Laser and laser system

Abstract

The invention provides a laser and a laser system, and relates to the technical field of photoelectricity, and the laser comprises an active layer and a grating layer. Wherein the grating layer is arranged on the active layer. The grating layer comprises a plurality of gratings which are arranged at intervals in the first direction. The plurality of gratings are divided into a first part and two second parts, the two second parts are respectively arranged at the two sides of the first part along the first direction, and the size of the gratings in the second parts in the second direction is smaller than the size of the gratings in the first part in the second direction. The first direction and the second direction are parallel to the active layer and are perpendicular to each other. The size of the grating in the second part in the second direction is smaller than the size of the grating in the first part in the second direction, so that the two second parts can be equivalent to two convex lenses, that is, an unstable cavity can be simulated, the unstable cavity can be used for inhibiting a first-order transverse mode, and the maximum useful power of the laser is further improved.

Description

Technical Field

[0001] This application relates to the field of optoelectronic technology, and more particularly to a laser and a laser system. Background Technology

[0002] In related technologies, increasing the width of the active region or ridge waveguide is commonly used to improve the optical output power of lasers, such as in distributed feedback (DFB) lasers. However, increasing the width of the ridge waveguide introduces higher-order transverse modes, mainly the first-order transverse mode (TE1). When the width of the ridge waveguide exceeds a certain critical value, the limitation factor and threshold gain of the first-order transverse mode (TE1) will approach or fall below the fundamental transverse mode (TE0), causing the first-order transverse mode to start oscillating, leading to mode competition. This results in unstable laser output, deterioration of beam quality, and "knotting" in the photocurrent (LI) curve, severely limiting the maximum useful power of the laser. Summary of the Invention

[0003] This application proposes a laser and a laser system that aims to make the size of the grating in the second part in the second direction smaller than the size of the grating in the first part in the second direction, so that the two second parts can be equivalent to two "convex lenses", that is, to simulate an unstable cavity. This unstable cavity can be used to suppress the first-order transverse mode, thereby improving the maximum useful power of the laser.

[0004] In a first aspect, this application provides a laser comprising an active layer and a grating layer. The grating layer is disposed on the active layer. The grating layer includes a plurality of gratings, which are spaced apart along a first direction. The plurality of gratings are divided into a first portion and two second portions, which are disposed on opposite sides of the first portion along the first direction. The size of the gratings in the second portions along the second direction is smaller than the size of the gratings in the first portion along the second direction. Both the first and second directions are parallel to the active layer and perpendicular to each other.

[0005] In this embodiment, by making the size of the grating in the second part smaller than the size of the grating in the first part in the second direction, that is, along the second direction, the end of the grating in the second part can be separated from the end of the grating in the first part. This allows the two second parts, which are set on both sides of the first part, to be equivalent to two "convex lenses". The two "convex lenses" can work together to form an unstable cavity, that is, to simulate an unstable cavity. This unstable cavity can then be used to increase the diffraction loss of higher-order transverse modes (e.g., first-order transverse modes) and achieve suppression of higher-order transverse modes.

[0006] Furthermore, the grating in the second part (i.e., the grating region within each "convex lens") and the end regions of the grating in the first part can form an incomplete resonant cavity, or even none at all. This means that light entering this region can only resonate in a small area or cannot resonate at all, resulting in limited or no enhancement of the intensity of the reflected wave. Consequently, the reflectivity of the two end regions of the grating layer decreases, weakening the coupling ability of the first-order transverse mode of the reflected beam, thus further suppressing the first-order transverse mode. Simultaneously, the middle region can form a complete resonant cavity, allowing light entering this region to undergo constructive interference enhancement when the Bragg condition is satisfied, thereby enhancing the intensity of the reflected wave and ensuring the coupling ability of the intermediate fundamental mode of the reflected beam.

[0007] In this way, the grating layer can effectively suppress the first-order transverse mode, thereby improving the single-mode output purity of the laser and thus increasing the maximum useful power of the laser.

[0008] In some embodiments, the grating layer includes a plurality of grating groups. The plurality of grating groups are spaced apart along a first direction, and each grating group includes a plurality of gratings.

[0009] In some embodiments, the number of gratings in the two second portions is equal.

[0010] In some embodiments, a plurality of gratings are arranged symmetrically about the center line of the plurality of gratings extending along the second direction as an axis of symmetry.

[0011] In some embodiments, the two ends of a plurality of gratings arranged along a first direction point to the center of the region where the plurality of gratings are located, and the size of the gratings gradually increases in a second direction.

[0012] In some embodiments, the pattern of the orthographic projection of the plurality of gratings onto the active layer is elliptical, prismatic, quasi-elliptical, or quasi-prismatic, and the two diameters or the two diagonals extend along the first direction and the second direction, respectively.

[0013] In some embodiments, the laser further includes a ridge waveguide. The ridge waveguide is disposed on the side of the grating layer away from the active layer, extends along a first direction, and its orthographic projection onto the active layer overlaps with the orthographic projections of the plurality of gratings onto the active layer. The gratings in the second portion have a smaller dimension in the second direction than the ridge waveguide in the second direction.

[0014] In some embodiments, the ridge waveguide includes a central portion and two edge portions disposed on either side of the central portion along a second direction. The distribution intensity of the fundamental mode in the central portion is greater than that in the two edge portions. The dimension of the grating in the second portion in the second direction is greater than or equal to the dimension of the central portion in the second direction, and the distance between the ends of the grating in the first portion and the ends of the grating in the second portion in the second direction is less than or equal to the dimension of the edge portions in the second direction.

[0015] In some embodiments, each grating is symmetrically arranged about the center line of the plurality of gratings extending along a first direction as an axis of symmetry.

[0016] In some embodiments, among a plurality of gratings, the ends of any two adjacent gratings located on the same side are spaced equally in a second direction.

[0017] In a second aspect, this application provides a laser system comprising a laser and an optical transmission system as described in any of the foregoing embodiments. The optical transmission system is coupled to the laser.

[0018] The technical effects of the aforementioned laser system can be found in the section on the technical effects of lasers in the first aspect, and will not be repeated here. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in some embodiments of this application will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not actual dimensions of the products or actual processes of the methods involved in the embodiments of this application.

