Plane metal grating laser based on two different gratings and with phase interval of lambda / 2

Abstract

The invention belongs to the technical field of optoelectronic devices, and particularly relates to a planar metal grating laser based on two different gratings and with a phase interval of lambda / 2, which comprises a gain chip, a gain chip optical waveguide, a grating optical waveguide substrate, a back optical waveguide and a planar metal grating. A unique outer cavity structure is adopted, a traditional interlayer semiconductor grating is replaced by two metal plane gratings with similar grating constants and a phase difference of lambda / 2, the advantages that the plane metal gratings do not need to be etched and are smoother and more regular are utilized, and a'mouth-to-mouth 'coupling butt joint mode of a gain chip and a grating optical waveguide substrate is combined; the covering layer grows on the plane metal grating, and the high-reflection HR film is plated on the covering layer, so that the grating reflection efficiency is effectively improved, the optical energy loss of the optical waveguide is reduced, meanwhile, secondary epitaxy is omitted, the process is simplified, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic devices, in particular to a plane metal grating laser based on two different gratings with a phase 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, a 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%, and 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, and 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 performance of the laser.

[0003] Traditional external cavity lasers (ECLs) mostly utilize a single grating structure, resulting in a side mode suppression ratio (SMSR) of only 45-50dB and a linewidth of approximately 20-50kHz, which cannot meet the stringent light source requirements of high-precision applications. They struggle to balance beam quality and integration, relying on complex optical alignment processes that increase production difficulty and cost, hindering large-scale integrated manufacturing. Furthermore, traditional ECLs cannot effectively address the upward diffraction energy loss caused by the grating structure, which compromises the light guidance 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 plane metal grating laser based on two different gratings with a phase interval of λ / 2.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a planar metal grating laser based on two different gratings with a phase interval of λ / 2, comprising: Gain chip; The gain chip optical waveguide is arranged in the center of the top of the gain chip; The grating optical waveguide substrate is arranged on the right end surface of the gain chip; A ridge optical waveguide is arranged centrally on top of the grating optical waveguide substrate; A planar metal grating is arranged on top of the ridge optical waveguide, and the planar metal grating includes a first planar metal Bragg grating and a second planar metal Bragg grating, wherein the grating constants of the first planar metal Bragg grating and the second planar metal Bragg grating are similar but different, and 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 grating period of the planar metal Bragg grating 1 is 224.5±0.3 nm, and the grating period of the planar metal Bragg grating 2 is 225.5±0.3 nm.

[0007] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure, and the lasing wavelength range of the gain chip is 1530-1610 nm.

[0008] 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%.

[0009] 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%.

[0010] Preferably, the duty cycle of the planar metal grating is 50±1%, 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 left end face of the grating optical waveguide substrate and the right end face of the gain chip are coupled and docked in a "mouth-to-mouth" manner.

[0012] Preferably, the covering layer is a SiO2 thin film layer, and the thickness of the covering layer is 0.5-2 μm.

[0013] Preferably, the high-reflection HR film is a dielectric reflective film or a metal reflective film.

[0014] Preferably, the ridge optical waveguide adopts a ridge structure with a width of 3-5 μm and a height of 2-4 μm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a unique external cavity structure, replacing the traditional sandwich semiconductor grating with two metal plane gratings with similar grating constants and a phase difference of λ / 2. Taking advantage of the planar metal grating's advantage of not requiring etching and being more flat and regular, combined with the "mouth-to-mouth" coupling docking method between the gain chip and the grating optical waveguide substrate, a covering layer is grown on top of the planar metal grating and a highly reflective HR film is plated on the covering layer, effectively improving the grating reflection efficiency and reducing the optical energy loss of the optical waveguide. At the same time, the secondary epitaxy is eliminated, the process is simplified, the cost is reduced, the SMSR performance of the laser beam is significantly improved, and the linewidth is compressed. This structural design reduces mode competition, improves the wavelength selection capability and stability of the laser, and facilitates the realization of laser output of different wavelengths in multi-wavelength application scenarios. 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 schematic diagram of the top structure of the present invention.

