Distributed feedback laser and preparation method thereof
By designing a segmented apodized Bragg coupling grating structure and a quarter-wavelength phase shift region, the problems of high manufacturing complexity and increased linewidth in existing distributed feedback lasers are solved, achieving uniform photon density and narrow linewidth laser output, thus reducing manufacturing difficulty and cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2026-04-10
Smart Images
Figure CN121840355A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of optoelectronic technology, in particular to a distributed feedback laser and a preparation method thereof. BACKGROUND
[0002] There are various existing grating structures for optimizing the field distribution by arranging multiple phase shift segments in the cavity or using a tapered or non-uniformly periodic modulation grating to gradually change the grating coupling coefficient or the number of phase shifts along the cavity length direction. These schemes can improve the light field distribution to some extent, but usually rely on high-precision design and alignment of the phase shift position and number, fine tuning of the grating period, and continuous controllable gradual change of the coupling coefficient, such as high-resolution electron beam exposure, multiple photolithography or re-epitaxy processes, etc. These requirements significantly increase the manufacturing complexity and tolerance sensitivity, resulting in multiple masks, multiple steps, strict critical dimension and alignment control, which easily pushes up the cost and affects the yield in mass production. SUMMARY
[0003] The main purpose of the present application is to provide a distributed feedback laser and a preparation method thereof, which can balance the cavity light field, suppress the longitudinal spatial hole burning effect and narrow the linewidth under the premise of not relying on continuous gradual change of the coupling coefficient and precise alignment of multiple phase shifts, while reducing the manufacturing complexity and sensitivity to process tolerance. It aims to solve the technical problems of the existing design that the various grating structures increase the difficulty of photolithography and epitaxy process, and adversely affect the cost and yield.
[0004] To achieve the above-mentioned purpose, the present application provides a distributed feedback laser, which comprises: a substrate layer; a separate confinement heterostructure arranged on the substrate layer, the separate confinement heterostructure comprising a lower cladding layer, an active region and an upper waveguide layer formed in sequence on the substrate, the active region being a multiple quantum well; a coupling grating layer arranged on the separate confinement heterostructure, the coupling grating layer being provided with a ridge waveguide, the ridge waveguide extending along the length direction of the resonant cavity, the Bragg coupling grating being arranged on the two side walls of the ridge waveguide, the Bragg coupling grating being a segmented structure and comprising at least two grating segments with different coupling coefficients; a dielectric layer arranged on the surface of the Bragg coupling grating, the dielectric layer covering the ridge waveguide; an anode arranged on the dielectric layer; a cathode arranged on the back surface of the substrate layer.
[0005] Optionally, the coupling grating layer comprises: a resonant cavity, the resonant cavity being provided with a ridge waveguide extending in the length direction of the resonant cavity; A Bragg coupling grating is arranged inside the resonant cavity, the Bragg coupling grating is a segmented apodized coupling grating arranged at the sidewalls of the ridge waveguide, the segmented apodized coupling grating is segmented along the length direction of the resonant cavity and includes at least two grating segments with different coupling coefficients; A phase shift region is arranged at the center of the resonant cavity, the phase shift region divides the Bragg coupling grating into two parts symmetric about the center of the resonant cavity; A coating layer is arranged on the end faces of the resonant cavity.
[0006] Optionally, the segmented apodized coupling grating includes a first grating segment and a second grating segment arranged in sequence along the cavity length direction, the coupling coefficient of the first grating segment is greater than that of the second grating segment, and the coupling coefficient and length ratio of the first grating segment and the second grating segment are determined according to the reflectivity combination of the coating layer.
[0007] Optionally, the phase shift region is a quarter wavelength phase shift structure, and each of the target regions on both sides of the phase shift region includes a segment of the first grating segment and a segment of the second grating segment.
[0008] Optionally, the coating layer is a double anti-reflection coating or an anti-reflection coating at one end and a high-reflection coating at the other end.
[0009] In addition, to achieve the above object, the application further provides a preparation method of the distributed feedback laser, for manufacturing the distributed feedback laser as described above, the preparation method of the distributed feedback laser includes the following steps: Generating a separate confinement heterostructure on a substrate layer in sequence by epitaxy, and generating a multi-quantum well active region in the separate confinement heterostructure; Defining and etching a ridge waveguide extending along the cavity length direction of the resonant cavity on the separate confinement heterostructure; Generating a coupling grating layer based on the reflectivity combination of the preset end face coating and the ridge waveguide; Depositing a dielectric layer on the surface of the ridge waveguide, generating an anode, and generating a cathode on the back of the substrate layer to obtain a distributed feedback laser.
[0010] Optionally, the step of generating a coupling grating layer based on the reflectivity combination of the preset end face coating and the ridge waveguide includes: Obtaining a preset reflectivity combination of a preset end face coating, and determining the cavity length of the resonant cavity and the path of the ridge waveguide; Determining the coupling coefficient and length ratio of the first grating segment and the second grating segment in the segmented apodized coupling grating according to the preset reflectivity combination; Based on the coupling coefficient and the length ratio, using patterned photoresist as a mask, Bragg coupling gratings are generated in segments along the cavity length direction along both sidewalls of the ridge waveguide. A quarter-wavelength phase-shift structure is set at the center of the cavity length of the resonant cavity to obtain a phase-shift region, thereby dividing the Bragg coupling grating into two parts symmetrical about the cavity center; The Bragg coupled grating is cleaved to obtain an end face, and a coating is deposited on the end face to obtain different combinations of reflectivity, thus obtaining a coupled grating layer.
[0011] Optionally, the step of generating Bragg coupling gratings segmentally along the two sidewalls of the ridge waveguide in the cavity length direction, using patterned photoresist as a mask, according to the coupling coefficient and the length ratio, includes: Photoresist is coated on the top of the ridge waveguide, and a mask pattern containing the first grating segment and the second grating segment is transferred onto the photoresist and / or a preset hard mask by photolithography. Using the patterned photoresist and / or hard mask as a mask, anisotropic dry etching is performed along both sidewalls of the ridge waveguide to transfer the pattern to the underlying semiconductor material, obtaining sidewall Bragg gratings segmented along the cavity length direction. The different coupling coefficients between the first and second grating segments can be obtained by controlling the sidewall etching depth. After etching, post-processing is performed to obtain the Bragg-coupled grating.
[0012] Optionally, before the step of generating Bragg coupling gratings segmentally along the two sidewalls of the ridge waveguide in the cavity length direction using patterned photoresist as a mask according to the coupling coefficient and the length ratio, the method further includes: The combination of reflectivity of the coatings on both ends of the resonant cavity is determined based on the preset laser linewidth target. Based on the aforementioned reflectivity combination, a preset simulation model is used to determine the target reflectivity range of the end-face coating; Accordingly, the step of determining the coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating based on the preset reflectivity combination includes: The coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating are determined based on the target reflectivity range and the preset reflectivity combination.
