A self-injection locked narrow linewidth laser based on waveguide resonant ring

Abstract

A self-injection locked narrow linewidth laser based on a waveguide resonant ring belongs to the field of semiconductor laser technology. It includes a distributed feedback semiconductor laser, a current driver, a first temperature controller, a polarization-maintaining fiber circulator, a waveguide resonant ring, a second temperature controller, a polarization-maintaining fiber coupler, and a polarization-maintaining fiber adjustable attenuator. In the self-injection locked narrow linewidth laser of the present invention, the input and output ends of the optical element are both polarization-maintaining fibers, and the all-fiber device solves the difficulty of accurately adjusting the position of the laser and the external cavity; the feedback light intensity is controlled by adjusting the polarization-maintaining fiber adjustable attenuator, which reduces the influence of environmental disturbances such as air flow and mechanical vibration on the feedback light path, and has better stability; a dual straight waveguide resonant ring structure is introduced in the external resonant cavity of the semiconductor laser, and the transmitted light is used for feedback, which suppresses high-frequency noise and can obtain a continuous narrow linewidth output.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor lasers, and in particular relates to a self-injection locked narrow linewidth laser based on a waveguide resonant ring, which can be applied to coherent communication, optical fiber sensing, quantum measurement and other fields. Background Art

[0002] Self-injection locked narrow linewidth lasers have broad application prospects and great application value in systems such as laser sensing, detection and measurement, high-sensitivity coherent optical communications and microwave photonics due to their ultra-stability, narrow linewidth, small size and low power consumption.

[0003] At present, the self-injection locked narrow linewidth laser mainly uses a single quantum well distributed feedback semiconductor laser as a laser source, and the resonant laser of the Fabry-Perot resonant cavity (confocal cavity) is re-injected into the distributed feedback semiconductor laser. As long as the frequency of the distributed feedback laser is close enough to the resonant frequency of the confocal cavity, the laser frequency will be locked to the resonant frequency of the confocal cavity. Since the locking range of the laser depends largely on the feedback power, it is necessary to insert an attenuator between the distributed feedback semiconductor laser and the confocal cavity to adjust the feedback power. The simple structure and small size of the confocal cavity make the entire laser module more compact, and the output linewidth of the resonant light feedback laser can be compressed to 15.7Hz, and the output power exceeds 50mW (Lewoczko-Adamczyk W, Pyrlik C, Hger J, et al. Ultra-narrow linewidth DFB-laser with optical feedback from a monolithic confocal Fabry-Perot cavity. Optics Express, 2015, 23 (8): 9705-9). However, the above scheme requires precise adjustment of the relative position between the laser and the external cavity, which is difficult to adjust in actual operation. In addition, the laser performance is very sensitive to the accuracy of the relative position. During operation, the relative position may be easily offset due to vibration and other reasons, resulting in a decrease in laser performance. At the same time, the unidirectional injection feedback of the above scheme cannot effectively suppress high-frequency noise. Summary of the invention

[0004] The purpose of the present invention is to propose a self-injection locked narrow linewidth laser based on a waveguide resonant ring in view of the problems existing in the background technology. The laser of the present invention uses the transmitted light of the waveguide resonant ring to perform feedback injection on the distributed feedback semiconductor laser. By adjusting the feedback intensity, the driving current of the distributed feedback semiconductor laser and the temperature, the narrow linewidth laser excited at different transmission peaks of the waveguide resonant ring can be output, thereby achieving continuous narrow linewidth laser output and improving the suppression of high-frequency frequency noise.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A self-injection locked narrow linewidth laser based on a waveguide resonant ring, comprising a distributed feedback semiconductor laser 1, a current driver 2, a first temperature controller 3, a polarization-maintaining fiber circulator 4, a waveguide resonant ring 5, a second temperature controller 6, a polarization-maintaining fiber coupler 7, and a polarization-maintaining fiber adjustable attenuator 8;

