A distributed feedback laser and its preparation method

Abstract

The present invention discloses a distributed feedback laser and a method for fabricating the same. The laser comprises: a laser epitaxial structure comprising a substrate and a multilayer epitaxial layer located on one side of the substrate; a first electrode layer located on a side of the epitaxial layer away from the substrate; wherein the multilayer epitaxial layer comprises at least one grating resonant cavity structure, the grating resonant cavity structure comprising a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along a first direction; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; and a second electrode layer located on a side of the substrate away from the epitaxial layer. The present invention effectively reduces the number of gratings prepared, lowers the grating preparation precision requirements, reduces the difficulty and cost of device preparation, and simultaneously reduces the optical loss of the device, improves the optical coupling efficiency, suppresses multimode lasing, and significantly improves the application performance of the device.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of laser technology, and in particular to a distributed feedback laser and a preparation method thereof. Background Art

[0002] Semiconductor lasers, also known as laser diodes, are lasers that use semiconductor materials such as gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), aluminum nitride (AlN), cadmium sulfide (CdS), and zinc sulfide (ZnS) as their working materials. They have the advantages of small size, high efficiency, and long life. Among them, narrow-linewidth semiconductor lasers, represented by distributed feedback (DFB) lasers, have good single-mode characteristics, narrow spectral half-width, and high modulation rate. They have important applications in laser communications, laser ranging, and lidar, and have attracted widespread attention from industry and academia.

[0003] Distributed feedback semiconductor lasers require the preparation of grating pairs for mode selection. Since the grating inside the laser needs to undergo secondary epitaxy, resulting in a complex preparation process, the gratings of conventional DFB (Distributed Feedback Laser, DFB) lasers are all made on the surface of the laser. Since the grating needs to be formed by etching, and etching not only affects the current injection, resulting in uneven current injection, but also produces surface states such as dangling bonds, causing non-radiative recombination, thereby affecting the efficiency of the device, conventional DFB lasers usually use a ridge sidewall grating structure, that is, the grating is made on the sidewall of the ridge. Since the laser light field is mainly distributed below the ridge, the coupling efficiency of the sidewall grating is low. It is usually necessary to prepare multiple pairs of low-order gratings and the grating etching depth is deep to ensure sufficiently high coupling efficiency and thus achieve mode selection. However, the large number of grating pairs to be written requires a relatively high grating writing accuracy, which not only increases the preparation cost and reduces the grating writing efficiency, but also introduces more writing errors, resulting in large laser grating scattering loss, low coupling efficiency, and the occurrence of multi-mode lasing, which ultimately affects the application performance of the laser. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides a distributed feedback laser and a preparation method thereof to solve the technical problems in the prior art caused by the use of multiple pairs of grating structures, such as high etching cost, low etching efficiency and precision, large laser grating scattering loss, low coupling efficiency and multi-mode lasing, which ultimately affect the application performance of the laser.

[0005] In a first aspect, an embodiment of the present invention provides a distributed feedback laser, comprising:

[0006] A laser epitaxial structure, comprising a substrate and a plurality of epitaxial layers located on one side of the substrate;

[0007] a first electrode layer located on a side of the epitaxial layer away from the substrate; wherein the multiple epitaxial layers include at least one grating resonant cavity structure, the grating resonant cavity structure including a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along a first direction; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; and the first direction is parallel to the plane of the substrate;

[0008] A second electrode layer is located on a side of the substrate away from the epitaxial layer.

[0009] Optionally, the grating period of the resonant cavity structure is greater than the grating periods of the first grating structure and the second grating structure.

[0010] Optionally, the grating equation of the first grating structure satisfies: mλ=2n L1, L1 is the grating period of the first grating structure, n1 is the refractive index of the first grating structure, λ is the laser wavelength, m≥2 and m is a positive integer;

[0011] The grating equation of the resonant cavity structure satisfies: gλ=2n2 L2, L2 is the grating period of the resonant cavity structure, n2 is the refractive index of the resonant cavity structure, and g≥2 and g is a positive integer;

[0012] The grating equation of the second grating structure satisfies: kλ=2n3 L3, L3 is the grating period of the second grating structure, n3 is the refractive index of the second grating structure, k≥2 and k is a positive integer;

[0013] Among them, the lowest common factor of m, g and k is 1.

[0014] Optionally, the first grating structure, the resonant cavity structure and the second grating structure have the same film layer structure.

[0015] Optionally, the multiple epitaxial layers include a buffer layer, a lower optical field limiting layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field limiting layer and an upper contact layer, which are sequentially arranged on one side of the substrate;

[0016] The distributed feedback laser further includes a ridge structure, the ridge structure extending along the first direction, and the ridge structure includes the first electrode layer, the upper contact layer and a portion of the upper optical field confinement layer;

[0017] The first grating structure includes a first sub-grating structure, a first ridge grating structure, and a second sub-grating structure sequentially arranged along a second direction; the second direction intersects the first direction and is parallel to the plane where the substrate is located;

[0018] The resonant cavity structure includes a first sub-resonant cavity structure, a ridge-shaped resonant cavity structure, and a second sub-resonant cavity structure sequentially arranged along the second direction;

[0019] The second grating structure includes a third sub-grating structure, a second ridge grating structure and a fourth sub-grating structure sequentially arranged along the second direction;

[0020] The first sub-grating structure, the second sub-grating structure, the first sub-resonant cavity structure, the second sub-resonant cavity structure, the third sub-grating structure and the fourth sub-grating structure all include a portion of the upper optical field confinement layer; the first ridge grating structure, the ridge resonant cavity structure and the second ridge grating structure include the first electrode layer, the upper contact layer and the upper optical field confinement layer;

[0021] Alternatively, the first sub-grating structure, the second sub-grating structure, the first sub-resonant cavity structure, the second sub-resonant cavity structure, the third sub-grating structure and the fourth sub-grating structure all include part of the upper light field limiting layer, the upper waveguide layer, the active area, the lower waveguide layer and the lower light field limiting layer; the first ridge grating structure, the ridge resonant cavity structure and the second ridge grating structure include the first electrode layer, the upper contact layer, the upper light field limiting layer, the upper waveguide layer, the active area, the lower waveguide layer and the lower light field limiting layer.

[0022] Optionally, the multiple epitaxial layers include a buffer layer, a lower optical field limiting layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field limiting layer and an upper contact layer, which are sequentially arranged on one side of the substrate;

[0023] The first grating structure, the resonant cavity structure and the second grating structure each include the first electrode layer, the upper contact layer and the upper optical field confinement layer;

[0024] Alternatively, the first grating structure, the resonant cavity structure and the second grating structure all include the first electrode layer, the upper contact layer, the upper optical field limiting layer, the upper waveguide layer, the active region, the lower waveguide layer and the lower optical field limiting layer.

[0025] Optionally, the laser epitaxial structure further includes a connecting electrode and a dielectric layer;

[0026] The dielectric layer partially covers the upper surfaces of the first grating structure, the resonant cavity structure and the second grating structure, exposing at least the first electrode layer;

[0027] The connecting electrode covers the first electrode layer, and a thickness of the connecting electrode is greater than a thickness of the first electrode layer.