[0020] Figure 1 This is a schematic diagram of the structure of a laser provided in an embodiment of this application; Figure 2 for Figure 1 A schematic diagram of the cross-section of the laser along section line C-C'; Figure 3 A top view of a grating layer of a laser provided in an embodiment of this application; Figure 4 A top view of the grating layer of another laser provided in an embodiment of this application; Figure 5 A top view of the grating layer of another laser provided in an embodiment of this application; Figure 6 A top view of the grating layer of another laser provided in an embodiment of this application; Figure 7A top view of the grating layer of another laser provided in an embodiment of this application; Figure 8 A top view of the grating layer of another laser provided in an embodiment of this application; Figure 9 for Figure 1 A schematic diagram of the cross-section of the laser along section line D-D'; Figure 10 The transmission spectrum is simulated using a uniformly sampled grating; Figure 11 For Figure 3 The transmission spectrum of the grating layer in the image was simulated. Figure 12 The reflection spectrum simulated using a uniformly sampled grating; Figure 13 For Figure 3 The reflection spectrum of the grating layer in the image was simulated. Figure 14 A schematic flowchart illustrating a laser fabrication method provided in this application embodiment; Figures 15-19 A schematic diagram of each step of the laser fabrication method provided in the embodiments of this application; Figure 20 This is a schematic diagram of a laser system provided in an embodiment of this application. Detailed Implementation

[0021] The technical solutions in some embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application are within the scope of protection of this application.

[0022] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open and encompassing, that is, "including, but not limited to".

[0023] Hereinafter, 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 indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this application, unless otherwise stated, "a plurality of" means two or more.

[0024] In describing some embodiments, the term "connection" and its derivative expressions may be used. The term "connection" should be interpreted broadly; for example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. For example, in describing some embodiments, the term "connection" may be used to indicate that two or more components have direct physical or electrical contact with each other.

[0025] In addition, the use of “based on” implies openness and inclusivity, because processes, steps, calculations or other actions “based on” one or more of the stated conditions or values ​​may in practice be based on additional conditions or values ​​beyond those stated.

[0026] In related technologies, increasing the width of the active region or ridge waveguide is commonly used to improve the optical output power of lasers, such as DFB lasers. However, increasing the width of the ridge waveguide introduces higher-order transverse modes, mainly the first-order transverse mode (TE1). That is, when the width of the ridge waveguide exceeds a certain critical value, the limitation factor and threshold gain of the first-order transverse mode (TE1) will approach or fall below the fundamental transverse mode (TE0), causing the TE1 mode to start oscillating, resulting in mode competition. This leads to unstable laser output, deterioration of beam quality, and "knotting" of the photocurrent (LI) curve, severely limiting the maximum useful power of the laser.

[0027] To address the aforementioned problems, embodiments of this application provide a laser. The laser 100 provided in this application embodiment can be based on a Bragg grating design.

[0028] A Bragg grating is a periodic structure in the active region (or adjacent to the active region) of a laser 100, whose refractive index or gain varies periodically along the direction of light propagation. It enables distributed feedback and dynamic single-mode lasing. Specifically, when light entering a laser with a Bragg grating is reflected weakly at each grating period instead of only at both ends, these reflected lights, when satisfying the Bragg condition, coherently interact with the incident light wave. This interaction enhances the intensity of the reflected light wave through constructive interference, thus forming strong feedback. Furthermore, due to the excellent frequency selectivity of the Bragg grating—that is, the grating can form a spatial filter through its periodic refractive index variation—it can selectively allow or block light of specific wavelengths, enabling the laser to operate very stably in a single longitudinal mode.

[0029] The above Bragg conditions can be expressed by the formula This indicates that λB is the Bragg wavelength, and n eff The effective refractive index is Λ, the grating period is m, and the diffraction order is m.

[0030] When the aforementioned Bragg grating is a uniform Bragg grating, its grating period Λ and refractive index n can both exhibit periodic variations. When the grating length is L, the refractive index function is: Where n(z) represents the instantaneous refractive index at a certain position along the length of the grating, n0 is the average effective refractive index of the grating, Δn represents the refractive index modulation amount, Λ is the grating period, and z is the position coordinate along the length of the grating, with a value range of [0, L].

[0031] Discontinuous settings of a uniform Bragg grating can form a sampling grating. This means that a uniformly modulated, continuously periodically modulated grating can be periodically "sampled and truncated" along its length, retaining a uniform grating unit of equal length. Blank intervals without refractive index modulation are set between the units, and the resulting discrete periodic structure is the sampling grating.

[0032] The sampling grating described above can be considered a special addressing function, whose reflection spectrum has a multi-peak structure, and the spacing between the reflection peaks is inversely proportional to the sampling period. Furthermore, the shape of each reflection peak depends on the overall apod shape of the grating. The refractive index modulation function of the sampling grating is composed of the superposition of many uniform grating refractive index modulation functions with different periods; correspondingly, the reflection spectrum of the sampling grating can be composed of the superposition of the reflection spectra of a series of uniform gratings. The period of the m-th order refractive index modulation can satisfy the following formula: , Among them, Λ m Λ represents the period of the m-order refractive index modulation, Λ represents the grating period, and P represents the sampling period.

[0033] And it can be determined by the Bragg condition and with the help of the formula. The m-th order center wavelength is derived, where λm represents the m-th order center wavelength, λ0 is the center wavelength of the grating unit, m represents the sampling order, n represents the average refractive index of the grating, Λ represents the grating period, and P represents the sampling period.

[0034] The wavelength spacing of the reflection peaks of the above sampling grating can be , where λ0 is the center wavelength of the grating unit and P represents the sampling period.

[0035] Figure 1 This is a schematic diagram of the structure of a laser provided in an embodiment of this application. Figure 2 for Figure 1 A schematic diagram of the cross-section of the laser along section line C-C'. Figure 3 This is a top view of a grating layer of a laser provided in an embodiment of this application. Figure 4 This is a top view of the grating layer of another laser provided in an embodiment of this application. Figure 5 This is a top view of the grating layer of another laser provided in an embodiment of this application. Figure 6 This is a top view of the grating layer of another laser provided in an embodiment of this application.

[0036] See Figures 1-6 The laser 100 mentioned above includes an active layer 1 and a grating layer 2.

