High-power distributed Bragg reflection laser

Abstract

A reflection region, a phase shift region and an active region are sequentially formed in the longitudinal direction, and an electrode, a substrate, a lower waveguide layer and an upper waveguide layer are sequentially formed in the transverse direction from bottom to top. The same or different currents are injected into the reflection region, the phase shift region and the active region through the electrodes; the active area is used for outputting end faces; wherein the longitudinal direction is the length direction of the laser, and the transverse direction is the epitaxial wafer growth direction of the laser; in the active region, an active layer and a grating layer are sequentially arranged between the lower waveguide layer and the upper waveguide layer from bottom to top, and a Bragg grating is engraved on the grating layer; a Bragg grating is engraved on the lower waveguide layer of the reflection area, and antireflection films are arranged at the ends, away from the phase shift area, of the reflection area and the active area. Injection currents of the active region, the phase shift region and the reflection region are independently adjusted, and the wavelength tuning range of the laser is widened.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor lasers and relates to a high-power distributed Bragg reflection laser. Background Art

[0002] High-power, low-noise semiconductor lasers are widely used in laser radar systems, optical phased arrays, silicon-based optoelectronics, and free-space optical communications. At present, there are two main solutions for high-power, low-noise semiconductor lasers: one is the distributed Bragg reflector (DBR) laser (Aho AT, Viheriala J, Virtanen H, et al. High Power 1.5μm Broad Area Laser Diodes Wavelength Stabilized by Surface Gratings [J]. IEEE Photonics Technology Letters, 2018, 30 (21): 1870-1873), which realizes light feedback by including a Bragg grating. The grating area is only on both sides or one side of the laser resonator, and there is no grating on the active layer; the other is the distributed feedback (DFB) laser (Mao. YF, Cheng. YB, Xu. BB, et al. Record-high power 1.55-μm distributed feedback laser diodes for optical communication [C] / / Optical Fiber Communication Conference (OSA), 2021: W1B.7), also realizes light feedback by containing a Bragg grating, but the distributed feedback grating is formed directly on the active layer of the full cavity length, and the grating length is consistent with the length of the active layer. Since the uniform grating structure of the DFB laser cannot achieve a single longitudinal mode, it is usually necessary to insert one or more phase shift regions into the uniform grating to achieve a single longitudinal mode. The photon density will have a peak at the phase shift distribution, and longitudinal spatial hole burning is likely to occur under high-power operating conditions, reducing the performance of the laser, and the tuning range of the DFB laser is narrow, usually only a few nanometers. In comparison, the tuning range of DBR lasers is usually very large, and the coordination of multiple electrodes can achieve a tuning range of tens of nanometers or even wider.

[0003] At present, high-power low-noise lasers mainly use the same periodic grating structure, and are coated with high-reflection film and anti-reflection film on the two end faces of the laser respectively (Wang.H, Zhang.R.Kan.K.et al.High-power wide-bandwidth 1.55-μmdirectly modulated DFB lasers for free space optical communications[C] / / :Conference on Lasers and Electro-Optics(CLEO),2019:JTu2A.72). Since effective feedback is provided by coating the end face with a high-reflection film, the uncertainty in the thickness of the high-reflection film will bring about a phase uncertainty, which will affect the laser wavelength emitted by the laser, reduce the side mode suppression ratio of the laser, and thus reduce the device yield. The traditional phase-shifted distributed feedback laser (Utaka, K, Akiba, et al. λ / 4-shifted InGaAsP / InP DFB lasers [J]. Quantum Electronics, IEEE Journal of, 1986, 22 (7): 1042-1051) requires anti-reflection coating on both end faces. Since the two end faces do not need to provide effective feedback, the uncertainty of the end face cleavage plane position is eliminated. At the same time, due to the use of the traditional λ B / 4 phase shift, the reflection peak wavelength of the grating is the Bragg wavelength of the grating, which is also the lasing wavelength of the laser, so the lasing wavelength of the laser is highly accurate. However, since this laser solution is coated with anti-reflection films at both ends, the output of the laser is equal in power at both end faces, and usually only the light energy output at one end is coupled to the optical fiber to become available power to the outside world, which will cause the output power of the laser to be lost by half. In addition, under high-power operating conditions, the cavity length of the laser is usually very long, and the coupling coefficient of the grating will be lower than that of ordinary distributed feedback lasers (usually only 10cm -1 In order to increase the saturation power of the laser and avoid the problem of longitudinal spatial hole burning, the threshold gain of the traditional phase-shifted distributed feedback laser is usually very high.

