A distributed grating laser structure

Abstract

The application relates to the technical field of semiconductors, and discloses a distributed grating laser structure which comprises an epitaxial layer structure; a current injection area and a Bragg grating are arranged on the epitaxial layer structure; the current injection area and the Bragg grating are arranged adjacently along a first direction, and the first direction is the light emitting direction of the distributed grating laser structure; a target Bragg grating is different from an original Bragg grating, so that a first reflectivity is greater than a second reflectivity; the first reflectivity is the reflectivity of the Bragg grating to a target feedback lateral mode; and the second reflectivity is the reflectivity of the Bragg grating to a target loss lateral mode. The application can reduce the process manufacturing and control difficulty while inhibiting high-order modes, and is beneficial to mass production.

Description

Technical Field

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

[0002] To increase power, distributed Bragg reflector (DBR) lasers increase the current injection stripe width. However, with the increase in stripe width, the significant increase in lateral modes leads to spectral broadening, which affects the application of DBR lasers to varying degrees.

[0003] To suppress higher-order modes, one approach for bar lasers and single-mode lasers involves placing grating structures parallel to the ridge waveguide on both sides. Compared to the fundamental mode, higher-order modes exhibit greater leakage loss and are thus suppressed. Another approach involves etching multiple micro-holes on the ridge, positioned at the peaks of the higher-order side-mode optical field distribution. This results in lower gain and very high loss for the higher-order side-modes compared to the fundamental mode, thereby suppressing higher-order modes. While these methods can suppress higher-order modes, the additional fabrication of these microstructures requires high lithographic precision, making fabrication and control difficult and hindering mass production. Summary of the Invention

[0004] This invention provides a distributed grating laser structure to solve the problems of increased spectral width when suppressing higher-order modes and the difficulty in manufacturing and controlling existing higher-order mode suppression schemes, which makes mass production difficult.

[0005] This invention provides a distributed grating laser structure, including an epitaxial layer structure; a current injection region and a target Bragg grating are disposed on the epitaxial layer structure; the current injection region and the target Bragg grating are disposed adjacent to each other along a first direction, which is the light emission direction of the distributed grating laser structure; the target Bragg grating is different from the original Bragg grating, so that the first reflectivity is greater than the second reflectivity, the first reflectivity is the reflectivity of the target Bragg grating for the target feedback lateral mode, and the second reflectivity is the reflectivity of the target Bragg grating for the target loss lateral mode.

[0006] This invention adjusts the structure of the original Bragg grating so that the difference between the first and second reflectivities is greater than a preset difference. This increases the grating's feedback capability to lower-order / higher-order modes, achieving the effect of prioritizing the gain of the target mode while suppressing higher-order modes. Furthermore, this invention does not require additional microstructures, reducing the difficulty of fabrication and control, and enabling mass production.

[0007] In one optional implementation, a target Bragg grating is set according to the feedback region and loss region arranged along the second direction, which are divided according to the region where the original Bragg grating is located; the target Bragg gratings in the feedback region and the loss region have the same length along the first direction; along the second direction, the normalized light field intensity of the target feedback lateral mode is subtracted from the normalized light field intensity of the target loss lateral mode to obtain the distribution of intensity difference, the region with intensity difference greater than zero is the feedback region, and the region with intensity difference less than zero is the loss region; the first direction and the second direction intersect.

[0008] In one alternative implementation, a target Bragg grating is provided in all or part of the feedback region, while no target Bragg grating is provided in the loss region.

[0009] In one alternative implementation, the target feedback lateral mode is the fundamental mode, the target Bragg grating is a single-column grating, the single-column grating is centered and aligned with the current injection region along the second direction, and the lateral width of the single-column grating is 25% to 75% of the width of the current injection region.

[0010] The structure of a distributed grating laser can increase the difference in the feedback capability of the DBR to low / high-order modes by specially defining the grating DBR pattern (narrowing from a single block along the side), thereby achieving the effect of suppressing high-order modes and narrowing the spectral width.

[0011] In one optional implementation, the target feedback lateral mode includes a fundamental mode and a first-order mode, and the target Bragg grating consists of two first Bragg gratings symmetrically arranged along the center line of the second direction. The lateral width of the first Bragg grating is 15% to 45% of the width of the current injection region, and the spacing between the two first Bragg gratings is 10% to 30% of the width of the current injection region.

