DFB laser based on two-section phase shift lambda / 2 top metal grating

Abstract

The invention relates to the technical field of semiconductor lasers, in particular to a DFB laser based on two sections of phase shift lambda / 2 top metal gratings. An optical waveguide; the metal BRAGG reflecting grating is arranged at the top of the optical waveguide, the metal BRAGG reflecting grating comprises a metal BRAGG reflecting grating I and a metal BRAGG reflecting grating II, and a phase lambda / 2 movement broadening is arranged between the metal BRAGG reflecting grating I and the metal BRAGG reflecting grating II. The SMSR ratio is effectively improved by adopting the two sections of gratings, meanwhile, the top metal grating replaces a traditional interlayer type semiconductor grating, secondary epitaxy is not needed, the technological process is simplified, the simplified process reduces steps in the manufacturing process and dependence on high-precision equipment, the manufacturing cost is reduced, the production efficiency and the product yield are improved, and the production cost is reduced. Therefore, the performance of the laser is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor lasers, and in particular to a DFB laser based on two-segment phase-shifted λ / 2 top metal gratings. Background Art

[0002] DFB (Distributed Feedback Laser) lasers, or distributed feedback lasers, are distinguished by their built-in Bragg gratings, making them side-emitting semiconductor lasers. DFB lasers primarily use semiconductor materials as their dielectric medium, including gallium antimonide (GaSb), gallium arsenide (GaAs), indium phosphide (InP), and zinc sulfide (ZnS). The most significant feature of DFB lasers is their excellent monochromaticity (i.e., spectral purity). Their linewidth can generally be less than 1 MHz, and they exhibit a very high side-mode suppression ratio (SMSR), reaching over 40-50 dB.

[0003] From a manufacturing perspective, the process is extremely complex, requiring costly secondary epitaxy operations and the preparation of a deeply embedded sandwich-structured semiconductor grating. This secondary epitaxy not only adds process steps, significantly increasing the difficulty of the fabrication process, but also places extremely high demands on the production environment and equipment, which undoubtedly increases production costs. The preparation of a deeply embedded sandwich-structured semiconductor grating requires precise control of the thickness, composition, and interface quality of each layer of material. Even the slightest deviation will affect the performance of the grating, resulting in a low product yield. Furthermore, the grating reflectivity of traditional DFB lasers is significantly insufficient, and their reflective filtering efficiency can only reach a certain level. In applications requiring high-performance light sources with demanding light source performance, such as quantum key distribution, which requires single-photon precision light sources, and coherent optical communications, which require light sources with high stability and narrow linewidth, traditional DFB lasers struggle to meet these application requirements. Due to their limited performance, additional equipment and technology are often required to compensate for the corresponding usage standards, further driving up costs and limiting their application and development in a wider range of fields. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a DFB laser based on two-segment phase-shifted λ / 2 top metal grating.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a DFB laser based on two phase-shifted λ / 2 top metal gratings, comprising: Gain chip; An optical waveguide is arranged centered on top of the gain chip; The metal BRAGG reflection grating is arranged on the top of the optical waveguide, and the metal BRAGG reflection grating includes a first metal BRAGG reflection grating and a second metal BRAGG reflection grating, and a phase difference is set between the first metal BRAGG reflection grating and the second metal BRAGG reflection grating.

[0006] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure.

[0007] Preferably, the gain chip lasing wavelength λ ranges from 1530 to 1610 nm.

[0008] Preferably, one side of the gain chip is set as a reflector end face, and the reflector end face is coated with a λ / 2 HR high reflective film, the λ / 2 HR high reflective film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 HR high reflective film is greater than 99.9%.

[0009] Preferably, the side of the gain chip away from the reflector end face is an anti-reflection end face, and the anti-reflection end face is coated with a λ / 4AR anti-reflection film. The λ / 4 AR anti-reflection film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 AR anti-reflection film is less than 0.03%.

