Narrow-linewidth external cavity laser based on phase difference regulation of bimetallic bragg grating

Abstract

The present application relates to the technical field of semiconductor laser, specifically to a double-metal Bragg grating phase difference regulation narrow-linewidth external cavity laser, and a regulation narrow-linewidth external cavity laser, which comprises a gain chip, a first high reflection (HR) film is coated on the left end face of the gain chip, and a first anti-reflection (AR) film is coated on the right end face 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 is aligned and attached to the left end face of the metal Bragg grating waveguide to form an external cavity structure, a second anti-reflection (AR) film is coated on the left end face of the metal Bragg grating waveguide, and a third anti-reflection (AR) film is coated on the right end face of the metal Bragg grating waveguide. Through tests, the present application uses interference enhancement effect and mode suppression mechanism to improve the side mode suppression ratio (SMSR) to 65 dB and compress the linewidth to 0.6 kHz.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to an external cavity laser with narrow linewidth achieved by phase difference modulation of a bimetallic Bragg grating. Background Technology

[0002] A laser is a device that generates high-intensity, highly directional, and highly monochromatic coherent light through stimulated emission. A laser consists of three parts: 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. The resonant cavity uses mirrors to make the photons oscillate repeatedly, amplifying the light and ultimately outputting laser light.

[0003] Limitations of existing technology:

[0004] 1. Performance limitations of DFB lasers

[0005] 1.1 Due to 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.

[0006] 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.

[0007] 1.3. The reflectivity of semiconductor gratings (93-95%) requires additional gain compensation, resulting in an increase in power consumption of 15-20%.

[0008] 2. Shortcomings of traditional external cavity lasers

[0009] 2.1 The single-grating structure has a side-mode suppression ratio (SMSR) of only 45-50dB and a linewidth of about 20-50kHz (IEEE Photonics Technology Letters, 2020).

[0010] 2.2 It is difficult to balance beam quality and integration, requiring complex optical alignment processes. Summary of the Invention

[0011] This invention provides a narrow-linewidth external cavity laser achieved by phase difference modulation of a bimetallic Bragg grating, in order to solve the problems mentioned in the background art.

[0012] To achieve the above objectives, the present invention provides the following technical solution: a narrow-linewidth external cavity laser achieved by phase difference modulation of a bimetallic Bragg grating, comprising: a gain chip, wherein a first high-reflectivity (HR) film is deposited on the left end face of the gain chip, and a first anti-reflection (AR) film is deposited on the right end face of the gain chip.

[0013] A metal Bragg grating waveguide is disposed on the right side of the gain chip. The right end face of the gain chip is aligned and bonded with the left end face of the metal Bragg grating waveguide to form an external cavity structure. A second anti-reflection AR film is deposited on the left end face of the metal Bragg grating waveguide, and a third anti-reflection AR film is deposited on the right end face of the metal Bragg grating waveguide.

[0014] The metal Bragg grating waveguide includes a grating waveguide substrate, a back ridge waveguide is disposed on the upper surface of the grating waveguide substrate, a first metal Gay Bragg reflection grating is disposed on the left side of the upper surface of the back ridge waveguide, and a second metal Gay Bragg reflection grating is disposed on the right side of the upper surface of the back ridge waveguide, with a phase difference between the first metal Gay Bragg reflection grating and the second metal Gay Bragg reflection grating.

[0015] 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 <0.8 nm.

[0016] As a preferred embodiment of the above technical solution, the metal Bragg grating waveguide has a length of 2cm, a period of 225nm, and a surface roughness of <0.8nm.

[0017] As a preferred embodiment of the above technical solution, the phase difference Δφ = π.

[0018] As a preferred embodiment of the above technical solution, the phase difference is controlled with a phase control accuracy of <λ / 50 by atomic layer deposition technology.

[0019] As a preferred embodiment of the above technical solution, the back ridge waveguide has a width of 3-5μm and a height of 2-4μm, and its mode field matching degree with the gain chip is >98%.

[0020] As a preferred embodiment of the above technical solution, the back ridge waveguide is 4μm wide and 3μm high, and its mode field matching degree with the gain chip is >98%.

[0021] This invention provides a narrow-linewidth external cavity laser achieved by phase difference modulation using a dual-metal Bragg grating, which has the following advantages:

[0022] 1. Enhanced interference: The reflected light from the two gratings undergoes constructive interference within the cavity, with the main peak reflectivity reaching 99.9% (compared to 95% for a traditional single grating).

[0023] 2. Mode suppression: Non-laser modes are suppressed due to destructive interference, with a theoretical SMSR of 65 dB.

[0024] 3. Equivalent cavity length doubled: Free spectral range extended to 100 GHz (traditional external cavity 50 GHz).

[0025] 4. Linewidth compression technology: Achieve Δν=0.6kHz (compared to approximately 1MHz for traditional DFB) through a 3cm external cavity length and 99.9% reflectivity.

[0026] 5. Process integration innovation: Nanoscale phase control: Electron beam lithography (EBL) combined with atomic layer deposition (ALD) achieves phase difference control accuracy of ±5nm.