[0012] In one alternative embodiment, the number of target Bragg gratings is multiple columns, the multiple columns of target Bragg gratings are spaced apart along a second direction, the current injection region includes a first side and a second side arranged opposite to each other along the second direction, the target Bragg grating closest to the first side in the multiple columns of target Bragg gratings is spaced apart from the extension line of the first side, and the target Bragg grating closest to the second side in the multiple columns of target Bragg gratings is spaced apart from the extension line of the second side.

[0013] The structure of a distributed grating laser can increase the difference in the feedback capability of the DBR to low- and high-order modes by specially defining the grating DBR pattern (changing it from a single block to multiple columns), thereby achieving the effect of suppressing high-order modes and narrowing the spectral width.

[0014] In one optional implementation, a target Bragg grating is provided in both the feedback region and the loss region. The duty cycle of the target Bragg grating in the feedback region is different from that in the loss region, so that the target Bragg grating in the feedback region produces a higher reflectivity for the target feedback lateral mode than the target loss mode, and the target Bragg grating in the loss region produces a higher loss for the target loss lateral mode than the target feedback lateral mode.

[0015] The distributed grating laser structure can increase the loss of higher-order modes by defining the duty cycle of the surface gratings in different regions of the DBR, thereby suppressing higher-order modes and narrowing the spectral width.

[0016] In one alternative implementation, a target Bragg grating is provided in both the feedback region and the loss region. The target Bragg grating in the loss region is filled with an absorbing material that has the ability to absorb laser light in the operating wavelength band of the distributed grating laser structure.

[0017] Distributed grating laser structures can increase the loss of higher-order modes by filling the grating slots in specific regions of the DBR with absorbing materials (while filling non-specific regions with insulating materials), thereby suppressing higher-order modes and narrowing the spectral width.

[0018] In one optional embodiment, the epitaxial layer structure includes a front cavity surface and a rear cavity surface disposed opposite to each other along a first direction. Both the front cavity surface and the rear cavity surface are coated with an antireflection film. The reflectivity of the antireflection film on the front cavity surface is less than 15%, and the reflectivity of the antireflection film on the rear cavity surface is less than 2%. 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 of the original distributed grating laser structure; Figure 2 This is a schematic diagram of the field intensity distribution from the fundamental mode to the third order according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the field strength distribution of the fourth to seventh order according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the field strength distribution of the eighth to eleventh order according to an embodiment of the present invention; Figure 5This is a schematic diagram of the field strength distribution of the twelfth to fourteenth orders according to an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the variation of the reflectivity of a Bragg grating with the lateral width of the Bragg grating according to an embodiment of the present invention; Figure 7 This is a top view of a portion of the first distributed grating laser structure according to an embodiment of the present invention. Figure 8 This is a top view of a portion of a second distributed grating laser structure according to an embodiment of the present invention. Figure 9 This is a top view of a portion of the third distributed grating laser structure according to an embodiment of the present invention; Figure 10 This is a top view of a portion of the fourth distributed grating laser structure according to an embodiment of the present invention. Figure 11 This is a schematic diagram of the reflection spectrum of a dual-row target Bragg grating for each lateral mode according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the reflection spectrum of each lateral mode of a three-column target Bragg grating according to an embodiment of the present invention; Figure 13 This is a schematic diagram of the reflection spectrum of each lateral mode of a four-column target Bragg grating according to an embodiment of the present invention; Figure 14 This is a schematic diagram of the first composite field strength distribution composed of the fundamental mode and the first-order mode according to an embodiment of the present invention; Figure 15 This is a schematic diagram of the second composite field strength distribution composed of second-order and higher lateral modes according to an embodiment of the present invention; Figure 16 This is a schematic diagram of the numerical difference between the first composite field strength and the second composite field strength and the grating distribution according to an embodiment of the present invention; Figure 17 This is a schematic diagram of the feedback and loss characteristics of a second-order target Bragg grating according to an embodiment of the present invention; Figure 18 This is a schematic diagram of the feedback and loss characteristics of a third-order target Bragg grating according to an embodiment of the present invention; Figure 19 This is a top view schematic diagram of a portion of the fifth distributed grating laser structure according to an embodiment of the present invention; Figure 20 This is a schematic diagram of the structure of a target Bragg grating according to an embodiment of the present invention; Figure 21 This is a top view of a portion of the sixth distributed grating laser structure according to an embodiment of the present invention.

