 is optional and in some embodiments, the phase section 101 can be omitted. In such embodiments, cavity mode tuning can be achieved either thermally (e.g., by applying an electrical current through a resistive heat strip) or through second order effects relating to carrier density or stress and strain in the gain region 102. In some embodiments, the comb mirror 103 may be pumped to induce gain either optically or electrically. In some embodiments, the gain region 102 can be divided into two or more portions by providing additional reflectors (e.g., reflector 105) in the gain region 102 as shown in
Yet another embodiment of the innovative tunable laser comprising a comb mirror incorporates Y-branch laser technology as shown in
The innovative tunable laser comprising a comb mirror described herein can be designed to operate in wavelength ranges between about 600 nm and about 1900 nm, less than 600 nm, greater than 1900 nm where spontaneous emission and stimulated emission are available. Embodiments of the innovative tunable laser comprising a comb mirror discussed herein can be fabricated from a variety of materials including but not limited to III-V semiconductor materials such as InP, GaAs, InGaAP, InAlAsP, GaN; erbium doped glasses; Silicon Germanium, and other laser materials. Embodiments of the innovative tunable laser comprising a comb mirror discussed herein can also comprise hybrid combinations of materials, for example, by butt-coupling or wafer bonding gain material to other active or passive material. Various implementations of the innovative tunable laser comprising a comb mirror described herein can be fabricated by monolithically integrating the gain region, the optional phase section, and the comb mirror on a substrate comprising a waveguide layer. The substrate can be a crystalline substrate. In some embodiments, the substrate can comprise a semiconductor material.
The radiation emitted from the gain region 102 when the tunable laser is not configured to lase can have a peak with a maximum gain value and a bandwidth which is equal to the spectral width at which the gain is half the maximum gain value. Without any loss generality, the bandwidth of the gain peak can be greater than the FSR of the comb mirror as shown in
In various embodiments, the gain region 102 can extend into the comb mirror 103. In some embodiments, the comb mirror 103 can be formed in the gain region 102. In some implementations of the tunable laser the comb mirror 103 can comprise an additional gain material different from the gain medium in the gain region 102. The additional gain material can be distributed through the entire length of the comb mirror 103 or distributed in one or more sections. The one or more sections of the comb mirror 103 can be separate from the gain region 102 as shown in
Operation of the Innovative Tunable Laser Comprising a Comb Mirror
Wavelength tuning in various embodiments of the innovative tunable laser comprising a comb mirror at one end and a broadband reflector at the other end as described herein can be accomplished by moving the reflection peaks of the comb mirror to select different cavity modes of the laser. For example, at least one of the reflection peaks of the comb mirror can be moved to select one of the cavity modes. To achieve continuous tuning, at least one of the reflection peaks of the comb mirror is capable of being moved by an amount greater than or equal to the distance between consecutive reflection peaks (also referred to as free spectral range (FSR)) of the comb mirror. In contrast, wavelength tuning in implementations of a sampled grating distributed Bragg reflector (SGDBR) laser comprising two sampled grating distributed Bragg reflectors (SGDBRs) at both ends of a laser cavity is accomplished by Vernier tuning of the two sampled grating distributed Bragg reflectors. In embodiments of a coupled cavity laser, wavelength tuning can be accomplished by Vernier tuning of cavity modes. Embodiments of the innovative tunable laser comprising a comb mirror at one end and a broadband reflector at the other end as described herein can be tuned using two tuning controls—for example, one tuning control for a phase section and a second tuning control for a mirror section instead of three tuning controls—for example, one tuning control for a phase section and two tuning controls for mirror sections that are used to achieve wavelength tuning in implementations of a SGDBR laser comprising two sampled grating distributed Bragg reflectors (SGDBRs) at both ends of a laser cavity. Reducing the number of tuning controls can be advantageous in reducing the complexity of operating the device and can also simplify packaging. Moreover, with one less section to control, there is an opportunity to reduce the footprint size and/or the power consumption of the semiconductor laser device.
The tuning operation of an embodiment of the innovative tunable laser comprising a comb mirror contemplated here is shown in
The tuning of the mirror and phase section can in some embodiments be achieved electrically or thermally, and the gain in the laser gain section can in some embodiments be achieved electrically or through optical pumping.