[0037] The active layer 1 is used to generate photons. When current is injected into the laser 100, electrons in the active layer 1 absorb electrical energy to form electrons, while holes remain in the valence band. Subsequently, electrons and holes release energy through a recombination process to generate photons.

[0038] See Figure 1 and Figure 2 The aforementioned grating layer 2 can be disposed on the active layer 1, for example, Figure 1 In this configuration, the upper surface of the active layer 1 is provided so that the active layer 1 and the grating layer 2 are directly coupled, reducing photon loss during transmission. Alternatively, the active layer 1 can be placed in the space above the active layer 1 so that the active layer 1 and the grating layer 2 are spatially separated, allowing the optical feedback mechanism and the injection and distribution of charge carriers to be independently controlled.

[0039] See Figures 1-6 The grating layer 1 may include multiple gratings 21 to enable wavelength selection, feedback and mode control of light.

[0040] The plurality of gratings 21 can be arranged at intervals along the first direction X, for example... Figure 5 In the middle, set at equal intervals along the first direction X, or, Figure 3 In the grating area, multiple gratings 21 are set at equal intervals along the first direction X.

[0041] The first direction X here can be the cavity length extension direction of the laser 100.

[0042] See Figures 3-6 The multiple gratings 21 in the grating layer 2 can be divided into a first part A1 and a second part A2.

[0043] For example, see Figures 3-6 Both the first part A1 and the second part A2 may include at least one grating 21 to enable flexible adjustment of wavelength selection, optical feedback and mode control, so that the laser 100 can meet a variety of application requirements.

[0044] For example, Figure 3 In the diagram, the first part A1 includes 5 gratings 21, and the second part A2 includes 1 grating 21. Figure 4 In the first part A1, there are 3 gratings 21, and in the second part A2, there are 3 gratings 21.

[0045] See Figures 3-6Along the first direction X, the second part A2 can be disposed on both sides of the first part A1, and the size of the grating 21 in the second part A2 in the second direction Y is smaller than the size of the grating 21 in the first part A1 in the second direction Y.

[0046] Here, the second direction Y is parallel to the active layer 1 and perpendicular to the first direction X.

[0047] Thus, along the second direction Y, the ends of the grating 21 in the second part A2 are separated from the ends of the grating 21 in the first part A1 by a distance. This allows the two second parts A2, with their scores located on either side of the first part A1, to be equivalent to two "convex lenses." These two "convex lenses" can work together to form an unstable cavity, simulating an unstable cavity. This unstable cavity can then be used to increase the diffraction loss for higher-order transverse modes (e.g., first-order transverse modes), thereby suppressing higher-order transverse modes. Furthermore, the grating 21 in the second part A2 (i.e., the grating region within each "convex lens") and the intermediate region of the grating 21 in the first part A1 can form a complete resonant cavity (e.g.,...). Figure 3 In the a2 region), while the end region can form an incomplete resonant cavity (e.g. Figure 3 In the a1 region), it is even impossible to form a resonant cavity (e.g., in the middle a1 region). Figure 4 This allows for further suppression of first-order transverse modes.

[0048] For example, see Figure 3 and Figure 4 In the second part A2, the grating 21 can have different dimensions in the second direction Y (e.g., Figure 3 ), or the same (e.g. Figure 4 This application does not impose any restrictions on this.

[0049] For example, when the gratings 21 in the second part A2 have different dimensions in the second direction Y, the ends of two adjacent gratings 21 in the second part A2 can form an incomplete resonant cavity along the first direction X, thereby further reducing the reflectivity of the two end regions of the grating layer 2.

[0050] For example, the grating layer 2 described above can be designed based on a uniform grating or a sampling grating, for example, in Figure 5 or Figure 6 In this process, based on a uniform grating, multiple gratings 21 are etched according to a design pattern to form the grating layer 2 of this application; or, in... Figure 3 and Figure 4 In this process, based on the sampling grating, multiple gratings 21 are etched according to the design pattern to form the grating layer 2 of this application.

[0051] For example, see Figure 2The laser 100 further includes a substrate 4, a buffer layer 5, a lower waveguide layer 6, and an upper waveguide layer 7, for example, Figure 2 In the middle, the buffer layer 5 and the lower waveguide layer 6 are epitaxially grown on the substrate 4 in sequence, and the upper waveguide layer 7 is grown on the active layer 1.

[0052] It is understood that, in the embodiments of this application, by making the size of the grating 21 in the second part A2 in the second direction Y smaller than the size of the grating 21 in the first part A1 in the second direction Y, that is, along the second direction Y, the end of the grating 21 in the second part A2 can be separated from the end of the grating 21 in the first part A1. Thus, the two second parts A2, which are set on both sides of the first part A1, can be equivalent to two "convex lenses". The two "convex lenses" can work together to form an unstable cavity, that is, an unstable cavity can be simulated. In this way, the unstable cavity can be used to increase the diffraction loss of higher-order transverse modes (e.g., first-order transverse modes) and achieve the suppression of higher-order transverse modes.

[0053] Furthermore, the grating 21 in the second part A2 (i.e., the grating region within each "convex lens") and the end region of the grating 21 in the first part A1 can form an incomplete resonant cavity (e.g., Figure 3 In the a1 region), it is even impossible to form a resonant cavity (e.g., in the middle a1 region). Figure 4 This means that light entering this region can only resonate in a small area or cannot resonate at all, resulting in limited or no enhancement of the intensity of the reflected wave. Consequently, the reflectivity of the two ends of the grating layer 2 decreases, weakening the coupling ability of the first-order transverse mode of the reflected beam, thus further suppressing the first-order transverse mode. Simultaneously, the middle region can form a complete resonant cavity (e.g., Figure 3 The a2 region is used to enhance the constructive interference of light entering the region when the Bragg condition is satisfied, thereby enhancing the intensity of the reflected wave and ensuring the coupling capability of the intermediate fundamental mode of the reflected beam.

[0054] In this way, the first-order transverse mode can be effectively suppressed by using the grating layer 2, thereby improving the single-mode output purity of the laser 100 and thus increasing the maximum useful power of the laser 100.

[0055] In some embodiments, see Figures 1-4 The aforementioned grating layer 2 may include multiple grating groups P, and these grating groups P may be spaced apart along the first direction X, for example, Figure 3 In the process, the grating layer 2 may include 4 grating groups P, and these 4 grating groups P are arranged at equal intervals along the first direction X.

