High-power surface grating semiconductor laser

Abstract

The invention discloses a high-power surface grating semiconductor laser which is characterized in that a uniform grating is arranged at the longitudinal front end, a plurality of distributed phase shift gratings are arranged in the middle, uniform gratings are arranged at the rear parts of the distributed phase shift gratings, and the laser is transversely provided with an electrode, a substrate, a lower waveguide layer, an active layer, an upper waveguide layer, an ohmic contact layer and an upper electrode layer in sequence from bottom to top; a ridge waveguide structure is formed on the upper waveguide layer and comprises an unetched layer and a ridge layer formed above the central area of the unetched layer, and an ohmic contact layer and an upper electrode layer are sequentially arranged on the ridge waveguide in the active area from bottom to top; surface gratings are manufactured on the ohmic contact layer and the upper waveguide layer in the active region, the upper electrode layer is arranged above the surface gratings, and uniform gratings of the surface gratings are Bragg gratings; the active layer comprises a lower limiting layer, a quantum well and an upper limiting layer which are sequentially arranged from bottom to top; the longitudinal direction is the length direction of the laser, and the transverse direction is the epitaxial wafer growth direction of the laser. The invention has the advantages of poor reliability and low manufacturing cost.

Description

Technical Field

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

[0002] High-power distributed feedback lasers have the characteristics of dynamic single longitudinal mode, narrow linewidth, and low chirp, and therefore have broad application prospects. Currently, common distributed feedback lasers mainly use buried grating structures (Yokokawa S, Nakamura A, Hamada S, et al. Over 100mW Uncooled Operation of SOA-integrated 1.3-μm Highly Reliable CW-DFB Laser [C] / / Optical Fiber Communications Conference and Exhibition (OFC), 2022: 1-3), the purpose of which is to enhance the coupling between the grating and the light field mode. However, the buried grating structure requires secondary epitaxy, and materials containing aluminum components may be oxidized by oxygen in the air during the secondary epitaxy process, reducing the yield of the device. In order to avoid secondary epitaxy, some distributed feedback lasers adopt a surface grating structure (Pengfei Z, Can L, Minwen X, et al. 850nm GaAs / AlGaAs DFB lasers with shallow surface gratings and oxide aperture [J] Optics Express 2019, 27 (22): 31225-31234). In order to reduce the loss of light field by metal electrodes, the electrodes are usually kept away from the waveguide, which will lead to a decrease in injection efficiency; or a gain-coupled grating is made using periodic metal electrodes (Xia L, Yongyi C, Yugang Z, et al. Tunable DFB laser diode based on high-order surface isolation grooves working at 905nm [J] Optics Communications 2021, 481: 126528), but there are problems such as large spontaneous emission factor and high absorption loss.

[0003] Traditional distributed feedback lasers use gratings with quarter-wavelength phase shifts to achieve single longitudinal mode operation (Yihui L, Jiankun W, Yongguang H, et al. High-Power AlGaInAs / InP DFB Lasers with Low Divergence Angle [C] / / Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO / Europe-EQEC), 2019: 1-1). The photon density distribution in the cavity will have a peak at the quarter-wavelength phase shift, and longitudinal spatial hole burning is prone to occur under high-power operating conditions. As the power increases, a wider range of wavelengths experience strong distributed reflection in a smaller part of the entire grating. The power of the main mode is concentrated in the center of the laser. Therefore, the carrier loss in the center is much greater than the average carrier loss. Since the average carrier concentration remains more or less unchanged with increasing power, the carrier concentration near the end face is relatively large as the power increases. Under sufficiently high excitation, the side mode begins to laser, thereby reducing the side mode suppression ratio.

