A polarization state electrically controlled switching distributed feedback semiconductor laser

Abstract

The application discloses a polarization state electrically controlled switching distributed feedback semiconductor laser, which comprises a substrate, a lower cladding layer, a first grating layer, a grating interval layer, a strain compensation multi-quantum well active layer, a second grating layer, an upper cladding layer and a plurality of injection electrodes which are electrically isolated from each other along the cavity length direction; the first grating period matches the TM mode Bragg condition, the second grating period matches the TE mode Bragg condition and is different from the TM mode Bragg condition, the strain compensation multi-quantum well active layer comprises M alternately stacked compressive strain quantum well layers and tensile strain barrier layers, uneven current is injected into the plurality of injection electrodes, the net gain of the TM or TE mode is selectively enhanced, so that the output laser is switched between the TE and TM polarization states; the polarization extinction ratio of the application is greater than 15 dB, the switching current tolerance is greater than 20 mA, an external polarization converter is not needed, the structure is compact, is compatible with the InP-based process and has low-cost production potential.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a distributed feedback semiconductor laser with polarization state electrically controlled switching. Background Technology

[0002] As fiber optic communication systems develop towards higher capacities, coherent technologies such as polarization multiplexing (PDM) place higher demands on the controllability of the polarization state of light sources. Distributed feedback (DFB) semiconductor lasers have become the preferred light source due to their advantages such as single longitudinal mode and high stability. However, the TE mode gain of traditional compressive strain quantum well DFB lasers is much greater than that of the TM mode, and the output light is fixed in TE polarization, which cannot meet the requirements for flexible polarization control.

[0003] In the prior art, a DFB laser with segmented electrodes attempts to achieve TE / TM polarization switching by altering the intracavity gain distribution through non-uniform current injection. However, this approach uses a single-layer grating, which cannot provide independent decoupling feedback for the two orthogonal polarization modes. This results in mutual coupling of mode selection, polarization switching being sensitive to end-face phase, low polarization extinction ratio, and poor stability.

[0004] Furthermore, some schemes employ a dual-grating DFB laser, with a grating of different periods placed above and below the strain-compensated multi-quantum-well active layer. However, the aim is to simultaneously lase two longitudinal modes with a large wavelength gap to generate terahertz signals, which promotes multi-mode coexistence. This is diametrically opposed to the technical goal of this invention, which achieves selective suppression through polarization mode competition. Existing technologies do not provide any inspiration for combining dual gratings with segmented electrodes for dynamic polarization switching.

[0005] Another approach involves integrating a polarization mode converter at the back end of the DFB laser, but this significantly increases device size, complexity, and manufacturing difficulty. Therefore, there is an urgent need for a technical solution that enables efficient, stable, and rapid electrically controlled polarization switching within a single, compact DFB laser. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a solution to the technical problems mentioned in the background art.

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a distributed feedback semiconductor laser with polarization state electronically controlled switching, thereby solving the technical problems mentioned in the background art.

[0008] A polarization-state electrically controlled distributed feedback semiconductor laser, characterized in that it includes a substrate; A lower cladding layer, a first grating layer, a grating spacer layer, a strain-compensated multi-quantum-well active layer, a second grating layer, and an upper cladding layer are sequentially stacked on the substrate, along with a plurality of injection electrodes disposed on the upper cladding layer and electrically isolated from each other along the length of the laser cavity; Wherein, the first grating layer has a first grating period, the second grating layer has a second grating period, and the first grating period and the second grating period are different; the first grating period matches the Bragg condition of the TM mode, and the second grating period matches the Bragg condition of the TE mode; The strain-compensated multi-quantum-well active layer comprises M alternating layers of compressive strain quantum wells and tensile strain barrier layers. Non-uniform currents are injected into the plurality of injection electrodes to selectively enhance the net gain of the TM mode or TE mode, so that the output laser switches between the TE polarization state and the TM polarization state.

