Single-frequency distributed feedback semiconductor laser and method for manufacturing the same

Abstract

The application provides a single-frequency distributed feedback semiconductor laser and a preparation method thereof, and relates to the technical field of lasers. The laser comprises an epitaxial structure, wherein the epitaxial structure comprises an active region, a grating layer and an upper P-side waveguide layer arranged in sequence along an epitaxial direction; along a cavity length direction, and from a high-reflection end to an anti-reflection end of the epitaxial structure, the epitaxial structure comprises a first longitudinal section, a second longitudinal section and a third longitudinal section; a λ / 4 phase shift region of the grating layer is located in the second longitudinal section; portions of the upper P-side waveguide layer located in the first longitudinal section, the second longitudinal section and the third longitudinal section are respectively set as a first portion, a second portion and a third portion; material compositions of the first portion, the second portion and the third portion are all different, and / or, thicknesses of the first portion, the second portion and the third portion are all different, so that a longitudinal optical confinement factor of the active region decreases from the high-reflection end to the anti-reflection end.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a single-frequency distributed feedback semiconductor laser and its fabrication method. Background Technology

[0002] Existing single-frequency distributed feedback (SRF) semiconductor lasers (ridge width 2-8 micrometers) exhibit enhanced coupling between optical field intensity distribution and thermal distribution along the cavity length under high power (>350mW), wide operating current (I>6Ith), or high temperature (>50℃) conditions. The peak intensity of the λ / 4 phase shift region square is typically 1.5-3 times higher than the average value, and the local optical power near the output end can reach 1.2-2.0 times the cavity average value. Especially near the output side, excessively high local optical power density and P-side absorption / heat accumulation are easily formed, which in turn leads to decreased single-mode stability, enhanced mode competition, fluctuations in side-mode suppression ratio (reduction of 5-15dB), and even a decrease in end-face reliability. Summary of the Invention

[0003] The purpose of this invention is to provide a single-frequency distributed feedback semiconductor laser and its fabrication method to reduce the optical field in the λ / 4 phase shift region.

[0004] In a first aspect, the present invention provides a single-frequency distributed feedback semiconductor laser, comprising: an epitaxial structure, the epitaxial structure comprising an active region, a grating layer and an upper P-side waveguide layer arranged sequentially along the epitaxial direction; Along the cavity length direction of the epitaxial structure, and from the high-reflection end to the anti-reflection end of the epitaxial structure, the epitaxial structure includes a first longitudinal segment, a second longitudinal segment, and a third longitudinal segment; the λ / 4 phase shift region of the grating layer is located in the second longitudinal segment; The portions of the upper P-side waveguide layer located in the first longitudinal section, the second longitudinal section, and the third longitudinal section are respectively designated as the first part, the second part, and the third part; the material composition of the first part, the second part, and the third part are all different, and / or the thickness of the first part, the second part, and the third part are all different, so that the longitudinal optical confinement factor of the active region decreases from the high reflection end to the anti-reflection end; And it satisfies: - (λ / 4) ; (λ / 4)- ; in, The equivalent refractive index of the first longitudinal segment; (λ / 4) is the equivalent refractive index of the second longitudinal section; The equivalent refractive index of the third longitudinal section.

[0005] Furthermore, a compensation layer is disposed between the active region and the grating layer, and the thickness of the compensation layer ranges from 100 nm. 300nm.

[0006] Furthermore, ;

[0007] in, This is the optical confinement factor of the active region in the first longitudinal segment. This is the optical confinement factor for the active region in the second longitudinal segment. It is the optical confinement factor of the active region in the third longitudinal segment.

[0008] Furthermore, the material compositions of the first, second, and third parts are all different; The material of the upper P-side waveguide layer is As or InP; The value range is 0.25. 0.45; The value range is 0.35. 0.65; The value range is 0.30 to 0.55; And it satisfies: ; .

[0009] Furthermore, the thicknesses of the first, second, and third parts are all different; The thickness values ​​of the first, second, and third parts are respectively , and ; The value range is 80 nm 150 nm; The value range is 40nm 100nm; The value range is 40 nm 100 nm; And it satisfies: - ≥20 nm; - ≥20 nm.

