Laser based on two different gratings and phase-spaced lambda / 2 metal gratings

Abstract

The invention relates to the technical field of optoelectronic devices, in particular to a laser based on two different gratings and a metal grating with a phase interval of lambda / 2, which comprises a gain chip, a gain chip optical waveguide, a grating optical waveguide substrate, an optical waveguide and a metal BRAGG reflecting grating. A unique outer cavity structure is adopted, a traditional interlayer semiconductor grating is abandoned, a top metal grating is adopted, a traditional DFB sandwich type secondary epitaxy manufacturing process is greatly simplified and avoided, the production cost is reduced, particularly, the metal grating is divided into two parts with similar but different grating constants, and the phase positions of the two gratings are pulled by lambda / 2, so that the performance of the DFB is improved. According to the design, the side mode rejection ratio (SMSR) of laser beams can be effectively improved, the laser line width is compressed, a guarantee is provided for stable work of the laser in a high-performance application scene, and the grating reflection efficiency is effectively improved by combining a'mouth-to-mouth 'coupling butt joint mode of the gain chip and the grating optical waveguide substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic devices, in particular to a laser based on two metal gratings with different gratings and a phase interval of λ / 2. Background Art

[0002] Affected by carrier density fluctuations and the typical 0.5mm laser cavity length, the linewidth of a DFB laser is usually 1-10MHz. In application scenarios such as coherent detection, a wider linewidth will cause serious signal interference, significantly reducing detection accuracy and system performance. Its secondary epitaxial process is complex, with a yield of only 65-70%, and the manufacturing cost is 2-3 times higher than that of an external cavity laser. The reflectivity of the semiconductor grating is only 93-95%, requiring additional gain compensation, resulting in a 15-20% increase in power consumption, and will also cause heat dissipation problems, affecting the stability and reliability of the laser. In addition, the semiconductor grating etching process is complex. Due to the anisotropy of the crystal lattice, the surface structure after etching is irregular, making it difficult to ensure the flatness and accuracy of the grating, which in turn affects the performance of the laser.

[0003] Traditional external cavity lasers mostly use a single grating structure with a side mode suppression ratio (SMSR) of only 45-50dB and a linewidth of approximately 20-50kHz. They cannot meet the strict requirements of high-precision applications for light sources, and it is difficult to balance beam quality and integration. They rely on complex optical alignment processes, which increases production difficulty and cost and is not conducive to large-scale integrated manufacturing. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a laser based on two different gratings and a metal grating with a phase interval of λ / 2.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a laser based on two different gratings with a phase interval of λ / 2 metal gratings, comprising: Gain chip; The gain chip optical waveguide is arranged in the center of the top of the gain chip; The grating optical waveguide substrate is arranged on the left end surface of the gain chip; An optical waveguide is arranged centrally on top of the grating optical waveguide substrate; The metal BRAGG reflection grating is arranged on the top of the optical waveguide, and the metal BRAGG reflection grating includes a metal BRAGG reflection grating 1 and a metal BRAGG reflection grating 2. The grating constants of the metal BRAGG reflection grating 1 and the metal BRAGG reflection grating 2 are similar but different. A phase shift port is provided between the metal BRAGG reflection grating 1 and the metal BRAGG reflection grating 2, and the length of the phase shift port is λ / 2.

[0006] Preferably, the grating period of the metal BRAGG reflection grating 1 is 224.5±0.3 nm, and the grating period of the metal BRAGG reflection grating 2 is 225.5±0.3 nm.

[0007] Preferably, the left end face of the grating optical waveguide substrate and the right end face of the gain chip are coupled and docked in a "mouth-to-mouth" manner.

[0008] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure.

[0009] Preferably, the lasing wavelength range of the gain chip is 1530-1610 nm.

[0010] 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 high reflective film, the λ / 2 high reflective film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 high reflective film is greater than 99.9%.

[0011] 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 / 4 anti-reflection film. The λ / 4 anti-reflection film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 anti-reflection film is less than 0.03%.

[0012] Preferably, the thickness of the metal BRAGG reflection grating is 200±5nm, the duty cycle of the metal BRAGG reflection grating is 50±1%, the metal BRAGG reflection grating adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50nm and 150nm respectively.