[0010] Preferably, the grating constant of the metal BRAGG reflection grating is λ / 2, the grating period is set to 225±0.3nm, and the duty cycle is 50±1%.

[0011] Preferably, the thickness of the metal BRAGG reflection grating is 200±5 nm.

[0012] Preferably, the metal BRAGG reflection grating adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

[0013] Preferably, the phase difference is λ / 2.

[0014] Preferably, the optical waveguide has a ridge structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses two-segment gratings to effectively improve the SMSR ratio. At the same time, the top metal grating replaces the traditional sandwich-type semiconductor grating, eliminating the need for secondary epitaxy and greatly simplifying the process flow. The simplified process reduces the steps in the production process and the dependence on high-precision equipment, reducing production costs, and improving production efficiency and product yield. In addition, the reflection and filtering efficiency of the metal grating is about 30% higher than that of the semiconductor grating, which significantly improves the performance of the laser and can better meet the needs of fields with high requirements for light source performance, such as quantum communication, coherent optical communication, and photonic integrated chips, and has broader application prospects. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a schematic diagram of the main structure of the present invention; Figure 2 It is a schematic diagram of the top view of the structure of the present invention; Figure 3 It is a side structural schematic diagram of the present invention.

[0016] In the figure: 1. Gain chip; 2. Optical waveguide; 3. Metal BRAGG reflection grating; 301. Metal BRAGG reflection grating 1; 302. Metal BRAGG reflection grating 2; 4. Phase difference; 5. λ / 2 HR high reflection film; 6. λ / 4 AR anti-reflection film. DETAILED DESCRIPTION The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are merely examples, and those skilled in the art may conceive of other obvious variations.

[0017] like Figure 1-Figure 3 As shown, the present application provides a DFB laser based on two-segment phase-shifted λ / 2 top metal grating, comprising: a gain chip 1; an optical waveguide 2, arranged in the center of the top of the gain chip 1; a metal BRAGG reflection grating 3, arranged on the top of the optical waveguide 2, and the metal BRAGG reflection grating 3 includes a metal BRAGG reflection grating 1 301 and a metal BRAGG reflection grating 2 302, and a phase difference 4 is set between the metal BRAGG reflection grating 1 301 and the metal BRAGG reflection grating 2 302.

[0018] Specifically, such as Figure 1 As shown, the gain chip 1 adopts an InP / InGaAsP quantum well structure; the lasing wavelength λ of the gain chip 1 ranges from 1530 to 1610 nm.

[0019] The InP / InGaAsP quantum well structure is selected as the basic architecture of the gain chip. This structure has good laser emission characteristics in the wavelength range of 1530-1610nm and can meet the needs of various application scenarios. At 25°C, its threshold current is less than 28mA, which means that laser emission can be achieved with lower energy consumption. The slope efficiency reaches 0.85W / A, indicating that under a certain current drive, electrical energy can be efficiently converted into light energy.

[0020] Specifically, such as Figure 1As shown, one side of the gain chip 1 is set as a reflector end face, and the reflector end face is coated with a λ / 2HR high-reflection film 5. The λ / 2 HR high-reflection film 5 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 HR high-reflection film 5 is greater than 99.9%; the side of the gain chip 1 away from the reflector end face is an anti-reflection end face, and the anti-reflection end face is coated with a λ / 4 AR anti-reflection film 6. The λ / 4 AR anti-reflection film 6 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 AR anti-reflection film 6 is less than 0.03%.

[0021] The λ / 2 HR high-reflection film 5 can effectively reduce the light loss at the reflective end face and enhance the light feedback in the cavity, and the λ / 4 AR anti-reflection film 6 can maximize the laser emission efficiency.

[0022] Specifically, such as Figure 1 As shown, the grating constant of the metal BRAGG reflection grating 3 is λ / 2, the grating period is set to 225±0.3nm, and the duty cycle is 50±1%.