[0004] In summary, existing high-power distributed feedback lasers have problems such as low yield, poor reliability, high manufacturing cost 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 surface grating semiconductor laser to solve the problems of low yield, poor reliability, high manufacturing cost and longitudinal space hole burning in the existing high-power distributed feedback laser.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a high-power surface grating semiconductor laser, the front end of the laser is a uniform grating 12, the middle is a plurality of distributed phase-shift gratings 13, the rear of the distributed phase-shift grating 13 is a uniform grating 12, and the laser is provided with an electrode 1, a substrate 3, a lower waveguide layer 4, an active layer 8, an upper waveguide layer 11, an ohmic contact layer 2 and an upper electrode layer in sequence from bottom to top; a ridge waveguide structure is formed on the upper waveguide layer 11, including an unetched layer 9 and a ridge waveguide structure formed at the center thereof. A ridge layer 10 is arranged above the region, and an ohmic contact layer 2 and an upper electrode layer are arranged on the ridge waveguide in the active region from bottom to top in sequence; a surface grating is made on the ohmic contact layer 2 and the upper waveguide layer 11 in the active region, and the upper electrode layer is above the surface grating, and the uniform grating of the surface grating is a Bragg grating; the active layer includes a lower confinement layer 5, a quantum well 6 and an upper confinement layer 7 arranged in sequence from bottom to top; 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.

[0009] Wherein, both ends of the laser are coated with a high reflection film and an anti-reflection film respectively, the anti-reflection film has a reflectivity less than 1%, and the high reflection film has a reflectivity greater than 95%; the end face coated with the anti-reflection film is used as the output end face.

[0010] The ohmic contact layer 2 and the upper waveguide layer 11 are heavily doped with P-type, and the doping concentration ranges from 1019 to 1020 cm -3 , the lower waveguide layer 4 is N-type doped, the active layer 8 is undoped, and the upper waveguide layer 11, the active layer 8 and the lower waveguide layer 4 together constitute a PiN structure.

[0011] The active layer 8 contains one or more quantum wells 6, and the quantum well 6 includes bulk material, quantum wires and quantum dots.

[0012] The periods of the distributed phase shift grating 13 and the uniform grating 12 are different, and a phase shift equivalent to a quarter wavelength is introduced.

[0013] Wherein, the period of the uniform grating of the surface grating is Λ=(mλ B ) / (2n eff ), where λ B and m are the Bragg wavelength and order of the grating respectively, n eff is the effective refractive index of the laser waveguide.

[0014] Wherein, the distributed phase shift grating of the surface grating adopts a fixed period grating or a gradient period grating. When the phase shift distributed grating is a fixed period grating, the period of the phase shift distributed grating is Λ c =Λ+θΛ c 2 / 2πL c , where Λ is the period of the uniform grating, θ is the phase shift introduced by the distributed phase shift grating, and Lc is the length of the distributed phase-shift grating.

[0015] Among them, the product of the coupling coefficient of the laser light field and the surface grating and the grating length is less than or equal to 1; the uniform grating and the distributed phase-shift grating of the surface grating are first-order Bragg gratings or high-order gratings; the uniform grating and the distributed phase-shift grating of the surface grating have the same or different depths.

[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 between the uniform grating 12 and the distributed phase-shift grating 13 is adjusted by adjusting the etching depth of the uniform grating 12 and the distributed phase-shift grating 13 , the refractive index of the material of the upper waveguide layer 11 , and the thickness of the upper waveguide layer 11 .

[0018] (III) Beneficial effects

[0019] The high-power surface grating semiconductor laser provided by the above technical solution uses a surface grating instead of a traditional buried grating in a distributed feedback semiconductor laser. No secondary epitaxy is required during the manufacturing process, which avoids oxidation of materials containing aluminum components, reduces manufacturing costs and improves yield rate. Since the coupling coefficient of the high-power semiconductor laser is low, there is less overlap between the laser light field and the surface grating, so metal can be directly manufactured on the surface grating, which improves the injection efficiency of current and reduces losses. A distributed phase-shift grating is introduced into the surface grating to replace a quarter-wavelength phase-shift grating, so that the photon density in the laser cavity is more evenly distributed along the longitudinal direction, thereby improving the longitudinal spatial hole burning threshold of the laser. The entire laser manufacturing process is the same as that of a traditional distributed feedback laser, so it has the characteristics of low cost, simple manufacturing, high yield rate, high reliability, etc. 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 2A This is a curve showing the relationship between the output optical power and the input current at the same distributed phase-shift grating position and different distributed phase-shift grating lengths for a specific example of the laser of the present invention.