[0013] Optionally, the step of determining the coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating based on the target reflectivity range and the preset reflectivity combination includes: A light field simulation model is obtained, which takes the combination of end face coating reflectivity, coupling coefficient and segment length ratio as input parameters, and the uniformity of intracavity photon density along the cavity length as the objective function. The target reflectivity range and the preset reflectivity combination are input into the light field simulation model to solve for a parameter set that satisfies the optimal photon density uniformity and maintains the single longitudinal mode oscillation condition. The parameter set includes the coupling coefficient and length ratio of the first grating segment and the second grating segment.
[0014] This application proposes a Step Apodized Coupling DFB (SAC-DFB) laser based on a sidewall (laterally coupled) segmented apodized grating. By dividing the grating into multiple segments, each with a different fixed coupling coefficient, and adjusting the coupling coefficient distribution and length ratio of each segment, powerful control of the intracavity optical field can be achieved, improving the uniformity of photon density distribution along the resonant cavity and effectively suppressing the longitudinal spatial hole burning (LSHB) effect, thus obtaining a narrower laser linewidth. The laser structure of this application divides the Bragg grating into two segments, assigning different and fixed coupling coefficients to each segment—one with a larger coupling coefficient and the other with a smaller coupling coefficient—and sets a quarter-wavelength phase shift region at the center of the resonant cavity. By adjusting the coupling coefficient distribution and length ratio of the two grating segments, powerful control of the intracavity optical field can be achieved. After rigorous simulation optimization, the uniformity of photon density distribution along the resonant cavity is significantly improved, the LSHB effect is effectively suppressed, and thus a narrower laser linewidth is obtained.
[0015] Compared to schemes relying on continuously varying coupling coefficients or multiphase shifts, this scheme replaces continuous control with fixed segmented coupling, reducing the dependence on precise gradual and multiphase shift alignment and facilitating manufacturing and mass production tolerance control. Under representative simulation conditions (e.g., injection current 120mA), this structure exhibits good adaptability and narrow linewidth output under different end-face reflectivity combinations and cavity lengths. When the cavity length is 1500μm and a high-reflectivity / anti-reflectivity end-face coating is used, the SAC... The DFB has a bus width of only 52.8 kHz; compared with the corresponding conventional quarter-wavelength DFB laser, the linewidth broadening caused by the LSHB effect can be reduced by more than 82%. In addition, this design is well-suited for different end-face reflectivities and cavity lengths, and can achieve narrow linewidth output under various operating conditions.
[0016] Furthermore, the structure of this application has good applicability to different end face reflectivities and different cavity lengths, and can achieve narrow linewidth output under various working conditions. The structure has a simple process flow, adopts fixed segmentation, and has low requirements for mask and etching accuracy. It can reduce the dependence on continuous control of coupling coefficient and multi-phase shift precision alignment, and has good process compatibility and applicability, adapting to narrow linewidth light sources with different cavity lengths and end face reflection conditions. Attached Figure Description
[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a schematic diagram of the structure of the first embodiment of the distributed feedback laser of this application; Figure 2 This is a schematic diagram of the SAC-DFB laser structure in this application; Figure 3 This is a schematic diagram of a segmented apodized grating; Figure 4 This is a schematic diagram showing the coupling coefficient distribution along the cavity direction for the large and small coupling coefficient segments under AR-AR and HR-AR end-face coating conditions. Figure 5 This is a schematic flowchart of the first embodiment of the method for fabricating the distributed feedback laser of this application; Figure 6 This is a schematic flowchart of the second embodiment of the method for fabricating the distributed feedback laser of this application; Figure 7 This is a schematic diagram of the segmented apodized grating of this application; Figure 8 This is a schematic diagram showing the results of the coupling coefficient distribution optimization and photon density in this application; Figure 9 A schematic diagram showing the intracavity optical field distribution of SAC-DFB lasers and the corresponding QWPS-DFB lasers under different large coupling coefficient grating lengths; Figure 10 For SAC-DFB and the corresponding QWPS-DFB laser and A schematic diagram showing the effect of injection current; Figure 11A comparison of bus width and output spectrum between SAC-DFB and the corresponding QWPS-DFB laser; Figure 12 Simulation results of linewidth for SAC-DFB lasers with different cavity lengths; Figure 13 A comparison chart showing the performance of SAC-DFB lasers under different combinations of end-face reflectivity.
[0020] Explanation of icon numbers: 1. Coupling grating layer; 2. Substrate layer; 3. Separation and confinement heterostructure; 4. Multiple quantum wells; 5. Dielectric layer; 6. Anode; 7. Cathode; 11. Resonant cavity; 12. Bragg coupling grating; 13. Phase shift region; 14. Coating layer.
[0021] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0022] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.
[0023] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.
[0024] Narrow-linewidth semiconductor lasers have significant applications in high-speed optical communication, integrated photonics, and spectral analysis. Distributed feedback (DFB) lasers, due to their single longitudinal mode output and high spectral purity, have become ideal light sources in communication systems. Semiconductor DFB lasers achieve feedback and mode selection by embedding Bragg gratings in the active region, with typical output powers reaching tens of milliwatts and linewidths of only hundreds of MHz. Compared to traditional Fabry-Pérot lasers, DFB lasers do not require external resonant cavities but rely on built-in periodic gratings, giving them advantages such as compact structure, high spectral stability, and ease of temperature and current tuning.
[0025] In traditional DFB laser design, a quarter-wave phase shift (QWPS) structure is typically introduced at the center of the grating to ensure single-mode output. However, this phase-shifted grating leads to significant non-uniformity in the intracavity optical field distribution: the field strength peaks at the cavity center. This strong field interacts with gain saturation / carrier recombination, resulting in uneven carrier depletion along the cavity length, thus producing the LSHB effect, manifested as longitudinal fluctuations in photon density and gain. The LSHB effect causes excessive concentration of carrier density in certain regions, leading to non-uniform gain distribution and significantly widening the linewidth under high output power or long cavity length conditions. Studies have shown that the LSHB effect can more than double the linewidth, thus affecting the design of high-performance lasers.
[0026] To address the aforementioned issues, various grating structure solutions have been proposed. For example, multiple phase-shifting segments can be arranged within the cavity to optimize the field distribution; apodized or non-uniform periodic modulation gratings can be used to gradually vary the grating coupling coefficient or period along the cavity length. While these methods can alleviate the non-uniformity of photon density along the cavity length to some extent, they place higher demands on manufacturing: the position and number of phase-shifting structures require high-precision design and alignment; the grating period and duty cycle require fine-tuning; the process for achieving a continuous and gradual change in the coupling coefficient is complex, and it is also affected by etching depth control and sidewall roughness effects in the sidewall etching path, making it difficult to achieve a smooth and reproducible coupling coefficient across the entire cavity. In actual mass production, this typically means multiple masks, multiple steps, and stricter critical dimension control, putting pressure on yield and cost; simultaneously, it is highly sensitive to the end-face reflectivity combination and cavity length, often requiring re-optimization of parameters for different end-face / cavity lengths. Therefore, there is still a need for a DFB laser design scheme that has a simpler structure and process, is more tolerant to process tolerances, and can improve the uniformity of photon density along the cavity length and suppress the LSHB effect under different end face and cavity length conditions.