[0021] Reference numerals: 100, epitaxial layer structure; 110, current injection region; 120, original Bragg grating; 121, feedback region; 122, loss region; 123, protrusion structure; 130, front cavity surface; 140, rear cavity surface; 150, target Bragg grating; 210, first antireflection coating; 220, second antireflection coating; 230, absorbing 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] This invention provides a distributed grating laser structure, which can be a DBR laser or the like. This invention uses a DBR laser as an example to provide a detailed description of the distributed grating laser structure.

[0025] A DBR laser is a semiconductor laser that forms a resonant cavity based on a periodic grating structure. By integrating periodic refractive index modulation regions (i.e., Bragg grating regions) at one or both ends of the laser diode, a highly reflective mirror is formed, thereby enabling the selection of the oscillation mode within the laser cavity. It can provide a very narrow linewidth and highly stable single-longitudinal-mode output.

[0026] The operation of a DBR laser includes exciting the gain medium, spontaneous emission, stimulated emission, feedback and selection, and laser output. First, an external power supply provides energy to the gain medium, exciting it. In this excited state, atoms or molecules within the gain medium can transition to higher energy levels. These excited atoms or molecules then spontaneously release photons, generating spontaneous emission. These spontaneously emitted photons are reflected back and forth within the laser cavity (resonant cavity). When these spontaneously emitted photons collide with other excited atoms or molecules, stimulated emission is triggered, producing more photons of the same wavelength, thus achieving light gain. Due to the presence of the DBR grating, only light of a specific wavelength can form effective feedback within the resonant cavity; other wavelengths are attenuated. After multiple reflections, the intensity of the specific wavelength continuously increases, eventually forming a stable laser output. When the light intensity within the resonant cavity reaches a certain level, some of the light is emitted through the cavity's output mirror, forming a laser beam.

[0027] Wide-strip structures are an effective solution for increasing the power of semiconductor lasers. However, for wide-strip DBR lasers, the significant increase in lateral modes with increasing stripe width leads to spectral broadening, which affects the laser's applications to varying degrees. To suppress higher-order modes, the following solutions are mainly employed: The first approach is to set gratings parallel to the ridge strips on both sides of the ridge. Compared with the fundamental mode, higher-order modes have greater leakage loss and are thus suppressed. The second approach is to etch many micro-holes on the ridge. The micro-holes are specially designed at the peaks of the optical field distribution of higher-order side modes, so that the higher-order side modes have lower gain and very high loss compared with the fundamental mode, thus achieving the purpose of suppressing higher-order modes. The third approach is to set a grating layer in the epitaxial structure. The grating layer consists of multiple sets of gratings arranged longitudinally. Each set of gratings has a different period, but the grating strips are all longitudinal. This design achieves the effect of suppressing higher-order modes by increasing the transmission loss of higher-order side modes. The fourth approach is to etch microstructures on the sidewalls of the MESA (channel / etched groove) and in the non-injection area outside the MESA to increase the optical loss of higher-order modes. The fifth approach is to create a raised structure on each side of the ridge of the semiconductor laser. This increases the actual refractive index of the waveguide beneath the raised structure, guiding higher-order modes propagating there to the waveguide layers on both sides and causing them to be lost, which is beneficial for the fundamental mode. The sixth approach is to etch channels or arrowhead structure arrays near the sides of the ridge, enabling the modulation of higher-order modes. The seventh approach is to fabricate narrow ridge structures on both sides of the ridge waveguide, etching and filling spaced-apart voids within these structures; this structure can dissipate higher-order modes. The eighth approach is to create multiple strip-shaped ion implantation regions along the longitudinal direction of the ridge, forming a laterally chirped electro-injection modulated ridge waveguide structure, making the loss of higher-order modes greater than that of the fundamental mode, thus suppressing higher-order modes.

[0028] The above solutions all require the addition of additional microstructures, which are complex. The additional microstructures require high precision in photolithography, and the manufacturing and control of the process are difficult, making mass production challenging.