[0028] Optionally, the multiple epitaxial layers include at least two grating resonant cavity structures arranged in sequence;

[0029] Two adjacent grating resonant cavity structures jointly include the first grating structure or the second grating structure.

[0030] In a second aspect, an embodiment of the present invention further provides a method for preparing a distributed feedback laser, which is used to prepare the distributed feedback laser provided in the first aspect, comprising:

[0031] preparing a laser epitaxial structure, the laser epitaxial structure comprising a substrate and a plurality of epitaxial layers located on one side of the substrate;

[0032] forming a first electrode layer on a side of the epitaxial layer away from the substrate;

[0033] Etching multiple layers of the epitaxial layer along the first direction to prepare a first grating structure, a resonant cavity structure, and a second grating structure; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; the first direction is parallel to the plane of the substrate;

[0034] preparing a second electrode layer on a side of the substrate away from the epitaxial layer;

[0035] The epitaxial structure is subjected to scribing, cleaving, coating and splitting processes to form a distributed feedback laser.

[0036] Optionally, after etching multiple layers of the epitaxial layer to prepare the first grating structure, the resonant cavity structure, and the second grating structure, the method further includes:

[0037] etching sidewalls of the first grating structure, the resonant cavity structure, and the second grating structure using an alkaline solution;

[0038] depositing a dielectric layer on a side of the first electrode layer away from the substrate, wherein the dielectric layer covers upper surfaces of the first grating structure, the resonant cavity structure, and the second grating structure;

[0039] Using photolithography and etching technology, remove a portion of the dielectric layer on the upper surfaces of the first grating structure, the resonant cavity structure, and the second grating structure to expose the first electrode layer;

[0040] A connecting electrode is prepared on a side of the dielectric layer away from the substrate, and the connecting electrode covers the exposed first electrode layer.

[0041] A distributed feedback laser provided by an embodiment of the present invention comprises a multi-layer epitaxial layer including at least one grating resonant cavity structure, wherein the grating resonant cavity structure comprises a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along a first direction, wherein the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode. By introducing a resonant cavity structure between the first grating structure and the second grating structure, the number of gratings prepared is effectively reduced, the grating preparation accuracy requirements are lowered, thereby reducing the difficulty and cost of device preparation and improving writing efficiency. Furthermore, by reasonably setting the grating period relationship between the first grating structure, the second grating structure, and the resonant cavity structure, the optical loss of the device is effectively reduced, thereby improving the optical coupling efficiency and suppressing multi-mode lasing, satisfying the requirement of having only one laser wavelength output, ensuring the stability of the laser operating mode, and significantly improving the application performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0043] Figure 1 A schematic top view of a distributed feedback laser epitaxial structure provided by an embodiment of the present invention;

[0044] Figure 2 for Figure 1 Schematic diagram of the cross section of the epitaxial structure along the AA' direction;

[0045] Figure 3 for Figure 1 Schematic diagram of the cross section of the epitaxial structure along the BB' direction;

[0046] Figure 4 A schematic flow chart of a method for preparing a distributed feedback laser provided by an embodiment of the present invention;

[0047] Figure 5 A schematic cross-sectional view of a laser epitaxial structure of a distributed feedback laser provided by an embodiment of the present invention;

[0048] Figure 6 for Figure 7 Schematic diagram of the cross section of the laser epitaxial structure along AA' after etching the ridge structure;

[0049] Figure 7 This is a schematic diagram of the surface of the semiconductor laser structure after the ridge is etched;

[0050] Figure 8 for Figure 5 Schematic diagram of the cross section of the semiconductor laser epitaxial structure after the dielectric film is deposited;

[0051] Figure 9 for Figure 8 Schematic cross-sectional view of the semiconductor laser epitaxial structure after stripping the dielectric film;

[0052] Figure 10 Schematic diagram of the surface of the semiconductor laser structure after preparing multi-segment gratings by photolithography;

[0053] Figure 11 for Figure 10 Schematic diagram of the cross section of the semiconductor laser structure along BB' after the multi-segment grating is fabricated by photolithography and etching;

[0054] Figure 12 for Figure 10 Schematic diagram of the cross section of the semiconductor laser structure along BB' after wet etching;

[0055] Figure 13 This is a schematic cross-sectional view of the semiconductor laser structure after the second electrode is prepared on the substrate surface.

[0056] Figure 14 A schematic flow chart of another method for preparing a distributed feedback laser provided by an embodiment of the present invention;

[0057] Figure 15 A schematic top view of another distributed feedback laser epitaxial structure provided by an embodiment of the present invention.

[0058] The following is a description of the accompanying drawings:

[0059] In the figure: 101 is the substrate, 102 is the buffer layer, 103 is the lower light field limiting layer, 104 is the lower waveguide layer, 105 is the active region, 106 is the upper waveguide layer, 107 is the upper light field limiting layer, 108 is the upper contact layer, 109 is the first electrode layer, 110 is the photoresist, 111 is the dielectric layer, 112 is the mask, 113 is the connecting electrode, 114 is the second electrode layer, 201 is the ridge structure, 202 is the first grating structure, 203 is the resonant cavity structure, and 204 is the second grating structure. DETAILED DESCRIPTION

[0060] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be fully described below in conjunction with the accompanying drawings of the embodiments of the present invention through specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0061] Example

[0062] An embodiment of the present invention provides a distributed feedback laser. Figure 1 A schematic top view of a distributed feedback laser epitaxial structure provided by an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the cross section of the epitaxial structure along the AA' direction; Figure 3 for Figure 1 Schematic diagram of the cross section of the epitaxial structure along the BB' direction. Figure 1-3 As shown, the distributed feedback laser includes:

[0063] A laser epitaxial structure, the laser epitaxial structure includes a substrate 101 and a multi-layer epitaxial layer 10 located on one side of the substrate 101;

[0064] The first electrode layer 109 is located on the side of the epitaxial layer away from the substrate; wherein the multi-layer epitaxial layer includes at least one grating resonant cavity structure 20, and the grating resonant cavity structure 20 includes sequentially along the first direction (such as Figure 1 The first grating structure 202, the resonant cavity structure 203, and the second grating structure 204 are arranged (as shown in the X direction); the grating period L of the first grating structure 202 and the second grating structure 204 is different from the grating period L of the resonant cavity structure 203, and the first grating structure 202, the resonant cavity structure 203, and the second grating structure 204 have only one common lasing mode λ; the first direction is parallel to the plane where the substrate 101 is located;

[0065] The second electrode layer 114 is located on a side of the substrate 101 away from the epitaxial layer.

[0066] For example, Figure 1-3 As shown, the distributed feedback laser provided by an embodiment of the present invention includes a laser epitaxial structure as the laser's main light-emitting structure, including a substrate 101 and multiple epitaxial layers grown on one side of the substrate 101. The substrate material can be selected from any one or a combination of two or more of GaAs, InP, GaN, AlGaN, InGaN, AlN, sapphire, SiC, Si, and SOI. Using a III-nitride substrate can fabricate a III-nitride semiconductor DFB laser. The multiple epitaxial layers are configured based on the laser epitaxial structure.

