A semiconductor laser

Abstract

The application relates to the technical field of semiconductors, and discloses a semiconductor laser, which comprises an epitaxial structure; the epitaxial structure comprises a current injection region, a first non-injection region and a second non-injection region, and the first non-injection region and the second non-injection region are respectively located on the two sides of the current injection region in a lateral direction; the current injection region comprises a plurality of waveguide discrete regions, a plurality of lateral regulation regions and at least two boundary adjustment regions, the plurality of lateral regulation regions and the plurality of waveguide discrete regions are arranged along a cavity length direction and are alternately arranged in the lateral direction, a waveguide discrete region closest to the first non-injection region in the lateral direction is connected with at least one boundary adjustment region, and a waveguide discrete region closest to the second non-injection region in the lateral direction is connected with at least one boundary adjustment region; and a target lateral structure parameter is configured to make the shape of a near-field envelope of a fundamental mode be flat-topped. The application can improve the mode stability, the light beam quality and the brightness of the device under high-power working conditions.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a semiconductor laser. Background Technology

[0002] For wide-ridge or wide-strip-edge emitting semiconductor lasers, the number of lateral modes that the device can support increases rapidly with the increase of ridge width. Under high-power (e.g., 10W and above) operating conditions, the device is prone to problems such as increased lateral far-field divergence angle, decreased beam quality, and unstable operation due to the influence of lateral mode competition, spatial hole burning, beam filamentation effect, and changes in transverse refractive index caused by temperature rise and non-uniform carrier distribution.

[0003] In related technologies, lateral periodic microstructures are typically set on both sides of the ridge region, such as air holes, trenches, slots, chirped microstructures, passive loss arrays, or lossy lateral photonic crystal arrays. By changing the propagation constant, coupling conditions, or loss characteristics of higher-order lateral modes, the threshold difference between the base-side mode and the higher-order lateral mode is increased, thereby achieving higher-order lateral mode suppression, lateral far-field compression, and low divergence angle output.

[0004] However, due to the presence of thermal lensing and carrier lensing effects, the light field concentrates in the central region, leading to decreased mode stability and degraded beam quality. Summary of the Invention

[0005] This invention provides a semiconductor laser to address the problems of decreased mode stability and beam quality degradation in semiconductor lasers.

[0006] In a first aspect, the present invention provides a semiconductor laser, including an epitaxial structure; the epitaxial structure includes a current injection region, a first non-injection region, and a second non-injection region, the first non-injection region and the second non-injection region being located on opposite sides of the current injection region in the lateral direction; the current injection region includes a plurality of discrete waveguide regions, a plurality of lateral control regions, and at least two boundary adjustment regions, the plurality of lateral control regions and the plurality of discrete waveguide regions extending along the cavity length direction and alternating in the lateral direction, the discrete waveguide region closest to the first non-injection region in the lateral direction being connected to at least one boundary adjustment region, and the discrete waveguide region closest to the second non-injection region in the lateral direction being connected to at least one boundary adjustment region; the target lateral structural parameters are configured such that the near-field envelope of the fundamental mode is flat-topped; the target lateral structural parameters include at least one of the target structural parameters of the current injection region, the target structural parameters of the discrete waveguide regions, the target structural parameters of the lateral control regions, and the target structural parameters of the boundary adjustment regions.

[0007] The semiconductor laser provided by this invention uses a ridge waveguide as the basic waveguide structure. It constructs a lateral control region and a boundary adjustment region in the current injection region. By adjusting the lateral structure parameters to the target lateral structure parameters, the shape of the near-field envelope of the fundamental mode evolves from a centrally convex single-peak distribution to a flat-top (approximately uniform) envelope. On this basis, the fundamental mode is maintained as the dominant working state, thereby taking into account high power output, low lateral far-field divergence angle and high mode stability.

[0008] In one optional implementation, based on constraints and an objective function, the lateral structure parameters are optimized using an optimization algorithm to obtain target lateral structure parameters that make the near-field envelope of the fundamental mode flat-topped. The constraints are a preset range of values ​​for the lateral structure parameters, and the objective function is used to characterize the correspondence between the lateral structure parameters and the near-field envelope of the fundamental mode.

[0009] In one optional implementation, the lateral structural parameters are adjusted with the goal of forming a preset transverse equivalent refractive index distribution to obtain the target lateral structural parameters that make the shape of the near-field envelope of the fundamental mode flat-topped. The flat-topped near-field envelope includes multiple continuous protrusions, the difference between the maximum and minimum values ​​of each protrusion is less than 0.1, and the difference between the maximum and minimum values ​​among the multiple protrusions is less than 0.2.

[0010] In one optional embodiment, the epitaxial structure includes a substrate layer, a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding layer, and a capping layer stacked from bottom to top. The conductivity types of the lower cladding layer and the upper cladding layer are different, and the conductivity types of the lower waveguide layer and the upper waveguide layer are different.

[0011] In one optional embodiment, a first groove formed by recessing along the capping layer toward the substrate layer constitutes a lateral adjustment region. The bottom of the first groove is located in the upper waveguide layer, and the first groove is filled with a target material whose refractive index is greater than that of the upper waveguide layer. A second groove formed by recessing along the capping layer toward the substrate layer constitutes a boundary adjustment region. The bottom of the second groove is located in the upper waveguide layer, and the second groove is filled with a target material. The width of the second groove is greater than that of the first groove.

[0012] In one optional implementation, a first epitaxial block located within the upper waveguide layer constitutes a lateral adjustment region, and the refractive index of the first epitaxial block is greater than that of the upper waveguide layer; a second epitaxial block located within the upper waveguide layer constitutes a boundary adjustment region, and the refractive index of the second epitaxial block is greater than that of the upper waveguide layer, and the width of the second epitaxial block is greater than that of the first epitaxial block.