[0004] In summary, existing high-power low-noise lasers have problems such as low yield, high threshold gain, and longitudinal spatial hole burning. Summary of the invention

[0005] (I) Purpose of the invention

[0006] The purpose of the present invention is to provide a high-power distributed Bragg reflector laser to solve the problems of low yield, high threshold gain and longitudinal spatial hole burning in existing high-power low-noise lasers.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a high-power distributed Bragg reflector laser, which is sequentially formed with a reflection area 13, a phase shift area 14 and an active area 15 along the longitudinal direction, and sequentially formed with an electrode 1, a substrate 3, a lower waveguide layer 4 and an upper waveguide layer 12 along the transverse direction from bottom to top; the reflection area 13, the phase shift area 14 and the active area 15 are injected with the same or different currents through the electrode 1; the active area 15 is used for the output end face; wherein the longitudinal direction is the length direction of the laser, and the transverse direction is the growth direction of the epitaxial wafer of the laser; in the active area 15, an active layer 8 and a grating layer 9 are sequentially arranged from bottom to top between the lower waveguide layer 4 and the upper waveguide layer 12, and the grating layer 9 is engraved with a Bragg grating; the lower waveguide layer 4 of the reflection area 13 is engraved with a Bragg grating, and the reflection area 13 and the active area 15 are both provided with an anti-reflection film 16 at one end away from the phase shift area 14.

[0009] A ridge waveguide structure is formed on the upper waveguide layer 12, and an ohmic contact layer 2 and an electrode 1 are sequentially arranged on the ridge waveguide in the active area 15 from bottom to top; the active layer 8 includes a lower confinement layer 5, a quantum well 6 and an upper confinement layer 7 sequentially arranged from bottom to top.

[0010] The coupling coefficient between the optical field of the grating layer 9 and the Bragg grating of the grating layer 9 is less than 100 cm -1 The optical field of the lower waveguide layer 4 and the Bragg grating coupling coefficient of the lower waveguide layer 4 are greater than 100cm -1 ; The Bragg gratings of the grating layer 9 and the lower waveguide layer 4 are first-order Bragg gratings or high-order gratings; the Bragg gratings of the grating layer 9 and the lower waveguide layer 4 have the same or different depths.

[0011] The period of the Bragg grating of the grating layer 9 is Λ 1 =m 1 λ B / 2n eff1 , where λ B and m 1 are the Bragg wavelength and order corresponding to the grating, n eff1 is the effective refractive index of the active region waveguide; the period of the Bragg grating of the lower waveguide layer 4 is Λ 2 =m 2 λ B / 2n eff2 , where λ B and m 2 are the Bragg wavelength and order corresponding to the grating, n eff2 is the effective refractive index of the waveguide in the reflection region.

[0012] The ohmic contact layer 2 and the upper waveguide layer 12 are heavily doped with P-type, and the doping concentration range is 10 19 ~10 20 cm -3 ; The lower waveguide layer 4 is N-type doped; the active layer 8 is undoped, and the upper waveguide layer 12, the active layer 8 and the lower waveguide layer 4 together constitute a PiN structure.

[0013] The active layer 8 contains one or more quantum wells 6, and the quantum well 6 is a bulk material, a quantum wire or a quantum dot.

[0014] The grating of the active area 15 is made in the grating layer 9 ; the grating of the reflective area 13 is made in the lower waveguide layer 4 , and the Bragg wavelength corresponding to the grating of the reflective area 13 is the same as the Bragg wavelength corresponding to the grating of the active area 15 .

[0015] The reflectivity of the anti-reflection film 16 is less than 1%.