[0016] In the figure: 1. Gain chip; 2. Ridge 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; 9. Grating optical waveguide substrate; 10. Gain chip optical waveguide. 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 planar metal grating laser based on two different gratings with a phase interval of λ / 2, including: a gain chip 1; a gain chip optical waveguide 10, arranged in the center of the top of the gain chip 1; a grating optical waveguide substrate 9, arranged on the right end face of the gain chip 1; a ridge optical waveguide 2, arranged in the center of the top of the grating optical waveguide substrate 9; a planar metal grating 3, arranged on the top of the ridge 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, the grating constants of the planar metal Bragg grating 1 301 and the planar metal Bragg grating 2 302 are similar but different, 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 dual-plane metallic Bragg gratings (G1 and G2) with a phase difference of Δφ = π (i.e., a spacing of λ / 2), the light reflected from the two gratings constructively interferes within the cavity, increasing the main peak reflectivity from 95% for a traditional single grating to 99.9%. This enhances the intracavity light field intensity and ensures high-power, stable laser output. The destructive interference properties of the dual gratings suppress non-lasing modes, effectively weakening the intensity of side modes and improving the purity and stability of the output light, meeting the requirements of high-precision applications.

[0019] Specifically, such as Figure 1 As shown, the grating period of the planar metal Bragg grating 301 is 224.5±0.3 nm, and the grating period of the planar metal Bragg grating 302 is 225.5±0.3 nm.

[0020] The parameters of the metal Bragg gratings were meticulously designed, with the grating periods of the two metal gratings set to Λ1 = 224.5 ± 0.3 nm and Λ2 = 225.5 ± 0.3 nm, respectively. This similar yet distinct grating period design, combined with a phase difference of λ / 2 between the two gratings, leverages the interference effect of the gratings to significantly enhance the main peak reflectivity and increase the intracavity light field intensity, ensuring high-power, stable laser output. Furthermore, it effectively suppresses non-lasing modes, theoretically achieving a higher side mode suppression ratio (SMSR), compressing the laser linewidth and improving the purity and stability of the output light, meeting the requirements of high-precision applications.

[0021] 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.

[0022] 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.

[0023] 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%.

[0024] The λ / 2 high-reflection film 5 can effectively reduce the light loss at the reflective end face and enhance the light feedback in the cavity, and the λ / 4 anti-reflection film 6 can maximize the laser emission efficiency.

[0025] Specifically, such as Figure 1 As shown, the duty cycle of the planar metal grating 3 is 50±1%, 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.

[0026] The duty cycle is 50±1%, which ensures the uniformity and stability of the grating structure. The Cr layer can enhance the adhesion between the metal and the substrate, and the Au layer has good conductivity and optical reflection properties.

[0027] Specifically, such as Figure 1 As shown, the left end face of the grating optical waveguide substrate 9 and the right end face of the gain chip 1 are coupled and docked in a "mouth-to-mouth" manner.

[0028] The left end face of the grating optical waveguide substrate 9 is coupled to the right end face of the gain chip 1 in a "mouth-to-mouth" coupling manner. Submicron alignment (accuracy ±0.2μm) is achieved through a high-precision flip-chip process, ensuring that the air gap between the two is less than 200nm. The total length of the external cavity Lcavity = 800μm + Lwg, and the free spectral range FSR > 100GHz. This external cavity coupling structure design, combined with other components, realizes efficient light transmission and feedback, improving the performance of the laser.

[0029] Specifically, such as Figure 1 As shown, the cover layer 4 is a SiO2 thin film layer, the thickness of the cover layer 4 is 0.5-2 μm, and the high-reflection HR film 5 is a dielectric reflective film or a metal reflective film.

[0030] 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 optical 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.

[0031] 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.

[0032] Specifically, such as Figure 1 As shown, the ridge optical waveguide 2 adopts a ridge structure with a width of 3-5 μm and a height of 2-4 μm.

