External cavity laser for realizing narrow linewidth by regulating and controlling phase difference of double-metal Bragg grating

Abstract

The invention relates to the technical field of semiconductor lasers, in particular to an external cavity laser for realizing narrow linewidth through phase difference regulation and control of a bimetallic Bragg grating, which comprises a gain chip, a first high-reflection (HR) film is plated on the left end surface of the gain chip, and a first anti-reflection (AR) film is plated on the right end surface of the gain chip; a metal Bragg grating waveguide is arranged on the right side of the gain chip, the right end face of the gain chip and the left end face of the metal Bragg grating waveguide are aligned and attached to form an outer cavity structure, and the left end face of the metal Bragg grating waveguide is plated with a second anti-reflection AR film. The right end face of the metal Bragg grating waveguide is plated with a third anti-reflection AR film. Tests show that the side mode rejection ratio (SMSR) is increased to 65dB and the line width is compressed to 0.6 kHz by using an interference enhancement effect and a mode suppression mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, in particular to an external cavity laser that realizes narrow linewidth by controlling the phase difference of a double metal Bragg grating. Background Art

[0002] A laser is a device that generates high-intensity, highly directional, and highly monochromatic coherent light through the principle of stimulated emission of radiation. A laser consists of three components: a working medium, a pump source, and a resonant cavity. The working medium (such as a crystal, gas, or semiconductor) absorbs energy and is excited to a high-energy state, releasing photons through stimulated emission of radiation. The resonant cavity, through mirrors, causes the photons to oscillate repeatedly, amplifying the light and ultimately producing laser light.

[0003] Limitations of existing technologies: 1. Performance limitations of DFB lasers 1.1. Limited by carrier density fluctuations and lasing cavity length (typically 0.5 mm), the linewidth is usually 1-10 MHz (Optics Express, 2021), which cannot meet the application requirements of coherent detection.

[0004] 1.2. The secondary epitaxial process results in a yield of only 65-70% (Photonics Research, 2021), and the manufacturing cost is 2-3 times higher than that of external cavity lasers.

[0005] 1.3. The reflectivity of semiconductor gratings (93-95%) requires additional gain compensation, resulting in a 15-20% increase in power consumption.

[0006] 2. Disadvantages of traditional external cavity lasers 2.1. The side mode suppression ratio (SMSR) of a single grating structure is only 45-50dB, and the linewidth is about 20-50kHz (IEEE Photonics Technology Letters, 2020).

[0007] 2.2. It is difficult to strike a balance between beam quality and integration, requiring complex optical alignment processes. Summary of the Invention

[0008] The present invention provides an external cavity laser that realizes narrow linewidth by controlling the phase difference of a double metal Bragg grating, so as to solve the problems raised in the above background technology.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution, in which a narrow-linewidth external cavity laser is realized by phase difference regulation of a double-metal Bragg grating, comprising: a gain chip, wherein the left end face of the gain chip is coated with a first highly reflective HR film, and the right end face of the gain chip is coated with a first anti-reflective AR film.

[0010] A metal Bragg grating waveguide is provided on the right side of the gain chip. The right end face of the gain chip and the left end face of the metal Bragg grating waveguide are aligned and bonded to form an external cavity structure. The left end face of the metal Bragg grating waveguide is plated with a second anti-reflection AR film, and the right end face of the metal Bragg grating waveguide is plated with a third anti-reflection AR film.

[0011] The metal Bragg grating waveguide includes a grating waveguide substrate, a ridge optical waveguide is provided on the upper end surface of the grating waveguide substrate, a first metal cover Bragg reflection grating is provided on the left side of the upper end surface of the ridge optical waveguide, and a second metal cover Bragg reflection grating is provided on the right side of the upper end surface of the ridge optical waveguide, and a phase difference is provided between the first metal cover Bragg reflection grating and the second metal cover Bragg reflection grating.

[0012] As a preferred embodiment of the above technical solution, the metal Bragg grating waveguide has a length of 1-3 cm, a period of 220-230 nm, and a surface roughness of less than 0.8 nm.

[0013] As a preferred embodiment of the above technical solution, the metal Bragg grating waveguide has a length of 2 cm, a period of 225 nm, and a surface roughness of less than 0.8 nm.

[0014] As a preferred embodiment of the above technical solution, the phase difference Δφ=π.

[0015] As a preferred embodiment of the above technical solution, the phase difference is achieved by atomic layer deposition technology with a phase control accuracy of <λ / 50.

[0016] As a preferred embodiment of the above technical solution, the ridge optical waveguide has a width of 3-5 μm and a height of 2-4 μm, and a mode field matching degree with the gain chip of >98%.