[0067] An optical device composed of a large number of parallel slits of equal width and equal spacing is called a grating. A commonly used grating is made by engraving a large number of parallel grooves on a glass sheet. The grooves are opaque parts, and the smooth part between the two grooves can transmit light, which is equivalent to a slit. A refined grating has thousands or even tens of thousands of grooves within a width of 1 cm. This kind of grating that uses the diffraction of transmitted light is called a transmission grating. There is also a grating that uses the diffraction of reflected light between two grooves. For example, many parallel grooves are engraved on a surface coated with a metal layer. The smooth metal surface between the two grooves can reflect light. This kind of grating is called a reflection grating. Preferably, the embodiment of the present invention uses a reflective grating structure.

[0068] Combine Figure 1 and Figure 3 As shown, the multi-layer epitaxial layer 10 includes a grating resonant cavity structure 20 as an example for explanation. Figure 1 As shown in the X direction, the grating resonant cavity structure 20 includes a first grating structure 202, a resonant cavity structure 203, and a second grating structure 204 arranged in sequence. The resonant cavity structure 203 is introduced between the first grating structure 202 and the second grating structure 204 to form a grating-resonant cavity-grating structure, which effectively reduces the number of grating preparations, improves the writing efficiency, and reduces the difficulty and cost of device preparation. Compared with the conventional continuous grating, the grating structure of the present invention is divided into multiple sections, and the waveguides between the gratings form a resonant cavity. The resonant cavity between the gratings can be used to select the mode. The resonant cavity has very small light loss relative to the grating. The DFB semiconductor laser light prepared is The grating scattering loss is small; further, the multi-segment grating and the resonant cavity between the gratings are used to work together, and by reasonably setting the grating period L1 of the first grating structure 202 and the grating period L3 of the second grating structure 204 to be different from the grating period L2 of the resonant cavity structure 203 and satisfying the grating equation of the common laser mode λ, the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204 are not limited to the first-order grating structure, and only one common laser mode λ is satisfied for output mode selection, which significantly reduces the etching selection ratio in the grating preparation process, thereby greatly improving the accuracy of grating preparation and achieving precise control of the output wavelength of the DFB laser. Conventional grating structures have a large number of grating pairs and relatively high writing accuracy requirements. In this embodiment, a grating-resonant cavity-grating structure is used, which effectively reduces the number of grating preparations, improves the writing efficiency, and reduces the grating preparation accuracy requirements, thereby reducing the difficulty and cost of device preparation; further, the use of Figure 1 The grating-resonant cavity-grating structure shown in FIG. Figure 3 As shown, the grating and resonant cavity surfaces are steep and smooth, which can effectively reduce the scattering and absorption loss of light at the grating interface, effectively improve the coupling performance of the device, and meet the function of having only one common lasing mode λ for mode selection output.

[0069] An ohmic contact metal is used to form an ohmic contact with the surface of the epitaxial layer away from the substrate, forming a first electrode layer 109. An ohmic contact metal is also used to form an ohmic contact with the surface of the substrate 101 away from the epitaxial layer, forming a second electrode layer 112. The ohmic contact metal includes any one or a combination of two or more of Ni, Ti, Pd, Pt, Au, Al, TiN, ITO, AuGe, AuGeNi, ITO, ZnO, IGZO, and graphene. Second electrode layer 112 forms an opposing electrode with first electrode layer 109, paving the way for subsequent external electrical connections to the laser.

[0070] In summary, the embodiment of the present invention provides a distributed feedback laser, which includes at least one grating resonant cavity structure along a first direction through multiple epitaxial layers. The grating resonant cavity structure includes a first grating structure, a resonant cavity structure, and a second grating structure arranged in sequence. The grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode. By introducing a resonant cavity structure between the first grating structure and the second grating structure, the number of grating preparations is effectively reduced, the grating preparation accuracy requirements are lowered, thereby reducing the difficulty and cost of device preparation and improving writing efficiency. Furthermore, by reasonably setting the grating period relationship between the first grating structure, the second grating structure, and the resonant cavity structure, a grating-resonant cavity-grating structure is adopted to effectively reduce the optical loss of the device, thereby improving the optical coupling efficiency and suppressing multi-mode lasing, satisfying the requirement of having only one laser wavelength output, ensuring the stability of the laser working mode, and significantly improving the application performance of the device.

[0071] Optionally, the grating period L2 of the resonant cavity structure 203 is greater than the grating periods of the first grating structure 202 and the second grating structure 204 .

[0072] For example, continue to refer to Figure 1 The grating period L2 of the resonant cavity structure 203 is greater than the grating period L1 of the first grating structure 202 and the grating period L 3, , effectively reducing the number of grating writing, reducing the loss of laser waveguide in the grating-resonance cavity-grating structure, and improving the laser coupling efficiency. For example, Figure 3 As shown, the first grating structure 202 may include two grating pairs 1-1' and 2-2'. Compared with conventional grating structures, the number of writing grating pairs is greatly reduced, thereby improving writing efficiency.

[0073] Optional, continue to refer to Figure 1 and Figure 3, the grating equation of the first grating structure 202 satisfies: mλ=2n1L1, L1 is the grating period of the first grating structure 202, n1 is the refractive index of the first grating structure 202, λ is the laser wavelength, m≥2 and m is a positive integer;

[0074] The grating equation of the resonant cavity structure 203 satisfies: gλ=2n2 L2, where L2 is the grating period of the resonant cavity structure 203, n2 is the refractive index of the resonant cavity structure 203, g≥2 and g is a positive integer;

[0075] The grating equation of the second grating structure 204 satisfies: kλ=2n3 L3, where L3 is the grating period of the second grating structure 204, n3 is the refractive index of the second grating structure 204, k≥2 and k is a positive integer;

[0076] Among them, the lowest common factor of m, g and k is 1.

[0077] For example, continue to refer to Figure 1 and Figure 3 As shown in the X direction in the figure, the grating period L1 of the first grating structure 202 includes the unetched area width a1 and the etched area width b1, and the grating period L3 of the second grating structure 204 includes the unetched area width a2 and the etched area width b2. The grating period can be changed by adjusting the sizes of the etched area widths b1 and b2.

[0078] For example, in actual production, depending on the different laser wavelengths λ used in the grating application and the requirements for writing accuracy, a symmetrical arrangement is typically employed, wherein the first grating structure 202 and the second grating structure 204 have the same structure, i.e., the grating period L1 of the first grating structure is equal to the grating period L2 of the second grating structure. Specifically, the refractive index n1 of the first grating structure 202 is equal to the refractive index n1 of the second grating structure, satisfying the same grating equation: mλ = 2n1 L1 or kλ = 2n3 L3. This means that an m-order high-order grating or a k-order high-order grating with a laser wavelength of λ can achieve mode selection for a laser operating wavelength of λ. Furthermore, the grating equation of the resonant cavity structure 203 between the two gratings satisfies: gλ=2n2 L2. The resonant cavity structure 203 acts as a grating and plays a mode selection role. When the grating period of the resonant cavity structure 203 is L2, a g-order high-order grating with a laser wavelength of λ is satisfied. By setting the lowest common factor of the grating orders m, g and k to 1, while reducing the number of grating pairs, the pillow grating and the resonant cavity have the same laser operating wavelength, and there is only one common laser lasing mode λ, thereby achieving precise locking of the DFB laser operating mode.