[0027] 6. Multifunctional metal layer: The top metal grating layer also serves as an electrode layer, reducing the number of process steps. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention;

[0029] Figure 2 for Figure 1 Top view;

[0030] Figure 3 This is a schematic diagram of the metal grating waveguide structure in this invention;

[0031] Figure 4 for Figure 3 The left view.

[0032] 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. Back ridge waveguide; 23. First metal Gamble Bragg reflection grating; 24. Second metal Gamble Bragg reflection grating; 25. Second anti-reflection AR film; 26. Third anti-reflection AR film; 27. Phase difference. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0034] Example 1

[0035] like Figures 1-4 As shown, in this embodiment, a narrow-linewidth external cavity laser is achieved by phase difference modulation of a bimetallic Bragg grating, including: a gain chip 1, wherein a first high-reflectivity HR film 11 is deposited on the left end face of the gain chip 1, and a first anti-reflection AR film 12 is deposited on the right end face of the gain chip 1.

[0036] In specific implementation, the gain chip 1 is an InP / InGaAsP quantum well structure with an emission center wavelength λ1530nm and a threshold current <22mA (25℃); the first high reflectivity HR film 11 is a multilayer structure of SiO2 / TiO2 with a reflectivity >99.9%; the first antireflection AR film 12 has a thickness λ / 4 and a reflectivity <0.03%.

[0037] A metal Bragg grating waveguide 2 is disposed on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and attached to the left end face of the metal Bragg grating waveguide to form an external cavity structure. A second anti-reflection AR film 25 is deposited on the left end face of the metal Bragg grating waveguide 2, and a third anti-reflection AR film 26 is deposited on the right end face of the metal Bragg grating waveguide 2.

[0038] 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 <0.8 nm.

[0039] The metal Bragg grating waveguide 2 includes a grating waveguide substrate 21. A back ridge waveguide 22 is disposed on the upper surface of the grating waveguide substrate 21. A first metal Gay Bragg reflection grating 23 is disposed on the left side of the upper surface of the back ridge waveguide 22, and a second metal Gay Bragg reflection grating 24 is disposed on the right side of the upper surface of the back ridge waveguide 22. A phase difference 27 is provided between the first metal Gay Bragg reflection grating 23 and the second metal Gay Bragg reflection grating 24.

[0040] Furthermore, the phase difference 27Δφ = π.

[0041] Furthermore, the phase difference 27 achieves a phase control accuracy of <λ / 50 through atomic layer deposition technology.

[0042] In specific implementation, the back ridge waveguide 22 is 3μm wide and 2μm high, and its mode field matching degree with the gain chip 1 is >98%.

[0043] It should be noted that the bimetallic Bragg grating phase difference modulation realizes a narrow-linewidth external cavity laser, with a total external cavity length L. cavity =800μm+L wg Free spectral range > 100 GHz.

[0044] Example 2

[0045] like Figures 1-4 As shown, in this embodiment, a narrow-linewidth external cavity laser is achieved by phase difference modulation of a bimetallic Bragg grating, including: a gain chip 1, wherein a first high-reflectivity HR film 11 is deposited on the left end face of the gain chip 1, and a first anti-reflection AR film 12 is deposited on the right end face of the gain chip 1.

[0046] In specific implementation, the gain chip 1 is an InP / InGaAsP quantum well structure with an emission center wavelength λ1610nm and a threshold current <22mA (25℃); the first high reflectivity HR film 11 is a multilayer structure of SiO2 / TiO2 with a reflectivity >99.9%; the first antireflection AR film 12 has a thickness λ / 4 and a reflectivity <0.03%.

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

[0048] In a specific implementation, the metal Bragg grating waveguide 2 has a length of 3cm, a period of 230nm, and a surface roughness of <0.8nm.

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

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

[0051] Furthermore, the phase difference 27 achieves a phase control accuracy of <λ / 50 through atomic layer deposition technology.

[0052] In specific implementation, the back ridge waveguide 22 is 5μm wide and 4μm high, and its mode field matching degree with the gain chip 1 is >98%.

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

[0054] Example 3

[0055] like Figures 1-4 As shown, in this embodiment, a narrow-linewidth external cavity laser is achieved by phase difference modulation of a bimetallic Bragg grating, including: a gain chip 1, wherein a first high-reflectivity HR film 11 is deposited on the left end face of the gain chip 1, and a first anti-reflection AR film 12 is deposited on the right end face of the gain chip 1.

[0056] In specific implementation, the gain chip 1 is an InP / InGaAsP quantum well structure with an emission center wavelength λ1530-1610nm and a threshold current <22mA (25℃); the first high reflectivity HR film 11 is a multilayer structure of SiO2 / TiO2 with a reflectivity >99.9%; the first antireflection AR film 12 has a thickness λ / 4 and a reflectivity <0.03%.

[0057] A metal Bragg grating waveguide 2 is disposed on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and attached to the left end face of the metal Bragg grating waveguide to form an external cavity structure. A second anti-reflection AR film 25 is deposited on the left end face of the metal Bragg grating waveguide 2, and a third anti-reflection AR film 26 is deposited on the right end face of the metal Bragg grating waveguide 2.