[0007] The output end of the current driver 2 is connected to the driving current input end of the distributed feedback semiconductor laser 1, the output end of the first temperature controller 3 is connected to the temperature control input end of the distributed feedback semiconductor laser 1, the light output end of the distributed feedback semiconductor laser 1 is connected to the port ② of the polarization-maintaining fiber circulator 4, the port ③ of the polarization-maintaining fiber circulator 4 is connected to the left port of the upper straight waveguide of the waveguide resonant ring 5, the left port of the lower straight waveguide of the waveguide resonant ring 5 is connected to the input end of the polarization-maintaining fiber coupler 7, one output end of the polarization-maintaining fiber coupler is connected to the input end of the polarization-maintaining fiber variable attenuator 8, and the other output end serves as the output end of the narrow linewidth laser, the output end of the polarization-maintaining fiber variable attenuator 8 is connected to the port ① of the polarization-maintaining fiber circulator 4, and the output end of the second temperature controller 6 is connected to the temperature control end of the waveguide resonant ring;

[0008] The driving current signal output by the current driver 2 and the temperature control signal output by the first temperature controller 3 are input to the distributed feedback semiconductor laser 1 to control the frequency and power of the laser output by the distributed feedback semiconductor laser; the laser output by the distributed feedback semiconductor laser is input to the waveguide resonant ring through the polarization-maintaining fiber circulator, and the transmission peak center frequency of the waveguide resonant ring is controlled by the temperature control signal output by the second temperature controller. The laser light having the same transmission peak center frequency as that of the waveguide resonant ring is output through the left port of the lower straight waveguide of the waveguide resonant ring, and after passing through the polarization-maintaining fiber coupler, one path is used as the output of the narrow linewidth laser to measure the linewidth. Since the high-frequency part of the laser light is filtered out through the waveguide resonant ring, the high-frequency noise is weakened during the linewidth measurement. After the intensity of the laser light is adjusted by the polarization-maintaining fiber variable attenuator, the other path is fed back and injected into the distributed feedback semiconductor laser 1 through the polarization-maintaining fiber circulator to realize injection locking of the distributed feedback semiconductor laser by the resonant laser light in the waveguide resonant ring. The injection of feedback light improves the equivalent quality factor of the laser resonant cavity, thereby realizing linewidth compression.

[0009] The core idea of ​​the present invention is to utilize the self-injection locking technology of the distributed feedback semiconductor laser, combined with the narrow transmission spectrum of the high-quality factor waveguide resonant ring to suppress the phase noise of the semiconductor laser, and realize the narrow linewidth output. The waveguide resonant ring is composed of an upper straight waveguide, a micro-ring waveguide and a lower straight waveguide. Due to the multi-beam interference effect, the transmission spectrum of the waveguide resonant ring is a series of comb-shaped narrow transmission peaks with equal frequency intervals. The frequency interval is related to the ring length of the micro-ring waveguide, which is usually in the order of GHz. These transmission peaks have a very high extinction ratio, and the light transmittance outside the transmission peak is very small. For semiconductor lasers, the instability caused by wide-spectrum strong light feedback can be avoided; at the same time, the waveguide resonant ring can work normally in the C band (1530-1565nm), and the long working range enables the distributed feedback semiconductor laser to obtain narrow linewidth lasers in a longer wavelength range. The distributed feedback semiconductor laser itself has a mode-selective characteristic that can avoid multi-mode oscillation; by setting the appropriate temperature and current, the output frequency of the distributed feedback semiconductor laser can be locked on the transmission peak of the waveguide resonant ring to achieve frequency locking; since the quality factor of the waveguide resonant ring is very high, the line width of the distributed feedback semiconductor laser can be compressed by more than 3 orders of magnitude through feedback injection.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] 1. The present invention provides a self-injection locked narrow linewidth laser based on a waveguide resonant ring. The input and output ends of the optical element are both polarization-maintaining optical fibers. The all-fiber device solves the problem of accurately adjusting the position of the laser and the external cavity.

[0012] 2. The present invention provides a self-injection locked narrow linewidth laser based on a waveguide resonant ring, which controls the feedback light intensity by adjusting the adjustable attenuator of the polarization-maintaining fiber, thereby reducing the influence of environmental disturbances such as air flow and mechanical vibration on the feedback light path and having better stability.

[0013] 3. The present invention provides a self-injection locked narrow linewidth laser based on a waveguide resonant ring, which introduces a double straight waveguide resonant ring structure in the external resonant cavity of a semiconductor laser, uses transmitted light for feedback, suppresses high-frequency noise, and can obtain a continuous narrow linewidth output. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the self-injection locked narrow linewidth laser of the present invention.