[0023] The grating period is set to 225±0.3nm. Precise period control helps to achieve optical feedback of a specific wavelength, and the duty cycle is 50±1%, ensuring the uniformity and stability of the grating structure.

[0024] Specifically, such as Figure 1 As shown, the thickness of the metal BRAGG reflection grating 3 is 200±5 nm; the metal BRAGG reflection grating 3 adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

[0025] The Cr layer can enhance the adhesion between the metal and the substrate, while the Au layer has good electrical conductivity and optical reflectivity.

[0026] Specifically, such as Figure 1 and Figure 2 As shown, the phase difference 4 is λ / 2.

[0027] The metal BRAGG reflection grating 3 is divided into a metal BRAGG reflection grating 1 and a metal BRAGG reflection grating 2, and the phase difference between them is 4 and the phase shift between the two segments is λ / 2. This unique structural design can achieve high performance.

[0028] Specifically, such as Figure 1 As shown, the optical waveguide 2 is a ridge structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0029] Theoretical basis: According to coupled-mode theory, for a conventional uniform grating DFB laser, the coupling coefficient is κ, and the light field distribution can be expressed by A(z), and satisfies the following coupled-mode equation: , where β is the propagation constant. In this equation, Describes the phase change of the light field during propagation. It reflects the coupling effect of the grating on the light field, and Represents the loss of light during propagation.

[0030] For a metal grating DFB laser with two phase shifts of λ / 2, the presence of the phase shift will profoundly affect the light field distribution. Assuming that the phase shift position is at z = 0, the light field distribution before and after the phase shift can be represented by A1(z) and A2(z), respectively, and the boundary conditions are satisfied: , which means that the light field produces a π / 2 phase jump at the phase shift. This phase jump will cause the redistribution of the light field, change the propagation characteristics of light in the laser cavity, and thus affect the mode selection characteristics of the laser. During the laser generation process, different modes of light will compete with each other, and this phase jump enables the main mode to more effectively suppress the side mode, thereby improving the SMSR.

[0031] According to the Bragg condition of the grating, for a traditional uniform grating DFB laser, its Bragg wavelength is satisfy: ,in is the effective refractive index, Λ is the grating period. When two phase shifts of λ / 2 are introduced, the effective refractive index of light during propagation will also change subtly due to the phase shift changing the light field distribution, resulting in a slight change in the actual Bragg wavelength. At the same time, the gains of the main mode and side modes will also be affected. The gain of the main mode will increase relatively, while the gain of the side mode will be relatively suppressed, which further promotes the improvement of SMSR.

[0032] Practical case: In the actual preparation process, electron beam lithography (EBG) technology is first used to draw a precise grating pattern on the gain chip of the InP / InGaAsP quantum well structure. The high precision of electron beam lithography ensures the accuracy of the grating pattern and provides a good foundation for the subsequent etching process. Then, inductively coupled plasma (ICP) etching technology is used to etch the drawn pattern into a grating structure with a certain depth. The grating depth is precisely controlled at 120±5nm. Then, a Cr / Au layer is deposited by magnetron sputtering to form a metal Bragg grating with a thickness of 200±5nm (Cr / Au=50nm / 150nm), and the surface flatness is guaranteed. Less than 0.08nmRMS. At the same time, the metal grating is divided into two metal gratings with a phase shift of λ / 2 between them. Accurate control of the phase shift is achieved through precise lithography and etching processes. After the preparation of the laser is completed, the linewidth and SMSR of the laser are measured by self-heterodyne interferometry. The results show that compared with the traditional DFB laser, the SMSR of the DFB laser with two-segment phase shift of λ / 2 metal grating has been significantly improved, and the measured SMSR value has reached more than 45dB; at the same time, the measured value of the 3dB linewidth is 50Hz, which is much better than the 125kHz of the traditional DFB laser, which fully verifies the excellent improvement effect of this structure on the laser performance.

