A tunable self-injection-locked narrow-linewidth semiconductor laser based on an fp cavity

Abstract

The application discloses a tunable self-injection locking narrow line width semiconductor laser based on an FP cavity and belongs to the technical field of semiconductor lasers. The laser comprises a distributed feedback semiconductor laser, a first temperature controller, a current driver, a first aspheric mirror, a first polarization beam splitter, a half-wave plate, a second polarization beam splitter, an electro-optic crystal, a second aspheric mirror, an FP cavity, a second temperature controller, an optical amplifier, a fiber coupling mirror, a fiber laser, a fiber coupler, a photoelectric balance detector, a spectrum analyzer, a signal generator, a first voltage amplifier, a second voltage amplifier and a third voltage amplifier. The laser utilizes partial output light of the FP external cavity to perform feedback injection, simultaneously adjusts the driving current of the distributed feedback semiconductor laser, the control voltage of the FP external cavity and the electro-optic crystal, controls the resonance frequency of the resonant cavity of the distributed feedback semiconductor laser, the resonance frequency of the FP external cavity and the phase of the feedback light, and realizes self-injection locking compression of the line width of the laser and tuning of the laser.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology, specifically relating to a tunable self-injection locked narrow linewidth semiconductor laser based on an FP (Fabry-Porosi) cavity. This laser can be applied to fields such as coherent optical communication, fiber optic sensing, precision spectral measurement, and lidar. Background Technology

[0002] Tunable self-injection locked narrow linewidth semiconductor lasers have advantages such as low cost, narrow linewidth, simple structure, tunable frequency and large tuning range. They have broad application prospects and great application value in laser sensing, detection and measurement, coherent optical communication and microwave photonics systems.

[0003] Currently, linewidth reduction techniques for semiconductor lasers are mainly divided into external optical injection and self-injection (also known as optical feedback, including internal cavity and external cavity methods). External optical injection involves injecting a specific wavelength of narrow-linewidth laser into the laser, causing a particular longitudinal mode to oscillate preferentially and suppressing the oscillation of side longitudinal modes, thus obtaining a narrow-linewidth single-mode output. Self-injection involves injecting laser light generated by the semiconductor laser itself. Internal cavity methods use gratings within the laser cavity to achieve optical feedback, such as distributed feedback lasers (DFB) and distributed Bragg reflector lasers (DBR). Using this method, the laser linewidth can be narrowed to the hundreds of kHz level. Further narrowing the linewidth presents significant challenges in fabrication processes. External cavity methods involve adding optical devices outside the laser cavity, such as FP cavities, gratings, and fiber resonator rings, achieving linewidth narrowing through a self-injection locking effect.

[0004] Among them, self-injection locked lasers based on FP cavities are simple in structure and low in cost, and the laser linewidth can be narrowed to within 100Hz. However, FP cavities are susceptible to external environmental influences, which in turn affect the stability of the output frequency. Furthermore, self-injection locking requires the resonant frequencies of the semiconductor laser resonator and the FP external cavity to be close, and the injected light must oscillate in phase with the laser light oscillating in the semiconductor laser resonator. To achieve stable operation and self-injection locking of the laser system, it is necessary to simultaneously and precisely control the resonant frequencies of the semiconductor laser resonator, the FP external cavity, and the phase of the feedback light. Failure to control these three simultaneously will disrupt the operating state of the laser system. Therefore, the traditional method of modulating only the FP external cavity resonant frequency is insufficient for achieving a wide range of tuning.

[0005] Based on the above problems, this invention proposes a tuning method that simultaneously controls the resonant frequency of the semiconductor laser resonant cavity, the resonant frequency of the FP external cavity, and the phase of the feedback light, which can realize broadband tuning of self-injection locked semiconductor lasers. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by proposing a tunable self-injection locked narrow-linewidth semiconductor laser based on a FP cavity, thereby achieving narrowing of the linewidth of the output laser and broadband tuning. This invention utilizes a portion of the output light from a V-type confocal FP external cavity for feedback injection. By simultaneously adjusting the driving current of the distributed feedback semiconductor laser, the control voltage of the FP external cavity, and the electro-optic crystal, the resonant frequency of the distributed feedback semiconductor laser resonant cavity, the resonant frequency of the FP external cavity, and the phase of the feedback light are simultaneously controlled, ultimately achieving laser self-injection locking, linewidth compression, and tuning of the laser system.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A tunable self-injection locked narrow-linewidth semiconductor laser based on a FP cavity includes a distributed feedback semiconductor laser 1, a first temperature controller 2, a current driver 3, a first aspherical mirror 4, a first polarizing beam splitter 5, a half-wave plate 6, a second polarizing beam splitter 7, an electro-optic crystal 8, a second aspherical mirror 9, an FP cavity 10, a second temperature controller 11, an optical amplifier 12, a fiber coupler 13, a fiber laser 14, a fiber coupler 15, a photoelectric balance detector 16, a spectrum analyzer 17, a signal generator 18, a first voltage amplifier 19, a second voltage amplifier 20, and a third voltage amplifier 21.