The tuning operation of the innovative tunable laser comprising a comb mirror discussed herein is significantly different from other existing lasers (e.g., the SGDBR laser). As discussed above, wavelength tuning in various embodiments of the tunable laser comprising a comb mirror discussed herein is accomplished by a Vernier effect between the FSR of the reflection peaks and the cavity modes. The cavity modes in various embodiments of the innovative tunable laser comprising a comb can be tuned over a small wavelength range by the phase section. In contrast, the comb mirrors can be tuned over a large wavelength. Accordingly, the mirror comb can be tuned over most of the available index tuning range, minus half a cavity mode spacing. Continuous tuning in the innovative tunable laser comprising a comb mirror can be achieved using a mirror comb with FSR that is substantially close to the index tuning range. In contrast, the comb spacing may be denser in a SGDBR tunable laser to allow for full tuning of one mirror comb spacing plus half the width of the comb of the other mirror. The wavelength maps from innovative tunable laser comprising a comb mirror show a constant hopping between the modes of the comb mirror, before repeating back to the first mirror comb on the next available cavity mode as depicted in
For comparison,
Example Wavelength Map of the Innovative Tunable Laser Comprising a Comb Mirror
A section of a tuning map generated by simulating the operation of the innovative tunable laser comprising a comb mirror discussed herein is shown in
The simulation shown in
Example Early Prototype Data
Some wavelength maps from early prototypes of the innovative tunable laser comprising a comb mirror are shown in
As the current applied to the comb mirror of the innovative tunable laser comprising a comb mirror is increased, the wavelengths of light output from the innovative tunable laser comprising a comb mirror cycle through wavelengths that are defined primarily by spacing of the mirror comb. One cycle may not result in a continuous tuning range, however, the tunable laser can be configured such that this series of comb modes can be repeated for multiple adjacent cavity modes as the mirror is further tuned and cycled through the mirror peaks. A continuous tuning range can be achieved this way if desired, as shown in
In contrast, the wavelength map obtained for an embodiment of a SGDBR laser illustrated in
Sampled Grating Distributed Bragg Reflector Laser
Another innovative aspect contemplated in this application is embodied in a laser structure comprising a gain region comprising optically active material disposed within a cavity formed by partially reflecting or a highly reflecting mirror on one end of the cavity and a sampled grating distributed Bragg reflector (SGDBR) on another end of the cavity. Such laser structures can have several advantages over a conventional Distributed Bragg Reflector (DBR) Laser as discussed below.
A conventional DBR laser comprises a grating reflector at one end of a gain medium and an at least partially reflecting element at the other end.
Some implementations of the DBR laser may further comprise a phase section 1101 positioned at either end of the gain region 1102, although it is has been chosen to be on the left side of the gain section for the embodiment illustrated in
The design of the DBR 1103 can affect the quality of the optical signal emitted by the laser. For example, if the reflectance peak of the DBR has a broad spectral bandwidth (e.g., determined by the full width at half maximum of the reflection peak), the side mode suppression ratio (SMSR) will be poor or reduced (e.g., SMSR can be less than about 20 dB), and in the worst case multiple cavity modes may lase. This concept is illustrated in
Higher power lasers generally can have longer cavities, e.g., to accommodate larger gain regions. The cavity mode spacing is inversely proportional to the length of the cavity and therefore the cavity modes may be tightly spaced in wavelength domain. In such embodiments of DBR with reflection peaks having very small spectral bandwidth may be used to achieve single-mode operation, providing SMSR greater than 20 dB. The spectral bandwidth of the reflection peak of a DBR is generally proportional to the coupling strength of the grating and can be modified by changing the depth of the grating or the index contrast between grating structures or the overlap of the optical mode with the grating. In various embodiments, the optical mode may be confined to a waveguide provided in a waveguide layer and the grating may be provided in a grating layer. In such embodiments, the overlap of the optical mode with the grating may depend on a position of grating layer with respect to the waveguide layer. Precise control of these parameters can be difficult. Additionally, manufacturability considerations can limit how low the coupling strength of the grating can be. Moreover, in photonic integrated circuits, multiple different devices may be desired on a single fabrication platform, and some devices may require a higher coupling coefficient (e.g. for tunable laser design) while others on the same chip may require a very narrow filter. Thus, it may be difficult to manufacture DBRs with reflection peaks with narrow spectral bandwidth that can be used to fabricate high power single-mode lasers.
These issues can all be addressed by replacing the DBR 1103 by a Sampled Grating Distributed Bragg Reflector (SGDBR) or a comb reflector. The SGDBR comprises a series of grating bursts or gratings in the optical path spaced apart from each other by a region that does not include grating structures. The length of the region comprising the individual grating bursts is referred to herein as the burst length and the length of the region that is in between consecutive grating bursts and does not include the grating bursts is referred to herein as blank length. The distance between two consecutive grating bursts is referred to as the sampling period. In some embodiments, the SGDBR can be used to design reflectors having a variety of filter bandwidths without changing the coupling strength of the grating. Without any loss of generality, in various embodiments, the SGDBR can be provided in the cavity (e.g., adjacent to the gain region 1102) or in the waveguide integrated with the gain region 1102.
