Laser based on top surface HR layer and planar metal grating and preparation method thereof

Abstract

The invention relates to the technical field of optoelectronic devices, in particular to a laser based on a top surface HR layer and a planar metal grating and a preparation method, and the laser comprises a gain chip, an optical waveguide, the planar metal grating and a covering layer, the planar metal grating prepared by adopting an electronic evaporation plating process replaces traditional complex three-dimensional etching, so that the controllable precision and flatness of the grating structure are greatly improved, an InP secondary epitaxy process is abandoned, the whole process flow is simplified, the production cost is reduced, the product performance consistency and the product yield are improved, and the production cost is reduced. The reflection filtering efficiency is remarkably improved, the purity of the Bragg reflection spectrum is guaranteed, the narrow linewidth performance of the laser is achieved, the covering layer covers the plane metal grating, the problem that semiconductor secondary epitaxial lattices are not matched is effectively solved, diffraction light can be restrained, light energy overflow is reduced, and the freedom degree is increased through the design of the outer cavity structure.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic devices, and in particular to a laser based on a top surface HR layer and a planar metal grating and a preparation method thereof. Background Art

[0002] DF optoelectronic device laser linewidth bottleneck: In the 1550nm band, the typical linewidth of traditional InP-based DF optoelectronic device lasers is in the range of 100-200kHz. According to the longitudinal mode spacing formula , when the cavity length L=300nm, ≈0.01nm, which intensifies mode competition and makes it difficult to meet the needs of emerging fields such as quantum communication (linewidth needs to be <1kHz), coherent optical communication (linewidth needs to be <10kHz) and terahertz photonics (linewidth needs to be <100Hz).

[0003] The production of traditional InP-based DF optoelectronic device lasers requires InP secondary epitaxial growth, and the process yield is only 65-70%, resulting in its manufacturing cost being 2-3 times higher than that of external cavity lasers. In addition, semiconductor grating etching is affected by the anisotropy of the crystal lattice, and the surface structure is irregular after lithography, which not only affects the laser performance but also increases the line width. The additional grating etching process also increases the cost. Moreover, the reflectivity of the semiconductor grating is about 93-95%. In order to ensure the output effect, additional gain compensation is required, which increases the power consumption by 15-20%. The M2 factor of the DF optoelectronic device laser with an internal cavity structure is usually greater than 1.5, and the coupling efficiency in the photonic integrated system is less than 85%, which is not conducive to the efficient transmission and integrated application of optical signals. 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 a top surface HR layer and a planar metal grating and a preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: an external cavity laser based on a top surface HR layer and a planar metal grating, comprising: Gain chip; An optical waveguide is arranged centered on top of the gain chip; A planar metal grating, disposed on top of the optical waveguide; The cover layer covers the planar metal grating and is coated with a high-reflection HR film.

[0006] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure, and the lasing wavelength range of the gain chip is 1530-1610 nm.

[0007] Preferably, one side of the gain chip is set as a reflector end face, and the reflector end face is coated with a high-reflection film. The high-reflection film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the high-reflection film is greater than 99.9%.

[0008] Preferably, the side of the gain chip away from the end face of the reflector is an anti-reflection end face, and the anti-reflection end face is coated with an anti-reflection film. The anti-reflection film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the anti-reflection film is less than 0.03%.

[0009] Preferably, the grating waveguide length of the planar metal grating is 1-3 cm, the grating period is set to 225±0.3 nm, and the duty cycle is 50±1%.

[0010] Preferably, the thickness of the planar metal grating is 200±5 nm, and a Cr / Au multilayer structure is adopted, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

[0011] Preferably, the cover layer is a SiO2 thin film layer, and the high-reflection HR film is a dielectric reflective film or a metal reflective film.

[0012] Preferably, the optical waveguide adopts a ridge structure with a depth of 1.2 μm±50 nm and a surface roughness of <0.8 nm.

[0013] Preferably, the optical waveguide uses Si3N4 or single crystal silicon or lithium niobate or SiO2 as the optical waveguide material.

[0014] The method for preparing an external cavity laser based on a top surface HR layer and a planar metal grating comprises the following steps: Grating processing: Electron beam lithography combined with inductively coupled plasma (ICP) etching technology is used to precisely control the grating depth to 120±5nm. Cr / Au layers are then deposited by magnetron sputtering. After deposition, white light interferometry is used to ensure surface flatness <0.08nm RMS. Chip packaging: The chip is packaged using eutectic soldering (AuSn80 / 20) technology, making the thermal resistance less than 0.08K / W. At the same time, a micro TEC (TEC1-12703) is integrated as a temperature control module. Through closed-loop control, the temperature fluctuation is controlled to <±0.003℃; External cavity coupling: Flip-chip bonding technology is used to achieve sub-micron alignment (accuracy ±0.3μm), ensuring precise connection between components and an air gap of <0.3μm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts the planar metal grating prepared by the electron evaporation plating process to replace the traditional complex three-dimensional etching, which greatly improves the controllable precision and flatness of the grating structure, abandons the InP secondary epitaxial process, simplifies the overall process flow, reduces production costs, and improves product performance consistency and product yield. It significantly improves the reflection filtering efficiency, ensures the purity of the Bragg reflection spectrum, and helps to achieve the narrow linewidth performance of the laser. Covering the cover layer above the planar metal grating effectively solves the lattice mismatch problem of semiconductor secondary epitaxy, and can also constrain diffracted light and reduce the overflow of light energy. The external cavity structure design increases the degree of freedom. The grating waveguide length is much longer than the gain chip length, which extends the effective cavity length and expands the filtering space. 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 side structural schematic diagram of the present invention.