[0016] There is a highly doped N ohmic contact layer between the lower waveguide layer 4 and the substrate 3 , and there is a highly doped P ohmic contact layer on the upper waveguide layer 12 .

[0017] The coupling coefficient of the grating in the active region 15 is adjusted by adjusting the etching depth of the grating in the active region 15, the refractive index of the material of the grating layer 9, and the distance from the grating layer 9 to the active layer 8; the reflectivity of the reflective region 13 is adjusted by adjusting the etching depth of the grating in the reflective region 13, the refractive index and thickness of the material of the lower waveguide layer 4, and the length of the reflective region 13.

[0018] (III) Beneficial effects

[0019] The high-power distributed Bragg reflector laser provided by the above technical solution introduces a reflection zone with a Bragg grating at the non-output end of the active region, which can improve the feedback of the laser resonant cavity and is used to replace the anti-reflection film plated at the non-output end, so the threshold gain can be reduced; at the same time, the reflection of the reflection zone is provided by the grating, and the generated reflection phase is controllable, so there will be no reduction in the side mode suppression ratio and mode jumping; the grating in the grating layer is responsible for providing gain in the active region and controlling the mode; the phase shift region is used to reduce the photon density peak value to avoid the longitudinal spatial hole burning phenomenon, and at the same time, the mode phases of the active region and the reflection region are matched; the injection currents of the active region, the phase shift region and the reflection region are adjusted separately to improve the wavelength tuning range of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of a specific example of the laser of the present invention.

[0021] Figure 2 A longitudinal cross-sectional view of a specific example of the laser of the present invention.

[0022] Figure 3A The product of the same coupling coefficient and grating length in the active region of a specific example of the laser of the present invention, and the relationship curve of the output light power with different grating lengths as the input current changes.

[0023] Figure 3B This is a spectrum diagram of different grating lengths for the product of the same coupling coefficient and grating length in the active region of a specific example of the laser of the present invention.

[0024] Figure 3C The product of the same coupling coefficient and grating length in the active region of a specific example of the laser of the present invention, and the distribution diagram of photon density along the cavity length direction with different grating lengths.

[0025] Figure 3D The product of the same coupling coefficient and grating length in the active region of a specific example of the laser of the present invention, and the distribution diagram of carrier density along the cavity length direction with different grating lengths.

[0026] Figure 4A The graph is a relationship curve of the output optical power with input current at the same grating length in the active region and different coupling coefficients for a specific example of the laser of the present invention.

[0027] Figure 4B This is a spectrum diagram of the same grating length and different coupling coefficients in the active region of a specific example of the laser of the present invention.

[0028] Figure 4C This is a distribution diagram of photon density along the cavity length direction for the same grating length in the active region of a specific example of the laser of the present invention and different coupling coefficients.

[0029] Figure 4D This is a distribution diagram of carrier density along the cavity length direction for the same grating length in the active region of a specific example of the laser of the present invention and different coupling coefficients.

[0030] Among them, electrode-1, ohmic contact layer-2, substrate-3, lower waveguide layer-4, lower confinement layer-5, quantum well-6, upper confinement layer-7, active layer-8, grating layer-9, unetched layer-10, ridge layer-11, upper waveguide layer-12, reflection region-13, phase shift region-14, active region-15, anti-reflection film-16. DETAILED DESCRIPTION

[0031] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0032] Reference Figure 1 to Figure 2As shown, the high-power distributed Bragg reflector laser of this embodiment is sequentially formed with a reflection area 13, a phase shift area 14 and an active area 15 along the longitudinal direction, and sequentially formed with an electrode 1, a substrate 3, a lower waveguide layer 4 and an upper waveguide layer 12 along the transverse direction from bottom to top; the reflection area 13, the phase shift area 14 and the active area 15 are injected with the same or different currents through the electrode 1; the active area 15 is used for the output end face; wherein the longitudinal direction is the length direction of the laser, and the transverse direction is the growth direction of the epitaxial wafer of the laser; in the active area 15, an active layer 8 and a grating layer 9 are sequentially arranged from bottom to top between the lower waveguide layer 4 and the upper waveguide layer 12, and the grating layer 9 is engraved with a Bragg grating; the lower waveguide layer 4 of the reflection area 13 is engraved with a Bragg grating, and the ends of the reflection area 13 and the active area 15 away from the phase shift area 14 are both provided with an anti-reflection film 16.