[0079] For example, using a symmetrical structure with the same grating shape, m, g, and k can be selected to be greater than or equal to 20, that is, a 20th-order high-order grating or higher for the laser wavelength λ. Taking the laser emission mode of a DFB laser, that is, the laser operating wavelength λ is 450nm as an example, the refractive indices n1 and n3 can be 2.5, and the refractive index n1 can be 3.5, as shown in Table 1. For example, if m and k are both selected to be 20, the grating period of the first grating structure 202 satisfies the grating equation: 20λ = 2n1L 1， The grating period of the second grating structure 204 satisfies the grating equation: 20λ = 2n3L2. The grating periods L1 and L2 are 1800nm, and g is selected as 189. The grating equation of the resonant cavity structure 203 satisfies: 189λ = 2n3L3, with a grating period L3 of 12150nm. When the laser wavelength is determined to be 450nm, the first-order grating λ corresponding to the laser wavelength of 450nm is 2nL, and the grating period L is 90nm. Resonant cavity structure 203 is used to replace a grating structure, reducing the number of grating pairs required for the grating structure. The first grating structure 202, the second grating structure 204, and the resonant cavity structure 203 all select the same laser operating wavelength of 450nm. By adopting a grating-resonant cavity-grating structure, the grating period can be increased by more than 20 times, and is not limited to grating structures with short grating periods of first-order gratings, thereby effectively reducing the difficulty and cost of device manufacturing.

[0080] Table 1 Grating equation

[0081]

[0082] The laser emission mode, i.e., the laser operating wavelength λ, of the DFB laser provided in this embodiment of the present invention meets the laser wavelength application of commercially available lasers. Preferably, the laser wavelength λ satisfies the range of 200nm≤λ≤2μm. It should be noted that this embodiment only uses a laser wavelength of 450nm as an example to illustrate a feasible grating-resonant cavity-grating structure combination. Further high-order grating combinations and wavelength applications are not listed in detail here.

[0083] Optional, continue to refer to Figure 2 and Figure 3 The first grating structure 202 , the resonant cavity structure 203 and the second grating structure 204 have the same film structure.

[0084] Exemplarily, the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204 are configured to have the same film structure to satisfy the excitation amplification of the laser in the light field cavity formed by the grating-resonant cavity-grating structure, thereby selecting and outputting a common lasing mode.

[0085] Optional, continue to refer to Figure 1-3The multi-layer epitaxial layer 10 includes a buffer layer 102, a lower optical field limiting layer 103, a lower waveguide layer 104, an active region 105, an upper waveguide layer 106, an upper optical field limiting layer 107 and an upper contact layer 108, which are sequentially arranged on one side of a substrate 101;

[0086] The distributed feedback laser further includes a ridge structure 201, which extends along a first direction (as shown in the X direction in the figure), and includes a first electrode layer 109, an upper contact layer 108 and a portion of an upper optical field confinement layer 107 (as shown in the figure). Figure 1 and Figure 2 shown);

[0087] The first grating structure 202 includes a first sub-grating structure 2021, a first ridge grating structure 2011, and a second sub-grating structure 2022 arranged in sequence along a second direction (as shown in the Y direction in the figure); the second direction intersects the first direction and is parallel to the plane where the substrate is located;

[0088] The resonant cavity structure 203 includes a first sub-resonant cavity structure 2031, a ridge-shaped resonant cavity structure 2012, and a second sub-resonant cavity structure 2032 arranged in sequence along the second direction;

[0089] The second grating structure 204 includes a third sub-grating structure 2041, a second ridge grating structure 2013 and a fourth sub-grating structure 2042 arranged in sequence along the second direction;

[0090] The first sub-grating structure 2021, the second sub-grating structure 2022, the first sub-resonant cavity structure 2031, the second sub-resonant cavity structure 2032, the third sub-grating structure 2041 and the fourth sub-grating structure 2042 all include a portion of the upper optical field confinement layer 107; the first ridge grating structure 2011, the ridge resonant cavity structure 2012 and the second ridge grating structure 2013 include a first electrode layer 109, an upper contact layer 108 and an upper optical field confinement layer 107 (such as Figure 2 and Figure 3 shown);

[0091] Alternatively, the first sub-grating structure 2021, the second sub-grating structure 2022, the first sub-resonant cavity structure 2031, the second sub-resonant cavity structure 2032, the third sub-grating structure 2041 and the fourth sub-grating structure 2042 all include part of the upper light field limiting layer 107, the upper waveguide layer 106, the active area 105, the lower waveguide layer 104 and the lower light field limiting layer 103; the first ridge grating structure 2011, the ridge resonant cavity structure 2012 and the second ridge grating structure 2013 include the first electrode layer 109, the upper contact layer 108 and the upper light field limiting layer 107, the upper waveguide layer 106, the active area 105, the lower waveguide layer 104 and the lower light field limiting layer 103.

[0092] For example, 1- Figure 3 As shown, the multilayer epitaxial layer 10 includes a lower optical field confinement layer 103, a lower waveguide layer 104, an active region 105, an upper waveguide layer 106, an upper optical field confinement layer 107, and an upper contact layer 108, which are sequentially arranged on one side of the substrate. The distributed feedback laser also includes a ridge structure 201. The ridge structure 201 facilitates external electric field contact and improves optical field coupling efficiency. As shown in the Y direction in the figure, the first grating structure 202 includes a first sub-grating structure 2021, a first ridge grating structure 2011, and a second sub-grating structure 2022, which are sequentially arranged along the second direction (as shown in the Y direction in the figure). The resonant cavity structure 203 includes a first sub-resonant cavity structure 2031, a ridge resonant cavity structure 2012, and a second sub-resonant cavity structure 2032, which are sequentially arranged along the second direction. The second grating structure 204 includes a third sub-grating structure 2041, a second ridge grating structure 103, and a fourth sub-grating structure 2042, which are sequentially arranged along the second direction.

[0093] Due to the introduction of the ridge structure, the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204 have a film structure with a height difference. Preferably, the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204 can be confined between the first electrode layer 109, the upper contact layer 108 and the upper optical field confinement layer 107. Figure 2 and Figure 3 as shown; alternatively, the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204 can be confined between the first electrode layer 109, the upper contact layer 108 and the upper light field limiting layer 107, the upper waveguide layer 106, the active region 105, the lower waveguide layer 104 and the lower light field limiting layer 103, and the lowest end of the grating structure reaches the upper surface of the buffer layer 102 (not shown in this structural diagram). Compared with conventional surface ridge sidewall gratings, the ridge grating structure proposed in the present invention has a first grating structure 202 and a second grating structure 204 that span the ridge structure 201 to form a film structure with a height difference, while the laser light field is mainly distributed below the ridge structure 201. Through this structural design, the ridge grating structure and the laser light field overlap more, the light field coupling effect is stronger, and better laser single longitudinal mode selective output can be achieved; at the same time, the resonant cavity has very small optical loss compared to the continuous ridge grating structure. Therefore, the DFB semiconductor laser proposed in the present invention has the advantages of high grating coupling efficiency and low grating scattering loss.