[0009] The beneficial effects of this invention are: This invention addresses the issues of feedback coupling and end-face sensitivity in single-layer gratings by setting a first grating layer and a second grating layer with different periods to match the Bragg conditions of TM and TE modes, respectively. By incorporating a strain-compensated multi-quantum-well active layer, the material gain of the strain-compensated multi-quantum-well active layer for TE and TM modes is essentially balanced near the operating wavelength. Multiple electrically isolated injection electrodes are arranged along the cavity length, and by injecting non-uniform current, the dominant net gain of either TM or TE mode can be selectively achieved, resulting in a polarization extinction ratio greater than 15 dB, a switching tolerance greater than 20 mA, and high-stability polarization switching. Polarization states are directly switched within a single DFB laser, eliminating the need for an external polarization converter. This results in a compact structure, high integration, and low loss. The device cavity length is comparable to that of traditional DFB lasers, and the fabrication process is compatible with InP-based processes, demonstrating potential for low-cost mass production.

[0010] Furthermore, the compressive strain of the compressive strain quantum well layer ranges from 0.3% to 0.8%, and the tensile strain of the tensile strain barrier layer ranges from -0.1% to -0.5%.

[0011] Furthermore, the coupling coefficient of the first grating layer to the TM mode is a first coupling coefficient, and the coupling coefficient of the second grating layer to the TE mode is a second coupling coefficient. Both the first and second coupling coefficients have a range of 20 cm. - ¹~100 cm - ¹, and the absolute value of the difference between the first coupling coefficient and the second coupling coefficient is less than 10 cm. - ¹.

[0012] Furthermore, the absolute value of the difference between the first grating period and the second grating period is 1.0 nm to 5.0 nm.

[0013] Furthermore, the value of M ranges from 5 to 8.

[0014] Furthermore, the material of the compressive strain quantum well layer is InGaAsP or AlGaInAs, and the material of the tensile strain barrier layer is InGaAsP or AlGaInAs. The materials of both the compressive strain quantum well layer and the tensile strain barrier layer are matched with the InP lattice.

[0015] Furthermore, a buffer layer is provided between the substrate and the lower cladding layer, a lower waveguide layer is provided between the lower cladding layer and the first grating layer, an upper waveguide layer is provided between the strain-compensated multi-quantum-well active layer and the second grating layer, and an ohmic contact layer is provided between the upper cladding layer and the injection electrode.

[0016] Furthermore, a bottom electrode is provided on the side of the substrate facing away from the lower cladding, and at least one electrical isolation trench is provided on the ohmic contact layer, the electrical isolation trench being located between adjacent injection electrodes.

[0017] Furthermore, the isolation resistance between adjacent injection electrodes is 1 kΩ to 50 kΩ.

[0018] Furthermore, the upper waveguide layer is made of InGaAsP, and the lower waveguide layer is made of InGaAsP. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of the first embodiment of the present invention; Figure 2 This is a schematic diagram of the transverse cross-sectional structure of the first embodiment of the present invention; Figure 3 shows the simulation results of the first embodiment of the present invention, wherein: (a) is the reflection spectrum of the first grating layer (TM mode); (b) is the reflection spectrum of the second grating layer (TE mode); (c) is the polarization switching characteristic curve; (d) is the output spectrum of TM mode; and (e) is the output spectrum of TE mode. Figure 4 shows the simulation results, where: (a) is a comparison curve of material gain in TE mode / TM mode for conventional compressive strain quantum wells; (b) is a comparison curve of material gain in TE mode / TM mode for strain-compensated multi-quantum wells according to the first embodiment of the present invention. Figure 5 This is a schematic diagram of the three-segment electrode structure according to the third embodiment of the present invention.

[0020] In the figure: 1. Substrate; 2. Buffer layer; 3. Lower cladding layer; 4. Lower waveguide layer; 5. First grating layer; 6. Grating spacer layer; 7. Strain-compensated multi-quantum-well active layer; 8. Upper waveguide layer; 9. Second grating layer; 10. Upper cladding layer; 11. Ohmic contact layer; 12. First injection electrode; 13. Second injection electrode; 14. Electrical isolation trench; 15. Insulating layer; 16. Bottom electrode; 17. Third injection electrode; The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0022] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Example 1 This embodiment provides a distributed feedback (DFB) semiconductor laser with electrically controlled polarization switching. By setting a first grating layer 5 and a second grating layer 9 with different periods below and above the strain-compensated multi-quantum-well active layer 7, respectively, and in conjunction with the strain-compensated multi-quantum-well 7 and segmented injection electrodes that are electrically isolated from each other along the cavity length, the output laser is electrically switched between TE polarization state and TM polarization state.