[0033] A ridge waveguide structure is formed on the upper waveguide layer 12, including an unetched layer 10 and a ridge layer 11 formed above the center thereof; an ohmic contact layer 2 and an electrode 1 are sequentially arranged on the ridge waveguide in the active area 15 from bottom to top; the active layer 8 includes a lower confinement layer 5, a quantum well 6 and an upper confinement layer 7 sequentially arranged from bottom to top.

[0034] The Bragg grating coupling coefficient between the optical field of the grating layer 9 and the grating layer 9 is less than 100 cm -1 The optical field of the lower waveguide layer 4 and the Bragg grating coupling coefficient of the lower waveguide layer 4 are greater than 100cm -1 .

[0035] The Bragg gratings of the grating layer 9 and the lower waveguide layer 4 are first-order Bragg gratings or high-order gratings; the Bragg gratings of the grating layer 9 and the lower waveguide layer 4 have the same or different depths.

[0036] The period of the Bragg grating of the grating layer 9 is Λ 1 =(m 1 λ B ) / (2n eff1 ), where λ B and m 1 are the Bragg wavelength and order corresponding to the grating, n eff1 is the effective refractive index of the waveguide in the active region.

[0037] The period of the Bragg grating of the lower waveguide layer 4 is Λ 2 =(m 2 λ B ) / (2n eff2 ), where λ B and m 2 are the Bragg wavelength and order corresponding to the grating, n eff2 is the effective refractive index of the waveguide in the reflection region.

[0038] In order to ensure that the ohmic contact layer 2 has sufficient carriers and the normal operation of the laser is guaranteed, the ohmic contact layer 2 and the upper waveguide layer 12 are heavily doped with P type, and the doping concentration range is 10 19 ~10 20 cm -3 ; The lower waveguide layer 4 is N-type doped; the active layer 8 is undoped, and the upper waveguide layer 12, the active layer 8 and the lower waveguide layer 4 together constitute a PiN structure.

[0039] Furthermore, the active layer 8 contains one or more quantum wells 6, and the quantum well 6 can be a bulk material, a quantum wire, or a quantum dot.

[0040] Furthermore, in order to ensure that the laser has sufficient single-mode characteristics and that the Bragg wavelength corresponding to the grating is consistent with the resonant wavelength of the resonant cavity, the grating of the active region 15 is fabricated in the grating layer 9 .

[0041] Furthermore, in order to improve the side mode suppression ratio, avoid the deviation of the laser wave, and increase the yield of the laser, the grating of the reflection area 13 is made in the lower waveguide layer 4, and the grating made is a uniform grating with the same period. The Bragg wavelength corresponding to the grating of the reflection area 13 is the same as the Bragg wavelength corresponding to the grating of the active area 15.

[0042] Furthermore, in order to reduce the influence of the etching interface reflection, a horizontally inclined etching interface can be used to avoid the influence of the etching interface reflection on the laser performance.

[0043] Furthermore, in order to improve the light transmittance of the anti-reflection film 16 , the reflectivity of the anti-reflection film 16 is less than 1%.

[0044] Furthermore, there may be a highly doped N ohmic contact layer 2 between the lower waveguide layer 4 and the substrate 3 , and there may be a highly doped P ohmic contact layer 2 on the upper waveguide layer 12 .

[0045] Furthermore, the coupling coefficient of the grating in the active region 15 is adjusted by adjusting parameters such as the etching depth of the grating in the active region 15, the refractive index of the material of the grating layer 9, and the distance from the grating layer 9 to the active layer 8; the reflectivity of the reflection region 13 is adjusted by adjusting the etching depth of the grating, the refractive index and thickness of the material of the lower waveguide layer 4, and the length of the reflection region 13.

[0046] Further, according to the instructions attached Figure 1 and attached Figure 2 The left side is in a semi-covered state, and the right side is in a fully covered state; the reflective region 13 is located at the left end of the phase shift region 14 in the length direction, and the active region 15 is located at the right end of the phase shift region 14 in the length direction.