[0013] In one alternative implementation, a plurality of lateral adjustment regions are symmetrically arranged along the central axis of the current injection region in the lateral direction, and at least two boundary adjustment regions are symmetrically arranged along the central axis of the current injection region in the lateral direction.

[0014] In one alternative implementation, the effective refractive index of both the lateral adjustment region and the boundary adjustment region gradually changes along the lateral direction.

[0015] In an alternative implementation, the target lateral structural parameters are further configured such that, within the current injection region, the gain overlap factor of the fundamental mode is greater than the gain overlap factor of the first-order side mode, and the loss of the first-order side mode is greater than the loss of the fundamental mode.

[0016] In this embodiment, not only can a flat-top or quasi-uniform lateral near field be obtained, but also the base-side mode preferential resonance can be maintained even when thermal lensing effect, carrier lensing effect or carrier accumulation is present, thereby suppressing side-mode crossing thresholds and mode jumps.

[0017] In one optional implementation, the effective refractive index difference between the lateral control region and the waveguide discrete region ranges from 1 × 10⁻⁶. -4 Up to 1×10 -3 .

[0018] In this embodiment, the ridge waveguide can be made wider in the lateral direction to achieve higher output power. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a top view schematic diagram of a semiconductor laser according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a traditional current injection region and non-injection region; Figure 3 This is a schematic diagram illustrating the evolution process of the near-field envelope shape of the fundamental mode according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the transverse field distribution of the fundamental mode and the first-order side mode according to an embodiment of the present invention; Figure 5 This is a schematic diagram of a preset transverse equivalent refractive index distribution according to an embodiment of the present invention; Figure 6 This is a cross-sectional schematic diagram of an extensional structure according to an embodiment of the present invention; Figure 7 This is a cross-sectional schematic diagram of a semiconductor laser according to an embodiment of the present invention; Figure 8This is a top view schematic diagram of another semiconductor laser according to an embodiment of the present invention; Figure 9 This is a top view schematic diagram of a wide-ridge device according to an embodiment of the present invention; Figure 10 This is a top view schematic diagram of a lateral photonic crystal device according to an embodiment of the present invention; Figure 11 This is a top view schematic diagram of an anti-waveguide flat-top structure according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the effective refractive index distribution of various devices according to embodiments of the present invention; Figure 13 This is a schematic diagram of the simulation results of a wide-ridge device according to an embodiment of the present invention; Figure 14 This is a schematic diagram of the simulation results of a lateral photonic crystal device according to an embodiment of the present invention; Figure 15 This is a schematic diagram of the simulation results of an anti-waveguide flat-top structure according to an embodiment of the present invention.

[0021] Reference numerals: 10, epitaxial structure; 11, current injection region; 111, waveguide discrete region; 112, lateral control region; 113, boundary adjustment region; 12, first non-injection region; 13, second non-injection region; 101, substrate layer; 102, lower cladding layer; 103, lower waveguide layer; 104, active layer; 105, upper waveguide layer; 1051, first epitaxial block; 1052, second epitaxial block; 106, upper cladding layer; 107, capping layer; 1071, first groove; 1072, second groove; 108, target material. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention, not the entire structure.

[0023] In the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These drawings are not to scale, and some details are enlarged for clarity, and some details may be omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0024] The semiconductor laser provided by this invention can specifically be a side-emitting semiconductor laser. Side-emitting semiconductor lasers are widely used in pump sources, materials processing, displays, lidar, and coherent combining due to their advantages such as compact structure, high conversion efficiency, and ease of integration. In these applications, in addition to providing high output power, semiconductor lasers typically require high brightness and good beam quality.

[0025] For wide-ridge or wide-strip-edge emitting semiconductor lasers, problems such as increased lateral far-field divergence angle, decreased beam quality, and unstable operation are prone to occur. Especially in wide-area devices, thermal lensing and carrier lensing effects further cause the optical field to concentrate in the central region, thereby exacerbating mode distortion and beam quality degradation.

[0026] Therefore, how to suppress higher-order side modes, improve the lateral far field, and enhance the mode stability of the device at high power while maintaining high output power has always been an important technical problem in the field of wide-area side-emitting semiconductor lasers.

[0027] In related technologies, narrow ridge waveguides, gain / current limiting structures, lateral waveguide-resistant structures, transverse Bragg or photonic bandgap limiting structures, and the introduction of periodic microstructures in or around the ridge region are commonly used to suppress higher-order lateral modes in wide-area edge-emitting semiconductor lasers. Additionally, methods combining lateral photonic crystals with tapered amplification regions, tilted waveguides, chirped ridge waveguides, or array structures also exist to suppress higher-order lateral modes.

[0028] By setting periodic microstructures on both sides of the ridge region, the propagation constant, coupling conditions, or loss characteristics of higher-order lateral modes can be changed, thereby increasing the threshold difference between the base-side mode and the higher-order lateral modes, thus achieving higher-order lateral mode suppression, lateral far-field compression, and low divergence angle output.

[0029] While the aforementioned lateral photonic crystals, lateral loss arrays, or chirped microstructures can achieve mode selection and compress the lateral far field to some extent, their main function is to achieve "mode selection / suppression" through mode selection, loss enhancement, or threshold differentiation. The evaluation focus is usually on reducing the far field divergence angle, single-mode output, or the suppression effect of higher-order modes.