[0056] The grating layer 2 of the laser 100 here can be obtained by etching the sampling grating.

[0057] See Figure 3 and Figure 4 Each grating group P can include multiple gratings 21 to achieve multi-wavelength screening and mode modulation of light entering the grating layer 2, and suppress stray mode interference.

[0058] For example, the above-mentioned grating group P may include grating regions and non-grating regions (e.g. Figure 3 (The gray area in the text).

[0059] The grating region is the area in each grating group P where multiple gratings 21 are set, and the non-grating region is the area in the same grating group P where no gratings 21 are set. Furthermore, along the first direction X, the interval between two adjacent grating groups P can be a non-grating region, for example... Figure 3 In the first direction X, from left to right, the interval between the first grating group P and the second grating group P can be the non-grating region of the first grating group P.

[0060] For example, the dimensions of the grating region and the non-grating region in the first direction X can be the same, that is, the duty cycle of forming the grating layer 2 can be 0.5, so as to reduce the fabrication difficulty while ensuring the wavelength selection, optical feedback and mode control of the laser 100.

[0061] For example, see Figure 3 and Figure 4 Each grating 21 in each grating group P can be divided into a part A1 and a second part A2. The size of the grating 21 in the second part A2 in the second direction Y can be smaller than the size of the grating 21 in the first part A1 in the second direction Y.

[0062] In this way, the performance of the laser 100 can be improved by utilizing the characteristics of the sampling grating, such as enabling multi-wavelength output and suppressing higher-order modes, allowing the laser 100 to operate in single-mode or specific transverse modes. Furthermore, by making the size of the grating 21 in the second part A2 in the second direction Y smaller than that of the grating 21 in the first part A1 in the second direction Y, the reflectivity of the two ends of the grating layer 2 can be effectively reduced, thereby effectively suppressing the first-order transverse mode, improving the purity of the single-mode output of the laser 100, and thus increasing the maximum useful power of the laser 100.

[0063] For example, see Figure 5 The grating group P may not include non-grating regions, and the spacing between two adjacent grating groups P along the first direction X is the same as the spacing between two adjacent gratings 21 in each grating group P, that is, the grating layer 2 can be obtained by etching a uniform grating.

[0064] Or, for example, see [link to relevant documentation] Figure 6The aforementioned grating layer 2 may not include grating group P, and multiple gratings 21 may be arranged at the same interval along the first direction X. In this case, the size of the grating 21 in the second part A2 in the second direction Y may also be smaller than the size of the grating in the first part A1 in the second direction Y. This application does not impose any restrictions on this.

[0065] In this way, the grating layer 2 of this application, based on the uniform grating design, can not only simplify the fabrication process and reduce the fabrication difficulty, but also reduce the reflectivity of the two end regions of the grating layer 2 by utilizing the fact that the size of the grating 21 in the second part A2 in the second direction Y is smaller than the size of the grating 21 in the first part A1 in the second direction Y, thereby suppressing the first-order transverse mode and improving the single-mode output purity of the laser 100.

[0066] In some embodiments, see Figures 3-6 The number of gratings 21 in the two second parts A2 can be the same, that is, along the first direction X, the number of gratings 21 in the two second parts A2 respectively set on both sides of the first part A1 can be the same, for example. Figure 3 In the first direction X, the second part A2, which is located on both sides of the first part A1, may each include 5 gratings 21, or... Figure 4 In the middle, both second parts A2 can each include 3 gratings 21.

[0067] For example, see Figures 3-6 The dimensions of the grating 21 in the second part A2 above can be different in the second direction Y (e.g. Figure 3 ), or the same (e.g. Figure 4 This application does not impose any restrictions on this.

[0068] For example, along the first direction X, two second parts A2 are respectively disposed on both sides of the first part A1. The distance between them and the first part A1 may be different, and this application does not limit this.

[0069] In this way, by making the number of gratings 21 in the two second parts A2 equal, when the two second parts A2 are equivalent to two "convex lenses" with the first part A1 as the dividing line, that is, when simulating an unstable cavity, the focal lengths of the two "convex lenses" can be equal to satisfy the confocal condition, so that the diffraction loss of higher-order transverse modes (e.g., the first-order transverse mode) is much higher than that of the fundamental mode, and thus can effectively suppress higher-order transverse modes (e.g., the first-order transverse mode).

[0070] In some embodiments, see Figures 3-6 The multiple gratings 21 in the grating layer 2 can be symmetrically arranged with the center line extending along the second direction Y as the axis of symmetry.

[0071] For example, the centerline extending along the second direction Y of the first portion A1 (e.g.) Figure 3 The center line F in the first part is the axis of symmetry. Along the first direction X, the grating 21 in the first part A1 is symmetrically arranged, and two second parts A2 are symmetrically arranged on both sides of the first part A1.

[0072] The number of gratings 21 in the two second parts A2 here can be equal.

[0073] For example, Figure 3 In the first part A1, when it includes one grating 21, the center line F of the grating 21 is taken as the axis of symmetry. Figure 4 In the first part A1, when it includes three gratings 21, the center line F of the three gratings 21 is taken as the axis of symmetry.

[0074] For example, see Figures 3-6 The two gratings 21 symmetrically arranged in the two second parts A2 may have equal or unequal dimensions in the second direction Y to enrich the structure of the grating layer 2, so that the laser 100 can meet a variety of application requirements. This application does not limit this.

[0075] For example, Figure 3 In the first direction X, the size of the first grating 21 located to the left of the axis of symmetry F in the second direction Y is equal to the size of the first grating 21 located to the right of the axis of symmetry F in the second direction Y.

[0076] In this way, by symmetrically arranging multiple gratings 21 with the center line extending along the second direction Y as the axis of symmetry, when the two second parts A2 are equivalent to two "convex lenses" with the first part A1 as the dividing line, that is, when simulating an unstable cavity, the focal lengths of the two "convex lenses" are made equal to satisfy the confocal condition. This makes the diffraction loss of higher-order transverse modes (e.g., first-order transverse modes) much higher than that of the fundamental mode, thereby effectively suppressing higher-order transverse modes (e.g., first-order transverse modes). Furthermore, symmetrically arranging multiple gratings 21 with the center line extending along the second direction Y as the axis of symmetry can also reduce the fabrication difficulty and thus reduce the fabrication cost.