[0047] Example:

[0048] Figure 3AThe following is a curve showing the relationship between the output optical power and the input current under the same grating length in the active area and different coupling coefficients in a specific embodiment of a high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be found that under the condition of the same coupling coefficient and the product of the grating length, the longer the grating length in the active area, the greater the slope efficiency of the laser and the higher the output power.

[0049] Figure 3B The spectrum diagram of different grating lengths for the same coupling coefficient and grating length product of the active region in the specific embodiment of the high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be seen that the output mode of the laser is still single-mode when the grating length is changed under the same coupling coefficient and grating length product.

[0050] Figure 3C The photon density distribution diagram along the cavity length direction for different grating lengths is the product of the same coupling coefficient and grating length in the active region under the specific embodiment of the high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be found that under the same coupling coefficient and grating length product conditions, the shorter the grating length in the active region, the lower the photon density peak of the laser and the flatter the distribution.

[0051] Figure 3D The photon density distribution along the cavity length direction for different grating lengths is the product of the same coupling coefficient and grating length in the active region under the specific embodiment of the high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be found that under the condition of the same coupling coefficient and grating length product, the grating length changes, and the carrier density peak value of the laser remains almost unchanged.

[0052] Figure 4A The following is a curve showing the relationship between the output optical power and the input current under the same grating length of the active region and different coupling coefficients under the specific embodiment of the high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be found that under the condition of the same grating length of the active region, the smaller the product of the active region coupling coefficient and the grating length, the greater the slope efficiency of the laser and the higher the output power.

[0053] Figure 4B This is a spectrum diagram of different coupling coefficients under the same grating length of the active region in a specific embodiment of the high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be found that under the same grating length condition, the smaller the product of the active region coupling coefficient and the grating length changes, the output mode of the laser is still single-mode.

[0054] Figure 4CThe photon density distribution diagram along the cavity length direction of the high-power distributed Bragg reflector laser of the present invention is the same grating length in the active area and different coupling coefficients. Through this embodiment, it can be found that under the condition of the same grating length, the smaller the product of the active area coupling coefficient and the grating length, the lower the peak value of the photon density of the laser and the flatter the distribution.

[0055] Figure 4D The figure is a distribution diagram of carrier density along the cavity length direction for different coupling coefficients under the same grating length in the active region under the specific embodiment of the high-power distributed Bragg reflector laser of the present invention. Through this embodiment, it can be found that under the condition of the same grating length, the smaller the product of the active region coupling coefficient and the grating length, the closer the carrier density peak position of the laser is to the output end. When the product of the active region coupling coefficient and the grating length is close to 0.8, the carrier density distribution is the flattest.

[0056] The grating of the reflection area 13 of the present invention is made on the lower waveguide layer 4, and the grating made is a uniform grating with the same period. The Bragg wavelength corresponding to the grating of the reflection area 13 is the same as the Bragg wavelength corresponding to the grating of the active area 15, and the period of the grating of the reflection area 13 is different from the period of the grating of the active area 15. The additional feedback introduced by the grating of the reflection area 13 replaces the traditional high-reflection film. Since the grating is processed by a high-precision manufacturing method, the threshold gain of the laser is reduced. At the same time, the reflection phase generated by the reflection area 15 is accurately controllable, which will not cause a reduction in the side mode suppression ratio and a shift in the lasing wavelength, thereby increasing the yield of the laser. The mode matching of the active area 15 and the reflection area 13 is achieved through the phase shift area 14, and the peak value of the photon density in the laser cavity is reduced to avoid the occurrence of longitudinal spatial hole burning. At the same time, the wavelength tuning range and single-mode characteristics of the laser are improved, and the reliability of the device is improved.

