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

Abstract

The present application relates to the technical field of optoelectronic devices, especially a laser based on two different gratings and phase interval lambda / 2 metal grating, comprising: a gain chip, a gain chip optical waveguide, a grating optical waveguide substrate, an optical waveguide and a metal BRAGG reflection grating. A unique external cavity structure is adopted, the traditional sandwich semiconductor grating is abandoned, the top metal grating is adopted, the traditional DFB sandwich type secondary epitaxy manufacturing process is greatly simplified and avoided, the production cost is reduced, in particular, the metal grating is divided into two grating constants which are similar but not the same, and the phase of the two gratings is pulled apart by lambda / 2, this design can effectively improve the side mode suppression ratio (SMSR) of the laser beam, compress the laser linewidth, and provide protection for the stable work of the laser in high-performance application scenarios, and the "mouth-to-mouth" coupling docking mode of the gain chip and the grating optical waveguide substrate effectively improves the grating reflection efficiency.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device technology, and more particularly to a laser based on two different metal gratings with a phase spacing of λ / 2. Background Technology

[0002] Due to carrier density fluctuations and the typical 0.5mm lasing cavity length, the linewidth of DFB lasers is usually between 1 and 10 MHz. In applications such as coherent detection, a wider linewidth can cause severe signal interference, significantly reducing detection accuracy and system performance. Its secondary epitaxial process is complex, with a yield of only 65-70%, and manufacturing costs are 2-3 times higher than external cavity lasers. The reflectivity of semiconductor gratings is only 93-95%, requiring additional gain compensation, leading to a 15-20% increase in power consumption and causing heat dissipation problems, affecting the stability and reliability of the laser. Furthermore, the etching process for semiconductor gratings is complex; due to the anisotropy of the crystal lattice, the surface structure after etching is irregular, making it difficult to guarantee the flatness and accuracy of the grating, thus affecting laser performance.

[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 about 20-50kHz. They cannot meet the stringent 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 this invention is to address the shortcomings of existing technologies by proposing a laser based on two different metal gratings with a phase spacing of λ / 2.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a laser based on two different metal gratings with a phase spacing of λ / 2, comprising:

[0006] Gain chip;

[0007] The gain chip optical waveguide is positioned at the top center of the gain chip;

[0008] A grating waveguide substrate is positioned to the right of the gain chip;

[0009] An optical waveguide is positioned at the top center of the grating waveguide substrate;

[0010] A metallic BRAGG reflective grating is disposed on top of the optical waveguide. The metallic BRAGG reflective grating includes metallic BRAGG reflective grating one and metallic BRAGG reflective grating two. The grating constants of metallic BRAGG reflective grating one and metallic BRAGG reflective grating two are similar but different. A phase shift port is provided between metallic BRAGG reflective grating one and metallic BRAGG reflective grating two. The length of the phase shift port is λ / 2.

[0011] Preferably, the grating period of the first metal BRAGG reflective grating is 224.5±0.3nm, and the grating period of the second metal BRAGG reflective grating is 225.5±0.3nm.

[0012] Preferably, the left end face of the grating waveguide substrate is coupled and docked with the right end face of the gain chip in a "mouth-to-mouth" configuration.

[0013] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure.

[0014] Preferably, the lasing wavelength range of the gain chip is 1530-1610nm.

[0015] Preferably, one side of the gain chip is set as a reflector end face, and a λ / 2 high reflectivity film is deposited on the reflector end face. The λ / 2 high reflectivity film adopts a SiO2 / TiO2 multilayer structure and the reflectivity of the λ / 2 high reflectivity film is greater than 99.9%.

[0016] Preferably, the side of the gain chip away from the reflector end face is the 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%.

[0017] Preferably, the thickness of the metal BRAGG reflective grating is 200±5nm, the duty cycle of the metal BRAGG reflective grating is 50±1%, and the metal BRAGG reflective grating adopts a Cr / Au multilayer structure, with the thicknesses of the Cr / Au layers being 50nm and 150nm, respectively.