[0030] This invention, through research, has found that the solutions provided in related technologies typically do not focus on establishing a matching relationship between the lateral distribution of injected carriers and the target lateral optical field envelope. However, in most cases, the lateral injection distribution of the device is mainly determined by the electrode morphology, current diffusion, and conduction path. The dominant lateral fundamental mode near-field envelope after mode selection often still exhibits a single-peak distribution with a convex center (i.e., a Gaussian single-peak envelope that is strong in the center and weak on both sides). This results in an inherent mismatch in the lateral direction of the light intensity distribution, carrier depletion distribution, and heat source distribution.

[0031] When a semiconductor laser enters a high-power operating state, the aforementioned mismatch will cause a redistribution of the transverse carrier concentration and temperature distribution, further inducing transverse refractive index perturbation. This refractive index perturbation, in turn, will enhance the light field concentration in the central region, forming a positive feedback loop of thermal lensing and carrier lensing effects. This leads to decreased mode stability, increased operating point sensitivity, and may even induce mode jumps, beam quality degradation, or filamentation.

[0032] In other words, the focus of related technologies is on how to select the fundamental mode and suppress higher-order modes, without paying attention to the instability of high-power modes caused by the mismatch between the injection envelope and the target light mode envelope.

[0033] It should be noted that high power is defined based on the size of the semiconductor laser. When the size of the semiconductor laser is small, an output power higher than 1W can be considered high power. When the size of the semiconductor laser is large, an output power higher than 10W is considered high power.

[0034] In view of this, the present invention provides a semiconductor laser that, by setting a lateral control region and a boundary adjustment region in the current injection region of the epitaxial structure, causes the lateral near-field output of the semiconductor laser to tend to a flat-topped envelope (also an approximately uniform envelope), thereby suppressing higher-order lateral modes, reducing the lateral far-field divergence angle, and weakening the disturbance of transverse mode distribution by thermal lensing effect and carrier lensing effect, thus improving the mode stability, beam quality and brightness of the device under high-power operating conditions.

[0035] The structure of the semiconductor laser provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0036] like Figure 1 As shown, the semiconductor laser includes an epitaxial structure, which includes a current injection region 11 and non-injection regions (denoted as the first non-injection region 12 and the second non-injection region 13) disposed on both sides of the current injection region 11 in the lateral direction X. That is, the first non-injection region 12 and the second non-injection region 13 are respectively located on both sides of the current injection region 11 in the lateral direction X.

[0037] The current injection region 11 corresponds to the area where the ridge waveguide is set, which is also the central waveguide region. It includes multiple waveguide discrete regions 111, multiple lateral control regions 112, and at least two boundary adjustment regions 113. The multiple lateral control regions 112 and multiple waveguide discrete regions 111 extend along the cavity length direction Y and are alternately arranged in the lateral direction X. The waveguide discrete region closest to the first non-injection region 12 in the lateral direction X is connected to at least one boundary adjustment region, and the waveguide discrete region closest to the second non-injection region 13 in the lateral direction X is connected to at least one boundary adjustment region.

[0038] In other words, in the lateral direction X, there is a lateral control region 112 between any two adjacent waveguide discrete regions 111, and the waveguide discrete region located at the outer edge is also connected to the boundary control region 113. At least two boundary control regions 113 constitute the boundary features between the current injection region 11 and the non-injection region.

[0039] The original current injection region, such as Figure 2 As shown, the waveguide structure is continuous and does not have a lateral control region 112 and a boundary adjustment region 113. The lateral control region 112 provided in this invention is used to change the equivalent refractive index distribution of the current injection region 11 in the lateral direction X (lateral) and the boundary conditions of the lateral mode. The boundary adjustment region 113 is used to further adjust the penetration behavior, loss characteristics and boundary sensitivity of the lateral mode near the boundary.

[0040] In this invention, the lateral structural parameters are target lateral structural parameters, which are configured to make the near-field envelope of the fundamental mode flat-topped. The target lateral structural parameters include at least one of the target structural parameters of the current injection region 11, the waveguide discrete region 111, the lateral control region 112, and the boundary adjustment region 113. The target structural parameters can refer to width, depth, or equivalent refractive index, etc. A flat-topped shape means that the target lateral width in the near-field envelope of the fundamental mode exceeds a preset flat-top width and / or the peak-to-valley undulation is less than or equal to a preset threshold. The target lateral width is the width range corresponding to a light field intensity greater than a preset light field intensity in the lateral direction X. The envelope is the distribution profile of the light field intensity (light field amplitude) of the lateral mode in the lateral direction.

[0041] In other words, by adjusting the lateral structural parameters, this invention can change the lateral distribution of the near-field envelope of the fundamental mode, transforming the shape of the near-field envelope from a centrally convex, unimodal distribution (see...). Figure 3 (a) in the middle is transformed into a flat-topped shape (see Figure 3 In (b) of the model, the near-field envelope of the fundamental mode no longer maintains the Gaussian single-peak envelope with a strong center and weak sides as in traditional wide-area devices, but instead forms a more uniform intensity distribution in the main output region.

[0042] The flat-topped near-field envelope includes multiple consecutive protrusions (see...). Figure 3 In (b) of the diagram, multiple protrusions are located in the region of the target's lateral width. The difference between the maximum and minimum values ​​of each protrusion is less than 0.1, and the difference between the upper envelope (the protrusion containing the maximum value among the multiple protrusions) and the lower envelope (the protrusion containing the minimum value among the multiple protrusions) is less than 0.2. That is, the difference between the maximum and minimum values ​​of all protrusions is less than 0.2. The difference between the peak values ​​of the flat-topped near-field envelope is not too high, which can avoid mode jumping, beam quality degradation, or filamentation phenomena in the beam spot under high current.