[0017] As a preferred embodiment of the above technical solution, the ridge optical waveguide is 4 μm wide and 3 μm high, and has a mode field matching degree with the gain chip greater than 98%.

[0018] The present invention provides an external cavity laser that realizes narrow linewidth by controlling the phase difference of a bimetallic Bragg grating, which has the following beneficial effects: 1. Interference enhancement: The reflected light from the two gratings constructively interferes in the cavity, and the main peak reflectivity reaches 99.9% (95% for traditional single grating).

[0019] 2. Mode suppression: The non-lasing mode is suppressed due to destructive interference, with a theoretical SMSR of 65dB.

[0020] 3. Equivalent cavity length doubled: the free spectral range is extended to 100 GHz (50 GHz for traditional external cavity).

[0021] 4. Linewidth compression technology: Through a 3cm external cavity length and 99.9% reflectivity, Δν=0.6kHz (traditional DFB is about 1MHz) is achieved.

[0022] 5. Process integration innovation: Nanoscale phase control: Electron beam lithography (EBL) combined with atomic layer deposition (ALD), with phase difference control accuracy of ±5nm.

[0023] 6. Multifunctional metal layer: The top metal grating layer also serves as the electrode layer, reducing process steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 for Figure 1 A top view of Figure 3 Schematic diagram of the structure of the metal grating waveguide in the present invention; Figure 4 for Figure 3 Left view of .

[0025] In the figure: 1. Gain chip; 11. First high-reflection HR film; 12. First anti-reflection AR film; 2. Metal Bragg grating waveguide; 21. Grating waveguide substrate; 22. Ridge optical waveguide; 23. First metal cover Bragg reflection grating; 24. Second metal cover Bragg reflection grating; 25. Second anti-reflection AR film; 26. Third anti-reflection AR film; 27. Phase difference. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] Example 1 like Figures 1-4 As shown, in this embodiment, the double metal Bragg grating phase difference regulation realizes the narrow linewidth external cavity laser, including: a gain chip 1, the left end surface of the gain chip 1 is coated with a first high-reflection HR film 11, and the right end surface of the gain chip 1 is coated with a first anti-reflection AR film 12.

[0028] In a specific implementation, the gain chip 1 is an InP / InGaAsP quantum well structure with an emission center wavelength of λ1530nm and a threshold current of <22mA (25°C); the first high-reflection HR film 11 is a multi-layer structure of SiO2 / TiO2 with a reflectivity of >99.9%; the first anti-reflection AR film 12 has a thickness of λ / 4 and a reflectivity of <0.03%.

[0029] A metal Bragg grating waveguide 2 is provided on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and bonded to the left end face of the metal Bragg grating waveguide to form an external cavity structure. The left end face of the metal Bragg grating waveguide 2 is coated with a second anti-reflection AR film 25, and the right end face of the metal Bragg grating waveguide 2 is coated with a third anti-reflection AR film 26.

[0030] In a specific implementation, the metal Bragg grating waveguide 2 has a length of 1 cm, a period of 220 nm, and a surface roughness of less than 0.8 nm.

[0031] The metal Bragg grating waveguide 2 includes a grating waveguide substrate 21, a ridge optical waveguide 22 is provided on the upper end surface of the grating waveguide substrate 21, a first metal cover Bragg reflection grating 23 is provided on the left side of the upper end surface of the ridge optical waveguide 22, and a second metal cover Bragg reflection grating 24 is provided on the right side of the upper end surface of the ridge optical waveguide 22, and a phase difference 27 is provided between the first metal cover Bragg reflection grating 23 and the second metal cover Bragg reflection grating 24.

[0032] Furthermore, the phase difference 27Δφ=π.

[0033] Furthermore, the phase difference 27 is achieved by atomic layer deposition technology to achieve a phase control accuracy of <λ / 50.

[0034] In a specific implementation, the ridge optical waveguide 22 has a width of 3 μm and a height of 2 μm, and a mode field matching degree with the gain chip 1 of >98%.

[0035] It should be noted that the bimetallic Bragg grating phase difference control realizes a narrow linewidth external cavity laser, and the total length of the external cavity L cavity =800μm+L wg , free spectral range > 100GHz.

[0036] Example 2 like Figures 1-4 As shown, in this embodiment, the double metal Bragg grating phase difference regulation realizes the narrow linewidth external cavity laser, including: a gain chip 1, the left end surface of the gain chip 1 is coated with a first high-reflection HR film 11, and the right end surface of the gain chip 1 is coated with a first anti-reflection AR film 12.