[0018] Preferably, the optical waveguide has a ridge-shaped structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention employs a unique external cavity structure, abandoning the traditional sandwich semiconductor grating and using a top metal grating. This greatly simplifies and avoids the traditional DFB sandwich-style secondary epitaxial fabrication process, reducing production costs. 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 rejection ratio (SMSR) of the laser beam and compress the laser linewidth, ensuring stable operation of the laser in high-performance applications. Combined with the "mouth-to-mouth" coupling between the gain chip and the grating waveguide substrate, the grating reflection efficiency is effectively improved, and the waveguide light energy loss is reduced. At the same time, the elimination of secondary epitaxy simplifies the process, reduces costs, significantly improves the SMSR performance of the laser beam, and compresses the linewidth. This structural design reduces mode competition, improves the wavelength selectivity and stability of the laser, and facilitates the realization of different wavelength laser outputs in multi-wavelength applications. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the main structure of the present invention;

[0022] Figure 2 This is a top view of the structure of the present invention.

[0023] In the figure: 1. Gain chip; 2. Optical waveguide; 3. Metal BRAGG reflective grating; 301. Metal BRAGG reflective grating one; 302. Metal BRAGG reflective grating two; 4. Phase shift port; 5. λ / 2 high reflectivity film; 6. λ / 4 antireflection film; 7. Grating waveguide substrate; 8. Gain chip optical waveguide. Detailed Implementation

[0024] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0025] like Figures 1-2As shown, this application provides a laser based on two different metal gratings with a phase spacing of λ / 2, including: a gain chip 1; a gain chip waveguide 8 disposed at the top center of the gain chip 1; a grating waveguide substrate 7 disposed to the right of the gain chip 1; an optical waveguide 2 disposed at the top center of the grating waveguide substrate 7; and a metal BRAGG reflection grating 3 disposed at the top of the optical waveguide 2. The metal BRAGG reflection grating 3 includes a first metal BRAGG reflection grating 301 and a second metal BRAGG reflection grating 302. The grating constants of the first metal BRAGG reflection grating 301 and the second metal BRAGG reflection grating 302 are similar but different. A phase shift port 4 is disposed between the first metal BRAGG reflection grating 301 and the second metal BRAGG reflection grating 302, and the length of the phase shift port 4 is λ / 2.

[0026] A dual-plane metallic Bragg grating (G1, G2) with a phase difference Δφ = π (i.e., a spacing λ / 2) is employed. The reflected light from the two gratings undergoes constructive interference within the cavity, increasing the main peak reflectivity from 95% to 99.9% compared to a traditional single grating. This enhances the intracavity optical field intensity, ensuring high-power and stable laser output. The destructive interference characteristics of the dual gratings are utilized to suppress non-laser modes, according to the formula... Theoretically, the side-mode suppression ratio (SMSR) can reach 65dB, effectively weakening side-mode intensity and improving the purity and stability of the output light to meet the requirements of high-precision applications. The dual-grating setup doubles the equivalent cavity length, extending the free spectral range from 50GHz in traditional external cavities to 100GHz, reducing mode competition, improving the wavelength selectivity and stability of the laser, and facilitating the realization of laser output at different wavelengths in multi-wavelength application scenarios.

[0027] Specifically, such as Figure 1 As shown, the grating period of metal BRAGG reflective grating 301 is 224.5±0.3nm, and the grating period of metal BRAGG reflective grating 302 is 225.5±0.3nm.

[0028] The parameters of the metal Bragg gratings were carefully designed. The grating periods of the two metal gratings were set to Λ1 = 224.5 ± 0.3 nm and Λ2 = 225.5 ± 0.3 nm, respectively. This design of similar but different grating periods, combined with the phase difference λ / 2 between the two gratings, utilizes the interference effect of the gratings to significantly improve the main peak reflectivity, enhance the intracavity optical field intensity, and ensure high-power, stable laser output. At the same time, it effectively suppresses non-laser modes, theoretically achieving a higher side-mode suppression ratio (SMSR), compressing the laser linewidth, and improving the purity and stability of the output light to meet the requirements of high-precision applications.

[0029] Specifically, such as Figure 1As shown, the left end face of the grating waveguide substrate 7 is coupled and docked with the right end face of the gain chip 1 in a "mouth-to-mouth" manner.

[0030] The left end face of the grating waveguide substrate 7 is coupled and mated to the right end face of the gain chip 1 in a "mouth-to-mouth" manner. Submicron-level alignment (accuracy ±0.2μm) is achieved through a high-precision flip-chip bonding process, ensuring that the air gap between the two is less than 200nm and the total external cavity length L cavity =800μm+L wg With a free spectral range (FSR) > 100 GHz, this external cavity coupling structure design, in conjunction with other components, enables efficient light transmission and feedback, thereby improving the performance of the laser.

[0031] 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.