[0029] In view of this, the present invention provides a distributed grating laser structure. By changing the Bragg grating contained in the distributed grating laser structure itself, the laser spectral width is reduced without the need for additional microstructures, which can reduce the difficulty of manufacturing and control and achieve mass production.

[0030] To facilitate understanding of this invention, the basic structure of the original distributed grating laser structure will first be described.

[0031] like Figure 1 As shown, the distributed grating laser structure includes an epitaxial layer structure 100, on which a current injection region 110 and a rudimentary Bragg grating 120 are disposed. The current injection region 110 and the rudimentary Bragg grating 120 are arranged adjacent to each other along a first direction X, which is the light emission direction of the distributed grating laser structure. The width (lateral width) of the rudimentary Bragg grating 120 in a second direction Y is flush with the width of the current injection region 110 in the second direction Y (see [reference]). Figure 1 The first direction X intersects with the second direction Y. Figure 1 Taking the first direction X and the second direction Y as an example, but not limited to this.

[0032] The epitaxial layer structure 100 also includes a front cavity surface 130 and a rear cavity surface 140 arranged opposite to each other along the first direction X. The front cavity surface 130 is coated with an antireflection film with a certain reflectivity (denoted as the first antireflection film 210) and is the side with laser output. The rear cavity surface 140 is also coated with an antireflection film (denoted as the second antireflection film 220). The reflectivity of the first antireflection film 210 is less than 15%, and the reflectivity of the second antireflection film 220 is less than 2%.

[0033] The original Bragg grating 120 is positioned close to the rear cavity surface 140 and can serve as the rear reflector of the resonant cavity of the distributed grating laser structure. The direction from the rear cavity surface to the front cavity surface is the light output direction of the distributed grating laser structure (i.e., the first direction X). In the direction from the front cavity surface to the rear cavity surface, there are, in sequence, the current injection region 110 and the Bragg grating region (the region where the original Bragg grating 120 is located).

[0034] The epitaxial layer structure 100 includes a multilayer epitaxial structure of the laser. It should be understood that the distributed grating laser structure may also include other structures of the DBR laser, such as a substrate, a confinement layer, an active layer, and an ohmic contact layer. Since other structures do not involve the improvement points of this invention, they will not be described here.

[0035] To reduce the difficulty of manufacturing and control, and to achieve mass production, this invention adjusts the original Bragg grating to a target Bragg grating, meaning the target Bragg grating is different from the original Bragg grating, so that the first reflectivity is greater than the second reflectivity. Specifically, the first reflectivity is the reflectivity of the target Bragg grating for the target feedback lateral mode, and the second reflectivity is the reflectivity of the target Bragg grating for the target loss lateral mode.

[0036] The distributed grating laser structure generates multiple lateral modes. The target feedback lateral mode is at least one of these multiple lateral modes, and the target loss lateral mode is at least one of these multiple lateral modes other than the target feedback lateral mode. The target feedback lateral mode can be a low-order mode (such as the fundamental mode, first-order mode, and / or second-order mode) generated by the distributed grating laser structure, and the target loss lateral mode can be a high-order mode (a mode with a higher order than the low-order mode, such as the third-order mode, fourth-order mode, etc.) generated by the distributed grating laser structure.

[0037] Wide-strip DBR lasers operate in multi-mode (side-mode) mode at high power output. Different side-modes have different optical field distributions, giving each mode a specific effective refractive index. According to Bragg's law, each side-mode corresponds to a single Bragg wavelength. As the mode order increases, the effective refractive index of the side-mode decreases, and the corresponding Bragg wavelength gradually decreases. The lasing of different side-modes leads to spectral broadening of the laser.

[0038] The following explains how to modify the structure of the original Bragg grating to make the first reflectivity greater than the second reflectivity.

[0039] Specifically, the lateral width of the gain region was set to 20 μm for optical field calculations in multiple modes. Figures 2 to 5 The light field intensity distribution along the lateral width of the low-order and high-order modes is shown. Figures 2 to 5 The horizontal axis represents the lateral width of the Bragg grating, in μm, with the center of the lateral width as the origin. The vertical axis represents the normalized light field intensity, describing the intensity distribution of the light field in the second direction. Figures 2 to 5 It can be seen that the optical field of low-order modes (such as fundamental mode, first-order mode, and second-order mode) is mainly concentrated in the middle of the waveguide, while as the mode order increases, the optical field gradually disperses laterally, and the distribution of the peak values ​​of each optical field tends to be uniform.