[0010] Furthermore, the upper P-side waveguide layer also includes a first transition portion connecting the first part and the second part; the first transition portion includes at least two first longitudinal transition stages arranged sequentially along the cavity length direction, the composition and / or thickness of two adjacent first longitudinal transition stages being different, so that the first part transitions to the second part in stages; or, the composition and / or thickness of the first transition portion changes continuously along the cavity length direction, so that the first part transitions to the second part continuously. And / or, the upper P-side waveguide layer further includes a second transition portion connecting the second part and the third part. The second transition portion includes at least two second longitudinal transition stages arranged sequentially along the cavity length direction. The composition and / or thickness of two adjacent second longitudinal transition stages are different, so that the second part transitions to the third part in stages; or, the composition and / or thickness of the second transition portion changes continuously along the cavity length direction, so that the second part transitions to the third part continuously.

[0011] Furthermore, κ HR Greater than κ λ / 4 κ λ / 4 Greater than κ AR ; Greater than ; Greater than , where κ HR κ λ / 4 and κ AR These are the grating coupling coefficients corresponding to the first, second, and third longitudinal sections, respectively.

[0012] Secondly, the present invention provides a method for fabricating a single-frequency distributed feedback semiconductor laser, the method being used to fabricate the aforementioned single-frequency distributed feedback semiconductor laser, comprising the following steps: Step S1. Provide an epitaxial base structure, the epitaxial base structure is grown to the grating layer, and the grating layer completes the fabrication of a single-frequency distributed feedback grating; Step S2. Along the cavity length direction of the epitaxial base structure, and from the high-reflection end to the anti-reflection end of the epitaxial base structure, the epitaxial base structure is divided into a first longitudinal segment, a second longitudinal segment, and a third longitudinal segment in sequence; and the λ / 4 phase shift region of the grating layer is located in the second longitudinal segment; The upper P-side waveguide layer is grown stepwise in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment, so that the portions of the upper P-side waveguide layer located in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment respectively form the first part, the second part, and the third part.

[0013] Furthermore, the specific steps for growing the upper P-side waveguide layer in the first, second, and third longitudinal segments include: Step S21. Using the first material, a first layer structure is grown on the epitaxial base structure. The first layer structure covers the first longitudinal section, the second longitudinal section and the third longitudinal section, and a single-frequency distributed feedback grating is embedded inside the first layer structure. Step S22. The first layer structure of one of the three longitudinal sections, the second longitudinal section and the third longitudinal section is masked, while the first layer structure of the other two is etched to a depth of L1 to form a first etch groove. Step S23. Use the second material to grow a second layer structure in the first etching trench, the height of the second layer structure being L2; Step S24. Mask the second layer structure of one of the two etched in step S22, and etch the second layer structure of the other to a depth of L3 to form a second etch groove. Step S25. Use a third material to grow a third layer structure in the second etching tank. The height of the third layer structure is L4. Step S26. Remove the obstruction; Wherein, at least two of the first material, the second material and the third material have different material compositions, and / or, L1 is not equal to L2, and / or, L3 is not equal to L4.

[0014] Furthermore, step S2 also includes the following steps: A first transition section is reserved between the first longitudinal section and the second longitudinal section; Along the direction from the first longitudinal segment to the second longitudinal segment, the first transition segment is etched in progressively deeper steps to obtain the first transition part in the form of a step. The number of steps in the first transition part is n, where n is an integer greater than 2. The first transition section is covered with growth materials of different compositions, and the composition of the growth material in each step of the first transition section is different. A second transition section is reserved between the second longitudinal section and the third longitudinal section; Along the direction from the second longitudinal segment to the third longitudinal segment, the second transition segment is etched in a progressively shallower manner to obtain the upper step-shaped second transition part. The number of steps in the second transition part is m, where m is an integer greater than 2. The second transition section is covered with growth materials of different compositions, and the composition of the growth material in each stage of the second transition section is different.

[0015] Furthermore, a compensation layer is provided between the active region and the grating layer, and the thickness of the compensation layer ranges from 100nm to 300nm. The fabrication method of a single-frequency distributed feedback semiconductor laser also includes the following steps: Step S31. Perform performance testing on the product prepared in step S2; Step S32. When the test results are not within the preset range, adjust the thickness and / or composition of the compensation layer until the product performance test results are within the preset range.