[0043] Specifically, during the adjustment of lateral structural parameters, the continuous evolution path of the near-field envelope shape of the fundamental mode is as follows: Figure 3 As shown, it first exhibits a centrally convex unimodal distribution, then a flat-topped or nearly uniform envelope, and finally a centrally concave shallow bimodal distribution (see [reference]). Figure 3 (c) in the middle. Figure 3 Taking the near-field envelope distribution of the fundamental mode under different boundary adjustment region widths as an example, (a) is the distribution when the boundary adjustment region width is equal to 1 μm, (b) is the distribution when the boundary adjustment region width is equal to 2 μm, and (c) is the distribution when the boundary adjustment region width is equal to 3 μm. The horizontal axis represents the normalized light field intensity (Au), and the vertical axis represents the lateral position, with the unit being micrometers (μm). In the figure, 0 μm is the center position of the current injection region in the lateral direction (the position where the central axis O is located).

[0044] When adjusting the lateral structural parameters, this invention selects the transition state in the above-mentioned evolution process ( Figure 3 (b) is used as the target working window. The lateral structure parameters corresponding to the target working window are the target lateral structure parameters. This ensures that the fundamental mode maintains a high gain while the near-field envelope tends to be flat-topped (quasi-uniform distribution), thereby reducing the concentration of the lateral heat source term and the carrier depletion term.

[0045] Unlike schemes that only aim to enhance the loss of higher-order modes, this invention controls the near-field envelope of the fundamental mode by adjusting the lateral structural parameters, thereby making the light intensity distribution in the main output region more uniform. As a result, under high-power operating conditions, the distribution of heat source terms and carrier depletion terms in the lateral direction also tends to be gentler, which helps to reduce the refractive index redistribution caused by excessive concentration of light intensity at the center.

[0046] The present invention does not limit the specific implementation of the lateral control region 112 and the boundary adjustment region 113, as long as the shape of the near-field envelope of the fundamental mode is flat-topped. For example, the lateral control region 112 and the boundary adjustment region 113 are not limited to periodic structures, and can be implemented by local etching, material distribution adjustment, local backfilling, cladding modification or a combination thereof.

[0047] Furthermore, the lateral control zone 112 and the boundary adjustment zone 113 can be formed by channels, slots, segmented etching zones, local backfill zones or combinations thereof distributed along the lateral direction.

[0048] It should be understood that under high-power operating conditions, the transverse refractive index distribution of a device is affected by both temperature rise and changes in carrier concentration. Traditional wide-area fundamental modes, due to the significant bulge of light intensity at the center, tend to form stronger heat accumulation and carrier depletion in the central region, thereby inducing transverse refractive index perturbations and further causing the light field to concentrate towards the center, forming a positive feedback loop of thermal lensing and carrier lensing effects.

[0049] This invention makes the near-field envelope of the fundamental mode more flat-topped (approximately uniform), making the intensity distribution within the coverage area of ​​the main mode (fundamental mode) more gradual. This, in turn, makes the transverse refractive index change caused by heat and charge carriers more consistent on the large envelope scale, thereby reducing transverse phase curvature change, self-focusing effect and filamentation tendency, and improving the mode stability and beam quality stability of semiconductor lasers under high power operation.

[0050] While obtaining a flat-top near-field window, the semiconductor laser can still maintain the dominance of the fundamental mode over the first-order side modes. That is, the gain overlap factor of the fundamental mode is greater than that of the first-order side modes. The gain overlap factor refers to the proportion of optical field energy that falls within the gain region (current injection region).

[0051] For any set of lateral structural parameters, the fundamental mode (TE) 00 ) and first-order side mold (TE) 01 The transverse field distribution of ) is as follows Figure 4As shown, since the first-order side mode has a node at the central axis of the semiconductor laser (the central axis O of the current injection region 11 in the lateral direction X), while the fundamental mode always maintains a non-zero field distribution at the central axis, under the same injection and gain coverage conditions, the fundamental mode's utilization of the central gain region is always higher than that of the first-order side mode. That is, the fundamental mode has a higher gain overlap factor, which makes the fundamental mode exhibit a gain-locked state to the first-order side mode.

[0052] The semiconductor laser provided by this invention uses a ridge waveguide as the basic waveguide structure. It constructs a lateral control region and a boundary adjustment region in the current injection region. By adjusting the lateral structure parameters to the target lateral structure parameters, the shape of the near-field envelope of the fundamental mode evolves from a centrally convex single-peak distribution to a flat-top (approximately uniform) envelope. On this basis, the fundamental mode is maintained as the dominant working state, thereby taking into account high power output, low lateral far-field divergence angle and high mode stability.

[0053] Optionally, the target lateral structural parameters are further configured such that, within the current injection region, the gain overlap factor of the fundamental mode is greater than the gain overlap factor of the first-order side mode, and the loss of the first-order side mode is greater than the loss of the fundamental mode.

[0054] Specifically, the existence of the boundary adjustment region increases the sensitivity of the first-order sidemode to the side boundary, making it easier for it to penetrate into the boundary adjustment region and generate additional radiation loss, scattering loss, or equivalent boundary loss. Therefore, within an appropriate parameter window, it is possible to simultaneously satisfy: the fundamental mode gain overlap factor is greater than the first-order sidemode gain overlap factor, and the total loss of the first-order sidemode is greater than the total loss of the fundamental mode. Consequently, the fundamental mode threshold is lower than the first-order sidemode threshold, manifesting as gain locking and threshold suppression of the first-order mode by the fundamental mode.

[0055] This mechanism enables the present invention not only to obtain a flat-top or quasi-uniform lateral near field, but also to maintain preferential resonance of the base-side mode even in the presence of thermal lensing effect, carrier lensing effect or carrier accumulation, thereby suppressing side-mode crossing thresholds and mode jumps.