[0040] See Figure 6 For different lateral modes, the reflectivity of the Bragg grating varies with the lateral width of the Bragg grating. Figure 6 Simulations were performed with a lateral width of 20 μm for the Bragg grating. The two sides of the grating gradually move towards the center, meaning the lateral width of the grating gradually decreases. As the lateral width of the grating decreases, the reflectivity of different modes of the grating decreases to varying degrees.

[0041] The present invention has found that the reflectivity of higher-order modes decreases faster than that of lower-order modes. This is because the light field distribution of the former is more divergent in the lateral direction (the light field is stronger near the sides), making its grating confinement factor more susceptible to the influence of lateral dimensions.

[0042] Based on the characteristic that the reflectivity of higher-order modes decreases faster than that of lower-order modes, this invention divides the Bragg grating into regions. By setting regions with different functions (such as optical feedback, optical absorption, and optical scattering), it is possible to maintain or enhance lower-order modes and cause loss or suppression of higher-order modes, thereby reducing higher-order modes and narrowing the spectral width.

[0043] For example, based on the feedback region and loss region arranged along the second direction, which are divided according to the area where the original Bragg grating is located, the original Bragg grating is adjusted to obtain the target Bragg grating. The target Bragg gratings in the feedback region and loss region have the same length along the first direction; along the second direction, the width of the feedback region and the loss region is determined based on the difference in light field intensity distribution between the target feedback lateral mode and the target loss lateral mode. The target feedback lateral mode has a larger field strength (light field intensity greater than the preset intensity) in the feedback region, and the target loss lateral mode has a larger field strength (light field intensity greater than the preset intensity) in the loss region.

[0044] Specifically, along the second direction, the normalized light field intensity of the target feedback lateral mode is subtracted from the normalized light field intensity of the target loss lateral mode to obtain the distribution of intensity difference. The region with an intensity difference greater than zero is the feedback region, and the region with an intensity difference less than zero is the loss region.

[0045] The first type of optional implementation method: dividing the grating into regional blocks, such as... Figures 7 to 10 As shown, a target Bragg grating 150 is set in all and part of the feedback region, while no target Bragg grating is set in the loss region.

[0046] In some embodiments, the target feedback lateral mode is the fundamental mode, and the target loss lateral mode is a first-order or higher lateral mode, such as... Figure 7 As shown, the target Bragg grating 150 is a single-row grating. The lateral width d1 of the single-row grating is smaller than the lateral width d2 of the current injection region 110. The single-row grating and the current injection region 110 are centered and aligned along the second direction.

[0047] The lateral width of a single-row grating is 25% to 75% of the width of the current injection region, i.e., d1 = [25% × d2, 75% × d2]. For example, the lateral width d1 of a single-row grating can be 25% × d2, 50% × d2, or 75% × d2, etc. In this embodiment, the lateral width of the single-row grating is limited to within 25% to 75% of the width of the current injection region, which can further increase the difference in the grating's feedback capability to low-order / high-order modes, achieving the effect of prioritizing the gain of the target mode while suppressing high-order modes.

[0048] The current injection region 110 includes a first side and a second side arranged opposite to each other along the second direction Y. The interval region A1 between the single-column grating and the extension line of the first side (first extension line 111) and the interval region A2 between the single-column grating and the extension line of the second side (second extension line 112) are loss regions, and the area occupied by the target Bragg grating 150 is the feedback region.

[0049] In other words, based on the original device structure, the sides of the original Bragg grating are contracted towards the center, reducing the lateral width of the original Bragg grating 120 to obtain the target Bragg grating. This increases the difference in the grating's feedback capability to low-order / high-order modes, achieving the effect of prioritizing the gain of the target mode while suppressing higher-order modes. It should be noted that the length of the Bragg grating in the first direction remains unchanged; that is, the length of the original Bragg grating in the first direction is the same as the length of the target Bragg grating in the first direction.