[0027] Therefore, this application provides a SAC-DFB laser to solve the aforementioned technical problems. The laser structure divides the Bragg grating into two segments: one with a large coupling coefficient and the other with a small coupling coefficient, forming a quarter-wavelength phase shift region at the center of the resonant cavity. By adjusting the coupling coefficient distribution and length ratio of the two grating segments, powerful control of the intracavity optical field can be achieved.
[0028] Reference Figure 1 , Figure 1 This is a schematic diagram of the structure of the first embodiment of the distributed feedback laser of this application.
[0029] In a first embodiment, the distributed feedback laser includes: a coupling grating layer 1; a substrate layer 2; a separation-confined heterostructure 3 disposed on the substrate layer 2, the separation-confined heterostructure including a lower cladding layer, an active region, and an upper waveguide layer sequentially epitaxially formed on the substrate, the active region being a multiple quantum well; the active region being a multiple quantum well 4; the multiple quantum well 4 being disposed in the separation-confined heterostructure 3; a dielectric layer 5 disposed on the surface of the coupling grating layer 1; an anode 6 disposed on the dielectric layer 5; and a cathode 7 disposed on the back side of the substrate layer 2. The coupling grating layer 1 is disposed on the separation-confined heterostructure 3.
[0030] For details, please refer to Figure 2 , Figure 2 This is a schematic diagram of the SAC-DFB laser structure of this application, showing the positional relationship between the segmented apodized gratings on the sidewalls and the active region of the waveguide. The coupling grating layer 1 is disposed on the separated and confined heterostructure 3, used for optical field modulation and feedback. A ridge waveguide is disposed in the coupling grating layer, extending along the length of the resonant cavity of the coupling grating layer. Bragg coupling gratings are disposed on both sidewalls of the ridge waveguide. These Bragg coupling gratings are segmented apodized coupling gratings disposed on both sidewalls of the ridge waveguide, and are segmented structures, including at least two grating segments with different coupling coefficients. The substrate layer 2 is the basic support layer of the device, serving as the functional layers above. A stable growth substrate is provided; the separated confinement heterostructure 3 is a layered structure located on the substrate layer 2, used to confine carriers and the light field, and improve the luminous efficiency; the multiple quantum wells 4 are located in the quantum confinement region of the separated confinement heterostructure 3, and realize photon generation through carrier recombination, which is the core luminous region of the laser; the dielectric layer 5 is an insulating layer covering the surface of the coupling grating layer 1, used to isolate current and protect the grating structure, and at the same time ensure current injection through a preset window; the anode 6 and the cathode 7 are electrodes located on the dielectric layer 5 and under the substrate layer 2, respectively, used to introduce external current into the device and provide energy for carrier transition.
[0031] Understandably, during operation, an external voltage is applied through the anode 6 and cathode 7, and current is injected into the separation and confinement heterostructure 3 through the window of the dielectric layer 5. Finally, carrier recombination is excited in the multiple quantum wells 4 to generate photons. The photons form a stable laser output under the grating feedback and resonance of the coupling grating layer 1.
[0032] It should be understood that in the design of segmented apodized coupling gratings, the Bragg grating is divided into multiple segments along the length of the laser cavity, each segment having a preset fixed coupling coefficient. By rationally designing the coupling coefficient distribution, the uniformity of the optical field can be improved, and the LSHB effect can be mitigated.
[0033] Further, the coupling grating layer 1 includes: a resonant cavity 11, with a ridge waveguide extending along the length of the resonant cavity; a Bragg coupling grating 12, disposed inside the resonant cavity, the Bragg coupling grating being a segmented apodized coupling grating disposed on both sidewalls of the ridge waveguide, arranged in segments along the length of the resonant cavity, and including at least two grating segments with different coupling coefficients; a phase shift region 13, disposed at the center of the resonant cavity, the phase shift region dividing the Bragg coupling grating into two parts symmetrical about the center of the resonant cavity; and a coating layer 14, disposed on both end faces of the resonant cavity.
[0034] For details, please refer to Figure 3 , Figure 3 This is a schematic diagram of a segmented apodized grating. The resonant cavity 11 is the core region within the coupling grating layer 1, used to constrain photon propagation and provide optical oscillation space, creating conditions for photon round-trip propagation and gain accumulation. The Bragg coupling grating 12 is a periodic structure set inside the resonant cavity 11 along its length, composed of grating segments with at least two different coupling coefficients, which achieves control of the optical field through differences in structural parameters. The phase shift region 13 is a special region located at the center of the resonant cavity 11 that can change the phase of the light, and can precisely divide the Bragg coupling grating 12 into two structurally symmetrical target regions. The coating layer 14 is a functional film layer covering the end faces of the resonant cavity 11, possessing specific reflection characteristics (such as double anti-reflection, high reflection at one end and anti-reflection at the other end), used to adjust the light reflection effect at the end faces.
[0035] It should be understood that after photons generated by the multiple quantum wells 4 enter the resonant cavity 11, the light propagates back and forth in the gain medium under the reflection feedback provided by the coating layers 14 at both ends. When the return gain is greater than the loss and the phase condition is met, laser oscillation is generated. After the oscillation is established, the gain saturation brings the system to a steady state, and part of the light is output. The Bragg coupling grating 12 couples and feeds back the photons in the cavity through the periodic refractive index change of the grating segments with different coupling coefficients, adjusting the distribution of photons along the length of the resonant cavity 11 and avoiding excessive concentration of local photons. The phase shift region 13 breaks the symmetry of the optical field in the cavity by introducing a specific phase shift (such as a quarter-wavelength shift), suppressing the oscillation of non-target longitudinal modes and ensuring that the laser outputs only a single longitudinal mode laser. At the same time, by setting coating layers 14 with different reflectivities and matching the parameters of the Bragg coupling grating 12 through appropriate reflectivity design, the optical feedback efficiency in the cavity can be further optimized, so that the laser can adjust the feedback conditions according to different application scenarios (such as high power output and low threshold operation), greatly improving the scenario adaptability and operational reliability of the device.
[0036] Furthermore, the segmented apodized coupling grating includes a first grating segment and a second grating segment arranged sequentially along the cavity length direction; the coupling coefficient of the first grating segment is greater than the coupling coefficient of the second grating segment; the ratio of the coupling coefficient and length of the first grating segment to the second grating segment is determined according to the reflectivity combination of the coating layer.
[0037] It should be noted that in the Bragg coupling grating 12, the first grating segment is the grating part with a higher coupling coefficient, and the second grating segment is the grating part with a lower coupling coefficient. Both are arranged along the length direction of the resonant cavity 11 and together form a complete segmented apodized coupling grating structure. The length ratio refers to the ratio of the number of segments of the first grating segment and the second grating segment along the length direction of the resonant cavity 11. This ratio is related to the reflectivity of the coating layer 14 (i.e., the light reflection effect at both ends of the resonant cavity 11) and the specific value needs to be determined according to the reflectivity requirements.