[0037] In a specific implementation, the gain chip 1 is an InP / InGaAsP quantum well structure with an emission center wavelength of λ1610nm and a threshold current of <22mA (25°C); the first high-reflection HR film 11 is a multi-layer structure of SiO2 / TiO2 with a reflectivity of >99.9%; the first anti-reflection AR film 12 has a thickness of λ / 4 and a reflectivity of <0.03%.

[0038] A metal Bragg grating waveguide 2 is provided on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and bonded to the left end face of the metal Bragg grating waveguide to form an external cavity structure. The left end face of the metal Bragg grating waveguide 2 is coated with a second anti-reflection AR film 25, and the right end face of the metal Bragg grating waveguide 2 is coated with a third anti-reflection AR film 26.

[0039] In a specific implementation, the metal Bragg grating waveguide 2 has a length of 3 cm, a period of 230 nm, and a surface roughness of less than 0.8 nm.

[0040] The metal Bragg grating waveguide 2 includes a grating waveguide substrate 21, a ridge optical waveguide 22 is provided on the upper end surface of the grating waveguide substrate 21, a first metal cover Bragg reflection grating 23 is provided on the left side of the upper end surface of the ridge optical waveguide 22, and a second metal cover Bragg reflection grating 24 is provided on the right side of the upper end surface of the ridge optical waveguide 22, and a phase difference 27 is provided between the first metal cover Bragg reflection grating 23 and the second metal cover Bragg reflection grating 24.

[0041] Furthermore, the phase difference 27Δφ=π.

[0042] Furthermore, the phase difference 27 is achieved by atomic layer deposition technology to achieve a phase control accuracy of <λ / 50.

[0043] In a specific implementation, the ridge optical waveguide 22 has a width of 5 μm and a height of 4 μm, and a mode field matching degree with the gain chip 1 of >98%.

[0044] It should be noted that the bimetallic Bragg grating phase difference control realizes a narrow linewidth external cavity laser, and the total length of the external cavity L cavity =800μm+L wg , free spectral range > 100GHz.

[0045] Example 3 like Figures 1-4 As shown, in this embodiment, the double metal Bragg grating phase difference regulation realizes the narrow linewidth external cavity laser, including: a gain chip 1, the left end surface of the gain chip 1 is coated with a first high-reflection HR film 11, and the right end surface of the gain chip 1 is coated with a first anti-reflection AR film 12.

[0046] In a specific implementation, the gain chip 1 is an InP / InGaAsP quantum well structure with an emission center wavelength of λ1530-1610nm and a threshold current of <22mA (25°C); the first high-reflection HR film 11 is a multi-layer structure of SiO2 / TiO2 with a reflectivity of >99.9%; the first anti-reflection AR film 12 has a thickness of λ / 4 and a reflectivity of <0.03%.

[0047] A metal Bragg grating waveguide 2 is provided on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and bonded to the left end face of the metal Bragg grating waveguide to form an external cavity structure. The left end face of the metal Bragg grating waveguide 2 is coated with a second anti-reflection AR film 25, and the right end face of the metal Bragg grating waveguide 2 is coated with a third anti-reflection AR film 26.

[0048] In a specific implementation, the metal Bragg grating waveguide 2 has a length of 2 cm, a period of 225 nm, and a surface roughness of less than 0.8 nm.

[0049] The metal Bragg grating waveguide 2 includes a grating waveguide substrate 21, a ridge optical waveguide 22 is provided on the upper end surface of the grating waveguide substrate 21, a first metal cover Bragg reflection grating 23 is provided on the left side of the upper end surface of the ridge optical waveguide 22, and a second metal cover Bragg reflection grating 24 is provided on the right side of the upper end surface of the ridge optical waveguide 22, and a phase difference 27 is provided between the first metal cover Bragg reflection grating 23 and the second metal cover Bragg reflection grating 24.

[0050] Furthermore, the phase difference 27Δφ=π.

[0051] Furthermore, the phase difference 27 is achieved by atomic layer deposition technology to achieve a phase control accuracy of <λ / 50.

[0052] In a specific implementation, the ridge optical waveguide 22 has a width of 4 μm and a height of 3 μm, and a mode field matching degree with the gain chip 1 of >98%.

[0053] It should be noted that the bimetallic Bragg grating phase difference control realizes a narrow linewidth external cavity laser, and the total length of the external cavity L cavity =800μm+L wg , free spectral range > 100GHz.

[0054] The bimetallic Bragg grating phase difference control provided by the present invention realizes a narrow linewidth external cavity laser, which improves performance through the following effects: 1. Interference enhancement: The reflected light from the two gratings constructively interferes in the cavity, and the main peak reflectivity reaches 99.9% (95% for traditional single grating).

[0055] 2. Mode suppression: The non-lasing mode is suppressed due to destructive interference, the theoretical SMSR = 65dB, formula:

[0056] Among them, R1 and R2 are the reflectivity at both ends of the resonant cavity.

