Laser based on top-hr layer and two spaced lambda / 2 planar metallic gratings

Abstract

The present application relates to the technical field of optoelectronic devices, especially to a top HR layer and two interval lambda / 2 plane metal grating laser, comprising: a gain chip; an optical waveguide; a plane metal grating and a cover layer. The present application controls the phase difference between the plane metal Bragg grating one and the plane metal Bragg grating two to be lambda / 2, uses interference enhancement and mode suppression mechanism, improves the side mode suppression ratio (SMSR) to 63dB, compresses the line width to 0.6kHz, the plane metal grating adopts high reflectivity Cr / Au structure, the thermal expansion coefficient is low, which ensures the wavelength stability of the device in a wide temperature range, the top cover layer effectively prevents the loss of upward diffraction light energy, optimizes the light field distribution, replaces the traditional semiconductor secondary epitaxial waveguide layer to reduce the cost, does not need grating etching, and the grating accuracy is controllable and the flatness is good.

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 two spaced λ / 2 planar metal gratings. Background Technology

[0002] Due to carrier density fluctuations and a 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 the manufacturing cost is 2-3 times higher than that of external cavity lasers. The reflectivity of semiconductor gratings is only 93-95%, requiring additional gain compensation, which increases power consumption by 15-20% and also causes heat dissipation problems, affecting the stability and reliability of the laser. In addition, the etching process of semiconductor gratings 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, thus affecting the 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. This cannot meet the stringent requirements of high-precision applications for light sources. It is difficult to balance beam quality and integration, and it relies on complex optical alignment processes, which increases production difficulty and cost, making it unsuitable for large-scale integrated manufacturing. Moreover, traditional external cavity lasers cannot effectively solve the problem of upward diffraction energy loss caused by the grating structure, which affects the light guiding performance of the grating waveguide. 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 HR layer and two spaced λ / 2 planar metal gratings.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: based on a top HR layer and two spaced λ / 2 planar metal grating lasers, comprising:

[0006] Gain chip;

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

[0008] A planar metal grating is disposed on the top of the optical waveguide, and the planar metal grating includes a planar metal Bragg grating one and a planar metal Bragg grating two. A phase difference is provided between the planar metal Bragg grating one and the planar metal Bragg grating two, and the length of the phase difference is λ / 2.

[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 planar metal grating 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. The planar metal grating has a reflectivity greater than 99.9% and a 3dB reflection bandwidth less than 0.1nm.

[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 width of 3-5μm and a height of 2-4μm, and the mode field matching degree with the gain chip is greater than 98%.

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

[0018] Preferably, the capping layer can be made of Si3N4, monocrystalline silicon, or lithium niobate.

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

[0020] This invention precisely controls the phase difference between planar metal Bragg grating one and planar metal Bragg grating two to λ / 2, and utilizes interference enhancement and mode suppression mechanisms to improve the side-mode rejection ratio (SMSR) to 63dB and compress the linewidth to 0.6kHz. The planar metal gratings adopt a high-reflectivity Cr / Au structure with a low coefficient of thermal expansion, ensuring the wavelength stability of the device over a wide temperature range. The top capping layer effectively prevents upward diffraction energy loss and optimizes the light field distribution. At the same time, it replaces the traditional semiconductor secondary epitaxial waveguide layer to reduce costs. The top high-reflectivity HR film further reduces light energy loss and enhances optical feedback. The use of planar metal gratings eliminates the need for etching processes, and its flatness and error are far better than those of semiconductor etched gratings. Moreover, the fabrication process is simple and low-cost. Attached image description:

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

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

[0023] In the figure: 1. Gain chip; 2. Optical waveguide; 3. Planar metal grating; 301. Planar metal Bragg grating one; 302. Planar metal Bragg grating two; 4. Covering layer; 5. High reflectivity (HR) film; 6. High reflectivity film; 7. Anti-reflection film; 8. Phase difference. Detailed implementation method:

[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 1-2 As shown, this application provides a laser based on a top-surface HR layer and two λ / 2 spaced planar metal gratings, including: a gain chip 1; an optical waveguide 2 disposed at the top center of the gain chip 1; a planar metal grating 3 disposed at the top of the optical waveguide 2, and the planar metal grating 3 includes a planar metal Bragg grating 1 301 and a planar metal Bragg grating 2 302, with a phase difference 8 between the planar metal Bragg grating 1 301 and the planar metal Bragg grating 2 302, the length of the phase difference 8 being λ / 2; and a capping layer 4 covering the planar metal grating 3, and a high-reflectivity HR film 5 coated on top of it.

[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 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 the intensity of side modes 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 gain chip 1 adopts an InP / InGaAsP quantum well structure, and the lasing wavelength range of the gain chip 1 is 1530-1610nm.