[0022] Figure 2B This is a distribution diagram of photon density along the cavity length direction for the same distributed phase-shift grating position and different distributed phase-shift grating lengths of a specific example of the laser of the present invention.

[0023] Figure 2C This is a distribution diagram of carrier density along the cavity length direction for the same distributed phase-shift grating position and different distributed phase-shift grating lengths of a specific example of the laser of the present invention.

[0024] Figure 3A The graph is a relationship curve of the output light power at different distributed phase-shift grating positions with the same distributed phase-shift grating length as a specific example of the laser of the present invention as a function of the input current.

[0025] Figure 3B The photon density distribution along the cavity length direction at different distributed phase-shift grating positions with the same distributed phase-shift grating length for a specific example of the laser of the present invention.

[0026] Figure 3C The figure is a distribution diagram of carrier density along the cavity length direction at different distributed phase-shift grating positions with the same distributed phase-shift grating length for a specific example of the laser of the present invention.

[0027] 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, unetched layer-9, ridge layer-10, upper waveguide layer-11, uniform grating-12, distributed phase-shift grating-13. DETAILED DESCRIPTION

[0028] 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.

[0029] Reference Figure 1 As shown, this embodiment provides a high-power surface grating semiconductor laser, the front end of the laser is a uniform grating 12, the middle is a plurality of distributed phase-shift gratings 13, the rear of the distributed phase-shift grating 13 is a uniform grating 12, the rear of the uniform grating 12 is an active area, and the laser is provided with an electrode 1, a substrate 3, a lower waveguide layer 4, an active layer 8, an upper waveguide layer 11, an ohmic contact layer 2 and an upper electrode layer in sequence from bottom to top in the horizontal direction; a ridge waveguide structure is formed on the upper waveguide layer 11, including an unetched layer 9 and a formed In the ridge layer 10 above the central area thereof, an ohmic contact layer 2 and an upper electrode layer are sequentially arranged on the ridge waveguide in the active area from bottom to top; a surface grating is made on the ohmic contact layer 2 and the upper waveguide layer 11 in the active area, the upper electrode layer is above the surface grating, and the uniform grating of the surface grating is a Bragg grating; the active layer includes a lower confinement layer 5, a quantum well 6 and an upper confinement layer 7 sequentially arranged from bottom to top; 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.

[0030] The two ends of the laser are respectively coated with a high reflection film and an anti-reflection film, the anti-reflection film has a reflectivity of less than 1%, and the high reflection film has a reflectivity of greater than 95%. The end face coated with the anti-reflection film is used as an output end face.

[0031] Furthermore, in order to ensure that the ohmic contact layer 2 has sufficient carriers and the normal operation of the laser is ensured, the ohmic contact layer 2 and the upper waveguide layer 11 are heavily doped with P-type, and the doping concentration ranges from 1019 to 1020 cm -3 , the lower waveguide layer 4 is N-type doped, the active layer 8 is undoped, and the upper waveguide layer 11, the active layer 8 and the lower waveguide layer 4 together constitute a PiN structure.

[0032] 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.

[0033] Furthermore, in order to improve the side mode suppression ratio, make the density in the laser cavity flatter, and increase the reliability of the laser, the periods of the distributed phase shift grating 13 and the uniform grating 12 are different, and a phase shift equivalent to a quarter wavelength is introduced.

[0034] The period of the uniform grating of the surface grating is Λ=(mλ B ) / (2n eff ), where λ B and m are the Bragg wavelength and order of the grating respectively, n eff is the effective refractive index of the laser waveguide.

[0035] The distributed phase shift grating of the surface grating can be a fixed period grating or a gradient period grating. When the phase shift distributed grating is a fixed period grating, the period of the phase shift distributed grating is Λ c =Λ+θΛ c 2 / 2πL c , where Λ is the period of the uniform grating, θ is the phase shift introduced by the distributed phase shift grating, and L c is the length of the distributed phase-shift grating.