[0057] 3. Equivalent cavity length doubled: the free spectral range is extended to 100 GHz (50 GHz for traditional external cavity).

[0058] 4. Linewidth compression technology: Based on the Hakki-Paoli model, the linewidth formula is modified to:

[0059] Where, hν: photon energy; P: laser output power; L: total length of the resonant cavity; L g : gain medium length; R1 and R2 are the reflectivities at both ends of the resonant cavity; α: linewidth enhancement factor.

[0060] : The effects of cavity length and gain medium on photon lifetime are comprehensively considered.

[0061] : The loss term in the traditional linewidth formula is corrected to include the coupling effect of phase noise and carrier fluctuations.

[0062] With a 3cm external cavity length and 99.9% reflectivity, Δν=0.6kHz (traditional DFB is about 1MHz) is achieved.

[0063] 5. Process integration innovation: Nanoscale phase control: Electron beam lithography (EBL) combined with atomic layer deposition (ALD), with phase difference control accuracy of ±5nm.

[0064] 6. Multifunctional metal layer: The top metal grating layer also serves as the electrode layer, reducing process steps.

[0065] After testing, by precisely controlling the phase difference 27 between the first metal cover Bragg reflection grating 23 and the second metal cover Bragg reflection grating 24, and utilizing the interference enhancement effect and mode suppression mechanism, the side mode suppression ratio (SMSR) was increased to 65dB and the linewidth was compressed to 0.6kHz.

[0066] The metal grating adopts a Cr / Au structure with a reflectivity of >99.9% and a low thermal expansion coefficient, ensuring the wavelength stability of the device over a wide temperature range. When the total length of the external cavity is 3cm, the free spectrum range reaches 100GHz.

[0067] The present invention is applicable to fields such as quantum communication, laser radar and photon integration, and provides a new light source solution for high-precision applications.

[0068] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A narrow linewidth external cavity laser achieved by controlling the phase difference of a double metal Bragg grating, comprising a gain chip (1), characterized in that: The left end surface of the gain chip (1) is plated with a first high-reflection HR film (11), and the right end surface of the gain chip (1) is plated with a first anti-reflection AR film (12); A metal Bragg grating waveguide (2) is provided on the right side of the gain chip (1); the right end face of the gain chip (1) is aligned and bonded to the left end face of the metal Bragg grating waveguide to form an external cavity structure; the left end face of the metal Bragg grating waveguide (2) is plated with a second anti-reflection AR film (25); and the right end face of the metal Bragg grating waveguide (2) is plated with a third anti-reflection AR film (26); The metal Bragg grating waveguide (2) comprises a grating waveguide substrate (21), a ridge optical waveguide (22) is provided on the upper end face of the grating waveguide substrate (21), a first metal cover Bragg reflection grating (23) is provided on the left side of the upper end face of the ridge optical waveguide (22), a second metal cover Bragg reflection grating (24) is provided on the right side of the upper end face of the ridge optical waveguide (22), and a phase difference (27) is provided between the first metal cover Bragg reflection grating (23) and the second metal cover Bragg reflection grating (24).

2. The external cavity laser with narrow linewidth achieved by phase difference control of a bimetallic Bragg grating according to claim 1, characterized in that: The phase difference (27) Δφ=π.

3. The external cavity laser with narrow linewidth achieved by phase difference control of a bimetallic Bragg grating according to claim 2, characterized in that: The phase difference (27) is achieved by atomic layer deposition technology with a phase control accuracy of less than λ / 50.

4. The external cavity laser with narrow linewidth achieved by phase difference control of a bimetallic Bragg grating according to claim 1, characterized in that: The metal Bragg grating waveguide (2) has a length of 1-3 cm, a period of 220-230 nm, and a surface roughness of less than 0.8 nm.

5. The external cavity laser with narrow linewidth achieved by controlling the phase difference of a bimetallic Bragg grating according to claim 4, characterized in that: The metal Bragg grating waveguide (2) has a length of 2 cm, a period of 225 nm, and a surface roughness of less than 0.8 nm.

6. The external cavity laser with narrow linewidth achieved by phase difference control of a bimetallic Bragg grating according to claim 1, characterized in that: The ridge optical waveguide (22) has a width of 3-5 μm and a height of 2-4 μm, and a mode field matching degree with the gain chip (1) of >98%.

7. The external cavity laser with narrow linewidth achieved by phase difference control of a bimetallic Bragg grating according to claim 6, characterized in that: The ridge optical waveguide (22) has a width of 4 μm and a height of 3 μm, and a mode field matching degree with the gain chip (1) of >98%.

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