Ultra-narrow linewidth wavelength-adjustable external cavity laser based on planar metal grating

Abstract

The invention relates to the technical field of semiconductor lasers, in particular to an ultra-narrow linewidth wavelength-adjustable external cavity laser based on a planar metal grating, which comprises a gain chip, and the left end face and the right end face of the gain chip are respectively plated with a high reflection film and a first antireflection film; a planar metal 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 planar metal grating waveguide, and a second antireflection film and a third antireflection film are plated on the left end face and the right end face of the planar metal grating waveguide respectively; the planar metal grating waveguide comprises a grating waveguide substrate, a ridge optical waveguide is arranged on the upper portion of the grating waveguide substrate, a planar metal grating is arranged on the upper portion of the ridge optical waveguide, and a top covering layer is arranged on the upper portion of the planar metal grating. Through the centimeter-level metal grating and the low-loss coupling structure, light beam quality with 3dB line width less than 700Hz and M2 less than 0.9 is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, in particular to an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating. Background Art

[0002] DFB lasers were invented in the 1970s to improve the monochromaticity and wavelength stability of lasers. They integrate a grating structure with periodic refractive index changes in the laser cavity, replacing the end mirrors of the traditional FP cavity, and using the Bragg condition to achieve wavelength selection and optical feedback.

[0003] Limitations of existing technologies: 1. DFB lasers require secondary epitaxial growth, and the process yield is only 65-70% (data source: Photonics Research, 2021). The manufacturing cost is 2-3 times higher than that of external cavity lasers.

[0004] 2. Semiconductor grating etching: Due to the anisotropy of the crystal lattice, there are many irregular surface structures after photolithography, which affects and increases the laser line width.

[0005] 3. An additional grating etching process increases costs.

[0006] 4. The reflectivity of semiconductor grating is about 93-95%, and additional gain compensation is required, resulting in a 15-20% increase in power consumption.

[0007] 5. Inner cavity structure M 2 The factor is typically >1.5, and the coupling efficiency in photonic integrated systems is <85% (Reference: Optics Express, 2019). Summary of the Invention

[0008] The object of the present invention is to provide an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating to solve the problems raised in the above background technology.

[0009] To achieve the above objectives, the present invention provides the following technical solution: an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating, comprising: a gain chip, wherein the left end surface of the gain chip is coated with a high reflective film, and the right end surface of the gain chip is coated with a first anti-reflection film; A planar metal grating waveguide is provided on the right side of the gain chip, the right end face of the gain chip is aligned and bonded to the left end face of the planar metal grating waveguide, the left end face of the planar metal grating waveguide is plated with a second anti-reflection film, and the right end face of the planar metal grating waveguide is plated with a third anti-reflection film; The planar metal grating waveguide comprises a grating waveguide substrate, a ridge optical waveguide is arranged on the top of the grating waveguide substrate, a planar metal grating is arranged on the top of the ridge optical waveguide, and a top covering layer is arranged on the top of the planar metal grating.

[0010] As a preferred embodiment of the above technical solution, the emission center wavelength of the gain chip is 1530-1610 nm.

[0011] As a preferred embodiment of the above technical solution, the emission center wavelength of the gain chip is 1550 nm.

[0012] As a preferred embodiment of the above technical solution, the length of the planar metal grating is 1-3 cm, the period is 220-230 nm, and the surface roughness is less than 0.8 nm; As a preferred embodiment of the above technical solution, the ridge optical waveguide has a ridge width of 3-5 μm, a ridge height of 2-4 μm, and an etching depth of 1-1.5 nm.

[0013] As a preferred embodiment of the above technical solution, the material of the ridge optical waveguide includes but is not limited to Si3N4, single crystal silicon and lithium niobate.

[0014] As a preferred embodiment of the above technical solution, a TEC temperature control module is provided below the gain chip and the planar metal grating waveguide.

[0015] As a preferred embodiment of the above technical solution, the top covering layer is an epitaxially grown SiO2 layer.

[0016] The present invention provides an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating, which has the following beneficial effects: 1. No etching is required, which simplifies the process flow and improves the controllable accuracy and flatness of the grating structure.

[0017] 2. The reflectivity of the planar metal grating is >99.5% (Cr / Au structure), which is significantly higher than that of the semiconductor grating with a relatively rough surface after traditional etching (reflectivity is about 93-95%).