[0094] As a feasible implementation method, the multi-layer epitaxial layer includes a buffer layer, a lower optical field confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field confinement layer and an upper contact layer, which are sequentially arranged on one side of the substrate;

[0095] The first grating structure, the resonant cavity structure and the second grating structure each include a first electrode layer, an upper contact layer and an upper optical field confinement layer;

[0096] Alternatively, the first grating structure, the resonant cavity structure and the second grating structure all include a first electrode layer, an upper contact layer, an upper optical field confinement layer, an upper waveguide layer, an active region, a lower waveguide layer and a lower optical field confinement layer.

[0097] Exemplarily, the first grating structure, the resonant cavity structure, and the second grating structure can also be arranged at the same height. Specifically, the first grating structure, the resonant cavity structure, and the second grating structure are all confined to the first electrode layer, the upper contact layer, and the upper optical field confinement layer; or the first grating structure, the resonant cavity structure, and the second grating structure are all confined between the first electrode layer, the upper contact layer, the upper optical field confinement layer, the upper waveguide layer, the active region, the lower waveguide layer, and the lower optical field confinement layer. Compared with the conventional continuous ridge grating structure, the present grating-resonant cavity-grating structure arrangement satisfies the requirement of having only one laser operating mode output by rationally adjusting the relationship between the grating period L of the first grating structure, the resonant cavity structure, and the second grating structure. This effectively reduces the number of grating pairs to be written and improves writing efficiency while achieving a single-mode laser output effect with high coupling efficiency and low loss, thus meeting the application requirements of the laser.

[0098] Optional, continue to refer to Figure 1-3 As shown, the laser epitaxial structure further includes a connecting electrode 113 and a dielectric layer 111;

[0099] The dielectric layer 111 partially covers the upper surfaces of the first grating structure 202 , the resonant cavity structure 203 and the second grating structure 204 , exposing at least the first electrode layer 109 ;

[0100] The connecting electrode 113 covers the first electrode layer 109 , and the thickness of the connecting electrode 113 is greater than the thickness of the first electrode layer 109 .

[0101] For example, Figure 2 and 3 As shown, since the ohmic contact metal of the first electrode layer 109 is relatively thin, which is not conducive to the actual production of electrical connections, an ohmic contact metal with good conductivity is added to form a connecting electrode 113, so that the connecting electrode 113 covers the first electrode layer 109, ensuring that the connecting electrode 113 and the second electrode 114 form a stable electric field, and the thickness of the connecting electrode 112 is set to be greater than the thickness of the first electrode layer 110, forming a thickened electrode. On the one hand, it increases the connection stability, and on the other hand, it reduces the difficulty of preparing an external power supply for the laser. Among them, the ohmic contact metal of the connecting electrode 113 includes any one or a combination of two or more of Ni, Ti, Pd, Pt, Au, Al, TiN, ITO, AuGe, AuGeNi, ITO, ZnO, IGZO and graphene.

[0102] For details, please refer to Figure 2 and Figure 3 In order to ensure that the connecting electrode 113 is effectively electrically connected only to the first electrode layer 109 and to avoid the introduction of electrodes into the sidewalls of the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204, which would affect the electric field distribution of the laser epitaxial structure, a dielectric layer 111 is used to partially cover the upper surfaces of the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204, exposing at least the first electrode layer 109 to form electrical insulation. The dielectric layer 111 includes materials such as HfO2, Si, SiO2, SiN x , SiON, Al2O3, AlON, SiAlON, TiO2, Ta2O5, ZrO2, MgO and polycrystalline silicon and other materials, any one or a combination of two or more.

[0103] Figure 15 A schematic diagram of the surface of the laser epitaxial structure of another distributed feedback laser provided by an embodiment of the present invention. Figure 15 As shown, optionally, the multi-layer epitaxial layer includes at least two grating resonant cavity structures arranged in sequence; the two adjacent grating resonant cavity structures jointly include the first grating structure or the second grating structure.

[0104] For example, by adjusting the laser epitaxial structure, the laser's structure, wavelength, power and other parameters can be improved, such as Figure 15 As shown, the multi-layer epitaxial layer in the laser epitaxial structure may include at least two grating resonant cavity structures arranged in sequence, and the grating resonant cavity structure includes a first grating structure 202, a resonant cavity structure 203 and a second grating structure 204 arranged in sequence, and two adjacent grating resonant cavity structures jointly include the first grating structure 202 (not shown in the figure) or the second grating structure 204 (as shown in the figure). Figure 15 As shown), the grating resonant cavity structure has one and only one lasing mode output.

[0105] In summary, the distributed feedback semiconductor laser structure proposed in the present invention effectively reduces the number of grating pairs to be written in the grating structure, reduces the difficulty of device preparation, improves the writing rate, greatly increases the grating preparation accuracy, reduces the optical loss of the device, and ultimately significantly improves the device performance and reduces the device cost.

[0106] An embodiment of the present invention provides a method for preparing a distributed feedback laser, which is used to prepare the distributed feedback laser shown in the above embodiment. Figure 4 A schematic flow chart of a method for preparing a distributed feedback laser according to an embodiment of the present invention is provided. Figure 5 A schematic cross-sectional view of a laser epitaxial structure of a distributed feedback laser provided by an embodiment of the present invention; Figure 6 for Figure 7 Schematic diagram of the cross section of the laser epitaxial structure along AA' after etching the ridge structure; Figure 7 This is a schematic diagram of the surface of the semiconductor laser structure after the ridge is etched; Figure 8 for Figure 5 Schematic diagram of the cross section of the semiconductor laser epitaxial structure after the dielectric film is deposited; Figure 9 for Figure 8 Schematic cross-sectional view of the semiconductor laser epitaxial structure after stripping the dielectric film; Figure 10 Schematic diagram of the surface of the semiconductor laser structure after preparing multi-segment gratings by photolithography; Figure 11 Figure 10 Schematic diagram of the cross section of the semiconductor laser structure along BB' after the multi-segment grating is fabricated by photolithography and etching; Figure 12 for Figure 10 Schematic diagram of the cross section of the semiconductor laser structure along BB' after wet etching; Figure 13 This is a schematic cross-sectional view of the semiconductor laser structure after the second electrode is prepared on the substrate surface. Figure 4 As shown, the preparation method of the distributed feedback laser includes:

[0107] S101 , preparing a laser epitaxial structure, where the laser epitaxial structure includes a substrate and a plurality of epitaxial layers located on one side of the substrate.