[0038] It should be understood that the first grating segment, due to its higher coupling coefficient, has a stronger ability to feedback and confine photons within the cavity, thus enhancing the local light field intensity. The second grating segment, with its lower coupling coefficient, has a weaker ability to feedback photons, resulting in a relatively gentler light field intensity. The combination of these two grating segments along the length of the resonant cavity 11 breaks the light field concentration phenomenon caused by traditional single grating structures. Furthermore, by determining the coupling coefficient and length ratio of the two segments based on the reflectivity of the coating layer 14, the grating's control effect on the light field can be precisely matched with the light feedback conditions at both ends of the resonant cavity 11. For example, when the coating layer 14 is a high-reflectivity-anti-reflectivity combination, by adjusting the length ratio of the first and second grating segments, the light field difference between the high-reflectivity and anti-reflectivity ends can be balanced, preventing excessive accumulation of photons in a certain area and ultimately achieving a uniform distribution of the light field within the cavity.
[0039] Specifically, the segmented apodized Bragg coupled grating includes a first grating segment and a second grating segment arranged sequentially along the cavity length direction, with coupling coefficients of respectively. , ,satisfy The lengths of the two segments are respectively , . , and The value is determined based on the combination of reflectivity of the end face coating, so as to improve the uniformity of photon density along the cavity length and maintain single longitudinal mode output.
[0040] Furthermore, the phase shift region 13 is a quarter-wavelength phase shift structure, and each target area divided by the phase shift region includes a segment of the first grating segment and a segment of the second grating segment.
[0041] It should be noted that the phase shift region 13 of the quarter-wavelength phase shift structure refers to the structural offset region that introduces an optical path difference equivalent to a quarter wavelength in the grating period direction, thereby achieving abrupt modulation of the optical phase by breaking the continuity of the grating period. The target region divided by the phase shift region 13 refers to the two symmetrical parts formed after the center of the resonant cavity is separated by the phase shift region. Each target region completely contains a first grating segment (large coupling coefficient) and a second grating segment (small coupling coefficient), ensuring the consistency of the optical field modulation structure on both sides.
[0042] Furthermore, the coating layer 14 is an AR-AR (Anti Reflective-Anti Reflective) coating or an HR-AR (High Reflective-High Reflective) coating.
[0043] In one example, reference Figure 4 , Figure 4 This diagram illustrates the coupling coefficient distribution along the cavity direction for large and small coupling coefficient segments under AR-AR and HR-AR end-face coating conditions. In high-reflectivity-antireflection or dual antireflection systems, a more uniform light field distribution is achieved by adjusting the grating length and coupling coefficient distribution of each segment, allowing selection of the same longitudinal mode even under different reflection conditions. When fabricating the coating layer, the coating type is first determined based on the laser's performance requirements (such as optical output efficiency and intracavity feedback intensity). The coating type can be flexibly selected according to actual needs, significantly expanding the application range of the laser. Dual anti-reflection coatings refer to films with low reflectivity deposited on both ends of a semiconductor wafer, significantly reducing photon reflection loss at the ends. To create a high-reflectivity (HR) and anti-reflection (AR) coating, high-reflectivity (HR) and anti-reflection (AR) films are first deposited in batches on two opposing natural cleavage surfaces of the wafer using photolithography and coating techniques. Then, utilizing the natural cleavage properties of the semiconductor crystal (such as GaAs or InP), precisely controlled mechanical stress causes the wafer to cleave along specific lattice planes (cleavage planes), thereby generating a laser with HR and AR coatings at both ends. Both coating types achieve their intended reflective function through specific material combinations and film structures.
[0044] In this embodiment, by dividing the grating into multiple segments, each with a different fixed coupling coefficient, and adjusting the coupling coefficient distribution and length ratio of each grating segment, the optical field inside the cavity can be effectively controlled, the uniformity of photon density along the resonant cavity can be improved, and the longitudinal spatial hole burning effect can be effectively suppressed, thus obtaining a narrower laser linewidth.
[0045] Reference Figure 5 , Figure 5This is a schematic flowchart of the first embodiment of the method for fabricating a distributed feedback laser according to this application, which presents the first embodiment of the method for fabricating a distributed feedback laser according to this application. In the first embodiment, the method for fabricating the distributed feedback laser includes the following steps: Step S10: Separate confinement heterostructures are sequentially epitaxially generated on the substrate layer, and multiple quantum well active regions are generated in the separated confinement heterostructures.
[0046] Understandably, the fabrication of separated confined heterostructures and multiple quantum wells on a substrate can employ metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). First, the substrate is pretreated by chemical cleaning to remove surface impurities and high-temperature deoxidation. Then, the substrate is placed in an epitaxial growth apparatus, and the constituent layers of the separated confined heterostructure (such as a buffer layer, lower confining layer, and lower waveguide layer) are grown sequentially according to the designed layer structure. When the pre-defined multiple quantum well positions are reached, quantum well layers and barrier layers are grown alternately, with precise control over the thickness and composition of each layer to form a multiple quantum well structure with specific quantum confining effects. After the multiple quantum wells are grown, the upper waveguide layer, upper confining layer, and other top-level structures of the separated confined heterostructure continue to grow. During the growth process, parameters such as growth temperature and reactive gas flow rate are adjusted in real time (e.g., by reflecting high-energy electron diffraction) to ensure that the thickness and composition of each layer meet the design requirements, ultimately forming a complete separated confined heterostructure and embedded multiple quantum wells.
[0047] Step S20: Define and etch a ridge waveguide extending along the cavity length direction of the resonant cavity on the separated confined heterostructure.
[0048] It should be noted that a ridge waveguide is a light transmission structure with a ridge-shaped cross-section. By etching a portion of the area to form a ridge, the refractive index difference between the ridge and the surrounding area can be used to constrain the light field to propagate along the extension direction of the ridge.
[0049] It is understood that defining and etching the ridge waveguide extending along the cavity length direction of the resonant cavity on the separated and confined heterostructure can be achieved by coating the surface of the heterostructure with photoresist, exposing it through a mask, transferring the pattern of the ridge waveguide extending along the cavity length direction onto the photoresist, and obtaining the photoresist mask pattern after development and fixing. Simultaneously, using the photoresist mask as protection, an etching process is employed to remove areas not covered by the photoresist, ensuring that the height of the formed ridge meets the light field confinement requirements, and that the etching direction strictly follows the cavity length direction of the resonant cavity.
[0050] Step S30: Based on the preset reflectivity combination of the end face coating and the ridge waveguide, a coupling grating layer is generated.
[0051] It should be noted that the preset end-face coating reflectivity combination refers to the combination of light reflection parameters of the two end faces of the resonant cavity that are preset according to the laser performance requirements (such as output power and spectral linewidth).