[0033] Theoretical basis: According to coupled-mode theory, for a conventional uniform grating DFB laser, the coupling coefficient is κ, and the light field distribution can be expressed by A(z), and satisfies the following coupled-mode equation: , where β is the propagation constant. In this equation, Describes the phase change of the light field during propagation. It reflects the coupling effect of the grating on the light field, and loss\terms represents the loss of light during the propagation process.

[0034] For the two metal grating DFB lasers with similar grating constants and a phase difference of λ / 2 in the present invention, the presence of phase shift profoundly affects the light field distribution. Assuming that the phase shift position is at z = 0, the light field distribution before and after the phase shift can be represented by A1(z) and A2(z), respectively, and the boundary conditions are satisfied: , which means that the light field produces a π / 2 phase jump at the phase shift. This phase jump will cause the redistribution of the light field, change the propagation characteristics of light in the laser cavity, and thus affect the mode selection characteristics of the laser. During the laser generation process, different modes of light will compete with each other, and this phase jump enables the main mode to more effectively suppress the side mode, thereby improving the SMSR.

[0035] The difference in grating constants and the setting of phase difference λ / 2 change the light field distribution, causing subtle changes in the effective refractive index of light during propagation. According to the Bragg condition of the grating, for traditional uniform grating DFB lasers, its Bragg wavelength is satisfy: ,in is the effective refractive index, and Λ is the grating period. In the present invention, due to the change in the light field distribution, the actual Bragg wavelength changes slightly, and the gains of the main mode and side mode are also affected. The main mode gain is relatively increased, and the side mode gain is relatively suppressed, which further promotes the improvement of SMSR. In addition, this structural change also compresses the laser linewidth, improving the purity and stability of the laser.

[0036] Example 1: Planar metal Bragg gratings with periods of 224.5nm and 225.5nm, respectively, were prepared using an electronic plating process. The grating pattern was precisely controlled by electron beam evaporation, and the waveguide was etched to a depth of 120nm using ICP. The Cr / Au layer was deposited by magnetron sputtering with a surface flatness of 0.07nmRMS. A top SiO2 waveguide layer with a thickness of 1μm was prepared by chemical vapor deposition. A λ / 2DBR dielectric reflective film was deposited on top of the top SiO2 waveguide layer as an HR film. The right end face of the gain chip 1 was flip-chip bonded to the left end face of the grating optical waveguide substrate 9 to achieve "mouth-to-mouth" coupling. The air gap was controlled to 180nm. Test results showed a linewidth of 0.6kHz, an SMSR of 63dB, and a threshold current of 22mA.

[0037] 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 showed that the wavelength drift was controlled within ±0.002nm in the range of -40~85℃. At the same time, the effects of top SiO2 waveguide layers of different thicknesses on laser performance were 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. This is because the λ / 2DBR dielectric reflective film achieves high reflectivity by periodically stacking multiple layers of media with different refractive indices using the principle of light interference. It has low absorption loss and good optical properties, which can more effectively enhance the feedback of light in the cavity and improve the overall performance of the laser.

[0038] Example 3: The external cavity length was optimized to 3 cm, at which point the free spectral range (FSR) was 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 light field confinement and energy loss were studied at different external cavity lengths. As the external cavity length increased, the propagation path of light in the cavity increased, and the interaction time and degree of the light field with the grating, SiO2 waveguide layer, and HR film changed. Experimental and simulation analysis revealed that, at a 3 cm external cavity length, a top 1 μm thick SiO2 waveguide layer combined with a λ / 2DBR dielectric reflective film as the HR film can achieve optimal confinement of the light field and minimize energy loss, thereby determining this parameter combination as the solution for achieving optimal laser performance.

[0039] Example 4: Based on the "mouth-to-mouth" coupling and docking of the right end face of the gain chip 1 and the left end face of the grating optical waveguide substrate 9, the influence of the coupling process on the laser performance was further studied. A high-precision flip-chip process was used in conjunction with an advanced optical alignment system to improve the coupling accuracy to ±0.1μm, while strictly controlling the air gap between the two to 150nm.