[0108] Specifically, a laser epitaxial structure is prepared, such as Figure 5 As shown, multiple epitaxial layers are sequentially grown on one side of the substrate 101 material, including a buffer layer 102, a lower optical field limiting layer 103, a lower waveguide layer 104, an active region 105, an upper waveguide layer 106, an upper optical field limiting layer 107, and an upper contact layer 108. The materials of the upper contact layer 108, the upper optical field limiting layer 107, the lower optical field limiting layer 103, the upper waveguide layer 106, and the active region 105 include

[0109] Al x1 In y1 Ga 1-x1-y1 As x2 P y2 N 1-x2-y2 , satisfying 0≤x1≤1, 0≤y1≤1, 0≤x2≤1, 0≤y2≤1, 0≤(x1+y1)≤1, 0≤(x2+y2)≤1. For example, GaN material, based on the characteristics of the distributed feedback laser, different epitaxial layer materials are selected, so that the epitaxial layer has a variety of materials to choose from, and no specific limitation is given here.

[0110] S102 , preparing a first electrode layer on a side of the epitaxial layer away from the substrate.

[0111] Specifically, the epitaxial structure is cleaned, and a first electrode layer 109 is deposited on the side of the upper contact layer 107 of the epitaxial layer away from the substrate 101. The first electrode layer 109 comprises any one or a combination of two or more of the materials selected from Ni, Ti, Pd, Pt, Au, Al, Cr, TiN, ITO, AuGe, AuGeNi, and IGZO. For example, Pt / Au can be selected, and rapid thermal annealing in air is performed to ensure that the Pt / Au forms a good ohmic contact with the upper contact layer 108. Finally, the first electrode layer 109 is formed on the side of the upper contact layer 108 away from the substrate 101, forming an ohmic contact electrode with the epitaxial structure.

[0112] S103. Etch a multilayer epitaxial layer along a first direction to prepare at least one grating resonant cavity structure, wherein the grating resonant cavity structure includes a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along the first direction; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; the first direction is parallel to the plane where the substrate is located.

[0113] Specifically, according to the lasing mode of the DFB laser, the number of grating pairs of the grating-resonant cavity-grating structure to be prepared and the grating period L are determined. Taking the preparation of the ridge grating structure as an example, the method of applying glue on the surface of the laser epitaxial structure is adopted. Specifically, conventional photolithography technology is used to etch the first electrode layer 109, the upper contact layer 108 and a part of the upper optical field confinement layer 107 to form the ridge structure 201, as shown in FIG. Figure 6 As shown; further, the etching width b1 passes through the ridge structure 201 to obtain the grating period L1 of the first grating structure 202, and the etching width b2 passes through the ridge structure 201 to obtain the grating period L3 of the second grating structure 204, and the first grating structure 202, the resonant cavity structure 203 and the second grating structure 204 are prepared by etching. Figure 1-3 As shown. Optionally, the contact surface between the upper optical field limiting layer 107 and the upper waveguide layer 106 can be etched (eg Figure 6 ), or etching to the contact surface between the lower optical field limiting layer and the buffer layer 102, preferably etching to the contact surface between the upper optical field limiting layer 107 and the upper waveguide layer 106, can effectively reduce optical loss. By controlling the width b1 of the etched area to be equal or different, the grating period L of the grating structure can be made the same or different, thereby obtaining a ridge grating structure, and further obtaining a resonant cavity structure 203 with a grating period of L2. Figure 1 As shown, the resonant cavity structure 203 is located between the grating structures, and the grating period L of the grating-resonant cavity-grating structure obtained by etching satisfies the high-order grating equation of the laser wavelength λ.

[0114] S104 , preparing a second electrode layer on a side of the substrate away from the epitaxial layer.

[0115] For example, Figure 13 As shown, the prepared epitaxial structure is further thinned, ground and polished, and an ohmic contact metal is deposited on the side of the substrate 101 away from the epitaxial layer to prepare a second electrode layer 114, which is arranged opposite to the first electrode layer 109 to form an ohmic contact electrode pair.

[0116] S105 , performing scribing, cleavage, coating, and splitting processes on the epitaxial structure to form a distributed feedback laser.

[0117] Specifically, according to the needs of laser production, the epitaxial structure is further subjected to reasonable scribing, cleavage, coating and splitting processes to prepare the required distributed feedback laser.

[0118] In summary, the method for preparing a distributed feedback laser provided by an embodiment of the present invention uses conventional photolithography technology to obtain a grating-resonance cavity-grating structure combination, which satisfies the function of selecting a mode with only one common lasing mode. Compared with the use of a full grating structure, the number of grating pairs is reduced, the grating period is increased, and the difficulty and cost of device preparation are effectively reduced. Furthermore, by reasonably setting the grating period relationship between the first grating structure, the second grating structure, and the resonant cavity structure, the grating-resonance cavity-grating structure is adopted to effectively reduce the optical loss of the device, thereby improving the optical coupling efficiency and suppressing multi-mode lasing, satisfying the output of one and only one laser wavelength, ensuring the stability of the laser operating mode, and significantly improving the application performance of the device.

[0119] On the basis of the above embodiment, after etching multiple epitaxial layers to prepare the first grating structure, the resonant cavity structure, and the second grating structure, the method further includes:

[0120] An alkaline solution is used to etch the sidewalls of the first grating structure, the ridge resonant cavity structure and the second grating structure.

[0121] For example, Figure 11 and Figure 12 As shown, ammonium hydroxide solution is used for wet etching to wet-etch the sidewalls of the first laser grating structure 202, the resonant cavity structure 203, and the second grating structure (not shown) prepared by dry etching to obtain smooth, steep, and flat sidewalls (as shown in FIG. Figure 12 As shown in the figure, it effectively improves the corrosion smoothness of the grating-resonance cavity-grating structure surface, reduces the loss of light in the cavity surface, eliminates the problems of non-radiative recombination and leakage caused by dry etching damage, reduces non-radiative recombination and leakage in the laser, and thus effectively reduces the threshold current of the device, improving the device performance and reliability.

[0122] Illustratively, in this embodiment, the wet etching solution for preparing the DFB laser can be an amino alkaline solution, including at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide. Specifically, a weak alkaline tetramethylammonium hydroxide solution is used to wet-etch the III-nitride semiconductor to remove the sidewall damage prepared by dry etching, thereby obtaining a smooth, steep, and flat surface. The amino weak alkaline solution does not react violently with the substrate, epitaxial layer, and metal, and thus can be used in the preparation of DFB lasers.

[0123] An embodiment of the present invention further provides a method for preparing a distributed feedback laser, which is used to prepare the distributed feedback laser shown in the above embodiment. Figure 14 A schematic flow chart of another method for preparing a distributed feedback laser provided by an embodiment of the present invention is shown in FIG. Figure 14 As shown, optionally, the preparation method of the distributed feedback laser includes:

[0124] S201 , preparing a laser epitaxial structure, where the laser epitaxial structure includes a substrate and a plurality of epitaxial layers located on one side of the substrate.

[0125] S202 , preparing a first electrode layer on a side of the epitaxial layer away from the substrate.

[0126] S203. Etching multiple epitaxial layers along a first direction to prepare at least one grating resonant cavity structure, wherein the grating resonant cavity structure includes a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along the first direction; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; the first direction is parallel to the plane where the substrate is located.

[0127] S204. Depositing a dielectric layer on a side of the first electrode layer away from the substrate, the dielectric layer covers the upper surfaces of the first grating structure, the resonant cavity structure, and the second grating structure; using photolithography and etching techniques, removing part of the dielectric layer on the upper surfaces of the first grating structure, the resonant cavity structure, and the second grating structure to expose the first electrode layer.

