Distributed feedback laser

Abstract

The embodiment of the invention provides a distributed feedback laser, relates to the technical field of lasers, and is used for solving the problem that the performance is affected by insertion of a phase shift grating. The laser comprises a ridge waveguide and feedback gratings arranged on the two sides of the ridge waveguide, each feedback grating comprises a Bragg grating and a phase shift grating inserted into the Bragg grating, the Bragg grating comprises two connecting gratings located on the two sides of the phase shift grating respectively, and each connecting grating comprises a chirp grating and a uniform grating which are connected. The uniform grating is away from the phase shift grating relative to the chirp grating. The length of grating teeth in the chirp grating is a first length, and the duty ratio is a first duty ratio; the width of a part, corresponding to the chirp grating, of the ridge waveguide is a first waveguide width; in the process of approaching the uniform grating from the phase shift grating along the first direction, at least one of the first length, the first duty ratio and the first waveguide width is gradually changed to realize grating coupling coefficient chirp of the chirp grating. The laser can be applied to the field of optical communication.

Description

Technical Field

[0001] This application relates to the technical field of lasers, and particularly to a distributed feedback laser. Background Art

[0002] A distributed feedback (DFB) laser includes a uniform Bragg grating distributed in a resonant cavity, and optical feedback is realized through the uniform Bragg grating. Due to its good single-mode performance, narrow linewidth, low noise and other characteristics, the DFB laser is widely used in large-capacity optical communication systems and optical measurement systems.

[0003] In the ideal case where the end face reflectivity is not considered or the end face reflectivity is zero, there are two degenerate modes at positions symmetrical to the Bragg wavelength in the DFB laser using a uniform Bragg grating. These two degenerate modes have the same and lowest threshold gain, which will cause serious mode competition when the DFB laser works, resulting in randomly selecting one of the modes to lasing or both modes lasing simultaneously (i.e., dual-mode lasing), seriously affecting the stability of the single-mode output of the DFB laser.

[0004] In order to enable the DFB laser to achieve stable single-mode output, related technologies usually introduce a quarter-wavelength (λ / 4) phase-shifted grating at the center of the uniform Bragg grating, and use the λ / 4 phase-shifted grating to generate a mode with a relatively lower threshold gain at the center of the grating stopband. This mode can lase better than other modes, so as to achieve single-mode output. However, the presence of the λ / 4 phase-shifted grating will cause the concentrated distribution of the longitudinal optical field in the phase-shifted region of the DFB laser. Especially at high injection currents, the concentrated distribution of the longitudinal optical field may cause a serious longitudinal spatial hole burning (SHB) effect, and the longitudinal spatial hole burning effect will cause the LI curve (the relationship curve of the output optical power of the laser varying with the injection current) of the DFB laser to have a non-linear kink, the output spectrum to have mode hopping or multi-mode, and performance deterioration phenomena such as linewidth broadening and relative intensity noise increase, affecting the performance of the DFB laser. Summary of the Invention

[0005] An embodiment of this application provides a distributed feedback laser, which is used to improve the problem of performance affected by inserting a phase-shifted grating.

[0006] To achieve the above object, the embodiments of this application adopt the following technical solutions:

[0007] An embodiment of the present application provides a distributed feedback laser, which includes a ridge waveguide, a structural surface, and a feedback grating. The ridge length direction of the ridge waveguide is parallel to the first direction, the ridge width direction is parallel to the second direction, and the ridge height direction is parallel to the third direction; and it is a waveguide structure symmetric with respect to the waveguide center plane. Among them, the first direction, the second direction, and the third direction are perpendicular to each other in pairs, and the waveguide center plane is parallel to the first direction and the third direction.

[0008] The ridge waveguide includes two sidewalls oppositely arranged in the second direction. The structural surface is perpendicular to the waveguide center plane and is connected to the bottom ends of the sidewalls in the third direction.

[0009] The feedback grating includes a plurality of grating teeth arranged along the first direction. The grating teeth include two sub-grating teeth located on both sides of the waveguide center plane and symmetrically arranged with respect to the waveguide center plane; the sub-grating teeth include a surface portion in contact with the structural surface, and the distance of the surface portion in the third direction is less than or equal to 0.5 times the ridge height of the ridge waveguide.

[0010] The grating teeth in the feedback grating are arranged to form a Bragg grating and a phase-shift grating inserted into the Bragg grating. The Bragg grating includes two connecting gratings respectively located on both sides of the phase-shift grating. The connecting grating includes a chirped grating and a uniform grating connected in the first direction, and the uniform grating is farther from the phase-shift grating than the chirped grating.

[0011] The length of the grating teeth of the chirped grating in the second direction is the first length, and the duty cycle is the first duty cycle; the distance between the corresponding part of the ridge waveguide and the chirped grating in the second direction is the first waveguide width; when moving from the phase-shift grating to the uniform grating along the first direction, at least one of the first length, the first duty cycle, and the first waveguide width gradually changes, so as to realize the gradual increase of the grating coupling coefficient of the chirped grating, and the maximum value of the grating coupling coefficient of the chirped grating is less than or equal to the grating coupling coefficient of the connected uniform grating.

[0012] In the DFB laser provided by the embodiment of the present application, by controlling at least one of the first length, the first duty cycle, and the first waveguide width to gradually change when moving from the phase-shift grating to the uniform grating along the first direction, the gradual increase of the grating coupling coefficient of the chirped grating can be realized, and at the same time, the maximum value of the grating coupling coefficient of the chirped grating is less than or equal to the grating coupling coefficient of the connected uniform grating.

[0013] With such a design, on the one hand, the situation that the longitudinal optical field is concentrated at the position of the phase-shift grating can be improved, the uniformity of the longitudinal optical field distribution can be enhanced, the longitudinal spatial hole burning effect can be effectively suppressed, which is beneficial to realizing the linear, stable single longitudinal mode, low noise, and narrow linewidth laser output, and improving the performance of the DFB laser.

[0014] On the other hand, the above structure is applicable to the application scenario of a straight waveguide, which can improve the problems caused by the chirping scheme of a bent waveguide, such as the inclination of the output port, the relatively large divergence angle of the output beam, and the influence on the output light spot, and is beneficial to improving the coupling efficiency with the optical fiber. In addition, compared with the feedback grating fabricated by using the reconstruction-equivalent chirping technology, the feedback grating in the embodiment of the present application has a larger feedback intensity due to the smaller number of chirped gratings and without reducing the total number of gratings, which is beneficial to achieving a high side mode suppression ratio and improving the performance of the DFB laser.

[0015] On the other hand, the chirping of the grating coupling coefficient can be achieved by adjusting different structural parameters, and the decoupling of the ridge waveguide and the feedback grating is realized, with more flexible design and higher degree of freedom.

[0016] In some embodiments, the lengths of the grating teeth in the second direction of the uniform grating and the phase shift grating are the second length and the third length respectively, and the second length is greater than the third length; when moving from the phase shift grating to the uniform grating along the first direction, the first length gradually increases between the third length and the second length according to a linear chirping function, a quadratic chirping function or a Gaussian chirping function.

[0017] In the DFB laser provided by the embodiment of the present application, by adjusting the length of the grating teeth, the chirping design of the grating coupling coefficient of the chirped grating is realized, with a simple structure, easy to process and implement; and it can be applicable to a variety of different length change modes, with good adaptability.

[0018] In some embodiments, the duty cycle of the uniform grating is the second duty cycle; when moving from the phase shift grating to the uniform grating along the first direction, the first duty cycle gradually changes relative to the second duty cycle according to a linear chirping function, a quadratic chirping function or a Gaussian chirping function.

[0019] In the DFB laser provided by the embodiment of the present application, by adjusting the duty cycle, the chirping design of the grating coupling coefficient of the chirped grating is realized, with a simple structure, easy to process and implement; and it can be applicable to a variety of different duty cycle change modes, with good adaptability.

[0020] In some embodiments, in the second direction, the distances between the ridge waveguide and the corresponding parts of the uniform grating and the phase shift grating are the second waveguide width and the third waveguide width respectively; the third waveguide width is greater than the second waveguide width; when moving from the phase shift grating to the uniform grating along the first direction, the first waveguide width gradually decreases between the third waveguide width and the second waveguide width according to a linear chirping function, a quadratic chirping function or a Gaussian chirping function.

[0021] In the DFB laser provided by the embodiments of the present application, by adjusting the waveguide width of the ridge waveguide, the chirp design of the grating coupling coefficient of the chirped grating is realized. The structure is simple and easy to process and implement; moreover, it can be applied to a variety of different waveguide width change methods, with good adaptability.