[0016] This invention has at least the following advantages or beneficial effects: This invention provides a single-frequency distributed feedback semiconductor laser, comprising: an epitaxial structure, the epitaxial structure including an active region, a grating layer, and an upper P-side waveguide layer sequentially arranged along the epitaxial direction; along the cavity length direction of the epitaxial structure, from the high-reflection end to the anti-reflection end, the epitaxial structure includes a first longitudinal segment, a second longitudinal segment, and a third longitudinal segment; the λ / 4 phase shift region of the grating layer is located in the second longitudinal segment; portions of the upper P-side waveguide layer located in the first, second, and third longitudinal segments are respectively designated as a first part, a second part, and a third part; the material composition of the first part, the second part, and the third part are all different, and / or the thickness of the first part, the second part, and the third part are all different, so that the longitudinal optical confinement factor of the active region decreases from the high-reflection end to the anti-reflection end; and satisfying: - (λ / 4) ; (λ / 4)- ; in, The equivalent refractive index of the first longitudinal segment; (λ / 4) is the equivalent refractive index of the second longitudinal section; The equivalent refractive index of the third longitudinal section.

[0017] In this embodiment, by adjusting the material composition and thickness of the first, second, and third parts of the upper P-side waveguide layer, the longitudinal optical confinement factor of the active region can be reduced from the high-reflection end to the anti-reflection end. This alters the confinement factor along the light field propagation direction, thereby achieving light field manipulation and reducing the light field intensity in the concentrated light field region. Furthermore, the scheme satisfies: - (λ / 4) ; (λ / 4)- This allows the single-frequency distributed feedback semiconductor laser to satisfy the Bragg condition.

[0018] Furthermore, the mode field overlap factor of the P-side waveguide layer and its adjacent high-absorption region decreases along the direction from the high-reflection section to the anti-reflection end, in order to reduce local absorption and heat accumulation near the anti-reflection end (light-emitting end). The phrase "reducing the light field intensity in the light field concentration region" has been replaced with an interpretable physical quantity.

[0019] Under the constraint of single-frequency distributed feedback and single-mode Bragg feedback, a non-uniform distribution of optical confinement factor is constructed along the cavity length direction, which reduces it in the λ / 4 phase shift region and the anti-reflection end (light output end), thereby adjusting the longitudinal optical field distribution and suppressing the spatial hole burning effect.

[0020] Although variations in the composition / thickness of the P-side waveguide layer along the cavity length can cause local changes in the effective refractive index, by controlling the compensation layer, the local Bragg wavelengths of different longitudinal sections (the first, second, and third sections) still fall within the same single-frequency distributed feedback bandwidth, thus avoiding the formation of multiple independent lock-in centers. In other words, it is not necessary for the lock-in wavelengths of the three regions (the first, second, and third sections) to be exactly the same; rather, it is sufficient that their local Bragg deviations are less than the tolerance range of the single-frequency distributed feedback. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A schematic diagram of a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of step S1 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of step S21 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of step S22 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of step S23 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of step S24 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of step S25 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of step S26 in the method for fabricating a single-frequency distributed feedback semiconductor laser provided in an embodiment of the present invention.

[0023] Icons: 1-Upper P-side waveguide; 11-First section; 12-Second section; 13-Third section; 14-First transition section; 15-Second transition section; 2-P-side cladding; 3-grating layer; 4-compensation layer; 5-active region; 6-N-type waveguide layer; 7-N-type cladding; 8-substrate; 9-capping layer; 110 - First layer structure; 120 - Second layer structure; 130 - Third layer structure; 210 - First etching groove; 220 - Second etching groove; 300-Shading structure. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0026] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0027] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0028] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," not that the structure must be completely horizontal, but can be slightly tilted.

[0029] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] like Figure 1 As shown, the single-frequency distributed feedback semiconductor laser provided by the present invention is particularly suitable for single-frequency narrow-linewidth devices with AR / HR coated asymmetric cavity surface and ridge waveguide current injection structure.

[0031] The single-frequency distributed feedback semiconductor laser includes an epitaxial structure, which includes an active region 5, a grating layer 3, and an upper P-side waveguide layer 1 arranged sequentially along the epitaxial direction.