[0040] Through this optimized coupling method, test results show that the laser's output power increased by 15% to 35mW, the side mode suppression ratio (SMSR) increased to 65dB, and the linewidth was further compressed to 0.4kHz. This is because the higher coupling accuracy and smaller air gap effectively reduce the reflection and scattering losses of light during transmission, allowing more light to be efficiently transmitted from the gain chip to the grating waveguide, enhancing the optical feedback effect and thus improving the overall performance of the laser.

[0041] Example 5: The influence of different duty cycles on the performance of metal planar Bragg gratings was studied. Grating structures with duty cycles of 45%, 50%, and 55% were prepared respectively. Other parameters remained unchanged. The grating periods were Λ1=224.5±0.3nm and Λ2=225.5±0.3nm, and the metal layer thickness was 200nm.

[0042] The test results show that when the duty cycle is 50%, the overall performance of the laser is the best. At this time, the reflection efficiency of the grating is the highest, the main mode reflectivity reaches 99.8%, the side mode suppression ratio (SMSR) is 64dB, and the linewidth is 0.5kHz. When the duty cycle deviates from 50%, the reflection characteristics of the grating change, resulting in a decrease in the main mode gain and a relative increase in the side mode gain, thereby affecting the performance of the laser. For example, when the duty cycle is 45%, the main mode reflectivity drops to 99.5% and the SMSR drops to 62dB; when the duty cycle is 55%, the main mode reflectivity is 99.6% and the SMSR is 61dB.

[0043] The present invention: A unique external cavity structure is adopted, and the traditional sandwich semiconductor grating is replaced by two metal plane gratings with similar grating constants and a phase difference of λ / 2. Taking advantage of the fact that the planar metal grating does not require etching and is more flat and regular, combined with the "mouth-to-mouth" coupling docking method between the gain chip 1 and the grating optical waveguide substrate 9, a cover layer 4 is grown on top of the planar metal grating 3, and a high-reflection HR film 5 is plated on the cover layer 4. This effectively improves the grating reflection efficiency and reduces the optical waveguide light energy loss. At the same time, it eliminates the need for secondary epitaxy, simplifies the process, reduces costs, significantly improves the SMSR performance of the laser beam, and compresses the linewidth. This structural design reduces mode competition, improves the wavelength selection capability and stability of the laser, and facilitates the realization of laser output of different wavelengths in multi-wavelength application scenarios.

[0044] 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 two different gratings with a phase interval of λ / 2, the plane metal grating laser is characterized by ,include: Gain chip (1); A gain chip optical waveguide (10) is arranged in the center of the top of the gain chip (1); A grating optical waveguide substrate (9) is arranged on the right end surface of the gain chip (1); A ridge optical waveguide (2) is arranged in the center of the top of the grating optical waveguide substrate (9); A planar metal grating (3) is arranged on the top of the ridge 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), the grating constants of the planar metal Bragg grating 1 (301) and the planar metal Bragg grating 2 (302) are different, 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) covers the planar metal grating (3) and is coated with a high-reflection HR film (5) thereon.

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

3. The planar metal grating laser based on two different gratings with a phase 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.

4. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 1, 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%.

5. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 4, 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%.

6. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The duty cycle of the planar metal grating (3) is 50±1%, 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.

7. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The left end face of the grating optical waveguide substrate (9) and the right end face of the gain chip (1) are coupled and docked in a "mouth-to-mouth" manner.

8. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The covering layer (4) is a SiO2 thin film layer, and the thickness of the covering layer (4) is 0.5-2 μm.

9. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The ridge optical waveguide (2) adopts a ridge structure with a width of 3-5 μm and a height of 2-4 μm.

10. The planar metal grating laser based on two different gratings with a phase interval of λ / 2 according to claim 1, characterized in that: The high-reflection HR film (5) is a dielectric reflective film or a metal reflective film.

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