[0022] In some embodiments, both of the two connecting gratings located on both sides of the phase-shifted grating in the Bragg grating include chirped gratings; in the first direction, the chirped gratings on both sides of the phase-shifted grating are symmetrically arranged with respect to the phase-shifted grating. With such a design, the chirped gratings on both sides of the phase-shifted grating can have the same chirp variation, which is beneficial to improving the uniformity of the longitudinal optical field distribution.

[0023] In some embodiments, the distributed feedback laser includes a substrate, a first confinement layer, an active layer, and a second confinement layer. The first confinement layer is disposed on one side of the substrate, the active layer is disposed on the side of the first confinement layer away from the substrate, and the second confinement layer is located on the side of the active layer away from the substrate; the second confinement layer includes a ridge waveguide, and the structural surface is the structural surface of the second confinement layer or the active layer; the material of the grating teeth in the feedback grating is different from that of the ridge waveguide.

[0024] In the DFB laser provided by the embodiments of the present application, the feedback grating and the ridge waveguide are designed to be fabricated separately, and the feedback grating can be fabricated again with a material different from that of the ridge waveguide after the ridge waveguide is fabricated; with such a design, decoupling of the feedback grating and the ridge waveguide can be achieved, enabling the fabrication of the feedback grating to be free from the restrictions of the ridge waveguide, with higher degrees of freedom; in particular, the coupling efficiency of the feedback grating can be improved by using different materials.

[0025] In some embodiments, the distributed feedback laser includes a substrate, a first confinement layer, an active layer, and a second confinement layer. The first confinement layer is disposed on one side of the substrate, the active layer is disposed on the side of the first confinement layer away from the substrate, and the second confinement layer is located on the side of the active layer away from the substrate; the second confinement layer includes a ridge waveguide, and the structural surface is the structural surface of the second confinement layer; the surface part in the sub-grating teeth is disposed in the second confinement layer.

[0026] In the DFB laser provided by the embodiments of the present application, the feedback grating and the ridge waveguide are designed to be fabricated separately, and the feedback grating can be directly fabricated in the existing structure after the ridge waveguide is fabricated. With such a design, decoupling of the feedback grating and the ridge waveguide can be achieved, enabling the fabrication of the feedback grating to be free from the restrictions of the ridge waveguide, with higher degrees of freedom; and it can simplify the fabrication process of the feedback grating, and also enable the feedback grating to be closer to the active layer, which is beneficial to improving the coupling efficiency of the feedback grating.

[0027] In some embodiments, in a cross-section perpendicular to the first direction, the cross-sectional shape of the ridge waveguide is an isosceles trapezoid, a square, or a rectangle; the isosceles trapezoid is a regular trapezoid or an inverted trapezoid with respect to the active layer. In the DFB laser provided by the embodiments of the present application, the ridge waveguide can be a waveguide structure of various different shapes, with good adaptability and high degrees of freedom, which is conducive to reducing the processing difficulty.

[0028] In some embodiments, in a cross-section perpendicular to the first direction, the cross-sectional shape of the ridge waveguide is an isosceles trapezoid and is a regular trapezoid with respect to the active layer; the sub-grating teeth further include a sidewall portion distributed on the sidewall of the ridge waveguide, and the surface portion and the sidewall portion are connected in the second direction; the distance of the sidewall portion in the direction perpendicular to the sidewall is less than or equal to 0.5 times the distance of the ridge waveguide in the third direction.

[0029] In the DFB laser provided by the embodiments of the present application, the sub-grating teeth in the feedback grating can further include a sidewall portion. With such a design, the structural characteristics of the regular trapezoid ridge waveguide can be fully utilized to extend the effective length of the sub-grating teeth as much as possible within a limited width, which is conducive to improving the coupling efficiency of the feedback grating.

[0030] In some embodiments, the material of the grating teeth is chromium, amorphous silicon, or silicon nitride. In the DFB laser provided by the embodiments of the present application, the feedback grating can be made of a variety of different materials, can be applied to different material systems, has good adaptability and high degrees of freedom, which is conducive to reducing the processing difficulty.

[0031] In some embodiments, the Bragg grating is a first-order or third-order Bragg grating. In the DFB laser provided by the embodiments of the present application, Bragg gratings of different orders can be applied and can be used in different application scenarios, with good adaptability.

[0032] In some embodiments, the feedback grating includes at least two phase-shifted gratings, and connection gratings are provided on both sides of at least one phase-shifted grating. In the DFB laser provided by the embodiments of the present application, application scenarios with multiple phase-shifted gratings can be applied, with good adaptability. Description of the Drawings

[0033] Figure 1 Schematic diagram of the structure of the feedback grating in a DFB laser provided by the related art;

[0034] Figure 2 Schematic diagram of the structure of the feedback grating in another DFB laser provided by the related art;

[0035] Figure 3 Schematic diagram of the structure of the feedback grating in yet another DFB laser provided by the related art;

[0036] Figure 4A three-dimensional schematic diagram of a DFB laser provided by an embodiment of the present application;

[0037] Figure 5 A front view of a DFB laser provided by an embodiment of the present application;

[0038] Figure 6 is Figure 5 The top view of the DFB laser in

[0039] Figure 7 is Figure 5 The side view of the DFB laser in

[0040] Figure 8 is Figure 6 The change schematic diagram of the feedback grating in

[0041] Figure 9 is for Figure 8 The test result diagram of the feedback grating in different situations in

[0042] Figure 10 is for Figure 8 The test result diagram of the feedback grating in different situations in

[0043] Figure 11 is for Figure 8 The test result diagram of the feedback grating in different situations in

[0044] Figure 12 The structural schematic diagram of the feedback grating in another DFB laser provided by an embodiment of the present application;

[0045] Figure 13 The structural schematic diagram of the feedback grating in yet another DFB laser provided by an embodiment of the present application. Detailed implementation manners

[0046] A distributed feedback (DFB) laser includes a uniform Bragg grating distributed in a resonant cavity, and optical feedback is achieved through the uniform Bragg grating. In the ideal case where the end face reflectivity is not considered or the end face reflectivity is zero, there are two degenerate modes in the DFB laser with a uniform Bragg grating at positions symmetric to the Bragg wavelength. These two degenerate modes have the same and lowest threshold gain, resulting in serious mode competition when the DFB laser operates, causing random selection of one of the modes for lasing or lasing of both modes simultaneously (i.e., dual-mode lasing), which seriously affects the stability of the single-mode output of the DFB laser.

[0047] In order to enable a DFB laser to achieve stable single-mode output, related technologies usually introduce a quarter-wavelength (λ / 4) phase-shifted grating at the center of a uniform Bragg grating. By using the λ / 4 phase-shifted grating to generate a mode with a relatively lower threshold gain at the center of the grating stopband, this mode can lase better than other modes, thereby achieving single-mode output. However, the presence of the λ / 4 phase-shifted grating will cause the longitudinal (parallel to the cavity length direction of the resonator) optical field in the DFB laser to be concentrated in the phase-shifted region. Especially at high injection currents, the concentrated distribution of the longitudinal optical field may cause a serious longitudinal spatial hole burning (SHB) effect. The longitudinal spatial hole burning effect will cause the LI curve (the relationship curve of the output optical power in the laser varying with the injection current) of the DFB laser to have a nonlinear kink, the output spectrum to have mode hopping or multimode, and also performance degradation phenomena such as linewidth broadening and increased relative intensity noise, affecting the performance of the DFB laser.

[0048] Based on this, in related technologies, a variety of solutions have been provided to improve the concentrated distribution of the longitudinal optical field in the phase-shifted region on the basis of introducing the λ / 4 phase-shifted grating.

[0049] For example, in Figure 1 the related technology shown, the feedback grating 1 in the DFB laser 100 adopts a chirping scheme for the grating period, that is, a design of introducing a phase-shifted grating 11 in the chirped Bragg grating 10. The chirped Bragg grating 10 refers to a Bragg grating whose grating period linearly changes in the cavity length direction of the resonator. By using the linear chirping of the grating period, the reflection characteristics of the Bragg grating can be changed, thereby improving the phenomenon of the concentrated distribution of the longitudinal optical field in the region where the phase-shifted grating 11 is located. However, the design freedom of this scheme is relatively single, and moreover, due to the distribution characteristics of the grating periods of the Bragg gratings on both sides of the phase-shifted grating 11 being one large and one small, the longitudinal optical field will be inclined to distribute towards the region with a large grating period and sparse gratings as a whole, ultimately resulting in a poor improvement effect on the uniformity of the longitudinal optical field distribution.