[0128] Specifically, a dielectric layer is deposited on the side of the first electrode layer away from the substrate, such as Figure 8 As shown, the dielectric layer uses insulating dielectric film materials, including SiO2, SiN x, SiON, Al2O3, AlON, SiAlON, TiO2, Ta2O5, ZrO2, HfO2, Si and polysilicon, or any one or a combination of two or more thereof, the dielectric layer covers the upper surfaces of the first grating structure, the resonant cavity structure and the second grating structure. It should be noted that, based on the above embodiment, when a ridge grating-resonant cavity structure is adopted and the ridge structure is prepared by dry etching, a dielectric layer can be first deposited on the side of the first electrode layer on the upper surface of the ridge structure away from the substrate to prepare a dielectric layer, and then the ridge grating-resonant cavity-grating structure is etched, such as Figure 8-10 As shown; the ridge grating-resonant cavity-grating structure can also be etched first, and then a dielectric layer is deposited on the side of the first electrode layer on the upper surface of the ridge structure away from the substrate to prepare a dielectric layer, and finally the dielectric layer covers the upper surfaces of the first grating structure, the resonant cavity structure and the second grating structure to play an insulating and protective role.

[0129] Furthermore, the dielectric layer on the upper surface of the ridge structure is removed by photolithography and etching techniques to expose the first electrode layer, such as Figure 9 As shown, it is used to prepare connecting electrodes.

[0130] S205 , preparing a connecting electrode on a side of the dielectric layer away from the substrate, wherein the connecting electrode covers the exposed first electrode layer.

[0131] Specifically, a highly conductive ohmic contact metal is deposited on the side of the dielectric layer away from the substrate to form a connecting electrode 113, covering the exposed first electrode layer 109. Because the ohmic contact metal of the first electrode layer 109 is relatively thin, which is not conducive to actual electrical connection in production, the addition of highly conductive ohmic contact metal ensures that a stable electric field is formed between the connecting electrode 113 and the second electrode 114. Furthermore, the thickness of the connecting electrode 113 is set to be greater than that of the first electrode layer 109, forming a thickened electrode. This not only increases connection stability, but also reduces the difficulty of manufacturing an external power supply for the laser.

[0132] S206 , preparing a second electrode layer on a side of the substrate away from the epitaxial layer.

[0133] S207 , performing scribing, cleavage, coating, and splitting processes on the epitaxial structure to form a distributed feedback laser.

[0134] Optional, see Figure 4 , preparing the laser epitaxial structure includes:

[0135] Provide lining 101.

[0136] A buffer layer 102 is formed on the substrate side.

[0137] A lower optical field confinement layer 103 is formed on a side of the buffer layer 102 away from the substrate 101 .

[0138] A lower waveguide layer 104 is formed on a side of the lower optical field confinement layer 103 away from the substrate 101 .

[0139] An active region 105 is formed on a side of the lower waveguide layer 104 away from the substrate 101 .

[0140] An upper waveguide layer 106 is formed on a side of the active region 105 away from the substrate 101 .

[0141] An upper optical field confinement layer 107 is formed on a side of the upper waveguide layer 106 away from the substrate 101 .

[0142] An upper contact layer 108 is formed on a side of the upper optical field confinement layer 107 away from the substrate 101 .

[0143] Exemplarily, a substrate material is provided, including any one or a combination of two or more of GaAs, InP, GaN, AlGaN, InGaN, AlN, sapphire, SiC, Si, and SOI, and an epitaxial structure is formed along a side away from the substrate 101. Specifically, a lower optical field confinement layer 103 is formed on a side of the buffer layer 102 away from the substrate 101, a lower waveguide layer 104 is formed on a side of the lower optical field confinement layer 103 away from the substrate 101, an active region 105 is formed on a side of the lower waveguide layer 104 away from the substrate 101, an upper waveguide layer 106 is formed on a side of the active region 105 away from the substrate 101, an upper optical field confinement layer 107 is formed on a side of the upper waveguide layer 106 away from the substrate 101, and an upper contact layer 109 is formed on a side of the upper optical field confinement layer 107 away from the substrate 101.

[0144] As a feasible implementation scheme, a specific example is given. Based on the preparation method provided in the above embodiment, an indium phosphide (InP) based semiconductor laser is prepared. For example, a resonant cavity structure with a ridge grating structure is prepared. Figure 4-13 The specific preparation method is as follows:

[0145] Provide an n-InP substrate 101 material, and use a metal organic chemical vapor deposition (MOCVD) device to epitaxially grow a 1 μm n-InP buffer layer, a 1 μm n-InP lower optical field confinement layer, a 100 nm AlGaAs lower waveguide layer, 8 pairs of AlGaInAs strained multi-quantum wells with a periodic thickness of 15 nm, a 100 nm InAlGaAs upper waveguide layer, a 1.2 μm p-InP upper optical field confinement layer, and a 50 nm p-InGaAs contact layer on the n-InP substrate 1. Figure 4 shown.

[0146] The epitaxial wafer is cleaned, and a first electrode Ti / Au is formed on the surface of the epitaxial wafer and subjected to rapid thermal annealing in an air atmosphere to form an ohmic contact with the upper contact layer p-InGaAs to form a first electrode layer 109 .

[0147] Spin-coat the photoresist on the surface of the epitaxial wafer, use conventional photolithography technology to photoetch the pattern of the ridge structure, and then perform inductively coupled plasma (ICP) etching or wet etching with a mixed solution of sulfuric acid, hydrogen peroxide and water to form a ridge structure. Figure 6 and Figure 7 shown.

[0148] Deposit dielectric layer, deposit 200nm SiO2 dielectric film on the surface of epitaxial wafer at low temperature, such as Figure 8 As shown, the photoresist on the ridge is then stripped to passivate the sidewalls of the ridge structure to form a dielectric layer, as shown in FIG. Figure 9 shown.

[0149] Etching a multi-segment grating structure, depositing a metal mask Ni on the surface of the epitaxial wafer, and then performing photolithography to prepare a multi-segment grating. The grating spans the ridge area, and there is a certain interval period between the gratings, forming a ridge-shaped grating-resonance cavity-grating structure, such as Figure 1 and Figure 11 As shown; then the sidewalls of the dry etching are wet-etched to form a steep and smooth sidewall structure, forming a laser structure, as shown Figure 12 shown.

[0150] Add a connecting electrode, remove the metal mask Ni by using hydrochloric acid and hydrogen peroxide solution, then spin-coat photoresist on the surface of the epitaxial wafer for photolithography, and then combine the coating and lift-off technology to prepare the thickened electrode Cr / Au of the first electrode on the upper surface of the laser epitaxial wafer to form a connecting electrode 113, as shown in FIG. Figure 13 shown.

[0151] The epitaxial wafer is thinned, ground and polished, and then a second electrode 114 is prepared on the back of the n-InP substrate 101. The ohmic metal material can be Cr / Pt / Au, such as Figure 13 shown.

[0152] Slicing, cleaving, coating and breaking are performed to form laser die.