[0018] 3. The surface flatness of the plane metal grating is less than 0.08nmRMS (detected by white light interferometer), and the reflection filtering efficiency is significantly improved.

[0019] 4. A top covering layer is provided on the top of the planar metal grating. The top covering layer is a SiO2 layer, which solves the problem of semiconductor secondary epitaxial lattice mismatch, while constraining diffracted light and reducing light energy overflow.

[0020] 5. The external cavity structure provides the freedom that the grating waveguide length is much larger than the gain chip length, making longer effective cavity length and filtering space possible, thereby further reducing the linewidth.

[0021] 6. The materials of the ridge optical waveguide include but are not limited to Si3N4, single crystal silicon and lithium niobate. The absorption coefficient at a wavelength of 1550nm is less than 0.08dB / cm (measured data), and the effective refractive index n eff =2.025±0.005 (ellipsometer test). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 for Figure 1 Top view of .

[0023] Figure 3 Schematic diagram of the structure of the planar metal grating waveguide in the present invention.

[0024] Figure 4 for Figure 3 Top view of .

[0025] In the figure: 1. Gain chip; 11. High-reflection film; 12. First anti-reflection film; 2. Planar metal grating waveguide; 21. Grating waveguide substrate; 22. Ridge optical waveguide; 23. Planar metal grating; 24. Second anti-reflection film; 25. Third anti-reflection film; 26. Top cover layer; 3. TEC temperature control module. 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] It should be noted that the PID control algorithm is implemented as follows: 1. Proportional (P) section: Calculates the error between the set temperature and the actual temperature and generates a control signal proportional to the error based on the proportional coefficient (Kp). For example, if the set temperature is 25°C, the current actual temperature is 24°C, the error is 1°C, and Kp = 10, the proportional output is 10 × 1 = 10.

[0028] 2. Integration (I) section: The error is accumulated and an integral control signal is generated based on the integral coefficient (Ki) to eliminate static error. The integral time constant (Ti) determines the strength of the integral effect. For example, if the error lasts for 1°C for 10 seconds and Ki = 0.1, the integral output is 0.1 × 1 × 10 = 1.

[0029] 3. Differentiation (D) section: Calculates the rate of change of the error and generates a differential control signal based on the differential coefficient (Kd) to predict the error trend and reduce overshoot and oscillation. The differential time constant (Td) determines the strength of the differential action. For example, if the error suddenly changes from 1°C to 2°C and Kd = 5, the differential output is 5×(2-1) / Δt, where Δt is the sampling time interval.

[0030] 4. Total Control Signal: The outputs of the proportional, integral, and differential components are summed to generate the total control signal, which is used to regulate the TEC current. The total control signal = proportional output + integral output + differential output. This signal is typically output to the TEC's driver circuit via PWM (pulse width modulation) or other methods.

[0031] 5. Initial parameter setting: Set the initial Kp, Ki, and Kd values ​​based on experience or reference to parameters of similar systems. For example, in some semiconductor laser temperature control systems, the initial parameters can be set to Kp=10, Ki=0.1, and Kd=5.

[0032] 6. Observe system response: During actual operation, observe the system's response to changes in the temperature set point, including overshoot, settling time, and steady-state error. For example, if the system exhibits a large overshoot after the set temperature, Kp may be set too large.

[0033] 7. Parameter Adjustment: Adjust PID parameters based on the response. If the system responds slowly, increase Kp appropriately; if there is static error, increase Ki; if oscillation occurs, increase Kd. This process may require multiple iterations until the system achieves satisfactory control. For example, reducing Ki can reduce the integral action and thus reduce oscillation.

[0034] In the specific implementation, TEC is connected to PID to realize TEC temperature control module 3, with temperature stability of ±0.003°C and wavelength stability of <±0.05pm / °C.

[0035] Example 1 like Figures 1-4 As shown, in this embodiment, an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating includes: a gain chip 1, wherein the left end surface of the gain chip 1 is coated with a high reflective film 11, and the right end surface of the gain chip 1 is coated with a first anti-reflection film 12; A planar metal 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 planar metal grating waveguide 2. The left end face of the planar metal grating waveguide 2 is plated with a second anti-reflection film 24, and the right end face of the planar metal grating waveguide 2 is plated with a third anti-reflection film 25.