[0013] Preferably, the optical waveguide has a ridge structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a unique external cavity structure, abandons the traditional sandwich semiconductor grating, and adopts a top metal grating, which greatly simplifies and circumvents the traditional DFB sandwich secondary epitaxial fabrication process and reduces production costs. In particular, the metal grating is divided into two parts with similar but different grating constants, and the two gratings are phase-shifted by λ / 2. This design can effectively improve the side mode suppression ratio (SMSR) of the laser beam, compress the laser linewidth, and provide a guarantee for the stable operation of the laser in high-performance application scenarios. Combined with the "mouth-to-mouth" coupling and docking method of the gain chip and the grating optical waveguide substrate, the grating reflection efficiency is effectively improved and the optical waveguide light energy loss is reduced. At the same time, the secondary epitaxy is eliminated, the process is simplified, the cost is reduced, the SMSR performance of the laser beam is significantly improved, and the linewidth is compressed. This structural design reduces mode competition, improves the wavelength selection capability and stability of the laser, and facilitates the realization of laser output of different wavelengths in multi-wavelength application scenarios. 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 structure of the present invention.

[0015] 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 shift port; 5. λ / 2 high reflection film; 6. λ / 4 anti-reflection film; 7. Grating optical waveguide substrate; 8. Gain chip optical waveguide. 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.

[0016] like Figure 1-Figure 2 As shown, the present application provides a laser based on two different gratings and a phase interval of λ / 2 metal grating, including: a gain chip 1; a gain chip optical waveguide 8, arranged in the center of the top of the gain chip 1; a grating optical waveguide substrate 7, arranged on the left end face of the gain chip 1; an optical waveguide 2, arranged in the center of the top of the grating optical waveguide substrate 7; 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, the grating constants of the metal BRAGG reflection grating 1 301 and the metal BRAGG reflection grating 2 302 are similar but different, and a phase shift port 4 is provided between the metal BRAGG reflection grating 1 301 and the metal BRAGG reflection grating 2 302, and the length of the phase shift port 4 is λ / 2.

[0017] Using a double-plane metal Bragg grating (G1, G2) with a phase difference of Δφ=π (i.e., spacing λ / 2), the light reflected from the two gratings constructively interferes in the cavity, increasing the main peak reflectivity from 95% of a traditional single grating to 99.9%, enhancing the light field intensity in the cavity and providing a guarantee for high-power, stable laser output. The destructive interference characteristics of the double grating are used to suppress the non-lasing mode. According to the formula Theoretically, the side mode suppression ratio (SMSR) can reach 65dB, effectively weakening the side mode intensity and improving the purity and stability of the output light to meet the requirements of high-precision applications. The dual-grating configuration doubles the equivalent cavity length, extending the free spectral range from 50GHz in a traditional external cavity to 100GHz, reducing mode competition and improving the wavelength selectivity and stability of the laser, facilitating the realization of different wavelength laser output in multi-wavelength applications.

[0018] Specifically, such as Figure 1As shown, the grating period of the metal BRAGG reflection grating 301 is 224.5±0.3 nm, and the grating period of the metal BRAGG reflection grating 302 is 225.5±0.3 nm.

[0019] The parameters of the metal Bragg gratings were meticulously designed, with the grating periods of the two metal gratings set to Λ1 = 224.5 ± 0.3 nm and Λ2 = 225.5 ± 0.3 nm, respectively. This similar yet distinct grating period design, combined with a phase difference of λ / 2 between the two gratings, leverages the interference effect of the gratings to significantly enhance the main peak reflectivity and increase the intracavity light field intensity, ensuring high-power, stable laser output. Furthermore, it effectively suppresses non-lasing modes, theoretically achieving a higher side mode suppression ratio (SMSR), compressing the laser linewidth and improving the purity and stability of the output light, meeting the requirements of high-precision applications.

[0020] Specifically, such as Figure 1 As shown, the left end face of the grating optical waveguide substrate 7 and the right end face of the gain chip 1 are coupled and docked in a "mouth-to-mouth" manner.