[0050] Another example is that in Figure 2 the related technology shown, the feedback grating 1 in the DFB laser adopts a chirping scheme for the curved waveguide, that is, a design of fabricating a uniform Bragg grating in the curved waveguide. The uniform Bragg grating refers to a Bragg grating whose grating period is equal in the cavity length direction of the resonator. By the bending angle of the curved waveguide, the equivalent chirping of the grating period and the equivalent phase shift in the uniform Bragg grating can be achieved, thereby improving the phenomenon of the concentrated distribution of the longitudinal optical field in the phase-shifted region. However, due to the curved waveguide, this feedback grating 1 will cause the output port to be inclined, and the divergence angle of the output beam is relatively large, affecting the output light spot, so it is difficult to efficiently couple with the optical fiber.

[0051] Another example is that in Figure 3In the related art shown, the feedback grating 1 in a DFB laser is fabricated using the Reconstruction equivalent chirp (REC) technique, that is, the mathematical reconstruction variation of a uniform Bragg grating is performed through a sampling function to achieve the equivalent chirp of the grating period in the uniform Bragg grating, and an equivalent phase shift is inserted; thereby improving the phenomenon that the longitudinal optical field is concentrated in the phase shift region. However, since the actual grating length of the feedback grating 1 is less than the cavity length of the resonator in the DFB laser, the number of gratings is significantly reduced, resulting in a relatively low overall grating coupling coefficient, and causing the problem that the feedback of the feedback grating 1 is not strong enough.

[0052] In addition, in a series of related arts such as Figures 1 to 3 shown, the DFB laser 100 is generally fabricated by two epitaxial processes. The feedback grating 1 therein is a buried grating formed during the two epitaxial processes. Specifically, during the fabrication of the DFB laser 100, first, an epitaxial structure including an active layer is fabricated by the first epitaxial process, and then the feedback grating 1 is formed by processing the epitaxial material on top of the active layer; after the feedback grating 1 is fabricated, the second epitaxial process is used to continue to generate a structure, such as a ridge waveguide, above the feedback grating 1; in this way, the already formed feedback grating 1 will be buried by the growth material of the second epitaxial process.

[0053] The DFB laser 100 formed by the above process will have some problems. On the one hand, there will be a process interruption between the two epitaxial processes, so that the epitaxial structure formed by the first epitaxial process and the subsequent fabricated feedback grating 1 are exposed to air and other pollution sources, affecting the performance of the DFB laser 100 and reducing the yield and reliability of the DFB laser 100. On the other hand, the feedback grating 1 will be buried by the epitaxial material in the second epitaxial process after being fabricated, resulting in inability to perform post-adjustment and having a low design freedom. On the other hand, the second epitaxial process may also affect the already fabricated feedback grating 1, so higher process requirements are imposed on the second epitaxial process, ultimately increasing the fabrication difficulty and cost of the DFB laser 100.

[0054] Based on this, the embodiments of the present application provide a distributed feedback laser for improving the above problems.

[0055] Next, the technical solutions in the embodiments of the present application will be described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0056] In the following embodiments of the present application, terms such as "first" and "second" are only used for convenience of description and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0057] In the embodiments of the present application, "upper", "lower", "left", and "right" are not defined only with respect to the orientation of the components shown in the drawings. It should be understood that these directional terms may be relative concepts, and they are used for relative description and clarification, and may change accordingly with the change of the orientation of the components shown in the drawings.

[0058] In the embodiments of the present application, unless otherwise required by the context, throughout the specification and claims, the term "comprising" is interpreted in an open, inclusive sense, that is, "including, but not limited to". In the description of the specification, terms such as "one embodiment", "some embodiments", "exemplary embodiments", "exemplarily" or "some examples" are intended to indicate that specific features, structures, materials or characteristics related to the embodiment or example are included in at least one embodiment or example of the present application. The schematic representations of the above terms do not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner.

[0059] As used herein, "about", "substantially" or "approximately" includes the stated value and the average value within an acceptable deviation range of the specific value, where the acceptable deviation range is determined by those of ordinary skill in the art considering the measurement being discussed and the errors associated with the measurement of the specific quantity (i.e., the limitations of the measurement system).

[0060] As used herein, "parallel", "perpendicular", "equal" include the stated situation and situations similar to the stated situation, and the range of the similar situations is within an acceptable deviation range, where the acceptable deviation range is determined by those of ordinary skill in the art considering the measurement being discussed and the errors associated with the measurement of the specific quantity (i.e., the limitations of the measurement system). For example, "parallel" includes absolute parallel and approximate parallel, where the acceptable deviation range of approximate parallel may be, for example, within 5° deviation; "perpendicular" includes absolute perpendicular and approximate perpendicular, where the acceptable deviation range of approximate perpendicular may also be, for example, within 5° deviation. "Equal" includes absolute equality and approximate equality, where the acceptable deviation range of approximate equality may be, for example, that the difference between the two equal ones is less than or equal to 5% of either one of them.

[0061] It should be understood that when a layer or element is referred to as being on another layer or substrate, it can be directly on the other layer or substrate, or there can be an intermediate layer between the layer or element and the other layer or substrate.

[0062] In the embodiments of the present application, exemplary embodiments are described with reference to cross-sectional views and / or plan views and / or equivalent circuit diagrams that are idealized exemplary drawings. In the drawings, the thicknesses of layers and regions are enlarged for clarity. Therefore, variations in the shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances can be envisioned. Thus, the exemplary embodiments should not be construed as being limited to the shapes of the regions shown herein, but include shape deviations caused by, for example, manufacturing. For example, an etched region shown as rectangular will generally have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shape of the regions of the device and are not intended to limit the scope of the exemplary embodiments.

[0063] Embodiments of the present application provide a distributed feedback laser (hereinafter simply referred to as a DFB laser), as Figures 4 to 7 shown, the DFB laser 100 includes a substrate 2, a first confinement layer 3, an active layer 4, and a second confinement layer 5. Among them, the material of the substrate 2 can be one of III-V group semiconductor materials such as gallium arsenide (GaAs), gallium antimonide (GaSb), gallium nitride (GaN), and indium phosphide (InP). In this embodiment, the substrate 2 is a plate-like structure parallel to the first direction and the second direction, and the thickness direction of the plate-like structure is parallel to the third direction; wherein, the first direction, the second direction, and the third direction are perpendicular to each other in pairs.

[0064] In the third direction, the first confinement layer 3 is disposed on one side of the substrate 2, the active layer 4 is disposed on the side of the first confinement layer 3 away from the substrate 2, and the second confinement layer is disposed on the side of the active layer 4 away from the first confinement layer 3. Taking Figure 5 the manner shown as an example, the third direction is the longitudinal direction in the figure, and the substrate 2, the first confinement layer 3, the active layer 4, and the second confinement layer 5 are stacked from bottom to top. During the manufacturing process of the DFB laser 100, the first confinement layer 3, the active layer 4, and the second confinement layer 5 can be formed on the substrate 2 by an epitaxial process.

[0065] As Figures 4 to 7As shown, the DFB laser 100 further includes a ridge waveguide 8 and a feedback grating 1. Among them, the ridge waveguide 8 is disposed on the side of the active layer 4 away from the substrate 2. The ridge length direction of the ridge waveguide 8 is parallel to the first direction, the ridge width direction is parallel to the second direction, and the ridge height direction is parallel to the third direction. The ridge waveguide 8 includes a top surface on the side away from the substrate 2 along the ridge height direction (the third direction), a bottom surface on the side close to the substrate 2 along the ridge height direction, and two side walls 81 disposed on both sides along the ridge width direction (the second direction); the top ends of the two side walls 81 are connected to the top surface in the ridge height direction, and the bottom ends are connected to the bottom surface in the ridge height direction.

[0066] The ridge waveguide 8 is a waveguide structure symmetric with respect to the waveguide center plane in the second direction (the ridge width direction), where the waveguide center plane is parallel to the first direction and the third direction. In a cross-section perpendicular to the first direction, the cross-sectional shape of the ridge waveguide 8 can be an isosceles trapezoid, a rectangle, a square, or the like. When the cross-sectional shape of the ridge waveguide 8 is an isosceles trapezoid, the longer base and the shorter base of the isosceles trapezoid are both parallel to the second direction (the ridge width direction) and are arranged in the third direction (the ridge height direction); the isosceles trapezoid can be a regular trapezoid or an inverted trapezoid. It should be noted that the regular trapezoid and the inverted trapezoid here are relative to the active layer 4. When the longer base of the isosceles trapezoid is close to the active layer 4, the isosceles trapezoid is a regular trapezoid; when the shorter base of the isosceles trapezoid is close to the active layer 4, the isosceles trapezoid is an inverted trapezoid.

[0067] When the cross-sectional shape of the ridge waveguide 8 is a rectangle and a square, two opposite sides in its cross-sectional shape are both parallel to the second direction (the ridge width direction), and the other two opposite sides are both parallel to the third direction (the ridge height direction).