[0036] The product of the coupling coefficient between the optical field of the laser and the surface grating and the grating length is less than or equal to 1; the uniform grating and the distributed phase-shift grating of the surface grating are first-order Bragg gratings or high-order gratings; the uniform grating and the distributed phase-shift grating of the surface grating have the same or different depths.

[0037] Furthermore, there may be a highly doped N ohmic contact layer between the lower waveguide layer 4 and the substrate 3 , and there may be a highly doped P ohmic contact layer on the upper waveguide layer 12 .

[0038] Furthermore, the coupling coefficient between the uniform grating 12 and the distributed phase-shift grating 13 is adjusted by adjusting parameters such as the etching depth of the uniform grating 12 and the distributed phase-shift grating 13 , the refractive index of the material of the upper waveguide layer 11 , and the thickness of the upper waveguide layer 11 .

[0039] Further, according to the instructions attached Figure 1The left side is half-covered and the right side is fully covered.

[0040] Example:

[0041] Figure 2A This is a curve showing the relationship between the output optical power and the input current under the same distributed phase shift grating position and different distributed phase shift grating lengths in the specific embodiment of the high-power surface grating semiconductor laser of the present invention. Through this embodiment, it can be found that under the premise of the same distributed phase shift grating position, the shorter the distributed phase shift grating length, the shorter the slope efficiency of the laser, and the higher the output power.

[0042] Figure 2B This is a distribution diagram of photon density along the cavity length direction for the same distributed phase shift grating position and different distributed phase shift grating lengths under a specific embodiment of the high-power surface grating semiconductor laser of the present invention. Through this embodiment, it can be found that under the premise of the same distributed phase shift grating position, the longer the distributed phase shift grating length, the lower the photon density peak of the laser and the flatter the distribution.

[0043] Figure 2C The photon density distribution diagram along the cavity length direction for the same distributed phase shift grating position and different distributed phase shift grating lengths under the specific embodiment of the high-power surface grating semiconductor laser of the present invention is shown in FIG. Through this embodiment, it can be found that under the premise of the same distributed phase shift grating position, when the distributed phase shift grating length accounts for 20% of the total grating length, the carrier density peak value of the laser is the lowest and the distribution is the flattest.

[0044] Figure 3A The following is a curve showing the relationship between the output optical power of different distributed phase shift grating positions and the input current under the same distributed phase shift grating length in the specific embodiment of the high power surface grating semiconductor laser of the present invention. Through this embodiment, it can be found that under the condition of the same distributed phase shift grating length, the closer the distributed phase shift grating is to the center of the laser, the greater the slope efficiency of the laser and the higher the output power.

[0045] Figure 3B The photon density distribution diagram along the cavity length direction for different distributed phase shift grating positions with the same distributed phase shift grating length under the specific embodiment of the high-power surface grating semiconductor laser of the present invention is shown in FIG. Through this embodiment, it can be found that under the condition of the same distributed phase shift grating length, the closer the distributed phase shift grating is to the center of the laser, the lower the photon density peak of the laser is and the flatter the distribution is.

[0046] Figure 3C The carrier density distribution diagram along the cavity length direction at different distributed phase-shift grating positions with the same distributed phase-shift grating length under the specific embodiment of the high-power surface grating semiconductor laser of the present invention is shown in FIG. Through this embodiment, it can be found that under the condition of the same grating length, the closer the distributed phase-shift grating is to the center of the laser, the lower the carrier density peak of the laser is and the flatter the distribution is.

[0047] The uniform grating 12 and the distributed phase-shift grating 13 of the present invention are made on the surface of the laser, without the need for a secondary epitaxial step, thus avoiding oxidation of the aluminum component of the laser material, improving the device yield, and reducing the manufacturing cost; due to the low coupling coefficient requirement of the high-power laser, the electrode is directly made on the laser ridge waveguide, reducing the manufacturing cost and improving the current injection efficiency; by optimizing the length and position of the distributed phase-shift grating 13, the peak values ​​of the carrier density and the photon density in the laser cavity can be reduced, making the carrier density and the photon density distribution flatter, reducing the probability of longitudinal spatial hole burning, and improving the reliability of the laser.