[0077] Figure 7 This is a top view of the grating layer of another laser provided in an embodiment of this application. Figure 8 This is a top view of the grating layer of another laser provided in an embodiment of this application.

[0078] For example, see Figure 7 and Figure 8The number of gratings 21 in the two second parts A2 may be different, or the number of gratings 21 in one of the second parts A2 may be 0, that is, the multiple gratings 21 are no longer symmetrically arranged with the center line of the multiple gratings 21 extending along the second direction Y as the axis of symmetry. This application does not impose any restrictions on this.

[0079] For example, Figure 7 In the process, each grating group P includes only one second part A2, and along the first direction X, from left to right, the size of each grating 21 gradually increases in the second direction Y.

[0080] In this way, a complete resonant cavity can be formed using the intermediate region between the grating 21 in the second part A2 and the grating 21 in the first part A1 (e.g. Figure 3 The incomplete resonant cavity formed by the end regions of grating 21 in the middle region (a2), the second part A2, and the first part A1, or the inability to form a resonant cavity, thereby reducing the reflectivity of the end regions of the grating layer 2, which can suppress the first-order transverse mode.

[0081] In some embodiments, see Figures 3-6 The two ends of the multiple gratings 21 arranged along the first direction X point towards the center of the region where the multiple gratings 21 are located. The size of the gratings 21 gradually increases in the second direction Y. That is, with the region where the first part A1 is located as the center region, the gratings 21 in the two second parts A2 on both sides of the first part A1 are arranged sequentially at intervals towards the center region (i.e., the first part A1) along the first direction X. And the size of the multiple gratings 21 in each second part A2 gradually increases in the second direction Y.

[0082] For example, Figure 3 In the example of the first grating group P, along the first direction X, the size of the multiple gratings 21 in the second part A2 on the left side gradually increases from left to right in the second direction Y, while the size of the multiple gratings 21 in the second part A2 on the right side gradually increases from right to left in the second direction Y.

[0083] For example, the refractive index modulation amount of the grating 21 in the second part A2 is greater than that of the grating 21 in the first part A1, and the refractive index modulation amount of the grating 21 in the second part A2 gradually decreases along the first direction X, so as to achieve strong feedback of light waves by using the grating 21 with refractive index modulation amount.

[0084] For example, Figure 3In the example of a grating group P, along the first direction X, the outermost grating 21 in the second part A2 has the largest refractive index modulation, that is, the grating 21 farthest from the first part A1 in the second part A2 has the largest refractive index modulation, and along the direction towards the first part A1, the refractive index modulation of grating 21 gradually decreases.

[0085] The aforementioned refractive index modulation amount refers to half the difference between the maximum and minimum refractive index values ​​of grating 21 within the periodic modulation region, which can describe the intensity of grating 21's modulation capability for light waves.

[0086] In this way, the dimensions of the multiple gratings 21 in the two second parts A2 gradually increase in the second direction Y along the direction towards the first part A1 (i.e., the central region). When the two second parts A2 are equivalent to two "convex lenses" with the first part A1 as the boundary, i.e., when simulating an unstable cavity, the radius of curvature of the two "convex lenses" is effectively reduced. This increases the geometric magnification of the grating layer 2, increases the diffraction loss of the grating layer 2 for higher-order transverse modes (e.g., first-order transverse modes), and thus effectively suppresses higher-order transverse modes. Furthermore, the grating 21 located in the "convex lens" has a larger refractive index modulation, which enables strong light feedback, while the grating 21 in the first part A1 has a smaller refractive index modulation and weaker light feedback. This allows for preferential excitation of the fundamental mode and suppression of the first-order transverse mode, thereby improving the single-mode output purity of the laser 100, i.e., improving the quality of the laser beam.

[0087] In some embodiments, see Figures 3-6 The pattern of the orthographic projection of multiple gratings 21 onto the active layer 1 can be elliptical, rhomboid, quasi-elliptical, or quasi-rhomboid, and the two diameters or two diagonals can extend along the first direction X and the second direction Y, respectively.

[0088] For example, see Figures 3-5 The pattern of the orthographic projection of the multiple gratings 21 in each grating group P onto the active layer 1 can be elliptical, rhomboid, quasi-elliptical, or quasi-rhomboid, etc., and this application does not impose any restrictions on this.

[0089] In this way, the pattern of the orthographic projection of each grating group P onto the active layer 1 is elliptical, rhomboid, quasi-elliptical, or quasi-rhomboid. The two second parts A2 can be equivalent to two "convex lenses" by taking the first part A1 or the center line of the first part A1 extending along the second direction Y as the dividing line, or the gratings 21 on both sides of the center line can be equivalent to two "convex lenses". That is, in simulating an unstable cavity, the diffraction loss of the grating layer 2 on higher-order transverse modes (such as first-order transverse modes) can be increased, thereby effectively suppressing higher-order transverse modes.

[0090] For example, Figure 3 or Figure 4 In each grating group P, the second part A2 on both sides of the first part A1 can be equivalent to two "convex lenses", or the multiple gratings 21 on both sides of the ellipse's short side diameter (i.e., short axis) can be equivalent to two "convex lenses".

[0091] For example, see Figure 6 The pattern of the orthographic projection of the multiple gratings 21 in the grating layer 2 onto the active layer 1 is generally elliptical, rhomboid, quasi-elliptical, or quasi-rhomboid. In this case, the multiple gratings 21 can be equivalent to two "convex lenses" to suppress higher-order transverse modes. This application does not impose any restrictions on this.

[0092] Alternatively, by way of example, the pattern of the orthographic projection of the plurality of gratings 21 onto the active layer 1 may also be in other shapes. In this case, the size of the grating 21 in the second part A2 in the second direction Y is still smaller than the size of the grating 21 in the first part A1 in the second direction Y. This application does not impose any restrictions on this.

[0093] Figure 9 for Figure 1 A schematic diagram of the cross-section of the laser along section line D-D'.

[0094] In some embodiments, see Figure 1 , Figure 2 and Figure 9 The laser 100 also includes a ridge waveguide 3.