The reflection peaks of the SGDBR can have relatively narrow spectral bandwidths as compared to an equivalent DBR. This is illustrated in
The mechanism for single mode lasing of the embodiment of laser device 1400 depicted in
The SGDBR 1403 can be tuned such that the reflectance peak of the SGDBR 1403 in the gain bandwidth overlaps with one or more of the cavity modes thereby selecting the one or more cavity modes in the region of the gain curve that has significant gain. The phase section 1101 can also be tuned so that one or more cavity modes are selected by the SGDBR mirror in the region of the gain curve that has significant gain. The SGDBR 1403 and/or the phase section 1101 can be tuned by supplying electrical current or voltage through an electrical contact disposed with respect to the SGDBR 1403 and/or the phase section 1101. In some embodiments, a temperature change can be introduced into the SGDBR 1403 and/or phase section 1101 by applying an electric current through a resistive strip disposed with respect to the SGDBR 1403 and/or phase section 1101 to alter the optical path length and tune the SGDBR mirror 1403 and/or phase section 1101 thereby translating the reflectance peak of the SGDBR 1403 with respect to the cavity modes. The SGDBR 1403 can have multiple reflection peaks in the wavelength space of the cavity modes. For example, as shown in
One of the factors that contribute to stable single mode operation of the embodiment of the laser device depicted in
An alternative or additional approach for ensuring single mode operation of the implementation depicted in
A laser comprising a SGDBR mirror designed to have a reflectance comb with one dominant reflectance peak (e.g., one peak having a reflectance magnitude that is at least 20% greater than reflectance magnitude of other reflectance peaks) as shown in
The Full Width Half Maximum (FWHM) of at least one of the reflectance peaks of the SGDBR 1403 in the implementation depicted in
Advanced numerical modelling techniques can be used potentially to attain the effective cavity mode spacing, which includes the effects of not just the gain and phase length, but also the effective length of the mirror itself. The longer the cavity length, the narrower the FWHM of the reflective peaks of the SGDBR will be in some designs. The placement of the reflectance peak of the SGDBR relative to the gain curve can in some embodiments be controlled by controlling the blank length and/or the sampling period. Long laser cavities can be advantageous to achieve high output powers. However, the spacing between consecutive cavity modes can be small in lasers with long cavities. Accordingly, in lasers with long cavities, SGDBRs with reflection peaks having small FWHM may be used to achieve stable operation. SGDBRs having reflection peaks with small FWHM may be realized by increasing the sampling period. The result of a larger sampling period is that the comb is more tightly spaced and the FWHM of the reflection peaks is smaller which in turn is useful for stable operation. However, if the reflection peak of the SGDBR 1403 of the implementation illustrated in
The implementation of a laser 1700 shown in
In various implementations, the reflectivity of the DBR 1704 and/or the SGDBR 1703 can be between 0.1% and about 99%. For example, the reflectivity of the DBR 1704 and/or the SGDBR 1703 can be between 0.1% and about 2%, between 0.5% and about 3%, between about 1% and about 5%, between about 1.75% and about 10%, between about 5% and about 15%, between about 10% and about 25%, between about 25% and about 45%, between about 30% and about 60%, between about 45% and about 75%, between about 50% and about 90%, between about 75% and about 95%, between about 80% and about 97%, between about 85% and about 99%, or any combination of these ranges or in any range/sub-range defined by any of these numbers.
For efficient operation of the laser 1700 depicted in
It is noted that the implementations illustrated in
Gratings of the SGDBR 1403/1703 or the DBR 1704 may be first order gratings, second order gratings, or other higher order gratings, and may have various duty cycles depending on the intended design. The gratings may also be chirped. The implementations depicted in
The device 1400 of
The DBR 1703 and/or the SGDBR 1403/1703 can be configured to have approximate reflectivity substantially less than about 1% (e.g., less than 0.9%, less than about 0.5%, less than about 0.1%, less than about 0.01%, less than about 0.001%) at wavelengths in a wavelength range greater than or equal to about 30 nm about the reflectance peak of the DBR 1703 and/or the SGDBR 1403/1703, greater than or equal to about 40 nm about the about the reflectance peak of the DBR 1703 and/or the SGDBR 1403/1703, greater than or equal to about 100 nm about the reflectance peak of the DBR 1703 and/or the SGDBR 1403/1703, greater than or equal to about 200 nm about the reflectance peak of the DBR 1703 and/or the SGDBR 1403/1703, or ranges/sub-ranges therebetween. Using such lasing devices can eliminate the use of an isolator to prevent stray light from the system from reflecting back into the system from the laser at wavelengths far from the lasing peak. Without any loss of generality, the AR coatings can comprise, for example, a plurality of thin films, an interference coating, one or more index matching materials, a quarter wavelength stack, or combinations thereof.
