Laser based on top-surface hr layer and planar metal grating and preparation method

Abstract

The present application relates to the technical field of optoelectronic devices, especially to a laser based on a top HR layer and a planar metal grating and a preparation method, comprising a gain chip, an optical waveguide, a planar metal grating and a cover layer, the planar metal grating prepared by an electron evaporation plating process is used to replace a traditional complex three-dimensional etching, so that the controllable precision and flatness of the grating structure are greatly improved, the InP secondary epitaxy process is abandoned, the overall process flow is simplified, the production cost is reduced, the product performance consistency and product yield are improved, the reflection filtering efficiency is significantly improved, the purity of the Bragg reflection spectrum is ensured, the narrow line width performance of the laser is helped to be realized, the cover layer is covered above the planar metal grating, the problem of lattice mismatch of semiconductor secondary epitaxy is effectively solved, the diffracted light can also be constrained, the light energy overflow is reduced, and the freedom degree of the external cavity structure design is increased.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic devices, and more particularly to lasers based on a top-surface HR layer and a planar metal grating, and their fabrication methods. Background Technology

[0002] Linearity bottleneck of DF optoelectronic lasers: In the 1550nm band, the typical linewidth of traditional InP-based DF optoelectronic lasers is in the 100-200kHz range. (Based on the longitudinal mode spacing formula...) When the cavity length L = 300 nm, The linewidth is approximately 0.01nm, which intensifies the competition between modes 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] Traditional InP-based DF optoelectronic lasers require secondary InP epitaxial growth, a process with a yield of only 65-70%, resulting in manufacturing costs 2-3 times higher than external cavity lasers. Furthermore, semiconductor grating etching is affected by crystal lattice anisotropy, leading to irregular surface structures after photolithography. This not only affects laser performance but also increases linewidth. The additional grating etching process further increases costs. Moreover, the reflectivity of semiconductor gratings is approximately 93-95%, requiring additional gain compensation to ensure output quality, which increases power consumption by 15-20%. Internal cavity DF optoelectronic lasers typically have an M² factor greater than 1.5, resulting in coupling efficiency below 85% in photonic integrated systems, which is detrimental to efficient optical signal transmission and integrated applications. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a laser based on a top surface HR layer and a planar metal grating, and a method for its fabrication.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: an external cavity laser based on a top surface HR layer and a planar metal grating, comprising:

[0006] Gain chip;

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

[0008] A planar metal grating is positioned at the top of the optical waveguide;

[0009] The overlay is placed on a planar metal grating and coated with a high-reflectivity HR film.

[0010] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure, and the lasing wavelength range of the gain chip is 1530-1610nm.

[0011] Preferably, one side of the gain chip is set as a reflector end face, and a high-reflection film is coated on the reflector end face. The high-reflection film adopts a SiO2 / TiO2 multilayer structure and the reflectivity of the high-reflection film is greater than 99.9%.

[0012] Preferably, the side of the gain chip away from the reflector end face is the anti-reflection end face, and an anti-reflection film is coated on the anti-reflection end face. The anti-reflection film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the anti-reflection film is less than 0.03%.

[0013] Preferably, the grating waveguide of the planar metal grating has a length of 1-3 cm, a grating period of 225±0.3 nm, and a duty cycle of 50±1%.

[0014] Preferably, the thickness of the planar metal grating is 200±5nm, and it adopts a Cr / Au multilayer structure, with the thicknesses of the Cr / Au layers being 50nm and 150nm, respectively.

[0015] Preferably, the covering layer is a SiO2 thin film layer, and the high-reflectivity (HR) film is a dielectric reflective film or a metal reflective film.

[0016] Preferably, the optical waveguide adopts a ridge structure with a depth of 1.2μm±50nm and a surface roughness of <0.8nm.

[0017] Preferably, the optical waveguide uses Si3N4, single-crystal silicon, lithium niobate, or SiO2 as the optical waveguide material.

[0018] The fabrication method of an external cavity laser based on a top surface HR layer and a planar metal grating includes the following steps:

[0019] Grating fabrication: Electron beam lithography combined with inductively coupled plasma (ICP) etching technology is used to precisely control the grating depth to 120±5nm. Then, a Cr / Au layer is deposited by magnetron sputtering. After the deposition is completed, a white light interferometer is used to inspect and ensure that the surface flatness is <0.08nmRMS.

[0020] Chip packaging: The chip is packaged using eutectic bonding (AuSn80 / 20) process, which makes the thermal resistance <0.08K / W. At the same time, a miniature TEC (TEC1-12703) is integrated as a temperature control module. Through closed-loop control, the temperature fluctuation is controlled within <±0.003℃.