[0052] It should be understood that the preset reflectivity of the end-face coating determines the mirror loss and feedback distribution of the resonant cavity. The high-reflectivity end enhances the standing wave and feedback within the cavity, while the anti-reflectivity end weakens the mirror feedback and improves the coupling output. Based on this, the segmented apodized coupling grating, through the synergistic effect of grating segments with different coupling coefficients, can specifically counteract the optical field inhomogeneity caused by differences in reflectivity. The phase-shifting region ensures single-longitudinal-mode oscillation through phase modulation, forming a synergy with the optical field modulation of the grating segments. Ultimately, the optical feedback characteristics of the coupling grating layer are precisely matched with the reflectivity of the coating layer, achieving a uniform distribution and stable oscillation of the optical field within the cavity. This, in turn, improves the uniformity of photon density along the cavity length and suppresses the LSHB effect while maintaining a single longitudinal mode, resulting in a narrower linewidth.
[0053] Step S40: A dielectric layer is deposited on the surface of the ridge waveguide to generate an anode, and a cathode is generated on the back side of the substrate layer to obtain a distributed feedback laser.
[0054] It should be understood that the insulating properties of the dielectric layer can prevent the current from spreading laterally on the surface of the coupled grating layer, so that the current can only be injected into the lower separated confinement heterostructure and multi-quantum well region through the preset window, thereby improving the carrier utilization efficiency. The anode and cathode serve as positive and negative electrodes, respectively, and form a positive bias under the action of the applied voltage, driving electrons to move from the cathode to the anode, and after passing through the substrate layer and the separated confinement heterostructure, they are injected into the multi-quantum well region, recombine with holes to generate photons.
[0055] Specifically, a dielectric layer is deposited on the surface of the ridge waveguide (above the area covering the sidewall grating) for insulation and surface passivation. Current injection windows and current-limiting bars are then created on the dielectric layer using photolithography to electrically isolate the current path from the area of the sidewall Bragg-coupled grating. Subsequently, an anode is formed on the dielectric layer, completing the fabrication of the top electrode. Simultaneously, the substrate layer undergoes back-side cleaning and surface treatment, and a cathode is deposited and patterned on its back side, completing the fabrication of the bottom electrode. After this step, the device can proceed to subsequent processes such as cleaving and end-face coating, forming the desired resonant cavity optical conditions together with the segmented apodized sidewall grating.
[0056] In this embodiment, a coupling grating layer is constructed based on the reflectivity of the coating layer, realizing a positive correlation between structural parameters and performance requirements. The process does not require complex multi-step epitaxy or precision alignment processes, simplifying the manufacturing process.
[0057] Reference Figure 6 , Figure 6This is a flowchart illustrating a second embodiment of the method for fabricating a distributed feedback laser according to this application, which presents a second embodiment of the method for fabricating a distributed feedback laser according to this application. In the second embodiment, step S30 includes: Step S301: Obtain the preset reflectivity combination of the preset end face coating, and determine the cavity length of the resonant cavity and the path of the ridge waveguide.
[0058] It should be noted that the sidewall Bragg coupling grating is a longitudinally periodic structure etched on both sidewalls of the ridge waveguide. It achieves Bragg scattering and distributed feedback of forward / backward waves through refractive index modulation along the cavity length. The lateral constraint is provided by the refractive index step of the ridge waveguide. The resonant cavity is defined by the end faces of the waveguide and their coatings. The sidewall grating does not change the cavity length, but rather modulates the feedback distribution within the cavity and works in conjunction with the subsequent half-wavelength phase shift region to achieve mode selection and field distribution optimization.
[0059] In one example, reference Figure 7 , Figure 7 This is a schematic diagram of the segmented apodized grating structure of this application. The SAC-DFB laser uses a sidewall Bragg grating, forming staggered rectangular grooves with the active region. The width of these grooves varies regularly (e.g., ...) on the waveguide sidewalls through etching. , and This process generates periodic refractive index contrasts, thereby obtaining a coupled grating. The grating is a first-order structure with a duty cycle of 50%. The etching depth can be precisely controlled, thus controlling the coupling coefficient of the grating. The SAC-DFB grating consists of alternating regions with two different coupling coefficients: one with a larger coupling coefficient... (The segment with a large coupling coefficient) has another segment with a smaller coupling coefficient. (Small coupling coefficient segment). Spacing between each grating segment. The grating period Λ is determined by the operating wavelength λ0 and the effective refractive index n. eff It is confirmed that Λ=λ0 / (2) neff A quarter-wavelength phase-shift grating layer (standard QWPS structure) is inserted at the center of the resonant cavity to ensure single-mode output. The ratio of the lengths of the two grating segments ( The optical field distribution within the cavity can be controlled by adjusting the end-face reflection conditions. For the end-face coating configuration, different combinations such as dual anti-reflection or one end with high reflectivity and the other with anti-reflection can be used to change the feedback distribution within the cavity, thereby maintaining a stable single longitudinal mode and narrow linewidth under different end-face conditions.
[0060] Step S302: Determine the coupling coefficient and length ratio of the first grating segment and the second grating segment in the segmented apodized coupling grating according to the preset reflectivity combination.
[0061] It is understandable that, in this embodiment, in order to obtain the best performance, the coupling coefficient distribution is first analyzed ( , The photon density uniformity parameter f was defined as follows: (The ratio of the lengths of the two grating segments was optimized using a global scan.) (S represents the photon density distributed along the cavity axis), used to evaluate the uniformity of photon distribution; the closer f is to 1, the more uniform the photon density distribution. In the simulation, the resonant cavity length is fixed at 600 μm, the cavity is divided into 61 segments, each containing 40 Bragg cycles, and an injected current of 50 mA is used as the reference. It can be seen that for different... There will be a corresponding To achieve a larger f, for AR-AR end-face coating, select one of the following groups. ≈27cm -1 , ≈8cm -1 At that time, the uniformity f≈0.80 is optimal. For HR-AR end face coating, ≈27cm -1 , ≈10cm -1 At this point, f≈0.67. Under the above optimized combination, the optical field inside the SAC-DFB laser cavity is more uniform, and the LSHB effect is significantly alleviated. Furthermore, the length of the large coupling coefficient segment was investigated. The effect on photon distribution, as The photon density at the phase-shift layer increases under AR-AR end-face coating conditions, while the photon density at the front end face increases under HR-AR end-face coating conditions. Increasing the length of the segment enhances photon accumulation at the phase shift or end face, thereby reducing the uniformity f. Therefore, in this embodiment, the photon density distribution at both ends and the center of the cavity is balanced by selecting appropriate length ratios of gratings with different coupling coefficients to improve laser performance. Overall, compared to the corresponding QWPS-DFB laser, the optimized SAC-DFB laser achieves a more uniform intracavity optical field distribution in both the phase-shift region and the end face. These optical field modulation behaviors effectively reduce local carrier perturbations caused by the LSHB effect, which is beneficial for achieving narrower laser linewidth and better laser performance.