[0032] Along the cavity length direction of the epitaxial structure, and from the high-reflection end to the anti-reflection end of the epitaxial structure ( Figure 1 In the diagram (from left to right), the epitaxial structure includes a first longitudinal segment, a second longitudinal segment, and a third longitudinal segment. These three segments are not independent parts, but rather are used to simplify the explanation of the single-frequency distributed feedback semiconductor laser structure, dividing the laser into three segments. The λ / 4 phase shift region of grating layer 3 is located in the second longitudinal segment.

[0033] In the upper P-side waveguide layer 1, the portions located in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment are respectively designated as the first portion 11, the second portion 12, and the third portion 13.

[0034] In the first feasible scheme, the material compositions of the first part 11, the second part 12, and the third part 13 are all different.

[0035] In the second feasible scheme, the thicknesses of the first part 11, the second part 12, and the third part 13 ( Figure 1 The vertical length values ​​(i.e., the outer extension direction) are all different.

[0036] In the third feasible scheme, the material composition of the first part 11, the second part 12 and the third part 13 are all different, and the thickness of the first part 11, the second part 12 and the third part 13 are all different.

[0037] All three options above satisfy the following: - (λ / 4) ; (λ / 4)- Furthermore, both methods can reduce the longitudinal optical confinement factor of the active region 5 from the high-reflection end to the anti-reflection end. Among them, The equivalent refractive index of the first longitudinal segment; (λ / 4) is the equivalent refractive index of the second longitudinal section; The equivalent refractive index of the third longitudinal section.

[0038] A compensation layer 4 is disposed between the active region 5 and the grating layer 3. The compensation layer 4 can be formed by a lower P-type waveguide layer and a space layer. The P-type waveguide layer and the space layer have different compositions and thicknesses, and together they form the compensation layer 4. During laser fabrication, compensation design can be performed using the compensation layer 4, i.e., adjusting the thickness, so that the equivalent refractive indices of the first longitudinal section, the second longitudinal section, and the third longitudinal section meet the aforementioned requirements. The thickness of the compensation layer 4 is within the range of 100 nm. 300nm, to control the effective refractive index change and maintain Bragg feedback conditions.

[0039] Preferred, ; in, The optical confinement factor is the active region 5 in the first longitudinal segment. The optical confinement factor is the active region 5 in the second longitudinal segment. This is the optical confinement factor for the active region 5 in the third longitudinal segment. The mode field overlap factor of the P-side waveguide layer and its adjacent high-absorption region decreases along the direction from the high-reflection section to the anti-reflection end, in order to reduce local absorption and heat accumulation near the anti-reflection end (light-emitting end). The phrase "reducing the light field intensity in the concentrated light field region" has been replaced with an interpretable physical quantity.

[0040] In the first scheme, the material compositions of the first part 11, the second part 12, and the third part 13 are all different. The material of the upper P-side waveguide layer 1 is... As or InP. In Part 1.11, Part 2.12, and Part 3.13, As or InP They are respectively , and , The value range is 0.25. 0.45; The value range is 0.35. 0.65; The value range is 0.30 to 0.55; and it satisfies: ; This allows us to understand the variation patterns of the equivalent refractive index in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment, with the mode field weakening as it expands towards the P side.

[0041] In the second scheme, the thicknesses of the first part 11, the second part 12, and the third part 13 are all different. The thickness values ​​of the first part 11, the second part 12, and the third part 13 are respectively... , and ; The value range is 80 nm 150nm; The value range is 40nm 100nm; The value range is 40 nm 100 nm; and satisfy: - ≥20nm; - ≥20 nm.

[0042] like Figure 1 As shown, the upper P-side waveguide layer 1 also includes a first transition portion 14 connecting the first portion 11 and the second portion 12. The first transition portion 14 includes at least two first longitudinal transition stages arranged sequentially along the cavity length direction. The components of two adjacent first longitudinal transition stages are different, or the thicknesses are different (the first transition portion 14 is generally stepped), or both the components and the thicknesses are different, so that the first portion 11 transitions to the second portion 12 in stages, avoiding abrupt changes in the structure of the first portion 11 and the second portion 12, thereby reducing the loss of light traveling through the first portion 11 and the second portion 12. The loss of the trapezoidal shape is lower than that of the abrupt change. In another possible implementation, the composition of the first transition portion 14 varies continuously, and the thickness varies continuously along the cavity length (the first transition portion is sloped as a whole), or both vary continuously, so that the first portion 11 transitions continuously to the second portion 12, thereby reducing the loss of light traveling between the first portion 11 and the second portion 12. The loss is lower with a gradual transition than with an abrupt change.