[0068] In addition, the ridge waveguide 8 can be a constant cross-section structure along the first direction, that is, at different positions in the first direction, the cross-sectional shape of the ridge waveguide 8 in a cross-section perpendicular to the first direction is the same and the size is the same. The ridge waveguide 8 can also be a non-constant cross-section structure along the first direction, that is, at different positions in the first direction, the cross-sectional shape of the ridge waveguide 8 in a cross-section perpendicular to the first direction is the same, but the size is different.

[0069] As Figure 6 and Figure 7 shown, in this embodiment, the ridge waveguide 8 is a constant cross-section structure along the first direction; in a cross-section perpendicular to the first direction, the cross-sectional shape is an isosceles trapezoid and is a regular trapezoid.

[0070] It should be noted that although the cross-sectional shape of the ridge waveguide 8 is described in this article by shapes formed by connecting straight lines such as an isosceles trapezoid, a rectangle, and a square, due to process and other reasons, the edge lines of the actual cross-sectional shape of the ridge waveguide 8 may not be strictly straight lines, but curves with a certain curvature.

[0071] Please continue to refer to Figures 4 to 7 In this embodiment, the ridge waveguide 8 can be formed by processing the second confinement layer 5. Such a design can make the ridge waveguide 8 as close to the active layer 4 as possible, so as to better confine the light to be transmitted in the active layer 4. The DFB laser 100 also includes a structure surface 7 located on both sides of the ridge waveguide 8 in the second direction (ridge width direction), the structure surface 7 is parallel to the first direction and the second direction, that is, perpendicular to the waveguide center plane; the structure surface 7 is connected to the bottom end of the side wall 81 in the ridge waveguide 8 away from the top surface. The structure surface 7 can be the structure surface 7 of the second confinement layer 5, or the structure surface 7 of the active layer 4.

[0072] For example, in the manufacturing process of the DFB laser 100, a ridge waveguide 8 is formed by processing the second confinement layer 5 on a side away from the substrate 2, and the ridge height of the ridge waveguide 8 is less than the thickness of the second confinement layer 5. In this case, part of the second confinement layer 5 still remains under the ridge waveguide 8, and the surface of the remaining part away from the substrate 2 is the structural surface 7.

[0073] For another example, during the manufacturing process of the DFB laser 100, a ridge waveguide 8 is formed by processing the second confinement layer 5 on the side away from the substrate 2. The ridge height of the ridge waveguide 8 is equal to the thickness of the second confinement layer 5. In this case, there is no remaining part of the second confinement layer 5 below the ridge waveguide 8, and the structure surface 7, i.e., the surface of the active layer 4 away from the substrate 2.

[0074] like Figure 6 and Figure 7 As shown, in this embodiment, part of the second confinement layer 5 still remains below the ridge waveguide 8 , and the structure surface 7 is the surface of the remaining part of the second confinement layer 5 below the ridge waveguide 8 that is away from the substrate 2 .

[0075] Please continue to refer to Figures 4 to 7 The DFB laser 100 also includes a feedback grating 1, which includes a first grating portion 1A and a second grating portion 1B respectively arranged on both sides of the ridge waveguide 8 along the ridge width direction (second direction). The feedback grating 1 realizes mode selection by acting on the evanescent field (also called evanescent field) of the light field in the active layer 4 located on both sides of the ridge waveguide 8 through the first grating portion 1A and the second grating portion 1B.

[0076] like Figures 4 to 7As shown, the feedback grating 1 includes a plurality of grating teeth 6 arranged in a first direction. The grating teeth 6 extend in a second direction and are separated by a ridge waveguide 8 into two sub-grating teeth 9. Each sub-grating tooth 9 includes a surface portion 91 and a sidewall portion 92 that are connected in the second direction. Among them, the surface portion 91 is distributed on the structure surface 7, and the sidewall portion 92 is distributed on the sidewall 81 of the ridge waveguide 8.

[0077] In this article, the height of the surface portion 91 relative to the structure surface 7 is defined as the first height, the height of the sidewall portion 92 relative to the sidewall 81 is defined as the second height, and the height of the ridge waveguide 8 relative to the structure surface 7 is defined as the third height. Among them, the first height is equal to or substantially equal to the second height, and both are less than or equal to 0.5 times the third height. Exemplarily, the first height and the second height can both be 0.5 times, 0.3 times, or 0.2 times the third height, etc. Such a design is beneficial to the processing of the grating teeth 6, can improve the etching footing phenomenon generated when etching the grating teeth 6, and can also make the action position of the grating teeth 6 as close as possible to the active layer 4, improving the coupling efficiency with the active layer 4.

[0078] Please continue to refer to Figures 4 to 7 , the two sub-grating teeth 9 in the grating teeth 6 are symmetrically arranged with respect to the waveguide center plane of the ridge waveguide 8. Combining the above description, it can be seen that the first grating portion 1A includes the sub-grating teeth 9 on one side of the ridge waveguide 8 in the ridge width direction (parallel to the second direction), and the second grating portion 1B includes the sub-grating teeth 9 on the other side of the ridge waveguide 8 in the ridge width direction (parallel to the second direction). The first grating portion 1A and the second grating portion 1B are symmetrically arranged with respect to the waveguide center plane of the ridge waveguide 8.

[0079] For the convenience of describing the structure and working principle of the feedback grating 1, the grating parameters related to the feedback grating 1 are defined and described in this article. Among them, the extension length of the grating teeth 6 in the second direction is the grating tooth length. From the above description, it can be seen that in this embodiment, the grating tooth length of the grating teeth 6 includes the sum of the extension distances of the two sub-grating teeth 9 in the second direction. The extension distance of each sub-grating tooth 9 in the second direction includes the extension distance of the surface portion 91 in the second direction and the extension distance of the sidewall portion 92 in the second direction.

[0080] The extension distance of the grating teeth 6 in the first direction is the grating tooth width, the distance between two adjacent grating teeth 6 in the first direction is the grating period, and the ratio of the grating tooth width to the grating period is the duty cycle.

[0081] And, for the convenience of describing the size and position relationship of the grating teeth 6 in the feedback grating 1, based on the top view of the feedback grating 1 and with reference to the X-Y coordinate system, a layout schematic diagram of the feedback grating 1 as shown in Figure 8 is formed;Figure 8 The X-axis therein is parallel to the first direction, and the Y-axis is parallel to the second direction; the central position of the feedback grating 1 in the first direction is at the position of x = 0, that is, the position where the Y-axis is located. The first grating portion 1A and the second grating portion 1B in the feedback grating 1 are respectively located on both sides of the X-axis, and Figure 8 In Figure 8 , ignoring the ridge waveguide 8, the sub-grating teeth 9 in the first grating portion 1A and the second grating portion 1B are moved along the second direction, so that the ends of the sub-grating teeth 9 close to the waveguide center plane are flush with the X-axis (y = 0).

[0082] As Figure 8 shown, the grating teeth 6 in the feedback grating 1 are arranged to form a Bragg grating and a phase-shift grating 11 inserted in the Bragg grating. Among them, the Bragg grating is a uniform Bragg grating with equal grating periods in the first direction, and the grating tooth widths of different grating teeth 6 in the Bragg grating are equal. From this, it can also be seen that the duty cycles of the Bragg grating at different positions in the first direction are also equal. In addition, the Bragg grating can be a grating structure of different orders such as the first order and the third order. The feedback grating 1 provided in the embodiment of the present application does not limit the order of the Bragg grating.

[0083] Please continue to refer to Figure 8 , the Bragg grating includes two connecting gratings 14 respectively arranged on both sides of the phase-shift grating 11. Each connecting grating 14 includes a chirped grating 12 and a uniform grating 13 connected in the first direction. The uniform grating 13 is farther from the phase-shift grating 11 than the chirped grating 12, and the chirped grating 12 is located between the uniform grating 13 and the phase-shift grating 11. The grating period, grating tooth width, and duty cycle of the uniform grating 13 are equal in the first direction, and the grating tooth lengths of different grating teeth 6 are also equal. The difference between the chirped grating 12 and the uniform grating 13 lies in the grating tooth length of the grating teeth 6.

[0084] In this article, the grating tooth length of the grating teeth 6 in the chirped grating 12 is defined as the first length, and the grating tooth length of the grating teeth 6 in the uniform grating 13 is defined as the second length. Through the above description, it can be known that the first lengths of different grating teeth 6 in the uniform grating 13 are equal; for the chirped grating 12, in the process of approaching the phase-shift grating 11 from the uniform grating 13 along the first direction, the first length shows a characteristic of gradually decreasing relative to the second length.