[0025] Please see Figure 1 and Figure 2The longitudinal cross-sectional structure of the laser is constructed sequentially from bottom to top on an n-InP substrate 1. Substrate 1 is n-type InP with a thickness of approximately 350 μm, serving as the epitaxial growth substrate and the contact layer for the bottom electrode 16. An n-InP buffer layer 2 (500 nm thick, n-type doped) is epitaxially grown sequentially on substrate 1 to block defects in substrate 1 and improve surface morphology, and an n-InP lower cladding layer 3 (1.5 μm thick, n-type doped), which, together with the upper cladding layer 10, constitute a vertical optical waveguide, confining the optical field to the vicinity of the strain-compensated multi-quantum-well active layer 7.

[0026] A lower waveguide layer 4 (material In0) is disposed on the lower cladding layer 3. 74 Ga0. 26 As0. 57 P0. 43 A layer with a thickness of 80 nm and no doping is used to reduce the scattering loss of the light field and to assist the coupling of the light field with the first grating layer 5. The first grating layer 5, made of InO, is located on the lower waveguide layer 4. 73 Ga0. 27 An As0.6P0.4 grating with a thickness of 80 nm was formed using electron beam lithography and reactive ion etching, resulting in a Bragg grating with a first grating period Λ1 of 240.5 nm, an etching depth of 50 nm, and a duty cycle of 50%. This period matches the Bragg condition of the TM mode: near the operating wavelength of 1550 nm, the effective refractive index of the TM mode is approximately 3.22, and according to the Bragg condition λ = 2·n eff The calculated value of Λ is approximately 2 × 3.22 × 240.5 ≈ 1550 nm, which is consistent with the target wavelength. Therefore, the first grating layer 5 provides independent distributed feedback for the TM mode.

[0027] The first grating layer 5 is covered by an InP grating spacer layer 6 (50 nm thick, undoped), which separates the upper and lower grating layers vertically to prevent mutual coupling and interference. Above the grating spacer layer 6 is a strain-compensated multi-quantum-well active layer 7, which is the core region for generating optical gain. The strain-compensated multi-quantum-well active layer 7 comprises six periodically alternating layers of compressive strain quantum wells and tensile strain barrier layers, wherein the compressive strain quantum well layers are InO. 68 Ga0. 32 As0. 72 P0. 28 The single-layer thickness is 6 nm, with an introduced compressive strain of +0.5%; the tensile strain barrier layer is In0. 78 Ga0. 22 As0. 45 P0. 55The single-layer thickness is 9 nm, introducing a tensile strain of -0.3%. Through strain compensation design of the compressive strain quantum well layer and the tensile strain barrier layer, the strain-compensated multi-quantum-well active layer 7 achieves a basic balance of material gain for TE and TM modes near the operating wavelength, providing a gain basis for subsequent electronically controlled competitive selection of polarization modes.

[0028] The strain-compensated multi-quantum-well active layer 7 consists of an upper waveguide layer 8 (made of the same material as the lower waveguide layer 4, with a thickness of 80 nm) and a second grating layer 9. The second grating layer 9 uses the same grating material (InO) as the first grating layer 5. 73 Ga0. 27 A second grating layer (As0.6P0.4), 80 nm thick, is formed through a second electron beam exposure and etching process, resulting in a grating with a period Λ2 of 238.0 nm, an etching depth of 50 nm, and a duty cycle of 50%. The effective refractive index of the TE mode is approximately 3.26. According to the Bragg condition 2 × 3.26 × 238.0 ≈ 1550 nm, this period matches the Bragg condition of the TE mode. Therefore, the second grating layer 9 provides independent distribution feedback for the TE mode.