[0036] It should be noted that the material parameters of the gain chip 1 are: InP / InGaAsP quantum well structure, lasing wavelength 1530-1610nm, threshold current <28mA (25°C), and slope efficiency 0.85W / A.

[0037] In a specific implementation, the right end face of the gain chip 1 is aligned with the left end face of the planar metal grating waveguide 2 to form an external cavity structure. The total length of the external cavity is L cavity =L wg +800μm, free spectral range >50GHz.

[0038] The planar metal grating waveguide 2 includes a grating waveguide substrate 21 , a ridge optical waveguide 22 is provided on the grating waveguide substrate 21 , a planar metal grating 23 is provided on the ridge optical waveguide 22 , and a top covering layer 26 is provided on the planar metal grating 23 .

[0039] As a preferred embodiment of the above technical solution, the emission center wavelength of the gain chip 1 is 1550 nm.

[0040] As a preferred embodiment of the above technical solution, the planar metal grating 23 has a length of 1 cm, a period of 220 nm, and a surface roughness of less than 0.8 nm.

[0041] As a preferred embodiment of the above technical solution, the ridge optical waveguide 22 has a ridge width of 3 μm, a ridge height of 2 μm, and an etching depth of 1 nm.

[0042] In a specific implementation, the ridge optical waveguide 22 uses a metal layer with a Cr / Au double-layer structure, and the thickness of the metal layer is 150 nm, including 30 nm of Cr and 120 nm of Au.

[0043] As a preferred embodiment of the above technical solution, the material of the ridge optical waveguide 22 includes but is not limited to Si3N4, single crystal silicon and lithium niobate.

[0044] In a specific implementation, Si3N4 has an absorption coefficient of less than 0.08 dB / cm and a refractive index n=2.025±0.005; single crystal silicon has an absorption coefficient of 0.1-0.2 dB / cm and a refractive index n=3.47; and lithium niobate has an absorption coefficient of less than 0.05 dB / cm and a refractive index n=2.28.

[0045] As a preferred embodiment of the above technical solution, a TEC temperature control module 3 is provided below the gain chip 1 and the planar metal grating waveguide 2 .

[0046] In practice, a TEC is used to closely attach to the heat sink or chip of a semiconductor laser for real-time temperature monitoring. A TEC is installed to heat or cool a semiconductor laser and is typically used in conjunction with a heat sink to ensure that heat is effectively dissipated into the environment.

[0047] The TEC is connected to the PID feedback control module to achieve precise temperature control.

[0048] It should be noted that the TEC temperature control module 3 uses an integrated micro TEC (TEC1-12703), and the temperature fluctuation is less than ±0.003°C (closed-loop control).

[0049] As a preferred embodiment of the above technical solution, the top cover layer 26 is an epitaxially grown SiO2 layer, which can confine diffracted light and reduce the overflow of light energy.

[0050] Example 2 like Figures 1-4 As shown, in this embodiment, an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating includes: a gain chip 1, wherein the left end surface of the gain chip 1 is coated with a high reflective film 11, and the right end surface of the gain chip 1 is coated with a first anti-reflection film 12; A planar metal 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 planar metal grating waveguide 2. The left end face of the planar metal grating waveguide 2 is plated with a second anti-reflection film 24, and the right end face of the planar metal grating waveguide 2 is plated with a third anti-reflection film 25.

[0051] It should be noted that the material parameters of the gain chip 1 are: InP / InGaAsP quantum well structure, lasing wavelength 1530-1610nm, threshold current <28mA (25°C), and slope efficiency 0.85W / A.

[0052] In a specific implementation, the right end face of the gain chip 1 is aligned with the left end face of the planar metal grating waveguide 2 to form an external cavity structure. The total length of the external cavity is L cavity =L wg +800μm, free spectral range >50GHz.

[0053] The planar metal grating waveguide 2 includes a grating waveguide substrate 21 , a ridge optical waveguide 22 is provided on the grating waveguide substrate 21 , a planar metal grating 23 is provided on the ridge optical waveguide 22 , and a top covering layer 26 is provided on the planar metal grating 23 .