[0015] Figure 2 It is the beat spectrum of the laser output by the self-injection locked narrow linewidth laser of the present invention.

[0016] Figure 3 is the relationship between the transmittance of the waveguide resonant ring and the light frequency. DETAILED DESCRIPTION

[0017] The present invention is described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the protection scope of the present invention is not limited to the scope described in the embodiments.

[0018] Example

[0019] Figure 1 The structure diagram of the self-injection locked narrow linewidth laser according to an embodiment of the present invention comprises a distributed feedback semiconductor laser 1, a current driver 2, a first temperature controller 3, a polarization-maintaining fiber circulator 4, a waveguide resonant ring 5, a second temperature controller 6, a polarization-maintaining fiber coupler 7, and a polarization-maintaining fiber variable attenuator 8; the output end of the current driver 2 is connected to the driving current input end of the distributed feedback semiconductor laser 1, the output end of the first temperature controller 3 is connected to the temperature control input end of the distributed feedback semiconductor laser 1, and the distributed feedback semiconductor laser 1 The optical output end of the polarization-maintaining fiber circulator is connected to the port ② of the polarization-maintaining fiber circulator 4, the port ③ of the polarization-maintaining fiber circulator 4 is connected to the left port of the upper straight waveguide of the waveguide resonant ring 5, the left port of the lower straight waveguide of the waveguide resonant ring 5 is connected to the input end of the polarization-maintaining fiber coupler 7, one output end of the polarization-maintaining fiber coupler is connected to the input end of the polarization-maintaining fiber variable attenuator 8, and the other output end serves as the output end of the narrow linewidth laser, the output end of the polarization-maintaining fiber variable attenuator 8 is connected to the port ① of the polarization-maintaining fiber circulator 4, the output end of the second temperature controller 6 is connected to the waveguide resonant The drive current signal output by the current driver 2 and the temperature control signal output by the first temperature controller 3 are input to the distributed feedback semiconductor laser 1 to control the frequency and power of the laser output by the distributed feedback semiconductor laser; the laser output by the distributed feedback semiconductor laser is input to the waveguide resonant ring through the polarization-maintaining fiber circulator, and the transmission peak center frequency of the waveguide resonant ring is controlled by the temperature control signal output by the second temperature controller. The laser with the same transmission peak center frequency as the waveguide resonant ring is output through the lower straight waveguide left port of the waveguide resonant ring, and after passing through the polarization-maintaining fiber coupler, one path is used as the output of the narrow linewidth laser to measure the linewidth. Since the high-frequency part of the laser is filtered out by the waveguide resonant ring, the high-frequency noise is weakened during the linewidth measurement; the other path is fed back and injected into the distributed feedback semiconductor laser 1 through the polarization-maintaining fiber circulator after the intensity of the laser is adjusted by the polarization-maintaining fiber adjustable attenuator, so as to realize the injection locking of the distributed feedback semiconductor laser by the resonant laser in the waveguide resonant ring. The injection of feedback light improves the equivalent quality factor of the laser resonant cavity, thereby realizing linewidth compression.

[0020] The specific steps of using the self-injection locked narrow linewidth laser in the embodiment are:

[0021] 1. Connect the output end of the current driver 2 and the first temperature controller 3 to the input end of the distributed feedback semiconductor laser 1, control the temperature at 25-35°C, adjust the current of the semiconductor laser within the range of 70-100 mA, and use the distributed feedback laser as the DFB laser diode L1550P5DFB produced by Thorlabs. Figure 1 The polarization-maintaining fiber circulator 4 , the waveguide resonant ring 5 , the polarization-maintaining fiber coupler 7 , and the polarization-maintaining fiber variable attenuator 8 are connected, and the power injected into the distributed feedback semiconductor laser 1 can be adjusted by adjusting the polarization-maintaining fiber variable attenuator 8 .