[0032] The InP / InGaAsP quantum well structure was selected as the basic architecture of the gain chip. This structure has good laser emission characteristics in the wavelength range of 1530-1610nm, which can meet the needs of various application scenarios. At 25℃, its threshold current is less than 28mA, which means that laser emission can be achieved with low energy consumption. The slope efficiency reaches 0.85W / A, indicating that under a certain current drive, it can efficiently convert electrical energy into light energy.

[0033] Specifically, such as Figure 1 As shown, one side of the gain chip 1 is set as a reflector end face, and a λ / 2 high reflectivity film 5 is coated on the reflector end face. The λ / 2 high reflectivity film 5 adopts a SiO2 / TiO2 multilayer structure and has a reflectivity greater than 99.9%. The side of the gain chip 1 away from the reflector end face is an anti-reflection end face, and a λ / 4 anti-reflection film 6 is coated on the anti-reflection end face. The λ / 4 anti-reflection film 6 adopts a SiO2 / TiO2 multilayer structure and has a reflectivity less than 0.03%.

[0034] The λ / 2 high-reflectivity film 5 can effectively reduce light loss at the reflective end face and enhance light feedback in the cavity, while the λ / 4 anti-reflectivity film 6 can maximize the laser emission efficiency.

[0035] Specifically, such as Figure 1 As shown, the thickness of the metal BRAGG reflective grating 3 is 200±5nm, the duty cycle of the metal BRAGG reflective grating 3 is 50±1%, and the metal BRAGG reflective grating 3 adopts a Cr / Au multilayer structure, with the thicknesses of the Cr / Au layers being 50nm and 150nm, respectively.

[0036] 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, while the Au layer has good electrical conductivity and optical reflection properties.

[0037] Specifically, such as Figure 1 As shown, the optical waveguide 2 has a ridge-shaped structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0038] An external cavity laser includes a phase difference λ / 2-based metallic grating waveguide.

[0039] Theoretical basis:

[0040] According to coupled-mode theory, for a traditional uniform grating DFB laser, its coupling coefficient is κ, and the optical field distribution can be represented by A(z), satisfying the following coupled-mode equation:

[0041] Where β is the propagation constant, in this equation, e i2βz This describes the phase change of the light field during propagation, -iκA * e i2βz This reflects the coupling effect of the grating on the light field, while loss terms represent the light loss during propagation.

[0042] For two metal grating DFB lasers with similar grating constants and a phase difference of λ / 2 in this invention, the presence of a phase shift profoundly affects the optical field distribution. Assuming the phase shift occurs at z = 0, the optical field distributions before and after the phase shift can be represented by A1(z) and A2(z) respectively, and satisfy the boundary condition: A2(0 + )=A1(0 - )e iπ / 2 This means that the optical field generates a π / 2 phase jump at the phase shift point. This phase jump will cause the optical field to redistribute, 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 dominant mode to suppress the side modes more effectively, thereby improving the SMSR.

[0043] The difference in grating constant and the setting of phase difference λ / 2 alter 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 a traditional uniform grating DFB laser, its Bragg wavelength λ... B Satisfy: λ B =2n eff Λ, where n effWhere Λ is the effective refractive index and Λ is the grating period, in this invention, due to the change in the optical field distribution, the actual Bragg wavelength is slightly altered. Simultaneously, the gains of the principal mode and side modes are also affected, with the principal mode gain relatively increasing and the side mode gain relatively decreasing, further promoting the improvement of the SMSR. Furthermore, this structural change also compresses the laser linewidth, improving the purity and stability of the laser.

[0044] Example 1:

[0045] In the actual fabrication process, firstly, electron beam lithography (EBG) is used to draw a precise grating pattern on the InP / InGaAsP quantum well structure gain chip. The high precision of electron beam lithography ensures the accuracy of the grating pattern, providing a good foundation for subsequent etching processes. Then, inductively coupled plasma (ICP) etching technology is used to etch the drawn pattern into a grating structure with a certain depth, precisely controlling the grating depth at 120±5nm. Next, 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). During the process, process parameters were strictly controlled, and a white light interferometer was used for inspection to ensure that the surface flatness was less than 0.08 nm RMS, thereby obtaining a high-quality metal grating surface. At the same time, precise control of the two grating constants and accurate setting of the phase difference λ / 2 between the two gratings were achieved through precise photolithography and etching processes. After the laser fabrication was completed, the linewidth and SMSR of the laser were measured using self-heterodyne interferometry. At the same time, its beam quality and coupling efficiency in the photonic integrated system were tested. The results showed that, compared with the traditional DFB laser, the SMSR of this external cavity laser with two metal gratings with similar grating constants and a phase difference of λ / 2 was significantly improved.