[0062] Furthermore, in order to quickly and accurately determine the optimal grating parameters and ensure the best match between the grating parameters and the reflection conditions, step S302 may include: A light field simulation model is obtained. The light field simulation model performs a global scan optimization on the coupling coefficient distribution and the length ratio of the two grating segments based on the simulation experiment. It includes the correspondence between the coating layer reflectivity, grating coupling coefficient and length ratio parameters. With the goal of optimal light field distribution uniformity, the preset reflectivity is input into the light field simulation model, and the coupling coefficient and length ratio of the first grating segment and the second grating segment are output.
[0063] Understandably, the optical field simulation model constructs a quantitative correspondence between the reflectivity of the coating layer, the grating coupling coefficient, and the length ratio by optimizing the global scanning distribution of the coupling coefficient and the length ratio of two gratings with different coupling coefficients. This model can simulate the behavior of the intracavity optical field under different parameter combinations. The uniformity of the optical field distribution is an indicator that characterizes the density distribution of photons in the resonant cavity. The higher the uniformity, the better the LSHB effect can be suppressed, thus improving the laser performance.
[0064] Specifically, simulation experiments are conducted to perform global traversal calculations on different parameter combinations, recording data such as the light field distribution and threshold gain corresponding to each combination. A mapping relationship is established between the reflectivity of the coating layer, the grating coupling coefficient, and the length ratio, forming a directly callable light field simulation model. When applying the model, the preset reflectivity parameters are input into the model, and the model automatically searches the optimal parameter space, using the highest uniformity of the light field distribution as the objective function, and outputs the corresponding coupling coefficient values and length ratios between the first and second grating segments.
[0065] In one example, reference Figure 8 , Figure 8 This is a schematic diagram illustrating the optimization of coupling coefficient distribution and photon density results in this application. Wherein, Figure 8 (a), (b), and (c) show the simulation results under AR-AR end-face coating conditions, while (d), (e), and (f) show the results under HR-AR conditions. (a) and (d) illustrate different... and Global scan results of photon density uniformity parameter f under combined conditions; (b) and (e) show different large coupling segment lengths. (c) shows the photon distribution along the longitudinal direction of the cavity; (f) and (c) show the comparison between the optimized SAC-DFB laser photon density distribution and the corresponding QWPS-DFB laser. The results show that the optimized SAC-DFB laser design significantly homogenizes the photon density distribution and reduces the LSHB effect.
[0066] In one example, reference Figure 9 , Figure 9 This diagram illustrates the intracavity optical field distribution of a SAC-DFB laser and its corresponding QWPS-DFB laser for grating lengths with different large coupling coefficients. Figure 9 (a) and (d) show different Figure 1 shows the normalized forward optical field distribution of SAC-DFB under AR-AR and HR-AR end-face coating conditions; (b) and (e) show the corresponding backward optical field distribution; (c) and (f) show the comparison between the optimized SAC-DFB and the corresponding QWPS-DFB laser optical field distribution. It can be seen from the figure that the SAC-DFB structure can be optimized by adjusting... It effectively suppresses excessive light field at the phase shift layer and end face, making the light field inside the cavity more uniform.
[0067] Step S303: Based on the coupling coefficient and the length ratio, using patterned photoresist as a mask, Bragg coupling gratings are generated in segments along the cavity length direction along both sidewalls of the ridge waveguide.
[0068] Furthermore, in order to accurately form grating segments with different coupling coefficients according to design requirements, the structural accuracy of the segmented apodized coupling grating is ensured. Step S203 may include: Photoresist is coated on the top of the ridge waveguide, and a mask pattern including the first grating segment and the second grating segment is transferred to the photoresist and / or a preset hard mask by photolithography. Using the patterned photoresist and / or hard mask as a mask, anisotropic dry etching is performed along the two sidewalls of the ridge waveguide to transfer the pattern to the underlying semiconductor material, thereby obtaining a sidewall Bragg grating segmented in the cavity length direction. The different coupling coefficients of the first grating segment and the second grating segment can be obtained by controlling the sidewall etching depth. After etching, post-processing is performed to obtain the Bragg coupled grating.
[0069] Understandably, during exposure, the photoresist undergoes polymerization or decomposition reactions in the light-exposed areas, causing changes in its solubility in the developer, thus enabling the transfer of the mask pattern to the photoresist layer. During etching, the patterned photoresist selectively protects the underlying material. Areas not covered by the photoresist are removed by chemical etching or physical sputtering with etching gases, while covered areas are preserved. By controlling the etching parameters, the etching depth can be precisely controlled. For example, the first grating segment requires a higher coupling coefficient and thus has a greater etching depth (more significant refractive index difference), while the second grating segment has a smaller etching depth. Post-processing removes residual photoresist and cleans the surface using chemical or physical methods to prevent impurities from affecting the optical performance of the grating and ensure that the grating structure can achieve the designed control of the light field.
[0070] Furthermore, in order to correlate the laser linewidth requirements with the coating type and then determine the reflectivity range through optical simulation, thereby avoiding mismatches between coating parameters and laser performance requirements and improving fabrication efficiency, the process prior to step S203 also includes: The reflectivity combination of the coatings on both ends of the resonant cavity is determined according to the preset laser linewidth target; based on the reflectivity combination, the target reflectivity range of the coatings on the ends is determined using a preset simulation model.
[0071] Accordingly, the step of determining the coupling coefficient and length ratio of the first grating segment and the second grating segment in the segmented apodized coupling grating according to the preset reflectivity combination includes determining the coupling coefficient and length ratio of the first grating segment and the second grating segment in the segmented apodized coupling grating according to the target reflectivity range and the preset reflectivity combination.
[0072] It is understandable that the laser linewidth is determined by the photon lifetime within the cavity; the longer the photon lifetime, the narrower the linewidth. Highly reflective coatings (such as high-reflectivity films) can extend the round-trip time of photons within the cavity, increasing the photon lifetime and thus compressing the linewidth. However, excessively high reflectivity may lead to uneven light field distribution. Lowly reflective coatings (such as anti-reflective films) will shorten the photon lifetime, resulting in a correspondingly wider linewidth, which is beneficial for increasing output power.