[0057] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high power distributed Bragg reflector laser, characterized in that: A reflection region (13), a phase shift region (14) and an active region (15) are sequentially formed in the longitudinal direction, and an electrode (1), a substrate (3), a lower waveguide layer (4) and an upper waveguide layer (12) are sequentially formed in the transverse direction from bottom to top; the reflection region (13), the phase shift region (14) and the active region (15) are injected with the same or different currents through the electrode (1); the active region (15) is used for the output end face; wherein the longitudinal direction is the length direction of the laser, and the transverse direction is the growth direction of the epitaxial wafer of the laser; in the active region (15), an active layer (8) and a grating layer (9) are sequentially arranged from bottom to top between the lower waveguide layer (4) and the upper waveguide layer (12), and the grating layer (9) is engraved with a Bragg grating; the lower waveguide layer (4) of the reflection region (13) is engraved with a Bragg grating, and an anti-reflection film (16) is arranged at one end of the reflection region (13) and the active region (15) away from the phase shift region (14).

2. The high power distributed Bragg reflector laser according to claim 1, characterized in that: A ridge waveguide structure is formed on the upper waveguide layer (12); an ohmic contact layer (2) and an electrode (1) are sequentially arranged on the ridge waveguide in the active region (15) from bottom to top; and the active layer (8) comprises a lower confinement layer (5), a quantum well (6) and an upper confinement layer (7) which are sequentially arranged from bottom to top.

3. The high power distributed Bragg reflector laser according to claim 2, characterized in that: The optical field of the grating layer (9) and the Bragg grating coupling coefficient of the grating layer (9) are less than 100 cm -1 The optical field of the lower waveguide layer (4) and the Bragg grating coupling coefficient of the lower waveguide layer (4) are greater than 100 cm -1 ; The Bragg gratings of the grating layer (9) and the lower waveguide layer (4) are first-order Bragg gratings or high-order gratings; the Bragg gratings of the grating layer (9) and the lower waveguide layer (4) have the same or different depths.

4. The high power distributed Bragg reflector laser according to claim 3, characterized in that: The period of the Bragg grating of the grating layer (9) is Λ1=(m1λ B ) / (2n eff1 ), where λ B and m1 are the Bragg wavelength and order of the grating respectively, n eff1 is the effective refractive index of the active region waveguide; the period of the Bragg grating of the lower waveguide layer (4) is Λ2=(m2λ B ) / (2n eff2 ), where λ B and m2 are the Bragg wavelength and order of the grating respectively, n eff2 is the effective refractive index of the waveguide in the reflection region.

5. The high power distributed Bragg reflector laser according to claim 4, characterized in that: The ohmic contact layer (2) and the upper waveguide layer (12) are heavily doped with P type, and the doping concentration ranges from 10 19 ~10 20 cm -3 The lower waveguide layer (4) is N-type doped; the active layer (8) is undoped, and the upper waveguide layer (12), the active layer (8) and the lower waveguide layer (4) together form a PiN structure.

6. The high power distributed Bragg reflector laser according to claim 5, characterized in that: The active layer (8) contains one or more quantum wells (6), and the quantum wells (6) are bulk materials, quantum wires or quantum dots.

7. The high power distributed Bragg reflector laser according to claim 6, characterized in that: The grating of the active region (15) is made in the grating layer (9); the grating of the reflective region (13) is made in the lower waveguide layer (4), and the Bragg wavelength corresponding to the grating of the reflective region (13) is the same as the Bragg wavelength corresponding to the grating of the active region (15).

8. The high power distributed Bragg reflector laser according to claim 7, characterized in that: The reflectivity of the anti-reflection film (16) is less than 1%.

9. The high power distributed Bragg reflector laser according to claim 8, characterized in that: A highly doped N ohmic contact layer is provided between the lower waveguide layer (4) and the substrate (3), and a highly doped P ohmic contact layer is provided on the upper waveguide layer (12).

10. The high power distributed Bragg reflector laser according to claim 9, characterized in that: The coupling coefficient of the grating in the active region (15) is adjusted by adjusting the etching depth of the grating in the active region (15), the refractive index of the material of the grating layer (9) and the distance from the grating layer (9) to the active layer (8); and the reflectivity of the reflective region (13) is adjusted by adjusting the etching depth of the grating in the reflective region (13), the refractive index and thickness of the material of the lower waveguide layer (4) and the length of the reflective region (13).

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