[0021] The left end face of the grating optical waveguide substrate 7 is coupled to the right end face of the gain chip 1 in a "mouth-to-mouth" coupling manner. Submicron alignment (accuracy ±0.2μm) is achieved through a high-precision flip-chip process, ensuring that the air gap between the two is less than 200nm. The total length of the external cavity Lcavity = 800μm + Lwg, and the free spectral range FSR > 100GHz. This external cavity coupling structure design, combined with other components, realizes efficient light transmission and feedback, improving the performance of the laser.

[0022] Specifically, such as Figure 1 As shown, the gain chip 1 adopts an InP / InGaAsP quantum well structure; the lasing wavelength range of the gain chip 1 is 1530-1610nm.

[0023] 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.

[0024] 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 / 2 high-reflection film 5. The λ / 2 high-reflection film 5 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 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 anti-reflection film 6. The λ / 4 anti-reflection film 6 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 anti-reflection film 6 is less than 0.03%.

[0025] The λ / 2 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 anti-reflection film 6 can maximize the laser emission efficiency.

[0026] Specifically, such as Figure 1 As shown, the thickness of the metal BRAGG reflection grating 3 is 200±5nm, the duty cycle of the metal BRAGG reflection grating 3 is 50±1%, the metal BRAGG reflection grating 3 adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50nm and 150nm respectively.

[0027] The duty cycle is 50±1%, which ensures the uniformity and stability of the grating structure. The Cr layer can enhance the adhesion between the metal and the substrate, and the Au layer has good conductivity and optical reflection properties.

[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] An external cavity laser comprises a metal grating waveguide based on a phase difference of λ / 2.

[0030] 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 loss\terms represents the loss of light during the propagation process.

[0031] For the two metal grating DFB lasers with similar grating constants and a phase difference of λ / 2 in the present invention, the presence of phase shift profoundly affects 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.

[0032] The difference in grating constants and the setting of phase difference λ / 2 change the light field distribution, causing subtle changes in the effective refractive index of light during propagation. According to the Bragg condition of the grating, for traditional uniform grating DFB lasers, its Bragg wavelength is satisfy: ,in Where λ is the effective refractive index and Λ is the grating period. In this invention, the actual Bragg wavelength slightly changes due to the altered light field distribution. This also affects the gains of the main and side modes, increasing the main mode gain while suppressing the side mode gain, further enhancing the SMSR. Furthermore, this structural change compresses the laser linewidth, improving laser purity and stability.

[0033] Example 1: In the actual preparation process, the 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, the inductively coupled plasma (ICP) etching technology is used to etch the drawn pattern into a grating structure with a certain depth, and the grating depth is precisely controlled at 120±5nm. Then, the Cr / Au layer is deposited by magnetron sputtering to form a metal Bragg grating with a thickness of 200±5nm (Cr / Au=50nm / 150nm). During the process, the process parameters are strictly controlled and white light interferometer is used for detection to ensure that the surface flatness is less than 0.08nmRMS, thereby obtaining a high-quality metal grating surface. At the same time, precise lithography and etching processes are used to achieve precise control of the two grating constants and accurate setting of the phase difference λ / 2 between the two gratings. After the laser is prepared, the linewidth and SMSR of the laser are measured by self-heterodyne interferometry, and its beam quality and coupling efficiency in the photonic integrated system are tested. The results show that compared with the traditional DFB laser, the SMSR of the external cavity laser with two metal gratings with similar grating constants and a phase difference of λ / 2 has been significantly improved.

[0034] Example 2: Comparing different metal materials (Al, Ag), it was found that the Cr / Au structure had the highest reflectivity, reaching 99.92%. Temperature change tests showed that within the range of -40~85℃, the wavelength drift was controlled within ±0.002nm.

[0035] Example 3: The external cavity length is optimized to 3 cm, at which point the free spectral range (FSR) is 100 GHz and the linewidth is further compressed to 0.5 kHz.

[0036] Example 4: Based on the "mouth-to-mouth" coupling and docking of the right end face of the gain chip 1 and the left end face of the grating optical waveguide substrate 7, the influence of the coupling process on the laser performance was further studied. A high-precision flip-chip process was used in conjunction with an advanced optical alignment system to improve the coupling accuracy to ±0.1μm, while strictly controlling the air gap between the two to 150nm.

[0037] Example 5: The influence of different duty cycles on the performance of metal planar Bragg gratings was studied. Grating structures with duty cycles of 45%, 50%, and 55% were prepared respectively. Other parameters remained unchanged. The grating periods were Λ1=224.5±0.3nm and Λ2=225.5±0.3nm, and the metal layer thickness was 200nm.