[0085] In the two connected gratings 14 respectively located on both sides of the phase-shift grating 11, the two uniform gratings 13 located on both sides of the phase-shift grating 11 have the same structure, that is, the grating parameters such as the grating period, the grating tooth width and the duty cycle are the same. The two chirped gratings 12 located on both sides of the phase-shift grating 11 are symmetrically arranged relative to the phase-shift grating 11 in the first direction. That is to say, in the two chirped gratings 12 respectively located on both sides of the phase-shift grating 11, the first length has the same variation characteristics relative to the phase-shift grating 11.

[0086] In the feedback grating 1, the phase shift grating 11 can be inserted at the center position of the Bragg grating in the first direction (ridge length direction) or at a non-center position to achieve a certain degree of phase change; illustratively, the phase shift grating 11 can be a λ / 4, λ / 8 or λ phase shift grating, wherein λ is the Bragg wavelength of the Bragg grating in the feedback grating 1. In this paper, the grating tooth widths of the grating teeth 6 in the chirped grating 12 and the uniform grating 13 are defined as the first width and the second width, respectively, and the grating tooth width of the phase shift grating 11 is defined as the third width; the first width and the second width are equal and both smaller than the third width; the size of the third width is related to the amount of phase change that the phase shift grating 11 needs to achieve.

[0087] like Figure 8 As shown, in this embodiment, the phase shift grating 11 is a λ / 4 phase shift grating, the third width is twice the first width; and the phase shift grating 11 is inserted into the center position of the Bragg grating in the first direction (ridge length direction), that is, Figure 8 The position of the intersection of the X-axis and the Y-axis.

[0088] The grating tooth length of the phase-shift grating 11 is defined as the third length herein. In the present embodiment, the third length is less than the second length and less than the minimum value of the first length in the chirped grating 12. That is, in the process of approaching the phase-shift grating 11 from the uniform grating 13 along the first direction, the first length in the chirped grating 12 presents a characteristic of gradually decreasing from the second length to the third length. From another perspective, in the process of approaching the uniform grating 13 from the phase-shift grating 11 along the first direction, the first length in the chirped grating 12 presents a characteristic of gradually increasing from the third length to the second length.

[0089] For the feedback grating 1, the grating tooth length affects the overlap integral of the evanescent field and the optical field of the feedback grating 1, and the overlap integral of the optical field is positively correlated with the grating coupling coefficient (Kappa). The grating coupling coefficient is used to represent the coupling strength of the grating to the optical field. The larger the grating coupling coefficient, the more conducive to the concentration of the optical field; the smaller the grating coupling coefficient, the less conducive to the concentration of the optical field. Therefore, the longer the grating tooth length in the evanescent field, the larger the overlap integral of the optical field, the larger the grating coupling coefficient, and the more conducive to the concentration of the optical field; the smaller the grating tooth length in the evanescent field, the smaller the overlap integral of the optical field, the smaller the grating coupling coefficient, and the less conducive to the concentration of the optical field.

[0090] According to the above description, in the feedback grating 1 with the above design, the third length of the phase-shifted grating 11 is less than the first length of the chirped grating 12, and the first length of the chirped grating 12 is less than the second length of the uniform grating 13; and, in the process of moving from the phase-shifted grating 11 towards the uniform grating 13 along the first direction, the first length in the chirped grating 12 shows a characteristic of gradually increasing from the third length to the second length. Such a design can make the overlap integral of the optical field between the chirped grating 12 and the evanescent field less than the overlap integral of the optical field between the uniform grating 13 and the evanescent field, and in the process of moving from the phase-shifted grating 11 towards the uniform grating 13 along the first direction, the overlap integral of the optical field between the chirped grating 12 and the evanescent field shows a characteristic of gradually increasing; therefore, in the feedback grating 1, the grating coupling coefficient of the uniform grating 13 is greater than the grating coupling coefficient of the chirped grating 12; and in the process of moving from the phase-shifted grating 11 towards the uniform grating 13 along the first direction, the grating coupling coefficient of the chirped grating 12 also shows a characteristic of gradually increasing; thus realizing the chirping of the grating coupling coefficient in the chirped grating 12. The above change characteristic of the grating coupling coefficient in the chirped grating 12 can improve the concentrated distribution of the longitudinal optical field at the position of the phase-shifted grating 11, enhance the uniformity of the longitudinal optical field distribution, can effectively suppress the longitudinal spatial hole burning effect, is conducive to realizing linear, stable single longitudinal mode, low noise and narrow linewidth laser output, and improves the performance of the DFB laser 100.

[0091] And the above structure is applicable to the application scenario of a straight waveguide, can improve problems such as the output port tilt caused by the chirping scheme of the curved waveguide, the large divergence angle of the output beam, and the influence on the output spot, and is conducive to improving the coupling efficiency with the optical fiber. In addition, compared with the feedback grating 1 fabricated by using the reconstruction-equivalent chirping technology, the feedback grating 1 in this embodiment has a larger feedback intensity due to the smaller number of chirped gratings and without reducing the total number of gratings.

[0092] In the feedback grating 1 with the above design, the variation of the first length of the chirped grating 12 in the first direction can be a stepped variation or a continuous variation. Here, the stepped variation means that the grating teeth 6 in the chirped grating 12 are divided into multiple groups of grating teeth in the first direction, and each group of grating teeth includes at least two adjacent grating teeth 6 in the first direction; the first lengths of the grating teeth 6 in the same group of grating teeth are equal, the first lengths between different groups of grating teeth 6 are not equal, and it follows that in the process of approaching the uniform grating 13 from the phase-shifted grating 11 along the first direction, the first length in the chirped grating 12 shows a characteristic of gradually increasing from the third length to the second length. The continuous variation means that the first lengths of the grating teeth 6 in the chirped grating 12 are all different, and in the process of approaching the uniform grating 13 from the phase-shifted grating 11 along the first direction, the first length in the chirped grating 12 shows a characteristic of gradually increasing from the third length to the second length.

[0093] In this embodiment, the first length in the chirped grating 12 varies continuously in the first direction, and in the process of approaching the uniform grating 13 from the phase-shifted grating 11 along the first direction, the first length gradually increases between the third length and the second length according to a linear (first-order) chirp function.

[0094] Exemplarily, as Figure 8 shown, in the first grating portion 1A (or the second grating portion 1B) of the feedback grating 1, the extension distance of the sub-grating teeth 9 in the uniform grating 13 along the second direction (Y coordinate axis) is a, the extension distance of the sub-grating teeth 9 in the phase-shifted grating 11 along the second direction (Y coordinate axis) is 0.2a, and the extension distance of the sub-grating teeth 9 in the chirped grating 12 along the second direction (Y coordinate axis) is a cg , a cg satisfies the following formula:

[0095]

[0096] In the above formula 1, x is the coordinate value of the sub-grating teeth 9 in the chirped grating 12 on the X coordinate axis; L is used to represent the chirp length of the chirped grating 12, which is the distance between the end of the chirped grating 12 far from the Y coordinate axis and the Y coordinate axis.

[0097] Since the first grating portion 1A and the second grating portion 1B in the feedback grating 1 are symmetric with respect to the waveguide center plane, that is, symmetric with respect to the X coordinate axis, the second length of the uniform grating 13 in the feedback grating 1 is 2a, the third length of the phase-shifted grating 11 is 0.4a, and the first length of the chirped grating 12 is 2a cg ; in the case where a cg in the first grating portion 1A (or the second grating portion 1B) satisfies the above formula 1, the first length 2a cgGradually increases between the third length (0.4a) and the second length (2a) according to a linear chirp function.

[0098] For the feedback grating 1 with the above design, experiments were carried out for different chirp lengths L respectively, and the longitudinal optical field distribution curves as shown in Figure 9 were obtained. Figure 9 In which M represents the ratio of the chirp length L in the feedback grating 1 to the length of the feedback grating 1 in the first direction. It can be seen from Figure 9 that when M is 0, that is, when the chirp length is 0, which means there is no chirped grating 12, the distribution of the longitudinal optical field at the position of the phase shift grating 11 (the abscissa is 0.5) is relatively concentrated, and there is a relatively large peak; as M increases, that is, the proportion of the chirp length increases, the distribution of the longitudinal optical field gradually becomes uniform, and the peak at the position of the phase shift grating 11 gradually decreases. It can be seen from the results shown in Figure 9 that by designing the first length of the chirped grating 12 to change according to a linear chirp function along the first direction, the concentration of the longitudinal optical field distribution at the position of the phase shift grating 11 can be improved, and the occurrence of the longitudinal spatial hole burning effect can be suppressed.

[0099] The embodiment of the present application also provides another DFB laser. The difference between the feedback grating 1 of this DFB laser and the feedback grating 1 in the above embodiment is that: the first length in the chirped grating 12 changes continuously in the first direction, and when moving from the phase shift grating 11 to the uniform grating 13 along the first direction, the first length gradually increases between the third length and the second length according to a quadratic chirp function.