[0028] 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.

[0029] 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%.

[0030] 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.

[0031] 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%.

[0032] 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.

[0033] Specifically, such as Figure 1As shown, 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. The reflectivity of the planar metal grating 3 is greater than 99.9%, and the 3dB reflection bandwidth is less than 0.1nm.

[0034] 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.

[0035] 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.

[0036] The capping layer 4 possesses excellent optical properties. On one hand, it effectively reduces upward diffraction energy loss caused by the presence of the top Bragg grating, guiding the light through its own waveguide structure and re-confining the upwardly diffracted light within the waveguide system, maintaining the light-guiding properties of the grating waveguide. On the other hand, the SiO2 waveguide layer forms a good optical match with the planar metal Bragg grating and the underlying waveguide, optimizing the light field distribution and further improving the laser's performance. Furthermore, compared to traditional semiconductor secondary epitaxial waveguide layers, the fabrication process of the SiO2 waveguide layer is relatively simple and cost-effective, contributing to a reduction in overall production costs.

[0037] Dielectric reflective films achieve high reflectivity by periodically stacking multiple layers of media with different refractive indices and utilizing the principle of light interference. They have 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, reduce light energy loss, further reduce the light energy loss of the grating waveguide, enhance the feedback of light in the cavity, and help improve the output power and stability of the laser.

[0038] Specifically, such as Figure 1 As shown, the optical waveguide 2 adopts a ridge structure with a width of 3-5μm and a height of 2-4μm. The mode field matching degree with the gain chip 1 is greater than 98%. The optical waveguide 2 uses Si3N4, single crystal silicon, lithium niobate, or SiO2 low-absorption light-absorbing materials as optical waveguide materials.

[0039] Si3N4 was selected as the low-absorption waveguide material. At a wavelength of 1550nm, its absorption coefficient is <0.08doptoelectronics / cm (measured data), and its effective refractive index n=2.025±0.005 (measured by ellipsometer). In addition, waveguide materials such as single-crystal silicon (absorption coefficient 0.1-0.2doptoelectronics / cm, refractive index n=3.47) or lithium niobate (absorption coefficient <0.05doptoelectronics / cm, refractive index n=2.28) with low absorption at the center working wavelength can also be selected.

[0040] Specifically, such as Figure 1 As shown, the capping layer 4 can be made of Si3N4, single-crystal silicon, or lithium niobate.

[0041] Based on the Hakki-Paoli model, an ultra-narrow linewidth output of Δν=0.6kHz was achieved by using an optical waveguide 2 with an external cavity length of 3cm and a reflectivity of 99.9%. In contrast, the linewidth of a traditional DFB laser is approximately 1MHz. Ultra-narrow linewidth lasers have significant application value in coherent optical communication, high-precision spectral analysis, and quantum key distribution. The use of a planar metal grating eliminates the need for etching processes, avoiding the complex photolithography and etching steps of traditional semiconductor etching processes. It also eliminates the need for high-precision equipment and special chemical reagents, effectively reducing equipment costs, raw material costs, and process complexity. Furthermore, the flatness and error of the metal grating are far superior to those of grating structures etched from semiconductors. Its high flatness (less than 0.08nm RMS) and low error characteristics ensure high purity of the reflection spectrum, which helps improve the overall performance of the laser. Performance optimization is achieved while reducing costs.

[0042] This solution's external cavity coupling system employs flip-chip bonding to achieve submicron alignment (accuracy ±0.2μm), with an air gap less than 200nm. The total external cavity length L_cavity = 800μm + L_wg, and the free spectral range FSR > 100GHz. A planar metal Bragg grating pattern is formed on the substrate using electron beam evaporation and other electroplating processes, eliminating the need for traditional semiconductor etching. By controlling the electron beam evaporation parameters, the grating period, duty cycle, and other parameters are precisely controlled. ICP etching is used to etch the waveguide to a depth controlled at 120±5nm. A Cr / Au layer is deposited by magnetron sputtering, ensuring a surface flatness of less than 0.08nm RMS. (Detected by white light interferometer) The top SiO2 waveguide layer is prepared using methods such as chemical vapor deposition (CVD) or physical vapor deposition (PVD), with precise control over its thickness and refractive index. Depending on the type of HR film, the HR film is prepared using appropriate processes. For example, the preparation of λ / 2DBR dielectric reflective film can be achieved by repeatedly depositing dielectric materials with different refractive indices. The preparation of metal reflective film can be achieved by methods such as magnetron sputtering or electron beam evaporation. The prepared structure is then surface-treated to make its surface roughness less than 0.8 nm. An AlN ceramic substrate with a matching coefficient of thermal expansion is used for encapsulation to ensure that the wavelength drift is less than 0.002 nm / ℃ under temperature changes of -40~85℃.

