Laser based on top surface HR layer and two spaced lambda / 2 plane metal gratings

Abstract

The invention relates to the technical field of optoelectronic devices, in particular to a laser based on a top surface HR layer and two planar metal gratings with an interval of lambda / 2. An optical waveguide; a planar metal grating; and a covering layer. The phase difference between the first planar metal Bragg grating and the second planar metal Bragg grating is precisely controlled to be lambda / 2, interference enhancement and mode suppression mechanisms are utilized, the side mode suppression ratio (SMSR) is improved to 63 dB, the compression line width is 0.6 kHz, the planar metal gratings adopt high-reflectivity Cr / Au structures, the thermal expansion coefficient is low, the wavelength stability of the device in a wide temperature range is guaranteed, and the device can be widely applied to the field of laser devices. The top covering layer effectively prevents upward diffraction light energy loss, optimizes light field distribution, replaces a traditional semiconductor secondary epitaxial waveguide layer, reduces cost, does not need grating etching, and is controllable in grating precision and good in flatness.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic devices, in particular to a laser based on a top surface HR layer and two plane metal gratings with an interval of λ / 2. Background Art

[0002] Affected by carrier density fluctuations and the typical 0.5mm laser cavity length, the linewidth of a DFB laser is usually 1-10MHz. In application scenarios such as coherent detection, the wider linewidth will cause serious signal interference, significantly reducing detection accuracy and system performance. Its secondary epitaxial process is complex, with a yield of only 65-70%. The manufacturing cost is 2-3 times higher than that of an external cavity laser. The reflectivity of the semiconductor grating is only 93-95%, requiring additional gain compensation, resulting in a 15-20% increase in power consumption. It will also cause heat dissipation problems, affecting the stability and reliability of the laser. In addition, the semiconductor grating etching process is complex. Due to the anisotropy of the crystal lattice, the surface structure after etching is irregular, making it difficult to ensure the flatness and accuracy of the grating, which in turn affects the 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 approximately 20-50kHz. These cannot meet the stringent light source requirements of high-precision applications. They struggle to balance beam quality and integration, and rely on complex optical alignment processes, increasing production difficulty and cost, hindering large-scale integrated manufacturing. Furthermore, traditional external cavity lasers cannot effectively address the problem of upward diffraction light energy loss caused by the grating structure, which affects the light guiding properties of the grating waveguide. 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 two plane metal gratings with an interval of λ / 2.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: based on the top surface HR layer and two λ / 2 spaced plane metal grating lasers, including: Gain chip; An optical waveguide is arranged centered on top of the gain chip; A planar metal grating is arranged on the top of the optical waveguide, and the planar metal grating includes a first planar metal Bragg grating and a second planar metal Bragg grating, a phase difference is set between the first planar metal Bragg grating and the second planar metal Bragg grating, and the length of the phase difference is λ / 2; 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±5nm, and a Cr / Au multilayer structure is adopted, and the thicknesses of the Cr / Au layers are 50nm and 150nm respectively. The reflectivity of the planar metal grating is greater than 99.9%, and the 3dB reflection bandwidth is less than 0.1nm.

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

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

[0014] Preferably, the cover layer may be made of Si3N4, single crystal silicon, or lithium niobate.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention precisely controls the phase difference between the first and second planar metal Bragg gratings to λ / 2, and utilizes interference enhancement and mode suppression mechanisms to improve the side mode suppression ratio (SMSR) to 63dB and compress the linewidth to 0.6kHz. The planar metal grating adopts a high-reflectivity Cr / Au structure with a low thermal expansion coefficient, which ensures the wavelength stability of the device under a wide temperature range. The top cover layer effectively prevents the loss of upward diffracted light energy, optimizes the light field distribution, and replaces the traditional semiconductor secondary epitaxial waveguide layer to reduce costs. The top highly reflective HR film further reduces light energy loss and enhances light feedback. The use of a planar metal grating does not require an etching process, and its flatness and error are far better than those of a semiconductor etched grating. In addition, the preparation process is simple and the cost is low. 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; 301. Planar metal Bragg grating 1; 302. Planar metal Bragg grating 2; 4. Covering layer; 5. High-reflection HR film; 6. High-reflection film; 7. Anti-reflection film; 8. Phase difference. 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 a laser based on a top surface HR layer and two planar metal gratings spaced apart by λ / 2, comprising: a gain chip 1; an optical waveguide 2, arranged centered on the top of the gain chip 1; a planar metal grating 3, arranged on the top of the optical waveguide 2, and the planar metal grating 3 comprises a planar metal Bragg grating 1 301 and a planar metal Bragg grating 2 302, a phase difference 8 is set between the planar metal Bragg grating 1 301 and the planar metal Bragg grating 2 302, and the length of the phase difference 8 is λ / 2; a covering layer 4, covering the planar metal grating 3, and coated with a high-reflection HR film 5 on the top.