[0100] Exemplarily, as shown in Figure 8 , in the first grating part 1A (or the second grating part 1B) of the feedback grating 1, the extension distance of the sub-grating teeth 9 in the uniform grating 13 along the second direction (Y coordinate axis) is a, the extension distance of the sub-grating teeth 9 in the phase shift grating 11 along the second direction (Y coordinate axis) is 0.2a, and the extension distance of the sub-grating teeth 9 in the chirped grating 12 along the second direction (Y coordinate axis) is a cg , a cg satisfies the following formula:

[0101]

[0102] In the above formula 2, x is the coordinate value of the sub-grating teeth 9 in the chirped grating 12 on the X coordinate axis; L is used to represent the chirp length of the chirped grating 12, which is the distance between the end of the chirped grating 12 far from the Y coordinate axis and the Y coordinate axis.

[0103] Since the first grating portion 1A and the second grating portion 1B in the feedback grating 1 are symmetric with respect to the waveguide center plane, that is, symmetric with respect to the X coordinate axis, the second length of the uniform grating 13 in the feedback grating 1 is 2a, the third length of the phase shift grating 11 is 0.4a, and the first length in the chirped grating 12 is 2a cg ; a in the first grating portion 1A (or the second grating portion 1B) cg When satisfying the above formula 2, the first length 2a cg Gradually increases between the third length (0.4a) and the second length (2a) according to the quadratic chirp function.

[0104] For the feedback grating 1 adopting the above design, experiments are carried out for different chirp lengths L respectively, and the longitudinal optical field distribution curves as shown in Figure 10 are obtained. Figure 10 In the figure, M represents the ratio of the chirp length L in the feedback grating 1 to the length of the feedback grating 1 in the first direction. It can be seen from Figure 10 the figure that when M is 0, that is, when the chirp length is 0, which means there is no chirped grating 12, the distribution of the longitudinal optical field is relatively concentrated at the position of the phase shift grating 11 (the abscissa is 0.5), and there is a relatively large peak; as M increases, that is, the proportion of the chirp length increases, the distribution of the longitudinal optical field gradually becomes uniform, and the peak at the position of the phase shift grating 11 gradually decreases. And when M = 0.3, the peak of the longitudinal optical field distribution curve disappears at the position of the phase shift grating 11. It can be seen from Figure 10 the results shown in the figure that by designing the first length of the chirped grating 12 to change according to the quadratic chirp function along the first direction, the concentration of the longitudinal optical field distribution at the position of the phase shift grating 11 can be improved, and the occurrence of the longitudinal spatial hole burning effect can be suppressed.

[0105] By comparison Figure 9 and Figure 10 it can be seen that the feedback grating 1 adopting formula 2 has a more obvious improvement effect on the concentrated distribution of the longitudinal optical field than the feedback grating 1 adopting formula 1.

[0106] The embodiment of the present application also provides another DFB laser. The difference between the feedback grating 1 of this DFB laser and the feedback grating 1 in the above embodiment is that: the first length in the chirped grating 12 changes continuously in the first direction, and when approaching the uniform grating 13 from the phase shift grating 11 along the first direction, the first length gradually increases between the third length and the second length according to the Gaussian chirp function.

[0107] Exemplarily, as shown in Figure 8As shown, in the first grating portion 1A (or the second grating portion 1B) of the feedback grating 1, the extension distance of the sub-grating teeth 9 in the uniform grating 13 along the second direction (Y coordinate axis) is a, the extension distance of the sub-grating teeth 9 in the phase-shift grating 11 along the second direction (Y coordinate axis) is 0.2a, and the extension distance of the sub-grating teeth 9 in the chirped grating 12 along the second direction (Y coordinate axis) is a cg , a cg satisfies the following formula:

[0108]

[0109] In the above formula 3, x is the coordinate value of the sub-grating teeth 9 in the chirped grating 12 on the X coordinate axis; L is used to represent the chirp length of the chirped grating 12, which is the distance between the end of the chirped grating 12 far from the Y coordinate axis and the Y coordinate axis.

[0110] Since the first grating portion 1A and the second grating portion 1B in the feedback grating 1 are symmetric with respect to the waveguide center plane, that is, symmetric with respect to the X coordinate axis, the second length of the uniform grating 13 in the feedback grating 1 is 2a, the third length of the phase-shift grating 11 is 0.4a, and the first length in the chirped grating 12 is 2a cg ; a in the first grating portion 1A (or the second grating portion 1B) cg When satisfying the above formula 3, the first length 2a cg gradually increases between the third length (0.4a) and the second length (2a) according to the Gaussian chirp function.

[0111] For the feedback grating 1 with the above design, experiments are carried out for different chirp lengths L respectively, and the longitudinal optical field distribution curves as shown in Figure 11 are obtained, Figure 11 where M represents the ratio of the chirp length L in the feedback grating 1 to the length of the feedback grating 1 in the first direction. It can be seen from Figure 11 that when M is 0, that is, when the chirp length is 0, that is, when there is no chirped grating 12, the distribution of the longitudinal optical field is relatively concentrated at the position of the phase-shift grating 11 (the abscissa is 0.5), and there is a relatively large peak; as M increases, that is, the proportion of the chirp length increases, the distribution of the longitudinal optical field gradually becomes uniform, and the peak at the position of the phase-shift grating 11 gradually decreases. It can be seen from the results shown in Figure 11 that by designing the first length of the chirped grating 12 to change according to the Gaussian chirp function along the first direction, the concentration of the longitudinal optical field distribution at the position of the phase-shift grating 11 can be improved, and the occurrence of the longitudinal spatial hole burning effect can be suppressed.

[0112] In the above embodiments, by designing the first length of the chirped grating 12 to vary in the first direction, the chirping of the grating coupling coefficient is achieved, thereby improving the concentrated distribution of the longitudinal optical field at the position where the phase shift grating 11 is located and suppressing the occurrence of the longitudinal spatial hole burning effect. However, the embodiments of the present application are not limited thereto.

[0113] For the feedback grating 1, the duty cycle also affects the grating coupling coefficient. The relationship between the duty cycle and the grating coupling coefficient is relatively complex. The value range of the duty cycle is from 0 to 1. There is a value n in the value range of the duty cycle from 0 to 1. n can be 0.5, 0.8, etc. The n values of the feedback grating 1 in different DFB lasers 100 may be different, but generally not less than 0.5. When the duty cycle gradually increases from 0 towards n, the grating coupling coefficient gradually increases from small; when the duty cycle gradually decreases from 1 towards n, the grating coupling coefficient also gradually increases from small; that is to say, when the duty cycle is n, the corresponding grating coupling coefficient is the largest, and when the duty cycle gradually changes from n to both sides, the grating coupling coefficient gradually decreases.

[0114] Based on this, the embodiments of the present application provide another DFB laser, as Figure 12 shown. The difference between the DFB laser 100 provided in this embodiment and the DFB laser 100 in the above embodiment lies in the chirped grating 12 and the phase shift grating 11 in the feedback grating 1. In this embodiment, the grating tooth lengths of different grating teeth 6 in the chirped grating 12 are equal, and are equal to the grating tooth lengths of the grating teeth 6 in the phase shift grating 11 and the uniform grating 13. The difference between the chirped grating 12 and the uniform grating 13 lies in the duty cycle, that is, the grating tooth width of the grating tooth 6. In this article, the duty cycle in the chirped grating 12 is defined as the first duty cycle, and the duty cycle in the uniform grating 13 is defined as the second duty cycle; the first duty cycle and the second duty cycle are not equal, and the corresponding grating coupling coefficients are not equal.

[0115] In this embodiment, by designing the grating tooth width of the grating tooth 6 in the chirped grating 12, the first duty cycle gradually changes towards the second duty cycle in the process of the chirped grating 12 approaching the uniform grating 13 along the first direction from the phase shift grating 11, so as to achieve that in the process of the chirped grating 12 approaching the uniform grating 13 along the first direction from the phase shift grating 11, the grating coupling coefficient gradually becomes larger towards the grating coupling coefficient of the uniform grating 13, and the maximum value of the grating coupling coefficient in the chirped grating 12 is less than or equal to the grating coupling coefficient of the uniform grating 13. The above-mentioned chirping change of the grating coupling coefficient in the chirped grating 12 can improve the concentrated distribution of the longitudinal optical field at the position where the phase shift grating 11 is located, enhance the uniformity of the longitudinal optical field distribution, suppress the occurrence of the spatial hole burning effect, and improve the performance of the DFB laser 100; and it also has advantages such as good coupling effect with the optical fiber and high feedback intensity.