[0073] Specifically, according to the linewidth theory of DFB lasers, the linewidth of a DFB laser... It can be divided into spontaneous emission contributions. Contribution of local carrier density fluctuations Photon-carrier cross term Three parts, among which This study primarily demonstrates the impact of the LSHB effect on linewidth. The simulation assumes temperature control via a thermoelectric cooler (TEC) and uses a calculation model based on room temperature conditions. Results show that as the injected current increases, the local carrier fluctuations... Significantly increases, tending to saturate at high currents; in contrast, It remains very low, almost negligible. The changing trend is consistent with the change in photon distribution uniformity f. Further comparison of the linewidth composition of the optimized SAC-DFB laser and the conventional QWPS-DFB laser at 120 mA reveals the contribution of the LSHB effect of the SAC-DFB laser to linewidth broadening under AR-AR end-face coating. The Hz frequency is only 7.5 kHz, while the QWPS-DFB laser reaches 222.5 kHz; under HR-AR end-face coating, The linewidths were 22.4 kHz and 118.9 kHz, respectively, representing reductions of 96.6% and 82.0%. This indicates that the SAC-DFB structure significantly mitigates the linewidth broadening caused by carrier inhomogeneity. The optimized SAC-DFB laser also exhibits a significant advantage in bus width. At an injection current of 120 mA, the bus width of the SAC-DFB laser with AR-AR end-face coating is 312.3 kHz, significantly better than the 536.5 kHz of the corresponding QWPS-DFB laser; with HR-AR end-face coating, the bus widths are 118.0 kHz and 235.5 kHz, respectively, representing reductions of approximately 41.8% and 50.0%, while maintaining stable single-mode operation of the output spectrum. Furthermore, extending the cavity length can further reduce the linewidth: simulations show that when the cavity length is extended to 1000 µm and 1500 µm, the linewidth of the AR-AR end-face coating at an injection current of 120 mA decreases to 165.9 kHz and 112.7 kHz, respectively, and to 75.8 kHz and 52.8 kHz, respectively, at HR-AR. This is mainly attributed to the fact that the longer cavity reduces mirror loss and improves photon uniformity, further suppressing linewidth broadening and spontaneous emission caused by the LSHB effect.
[0074] In one example, reference Figure 10 , Figure 10 For SAC-DFB and the corresponding QWPS-DFB laser and A schematic diagram showing the effect of injection current. (The diagram shows the effect of injection current.) Figure 10 (a), (b), and (c) represent different AR-AR end-face conditions. SAC-DFB laser , The figures show the variation with current; (d), (e), and (f) represent the corresponding variations of SAC-DFB under different coating conditions on the HR-AR end face. Figures (a)(d) and (b)(e) show the variations of SAC-DFB under different current conditions. The linewidth contribution under the given condition is shown in (c) and (f), which compare the optimized SAC-DFB with the corresponding QWPS-DFB. The results indicate that the optimized SAC-DFB laser contributes significantly to linewidth broadening due to the LSHB effect at an injection current of 120 mA. At only 7.5 kHz (AR-AR) and 22.4 kHz (HR-AR), it is far lower than QWPS-DFB's 222.5 kHz and 118.9 kHz.
[0075] In one example, reference Figure 11 , Figure 11 This is a comparison of the bus width and output spectrum of the SAC-DFB and its corresponding QWPS-DFB lasers. Figure 11(a) and (c) show the simulated linewidth curves for the two end-face coating conditions under different injection currents; (b) and (d) show the corresponding output spectra. The results show that the linewidth of the SAC-DFB laser under AR-AR end-face coating is 312.3 kHz at an injection current of 120 mA, and 536.5 kHz for the QWPS-DFB laser; under HR-AR, the linewidths are 118.0 kHz and 235.5 kHz, respectively, representing reductions of approximately 41.8% and 50.0% in the two cases.
[0076] In one example, reference Figure 12 , Figure 12 The figures show the simulated linewidth results of the SAC-DFB laser under different cavity lengths. Figure 12 The figure shows the linewidth versus current curves of SAC-DFB lasers with AR-AR and HR-AR end-face coatings at cavity lengths of 1000 µm and 1500 µm. At 120 mA, the linewidths of the SAC-DFB with cavity lengths of 1000 µm and 1500 µm are 165.9 kHz and 112.7 kHz (AR-AR), and 75.8 kHz and 52.8 kHz (HR-AR), respectively.
[0077] Step S204: A quarter-wavelength phase shift structure is set at the center of the cavity length of the resonant cavity to obtain a phase shift region, so as to divide the Bragg coupling grating into two parts symmetrical about the cavity center.
[0078] It should be understood that in a conventional grating structure, when the light field propagates along the resonant cavity, it will form a periodic standing wave distribution, and multiple longitudinal modes may simultaneously satisfy the oscillation condition. After inserting a quarter-wavelength phase shift layer, this region will cause an additional π / 2 phase abrupt change in the light field, resulting in only light of a specific wavelength being able to form constructive interference after passing through the phase shift region and satisfy the resonance condition, while light of other wavelengths is suppressed due to phase mismatch. This phase selection mechanism can effectively screen out a single longitudinal mode. At the same time, since the phase shift region is located in the center, it can ensure the symmetry of the light field distribution on both sides when the AR-AR end face is coated, and avoid the shift of the center of gravity of the light field caused by phase shift.
[0079] Understandably, when forming a quarter-wavelength phase-shift grating layer at the center of the resonant cavity, the precise center coordinates of the resonant cavity can first be determined by measurement or simulation, marking the fabrication range of the phase-shift region. On the sample with the basic photolithography of the segmented apodized coupling grating already completed, a secondary photolithography process is used to overlay a photoresist pattern matching the quarter-wavelength phase-shift structure in the central marked area, ensuring the alignment accuracy between the pattern and the gratings on both sides. Using the newly patterned photoresist as a mask, a high-precision etching process (such as electron beam etching) is used to locally etch the central area, causing the phase of the grating in this area to shift by a quarter-wavelength relative to the sides, forming an independent phase-shift grating layer. After etching, the photoresist is removed and the surface is cleaned, finally forming a phase-shift region at the center of the resonant cavity, and this region divides the segmented apodized coupling grating into two symmetrical parts.
[0080] Step S205: The Bragg coupled grating is cleaved to obtain an end face, and a coating is deposited on the end face to obtain different reflectivity combinations, thus obtaining a coupled grating layer.
[0081] Understandably, after the design and fabrication of the coupled grating structure are completed, in order to form the final resonant cavity and precisely control its lasing mode and output characteristics, it is necessary to deposit a film on both ends of the semiconductor chip containing the grating obtained through the cleaving process.
[0082] Specifically, based on the preset reflectivity requirements, the film structure, including materials, thickness, and number of layers, is calculated using sophisticated optical thin-film design software. A suitable coating process, such as electron beam evaporation or ion-assisted deposition, is then selected. Next, in an ultra-clean environment, the cleaved chip strip is fixed to a fixture with one end facing the coating source. By precisely controlling the evaporation rate, substrate temperature, and film thickness monitoring, high-refractive-index and low-refractive-index dielectric materials (such as...) are deposited alternately. / To form a high reflectance (HR) film on the end face; after completing one end, the end face is flipped and the same principle but different film system is applied to the other cleaved end face to form a specific low reflectance antireflection (AR) film; finally, the two coated end faces that respectively meet the preset reflectance index and the grating structure inside the end face together constitute a complete coupled grating layer.
[0083] It should be understood that the end face reflectivity does not necessarily need to reach a specific preset value. Intermediate or semi-reflective surfaces can also be used, and the segmented design can be adjusted accordingly.
[0084] In one example, reference Figure 13 , Figure 13 A comparison chart showing the performance of SAC-DFB lasers under different combinations of end-face reflectivity. Figure 13The linewidth performance of SAC-DFB and QWPS-DFB lasers at 120 mA was compared: where (a), (b), and (c) are... and The relationship between current and bus width is shown in (d), (e), and (f). The results show that under the three end-face conditions, the linewidth increase caused by the LSHB effect of SAC-DFB is significantly reduced, with bus widths ranging from 115.8 to 112.2 kHz, all much lower than the corresponding 205.7 to 289.7 kHz of QWPS-DFB.