[0018] Using a double-plane metal Bragg grating (G1, G2) with a phase difference of Δφ=π (i.e., spacing λ / 2), the light reflected from the two gratings constructively interferes in the cavity, increasing the main peak reflectivity from 95% of a traditional single grating to 99.9%, enhancing the light field intensity in the cavity and providing a guarantee for high-power, stable laser output. The destructive interference characteristics of the double grating are used to suppress the non-lasing mode. According to the formula Theoretically, the side mode suppression ratio (SMSR) can reach 65dB, effectively weakening the side mode intensity and improving the purity and stability of the output light to meet the requirements of high-precision applications. The dual-grating configuration doubles the equivalent cavity length, extending the free spectral range from 50GHz in a traditional external cavity to 100GHz, reducing mode competition and improving the wavelength selectivity and stability of the laser, facilitating the realization of different wavelength laser output in multi-wavelength applications.

[0019] 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.

[0020] 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.

[0021] Specifically, such as Figure 1 As 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%.

[0022] 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.

[0023] 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%.

[0024] 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.

[0025] Specifically, such as Figure 1 As shown, the thickness of the planar metal grating 3 is 200±5nm, and a Cr / Au multilayer structure is adopted, and the thicknesses of the Cr / Au layers are 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.

[0026] 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.

[0027] 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.

[0028] The cover layer 4 has excellent optical properties. On the one hand, it can effectively reduce the loss of upward diffracted light energy caused by the presence of the top Bragg grating, guide the light through its own waveguide structure, and re-constrain the upward 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 optical waveguide, optimizing the light field distribution and further improving the performance of the laser. In addition, compared with traditional semiconductor secondary epitaxial waveguide layers, the preparation process of the SiO2 waveguide layer is relatively simple and the cost is lower, which helps to reduce the overall production cost.

[0029] Dielectric reflective films achieve high reflectivity by periodically stacking multiple layers of media with different refractive indices, utilizing the principle of light interference, and have low absorption loss and good optical performance. Metal reflective films such as silver and aluminum have high reflectivity and good conductivity, can effectively reflect light, reduce light energy escape, 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.

[0030] Specifically, such as Figure 1 As shown, the optical waveguide 2 adopts a ridge structure with a width of 3-5 μm and a height of 2-4 μm. The mode field matching degree with the gain chip 1 is greater than 98%. The optical waveguide 2 adopts Si3N4 or single crystal silicon or lithium niobate or SiO2 low absorption light material as the optical waveguide material.

[0031] Si3N4 is selected as the low-absorption waveguide material. At a wavelength of 1550nm, its absorption coefficient is <0.08d / cm (measured data), 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 / cm, refractive index n=3.47) or lithium niobate (absorption coefficient <0.05d / cm, refractive index n=2.28).

[0032] Specifically, such as Figure 1 As shown, the cover layer 4 can be made of Si3N4 or single crystal silicon or lithium niobate.

[0033] Based on the Hakki-Paoli model, by using an optical waveguide 2 with a 3cm external cavity length and a reflectivity of 99.9%, an ultra-narrow linewidth output with a linewidth of Δν=0.6kHz is achieved. The linewidth of a traditional DFB laser is about 1MHz. Lasers with ultra-narrow linewidth have important application value in coherent optical communications, high-precision spectral analysis, and quantum key distribution. The use of a planar metal grating does not require an etching process, avoiding the complex photolithography and etching steps in traditional semiconductor etching processes. It does not require reliance on high-precision equipment and special chemical reagents, effectively reducing equipment costs, raw material costs, and process complexity. At the same time, the flatness and error of the metal grating are far better than those of grating structures etched from semiconductors. Its high flatness (less than 0.08nmRMS) and low error characteristics ensure the high purity of the reflection spectrum, which helps to improve the overall performance of the laser and achieve performance optimization while reducing costs.

[0034] The external cavity coupling system of this scheme uses a flip-chip process to achieve submicron alignment (accuracy ±0.2μm), an air gap of less than 200nm, a total external cavity length L_cavity = 800μm + L_wg, and a free spectral range FSR>100GHz. Electron plating processes such as electron beam evaporation are used to form a planar metal Bragg grating pattern on the substrate, without the need for traditional semiconductor etching processes. By controlling the electron beam evaporation parameters, the grating period, duty cycle and other parameters can be precisely controlled. The waveguide is etched using ICP etching technology with a depth controlled at 120±5nm. The Cr / Au layer is deposited by magnetron sputtering to ensure a surface flatness of less than 0.08nmRMS ( White light interferometer detection), the top SiO2 waveguide layer is prepared by chemical vapor deposition (CVD) or physical vapor deposition (PVD) methods, and its thickness and refractive index are precisely controlled. Depending on the type of HR film, the corresponding process is used to prepare the HR film. For example, the preparation of λ / 2DBR dielectric reflective film can be achieved by repeatedly alternating the deposition of dielectric materials with different refractive indices. The preparation of metal reflective film can be achieved by magnetron sputtering or electron beam evaporation. The prepared structure is surface treated to make its surface roughness less than 0.8nm. It is packaged using an AlN ceramic base with a matching thermal expansion coefficient to ensure that the wavelength drift is less than 0.002nm / ℃ under temperature fluctuations of -40~85℃.