[0016] In the figure: 1. Gain chip; 2. Optical waveguide; 3. Planar metal grating; 4. Covering layer; 5. High-reflection HR film; 6. High-reflection film; 7. 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 2 As shown, the present application provides an external cavity laser based on a top surface HR layer and a planar metal grating, comprising: a gain chip 1; an optical waveguide 2, arranged in the center of the top of the gain chip 1; a planar metal grating 3, arranged on the top of the optical waveguide 2; a covering layer 4, covering the planar metal grating 3, and coated with a high-reflection HR film 5 on the top.

[0018] Specifically, such as Figure 1 As shown, the gain chip 1 adopts an InP / InGaAsP quantum well structure, and the lasing wavelength range of the gain chip 1 is 1530-1610 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 high-reflection film 6. The high-reflection film 6 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the high-reflection film 6 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 an anti-reflection film 7. The anti-reflection film 7 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the anti-reflection film 7 is less than 0.03%.

[0021] The high-reflection film 6 can effectively reduce the loss of light at the reflective end face and enhance the feedback of light in the cavity, and the anti-reflection film 7 can maximize the emission efficiency of the laser.

[0022] Specifically, such as Figure 1 As shown, the grating waveguide length of the planar metal grating 3 is 1-3 cm, the grating period is set to 225±0.3 nm, 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 planar metal grating 3 is 200±5 nm, and a Cr / Au multilayer structure is adopted, 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 conductivity and optical reflective properties. The thermal expansion coefficient of the optical waveguide 2 (1.4x10-6 / ℃) is much lower than that of the semiconductor material (3.5x10-6 / ℃), which greatly improves the controllable accuracy and flatness of the grating structure.

[0026] Specifically, such as Figure 1 As shown, the cover layer 4 is a SiO2 thin film layer, and the high-reflection HR film 5 is a dielectric reflection film or a metal reflection film.

[0027] The covering layer 4 reduces the optical energy loss of the optical waveguide, enhances the feedback of light in the cavity, and helps to improve the output power and stability of the laser. The dielectric reflective film achieves high reflectivity by periodically stacking multiple layers of media with different refractive indices and utilizing the interference principle of light. It has low absorption loss and good optical properties. Metal reflective films such as silver and aluminum have high reflectivity and good conductivity, can effectively reflect light, and reduce the escape of light energy.

[0028] Specifically, such as Figure 1 As shown, the optical waveguide 2 adopts a ridge structure with a depth of 1.2 μm ± 50 nm and a surface roughness of < 0.8 nm.

[0029] Specifically, such as Figure 1 As shown, the optical waveguide 2 uses Si 3 N 4 or single crystal silicon or lithium niobate or SiO 2 as the material of the optical waveguide 2 .

[0030] Si3N4 is selected as the low-absorption waveguide material. At a wavelength of 1550nm, its absorption coefficient is <0.08d and its effective refractive index n=2.025±0.005 (tested by ellipsometer). In addition, other waveguide materials with low absorption at the central working wavelength can be selected, such as single crystal silicon (absorption coefficient 0.1-0.2d, refractive index n=3.47) or lithium niobate (absorption coefficient <0.05d, refractive index n=2.28).

[0031] The method for preparing an external cavity laser based on a top surface HR layer and a planar metal grating comprises the following steps: Grating processing: Electron beam lithography combined with inductively coupled plasma (ICP) etching technology is used to precisely control the grating depth to 120±5nm. Cr / Au layers are then deposited by magnetron sputtering. After deposition, white light interferometry is used to ensure surface flatness <0.08nm RMS. Chip packaging: The chip is packaged using eutectic soldering (AuSn80 / 20) technology, making the thermal resistance less than 0.08K / W. At the same time, a micro TEC (TEC1-12703) is integrated as a temperature control module. Through closed-loop control, the temperature fluctuation is controlled to <±0.003℃; External cavity coupling: Flip-chip bonding technology is used to achieve sub-micron alignment (accuracy ±0.3μm), ensuring precise connection between components and an air gap of <0.3μm.

[0032] Example 1: Set the grating waveguide length L=2cm and the working wavelength =1550nm, the high-reflection HR film 5 adopts a dielectric reflective film, and the test shows a line width of 720Hz and an output power of 150mW. In this embodiment, the various components work together, the planar metal grating 3, the covering layer 4 and the high-reflection HR film 5 effectively reduce the light energy loss and achieve good performance output.

[0033] Example 2: When the grating waveguide length L=3cm, the working wavelength =1530nm, when the high-reflection HR film 5 adopts a metal reflective film, the line width is 680Hz and the output power reaches 180mW. As the grating waveguide length increases, the effective cavity length becomes longer, the line width further decreases, and the output power increases, verifying the effectiveness of the design under different high-reflection HR film 5 selections.