[0038] The test results show that when the duty cycle is 50%, the overall performance of the laser is the best. At this time, the reflection efficiency of the grating is the highest, the main mode reflectivity reaches 99.8%, the side mode suppression ratio (SMSR) is 64dB, and the linewidth is 0.5kHz. When the duty cycle deviates from 50%, the reflection characteristics of the grating change, resulting in a decrease in the main mode gain and a relative increase in the side mode gain, thereby affecting the performance of the laser. For example, when the duty cycle is 45%, the main mode reflectivity drops to 99.5% and the SMSR drops to 62dB; when the duty cycle is 55%, the main mode reflectivity is 99.6% and the SMSR is 61dB.

[0039] Working principle of the present invention: The unique external cavity structure is adopted, and the traditional sandwich semiconductor grating is abandoned. In favor of a top metal grating, the manufacturing process is greatly simplified and the production cost is reduced. In particular, the metal grating is divided into two parts with similar but different grating constants, and the two gratings are phase-separated by λ / 2. This design can effectively improve the side mode suppression ratio (SMSR) of the laser beam, compress the laser linewidth, and provide a guarantee for the stable operation of the laser in high-performance application scenarios. Combined with the "mouth-to-mouth" coupling and docking method of the gain chip 1 and the grating optical waveguide substrate 7, the grating reflection efficiency is effectively improved and the optical waveguide light energy loss is reduced. At the same time, the secondary epitaxy is eliminated, the process is simplified, the cost is reduced, the SMSR performance of the laser beam is significantly improved, and the linewidth is compressed. This structural design reduces mode competition, improves the wavelength selection capability and stability of the laser, and facilitates the realization of laser output of different wavelengths in multi-wavelength application scenarios.

[0040] The application of top metal grating brings about performance optimization in many aspects. The good optical reflection properties of metal materials greatly improve the reflection efficiency compared with traditional semiconductor gratings, which enhances the optical feedback capability of the laser, effectively narrows the laser linewidth, and makes the laser output purer. At the same time, the introduction of metal grating reduces the threshold current of the laser, improves energy utilization efficiency, and reduces power consumption.

[0041] 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 laser based on two different gratings with a phase interval of λ / 2 metal gratings, characterized by ,include: Gain chip (1); A gain chip optical waveguide (8) is arranged in the center of the top of the gain chip (1); A grating optical waveguide substrate (7) is arranged on the left end surface of the gain chip (1); An optical waveguide (2) is arranged in the center of the top of the grating optical waveguide substrate (7); 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), the grating constants of the metal BRAGG reflection grating 1 (301) and the metal BRAGG reflection grating 2 (302) are different, and a phase shift port (4) is provided between the metal BRAGG reflection grating 1 (301) and the metal BRAGG reflection grating 2 (302), and the length of the phase shift port (4) is λ / 2.

2. The laser based on two different gratings and metal gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The grating period of the metal BRAGG reflection grating 1 (301) is 224.5±0.3 nm, and the grating period of the metal BRAGG reflection grating 2 (302) is 225.5±0.3 nm.

3. The laser based on two different metal gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The left end face of the grating optical waveguide substrate (7) is coupled and docked with the right end face of the gain chip (1) in a "mouth-to-mouth" manner.

4. The laser based on two different gratings and metal gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The gain chip (1) adopts an InP / InGaAsP quantum well structure.

5. The laser based on two different metal gratings with a phase interval of λ / 2 according to claim 4, characterized in that: The lasing wavelength range of the gain chip (1) is 1530-1610 nm.

6. The laser based on two different metal gratings with a phase interval of λ / 2 according to claim 5, 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 high reflective film (5), the λ / 2 high reflective film (5) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 high reflective film (5) is greater than 99.9%.

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

8. The laser based on two different metal gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The thickness of the metal BRAGG reflection grating (3) is 200±5 nm, and the duty cycle of the metal BRAGG reflection grating (3) is 50±1%.

9. The laser based on two different metal gratings with a phase interval of λ / 2 according to claim 8, 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.

10. The laser based on two different metal gratings with a phase interval of λ / 2 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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