[0043] Similarly, the upper P-side waveguide layer 1 also includes a second transition portion 15 connecting the second portion 12 and the third portion 13. The second transition portion 15 includes at least two second longitudinal transition stages arranged sequentially along the cavity length direction. The components, thicknesses, or both of adjacent second longitudinal transition stages are different, so that the second portion 12 transitions to the third portion 13 in stages. In another possible implementation, the components and thickness of the second transition portion 15 change continuously along the cavity length direction, or both change continuously along the cavity length direction, so that the second portion 12 transitions to the third portion 13 continuously, thereby reducing energy loss.

[0044] Preferred, κ HR Greater than κ λ / 4 κ λ / 4 Greater than κ AR ; Greater than ; Greater than , where κ HR κ λ / 4 and κ AR These are the grating coupling coefficients corresponding to the first, second, and third longitudinal sections, respectively, thus enabling the laser to maintain single-mode operation and suppress sub-modes. Among them, and The optimal difference is 5% to 25%.

[0045] The present invention provides a method for fabricating a single-frequency distributed feedback semiconductor laser, the method being used to fabricate the aforementioned single-frequency distributed feedback semiconductor laser, comprising the following steps: like Figure 2 As shown, step S1. provides an epitaxial base structure, the epitaxial base structure is grown to grating layer 3, and grating layer 3 completes the fabrication of a single-frequency distributed feedback grating.

[0046] The epitaxial basic structure includes, from top to bottom, a substrate 8, an N-type cladding layer 7, an N-type waveguide layer 6, an active region 5, a lower P-type waveguide layer, a space layer, and a grating layer 3. The lower P-type waveguide layer and the space layer have different compositions and thicknesses, and together they form a compensation layer 4. The thickness of the compensation layer 4 ranges from 100 nm to 300 nm.

[0047] like Figure 3 As shown, a single-frequency distributed feedback grating pattern can be formed using EBL, interferometric lithography, or DUV lithography, and a periodic grating and λ / 4 phase shift region can be etched. Then, a capping layer 9 is grown to form a buried grating single-frequency distributed feedback structure.

[0048] like Figure 3As shown, in step S2, along the cavity length direction of the epitaxial base structure, from the high-reflection end to the anti-reflection end, the epitaxial base structure is sequentially divided into a first longitudinal segment, a second longitudinal segment, and a third longitudinal segment. The length of the first longitudinal segment is approximately 30% of the total length of the epitaxial base structure, the length of the second longitudinal segment is approximately 40% of the total length of the epitaxial base structure, and the length of the third longitudinal segment is approximately 30% of the total length of the epitaxial base structure. Furthermore, the λ / 4 phase shift region of the grating layer 3 is located in the second longitudinal segment.

[0049] The upper P-side waveguide layer 1 is grown stepwise in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment, so that the portions of the upper P-side waveguide layer 1 located in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment respectively form the first part 11, the second part 12, and the third part 13, thereby forming the above-mentioned single-frequency distributed feedback semiconductor laser.

[0050] Specifically, the steps for growing the upper P-side waveguide layer 1 in the first, second, and third longitudinal sections include: like Figure 3 As shown, in step S21, a first layer structure 110 is grown on the epitaxial base structure using the first material. The first layer structure 110 covers the first longitudinal section, the second longitudinal section and the third longitudinal section, and a single-frequency distributed feedback grating is embedded inside the first layer structure 110.

[0051] A first layer structure 110 is grown on the capping layer 9. The thickness and composition of the first layer structure 110 are the same in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment. For example, Al... 0.35 Ga 0.65 As, thickness 120 nm.

[0052] Step S22. The first layer structure 110 of one of the three longitudinal sections, the second longitudinal section and the third longitudinal section is masked, while the first layer structure 110 of the other two is etched to a depth of L1 to form a first etched groove 210.