[0056] In some optional embodiments, the lateral structure parameters are optimized by an optimization algorithm based on constraints and an objective function to obtain target lateral structure parameters that make the shape of the near-field envelope of the fundamental mode flat-topped; the constraints are preset ranges of values ​​for the lateral structure parameters, and the objective function is used to characterize the correspondence between the lateral structure parameters and the near-field envelope of the fundamental mode.

[0057] Specifically, the process of determining the target lateral structural parameters includes the following steps: Step a1: Obtain the range of values ​​for the lateral structural parameters to determine the constraint conditions.

[0058] The range of values ​​for the lateral structure parameters can be determined by designers based on process limitations and the design requirements of the semiconductor laser (such as output power). In simulation software, this range of values ​​is used as a constraint. The lateral structure parameters can include the width of the gain region (lateral width of the current injection region), the width of the waveguide discrete region, the width of the lateral control region, the width of the boundary adjustment region, and the corresponding local equivalent refractive index parameters for each region. Each region refers to the current injection region, the waveguide discrete region, the lateral control region, and the boundary adjustment region.

[0059] Step a2: Based on the epitaxial structure, obtain the actual equivalent refractive index distribution of each region using the equivalent refractive index method. .

[0060] The equivalent refractive index method is a method that simplifies complex three-dimensional optical structures into two-dimensional or one-dimensional problems, and approximates the light field distribution and propagation constant by calculating the equivalent refractive index. This indicates the width of each region in the lateral direction.

[0061] Step a3, based on the actual equivalent refractive index distribution Solving the lateral eigenmode equations yields the field distribution of the fundamental modes. .

[0062] Among them, field distribution To characterize the change in optical field intensity of the lateral mode as the lateral width changes, the field distribution can be... As the objective function.

[0063] Step a4: Based on the obtained field distribution, determine the near-field envelope features corresponding to the fundamental mode.

[0064] Among them, the near-field envelope characteristics of the fundamental mode refer to the shape of the spatial distribution of light intensity in the transverse direction, which can be the peak-valley undulation, peak-valley uniformity, and flat-top width.

[0065] Step a5: Using the flat-top near-field index as the optimization objective, the lateral structural parameters are scanned under constraints using an optimization algorithm to determine the target lateral structural parameters that can satisfy the flat-top near-field envelope.

[0066] The optimization algorithm can be a genetic algorithm, and the flat-top near-field index can be characterized by at least one of the following: peak-valley undulation (less than a set threshold), peak-valley uniformity (greater than a set threshold), and flat-top width (greater than a set threshold).

[0067] When it is necessary to ensure the fundamental mode dominates, step a3 specifically involves: based on the actual equivalent refractive index distribution Solving the lateral eigenmode equations yields the field distributions of the fundamental mode and the first-order lateral mode. Step a4 specifically involves determining the near-field envelope characteristics, gain overlap factor, boundary penetration degree, and threshold difference of each mode (fundamental mode and first-order side mode) based on the obtained field distribution. Step a5 specifically involves scanning the lateral structure parameters under the constraint conditions using an optimization algorithm, with the flat-top near-field index and fundamental mode dominance as joint constraints, to determine the target lateral structure parameters that can simultaneously satisfy the flat-top near-field envelope and fundamental mode stability dominance.

[0068] Here, boundary penetration (loss) refers to the degree (proportion or depth) of light field leakage from the lateral mode outwards, which is related to the equivalent refractive index; threshold difference refers to the difference in lasing threshold current (or threshold gain) between the fundamental mode and the first-order lateral mode. Whether the fundamental mode is dominant can be characterized by at least one of the following: gain overlap factor (also known as optical confinement factor) between the fundamental mode and the first-order lateral mode, threshold difference, and equivalent loss difference. The optimization algorithm can be a multi-objective genetic algorithm or other multi-objective optimization algorithms.

[0069] For example, the flat-top near-field window and the fundamental mode locking window can be jointly optimized by changing the width of the lateral regions (current injection region, waveguide discrete region, lateral control region, boundary adjustment region), the equivalent refractive index difference, the boundary gradient function, the number of segments, or the boundary transition form.

[0070] In some alternative embodiments, the lateral structural parameters are adjusted with the goal of forming a preset transverse equivalent refractive index distribution, resulting in target lateral structural parameters that make the near-field envelope of the fundamental mode flat-topped.

[0071] Specifically, by adjusting the lateral structural parameters, the lateral equivalent refractive index of each lateral region is made to follow a preset lateral equivalent refractive index distribution, which can make the shape of the near-field envelope of the fundamental mode flat-topped.

[0072] The preset transverse equivalent refractive index distribution can be a continuous distribution (see...). Figure 5 (a) in the middle), segmented distribution form (see Figure 5 (b) or gradual distribution form (see Figure 5 (c) Figure 5 Taking the extensional structure including two boundary adjustment regions as an example, the equivalent refractive index (effective refractive index) of the two outermost protrusions corresponds to the effective refractive index of the boundary adjustment region. The multiple protrusions other than the two outermost protrusions correspond one-to-one with the lateral adjustment regions, representing the effective refractive index of the corresponding lateral adjustment regions.

[0073] This embodiment does not specifically limit the structural form of the lateral control region 112 and the boundary adjustment region 113. The lateral control region 112 and the boundary adjustment region 113 can be adjusted by changing the geometry of the current injection region, the material distribution, the local etching depth, or a combination thereof, so as to form a predetermined lateral equivalent refractive index distribution.