[0029] In this embodiment, by selecting an etching depth of 50 nm and a duty cycle of 50%, the coupling coefficient κ of the first grating layer 5 to the TM mode is... TM Approximately 48 cm - ¹, The coupling coefficient κ of the second grating layer 9 to the TE mode TE Approximately 44 cm - ¹, the absolute value of the difference between the two is approximately 4 cm. - ¹. The etching depth determines the refractive index modulation amplitude of the grating; the greater the depth, the larger the coupling coefficient. A 50% duty cycle maximizes the fundamental coupling coefficient, avoiding high-order harmonic interference. (The last part, "κ," appears to be an unrelated fragment and is omitted from the translation.) TM and κ TE All are controlled within 20 cm - ¹~100cm - ¹ This design ensures sufficient feedback strength to achieve a low threshold and high side-mode suppression ratio, while avoiding the spatial hole-burning effect caused by excessive coupling. Simultaneously, by making the two coupling coefficients nearly equal, the intensity of the TM and TE modes in the feedback channel is essentially balanced. This allows the two modes to compete fairly when non-uniform current is injected into the segmented electrodes, achieving stable switching with a high polarization extinction ratio.

[0030] The second grating layer 9 consists of a p-InP cladding layer 10 (1.5 μm thick, p-type doped) and p... + -InGaAs ohmic contact layer 11 (thickness 200 nm, p) + (Heavy doping), the latter is used to reduce the contact resistance between the metal electrode and the semiconductor.

[0031] On the ohmic contact layer 11, two electrically isolated injection electrodes (first injection electrode 12 and second injection electrode 13) are arranged along the length of the laser cavity. Electrical isolation between them is achieved through an etched isolation trench 14 (20 μm wide, etched to near the lower part of the upper cladding layer 10). A bottom electrode 16 (AuGe / Ni / Au multilayer metal) is provided on the back side of the substrate 1. By injecting different proportions of current into the two injection electrodes (e.g., TM mode is dominant when I1 / I2≈2.67, and TE mode is dominant when I1 / I2≈0.38), the dominant net gain of either the TM or TE mode can be selectively enhanced, thereby achieving direct switching of the output laser polarization state within a single chip. In this embodiment, the isolation resistor is approximately 5 kΩ, ensuring the independence of the segmented injection.

[0032] The laser's emitting surface can be coated with an anti-reflection film, and the back surface can be coated with a high-reflection film to further reduce the impact of end-face reflection on polarization switching. The entire ridge waveguide is covered with a SiO2 insulating layer 15 to protect the ridge waveguide sidewalls and limit the injection current to be injected only through the electrode window area.

[0033] Compared with segmented electrode DFB lasers that only use a single-layer grating, this embodiment uses two independent gratings to provide feedback for TE mode and TM mode respectively, fundamentally decoupling the competition between the two polarization modes. The simulation results are shown in Table 1.

[0034] Table 1. Performance Comparison of the Invention and Single-Grate DFB Laser

[0035] As shown in Table 1, the polarization extinction ratio of this embodiment is greater than 15 dB (only 5~8 dB for the single grating scheme), the side mode suppression ratio is greater than 45 dB (about 30 dB for the single grating scheme), the switching current tolerance is greater than 20 mA (less than 5 mA for the single grating scheme), and it is extremely insensitive to the end face phase, so it can work stably without complex coating.

[0036] The laser performance in this embodiment was verified through simulation. The simulation used a transmission matrix model based on coupled-wave theory and was conducted at a target wavelength of 1550 nm.

[0037] Verification of independent feedback of the grating: Figures 3(a) and 3(b) show the reflection spectra of the double-layer grating. The two reflection peaks correspond to Λ1=240.5 nm (TM mode) and Λ2=238.0 nm (TE mode), respectively, with the center wavelengths offset by about 2 nm, proving that the two layers of grating provide independent feedback channels for different polarization modes.

[0038] Polarization switching characteristics: Figure 3(c) shows the output power as a function of the current ratio I1 / I2. As can be seen from Figure 3(c), there exists a switching threshold. When I1 / I2 is greater than this threshold, the TM mode gains dominant net gain and outputs TM-polarized light; when I1 / I2 is less than this threshold, the TE mode gains dominant net gain and outputs TE-polarized light. For example, the TM mode is dominant when I1 / I2 ≈ 2.67, and the TE mode is dominant when I1 / I2 ≈ 0.38. This directly demonstrates that the net gain of a specific polarization mode can be selectively enhanced by non-uniform current injection through segmented electrodes.

[0039] Single-mode characteristics: Figure 3(d) shows the output spectrum of the TM mode, and Figure 3(e) shows the output spectrum of the TE mode. Reading from the figures, the difference between the main peak and the secondary peak in the TM mode is approximately 48 dB, and in the TE mode, it is approximately 47 dB, both greater than 45 dB, indicating excellent side-mode suppression ratios in both polarization states.