[0050] In other embodiments, such as Figure 8 , Figure 9 and Figure 10 As shown, the original single-column Bragg grating is adjusted to a multi-column Bragg grating, that is, the target Bragg grating 150 is multi-column. The multi-column target Bragg grating 150 is spaced apart along the second direction Y. The target Bragg grating closest to the first side in the multi-column target Bragg grating has a gap with the first extension line 111, and the target Bragg grating closest to the second side in the multi-column target Bragg grating has a gap with the second extension line 112.

[0051] Figure 8 Taking a distributed grating laser structure comprising two rows of Bragg gratings as an example, Figure 9 Taking a distributed grating laser structure comprising three rows of Bragg gratings as an example, Figure 10 Taking a distributed grating laser structure comprising four Bragg gratings as an example, the reflection spectrum of a double-column Bragg grating for each lateral mode is as follows: Figure 11 As shown, the reflection spectra of the three Bragg gratings for each lateral mode are as follows: Figure 12 As shown, the reflection spectra of the four Bragg gratings for each lateral mode are as follows: Figure 13 As shown, from Figure 11It can be seen that the reflectivity of the bi-row Bragg grating for the fundamental and first-order modes is greater than that for second-order and higher lateral modes. The bi-row grating is designed to preferentially feed back the fundamental and first-order modes. Figure 12 It can be seen that the three-column grating is designed to provide feedback for the fundamental mode, first-order mode, and second-order mode. Figure 13 As can be seen, the four-column grating is designed to provide feedback for the fundamental mode, first-order mode, second-order mode, and third-order mode. The lateral widths of the multiple target Bragg gratings can be the same or different.

[0052] After determining the target feedback lateral mode and the target loss lateral mode, the number of target Bragg gratings and the lateral width of each column of target Bragg gratings are determined based on the light field intensity distribution (field strength distribution) of the lateral modes. Specifically, the field strength distribution of the target feedback lateral mode and the target loss lateral mode are jointly determined. Target Bragg gratings are placed in areas with a large field strength in the target feedback lateral mode, while gratings are removed in areas with a large field strength in the target loss lateral mode. This achieves strong feedback from the gratings to the target feedback lateral mode and weak or no feedback to the target loss lateral mode, thereby selecting the target feedback lateral mode (lower-order mode) and suppressing the target loss lateral mode (higher-order mode).

[0053] It should be understood that in a laser resonant cavity, modes that receive feedback (reflection) will gain (amplification) and have a greater competitive advantage, while modes with weak feedback or no feedback will be suppressed due to insufficient gain and lose their competitive ability.

[0054] Taking the target feedback lateral mode as the fundamental mode and first-order mode as an example, strong feedback (reflection) is required for the fundamental mode and first-order mode, while weak or no feedback is required for the second-order and higher lateral modes. During the design process, the first composite field strength distribution formed by the fundamental mode and first-order mode is obtained (see...). Figure 14 ) and the second composite field strength distribution consisting of second-order and higher lateral modes (see Figure 15 Then, based on the difference between the first and second composite field intensity distributions, the difference between the normalized target feedback lateral mode and the target loss mode light field intensity distributions is processed (the former minus the latter) to determine the feedback region with a larger field intensity in the target feedback lateral mode, such as... Figure 16 The difference intensity distribution. By setting gratings in certain locations along the second direction in regions where the light field intensity is greater than zero, a DBR design for the target feedback side modes (fundamental mode and first-order mode) can be obtained.

[0055] The number of feedback regions corresponds to the number of rows of the target Bragg grating, the location of the feedback regions corresponds to the placement position of the target Bragg grating, and the width of the feedback regions corresponds to the lateral width of the target Bragg grating. The final grating distribution can be as follows: Figure 8 As shown, Figure 8 The spacing of the target Bragg gratings shown represents the loss region with high field strength in the target loss lateral mode. The same method can be used to obtain DBR designs for other target feedback lateral modes.

[0056] In other words, if the target feedback lateral mode includes both the fundamental mode and the first-order mode, then as follows: Figure 8 As shown, the target Bragg grating 150 includes two first Bragg gratings 151 symmetrically arranged along the center line O of the second direction Y.