[0048] 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 surface grating semiconductor laser, characterized in that: The front end of the laser is a uniform grating (12), the middle is a plurality of distributed phase-shift gratings (13), the rear of the distributed phase-shift grating (13) is a uniform grating (12), and the laser is provided with an electrode (1), a substrate (3), a lower waveguide layer (4), an active layer (8), an upper waveguide layer (11), an ohmic contact layer (2) and an upper electrode layer in sequence from bottom to top in the transverse direction; a ridge waveguide structure is formed on the upper waveguide layer (11), comprising an unetched layer (9) and a ridge layer (10) formed above the central region thereof An ohmic contact layer (2) and an upper electrode layer are sequentially arranged on the ridge waveguide in the active region from bottom to top; a surface grating is made on the ohmic contact layer (2) and the upper waveguide layer (11) in the active region, the upper electrode layer is above the surface grating, and the uniform grating of the surface grating is a Bragg grating; the active layer includes a lower confinement layer (5), a quantum well (6) and an upper confinement layer (7) sequentially arranged from bottom to top; 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.

2. The high-power surface grating semiconductor laser according to claim 1, characterized in that: Both ends of the laser are coated with a high reflection film and an anti-reflection film respectively, the anti-reflection film has a reflectivity less than 1%, and the high reflection film has a reflectivity greater than 95%; the end face coated with the anti-reflection film is used as the output end face.

3. The high-power surface grating semiconductor laser according to claim 2, characterized in that: The ohmic contact layer (2) and the upper waveguide layer (11) are heavily doped with P type, and the doping concentration ranges from 1019 to 1020 cm -3 The lower waveguide layer (4) is N-type doped, the active layer (8) is undoped, and the upper waveguide layer (11), the active layer (8) and the lower waveguide layer (4) together form a PiN structure.

4. The high-power surface grating semiconductor laser according to claim 3, characterized in that: The active layer (8) contains one or more quantum wells (6), and the quantum wells (6) include bulk material, quantum wires and quantum dots.

5. The high-power surface grating semiconductor laser according to claim 4, characterized in that: The periods of the distributed phase shift grating (13) and the uniform grating (12) are different, and a phase shift equivalent to a quarter wavelength is introduced.

6. The high-power surface grating semiconductor laser according to claim 5, characterized in that: The period of the uniform grating of the surface grating is Λ=(mλ B ) / (2n eff ), where λ B and m are the Bragg wavelength and order of the grating respectively, n eff is the effective refractive index of the laser waveguide.

7. The high-power surface grating semiconductor laser according to claim 6, characterized in that: The distributed phase shift grating of the surface grating adopts a fixed period grating or a gradient period grating. When the phase shift distributed grating is a fixed period grating, the period of the phase shift distributed grating is Λ c =Λ+θΛ c 2 / 2πL c , where Λ is the period of the uniform grating, θ is the phase shift introduced by the distributed phase shift grating, and L c is the length of the distributed phase-shift grating.

8. The high-power surface grating semiconductor laser according to claim 7, characterized in that: The product of the coupling coefficient between the laser light field and the surface grating and the grating length is less than or equal to 1; the uniform grating and the distributed phase-shift grating of the surface grating are first-order Bragg gratings or high-order gratings; the uniform grating and the distributed phase-shift grating of the surface grating have the same or different depths.

9. The high-power surface grating semiconductor 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 (11).

10. The high power surface grating semiconductor laser according to claim 9, characterized in that: The coupling coefficient of the uniform grating (12) and the distributed phase-shift grating (13) is adjusted by adjusting the etching depth of the uniform grating (12) and the distributed phase-shift grating (13), the refractive index of the material of the upper waveguide layer (11) and the thickness of the upper waveguide layer (11).

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