[0058] In a specific implementation, the metal Bragg grating waveguide 2 has a length of 2cm, a period of 225nm, and a surface roughness of <0.8nm.

[0059] The metal Bragg grating waveguide 2 includes a grating waveguide substrate 21. A back ridge waveguide 22 is disposed on the upper surface of the grating waveguide substrate 21. A first metal Gay Bragg reflection grating 23 is disposed on the left side of the upper surface of the back ridge waveguide 22, and a second metal Gay Bragg reflection grating 24 is disposed on the right side of the upper surface of the back ridge waveguide 22. A phase difference 27 is provided between the first metal Gay Bragg reflection grating 23 and the second metal Gay Bragg reflection grating 24.

[0060] Furthermore, the phase difference 27Δφ = π.

[0061] Furthermore, the phase difference 27 achieves a phase control accuracy of <λ / 50 through atomic layer deposition technology.

[0062] In specific implementation, the back ridge waveguide 22 is 4μm wide and 3μm high, and its mode field matching degree with the gain chip 1 is >98%.

[0063] It should be noted that the bimetallic Bragg grating phase difference modulation realizes a narrow-linewidth external cavity laser, with a total external cavity length L. cavity =800μm+L wg Free spectral range > 100 GHz.

[0064] The dual-metal Bragg grating phase difference modulation provided by this invention enables a narrow-linewidth external cavity laser, improving performance through the following effects:

[0065] 1. Enhanced interference: The reflected light from the two gratings undergoes constructive interference within the cavity, with the main peak reflectivity reaching 99.9% (compared to 95% for a traditional single grating).

[0066] 2. Mode Suppression: Non-laser modes are suppressed due to destructive interference; theoretically, SMSR = 65 dB. Formula:

[0067]

[0068] Where R1 and R2 are the reflectivities at both ends of the resonant cavity.

[0069] 3. Equivalent cavity length doubled: Free spectral range extended to 100 GHz (traditional external cavity 50 GHz).

[0070] 4. Linewidth compression technique: Based on the Hakki-Paoli model, the linewidth formula is modified as follows:

[0071]

[0072] Where hν: photon energy; P: laser output power; L: total length of the resonant cavity; L g : Length of the gain medium; R1 and R2 are the reflectivities at both ends of the resonant cavity; α: Linewidth enhancement factor.

[0073] It integrates the effects of cavity length and gain medium on photon lifetime.

[0074] The loss term in the traditional linewidth formula has been corrected to include the coupling effect of phase noise and carrier fluctuations.

[0075] Achieving Δν=0.6kHz (compared to approximately 1MHz for conventional DFB) is achieved through an external cavity length of 3cm and a reflectivity of 99.9%.

[0076] 5. Process integration innovation: Nanoscale phase control: Electron beam lithography (EBL) combined with atomic layer deposition (ALD) achieves phase difference control accuracy of ±5nm.

[0077] 6. Multifunctional metal layer: The top metal grating layer also serves as an electrode layer, reducing the number of process steps.

[0078] Through testing, by precisely controlling the phase difference 27 between the first metallic Geiger-Bragg reflection grating 23 and the second metallic Geiger-Bragg reflection grating 24, the side-mode rejection ratio (SMSR) was increased to 65dB and the linewidth was compressed to 0.6kHz by utilizing the interference enhancement effect and mode suppression mechanism.

[0079] The metal grating adopts a Cr / Au structure with a reflectivity >99.9% and a low coefficient of thermal expansion, ensuring the wavelength stability of the device over a wide temperature range. With a total external cavity length of 3cm, the free spectral range reaches 100GHz.

[0080] This invention is applicable to fields such as quantum communication, lidar, and photonics integration, and provides a novel light source solution for high-precision applications.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A narrow-linewidth external cavity laser achieved by phase difference modulation of a dual-metal Bragg grating, comprising a gain chip (1), characterized in that: The gain chip (1) has a first high reflectance HR film (11) deposited on its left end face and a first antireflection AR film (12) deposited on its right end face. 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 attached to the left end face of the metal Bragg grating waveguide to form an external cavity structure. A second anti-reflection AR film (25) is deposited on the left end face of the metal Bragg grating waveguide (2), and a third anti-reflection AR film (26) is deposited on the right end face of the metal Bragg grating waveguide (2). The metal Bragg grating waveguide (2) includes a grating waveguide substrate (21), a back ridge waveguide (22) is provided on the upper surface of the grating waveguide substrate (21), a first metal Gag Bragg reflection grating (23) is provided on the left side of the upper surface of the back ridge waveguide (22), a second metal Gag Bragg reflection grating (24) is provided on the right side of the upper surface of the back ridge waveguide (22), and a phase difference (27) is provided between the first metal Gag Bragg reflection grating (23) and the second metal Gag Bragg reflection grating (24).

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

4. The external cavity laser with narrow linewidth achieved by phase difference modulation 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 <0.8 nm.

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

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

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

Images