[0153] An embodiment of the present invention proposes a method for preparing a distributed feedback semiconductor laser structure. The prepared structure is a combination of a multi-segment high-order grating and a resonant cavity structure prepared by conventional photolithography technology. The structure can achieve high selectivity of the first-order grating, lock the laser emission mode of the indium phosphate (InP)-based semiconductor laser, that is, the laser wavelength λ, effectively reduce the number of grating structure writings, improve the writing efficiency, and reduce the difficulty of device preparation. The structure has the advantages of high grating coupling efficiency and low grating scattering loss. Not only can single longitudinal mode operation be achieved, but also the device performance of the DFB laser can be significantly improved to meet the high requirements of practical applications.

[0154] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and the features of the various embodiments of the present invention may be partially or completely coupled or combined with each other, and may cooperate with each other in various ways and be technically driven. It is possible for those skilled in the art to make various obvious changes, readjustments, combinations and substitutions without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A distributed feedback laser, characterized in that: include: A laser epitaxial structure, comprising a substrate and a plurality of epitaxial layers located on one side of the substrate; a first electrode layer located on a side of the epitaxial layer away from the substrate; wherein the multiple epitaxial layers include at least one grating resonant cavity structure, the grating resonant cavity structure including a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along a first direction; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; and the first direction is parallel to the plane of the substrate; A second electrode layer is located on a side of the substrate away from the epitaxial layer.

2. The distributed feedback laser according to claim 1, characterized in that The grating period of the resonant cavity structure is greater than the grating periods of the first grating structure and the second grating structure.

3. The distributed feedback laser according to claim 1, wherein: The grating equation of the first grating structure satisfies: mλ=2n1 L1, L1 is the grating period of the first grating structure, n1 is the refractive index of the first grating structure, λ is the laser wavelength, m≥2 and m is a positive integer; The grating equation of the resonant cavity structure satisfies: gλ=2n2 L2, L2 is the grating period of the resonant cavity structure, n2 is the refractive index of the resonant cavity structure, g≥2 and g is a positive integer; The grating equation of the second grating structure satisfies: kλ=2n3 L3, L3 is the grating period of the second grating structure, n3 is the refractive index of the first grating structure, k≥2 and k is a positive integer; Among them, the lowest common factor of m, g and k is 1.

4. The distributed feedback laser according to claim 1, wherein: The first grating structure, the resonant cavity structure and the second grating structure have the same film layer structure.

5. The distributed feedback laser according to claim 4, characterized in that The multiple epitaxial layers include a buffer layer, a lower optical field limiting layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field limiting layer and an upper contact layer, which are sequentially arranged on one side of the substrate; The distributed feedback laser further includes a ridge structure, the ridge structure extending along the first direction, and the ridge structure includes the first electrode layer, the upper contact layer and a portion of the upper optical field confinement layer; The first grating structure includes a first sub-grating structure, a first ridge grating structure, and a second sub-grating structure sequentially arranged along a second direction; the second direction intersects the first direction and is parallel to the plane where the substrate is located; The resonant cavity structure includes a first sub-resonant cavity structure, a ridge-shaped resonant cavity structure, and a second sub-resonant cavity structure sequentially arranged along the second direction; The second grating structure includes a third sub-grating structure, a second ridge grating structure and a fourth sub-grating structure sequentially arranged along the second direction; The first sub-grating structure, the second sub-grating structure, the first sub-resonant cavity structure, the second sub-resonant cavity structure, the third sub-grating structure and the fourth sub-grating structure all include a portion of the upper optical field confinement layer; the first ridge grating structure, the ridge resonant cavity structure and the second ridge grating structure include the first electrode layer, the upper contact layer and the upper optical field confinement layer; Alternatively, the first sub-grating structure, the second sub-grating structure, the first sub-resonant cavity structure, the second sub-resonant cavity structure, the third sub-grating structure and the fourth sub-grating structure all include part of the upper light field limiting layer, the upper waveguide layer, the active area, the lower waveguide layer and the lower light field limiting layer; the first ridge grating structure, the ridge resonant cavity structure and the second ridge grating structure include the first electrode layer, the upper contact layer, the upper light field limiting layer, the upper waveguide layer, the active area, the lower waveguide layer and the lower light field limiting layer.

6. The distributed feedback laser according to claim 4, characterized in that The multiple epitaxial layers include a buffer layer, a lower optical field limiting layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field limiting layer and an upper contact layer, which are sequentially arranged on one side of the substrate; The first grating structure, the resonant cavity structure and the second grating structure each include the first electrode layer, the upper contact layer and the upper optical field confinement layer; Alternatively, the first grating structure, the resonant cavity structure and the second grating structure all include the first electrode layer, the upper contact layer, the upper optical field limiting layer, the upper waveguide layer, the active region, the lower waveguide layer and the lower optical field limiting layer.

7. The distributed feedback laser according to any one of claims 1 to 6, characterized in that: The laser epitaxial structure further includes a connecting electrode and a dielectric layer; The dielectric layer partially covers the upper surfaces of the first grating structure, the resonant cavity structure and the second grating structure, exposing at least the first electrode layer; The connecting electrode covers the first electrode layer, and a thickness of the connecting electrode is greater than a thickness of the first electrode layer.

8. The distributed feedback laser according to claim 1, characterized in that The multiple epitaxial layers include at least two grating resonant cavity structures arranged in sequence; Two adjacent grating resonant cavity structures jointly include the first grating structure or the second grating structure.

9. A method for preparing a distributed feedback laser, for preparing the distributed feedback laser according to any one of claims 1 to 8, characterized in that: include: preparing a laser epitaxial structure, the laser epitaxial structure comprising a substrate and a plurality of epitaxial layers located on one side of the substrate; forming a first electrode layer on a side of the epitaxial layer away from the substrate; Etching multiple layers of the epitaxial layer along the first direction to prepare at least one grating resonant cavity structure, wherein the grating resonant cavity structure includes a first grating structure, a resonant cavity structure, and a second grating structure sequentially arranged along the first direction; the grating period of the first grating structure and the second grating structure is different from the grating period of the resonant cavity structure, and the first grating structure, the resonant cavity structure, and the second grating structure have only one common lasing mode; and the first direction is parallel to the plane of the substrate; preparing a second electrode layer on a side of the substrate away from the epitaxial layer; The epitaxial structure is subjected to scribing, cleaving, coating and splitting processes to form a distributed feedback laser.

10. The preparation method according to claim 9, characterized in that After etching multiple layers of the epitaxial layer to prepare the first grating structure, the resonant cavity structure, and the second grating structure, the method further includes: etching sidewalls of the first grating structure, the resonant cavity structure, and the second grating structure using an alkaline solution; depositing a dielectric layer on a side of the first electrode layer away from the substrate, wherein the dielectric layer covers upper surfaces of the first grating structure, the resonant cavity structure, and the second grating structure; Using photolithography and etching technology, remove a portion of the dielectric layer on the upper surfaces of the first grating structure, the resonant cavity structure, and the second grating structure to expose the first electrode layer; A connecting electrode is prepared on a side of the dielectric layer away from the substrate, and the connecting electrode covers the exposed first electrode layer.

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