[0021] External cavity coupling: Submicron-level alignment (accuracy ±0.3μm) is achieved using flip-chip bonding technology, ensuring precise connection between components with an air gap of <0.3μm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention employs an electronic evaporation deposition process to fabricate a planar metal grating, replacing the traditional complex three-dimensional etching. This significantly improves the controllable precision and flatness of the grating structure. It eliminates the InP secondary epitaxy process, simplifies the overall process flow, reduces production costs, and simultaneously improves product performance consistency and yield. It also significantly enhances reflection filtering efficiency, ensures the purity of the Bragg reflection spectrum, and helps achieve narrow linewidth performance in lasers. Covering the planar metal grating with a capping layer effectively solves the problem of lattice mismatch in semiconductor secondary epitaxy, and can also constrain diffracted light, reducing light energy leakage. The external cavity structure design increases the degree of freedom, and the grating waveguide length is much greater than the gain chip length, extending the effective cavity length and expanding the filtering space. Attached image description:

[0024] Figure 1 This is a schematic diagram of the main structure of the present invention;

[0025] Figure 2 This is a side view of the structure of the present invention.

[0026] In the diagram: 1. Gain chip; 2. Optical waveguide; 3. Planar metal grating; 4. Covering layer; 5. High reflectivity (HR) film; 6. High reflectivity film; 7. Anti-reflection film. Detailed implementation method:

[0027] 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.

[0028] like Figures 1-2 As shown, this 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 disposed at the top center of the gain chip 1; a planar metal grating 3 disposed on top of the optical waveguide 2; and a capping layer 4 covering the planar metal grating 3, and having a high-reflectivity HR film 5 deposited on top of it.

[0029] 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 1530-1610nm.

[0030] 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.

[0031] Specifically, such as Figure 1 As shown, one side of the gain chip 1 is set as a reflector end face, and a high-reflection film 6 is coated on the reflector end face. The high-reflection film 6 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 an anti-reflection film 7 is coated on the anti-reflection end face. The anti-reflection film 7 adopts a SiO2 / TiO2 multilayer structure and has a reflectivity less than 0.03%.

[0032] The high-reflectivity film 6 can effectively reduce light loss at the reflective end face and enhance light feedback in the cavity, while the anti-reflectivity film 7 can maximize the laser emission efficiency.

[0033] Specifically, such as Figure 1 As shown, the grating waveguide of the planar metal grating 3 has a length of 1-3 cm, a grating period of 225±0.3 nm, and a duty cycle of 50±1%.

[0034] The grating period is set to 225±0.3nm. Precise period control helps to achieve optical feedback at a specific wavelength. The duty cycle is 50±1%, which ensures the uniformity and stability of the grating structure.

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

[0036] The Cr layer enhances the adhesion between the metal and the substrate, while the Au layer has good electrical conductivity and optical reflection properties. The thermal expansion coefficient of the optical waveguide 2 (1.4x10-6 / ℃) is much lower than that of semiconductor materials (3.5x10-6 / ℃), which greatly improves the controllability and flatness of the grating structure.

[0037] Specifically, such as Figure 1 As shown, the capping layer 4 is a SiO2 thin film layer, and the high-reflectivity HR film 5 is a dielectric reflective film or a metal reflective film.

[0038] The cladding layer 4 reduces the optical energy loss of the optical waveguide and enhances the feedback of light in the cavity, which 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 principle of light interference. It has low absorption loss and good optical performance. Metal reflective films such as silver and aluminum have high reflectivity and good conductivity, which can effectively reflect light and reduce light energy loss.

[0039] Specifically, such as Figure 1 As shown, the optical waveguide 2 adopts a ridge structure with a depth of 1.2μm±50nm and a surface roughness of <0.8nm.

[0040] Specifically, such as Figure 1 As shown, the optical waveguide 2 uses Si3N4, single-crystal silicon, lithium niobate, or SiO2 as the material of the optical waveguide 2.

[0041] Si3N4 was 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 (measured by an ellipsometer). In addition, waveguide materials 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) with low absorption at the center working wavelength can also be selected.

[0042] The fabrication method of an external cavity laser based on a top surface HR layer and a planar metal grating includes the following steps:

[0043] Grating fabrication: Electron beam lithography combined with inductively coupled plasma (ICP) etching technology is used to precisely control the grating depth to 120±5nm. Then, a Cr / Au layer is deposited by magnetron sputtering. After the deposition is completed, a white light interferometer is used to inspect and ensure that the surface flatness is <0.08nmRMS.