[0054] As a preferred embodiment of the above technical solution, the emission center wavelength of the gain chip 1 is 1530 nm.

[0055] As a preferred embodiment of the above technical solution, the planar metal grating 23 has a length of 3 cm, a period of 230 nm, and a surface roughness of less than 0.8 nm.

[0056] As a preferred embodiment of the above technical solution, the ridge optical waveguide 22 has a ridge width of 5 μm, a ridge height of 4 μm, and an etching depth of 1.5 nm.

[0057] In a specific implementation, the ridge optical waveguide 22 uses a metal layer with a Cr / Au double-layer structure, with a thickness of 250 nm, including 70 nm of Cr and 180 nm of Au.

[0058] As a preferred embodiment of the above technical solution, the material of the ridge optical waveguide 22 includes but is not limited to Si3N4, single crystal silicon and lithium niobate.

[0059] In a specific implementation, Si3N4 has an absorption coefficient of less than 0.08 dB / cm and a refractive index n=2.025±0.005; single crystal silicon has an absorption coefficient of 0.1-0.2 dB / cm and a refractive index n=3.47; and lithium niobate has an absorption coefficient of less than 0.05 dB / cm and a refractive index n=2.28.

[0060] As a preferred embodiment of the above technical solution, a TEC temperature control module 3 is provided below the gain chip 1 and the planar metal grating waveguide 2 .

[0061] In practice, a TEC is used to closely attach to the heat sink or chip of a semiconductor laser for real-time temperature monitoring. A TEC is installed to heat or cool a semiconductor laser and is typically used in conjunction with a heat sink to ensure that heat is effectively dissipated into the environment.

[0062] The TEC is connected to the PID feedback control module to achieve precise temperature control.

[0063] It should be noted that the TEC temperature control module 3 uses an integrated micro TEC (TEC1-12703), and the temperature fluctuation is less than ±0.003°C (closed-loop control).

[0064] As a preferred embodiment of the above technical solution, the top cover layer 26 is an epitaxially grown SiO2 layer, which can confine diffracted light and reduce the overflow of light energy.

[0065] Example 3 like Figures 1-4 As shown, in this embodiment, an ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating includes: a gain chip 1, wherein the left end surface of the gain chip 1 is coated with a high reflective film 11, and the right end surface of the gain chip 1 is coated with a first anti-reflection film 12; A planar metal 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 planar metal grating waveguide 2. The left end face of the planar metal grating waveguide 2 is plated with a second anti-reflection film 24, and the right end face of the planar metal grating waveguide 2 is plated with a third anti-reflection film 25.

[0066] It should be noted that the material parameters of the gain chip 1 are: InP / InGaAsP quantum well structure, lasing wavelength 1530-1610nm, threshold current <28mA (25°C), and slope efficiency 0.85W / A.

[0067] In a specific implementation, the right end face of the gain chip 1 is aligned with the left end face of the planar metal grating waveguide 2 to form an external cavity structure. The total length of the external cavity is L cavity =L wg +800μm, free spectral range >50GHz.

[0068] The planar metal grating waveguide 2 includes a grating waveguide substrate 21 , a ridge optical waveguide 22 is provided on the grating waveguide substrate 21 , a planar metal grating 23 is provided on the ridge optical waveguide 22 , and a top covering layer 26 is provided on the planar metal grating 23 .

[0069] As a preferred embodiment of the above technical solution, the emission center wavelength of the gain chip 1 is 1610 nm.

[0070] As a preferred embodiment of the above technical solution, the planar metal grating 23 has a length of 2 cm, a period of 225 nm, and a surface roughness of less than 0.8 nm.

[0071] As a preferred embodiment of the above technical solution, the ridge optical waveguide 22 has a ridge width of 4 μm, a ridge height of 3 μm, and an etching depth of 1.2 nm.

[0072] In a specific implementation, the ridge optical waveguide 22 uses a metal layer of a Cr / Au double-layer structure with a thickness of 200 nm, including 40 nm of Cr and 160 nm of Au.

[0073] As a preferred embodiment of the above technical solution, the material of the ridge optical waveguide 22 includes but is not limited to Si3N4, single crystal silicon and lithium niobate.