[0040] Gain balance verification: Figure 4(a) shows the gain comparison curve of TE / TM material in conventional compressive strain quantum well active layer. It can be seen that the gain of TE mode is much greater than that of TM mode. Figure 4(b) shows the gain comparison curve of TE / TM material in strain-compensated multi-quantum well active layer in this embodiment. It can be seen that the gain curves of TE and TM modes basically overlap around 1550 nm, which proves that the gain is basically balanced.

[0041] In summary, the simulation results verify that this embodiment can stably achieve polarization state electronic control switching, and has a high polarization extinction ratio (>15 dB), a high side-mode suppression ratio (>45 dB), and a high switching tolerance (>20 mA).

[0042] The preparation method in this embodiment is as follows: On the n-InP substrate 1, the first epitaxial growth was performed by metal-organic chemical vapor deposition (MOCVD), in which the n-InP buffer layer 2 (500 nm thick, n-type doped), the n-InP lower cladding layer 3 (1.5 μm thick, n-type doped), and the lower waveguide layer 4 (In0) were deposited sequentially. 74 Ga0. 26 As0. 57 P0. 43 (with a thickness of 80 nm) and the first grating material layer (In0). 73 Ga0. 27 As0.6P0.4, thickness 80 nm).

[0043] Electron beam lithography (EBL) is used to form a grating pattern with a period of Λ1 = 240.5 nm on the first grating material layer. Then, reactive ion etching (RIE) is used to transfer the pattern to the grating material layer to form a first grating layer 5 with an etching depth of 50 nm and a duty cycle of 50%.

[0044] A second MOCVD epitaxial growth was performed, sequentially depositing an InP grating spacer layer 6 (50 nm thick), a strain-compensated multi-quantum-well active layer 7, and an upper waveguide layer 8 (In0). 74 Ga0. 26 As0. 57 P0. 43 (with a thickness of 80 nm) and a second grating material layer (In0). 73 Ga0. 27 As0.6P0.4, with a thickness of 80 nm). Among them, the strain-compensated multi-quantum-well active layer 7 consists of 6 periodically alternating layers of compressive strain quantum well layers and tensile strain barrier layers: the material of the compressive strain quantum well layers is In0. 68 Ga0. 32 As0. 72 P0. 28 The thickness is 6 nm, and the compressive strain is +0.5%; the tensile strain barrier layer is made of In0. 78 Ga0. 22 As0. 45 P0. 55 The thickness is 9nm and the tensile strain is -0.3%.

[0045] Electron beam lithography and reactive ion etching (RIE) were used again to form a grating pattern with a period of Λ2 = 238.0 nm on the second grating material layer. The etching depth was 50 nm and the duty cycle was 50%, forming the second grating layer 9.

[0046] A third MOCVD epitaxial growth was performed, sequentially depositing a p-InP cladding layer 10 (1.5 μm thick, p-type doped) and p-type doped layers. + -InGaAs ohmic contact layer 11 (thickness 200 nm, p) + Heavy doping).

[0047] Then, a ridge waveguide with a width of 2.5 μm is etched by inductively coupled plasma (ICP) dry etching. Next, an electrically isolated trench 14 with a width of 20 μm is formed on the top of the ridge waveguide by photolithography and dry etching, with the etching depth reaching close to the upper surface of the upper cladding 10, thereby dividing the top electrode region into two independent electrode regions.

[0048] A SiO2 insulating layer 15 with a thickness of approximately 200 nm was deposited on the entire device surface using plasma-enhanced chemical vapor deposition (PECVD). Then, ohmic contact layers 11 were exposed by opening windows in the electrode sections through photolithography and etching processes.

[0049] A first implantation electrode 12 and a second implantation electrode 13 (Ti / Pt / Au multilayer metal) were fabricated in the windowed area using metal evaporation and stripping processes. After thinning the back side of the substrate 1 to approximately 150 μm, a bottom electrode 16 (AuGe / Ni / Au multilayer metal) was deposited by vapor deposition. Finally, cleaving, end-face coating (antireflection coating on the light-emitting side and high-reflection coating on the back-lighting side) and chip testing were performed.

