Semiconductor laser linewidth narrowing device

Abstract

The application discloses a semiconductor laser linewidth narrowing device, and belongs to the technical field of optoelectronic devices.The device comprises a semiconductor gain chip arranged obliquely, a mode field matching lens, a silicon light micro-ring resonator, a thermoelectric refrigerator, a monitoring component, a collimating lens, an optical isolator and a signal output light window; the semiconductor gain chip is integrated with a grating, a gain, a phase adjustment and a reflection structure, and a first free spectral range comb-shaped reflection spectrum is formed inside; the silicon light micro-ring resonator is used as an external cavity feedback and a mode selection element, a second free spectral range comb-shaped feedback spectrum is formed, single longitudinal mode screening and linewidth narrowing are realized by using a vernier effect; the mode field matching lens reduces oblique end surface beam coupling loss; the thermoelectric refrigerator realizes precise wavelength locking and temperature stability; and the optical isolator inhibits external echo interference.The device has high integration, narrow linewidth, strong stability, wavelength electrically controllable tuning, and can meet the demand of coherent optical communication, laser radar and precise optical measurement on high-purity narrow linewidth light sources.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device technology, specifically relating to a semiconductor laser linewidth narrowing device, which is suitable for scenarios requiring high stability, narrow linewidth, and tunable laser light sources, such as coherent optical communication, lidar, precision spectral measurement, and fiber optic sensing. Background Technology

[0002] Semiconductor lasers have advantages such as small size, high electro-optical conversion efficiency, and ease of integration and modulation, and are widely used in optical communication, sensing, and industrial measurement. Traditional single-chip semiconductor lasers, due to their short cavity length, strong spontaneous emission noise in the gain medium, and linewidth typically on the order of MHz, cannot meet the requirements of high-end applications such as coherent communication, high-resolution spectroscopy, and lidar for narrow linewidth, high side-mode rejection ratio, and frequency-stable light sources.

[0003] Existing linewidth narrowing techniques mostly employ external cavity feedback schemes, such as bulk Bragg gratings, fiber gratings, and external mirrors, to extend the equivalent cavity length and filter longitudinal modes. However, traditional external cavity structures have significant drawbacks: large size, complex assembly, and difficulty in miniaturization and integration; sensitivity to external vibrations and temperature drift, leading to mode jumps and frequency drifts; wavelength tuning relies on mechanical adjustment, resulting in slow response and low accuracy; mode mismatch leads to high coupling loss, and external echoes can easily disrupt laser stability. Therefore, there is an urgent need in this field for a semiconductor laser linewidth narrowing device with high integration, narrow linewidth, high stability, electrically tunable design, and resistance to echo interference. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a semiconductor laser linewidth narrowing device. By integrating a semiconductor gain chip with a silicon photonic microring resonator, it utilizes the vernier effect to achieve extremely narrow linewidth and stable single-mode lasing, thus solving the problems of low integration, poor stability, wide linewidth, and inconvenient tuning of traditional external cavity lasers.

[0005] The core components of the device include: a tilted semiconductor gain chip, a mode field matching lens, a silicon photonics microring resonator, a thermoelectric cooler, a monitoring component, a collimating lens, an optical isolator, and a signal output window. The semiconductor gain chip incorporates a grating, gain, phase adjustment, and reflection structure to form an internal cavity comb-shaped reflection spectrum. The silicon photonics microring resonator, acting as a high-Q external cavity mode selection element, forms an external cavity comb-shaped feedback spectrum. The two cavity spectra achieve single-mode locking through the vernier effect, significantly narrowing the linewidth. The mode field matching lens reduces the coupling loss between the outgoing light from the tilted end face and the silicon photonics waveguide. The thermoelectric cooler enables precise temperature control and wavelength locking of the microring. The output isolator suppresses external echoes, ensuring frequency stability.