[0046] Example 2:

[0047] Comparing different metallic materials (Al, Ag), it was found that the Cr / Au structure has the highest reflectivity, reaching 99.92%. Temperature change tests showed that the wavelength drift was controlled within ±0.002nm in the range of -40 to 85℃.

[0048] Example 3:

[0049] The external cavity length was optimized to 3cm, at which point the free spectral range FSR = 100GHz and the linewidth was further compressed to 0.5kHz.

[0050] Example 4:

[0051] 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 waveguide substrate 7, the influence of the coupling process on the laser performance was further studied. A high-precision flip-chip bonding process was adopted, combined 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.

[0052] Example 5:

[0053] The effects of different duty cycles on the performance of planar metallic Bragg gratings were investigated. Grating structures with duty cycles of 45%, 50%, and 55% were fabricated, with other parameters kept constant. The grating periods were Λ1 = 224.5 ± 0.3 nm and Λ2 = 225.5 ± 0.3 nm, and the metal layer thickness was 200 nm.

[0054] Test results show that the laser's overall performance is optimal at a duty cycle of 50%. At this point, the grating's reflection efficiency is highest, with a principal mode reflectivity of 99.8%, a side mode rejection ratio (SMSR) of 64 dB, and a linewidth of 0.5 kHz. When the duty cycle deviates from 50%, the grating's reflection characteristics change, leading to a decrease in principal mode gain and a relative increase in side mode gain, thus affecting the laser's performance. For example, at a duty cycle of 45%, the principal mode reflectivity drops to 99.5%, and the SMSR decreases to 62 dB; at a duty cycle of 55%, the principal mode reflectivity is 99.6%, and the SMSR is 61 dB.

[0055] Working principle of this invention:

[0056] Employing a unique external cavity structure, this design abandons the traditional sandwich semiconductor grating and adopts a top metal grating, greatly simplifying the manufacturing process and reducing production costs. 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 effectively improves the side-mode rejection ratio (SMSR) of the laser beam and compresses the laser linewidth, ensuring stable operation of the laser in high-performance applications. Combined with the "mouth-to-mouth" coupling between the gain chip 1 and the grating waveguide substrate 7, the grating reflection efficiency is effectively improved, and the optical waveguide energy loss is reduced. At the same time, it eliminates the need for secondary epitaxy, simplifies the process, reduces costs, and significantly improves the SMSR performance of the laser beam, compressing the linewidth. This structural design reduces mode competition, improves the wavelength selectivity and stability of the laser, and facilitates the realization of different wavelength laser outputs in multi-wavelength applications.

[0057] The application of the top metal grating brings about multiple performance optimizations. The excellent optical reflection characteristics of metal materials significantly improve the reflection efficiency compared to traditional semiconductor gratings. This enhances the laser's optical feedback capability, effectively narrows the laser linewidth, and makes the laser output purer. At the same time, the introduction of the metal grating reduces the laser's threshold current, improves energy utilization efficiency, and reduces power consumption.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A laser based on two different metal gratings with a phase spacing of λ / 2, characterized in that, include: Gain chip (1); The gain chip optical waveguide (8) is disposed at the top center of the gain chip (1); A grating waveguide substrate (7) is disposed on the right side of the gain chip (1); An optical waveguide (2) is disposed at the top center of the grating optical waveguide substrate (7); A metal BRAGG reflective grating (3) is disposed on the top of the optical waveguide (2), and the metal BRAGG reflective grating (3) includes a metal BRAGG reflective grating one (301) and a metal BRAGG reflective grating two (302). The grating constants of the metal BRAGG reflective grating one (301) and the metal BRAGG reflective grating two (302) are different. A phase shift port (4) is provided between the metal BRAGG reflective grating one (301) and the metal BRAGG reflective grating two (302), and the length of the phase shift port (4) is λ / 2.

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

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

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

7. The laser based on two different metal gratings with a phase spacing of λ / 2 according to claim 6, characterized in that, The metal BRAGG reflective grating (3) adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50nm and 150nm, respectively.

8. The laser based on two different metal gratings with a phase spacing of λ / 2 according to claim 1, characterized in that, The optical waveguide (2) has a ridge-shaped structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

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