[0116] As described above regarding the relationship between the duty cycle and the grating coupling coefficient, during the process of the self-phase shift grating 11 approaching the uniform grating 13 along the first direction, the gradual change of the first duty cycle to the second duty cycle can gradually increase or gradually decrease. The way of its gradual increase or gradual decrease can be arbitrary. Exemplarily, referring to the description of the first length change mode above, the first duty cycle can be changed according to a linear chirp function, a quadratic chirp function, or a Gaussian chirp function. Since gratings with a smaller duty cycle are easier to fabricate than those with a larger duty cycle, the first duty cycle usually approaches the second duty cycle in a gradually increasing manner.

[0117] For the feedback grating 1, since the grating tooth 6 includes a surface portion 91 and a sidewall portion 92 connected in the second direction, the surface portion 91 is located on the structural surface 7, and the sidewall portion 92 is located on the sidewall 81 of the ridge waveguide 8; therefore, in the case where the ridge waveguide 8 is a non-uniform cross-section structure along the first direction, the waveguide width of the ridge waveguide 8 will affect the position of the grating tooth 6 in the feedback grating 1, thereby affecting the optical field overlap integral between the feedback grating 1 and the evanescent field, so as to change the grating coupling coefficient and achieve the chirp change of the grating coupling coefficient in the first direction. Here, the waveguide width of the ridge waveguide 8 is the extension distance of the ridge waveguide 8 in the second direction. Since the waveguide width of the ridge waveguide 8 may be different at different heights relative to the structural surface 7. When describing the influence of the ridge waveguide 8 on the arrangement position of the grating teeth 6, the waveguide width can be selected as the value at any height, as long as the value at the same height is always used as the object during the description.

[0118] Based on this, the embodiment of the present application provides another DFB laser, as Figure 13 shown, the difference between the DFB laser 100 provided in this embodiment and the Figure 8 DFB laser 100 lies in the feedback grating 1 and the ridge waveguide 8; in this embodiment, the grating tooth lengths of different grating teeth 6 in the chirp grating 12 are equal, and are equal to the grating tooth lengths of the grating teeth 6 in the phase shift grating 11 and the uniform grating 13. The duty cycles and the grating tooth widths of the grating teeth 6 of the chirp grating 12 and the uniform grating 13 are also equal. The ridge waveguide 8 is a non-uniform cross-section structure along the first direction. In this article, the parts of the ridge waveguide 8 corresponding to the chirp grating 12, the uniform grating 13, and the phase shift grating 11 are respectively defined as the first waveguide part, the second waveguide part, and the third waveguide part; the waveguide widths of the first waveguide part, the second waveguide part, and the third waveguide part are respectively the first waveguide width, the second waveguide width, and the third waveguide width. Based on the above description, the first waveguide width, the second waveguide width, and the third waveguide width are respectively the values of the first waveguide part, the second waveguide part, and the third waveguide part at the same height relative to the structural surface 7.

[0119] At different positions of the second waveguide portion along the first direction, the widths of the second waveguides are equal and smaller than the width of the third waveguide; when the first waveguide portion approaches the third waveguide portion along the first direction from the second waveguide portion, the width of the first waveguide gradually increases between the width of the second waveguide and the width of the third waveguide. The way of gradual increase here can be arbitrary. Exemplarily, reference can be made to the description of the first length change method above, and the width of the first waveguide can be changed according to a linear chirp function, a quadratic chirp function, or a Gaussian chirp function.

[0120] The above-mentioned characteristic that the width of the first waveguide gradually increases makes the optical field overlap integral between the chirped grating 12 and the evanescent field smaller than that between the uniform grating 13 and the evanescent field, and gradually decreases during the process of approaching the phase-shifted grating 11 from the uniform grating 13 along the first direction; thus, during the process of approaching the uniform grating 13 from the phase-shifted grating 11 along the first direction, the grating coupling coefficient of the chirped grating 12 shows a characteristic of gradually increasing, and the maximum value of the grating coupling coefficient of the chirped grating 12 is less than or equal to the grating coupling coefficient of the uniform grating 13; thus, the chirp of the grating coupling coefficient in the chirped grating 12 is realized. The above-mentioned change characteristic of the grating coupling coefficient in the chirped grating 12 can improve the concentrated distribution of the longitudinal optical field at the position where the phase-shifted grating 11 is located, enhance the uniformity of the longitudinal optical field distribution, effectively suppress the occurrence of the longitudinal spatial hole burning effect, and improve the performance of the DFB laser 100; and it also has advantages such as good coupling effect with the optical fiber and high feedback intensity.

[0121] In the above embodiments, by adjusting the grating tooth length, duty cycle, or the waveguide width of the ridge waveguide 8 respectively, while keeping the two ends of the DFB laser 100 as straight waveguides, the chirp of the grating coupling coefficient of the chirped grating 12 is realized, thereby improving the concentrated distribution of the longitudinal optical field at the position where the phase-shifted grating 11 is located, enhancing the uniformity of the longitudinal optical field distribution, and being able to suppress and avoid the occurrence of the longitudinal spatial hole burning effect, and improving the performance of the DFB laser 100; and the feedback intensity is relatively high. In some embodiments, the feedback grating 1 in the DFB laser 100 can further improve the above technical effects by simultaneously adjusting at least two of the grating tooth length, duty cycle, and the waveguide width of the ridge waveguide 8.

[0122] It can be seen from this that in the DFB laser 100 provided in the embodiments of the present application, there are many ways to achieve the above technical effects, and the design freedom is relatively high.

[0123] In the above embodiments, the cross-sectional shape of the ridge waveguide 8 in the cross-section perpendicular to the first direction is an isosceles trapezoid and a regular trapezoid. The grating teeth 6 of the feedback grating 1 include a surface portion 91 and a sidewall portion 92 connected in the second direction; wherein, the surface portion 91 is distributed on the structure surface 7, and the sidewall portion 92 is distributed on the sidewall 81 of the ridge waveguide 8. Moreover, the height of the surface portion 91 relative to the structure surface 7 and the height of the sidewall portion 92 relative to the sidewall 81 are both less than or equal to 0.5 times the height of the ridge waveguide 8 relative to the structure surface 7. However, the DFB laser 100 provided in the embodiments of the present application is not limited thereto. When the cross-sectional shape of the ridge waveguide 8 in the cross-section perpendicular to the first direction is an isosceles trapezoid and an inverted trapezoid, and when the cross-sectional shape is a rectangle and a square, the grating teeth 6 of the feedback grating 1 only include the surface portion 91 distributed on the structure surface 7, and the height of the surface portion 91 relative to the structure surface 7 is less than or equal to 0.5 times the height of the ridge waveguide 8 relative to the structure surface 7. Moreover, in the positive projection onto the structure surface 7, the end of the surface portion 91 close to the ridge waveguide 8 is in contact with the ridge waveguide 8 or has a fixed spacing. In such a case, the grating coupling coefficient chirp of the chirped grating 12 can still be achieved by adjusting at least one parameter among the grating tooth length, duty cycle, or waveguide width of the ridge waveguide 8, so as to achieve the same technical effects as those in the above embodiments.

[0124] The above structural features of the feedback grating 1 are related to the manufacturing method of the feedback grating 1. In the DFB laser 100 provided in the embodiments of the present application, the feedback grating 1 and the ridge waveguide 8 are manufactured separately, that is, after the ridge waveguide 8 is manufactured, the feedback grating 1 is manufactured. With such a design, on the one hand, decoupling between the ridge waveguide 8 and the feedback grating 1 can be achieved, and both the ridge waveguide 8 and the feedback grating 1 are non-buried structures, which is beneficial for subsequent adjustment. The design is more flexible and has a high degree of freedom. On the other hand, the manufacturing of the DFB laser 100 only requires one epitaxial process to manufacture the epitaxial structure including the active layer 4, reducing the process difficulty and manufacturing cost.

[0125] The manufacturing method of the feedback grating 1 can include the following two types. The first type is to remanufacture the material film layer and then remove part of the material film layer according to the pattern of the feedback grating 1 to form the feedback grating 1; in this article, such a feedback grating 1 is defined as a coupled grating. The second type is to etch an existing structure to form the feedback grating 1, and in this article, such a feedback grating 1 is defined as an etched grating.

[0126] For the case where the feedback grating 1 is a coupled grating, the material of the feedback grating 1 may include a metal or an optical dielectric material. Among them, the metal may be chromium (Cr), and the optical dielectric material may be amorphous silicon, silicon nitride, etc. It should be noted that when the feedback grating 1 is a coupled grating and the sub-grating teeth 9 include a surface portion 91 and a sidewall portion 92, the surface portion 91 is away from the substrate 2 relative to the structural surface 7, and due to the different materials between the surface portion 91 and the structural surface 7, there is a material interface; the sidewall portion 92 is away from the ridge waveguide 8 relative to the sidewall 81 of the ridge waveguide 8, and due to the different materials between the sidewall portion 92 and the ridge waveguide 8, there is a material interface. The coupled grating can be applicable to the cases where the structural surface 7 is the structural surface 7 of the active layer 4 and the structural surface 7 of the second confinement layer 5.