[0085] In this embodiment, a sidewall Bragg grating is used to define the resonant cavity, ensuring the optical field confinement effect. The grating parameters are determined and a quarter-wavelength phase shift layer is formed, ensuring the effectiveness of optical field modulation and single longitudinal mode output. The finally constructed coupled grating layer can maximize the optical field optimization effect and significantly improve the linewidth performance and operational reliability of the laser.
[0086] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on the fabrication method of the distributed feedback laser of this application. Any simple modifications based on this technical concept are within the protection scope of this application.
[0087] The above description is only a part of the embodiments of this application and does not limit the scope of this application. All equivalent structural transformations made under the technical concept of this application and using the content of this application specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of this application.
Claims
1. A distributed feedback laser, characterized in that, The distributed feedback laser includes: Substrate layer; A separation-confined heterostructure is disposed on the substrate layer. The separation-confined heterostructure includes a lower cladding layer, an active region, and an upper waveguide layer sequentially epitaxially formed on the substrate. The active region is a multiple quantum well. A coupling grating layer is disposed on the separated and confined heterostructure. A ridge waveguide is disposed in the coupling grating layer. The ridge waveguide extends along the resonant cavity length direction of the coupling grating layer. Bragg coupling gratings are disposed on the sidewalls of the ridge waveguide. The Bragg coupling gratings are segmented structures and include at least two grating segments with different coupling coefficients. A dielectric layer is disposed on the surface of the Bragg coupling grating, and the dielectric layer covers the ridge waveguide; The anode is disposed on the dielectric layer; The cathode is located on the back side of the substrate layer.
2. The distributed feedback laser as described in claim 1, characterized in that, The coupling grating layer includes: A resonant cavity, wherein a ridge-shaped waveguide extends along the length direction of the resonant cavity; A Bragg coupling grating is disposed inside the resonant cavity. The Bragg coupling grating is a segmented apod coupling grating disposed on both sides of the ridge waveguide. The segmented apod coupling grating is arranged in segments along the length of the resonant cavity and includes at least two grating segments with different coupling coefficients. A phase-shifting region is located at the center of the resonant cavity, and the phase-shifting region divides the Bragg coupling grating into two parts that are symmetrical about the center of the resonant cavity. A coating layer is disposed on both end faces of the resonant cavity.
3. The distributed feedback laser as described in claim 2, characterized in that, The segmented apodized coupling grating includes a first grating segment and a second grating segment arranged sequentially along the cavity length direction; the coupling coefficient of the first grating segment is greater than the coupling coefficient of the second grating segment; the ratio of the coupling coefficient and length of the first grating segment to the second grating segment is determined according to the reflectivity combination of the coating layer.
4. The distributed feedback laser as described in claim 3, characterized in that, The phase shift region is a quarter-wavelength phase shift structure, and each of the target regions on both sides of the phase shift region contains a segment of the first grating and a segment of the second grating.
5. The distributed feedback laser as described in claim 3, characterized in that, The coating layer is a double anti-reflective coating or a coating with high reflectivity at one end and anti-reflective coating at the other end.
6. A method for fabricating a distributed feedback laser, characterized in that, A method for fabricating a distributed feedback laser as described in any one of claims 1 to 5, the method comprising the following steps: Separate confinement heterostructures are sequentially epitaxially generated on the substrate layer, and multiple quantum well active regions are generated in the separated confinement heterostructures; A ridge waveguide extending along the cavity length direction of the resonant cavity is defined and etched on the separated confined heterostructure. Based on the preset reflectivity combination of the end-face coating and the ridge waveguide, a coupling grating layer is generated; A dielectric layer is deposited on the surface of the ridge waveguide to generate an anode, and a cathode is generated on the back side of the substrate layer to obtain a distributed feedback laser.
7. The method for fabricating a distributed feedback laser as described in claim 6, characterized in that, The step of generating a coupled grating layer based on the preset reflectivity combination of the end-face coating and the ridge waveguide includes: Obtain a preset combination of reflectivity for the end face coating, and determine the cavity length of the resonant cavity and the path of the ridge waveguide; The coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating are determined based on the preset reflectivity combination. Based on the coupling coefficient and the length ratio, using patterned photoresist as a mask, Bragg coupling gratings are generated in segments along the cavity length direction along both sidewalls of the ridge waveguide. A quarter-wavelength phase-shift structure is set at the center of the cavity length of the resonant cavity to obtain a phase-shift region, thereby dividing the Bragg coupling grating into two parts symmetrical about the cavity center; The Bragg coupled grating is cleaved to obtain an end face, and a coating is deposited on the end face to obtain different combinations of reflectivity, thus obtaining a coupled grating layer.
8. The method for fabricating a distributed feedback laser as described in claim 7, characterized in that, The step of generating Bragg coupling gratings segmentally along the cavity length direction using patterned photoresist as a mask, based on the coupling coefficient and the length ratio, includes: Photoresist is coated on the top of the ridge waveguide, and a mask pattern containing the first grating segment and the second grating segment is transferred onto the photoresist and / or a preset hard mask by photolithography. Using the patterned photoresist and / or hard mask as a mask, anisotropic dry etching is performed along the two sidewalls of the ridge waveguide to transfer the pattern to the underlying semiconductor material, thereby obtaining a sidewall Bragg grating segmented in the cavity length direction. The different coupling coefficients between the first grating segment and the second grating segment can be obtained by controlling the sidewall etching depth. After etching, post-processing is performed to obtain the Bragg-coupled grating.
9. The method for fabricating a distributed feedback laser as described in claim 7, characterized in that, Before the step of generating Bragg coupling gratings in segments along the two sidewalls of the ridge waveguide in the cavity length direction, using patterned photoresist as a mask according to the coupling coefficient and the length ratio, the method further includes: The combination of reflectivity of the coatings on both ends of the resonant cavity is determined based on the preset laser linewidth target. Based on the aforementioned reflectivity combination, a preset simulation model is used to determine the target reflectivity range of the end-face coating; Accordingly, the step of determining the coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating based on the preset reflectivity combination includes: The coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating are determined based on the target reflectivity range and the preset reflectivity combination.
10. The method for fabricating a distributed feedback laser as described in claim 7, characterized in that, The step of determining the coupling coefficient and length ratio between the first grating segment and the second grating segment in the segmented apodized coupling grating based on the target reflectivity range and the preset reflectivity combination includes: A light field simulation model is obtained, which takes the combination of end face coating reflectivity, coupling coefficient and segment length ratio as input parameters, and the uniformity of intracavity photon density along the cavity length as the objective function. The target reflectivity range and the preset reflectivity combination are input into the light field simulation model to solve for a parameter set that satisfies the optimal photon density uniformity and maintains the single longitudinal mode oscillation condition. The parameter set includes the coupling coefficient and length ratio of the first grating segment and the second grating segment.