[0074] In a specific implementation, Si3N4 has an absorption coefficient of less than 0.08 dB / cm and a refractive index n=2.025±0.005; single crystal silicon has an absorption coefficient of 0.1-0.2 dB / cm and a refractive index n=3.47; and lithium niobate has an absorption coefficient of less than 0.05 dB / cm and a refractive index n=2.28.

[0075] As a preferred embodiment of the above technical solution, a TEC temperature control module 3 is provided below the gain chip 1 and the planar metal grating waveguide 2 .

[0076] In practice, a TEC is used to closely attach to the heat sink or chip of a semiconductor laser for real-time temperature monitoring. A TEC is installed to heat or cool a semiconductor laser and is typically used in conjunction with a heat sink to ensure that heat is effectively dissipated into the environment.

[0077] The TEC is connected to the PID feedback control module to achieve precise temperature control.

[0078] It should be noted that the TEC temperature control module 3 uses an integrated micro TEC (TEC1-12703), and the temperature fluctuation is less than ±0.003°C (closed-loop control).

[0079] As a preferred embodiment of the above technical solution, the top cover layer 26 is an epitaxially grown SiO2 layer, which can confine diffracted light and reduce the overflow of light energy.

[0080] Comparative Example 1 Conventional DFB laser.

[0081] Comparative Example 2 Commercial external cavity lasers.

[0082] The lasers provided in the above three embodiments and two comparative examples were tested for various technical indicators. The test results are shown in the following table: As can be seen from the table above, the ultra-narrow linewidth tunable wavelength external cavity laser based on planar metal grating provided by the present invention achieves 3dB linewidth <700Hz and M 2 The device boasts a beam quality of less than 0.9. It utilizes low-absorption waveguide materials (absorption coefficient less than 0.08dB / cm), integrates a high-precision temperature control system (±0.003°C), and offers wavelength stability of ±0.04pm / °C. It is suitable for applications in quantum communications, coherent optical communications, and photonic integrated chips.

[0083] It should be noted that the gain chip 1 is also suitable for other emission center wavelengths such as 1310 nm, 1650 nm, and even 905 nm, as long as the light-emitting structure and material of the gain chip match the grating constant of the grating waveguide.

[0084] 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. An ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating, comprising a gain chip (1), characterized in that: The left end surface of the gain chip (1) is plated with a high-reflection film (11), and the right end surface of the gain chip (1) is plated with a first anti-reflection film (12); A planar metal 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 planar metal grating waveguide (2), the left end face of the planar metal grating waveguide (2) is plated with a second anti-reflection film (24), and the right end face of the planar metal grating waveguide (2) is plated with a third anti-reflection film (25); The planar metal grating waveguide (2) comprises a grating waveguide substrate (21), a ridge optical waveguide (22) is provided on the upper portion of the grating waveguide substrate (21), a planar metal grating (23) is provided on the upper portion of the ridge optical waveguide (22), and a top covering layer (26) is provided on the upper portion of the planar metal grating (23).

2. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 1, characterized in that: The top covering layer (26) is an epitaxially grown SiO2 layer.

3. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 1, characterized in that: A TEC temperature control module (3) is provided below the gain chip (1) and the planar metal grating waveguide (2).

4. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 1, characterized in that: The material of the ridge optical waveguide (22) includes but is not limited to Si3N4, single crystal silicon and lithium niobate.

5. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 1, characterized in that: The emission center wavelength of the gain chip (1) is 1530-1610 nm.

6. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 2, characterized in that: The emission center wavelength of the gain chip (1) is 1550 nm.

7. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 1, characterized in that: The plane metal grating (23) has a length of 1-3 cm, a period of 220-230 nm, and a surface roughness of less than 0.8 nm.

8. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 4, characterized in that: The plane metal grating (23) has a length of 2 cm, a period of 225 nm, and a surface roughness of less than 0.8 nm.

9. The ultra-narrow linewidth tunable wavelength external cavity laser based on a planar metal grating according to claim 1, characterized in that: The ridge optical waveguide (22) has a ridge width of 3-5 μm, a ridge height of 2-4 μm, and an etching depth of 1-1.5 nm.

10. The ultra-narrow linewidth tunable wavelength external cavity laser based on planar metal grating according to claim 6, characterized in that: The ridge optical waveguide (22) has a ridge width of 4 μm, a ridge height of 3 μm, and an etching depth of 1.2 nm.

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