[0053] like Figure 4 As shown, specifically in this embodiment, a partitioned windowing operation is adopted. The first longitudinal section is shielded and protected by the shielding structure 300, while the second and third longitudinal sections are exposed by opening windows. The upper P-side waveguide layer 1 of the exposed second and third longitudinal sections is selectively etched to remove part of the surface material to obtain the first etched groove 210, for example, with an etching depth of 20 nm. like Figure 5As shown, in step S23, a second layer structure 120 is grown in the first etching groove 210 using the second material, and the height of the second layer structure 120 is L2.

[0054] A second material, such as Al, is regrown in the second and third longitudinal sections. 0.42 Ga 0.58 As, to form the second layer structure 120. At this time, the first longitudinal segment maintains Al. 0.35 Ga 0.65 As, the second and third longitudinal sections are formed with Al material. 0.42 Ga 0.58 As layer structure. like Figure 6 As shown, in step S24, the second layer structure 120 of one of the two etched structures in step S22 is masked, while the second layer structure 120 of the other structure is etched to a depth of L3 to form a second etch groove 220.

[0055] The first and second longitudinal sections are then partitioned and windowed using photolithography. The first and second longitudinal sections are shielded and protected by a shielding structure 300, exposing only the third longitudinal section. The upper P-side waveguide layer 1 in the third longitudinal section is selectively etched to remove part of the second material. The etching depth can also be 20 nm to form the second etch groove 220. like Figure 7 As shown, in step S25, a third layer structure 130 is grown in the second etching groove 220 using a third material, and the height of the third layer structure 130 is L4.

[0056] A third material, such as Al, is regrown in the third longitudinal section. 0.50 Ga 0.50 As, to make the final satisfaction: Less than ; Less than .

[0057] like Figure 8 Step S26. Remove the occluding structure 300.

[0058] In one feasible scheme, L1 can be equal to L2, L3 can be equal to L4, and at least two of the first, second, and third materials have different material compositions.

[0059] In another possible implementation, the material composition of the first material, the second material, and the third material can be the same, but L1 is not equal to L2 and L3 is equal to L4; or L1 is equal to L2 and L3 is not equal to L4, or L1 is not equal to L2 and L3 is not equal to L4.

[0060] In another feasible implementation, step S2 further includes the following step: like Figure 1 As shown, a first transition section is reserved between the first longitudinal section and the second longitudinal section; the first transition section is etched stepwise in the direction from the first longitudinal section to the second longitudinal section to obtain a step-like first transition portion 14, the number of steps of the first transition portion 14 is n, where n is an integer greater than 2; the first transition portion 14 is covered with growth materials of different compositions, and the composition of the growth material of each step in the first transition portion 14 is different. The first and second longitudinal segments are not continuous; they are connected by a first transition segment. The left side of the first transition segment connects to the first longitudinal segment, and the right side connects to the second longitudinal segment. The length of the first transition segment can range from 10 to 50 μm. The first transition segment is also implemented using segmented photolithography. During photolithography, multiple windows are set. For example, if the total length of the first longitudinal segment is 20 μm, it is divided into 4 to 10 smaller segments. Different opening areas or different exposure doses are set for different segments to gradually increase the etching exposure. For example, from left to right, the etching depths of the first transition segment are 0 nm, 5 nm, 10 nm, 15 nm, and 20 nm. Then, routine cleaning operations such as resist removal, washing, and surface treatment are performed. Subsequently, selective regrowth is performed, allowing the regrowth material to gradually cover the first transition segment. For example, the Al composition in the material gradually transitions from 0.35 to 0.42.

[0061] A second transition section is reserved between the second longitudinal section and the third longitudinal section; the second transition section is etched in a progressively shallower manner along the direction from the second longitudinal section to the third longitudinal section to obtain a step-like second transition portion 15, the number of steps of the second transition portion 15 is m, where m is an integer greater than 2; the second transition portion 15 is covered with growth materials of different compositions, and the composition of the growth material of each step in the second transition portion 15 is different.