[0033] The present invention: Abandoning the traditional sandwich-type semiconductor grating, the innovative use of a top metal grating greatly simplifies the manufacturing process. This structural change eliminates the need for complex secondary epitaxy and the preparation of deeply buried sandwich-structured semiconductor gratings, directly reducing production costs. More importantly, the metal grating is cleverly divided into two parts, and two phase shifts of λ / 2 are introduced between them. This unique design significantly improves the side mode suppression ratio (SMSR) performance of the laser beam, laying a solid foundation for the stable operation of the laser in high-performance application scenarios.

[0034] The application of top metal grating brings about multi-faceted performance optimization. The metal material itself has good optical reflection properties and can greatly improve the reflection efficiency compared to traditional semiconductor gratings. This not only enhances the optical feedback capability of the laser, but also effectively narrows the laser linewidth, making the laser output purer. At the same time, the introduction of the metal grating reduces the threshold current of the laser, which means that laser emission can be achieved at a lower driving current, effectively improving the energy utilization efficiency of the laser and reducing power consumption.

[0035] Compared with traditional DFB lasers, the present invention has significant cost and efficiency advantages. Traditional DFB lasers require high-cost secondary epitaxy and the preparation of deeply buried sandwich-structured semiconductor gratings, which not only leads to complex manufacturing processes, but also long production cycles and high costs. The present invention uses a top metal grating to replace the traditional sandwich-type semiconductor grating, eliminating the need for secondary epitaxy and greatly simplifying the process flow. The simplified process reduces the steps in the manufacturing process and the dependence on high-precision equipment, reducing manufacturing costs while improving production efficiency and product yield. In addition, the reflection and filtering efficiency of the metal grating is about 30% higher than that of the semiconductor grating, which significantly improves the performance of the laser and can better meet the needs of fields with high requirements for light source performance, such as quantum communication, coherent optical communication, and photonic integrated chips, and has broader application prospects.

[0036] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. Various changes and improvements are possible without departing from the spirit and scope of the present invention, and such changes and improvements fall within the scope of the invention as claimed.

Claims

1. A DFB laser based on two phase-shifted λ / 2 top metal gratings, characterized in that: include: Gain chip (1); An optical waveguide (2) is arranged in the center of the top of the gain chip (1); A metal BRAGG reflection grating (3) is arranged on the top of the optical waveguide (2), and the metal BRAGG reflection grating (3) includes a metal BRAGG reflection grating 1 (301) and a metal BRAGG reflection grating 2 (302), and a phase difference (4) is set between the metal BRAGG reflection grating 1 (301) and the metal BRAGG reflection grating 2 (302).

2. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 1, characterized in that: The gain chip (1) adopts an InP / InGaAsP quantum well structure.

3. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 2, characterized in that: The lasing wavelength λ of the gain chip (1) ranges from 1530 to 1610 nm.

4. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 3, characterized in that: One side of the gain chip (1) is set as a reflector end face, and the reflector end face is plated with a λ / 2 HR high reflective film (5), the λ / 2 HR high reflective film (5) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 HR high reflective film (5) is greater than 99.9%.

5. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 4, characterized in that: The side of the gain chip (1) away from the reflector end face is an anti-reflection end face, and the anti-reflection end face is plated with a λ / 4 AR anti-reflection film (6), the λ / 4 AR anti-reflection film (6) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 AR anti-reflection film (6) is less than 0.03%.

6. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 1, characterized in that: The grating constant of the metal BRAGG reflection grating (3) is λ / 2, the grating period is set to 225±0.3nm, and the duty cycle is 50±1%.

7. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 6, characterized in that: The thickness of the metal BRAGG reflection grating (3) is 200±5nm.

8. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 7, characterized in that: The metal BRAGG reflection grating (3) adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

9. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 8, characterized in that: The phase difference (4) is λ / 2.

10. The DFB laser based on two-segment phase-shifted λ / 2 top metal grating according to claim 1, characterized in that: The optical waveguide (2) is a ridge-shaped structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

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