[0074] In other embodiments, the number of boundary adjustment regions can be 4 or 6, etc. When the number of boundary adjustment regions is 4, 2 are set on each side of the central axis O of the current injection region; when the number of boundary adjustment regions is 6, 3 are set on each side of the central axis O of the current injection region. The width of the multiple boundary adjustment regions on each side can vary continuously or in stages to adjust the boundary coupling strength and mode boundary penetration behavior.

[0075] For example, such as Figure 6 As shown, the epitaxial structure 10 includes a substrate layer 101, a lower cladding layer 102, a lower waveguide layer 103, an active layer 104, an upper waveguide layer 105, an upper cladding layer 106, and a capping layer 107 stacked from bottom to top. The conductivity type of the lower cladding layer 102 is different from that of the upper cladding layer 106, and the conductivity types of the lower waveguide layer 103 and the upper waveguide layer 105 are different. The substrate layer 101 can be an N-type substrate, the lower cladding layer 102 can be an N-type cladding layer, the lower waveguide layer 103 can be an N-type waveguide layer, the upper waveguide layer 105 can be a P-type waveguide layer, and the upper cladding layer 106 can be a P-type cladding layer.

[0076] In some alternative embodiments, such as Figure 7 As shown, a first groove 1071 formed by recessing along the capping layer 107 toward the substrate layer 101 constitutes a lateral adjustment region. The bottom of the first groove 1071 is located in the upper waveguide layer 105, and the first groove 1071 is filled with a target material 108, the refractive index of which is greater than that of the upper waveguide layer. A second groove 1072 formed by recessing along the capping layer 107 toward the substrate layer 101 constitutes a boundary adjustment region. The bottom of the second groove 1072 is located in the upper waveguide layer 105, and the second groove 1072 is filled with a target material. The width of the second groove 1072 is greater than that of the first groove 1071.

[0077] Specifically, in this embodiment, a predetermined lateral equivalent refractive index distribution is formed by etching the channel and backfilling with a high refractive index material (target material). After etching the predetermined channel structure, material backfilling can be performed by epitaxial deposition, and additional high refractive index material can be grown on the channel surface. In infrared semiconductor lasers, the waveguide layer material is aluminum gallium arsenide (AlGaAs), and in this case, the target material can be gallium arsenide (GaAs).

[0078] Optionally, the effective refractive index difference range between the lateral control region 112 and the waveguide discrete region 111 is... 1×10 -4 Up to 1×10 -3 This allows for a wider ridge waveguide in the lateral direction, resulting in higher output power.

[0079] In some other alternative embodiments, such as Figure 8 As shown, the first epitaxial block 1051 located within the upper waveguide layer 105 constitutes a lateral adjustment region, and the refractive index of the first epitaxial block 1051 is greater than the refractive index of the upper waveguide layer 105; the second epitaxial block 1052 located within the upper waveguide layer 105 constitutes a boundary adjustment region, and the refractive index of the second epitaxial block 1052 is greater than the refractive index of the upper waveguide layer 105, and the width of the second epitaxial block 1052 is greater than the width of the first epitaxial block 1051.

[0080] Specifically, this embodiment forms a predetermined lateral equivalent refractive index distribution by setting a high refractive index material in the waveguide layer. After the waveguide layer is applied to the growth portion, a high refractive index material (target material) is grown. After etching out the predetermined morphology, epitaxial growth is performed again to form the predetermined lateral equivalent refractive index distribution. Compared to etching channels and backfilling with high refractive index material, this embodiment has a higher process tolerance and is easier to process.

[0081] Optionally, the effective refractive index of both the lateral control region and the boundary control region gradually changes along the lateral direction.

[0082] In some optional embodiments, a plurality of lateral adjustment regions 112 are symmetrically arranged along the central axis O of the current injection region in the lateral direction, and at least two boundary adjustment regions 113 are symmetrically arranged along the central axis of the current injection region in the lateral direction.

[0083] In this embodiment, the lateral control region 112 and the boundary adjustment region 113 are symmetrically arranged, so that the shaping effect on the near-field envelope of the fundamental mode is balanced from left to right, avoiding the non-uniform distribution of one side being strong and the other side being weak, and making it easier to achieve a flat-top uniform near-field envelope.

[0084] The semiconductor laser provided by this invention has the following seven advantages: (1) Achieved lateral flat-top (approximately uniform) near-field output; This invention, by setting a lateral control region and a boundary adjustment region and configuring them synergistically, enables the near-field envelope of the fundamental mode of a semiconductor laser to evolve from a traditional centrally convex single-peak distribution to a flat-top (approximately uniform) distribution. Compared to schemes that focus on compressing the lateral far field or suppressing higher-order side modes, this invention further achieves uniformity of the lateral intensity envelope, thereby providing a more stable near-field foundation for high-brightness wide-area output.

[0085] (2) It enhanced the boundary response difference between the fundamental mode and higher-order side modes, and improved the suppression capability of higher-order modes; This invention enhances the response difference between the fundamental mode and higher-order side modes near the outer boundary by setting a boundary adjustment region outside the lateral control region and using methods such as width gradient, refractive index gradient, segmented transition, or termination unit size change. This makes higher-order side modes, especially first-order side modes, more sensitive to boundary disturbances and more prone to additional radiation loss, scattering loss, or equivalent boundary loss.

[0086] Therefore, this invention not only improves mode selection capability, but also helps to enhance the suppression effect on higher-order side modes and reduce the fluctuation of working state caused by mode competition.