[0057] For example, the lateral width d3 of the first Bragg grating is 15% to 45% of the current injection region width d2, and the interval d4 between the two first Bragg gratings is 10% to 30% of the current injection region width d2. That is, d3 = [15% × d2, 45% × d2], d4 = [10% × d2, 30% × d2]. For example, the lateral width d3 of the first Bragg grating can be 15% × d2, 20% × d2, 36% × d2, or 45% × d2, etc.; the interval d4 between the two first Bragg gratings can be 10% × d2, 20% × d2, or 30% × d2, etc.

[0058] The second optional implementation method is: regional definition of grating feedback capability, wherein a target Bragg grating 150 is provided in both the feedback region 121 and the loss region 122.

[0059] Specifically, the feedback characteristics of a Bragg grating are determined by structural parameters such as duty cycle, depth, groove bottom width, and filling material. Figure 17 The feedback and loss characteristics of a second-order surface Bragg grating are shown. Figure 18 The feedback and loss characteristics of a third-order surface Bragg grating are shown. From Figure 17 and Figure 18 It can be seen that surface gratings can achieve high reflectivity and low loss at high duty cycles (e.g., above 0.8), a characteristic that can be used for the design and optimization of distributed grating laser structures. Second-order and third-order surface Bragg gratings are defined according to the Bragg diffraction order (m). When m=2, the grating is a second-order grating; when m=3, the grating is a third-order grating. Here, DC represents the duty cycle of the surface Bragg grating, L represents the loss, and R represents the reflectivity.

[0060] like Figure 17As shown, when the duty cycle of a second-order surface grating is around 0.35, the grating's feedback capability is significantly weakened, while its loss capability is significantly enhanced. When the duty cycle is around 0.85, the grating's feedback capability is relatively high, while its loss capability is relatively weak. Based on this characteristic, setting the grating near the center of the DBR along the side to a high duty cycle (e.g., 0.85) and setting the grating near the edge of the DBR to a low duty cycle (e.g., 0.35) is beneficial for enhancing the loss of higher-order modes. Similarly, using a third-order surface grating to regionally set the duty cycle of the DBR grating can achieve the same effect.

[0061] In other words, when a target Bragg grating is set in both the feedback region and the loss region, the duty cycle of the target Bragg grating located in the feedback region 121 can be different from that of the target Bragg grating located in the loss region 122, so that the target Bragg grating located in the feedback region produces a higher reflectivity for the target feedback lateral mode than the target loss mode, and the target Bragg grating located in the loss region produces a higher loss for the target loss lateral mode than the target feedback lateral mode.

[0062] For example, such as Figure 19 As shown, the duty cycle of the target Bragg grating located in the feedback region 121 is greater than that of the target Bragg grating located in the loss region 122.

[0063] Specifically, such as Figure 20 As shown, the Bragg grating (original Bragg grating and target Bragg grating) consists of a plurality of protrusions 123 spaced apart along a first direction, and the duty cycle DC of the Bragg grating is... a / ( a+b ),in, a This indicates the width of the protruding structure in the first direction. b It represents the interval between any two adjacent protrusions.

[0064] Based on DC= a / ( a+b This formula can be adjusted. a or b Change the duty cycle of the Bragg grating, for example, in a Without changing, by reducing b Increase the duty cycle, by increasing b Reduce the duty cycle.

[0065] In some optional embodiments, both the feedback region 121 and the loss region 122 are provided with target Bragg gratings, such as... Figure 21As shown, the target Bragg grating 150 located in the loss region 122 is filled with an absorbing material 230. The absorbing material is a material that has the ability to absorb lasers in the working band of the distributed grating laser structure. The absorbing material can be germanium (Ge) or silicon nitride (SiN), etc. The absorbing material fills the grating grooves (the intervals between each protrusion structure 123).

[0066] Optionally, to avoid the influence of air, water vapor, impurities, etc. on the function of the Bragg grating, insulating materials such as silicon oxide (SiO) and aluminum oxide (AlO) are used to fill the target Bragg grating 150 located in the feedback region 121, and the insulating material fills the grating groove.