[0006] The beneficial effects of this invention are as follows: The outer cavity is constructed using a high-Q silicon photonics microring resonator, significantly extending the equivalent cavity length; combined with the vernier effect, it achieves ultra-narrow linewidth and high side-mode suppression ratio; the mode-field matching lens solves the mode-field mismatch problem between the tilted chip and the silicon photonics waveguide, resulting in low coupling loss and high feedback efficiency; the vernier effect of the inner and outer cavities, combined with thermoelectric cooler temperature control, enables wide-range, high-speed, and high-precision wavelength tuning and locking; an integrated optical isolator at the output effectively suppresses external echo interference and improves operational stability in complex environments; the overall structure is compact, can be hybridized and integrated, and is suitable for miniaturization, modularization, and mass production. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0008] Figure 1. Schematic diagram of the device structure in Example 1; Figure 2. Schematic diagram of the device structure using the SG-DBR gain chip in Example 2; Figure 3. Schematic diagram of the device structure using the signal detection optical window for monitoring in Example 3; Figure 4. Schematic diagram of the device structure using the SG-DBR chip and the signal detection optical window in Example 4.

[0009] The diagram is labeled as follows: 1-Semiconductor gain chip; 1'-SG-DBR chip; 1a-Front grating area; 1b-Gain area; 1c-Phase adjustment area; 1d-Reflective film; 1e-Rear grating area; 2-Mode field matching lens; 3-Silicon photonic microring resonator; 4-Thermoelectric cooler; 5-First vertical coupling grating; 5'-Signal detection window; 6-Collimating lens; 7-Isolator; 8-Signal output window; 9-Second vertical coupling grating. Detailed Implementation

[0010] Example 1 As shown in Figure 1, a semiconductor laser linewidth narrowing device includes: a semiconductor gain chip 1, a mode field matching lens 2, a silicon photonic microring resonator 3, a thermoelectric cooler 4, a first vertical coupling grating 5, a collimating lens 6, an isolator 7, a signal output window 8, and a second vertical coupling grating 9.

[0011] The semiconductor gain chip 1 is tilted, and its internal components, arranged sequentially along the optical path, include a front grating region 1a, a gain region 1b, a phase adjustment region 1c, and a reflective film 1d. The front grating region 1a provides a broadband reflection envelope and coarsely selects the wavelength; the gain region 1b injects current to provide optical gain; the phase adjustment region 1c tunes the refractive index through current to fine-tune the longitudinal mode phase of the cavity; the reflective film 1d has a reflectivity of 30%-70%, forming a comb-shaped reflection spectrum within the cavity in the first free spectral range with the front grating region 1a. The tilted structure suppresses parasitic FP cavities at the end face.

[0012] The mode field matching lens 2 achieves mode field matching between the chip and the silicon photonics microring 3, reducing coupling loss and improving feedback efficiency. The first vertical coupling grating 5 guides the forward light as a power reference; the second vertical coupling grating 9 monitors the resonance state, and the weakest transmitted light indicates critical coupling, resulting in the optimal linewidth narrowing effect.

[0013] The silicon photonic microring resonator 3 is temperature-controlled by the thermoelectric cooler 4, forming an external cavity comb-shaped feedback spectrum in the second free spectral range. The two cavity spectra exhibit a vernier effect, with only a single wavelength peak overlapping, achieving single-mode lasing and linewidth narrowing. The thermoelectric cooler 4 achieves wavelength locking and switching by temperature-tuning the microring resonant wavelength.

[0014] Main optical path: The laser emitted from the front grating area 1a is collimated by the collimating lens 6, the echo is blocked by the isolator 7, and then coupled into the optical fiber for output through the signal output window 8.

[0015] Example 2 As shown in Figure 2, the difference from Example 1 is that the semiconductor gain chip 1' has an SG-DBR structure, with the following internal components: a front grating region 1a, a gain region 1b, a phase adjustment region 1c, and a rear grating region 1e. The rear grating region 1e replaces the reflective film and forms an internal cavity comb-shaped reflection spectrum with the front grating region 1a. The remaining structure, connection relationships, and working principle are the same as in Example 1.

[0016] Example 3 As shown in Figure 3, the difference from Embodiment 1 is that the monitoring component uses a signal detection optical window 5', which is directly located in the output optical path of the silicon photonic microring resonator 3. The output sampling optical signal is used to monitor lasing, wavelength locking, and power stability. The first and second vertically coupled gratings are eliminated, resulting in a simpler structure. The remaining components and principles are the same as in Embodiment 1.