[0022] 2. Connect the other output end of the polarization-maintaining fiber coupler 7 to the input port of the linewidth measurement system, measure the output laser linewidth, slowly adjust the polarization-maintaining fiber variable attenuator 8, and carefully observe the spectrum shape on the spectrum analyzer until the spectral linewidth of the distributed feedback semiconductor laser is significantly compressed, such as Figure 2 As shown, it indicates that the laser is in feedback injection locking state at this time, the line width is compressed to the kHz level, and the spectrum analyzer used is the spectrum analyzer model MS2725C produced by Anritsu.

[0023] 3. Based on the above operation 2, slowly adjust the current of the semiconductor laser, and observe that the spectrum shape on the spectrum analyzer gradually broadens from an obvious compression state, and then the spectrum shape becomes a compression state again as the current increases, which indicates that the laser frequency has been locked to the adjacent transmission peak.

[0024] 4. Place the distributed feedback semiconductor laser 1, polarization-maintaining fiber circulator 4, waveguide resonant ring 5, polarization-maintaining fiber coupler 7, and polarization-maintaining fiber variable attenuator 8 into a constant temperature and vibration-isolated sealed chassis.

[0025] Figure 3 The relationship between the transmittance of the waveguide resonant ring and the optical frequency near 193THz (about 1550nm). The selected waveguide ring length is l = 15mm, the ring refractive index is n = 1.5, the coupling efficiency is α = 50%, and the transmittance formula is:

[0026]

[0027] The simulation results are as follows Figure 3 As shown, the transmittance of the waveguide resonant ring is a series of comb-shaped narrow transmission peaks with equal frequency intervals. The laser transmittance at the transmission peak is 1, and the laser frequency outside the transmission peak is almost not transparent.

[0028] In summary, the present invention proposes a self-injection locked narrow linewidth laser based on a waveguide resonant ring, which uses the waveguide resonant ring as the external resonant cavity of the laser and realizes narrow linewidth laser output by injecting the transmitted light of the waveguide resonant ring into the distributed feedback semiconductor laser.

Claims

1. A self-injection locked narrow linewidth laser based on a waveguide resonant ring, characterized in that: It comprises a distributed feedback semiconductor laser (1), a current driver (2), a first temperature controller (3), a polarization-maintaining fiber circulator (4), a waveguide resonant ring (5), a second temperature controller (6), a polarization-maintaining fiber coupler (7), and a polarization-maintaining fiber adjustable attenuator (8); The output end of the current driver (2) is connected to the driving current input end of the distributed feedback semiconductor laser (1), the output end of the first temperature controller (3) is connected to the temperature control input end of the distributed feedback semiconductor laser (1), the light output end of the distributed feedback semiconductor laser (1) is connected to the port ② of the polarization-maintaining fiber circulator (4), the port ③ of the polarization-maintaining fiber circulator (4) is connected to the left port of the upper straight waveguide of the waveguide resonant ring (5), the left port of the lower straight waveguide of the waveguide resonant ring (5) is connected to the input end of the polarization-maintaining fiber coupler (7), one output end of the polarization-maintaining fiber coupler is connected to the input end of the polarization-maintaining fiber variable attenuator (8), and the other output end serves as the output end of the narrow linewidth laser, the output end of the polarization-maintaining fiber variable attenuator (8) is connected to the port ① of the polarization-maintaining fiber circulator (4), and the output end of the second temperature controller (6) is connected to the temperature control end of the waveguide resonant ring; The driving current signal output by the current driver and the temperature control signal output by the first temperature controller are input to the distributed feedback semiconductor laser to control the frequency and power of the laser output by the distributed feedback semiconductor laser; the laser output by the distributed feedback semiconductor laser is input to the waveguide resonant ring through the polarization-maintaining fiber circulator, and the transmission peak center frequency of the waveguide resonant ring is controlled by the temperature control signal of the second temperature controller, and the laser light equal to the transmission peak center frequency of the waveguide resonant ring is output through the lower straight waveguide left port of the waveguide resonant ring, and after passing through the polarization-maintaining fiber coupler, one path is used as the output of the narrow linewidth laser, and the other path is fed back and injected into the distributed feedback semiconductor laser through the polarization-maintaining fiber circulator after the intensity of the laser light is adjusted through the polarization-maintaining fiber adjustable attenuator, so as to realize the injection locking of the distributed feedback semiconductor laser by the resonant laser light in the waveguide resonant ring.

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