[0087] (3) Establish the dominant working state of the fundamental model and improve the threshold suppression capability; Because the lateral structure of this invention not only adjusts the transverse equivalent refractive index distribution but also changes the boundary adjustment region, it can simultaneously achieve the following two effects at the structural level: on the one hand, the fundamental mode maintains higher utilization in both the central gain region and the edge gain region; on the other hand, the first-order side mode bears greater additional losses near the outer boundary. The combined effect of these two factors allows the fundamental side mode to maintain its dominant operating state relative to the first-order side mode and increases the oscillation threshold of the first-order side mode.

[0088] Therefore, the present invention can effectively suppress first-order side-mode threshold crossing, mode switching and mode competition under high-power operating conditions, thereby improving the mode stability and output consistency of the device.

[0089] (4) It reduces the sensitivity to thermal lensing and carrier lensing effects, and improves stability at high power; Because this invention achieves flattening (approximate homogenization) of the near-field envelope of the fundamental mode, the light intensity distribution in the main output region of the device is more gradual. Correspondingly, the heat source distribution and carrier depletion distribution are also more uniform, thereby reducing the lateral refractive index redistribution caused by thermal lensing effect and carrier lensing effect.

[0090] This can reduce transverse phase curvature variation, self-focusing positive feedback, and beam filamentation tendency, improve the mode stability, beam quality, and operating point repeatability of the device under high current and high power operating conditions, and reduce beam quality abrupt changes caused by operating point drift.

[0091] (5) Improve beam quality and brightness; In this invention, because higher-order side modes are suppressed and the fundamental mode is protected by the dominant operating state, the lateral far-field divergence angle and beam quality factor of the device can be improved, thereby contributing to increased brightness. Simultaneously, due to improved mode stability, the output beam quality variation at different operating points tends to be smoother, thus improving stable output capability in practical applications.

[0092] (6) It has good adaptability and robustness to process errors; This invention provides additional adjustable degrees of freedom for structural parameters by coordinating the design of the lateral control region and the boundary adjustment region. Therefore, when there are process deviations in parameters such as effective refractive index difference, element width, boundary size, or ridge width, the mode boundary conditions can still be compensated by adjusting the parameters of the boundary adjustment region or the termination region, thereby maintaining the target envelope shaping effect and the fundamental mode's dominant working state.

[0093] In implementations employing gradually widened boundary adjustment zones, segmented transitions, or localized refractive index variations, it is more advantageous to expand the acceptable range of process tolerances and improve the robustness of structural design.

[0094] (7) It has strong applicability and is easy to be compatible with processes and expand applications.

[0095] The lateral structure of this invention is compatible with III-V group side-emitting semiconductor laser process platforms. It can be used for single-device wide-area output, as well as for array devices or further extended to composite structures to improve total output power and overall brightness.

[0096] Meanwhile, since this invention is not limited to a specific unit shape, but rather focuses on flattening the near-field envelope shape of the fundamental mode, it has good application value under different material systems, different device sizes and different process routes.

[0097] To further clarify the effectiveness of this scheme, the near-field and far-field and intracavity optical field distribution characteristics of a wide-ridge device, a traditional side-facing photonic crystal device, and an anti-waveguide flat-top device (the semiconductor laser designed in this invention) under the same current are analyzed using a traveling wave model of optocoupler.

[0098] The structure of a wide-ridge device can be as follows: Figure 9 As shown, its main parameters are as follows: lasing wavelength λ is 973 nm, ridge width W is 43 μm, cavity length L is 2000 μm, injection current window width is the same as ridge width, and injection current magnitude I is 5 A, and the effective refractive index difference generated between the ridge waveguide and the etched channel is... 6×10 -4 Effective refractive index of ridge waveguide It is 3.27.

[0099] The structure of traditional lateral photonic crystal devices can be as follows: Figure 10 As shown, the anti-waveguide flat-top structure designed in this invention can be as follows: Figure 11As shown, the traditional lateral photonic crystal device has an etched channel width of 1 μm, a waveguide discrete region 111 width of 3 μm, and a total of 10 cycles. The outermost two waveguides are further widened by 2 μm, for a total width of 43 μm. Furthermore, the current injection region only includes the waveguide location, while the anti-waveguide flat-top structure backfills the lateral control region 112 with GaAs. The outermost extra-widened portion (boundary adjustment region 113) is also etched and backfilled with GaAs, while the non-injection region is not etched. This results in an anti-waveguide configuration for the lateral effective refractive index distribution, increasing the effective refractive index by 6 × 10⁻⁶ compared to a ridge waveguide. -4 The distribution of each effective refractive index is as follows Figure 12 As shown, Figure 12 In the diagram, (a) represents the effective refractive index distribution of a wide-ridge device, (b) represents the effective refractive index distribution of a traditional side-facing photonic crystal device, and (c) represents the effective refractive index distribution of an anti-waveguide flat-top device.

[0100] The simulation results can be as follows Figures 13 to 15 As shown, Figure 13 (a) shows the near-field distribution of the cold cavity fundamental mode of the wide-ridge device, (b) shows the near-field distribution under a current of 5A, (c) shows the optical field distribution characteristics in the resonant cavity, and (d) shows the far-field distribution under a current of 5A. Figure 14 (a) shows the near-field distribution of the cold cavity fundamental mode in a traditional lateral photonic crystal structure; (b) shows the near-field distribution under a 5A current; (c) shows the optical field distribution characteristics within the resonant cavity; and (d) shows the far-field distribution under a 5A current. Figure 15 (a) shows the near-field distribution of the cold cavity fundamental mode of the anti-waveguide flat-top device, (b) shows the near-field distribution under a current of 5A, (c) shows the optical field distribution characteristics in the resonant cavity, and (d) shows the far-field distribution under a current of 5A.