[0095] Among them, the ridge waveguide 3 can confine the light field within the ridge region through the refractive index difference to ensure the single-mode nature of the output beam. At the same time, it can also limit the lateral expansion of the light field and avoid light field divergence, so as to efficiently couple with other components and reduce transmission loss.

[0096] See Figure 1 , Figure 2 and Figure 9 The aforementioned ridge waveguide 3 can be disposed on the side of the grating layer 2 away from the active layer 1, and can extend along the first direction X, so that the light modulated by the grating layer 2 can propagate along the first direction X after entering the ridge waveguide 3. At the same time, it can make the impedance of the ridge waveguide 2 more uniform, thereby reducing the transmission loss of light.

[0097] See Figure 1 , Figure 2 and Figure 9 The orthographic projection of the aforementioned ridge waveguide 3 onto the active layer 1 can overlap with the orthographic projections of the multiple gratings 21 onto the active layer 1, for example, Figure 1In this configuration, the orthographic projection of the ridge waveguide 3 onto the active layer 1 can be located in the middle region of the orthographic projections of the multiple gratings 21 onto the active layer 1. In this way, the orthographic projection of the ridge waveguide 3 onto the active layer 1 overlaps with the orthographic projections of the multiple gratings 21 onto the active layer 1, which can make the light entering the ridge waveguide 3 as much as possible as light modulated by the multiple gratings 21, thereby effectively optimizing the distribution of the optical field, for example, making the optical field have a fundamental mode distribution, thereby improving the purity of the single-mode (e.g., fundamental mode) output of the laser 100.

[0098] See Figure 1 and Figure 9 The dimension of the grating 21 in the second part A2 in the second direction Y can be smaller than the dimension of the ridge waveguide 3 in the second direction Y, so as to utilize the structure formed by the middle portion of the grating 21 in the second part A2 and the first part A1, i.e., the resonant cavity (e.g. Figure 3 In the a2 region, the light about to enter the ridge waveguide 3 is modulated to optimize the optical field, making the ridge waveguide 3 more supportive of fundamental mode transmission, such as TE0 fundamental mode transmission, thereby improving the purity of the single-mode output of the laser 100.

[0099] In some embodiments, see Figure 1 and Figure 9 The aforementioned ridge waveguide 3 may include a middle portion 31 and two edge portions 32.

[0100] The two edge portions 32 here can be disposed on both sides of the middle portion 31 along the second direction Y. For example, Figure 9 In the middle, along the second direction Y, the two edge portions 32 are located on the left and right sides of the middle portion 31, respectively.

[0101] The intensity distribution of the fundamental mode (i.e., light intensity) in the middle part 31 is greater than that in the two edge parts 32. That is, the light intensity of the fundamental mode generally reaches its maximum value in the middle of the ridge waveguide 3 and gradually decreases along the second direction Y to both sides. Its light field is bright in the middle and dark on both sides, so that the fundamental mode is mainly distributed in the middle part 31.

[0102] Unlike the fundamental mode, the first-order transverse mode has a light field that is dark in the middle and bright on both sides, so that the light intensity is mainly distributed at the two edges 32 of the ridge waveguide 3.

[0103] See Figure 9 The size of the grating 21 in the second part A2 in the second direction Y can be greater than or equal to the size of the middle part 31 in the second direction Y, and the distance between the end of the grating 21 in the first part A1 and the end of the grating 21 in the second part A2 in the second direction Y can be less than or equal to the size of the edge part 32 in the second direction Y.

[0104] In this way, the size of the grating 21 in the second part A2 in the second direction Y is greater than or equal to the size of the middle part 31 in the second direction Y. This allows the distribution of the grating 21 in the second part A2 and the grating 21 in the first part A1 to correspond to the fundamental mode intensity distribution. As a result, the resonant cavity formed by the adjacent gratings 21 in the second part A2 and the resonant cavity formed by the gratings 21 in the second part A2 and the gratings 21 in the first part A1 can be used to improve the beam reflectivity of the middle part 31, thereby enhancing the coupling capability to the fundamental mode.

[0105] At the same time, the distance between the end of the grating 21 in the first part A1 and the end of the grating 21 in the second part A2 in the second direction Y is (e.g.) Figure 3 If d1 is less than or equal to the dimension of edge portion 32 in the second direction Y, the end distribution of grating 21 in the first part A1 and the end distribution of grating 21 in the second part A2 can correspond to the intensity distribution of the first-order transverse mode. This allows for the formation of an incomplete resonant cavity (e.g., using the end regions of grating 21 in the first part A1 and the end regions of grating 21 in the second part A2) that can be utilized. Figure 3 When the beam is modulated using only part of the grating 21 (in the a1 region), the reflectivity of the beam in the edge portion 32 is lower, thereby suppressing the first-order transverse mode and ultimately improving the purity of the single-mode (e.g., fundamental mode) output of the laser 100 and increasing its maximum useful power.

[0106] In some embodiments, see Figures 3-8 Each grating 21 can be symmetrically arranged with the center line extending along the first direction X of the plurality of gratings 21 as the axis of symmetry, that is, the physical center of each grating 21 can be located on the same straight line (e.g. Figure 3 The line is on the straight line E in the diagram, and the straight line can extend along the first direction X.

[0107] For example, Figure 3 In the process, the grating 21 in each grating group P can be symmetrically set with the straight line E as the axis of symmetry. The straight line E can be the line containing the major axis of the ellipse.

[0108] Thus, each grating 21 is positioned along a centerline extending from a plurality of gratings 21 in the first direction X (e.g. Figure 3The straight line E in the middle is symmetrically set with the axis of symmetry, so that the two ends of the grating 21 in the second part A2 and the two ends of the grating 21 in the first part A1 can also be symmetrically set with the center line as the axis of symmetry. Thus, the modulation range of the beam by the incomplete resonant cavity or the partial grating 21 corresponds to the two edge parts 32 of the ridge waveguide 3, that is, it can accurately correspond to the intensity distribution of the first-order transverse mode, thereby effectively suppressing the first-order transverse mode and improving the purity of the single-mode output of the laser 100.

[0109] In some embodiments, see Figures 3-8 Among the multiple gratings 21, along the first direction X, the ends of any two adjacent gratings 21 located on the same side have equal spacing in the second direction Y.