[0062] Similar to the preparation method of the first transition section, the second transition section is also obtained by photolithography with multi-level windows and graded growth of materials. From left to right, in the growth material of the second transition section, the Al composition gradually changes from 0.42 to 0.50, and the thickness gradually changes from 100 nm to 80 nm.

[0063] The fabrication method of a single-frequency distributed feedback semiconductor laser also includes the following steps: Step S31. Perform performance testing on the product prepared in step S2; Step S32. When the test results are not within the preset range, adjust the thickness and / or composition of the compensation layer 4 until the product performance test results are within the preset range.

[0064] Steps S31 and S32 are testing steps. The test results reflect the performance of the laser. When the performance of the manufactured product does not meet the standards, the parameters are adjusted and the product is remade to optimize its performance. The performance test may include at least one of power testing, spectral testing, and series resistance testing.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-frequency distributed feedback semiconductor laser, characterized in that, include: The epitaxial structure includes an active region (5), a grating layer (3), and an upper P-side waveguide layer (1) arranged sequentially along the epitaxial direction. Along the cavity length direction of the epitaxial structure, and from the high-reflection end to the anti-reflection end of the epitaxial structure, the epitaxial structure includes a first longitudinal section, a second longitudinal section, and a third longitudinal section; the λ / 4 phase shift region of the grating layer (3) is located in the second longitudinal section; The portions of the upper P-side waveguide layer (1) located in the first longitudinal section, the second longitudinal section, and the third longitudinal section are respectively set as a first part (11), a second part (12), and a third part (13); the material composition of the first part (11), the second part (12), and the third part (13) are all different, and / or the thickness of the first part (11), the second part (12), and the third part (13) is all different, so that the longitudinal optical confinement factor of the active region (5) is reduced from the high reflection end to the anti-reflection end; And it satisfies: - (l / 4) ; (l / 4)- ; in, The equivalent refractive index of the first longitudinal segment; (λ / 4) is the equivalent refractive index of the second longitudinal section; The equivalent refractive index of the third longitudinal section.

2. The single-frequency distributed feedback semiconductor laser according to claim 1, characterized in that, A compensation layer (4) is disposed between the active region (5) and the grating layer (3), and the thickness of the compensation layer (4) is in the range of 100 nm. 300nm.

3. The single-frequency distributed feedback semiconductor laser according to claim 1, characterized in that, ； in, The optical confinement factor of the active region (5) in the first longitudinal segment, The optical confinement factor of the active region (5) in the second longitudinal segment, The optical confinement factor of the active region (5) in the third longitudinal section.

4. The single-frequency distributed feedback semiconductor laser according to claim 1, characterized in that, The material compositions of the first part (11), the second part (12), and the third part (13) are all different; The material of the upper P-side waveguide layer (1) is As or InP; The value range is 0.

25. 0.45; The value range is 0.

35. 0.65; The value range is 0.30 to 0.55; And it satisfies: ； 。 5. The single-frequency distributed feedback semiconductor laser according to claim 1, characterized in that, The thicknesses of the first part (11), the second part (12), and the third part (13) are all different; The thickness values ​​of the first part (11), the second part (12), and the third part (13) are respectively , and ; The value range is 80 nm 150 nm; The value range is 40nm 100nm; The value range is 40 nm 100 nm; And it satisfies: - ≥20 nm; - ≥20 nm.

6. The single-frequency distributed feedback semiconductor laser according to claim 1, characterized in that, The upper P-side waveguide layer (1) further includes a first transition portion connecting the first portion (11) and the second portion (12); The first transition portion includes at least two first longitudinal transition stages arranged sequentially along the cavity length direction, with the components and / or thicknesses of two adjacent first longitudinal transition stages being different, so that the first portion (11) transitions to the second portion (12) in stages; or, the components and / or thicknesses of the first transition portion change continuously along the cavity length direction, so that the first portion (11) transitions to the second portion (12) continuously. And / or, the upper P-side waveguide layer (1) further includes a second transition portion connecting the second portion (12) and the third portion (13), the second transition portion including at least two second longitudinal transition stages arranged sequentially along the cavity length direction, the components and / or thicknesses of two adjacent second longitudinal transition stages being different, so that the second portion (12) transitions to the third portion (13) in stages; or, the components and / or thicknesses of the second transition portion change continuously along the cavity length direction, so that the second portion (12) transitions to the third portion (13) continuously.