[0017] Example 4 Figure 4 shows the preferred combination scheme of the present invention: an SG-DBR semiconductor gain chip 1' is used, and a signal detection optical window 5' is used as the monitoring component. The optical path structure, component function, vernier effect linewidth narrowing and wavelength locking principle are the same as those in the previous embodiments, and it has the advantages of high integration, wide tuning range and simplified assembly.

Claims

1. A semiconductor laser linewidth narrowing device, characterized in that, include: The system comprises a semiconductor gain chip, a mode-field matching lens, a silicon photonics microring resonator, a thermoelectric cooler, a monitoring component, a collimating lens, an isolator, and a signal output window. The semiconductor gain chip integrates a laser generation and mode selection structure, and is tilted to suppress the Fabry-Perot cavity effect at the end face. The mode-field matching lens is positioned between the semiconductor gain chip and the silicon photonics microring resonator to achieve optical mode-field matching between the two. The silicon photonics microring resonator is located in the optical path on the reflective side of the semiconductor gain chip, serving as an external cavity feedback and mode-selection element. The thermoelectric cooler supports and controls the operating temperature of the silicon photonics microring resonator. The monitoring component is located in the relevant optical path of the silicon photonics microring resonator and outputs an optical signal to monitor the laser's operating status. The collimating lens and isolator are sequentially arranged on the main output optical path on one side of the front grating area of ​​the semiconductor gain chip; the signal output optical window is located at the output end of the isolator and is used to couple narrow linewidth laser to an external optical fiber.

2. The apparatus according to claim 1, characterized in that, The semiconductor gain chip integrates a front grating region, a gain region, a phase adjustment region, and a reflective film sequentially along the optical path. The front grating region is used to provide the reflection spectrum envelope and achieve coarse wavelength selection. The gain region provides optical gain under current injection. The phase adjustment region achieves fine-tuning of the longitudinal mode phase of the cavity by adjusting the injection current. The reflective film has a reflectivity of 30% to 70%, forming an internal comb-shaped reflection spectrum with the front grating region having a first free spectral range.

3. The apparatus according to claim 1, characterized in that, The semiconductor gain chip is a sampling grating distributed Bragg reflector (SG-DBR) structure, which integrates a front grating region, a gain region, a phase adjustment region, and a rear grating region sequentially along the optical path. The rear grating region and the front grating region work together to form an internal comb-shaped reflection spectrum with a first free spectral range.

4. The apparatus according to claim 1, characterized in that, The silicon photonic microring resonator and the semiconductor gain chip form a coupled cavity structure, providing an external comb feedback spectrum with a second free spectral range; through the vernier effect, the internal comb reflection spectrum and the external comb feedback spectrum overlap at a single wavelength peak, screening a single longitudinal mode, and realizing single-mode lasing and linewidth narrowing.

5. The apparatus according to claim 4, characterized in that, The silicon photonic microring resonator is either a single microring resonator or composed of two coupled microrings with a Fermat spiral topology.

6. The apparatus according to claim 1, characterized in that, The monitoring component includes a first vertically coupled grating and a second vertically coupled grating; the first vertically coupled grating outputs a portion of the forward light as an optical power reference; the second vertically coupled grating outputs the resonant optical signal to determine the resonant lock-in state.

7. The apparatus according to claim 1, characterized in that, The monitoring component is a signal detection optical window, which is directly set in the output optical path of the silicon photonic microring resonator. It outputs a sampled optical signal to monitor the lasing state, wavelength lock, and optical power stability.

8. The apparatus according to claim 1, characterized in that, The thermoelectric cooler is used to maintain the temperature stability of the silicon photonic microring resonator and to adjust its resonant wavelength using the thermo-optical effect. It works in conjunction with the comb-shaped reflection spectrum inside the cavity to achieve wavelength selection, switching and locking.

9. The apparatus according to claim 1, characterized in that, The mode field matching lens shapes and converts the obliquely emitted beam from the semiconductor gain chip, reducing coupling loss between the chip and the external cavity and improving optical feedback efficiency.

10. The apparatus according to claim 1, characterized in that, The isolator is a unidirectional optical transmission device that allows the laser to be output in the forward direction and blocks external reverse echoes, thus avoiding disruption of the vernier effect phase balance and frequency stability.

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