[0110] For example, Figure 3 In the first direction X, from left to right, the distance between the upper ends of the first grating 21 and the second grating 21 along the second direction Y is d1. The distance between the ends of the second grating 21 and the third grating 21 on the same side in the second direction Y is also d1. That is, the distance between the ends of two adjacent gratings 21 on the same side in the second direction Y can both be d1.

[0111] In this way, along the first direction X, the ends of any two adjacent gratings 21 located on the same side are spaced equally in the second direction Y. This allows the two end regions of the gratings 21 in the second part A2 to form incomplete resonant cavities (e.g., the two end regions of the gratings 21 in the first part A1) with the two end regions of the gratings 21 in the first part A1. Figure 3 The dimensions of the a1 region in the second direction Y are equal, so that when the beam reflectivity of the edge region is reduced by using an incomplete resonant cavity or a partial grating 21, the beam reflectivity reduction is consistent, and the light intensity attenuation of the two edge parts 32 is the same, so as to better suppress the first-order transverse mode.

[0112] For example, see Figures 3-8 Each grating 21 can be symmetrically arranged with the center line extending along the first direction X as the axis of symmetry. Furthermore, among the multiple gratings 21, along the first direction X, the ends of any two adjacent gratings 21 located on the same side have equal spacing in the second direction Y. This allows for the formation of an incomplete resonant cavity (e.g., in the second part A2 and the first part A1) between the ends of the gratings 21 and the ends of the gratings 21. Figure 3The modulation range of the beam (in the a1 region) or part of the grating 21 can precisely correspond to the intensity distribution of the first-order transverse mode, thereby reducing the beam reflectivity in the edge region. It can also reduce the beam reflectivity in the edge region by using an incomplete resonant cavity or part of the grating 21, so that the reduction in beam reflectivity is consistent, thereby better suppressing the first-order transverse mode and effectively improving the purity of the single-mode output of the laser 100.

[0113] In this application, to verify the effectiveness of the grating layer 2 of the laser 100 in suppressing the first-order transverse mode in the above embodiments, Figure 3 Taking the grating layer 2 shown as an example for modeling and simulation, the ridge waveguide 3 of the laser 100 has a size of 6 μm in the second direction Y, and the distance between two adjacent gratings 21 along the first direction X is 227.9 nm (i.e., one small period Λ). The size of the grating group P in the first direction X is 22.79 μm, the duty cycle is 0.5, the refractive index of the ridge waveguide 3 material is 3.48, the refractive index of the substrate 4 material is 3.475, the incident mode of the incident light source is TE1 mode, i.e., first-order transverse mode, and the wavelength range of the incident light source is 1.45 μm to 1.85 μm.

[0114] by Figure 3 The modeling and simulation process of the grating layer 2 shown is as follows: (1) Construct a set of uniform gratings with a period of 227.9 nm as the substrate. The uniform grating includes 1000 gratings 21. At this time, the size of the ridge waveguide 3 in the first direction X is about 228 μm, and the refractive index modulation of the grating 21 is about 0.004. (2) On the basis of the uniform grating, a set of large-period gratings is superimposed. That is, multiple grating groups P can be determined by using window functions to construct a uniform sampling grating. Each grating group P includes 100 gratings 21, that is, the size of the grating group P in the first direction X is 22.79 μm. (3) Using a preset circular ring as the intercepting area, the grating region of each grating group P is covered by a circular ring on the structure of the uniformly sampled grating. The grating 21 in each grating group P is divided into a first part A1 and a second part A2. The size of the grating 21 in the second part A2 in the second direction Y is smaller than the size of the grating 21 in the first part A1 in the second direction Y, thus realizing a grating structure similar to an elliptical gradient. In this process, in order to reduce the amount of computation and ensure the reliability of the simulation results, a rectangular structure with the same refractive index as the substrate material can be superimposed to cover the excess area of ​​the circular ring that extends beyond the waveguide.

[0115] Figure 10 The transmission spectrum is simulated using a uniformly sampled grating. Figure 11 For Figure 3 The transmission spectrum of the grating layer in the image was simulated. Figure 12 The reflection spectrum is simulated using a uniformly sampled grating. Figure 13For Figure 3 The reflection spectrum of the grating layer in the simulation is obtained.

[0116] During simulation experiments, a detector can be placed at both the front and rear ends of grating layer 2 to monitor the reflection and transmission spectra, respectively. (See [reference needed]). Figure 10 and Figure 11 It can be seen that when the wavelength range of the incident light source is 1.45um~1.85um, compared with the uniform sampling grating, the grating structure designed in this application improves the transmittance of the light beam in this wavelength range.

[0117] See Figure 12 and Figure 13 It can be seen that the side peaks of the uniform sampling grating are higher on both sides of the main peak compared to the grating structure (i.e., grating layer 2) in this application. Comparing at the same wavelength, for example, at 1557.24 nm, the reflectivity of the first-order optical field (i.e., the first-order transverse mode) of the uniform sampling grating is 0.00699485, while the reflectivity of the grating structure in this application for the first-order optical field at the same wavelength is 0.00540971. Therefore, compared to the uniform sampling grating, the grating structure in this application has lower reflectivity for the ±1st-order optical field, meaning that the grating structure in this application has lower coupling capability for the ±1st-order optical field and stronger coupling capability for the 0th-order optical field. In summary, the laser 100 proposed in this application does indeed have a suppression effect on the first-order transverse mode.

[0118] Figure 14 This is a schematic flowchart of a laser fabrication method provided in an embodiment of this application. Figures 15-19 The diagram illustrates the steps of the laser fabrication method provided in the embodiments of this application.

[0119] For example, this application provides a laser fabrication method, which includes the following steps S1 to S6: Step S1: See Figure 15 A buffer layer 5, a lower waveguide layer 6, an active layer 1, an upper waveguide layer 7, and an initial grating layer 2' are sequentially formed on the substrate 4.

[0120] The initial grating layer 2' refers to the semiconductor material layer before multiple gratings 21 are set, which provides a physical basis for the subsequent fabrication of the grating layer 2.

[0121] For example, metal-organic chemical vapor deposition, molecular beam epitaxy, and other techniques can be used to sequentially form a buffer layer 5, a lower waveguide layer 6, an active layer 1, an upper waveguide layer 7, and an initial grating layer 2' on a substrate 4, which is the bottom epitaxial structure.