[0067] Distributed grating laser structures can increase the difference in the feedback capability of the DBR for low / high-order modes by specially defining the grating DBR pattern (by narrowing it laterally from a single block or changing it to multiple columns), thereby suppressing high-order modes and narrowing the spectral width. Distributed grating laser structures can also increase the loss of high-order modes by defining the duty cycle of the surface gratings in different regions of the DBR, thus suppressing high-order modes and narrowing the spectral width. Furthermore, distributed grating laser structures can also increase the loss of high-order modes by filling the grating slots in specific regions of the DBR with absorbing materials (while using insulating materials to fill non-specific regions), thereby suppressing high-order modes and narrowing the spectral width.

[0068] Moreover, the distributed grating laser structure does not introduce additional microstructures in the process of suppressing higher-order modes. It has a simple structure, low manufacturing difficulty, and can be mass-produced.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 distributed grating laser structure, characterized in that, Including epitaxial layer structures; The epitaxial layer structure is provided with a current injection region and a target Bragg grating; the current injection region and the target Bragg grating are arranged adjacent to each other along a first direction, which is the light output direction of the distributed grating laser structure. The target Bragg grating is different from the original Bragg grating so that the first reflectivity is greater than the second reflectivity. The first reflectivity is the reflectivity of the target Bragg grating to the target feedback lateral mode, and the second reflectivity is the reflectivity of the target Bragg grating to the target loss lateral mode. The target Bragg grating is set according to the feedback region and loss region arranged along the second direction, which are divided according to the region where the original Bragg grating is located; The target Bragg gratings in the feedback region and the loss region have the same length along the first direction; along the second direction, the normalized light field intensity of the target feedback lateral mode is subtracted from the normalized light field intensity of the target loss lateral mode to obtain the distribution of intensity difference values. The region with an intensity difference greater than zero is the feedback region, and the region with an intensity difference less than zero is the loss region. The first direction and the second direction intersect.

2. The distributed grating laser structure according to claim 1, characterized in that, The target Bragg grating is set in all or part of the feedback region, while the target Bragg grating is not set in the loss region.

3. The distributed grating laser structure according to claim 2, characterized in that, The target feedback lateral mode is the fundamental mode, the target Bragg grating is a single-column grating, the single-column grating and the current injection region are centered and aligned in the laser chip along the second direction, and the lateral width of the single-column grating is 25% to 75% of the width of the current injection region.

4. The distributed grating laser structure according to claim 2, characterized in that, The target feedback lateral mode is a fundamental mode and a first-order mode. The target Bragg grating includes two first Bragg gratings symmetrically arranged along the center line of the second direction. The lateral width of the first Bragg grating is 15% to 45% of the width of the current injection region, and the spacing between the two first Bragg gratings is 10% to 30% of the width of the current injection region.

5. The distributed grating laser structure according to claim 2, characterized in that, The target Bragg grating is in multiple columns, and the multiple columns of target Bragg gratings are spaced apart along the second direction. The current injection region includes a first side and a second side that are arranged opposite to each other along the second direction. The target Bragg grating closest to the first side in the multiple columns of target Bragg gratings is spaced apart from the extension line of the first side. The target Bragg grating closest to the second side in the multiple columns of target Bragg gratings is also spaced apart from the extension line of the second side.

6. The distributed grating laser structure according to claim 1, characterized in that, Both the feedback region and the loss region are provided with the target Bragg grating. The duty cycle of the target Bragg grating in the feedback region is different from that in the loss region, so that the target Bragg grating in the feedback region produces a higher reflectivity for the target feedback lateral mode than the target loss mode, and the target Bragg grating in the loss region produces a higher loss for the target loss lateral mode than the target feedback lateral mode.

7. The distributed grating laser structure according to claim 1, characterized in that, Both the feedback region and the loss region are provided with the target Bragg grating. The target Bragg grating located in the loss region is filled with an absorbing material, which is a material that has the ability to absorb laser light in the operating wavelength band of the distributed grating laser structure.

8. The distributed grating laser structure according to claim 1, characterized in that, The epitaxial layer structure includes a front cavity surface and a rear cavity surface disposed opposite to each other along the first direction. Both the front cavity surface and the rear cavity surface are coated with an antireflection film. The reflectivity of the antireflection film on the front cavity surface is less than 15%, and the reflectivity of the antireflection film on the rear cavity surface is less than 2%.

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