[0044] Chip packaging: The chip is packaged using eutectic bonding (AuSn80 / 20) process, which makes the thermal resistance <0.08K / W. At the same time, a miniature TEC (TEC1-12703) is integrated as a temperature control module. Through closed-loop control, the temperature fluctuation is controlled within <±0.003℃.

[0045] External cavity coupling: Submicron-level alignment (accuracy ±0.3μm) is achieved using flip-chip bonding technology, ensuring precise connection between components with an air gap of <0.3μm.

[0046] Example 1:

[0047] Set the grating waveguide length L=2cm, and the operating wavelength... =1550nm, the high-reflectivity HR film 5 is a dielectric reflective film, and the linewidth obtained by testing is 720Hz and the output power is 150mW. In this embodiment, the components work together, and the planar metal grating 3, the cover layer 4 and the high-reflectivity HR film 5 effectively reduce light energy loss and achieve good performance output.

[0048] Example 2:

[0049] When the grating waveguide length L = 3cm, the operating wavelength =1530nm. When the high-reflectivity HR film 5 uses a metal reflective film, the linewidth is 680Hz and the output power reaches 180mW. As the grating waveguide length increases, the effective cavity length becomes longer, the linewidth decreases further, and the output power increases, verifying the effectiveness of the design under different high-reflectivity HR film 5 selections.

[0050] This invention:

[0051] Planar metal gratings fabricated using an electronic evaporation deposition process replace traditional complex three-dimensional etched semiconductor gratings. These planar metal gratings have a surface roughness of <0.8 nm, reflectivity >99.5% (e.g., Cr / Au structure), and a thermal expansion coefficient (1.4 x 10⁻⁶ / ℃) significantly lower than semiconductor materials (3.5 x 10⁻⁶ / ℃). This greatly improves the controllable precision and flatness of the grating structure, eliminates the need for InP secondary epitaxy, simplifies the overall process, reduces production costs, and simultaneously improves product performance consistency and yield. The surface flatness of the planar metal grating is <0. The .08nm RMS (detected by a white light interferometer) 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 planar metal grating 3 with a capping layer 4 effectively solves the problem of semiconductor secondary epitaxial lattice mismatch, and can also constrain diffracted light and reduce light energy leakage. The external cavity structure design increases the degree of freedom. The grating waveguide length is much larger 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.

[0052] By employing a centimeter-scale planar metal grating 3 (1-3cm in length), a low-loss coupling structure (total loss <0.2d optoelectronic device), and a high-reflectivity HR film 5 (dielectric or metal reflective film) above the capping layer 4, excellent beam quality with a linewidth <750Hz and M2 <1.1 is achieved for the 3d optoelectronic device. The optical waveguide 2 uses Si3N4 as a low-absorption waveguide material and integrates a high-precision temperature control system (±0.003℃), achieving a wavelength stability of ±0.05pm / ℃. This eliminates the need for InP secondary epitaxy, simplifying the fabrication process. It is suitable for quantum communication, coherent optical communication, and photonic integrated chips, providing high-performance light source solutions for related fields.

[0053] 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 a top surface HR layer and a planar metal grating, characterized in that, include: Gain chip (1); An optical waveguide (2) is positioned at the top center of the gain chip (1); A planar metal grating (3) is disposed on top of the optical waveguide (2); A cover layer (4) is applied over the planar metal grating (3) and coated with a high-reflectivity HR film (5).

2. The laser based on a top surface HR layer and a 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 1530-1610nm.

3. The laser based on the top surface HR layer and 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 a high reflectivity film (6) is coated on the reflector end face. The high reflectivity film (6) adopts a SiO2 / TiO2 multilayer structure and the reflectivity of the high reflectivity film (6) is greater than 99.9%.

4. The laser based on the top surface HR layer and planar metal grating according to claim 3, characterized in that, The side of the gain chip (1) away from the reflector end face is the 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%.

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

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

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

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

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

10. A method for fabricating a laser based on a top-surface HR layer and a planar metal grating, characterized in that, The method, comprising a laser based on a top-surface HR layer and a planar metal grating as described in any one of claims 1-9, includes the following steps: Grating fabrication: Electron beam lithography combined with inductively coupled plasma etching technology is used to precisely control the grating depth to 120±5nm. Then, a Cr / Au layer is deposited by magnetron sputtering. After deposition, a white light interferometer is used to ensure that the surface flatness is <0.08nmRMS. Chip packaging: The chip is packaged using a eutectic bonding process, resulting in a thermal resistance of <0.08K / W. At the same time, a miniature TEC is integrated as a temperature control module, which controls the temperature fluctuation within <±0.003℃ through closed-loop control. External cavity coupling: Submicron-level alignment is achieved using flip-chip bonding technology to ensure precise connection between components, with an air gap of <0.3μm.

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