[0043] Example 1: A planar metal Bragg grating with a period of 225 nm was fabricated using an electron plating process. The grating pattern was precisely controlled by electron beam evaporation. The waveguide was etched by ICP to a depth of 120 nm. A Cr / Au layer was deposited by magnetron sputtering, achieving a surface flatness of 0.07 nm RMS. A top SiO2 waveguide layer with a thickness of 1 μm was fabricated by chemical vapor deposition. A λ / 2 DBR dielectric reflective film was deposited on top of the top SiO2 waveguide layer as a HR film. The gain chip and the grating waveguide were aligned by flip-chip bonding with an air gap of 180 nm. The test results showed that the linewidth was 0.6 kHz, the SMSR was 63 dB, and the threshold current was 22 mA.

[0044] 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 were conducted, and the wavelength drift was controlled within ±0.002nm in the range of -40~85℃. At the same time, the effect of different thicknesses of the top SiO2 waveguide layer on the laser performance was tested. The results showed that the 1μm thick SiO2 waveguide layer was the most effective in reducing light energy loss and improving laser performance. In addition, comparing the effects of different types of HR films (λ / 2DBR dielectric reflective film and metal reflective film) on laser performance, it was found that when using λ / 2DBR dielectric reflective film, the output power and stability of the laser were slightly better than those when using metal reflective film.

[0045] Example 3: The external cavity length was optimized to 3 cm, at which point the free spectral range FSR = 100 GHz and the linewidth was further compressed to 0.5 kHz. During the optimization process, the effects of the top SiO2 waveguide layer and HR film on optical field confinement and energy loss under different external cavity lengths were studied. The optimal combination of parameters for external cavity length, top SiO2 waveguide layer thickness and HR film type was determined to achieve optimal laser performance.

[0046] Working principle of this invention:

[0047] By precisely controlling the phase difference between planar metal Bragg grating 301 and planar metal Bragg grating 302 to λ / 2, and utilizing interference enhancement and mode suppression mechanisms, the side-mode suppression ratio (SMSR) is improved to 63dB, and the linewidth is compressed to 0.6kHz. The planar metal grating adopts a high-reflectivity Cr / Au structure with a low coefficient of thermal expansion, ensuring the wavelength stability of the device over a wide temperature range. The top capping layer 4 effectively prevents upward diffraction energy loss and optimizes the light field distribution. At the same time, it replaces the traditional semiconductor secondary epitaxial waveguide layer to reduce costs. The top high-reflectivity HR film 5 further reduces light energy loss and enhances optical feedback. The planar metal grating 3 eliminates the need for etching processes, and its flatness and error are far better than those of semiconductor etched gratings. Moreover, the fabrication process is simple and low-cost. The device uses a flip-chip bonding process to achieve submicron alignment, and the free spectral range reaches 100GHz when the total external cavity length is 3cm. This invention provides a high-performance, low-cost new light source solution for quantum communication, lidar, and photonic integration.

[0048] 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 two spaced λ / 2 planar metal grating lasers, 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 the top of the optical waveguide (2), and the planar metal grating (3) includes a planar metal Bragg grating one (301) and a planar metal Bragg grating two (302). A phase difference (8) is provided between the planar metal Bragg grating one (301) and the planar metal Bragg grating two (302), and the length of the phase difference (8) is λ / 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 two spaced λ / 2 planar metal gratings 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 a top-surface HR layer and two spaced λ / 2 planar metal gratings 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 a top-surface HR layer and two spaced λ / 2 planar metal gratings 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 two spaced λ / 2 planar metal gratings 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 two spaced λ / 2 planar metal gratings according to claim 5, 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. The reflectivity of the planar metal grating (3) is greater than 99.9%, and the 3dB reflection bandwidth is less than 0.1nm.

7. The laser based on a top-surface HR layer and two spaced λ / 2 planar metal gratings 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 two spaced λ / 2 planar metal gratings according to claim 1, characterized in that, The optical waveguide (2) adopts a ridge structure with a width of 3-5 μm and a height of 2-4 μm, and its mode field matching degree with the gain chip (1) is greater than 98%.

9. The laser based on a top-surface HR layer and two spaced λ / 2 planar metal gratings according to claim 1, characterized in that, The optical waveguide (2) uses Si3N4, single crystal silicon, lithium niobate, or SiO2 low-absorption light material as the optical waveguide material.

10. The laser based on a top-surface HR layer and two spaced λ / 2 planar metal gratings according to claim 7, characterized in that, The covering layer (4) can be made of Si3N4, monocrystalline silicon, or lithium niobate.

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