[0101] from Figures 13 to 15 As can be seen, under the same injected current, the device with the anti-waveguide structure exhibits the best lateral far-field divergence angle, only 1.73° in FWHM, and still maintains a certain degree of Gaussian envelope characteristics in the near field, through 1 / e of the peak intensity. 2 Calibrated side beam quality factor M x 2 Approximately 1.94. The next most common structure is the traditional lateral photonic crystal structure, which exhibits some degradation under high current, leading to the lasing of higher-order modes, through 1 / e of the peak intensity. 2 Calibrated side beam quality factor M x 2 The value is approximately 4.11. The worst performing device is the traditional wide-waveguide device, with a far-field divergence angle (FWHM) of 5.81° and severe near-field distortion, exceeding 1 / e of the peak intensity. 2 Calibrated side beam quality factor M x2 It is approximately 5.04. Full Width at Half Maximum (FWHM) refers to the divergence angle of the far-field light intensity distribution at half maximum, and is a core parameter for measuring the degree of beam divergence.

[0102] In summary, the simulation results demonstrate that constructing an anti-waveguide structure can effectively suppress higher-order modes and beam filamentation.

[0103] In the description of this specification, the references to terms such as "this embodiment," "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present 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. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction.

[0104] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0105] The above description does not provide detailed explanations of the technical aspects of each layer's patterning and etching. However, those skilled in the art should understand that various technical means can be used to form layers and regions of the desired shape. Furthermore, to form the same structure, those skilled in the art can design methods that are not entirely identical to those described above. Additionally, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be effectively combined.

[0106] The above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention.

[0107] Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention.

Claims

1. A semiconductor laser, characterized in that, Including epitaxial structures; The epitaxial structure includes a current injection region, a first non-injection region, and a second non-injection region, wherein the first non-injection region and the second non-injection region are located on both sides of the current injection region in the lateral direction. The current injection region includes multiple waveguide discrete regions, multiple lateral control regions, and at least two boundary adjustment regions. The multiple lateral control regions and the multiple waveguide discrete regions extend along the cavity length direction and are alternately arranged in the lateral direction. The waveguide discrete region closest to the first non-injection region in the lateral direction is connected to at least one of the boundary adjustment regions. The waveguide discrete region closest to the second non-injection region in the lateral direction is connected to at least one of the boundary adjustment regions. The target lateral structural parameters are configured such that the near-field envelope of the fundamental mode has a flat-top shape; the target lateral structural parameters include at least one of the target structural parameters of the current injection region, the target structural parameters of the waveguide discrete region, the target structural parameters of the lateral control region, and the target structural parameters of the boundary adjustment region.

2. The semiconductor laser according to claim 1, characterized in that, Based on constraints and an objective function, the lateral structure parameters are optimized using an optimization algorithm to obtain the target lateral structure parameters that make the near-field envelope of the fundamental mode flat-topped. The constraints are preset ranges of values ​​for the lateral structure parameters, and the objective function is used to characterize the correspondence between the lateral structure parameters and the near-field envelope of the fundamental mode.

3. The semiconductor laser according to claim 1, characterized in that, The lateral structural parameters are adjusted with the goal of forming a preset transverse equivalent refractive index distribution, resulting in the target lateral structural parameters that make the shape of the near-field envelope of the fundamental mode flat-topped. The flat-topped near-field envelope includes multiple continuous protrusions, the difference between the maximum and minimum values ​​of each protrusion is less than 0.1, and the difference between the maximum and minimum values ​​among the multiple protrusions is less than 0.

2.

4. The semiconductor laser according to claim 3, characterized in that, The epitaxial structure includes a substrate layer, a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding layer, and a capping layer stacked from bottom to top. The conductivity type of the lower cladding layer is different from that of the upper cladding layer, and the conductivity type of the lower waveguide layer is different from that of the upper waveguide layer.

5. The semiconductor laser according to claim 4, characterized in that, A first groove formed by recessing along the capping layer toward the substrate layer constitutes the lateral control region. The bottom of the first groove is located on the upper waveguide layer, and the first groove is filled with a target material, the refractive index of which is greater than that of the upper waveguide layer. The second groove formed by recessing along the cover layer toward the substrate layer constitutes the boundary adjustment region. The bottom of the second groove is located on the upper waveguide layer, and the second groove is filled with the target material. The width of the second groove is greater than the width of the first groove.

6. The semiconductor laser according to claim 4, characterized in that, The first epitaxial block located within the upper waveguide layer constitutes the lateral control region, and the refractive index of the first epitaxial block is greater than the refractive index of the upper waveguide layer. The second epitaxial block located within the upper waveguide layer constitutes the boundary adjustment region. The refractive index of the second epitaxial block is greater than that of the upper waveguide layer, and the width of the second epitaxial block is greater than that of the first epitaxial block.

7. The semiconductor laser according to any one of claims 1 to 6, characterized in that, The plurality of lateral adjustment regions are symmetrically arranged along the central axis of the current injection region in the lateral direction, and the at least two boundary adjustment regions are symmetrically arranged along the central axis of the current injection region in the lateral direction.

8. The semiconductor laser according to claim 7, characterized in that, The effective refractive index of the lateral adjustment region and the effective refractive index of the boundary adjustment region both gradually change along the lateral direction.

9. The semiconductor laser according to any one of claims 1 to 6, characterized in that, The target lateral structural parameters are further configured such that, within the current injection region, the gain overlap factor of the fundamental mode is greater than the gain overlap factor of the first-order side mode, and the loss of the first-order side mode is greater than the loss of the fundamental mode.

10. The semiconductor laser according to any one of claims 1 to 6, characterized in that, The effective refractive index difference between the lateral control region and the waveguide discrete region ranges from 1×10⁻⁶. -4 Up to 1×10 -3 .

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