[0009] The FP cavity 10 is a confocal cavity, placed at a 15° tilt angle; both the electro-optic crystal 8 and the FP cavity 10 are made of lithium tantalate (TaLiO3).

[0010] The output of the first temperature controller 2 is connected to the temperature control input of the distributed feedback semiconductor laser 1, and the output of the current driver 3 is connected to the current input of the distributed feedback semiconductor laser 1, respectively controlling the temperature and operating current of the distributed feedback semiconductor laser 1. The laser output from the distributed feedback semiconductor laser 1 is collimated by the first aspherical mirror 4, and the collimated parallel beam passes sequentially through the first polarizing beam splitter 5, the half-wave plate 6, and the second polarizing beam splitter 7, thereby controlling the polarization direction and optical power of the entire optical path. The laser output from the second polarizing beam splitter 7 then passes through the electro-optic crystal 8 and is focused by the second aspherical mirror 9. The focused laser is then incident on... The FP cavity 10 achieves matching between the incident laser's optical field distribution and the resonant optical field distribution within the FP cavity; the second temperature controller 11 controls the temperature of the FP cavity 10 to ensure its stable operation; part of the resonant light within the FP cavity 10 returns along its original path to be injected into the distributed feedback semiconductor laser 1, part is emitted along the incident direction and amplified by the optical amplifier 12 before being output, and the other part is emitted along the FP cavity's output direction and coupled into the fiber coupler 13. The laser coupled into the fiber coupler 13 and the reference laser output from the fiber laser 14 are coupled through the fiber coupler 15 and then input to the photoelectric balance detector 16 for mixing, and then the beat frequency signal is obtained through the spectrum analyzer 17;

[0011] Based on the beat frequency signal from the spectrum analyzer 17, the amplification factors of the first voltage amplifier 19, the second voltage amplifier 20, and the third voltage amplifier 21 are set. The DC component signal output by the signal generator 18 is amplified by the first voltage amplifier 19, the second voltage amplifier 20, and the third voltage amplifier 21, and then injected into the current driver 3, the electro-optic crystal 8, and the FP cavity 10, respectively. The first voltage amplifier 19 applies a voltage control signal to the current driver 3, thereby changing the operating current of the distributed feedback semiconductor laser 1 to regulate the resonant frequency of the semiconductor laser resonator. The second voltage amplifier 20 applies a voltage control signal to the electro-optic crystal 8, thereby controlling the refractive index of the electro-optic crystal 8 through the electro-optic effect to regulate the phase of the feedback light. The third voltage amplifier 21 applies a voltage control signal to the FP cavity 10, thereby changing the refractive index of the FP cavity through the electro-optic effect to regulate the resonant frequency of the FP cavity 10.

[0012] Furthermore, by adjusting the resonant frequency of the distributed feedback semiconductor laser resonator cavity, the resonant frequency of the FP external cavity, and the phase of the feedback light, self-injection locking of the semiconductor laser can be achieved; by superimposing a sawtooth wave signal on the DC component signal output by the signal generator 18, the output laser frequency of the laser can be adjusted, thereby achieving broadband tuning of the laser.

[0013] The Lang-Kobayashi rate equation for the nonlinear dynamic characteristics of a semiconductor laser under optical feedback is as follows:

[0014]

[0015] Where E(t) is the electric field intensity varying with time; ω is the laser frequency output by the laser; φ(t) is the phase varying with time; ω N τ is the resonant frequency of the distributed feedback semiconductor laser 1; G is the net gain coefficient of the laser resonant cavity; Γ is the total loss coefficient of the laser resonant cavity; α is the linewidth broadening factor, which is the ratio of the change in the real part to the change in the imaginary part of the refractive index; τ m The round-trip delay (τ) between the laser and the FP cavity during each reflection is given by the FP cavity. m =τ d +(2m+1)τ p , τ d τ is the time it takes for light to travel one round trip between the laser and the FP cavity. p (i is the time it takes for light to travel one round trip within the confocal FP cavity 10); i is the imaginary unit, m is the number of times light travels round trip within the confocal FP cavity 10, and t is the time; K m The optical feedback coupling rate is expressed as:

[0016]

[0017] Where, ηl d denoted as the optical path length of the semiconductor laser resonator; c is the speed of light in vacuum; β is the power mode coupling factor of the laser; r0 is the mirror reflection coefficient of the semiconductor laser; and r is the cavity mirror reflection coefficient of the FP cavity.