[0122] Step S2: See Figure 16 This forms a grating mask layer.

[0123] For example, a layer of photoresist can be coated on the initial grating layer 2', and a long-period pattern can be defined using conventional photolithography, electron beam lithography, or other processes (i.e., forming multiple grating groups P, the size of which in the second direction Y can be 22.8 μm). This involves periodically removing grating regions to form multiple openings K. Subsequently, a coverage size can be selected along the second direction Y in the opening K region of each grating group P, which can be equivalent to the length of the minor axis of an ellipse (e.g., 5.76 μm). Next, a second layer of high-resolution photoresist is coated within the opening K of each grating group P, and multiple photoresist patterns (e.g., photoresist patterns M1 and M2, where the distance between two adjacent photoresist patterns M2 along the first direction X can be 0.228 μm, i.e., a small period Λ can be 0.228 μm) can be formed within the opening K3 using holographic lithography, i.e., using dual-beam interference technology. This results in a grating mask layer (e.g., a grating mask layer with multiple photoresist patterns periodically arranged within the opening K of each grating group P). Figure 16 (The grating mask layer in the middle).

[0124] The photoresist patterns M1 and M2 here correspond to the grating 21 in the first part A1 and the grating 21 in the second part A2, respectively.

[0125] For example, multiple photoresist patterns, such as photoresist pattern M1 and photoresist pattern M2, can be formed using electron beam direct writing, X-ray lithography, nanoimprinting, sol-gel method combined with photolithography / interference, etc., to improve the uniformity of etching and thus improve the performance of the formed grating layer 2. This application does not limit this.

[0126] For example, along the second direction Y, gratings 21 of different sizes can be designed by adjusting the size of the opening K covering each grating group P to adapt to various application requirements. For instance, along the second direction Y, the size of the opening K covering each grating group P can be set to 5.76 μm, and along the first direction X, the size of the opening K covering each grating group P can be 8 μm. In this case, the inner radius of the ellipse covering the opening K in each grating group P can be 2.88 μm, and the outer radius can be 4 μm.

[0127] Step S3: See Figure 17 The initial grating layer 2' is etched based on the grating mask layer to form the grating layer 2.

[0128] For example, the photoresist pattern on the grating mask layer is transferred to the initial grating layer 2', and the initial grating layer 2' is etched using dry etching to form the grating layer 2.

[0129] Step S4: Remove residual photoresist.

[0130] This involves thoroughly removing all residual photoresist and etching byproducts, cleaning the surface of grating layer 2, and preparing it for subsequent epitaxial growth.

[0131] Step S5: See Figure 18 and Figure 19 , forming the upper cladding layer 3'.

[0132] For example, the etched grating layer 2 can be placed back into the epitaxial furnace to grow the cladding layer 3', and then the grating can be buried so that the newly grown material fills the grating groove, thereby completely embedding the grating layer 2 into the semiconductor material.

[0133] Step S6: See Figure 9 This forms a ridge waveguide 3.

[0134] For example, the upper cladding 3' can be etched to form a ridge waveguide 3.

[0135] For example, after forming the ridge waveguide 3, a passivation layer can be provided on both sides of the ridge waveguide 3 along the second direction Y. Then, an electrode is formed on the ridge waveguide 3 so as to protect the ridge waveguide 3 with the passivation layer and to realize the injection of current with the electrode.

[0136] This application also provides a laser system. Figure 20 This is a schematic diagram of the structure of a laser system provided in an embodiment of this application.

[0137] See Figure 20 The laser system 200 mentioned above includes the laser 100 and the optical transmission system L in the above embodiments.

[0138] The optical transmission system L can be coupled to the laser 100 to achieve efficient light transmission.

[0139] The technical effects of the laser system 200 provided in this application embodiment can be seen in the technical effects of the laser 100 in the above embodiment, and will not be repeated here.

[0140] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A laser, characterized in that, include: Active layer; A grating layer is disposed on the active layer; The grating layer includes multiple gratings, which are spaced apart along a first direction. The multiple gratings are divided into a first part and two second parts. The two second parts are located on both sides of the first part along the first direction. The size of the grating in the second part in the second direction is smaller than the size of the grating in the first part in the second direction. The first direction and the second direction are both parallel to the active layer and perpendicular to each other.

2. The laser according to claim 1, characterized in that, The grating layer includes multiple grating groups, which are spaced apart along the first direction, and each grating group includes the multiple gratings.

3. The laser according to claim 1, characterized in that, The plurality of gratings are arranged symmetrically about the center line of the plurality of gratings extending along the second direction.

4. The laser according to claim 1, characterized in that, The two ends of the plurality of gratings arranged along the first direction point to the center of the region where the plurality of gratings are located, and the size of the gratings gradually increases in the second direction.

5. The laser according to claim 1, characterized in that, The orthographic projection of the plurality of gratings onto the active layer is elliptical, prismatic, quasi-elliptical, or quasi-prismatic, and the two diameters or two diagonals extend along the first direction and the second direction, respectively.

6. The laser according to claim 1, characterized in that, Also includes: A ridge waveguide is disposed on the side of the grating layer away from the active layer. The ridge waveguide extends along the first direction, and the orthographic projection of the ridge waveguide on the active layer overlaps with the orthographic projection of the plurality of gratings on the active layer. Wherein, the dimension of the grating in the second part in the second direction is smaller than the dimension of the ridge waveguide in the second direction.

7. The laser according to claim 6, characterized in that, The ridge waveguide includes a middle section and two edge sections disposed on both sides of the middle section along the second direction; the distribution intensity of the fundamental mode in the middle section is greater than the distribution intensity of the fundamental mode in the two edge sections; Wherein, the size of the grating in the second part in the second direction is greater than or equal to the size of the middle part in the second direction, and the distance between the end of the grating in the first part and the end of the grating in the second part in the second direction is less than or equal to the size of the edge part in the second direction.

8. The laser according to claim 1, characterized in that, Each grating is symmetrically arranged about the center line of the plurality of gratings extending along the first direction as an axis of symmetry.

9. The laser according to claim 1, characterized in that, In the plurality of gratings, the ends of any two adjacent gratings located on the same side are spaced equally in the second direction.

10. A laser system, characterized in that, include: The laser as described in any one of claims 1 to 9; An optical transmission system is coupled to the laser.

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