7. The single-frequency distributed feedback semiconductor laser according to claim 1, characterized in that, κ HR Greater than κ λ / 4 , κ λ / 4 Greater than κ AR ; Greater than ; Greater than , where κ HR κ λ / 4 and κ AR These are the grating coupling coefficients corresponding to the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment, respectively.

8. A method for fabricating a single-frequency distributed feedback semiconductor laser, characterized in that, The method is used to prepare the single-frequency distributed feedback semiconductor laser according to any one of claims 1-7, comprising the following steps: Step S1. Provide an epitaxial base structure, wherein the epitaxial base structure is grown to a grating layer (3), and the grating layer (3) completes the fabrication of a single-frequency distributed feedback grating; Step S2. Along the cavity length direction of the epitaxial base structure, and from the high reflection end to the antireflection end of the epitaxial base structure, the epitaxial base structure is sequentially divided into a first longitudinal section, a second longitudinal section, and a third longitudinal section; and the λ / 4 phase shift region of the grating layer (3) is located in the second longitudinal section; The upper P-side waveguide layer (1) is grown stepwise in the first longitudinal segment, the second longitudinal segment and the third longitudinal segment, so that the portions of the upper P-side waveguide layer (1) located in the first longitudinal segment, the second longitudinal segment and the third longitudinal segment respectively form the first part (11), the second part (12) and the third part (13).

9. The method for fabricating a single-frequency distributed feedback semiconductor laser according to claim 8, characterized in that, The step-by-step growth of the upper P-side waveguide layer (1) in the first longitudinal segment, the second longitudinal segment, and the third longitudinal segment specifically includes: Step S21. Using the first material, a first layer structure (110) is grown on the epitaxial base structure. The first layer structure (110) covers the first longitudinal section, the second longitudinal section and the third longitudinal section, and a single-frequency distributed feedback grating is buried inside the first layer structure (110). Step S22. The first layer structure (110) of one of the three longitudinal sections (first, second, and third) is masked, while the first layer structure (110) of the other two is etched to a depth of L1 to form a first etched groove (210). Step S23. Use the second material to grow a second layer structure (120) in the first etching groove (210), the height of the second layer structure (120) is L2; Step S24. The second layer structure (120) of one of the two etched in step S22 is masked, while the second layer structure (120) of the other is etched to a depth of L3 to form a second etch groove (220). Step S25. A third layer structure (130) is grown in the second etching groove (220) using a third material, wherein the height of the third layer structure (130) is L4; Step S26. Remove the obstruction; Wherein, at least two of the first material, the second material and the third material have different material compositions, and / or, L1 is not equal to L2, and / or, L3 is not equal to L4.

10. The method for fabricating a single-frequency distributed feedback semiconductor laser according to claim 8, characterized in that, Step S2 further includes the following step: A first transition section is reserved between the first longitudinal section and the second longitudinal section; Along the direction from the first longitudinal section to the second longitudinal section, the first transition section is etched in progressively deeper steps to obtain a step-shaped first transition portion (14), where the number of steps in the first transition portion (14) is n, and n is an integer greater than 2. The first transition portion (14) is covered with growth materials of different compositions, and the composition of the growth material of each step in the first transition portion (14) is different. A second transition section is reserved between the second longitudinal section and the third longitudinal section; Along the direction from the second longitudinal section toward the third longitudinal section, the second transition section is etched in a progressively shallower manner to obtain an upper stepped second transition portion (15), the number of steps of the second transition portion (15) is m, where m is an integer greater than 2; The second transition section (15) is covered with growth materials of different compositions, and the composition of the growth material in each stage of the second transition section (15) is different.

11. The method for fabricating a single-frequency distributed feedback semiconductor laser according to claim 9, characterized in that, A compensation layer (4) is provided between the active region (5) and the grating layer (3), and the thickness of the compensation layer is in the range of 100nm~300nm; The method for fabricating a single-frequency distributed feedback semiconductor laser further includes the following steps: Step S31. Perform performance testing on the product prepared in step S2; Step S32. When the test results are not within the preset range, adjust the thickness and / or composition of the compensation layer (4) until the product performance test results are within the preset range.

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