Y branch configurations are also envisioned in which the DBR or SGDBR is split into one or more branches, or are on two branches of the same laser, as shown in
A skilled person would realize that embodiments of the Y branch laser 2000 such as depicted in
The implementations depicted in
In some implementations, the DBR 1704 or the DBR 2009 of the implementations depicted in
The various implementations and/or examples of lasers described herein can be configured to operate in a wide range of wavelengths, such as, for example, between about 360 nm and about 700 nm, between about 650 nm and about 1.1 μm, between about 980 nm and about 1.3 μm, between about 1.0 μm and about 1.5 μm, between about 1.3 μm and about 3.0 μm, between about 3.0 μm and about 7.0 μm, between about 5.0 μm and about 12.0 μm, between 12 μm and 40 um, or any wavelength in any range/sub-range defined by any of these values.
The various implementations and/or examples of lasers described herein can be configured to output a wide range of optical powers such as, for example, between about 0.01 mW and about 1.0 mW, between about 1.0 mW and about 10.0 mW, between about 10.0 mW and about 25 mW, between about 15 mW and about 50 mW, between about 20 mW and about 100 mW, between about 50 mW and about 500 mW, between about 100 mW and about 1 W, between about 500 mW and about 1.5 W, between about 1.0 W and about 2.0 W, between about 1.5 W and about 3.0 W, between 3 W and 100 W or any optical power in any range/sub-range defined by any of these values.
The various implementations and/or examples of lasers described herein can be configured to output a laser signal with side mode suppression ratio (SMSR) greater than or equal to about 10 dB. For example, the SMSR of the laser signal can be between about 10 dB and about 60 dB, between about 30 dB and about 70 dB, between about 40 dB and about 100 dB, between about 50 dB and about 200 dB, or any value in any range/sub-range defined by any of these values.
Various implementations and/or examples of lasers described herein comprising a single SGDBR can be configured to have limited wavelength tunability. For example, the wavelength of the laser light output by the various implementations and/or examples of lasers comprising a single SGDBR as described herein can be varied over a wavelength range less than or equal to about 16 nm. The wavelength of the laser light output by the various implementations and/or examples of lasers described herein can be varied, for example, by tuning the SGDBR, the DBR and/or the phase section using electrical and/or thermal methods discussed herein. Various implementations and/or examples of lasers described herein can be configured as high power lasers having limited wavelength tunability.
Various implementations and/or examples of lasers described herein can comprise semiconductor materials or doped glass. Various implementations and/or examples of lasers described herein can comprise one or more waveguide structures.
While the foregoing detailed description discloses several embodiments of the present invention, it should be understood that this disclosure is illustrative only and is not limiting of the present invention. It should be appreciated that the specific configurations and operations disclosed can differ from those described above, and that the apparatus and methods described herein can be used in contexts. Additionally, components can be added, removed, and/or rearranged. Additionally, processing steps may be added, removed, or reordered. A wide variety of designs and approaches are possible.
Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations. Additionally, a person having ordinary skill in the art will readily appreciate, the terms “upper” and “lower” are sometimes used for ease of describing the figures, and indicate relative positions corresponding to the orientation of the figure on a properly oriented page, and may not reflect the proper orientation of the device as implemented.
Certain features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.
This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/489,922 filed on Apr. 25, 2017 titled “Microtune Laser;” and U.S. Provisional Application No. 62/596,655 filed on Dec. 8, 2017 titled “Microtune Laser.” Each of the above-identified application is hereby expressly incorporated by reference herein in its entirety. This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/489,928 filed on Apr. 25, 2017 titled “SGDBR-Enhanced DBR;” U.S. Provisional Application No. 62/490,479 filed on Apr. 26, 2017 titled “SGDBR-Enhanced DBR;” and U.S. Provisional Application No. 62/594,973 filed on Dec. 5, 2017 titled “SGDBR-Enhanced DBR.” Each of the above-identified application is hereby expressly incorporated by reference herein in its entirety. This application is a continuation-in-part of U.S. application Ser. No. 15/938,842 filed on Mar. 28, 2018 which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/477,908 filed on Mar. 28, 2017 titled “Microtune Laser;” U.S. Provisional Application No. 62/489,922 filed on Apr. 25, 2017 titled “Microtune Laser;” and U.S. Provisional Application No. 62/596,655 filed on Dec. 8, 2017 titled “Microtune Laser.” Each of the above-identified application is hereby expressly incorporated by reference herein in its entirety.
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| Number | Date | Country | |
|---|---|---|---|
| 20180287343 A1 | Oct 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62489922 | Apr 2017 | US | |
| 62596655 | Dec 2017 | US | |
| 62489928 | Apr 2017 | US | |
| 62490479 | Apr 2017 | US | |
| 62594973 | Dec 2017 | US | |
| 62477908 | Mar 2017 | US | |
| 62489922 | Apr 2017 | US | |
| 62596655 | Dec 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15938842 | Mar 2018 | US |
| Child | 15962972 | US |