[0035] Example 1: A planar metal Bragg grating with a period of 225 nm was prepared using an electroplating process. The grating pattern was precisely controlled by electron beam evaporation. The waveguide was etched to a depth of 120 nm using ICP. A Cr / Au layer was deposited by magnetron sputtering with a surface flatness of 0.07 nm RMS. A top SiO2 waveguide layer with a thickness of 1 μm was prepared using chemical vapor deposition. A λ / 2DBR dielectric reflective film was deposited on top of the top SiO2 waveguide layer as a HR film. The gain chip and grating waveguide were flip-chip aligned with each other, with an air gap of 180 nm. Test results showed a linewidth of 0.6 kHz, an SMSR of 63 dB, and a threshold current of 22 mA.

[0036] Example 2: Comparing different metal materials (Al and Ag), it was found that the Cr / Au structure had the highest reflectivity, reaching 99.92%. Temperature variation 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 top SiO2 waveguide layer of different thicknesses on laser performance was tested. The results showed that a 1μm thick SiO2 waveguide layer was most effective in reducing light energy loss and improving laser performance. In addition, a comparison of the effects of different types of HR films (λ / 2DBR dielectric reflective film and metal reflective film) on laser performance showed that the output power and stability of the laser were slightly better when using the λ / 2DBR dielectric reflective film than when using the metal reflective film.

[0037] Example 3: The external cavity length is optimized to 3 cm. At this time, the free spectral range (FSR) is 100 GHz, and the linewidth is further compressed to 0.5 kHz. During the optimization process, the effects of the top SiO2 waveguide layer and HR film on the light field confinement and energy loss at different external cavity lengths are studied, and the optimal parameter combination of external cavity length, top SiO2 waveguide layer thickness, and HR film type is determined to achieve the best laser performance.

[0038] Working principle of the present invention: By precisely controlling the phase difference between the first and second planar metal Bragg gratings 301 and 302 to λ / 2 and utilizing interference enhancement and mode suppression mechanisms, the side mode suppression ratio (SMSR) is increased to 63 dB and the linewidth is compressed to 0.6 kHz. The planar metal grating utilizes a high-reflectivity Cr / Au structure with a low thermal expansion coefficient, ensuring the wavelength stability of the device over a wide temperature range. The top cover layer 4 effectively prevents upward diffraction light energy loss, optimizes the light field distribution, and replaces the traditional semiconductor secondary epitaxial waveguide layer to reduce costs. The top highly reflective HR film 5 further reduces light energy loss and enhances optical feedback. The planar metal grating 3 does not require an etching process, and its flatness and error are far better than those of semiconductor etched gratings. The fabrication process is simple and low-cost. The device uses a flip-chip process to achieve submicron alignment. When the total external cavity length is 3 cm, the free spectral range reaches 100 GHz. The present invention provides a high-performance, low-cost new light source solution for fields such as quantum communication, lidar, and photonic integration.

[0039] 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. Based on the top surface HR layer and two λ / 2 spaced plane metal grating lasers, characterized by ,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 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), a phase difference (8) is provided between the planar metal Bragg grating 1 (301) and the planar metal Bragg grating 2 (302), and the length of the phase difference (8) is λ / 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 two plane metal gratings with an interval of λ / 2 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 two plane metal gratings with an interval of λ / 2 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 two plane metal gratings with an interval of λ / 2 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 two plane metal gratings with an interval of λ / 2 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 two plane metal gratings with an interval of λ / 2 according to claim 5, 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. The reflectivity of the planar metal grating (3) is greater than 99.9%, and the 3dB reflection bandwidth is less than 0.1 nm.

7. The laser based on the top surface HR layer and two plane metal gratings with an interval of λ / 2 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 two plane metal gratings with an interval of λ / 2 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 a mode field matching degree with the gain chip (1) greater than 98%.

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

10. The laser based on the top surface HR layer and two plane metal gratings with an interval of λ / 2 according to claim 7, characterized in that: The covering layer (4) may be made of Si3N4, single crystal silicon or lithium niobate.

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