[0050] Example 2 This embodiment has a structure that is basically the same as that of Embodiment 1, except that the AlGaInAs material system is used instead of the InGaAsP / InP system. AlGaInAs material has a larger conduction band level, which can more effectively confine charge carriers, reduce leakage current at high temperatures, and thus improve the high-temperature operating stability of the laser.

[0051] Specifically, in this embodiment, the lower waveguide layer 4 and the upper waveguide layer 8 adopt (Al0) lattice matching InP. 24 Ga0. 23 In0. 53 As, thickness 80 nm.

[0052] The first grating layer 5 and the second grating layer 9 use (Al0). 18 Ga0. 29 In0. 53 AlGaInAs waveguides have a thickness of 80 nm, an etching depth of 50 nm, and a duty cycle of 50%. Since the effective refractive index of AlGaInAs waveguides differs slightly from that of InGaAsP, the grating period was redesigned for a working wavelength of 1550 nm: the period Λ1 of the first grating layer 5 (matching TM mode) is 242.2 nm, and the period Λ2 of the second grating layer 9 (matching TE mode) is 239.2 nm, with a difference of 3.0 nm between the two grating periods.

[0053] By selecting an etching depth of 50 nm and a duty cycle of 50%, the coupling coefficient κ of the first grating layer 5 pairs of TM modes is... TM Approximately 46 cm - ¹, The coupling coefficient κ of the second grating layer 9 to the TE mode TE Approximately 42 cm - ¹, the absolute value of the difference between the two is approximately 4 cm. - ¹.

[0054] The strain-compensated multi-quantum-well active layer 7 comprises six periodically alternating layers of compressive strain quantum well layers and tensile strain barrier layers, wherein the compressive strain quantum well layers are (Al0). 14 Ga0. 27 In0. 59 As, with a single-layer thickness of 6 nm and a compressive strain of +0.4%; the tensile strain barrier layer is (Al0). 26 Ga0. 25 In0. 49 As, with a single-layer thickness of 8 nm and a tensile strain of -0.25%. Through strain compensation, the strain-compensated multi-quantum-well active layer 7 achieves a basic balance in material gain for TE and TM modes near the operating wavelength.

[0055] The materials, thicknesses, doping, and fabrication processes of the remaining layers (substrate 1, buffer layer 2, lower cladding layer 3, grating spacer layer 6, upper cladding layer 10, ohmic contact layer 11, electrical isolation trench 14, bottom electrode 16, etc.) are the same as in Example 1, and will not be repeated here.

[0056] Since AlGaInAs material has a larger conduction band level than InGaAsP, it can more effectively confine charge carriers in the quantum well and reduce charge carrier leakage at high temperatures. Therefore, this embodiment has better polarization switching stability at high temperatures than Embodiment 1, such as lower temperature sensitivity of switching current tolerance and polarization extinction ratio.

[0057] This embodiment demonstrates that the present invention does not depend on a specific material system; both InGaAsP and AlGaInAs can achieve electrically controlled polarization switching, and the specific parameters under different material systems can achieve the expected technical effects.

[0058] Example 3 Based on the dual-layer composite grating and strain-compensated active layer structure of Example 1, this embodiment changes the top electrode from two segments to three segments to provide more flexible longitudinal current regulation capability and realize the coordinated control of polarization switching and wavelength tuning.

[0059] Specifically, refer to Figure 5 Along the 400 μm cavity length, the top electrode is divided into three segments: the first injection electrode 12 (120 μm in length), the second injection electrode 13 (160 μm in length), and the third injection electrode 17 (120 μm in length). An electrical isolation groove 14 with a width of 20 μm is provided between each adjacent electrode, with an isolation resistance of approximately 4 kΩ.

[0060] The materials, thicknesses, doping, and fabrication processes of the remaining layers (substrate 1, buffer layer 2, lower cladding layer 3, lower waveguide layer 4, first grating layer 5, grating spacer layer 6, strain-compensated multi-quantum-well active layer 7, upper waveguide layer 8, second grating layer 9, upper cladding layer 10, ohmic contact layer 11, bottom electrode 16, etc.) are the same as in Example 1, and will not be repeated here.