[0034] The present invention: The planar metal grating prepared by electron evaporation plating process replaces the traditional complex three-dimensional etched semiconductor grating. The surface roughness of the planar metal grating is <0.8nm, the reflectivity is >99.5% (such as Cr / Au structure), and the thermal expansion coefficient (1.4x10-6 / ℃) is much lower than that of semiconductor materials (3.5x10-6 / ℃), which greatly improves the controllable accuracy and flatness of the grating structure, abandons the InP secondary epitaxial process, simplifies the overall process flow, reduces production costs, and improves product performance consistency and product yield. The surface flatness of the planar metal grating is <0 .08nmRMS (detected by white light interferometer), which significantly improves the reflection filtering efficiency, ensures the purity of the Bragg reflection spectrum, and helps to achieve the narrow linewidth performance of the laser. Covering the cover layer 4 above the planar metal grating 3 effectively solves the lattice mismatch problem of semiconductor secondary epitaxy, and can also constrain the diffracted light and reduce the overflow of light energy. The external cavity structure design increases the degree of freedom. The grating waveguide length is much longer than the gain chip length, which extends the effective cavity length, expands the filtering space, and further reduces the linewidth. Theoretically, when the external cavity length is extended to the centimeter level, the linewidth limit can reach 0.1Hz.

[0035] Excellent beam quality with a linewidth of <750Hz and M2<1.1 for 3D optoelectronic devices is achieved through a centimeter-level planar metal grating 3 (length 1-3cm), a low-loss coupling structure (total loss <0.2d optoelectronic device), and a highly reflective HR film 5 (dielectric or metal reflective film) above the cover layer 4. The optical waveguide 2 uses Si3N4 as the low-absorption waveguide material and integrates a high-precision temperature control system (±0.003°C). The wavelength stability can reach ±0.05pm / °C, and the InP secondary epitaxial growth process is abandoned, simplifying the production process. It is suitable for fields such as quantum communication, coherent optical communication, and photonic integrated chips, providing high-performance light source solutions for related fields.

[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. Laser based on top surface HR layer and planar metal grating, 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 planar metal grating (3) is arranged on top of the optical waveguide (2); A covering layer (4) covers the planar metal grating (3) and is coated with a high-reflection HR film (5) thereon.

2. The laser based on the top surface HR layer and the planar metal grating according to claim 1, characterized in that: The gain chip (1) adopts an InP / InGaAsP quantum well structure, and the lasing wavelength range of the gain chip (1) is 1530-1610 nm.

3. The laser based on the top surface HR layer and the planar metal grating according to claim 2, 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 high-reflection film (6). The high-reflection film (6) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the high-reflection film (6) is greater than 99.9%.

4. The laser based on the top surface HR layer and the planar metal grating according to claim 3, 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 an anti-reflection film (7), the anti-reflection film (7) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the anti-reflection film (7) is less than 0.03%.

5. The laser based on the top surface HR layer and the planar metal grating according to claim 1, characterized in that: The grating waveguide length of the planar metal grating (3) is 1-3 cm, the grating period is set to 225±0.3 nm, and the duty cycle is 50±1%.

6. The laser based on the top surface HR layer and the planar metal grating according to claim 1, characterized in that: The thickness of the planar metal grating (3) is 200±5 nm, and a Cr / Au multilayer structure is adopted, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

7. The laser based on the top surface HR layer and the planar metal grating according to claim 1, characterized in that: The covering layer (4) is a SiO2 thin film layer, and the high-reflection HR film (5) is a dielectric reflection film or a metal reflection film.

8. The laser based on the top surface HR layer and the planar metal grating according to claim 1, characterized in that: The optical waveguide (2) adopts a ridge structure with a depth of 1.2 μm ± 50 nm and a surface roughness of < 0.8 nm.

9. The laser based on the top surface HR layer and the planar metal grating according to claim 1, characterized in that: The optical waveguide (2) uses Si3N4 or single crystal silicon or lithium niobate or SiO2 as the material of the optical waveguide (2).

10. A method for preparing an external cavity laser based on a top surface HR layer and a planar metal grating, characterized in that: The external cavity laser based on the top surface HR layer and the planar metal grating according to any one of claims 1 to 9, wherein the method comprises the following steps: Grating processing: Electron beam lithography combined with inductively coupled plasma (ICP) etching technology is used to precisely control the grating depth to 120±5nm. Cr / Au layers are then deposited by magnetron sputtering. After deposition, white light interferometry is used to ensure surface flatness <0.08nm RMS. Chip packaging: The chip is packaged using eutectic soldering (AuSn80 / 20) technology, making the thermal resistance less than 0.08K / W. At the same time, a micro TEC (TEC1-12703) is integrated as a temperature control module. Through closed-loop control, the temperature fluctuation is controlled to <±0.003℃; External cavity coupling: Flip-chip bonding technology is used to achieve sub-micron alignment (accuracy ±0.3μm), ensuring precise connection between components and an air gap of <0.3μm.

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