[0127] For the case where the feedback grating 1 is an etched grating, the material of the feedback grating 1 includes the same material as that of the etched structure; and in order to avoid affecting the function of the active layer 4 by etching the active layer 4, it is only applicable to the case where the structural surface 7 is the structural surface 7 of the second confinement layer 5. When the feedback grating 1 is an etched grating and the sub-grating teeth 9 include a surface portion 91 and a sidewall portion 92, the surface portion 91 is close to the substrate 2 relative to the structural surface 7. At this time, the height of the surface portion 91 relative to the structural surface 7 is also the distance relative to the structural surface 7 in the direction perpendicular to the structural surface 7. Since the surface portion 91 and the structural surface 7 contain the same material, there may be no obvious material interface. The sidewall portion 92 is close to the ridge waveguide 8 relative to the sidewall 81 of the ridge waveguide 8. At this time, the height of the sidewall portion 92 relative to the sidewall 81 is also the distance relative to the sidewall 81 in the direction perpendicular to the sidewall 81. Since the sidewall portion 92 and the ridge waveguide 8 contain the same material, there may be no obvious material interface.

[0128] In the above embodiments, the case where the feedback grating 1 includes a phase shift grating 11 is taken as an example to illustrate the solution. However, the embodiments of the present application are not limited thereto. In some embodiments, two or more phase shift gratings 11 may be provided in the feedback grating 1, and the above design is adopted on both sides of at least one phase shift grating 11.

[0129] In the above embodiments, the chirped gratings 12 located on both sides of the phase shift grating 11 are symmetrically arranged relative to the phase shift grating 11 in the first direction. Such a design can make the grating coupling coefficient chirp on both sides of the phase shift grating 11 the same, which is beneficial to improving the improvement effect of the longitudinal optical field distribution uniformity in the region where the phase shift grating 11 is located. However, in some embodiments, the chirped gratings 12 located on both sides of the phase shift grating 11 are asymmetrically arranged relative to the phase shift grating 11 in the first direction. Such a design can make the longitudinal optical field distribution deviate to one side of the phase shift grating 11, which is beneficial to improving the output efficiency of the DFB laser.

[0130] The DFB laser 100 provided by the embodiment of the present application further includes a first electrode layer and a second electrode layer. The first electrode layer is disposed on the side of the substrate 2 away from the first confinement layer 3, and the second electrode layer is disposed on the side of the ridge waveguide 8 away from the active layer 4. The first electrode layer and the second electrode layer are used to be connected to a power supply, and electrical pumping of the DFB laser 100 can be achieved through the first electrode layer and the second electrode layer.

[0131] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A distributed feedback laser, characterized in that, It includes a ridge waveguide, a structural surface, and a feedback grating. The ridge length direction of the ridge waveguide is parallel to the first direction, the ridge width direction is parallel to the second direction, and the ridge height direction is parallel to the third direction; and it is a waveguide structure symmetric with respect to the waveguide center plane. Among them, the first direction, the second direction, and the third direction are perpendicular to each other in pairs, and the waveguide center plane is parallel to the first direction and the third direction. The ridge waveguide includes two side walls oppositely arranged in the second direction. The structural surface is perpendicular to the waveguide center plane and is connected to the bottom ends of the side walls in the third direction. The feedback grating includes a plurality of grating teeth arranged along the first direction. The grating teeth include two sub-grating teeth located on both sides of the waveguide center plane and symmetrically arranged with respect to the waveguide center plane. The sub-grating teeth include a surface portion in contact with the structural surface, and the distance of the surface portion in the third direction is less than or equal to 0.5 times the ridge height of the ridge waveguide. The grating teeth in the feedback grating are arranged to form a Bragg grating and a phase-shifted grating inserted into the Bragg grating. The Bragg grating includes two connecting gratings respectively located on both sides of the phase-shifted grating. The connecting grating includes a chirped grating and a uniform grating connected in the first direction, and the uniform grating is farther from the phase-shifted grating than the chirped grating. The length of the grating teeth of the chirped grating in the second direction is the first length, and the duty cycle is the first duty cycle; the distance of the corresponding part of the ridge waveguide and the chirped grating in the second direction is the first waveguide width; when moving along the first direction from the phase-shifted grating towards the uniform grating, at least one of the first length, the first duty cycle, and the first waveguide width gradually changes to realize the gradual increase of the grating coupling coefficient of the chirped grating, and the maximum value of the grating coupling coefficient of the chirped grating is less than or equal to the grating coupling coefficient of the connected uniform grating.

2. The distributed feedback laser according to claim 1, wherein The lengths of the grating teeth of the uniform grating and the phase-shifted grating in the second direction are the second length and the third length respectively, and the second length is greater than the third length. When moving along the first direction from the phase-shifted grating towards the uniform grating, the first length gradually increases between the third length and the second length according to a linear chirp function, a quadratic chirp function, or a Gaussian-type chirp function.

3. The distributed feedback laser according to claim 1, characterized in that, The duty cycle of the uniform grating is the second duty cycle. When moving along the first direction from the phase-shifted grating towards the uniform grating, the first duty cycle gradually changes with respect to the second duty cycle according to a linear chirp function, a quadratic chirp function, or a Gaussian-type chirp function.

4. The distributed feedback laser according to claim 1, characterized in that, In the second direction, the distances of the corresponding parts of the ridge waveguide and the uniform grating and the phase-shifted grating are the second waveguide width and the third waveguide width respectively; the third waveguide width is greater than the second waveguide width. When moving from the phase-shift grating towards the uniform grating along the first direction, the width of the first waveguide gradually decreases between the third waveguide width and the second waveguide width according to a linear chirp function, a quadratic chirp function, or a Gaussian chirp function.

5. The distributed feedback laser according to any one of claims 1 to 4, characterized in that, Both of the two connecting gratings located on both sides of the phase-shift grating in the Bragg grating include the chirped grating. In the first direction, the chirped gratings on both sides of the phase-shift grating are symmetrically arranged with respect to the phase-shift grating.

6. The distributed feedback laser according to any one of claims 1 to 5, characterized in that, The distributed feedback laser includes a substrate, a first confinement layer, an active layer, and a second confinement layer. The first confinement layer is disposed on one side of the substrate, the active layer is disposed on the side of the first confinement layer away from the substrate, and the second confinement layer is located on the side of the active layer away from the substrate. The second confinement layer includes the ridge waveguide, and the structural surface is the structural surface of the second confinement layer or the active layer. The material of the grating teeth in the feedback grating is different from the material of the ridge waveguide.

7. The distributed feedback laser according to any one of claims 1 to 5, characterized in that, The distributed feedback laser includes a substrate, a first confinement layer, an active layer, and a second confinement layer. The first confinement layer is disposed on one side of the substrate, the active layer is disposed on the side of the first confinement layer away from the substrate, and the second confinement layer is located on the side of the active layer away from the substrate. The second confinement layer includes the ridge waveguide, and the structural surface is the structural surface of the second confinement layer; the surface part of the sub-grating teeth is disposed in the second confinement layer.

8. The distributed feedback laser according to claim 6 or 7, characterized in that, In a cross-section perpendicular to the first direction, the cross-sectional shape of the ridge waveguide is an isosceles trapezoid, a square, or a rectangle; the isosceles trapezoid is a positive trapezoid or an inverted trapezoid with respect to the active layer.

9. The distributed feedback laser according to claim 7, wherein In a cross-section perpendicular to the first direction, the cross-sectional shape of the ridge waveguide is an isosceles trapezoid and is a positive trapezoid with respect to the active layer. The sub-grating teeth further include a sidewall part distributed on the sidewall of the ridge waveguide, and the surface part and the sidewall part are connected in the second direction. The distance of the sidewall part in the direction perpendicular to the sidewall is less than or equal to 0.5 times the distance of the ridge waveguide in the third direction.

10. The distributed feedback laser according to claim 7, wherein The material of the grating teeth is chromium, amorphous silicon, or silicon nitride.

11. The distributed feedback laser according to any one of claims 1 to 10, characterized in that, The Bragg grating is a first-order or third-order Bragg grating.

12. The distributed feedback laser according to any one of claims 1 to 11, characterized in that, The feedback grating includes at least two phase-shift gratings, and connecting gratings are disposed on both sides of at least one of the phase-shift gratings.

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