[0061] During operation, by independently adjusting the three injection currents, it is possible not only to selectively enhance the dominant net gain of TM or TE modes (e.g., for TE polarized output, I1=30 mA, I2=90 mA, I3=30 mA; for TM polarized output, I1=75 mA, I2=35 mA, I3=75 mA), but also to independently adjust the cavity temperature distribution and carrier concentration gradient using the current of the intermediate electrode (second injection electrode 13), thereby finely tuning the lasing wavelength.

[0062] Compared to a two-segment electrode structure, a three-segment electrode structure can achieve a more symmetrical gain and temperature distribution. By injecting similar currents into the two end electrodes and different currents into the middle electrode, the uneven refractive index distribution caused by a large current concentrated on one side is avoided, thus effectively mitigating the spectral drift caused by a large current injection on one side. While maintaining a high polarization extinction ratio and a high side-mode suppression ratio, this embodiment can achieve wavelength tuning within a certain range, and the wavelength drift during polarization switching is significantly reduced compared to a two-segment electrode structure. Therefore, the three-segment electrode structure helps improve wavelength stability.

[0063] Compared to a three-electrode DFB laser that uses only a single-layer grating, this embodiment utilizes two independent gratings, one above the other, to provide feedback for TE and TM modes respectively. The introduction of the three-electrode configuration does not cause mode crosstalk and allows for stable wavelength control during polarization switching.

[0064] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A distributed feedback semiconductor laser with electrically controlled polarization state switching, characterized in that: Including substrate; A lower cladding layer, a first grating layer, a grating spacer layer, a strain-compensated multi-quantum-well active layer, a second grating layer, and an upper cladding layer are sequentially stacked on the substrate, along with a plurality of injection electrodes disposed on the upper cladding layer and electrically isolated from each other along the length of the laser cavity; Wherein, the first grating layer has a first grating period, the second grating layer has a second grating period, and the first grating period and the second grating period are different; the first grating period matches the Bragg condition of the TM mode, and the second grating period matches the Bragg condition of the TE mode; The strain-compensated multi-quantum-well active layer comprises M alternating layers of compressive strain quantum wells and tensile strain barrier layers. By injecting non-uniform current into multiple injection electrodes, the net gain of the TM mode or TE mode is selectively enhanced to enable the output laser to switch between TE polarization and TM polarization states.

2. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 1, characterized in that: The compressive strain of the quantum well layer ranges from 0.3% to 0.8%, and the tensile strain of the barrier layer ranges from -0.1% to -0.5%.

3. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 1, characterized in that: The coupling coefficient of the first grating layer to the TM mode is the first coupling coefficient, and the coupling coefficient of the second grating layer to the TE mode is the second coupling coefficient. Both the first coupling coefficient and the second coupling coefficient have a range of 20 cm. - ¹~100 cm - ¹, and the absolute value of the difference between the first coupling coefficient and the second coupling coefficient is less than 10 cm. - ¹.

4. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 1, characterized in that: The absolute value of the difference between the first grating period and the second grating period is 1.0 nm to 5.0 nm.

5. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 1, characterized in that: The value of M ranges from 5 to 8.

6. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 1, characterized in that: The compressive strain quantum well layer is made of InGaAsP or AlGaInAs, and the tensile strain barrier layer is made of InGaAsP or AlGaInAs. Both the compressive strain quantum well layer and the tensile strain barrier layer are lattice-matched with InP.

7. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 1, characterized in that: A buffer layer is provided between the substrate and the lower cladding layer, a lower waveguide layer is provided between the lower cladding layer and the first grating layer, an upper waveguide layer is provided between the strain-compensated multi-quantum-well active layer and the second grating layer, and an ohmic contact layer is provided between the upper cladding layer and the injection electrode.

8. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 7, characterized in that: The substrate has a bottom electrode on the side facing away from the lower cladding, and the ohmic contact layer has at least one electrical isolation trench located between adjacent injection electrodes.

9. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 8, characterized in that: The isolation resistance between adjacent injection electrodes is 1 kΩ to 50 kΩ.

10. The distributed feedback semiconductor laser with polarization state electrically controlled switching according to claim 7, characterized in that: The upper waveguide layer is made of InGaAsP, and the lower waveguide layer is made of InGaAsP.

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