[0018] By solving the steady-state solution of the rate equation (1), the resonant frequency ω of the resonant cavity of the distributed feedback semiconductor laser can be obtained. N The relationship between the system output laser frequency ω and the frequency ω:

[0019]

[0020] Among them, F cfp =πr / (1-r 2 ) indicates the precision of FP cavity 10; The fineness of the resonant cavity of the distributed feedback semiconductor laser is represented by θ = arctan(α).

[0021] Combining formula (3) and appendix Figure 2Simulation results show that when the resonant frequency of the distributed feedback semiconductor laser 1 resonant cavity is close to the resonant frequency of the FP cavity 10, the feedback light will lock the laser frequency of a certain frequency range output by the distributed feedback semiconductor laser 1 at the resonant frequency of the FP cavity 10. Therefore, the laser frequency is mainly determined by the resonant frequency of the FP cavity. To ensure stable laser operation and achieve self-injection locking, compressed linewidth, and broadband tuning, two conditions must be met: firstly, the phase condition must be satisfied, i.e., the laser oscillating in the resonant cavity of the distributed feedback semiconductor laser 1 must oscillate in phase with the feedback-injected laser; secondly, the frequency condition must be satisfied, i.e., the resonant frequency of the distributed feedback semiconductor laser 1 resonant cavity and the resonant frequency of the FP cavity 10 should be close.

[0022] This invention achieves simultaneous control of phase and frequency conditions by regulating the resonant frequency of the distributed feedback semiconductor laser 1, regulating the resonant frequency of the FP cavity 10, and regulating the phase of the feedback light through the electro-optic crystal 8. This enables the FP cavity 10 to self-inject and lock onto the distributed feedback semiconductor laser 1, and also enables broadband tuning of the laser.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The present invention proposes a tunable self-injection locked narrow linewidth semiconductor laser based on a FP cavity. It utilizes a V-shaped FP cavity as an external resonant cavity and achieves wide-range tunable narrow linewidth laser output of the laser system by simultaneously controlling the resonant frequency of the distributed feedback semiconductor laser resonant cavity, the resonant frequency of the FP cavity, and the phase of the feedback light.

[0025] 2. This invention provides precise temperature control for both the distributed feedback semiconductor laser and the FP cavity, reducing the interference of the external environment on the feedback optical path and resulting in better stability. Attached Figure Description

[0026] Figure 1 A schematic diagram of a tunable self-injection locked narrow linewidth semiconductor laser based on an FP cavity provided by the present invention;

[0027] Figure 2 This is a curve showing the relationship between the resonant frequency of the semiconductor laser cavity and the output laser frequency of the laser in this invention; where ω N ω is the resonant frequency of the cavity of the distributed feedback semiconductor laser 1. res ω is the resonant frequency of the FP cavity 10, and ω is the laser output frequency of the laser.

[0028] Figure label:

[0029] 1 is a distributed feedback semiconductor laser, 2 is a first temperature controller, 3 is a current driver, 4 is a first aspherical mirror, 5 is a first polarizing beam splitter, 6 is a half-wave plate, 7 is a second polarizing beam splitter, 8 is an electro-optic crystal, 9 is a second aspherical mirror, 10 is an FP cavity, 11 is a second temperature controller, 12 is an optical amplifier, 13 is a fiber coupler, 14 is a fiber laser, 15 is a fiber coupler, 16 is a photoelectric balance detector, 17 is a spectrum analyzer, 18 is a signal generator, 19 is a first voltage amplifier, 20 is a second voltage amplifier, and 21 is a third voltage amplifier. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0031] Example

[0032] A tunable self-injection locked narrow-linewidth semiconductor laser based on a FP cavity includes a distributed feedback semiconductor laser 1, a first temperature controller 2, a current driver 3, a first aspherical mirror 4, a first polarizing beam splitter 5, a half-wave plate 6, a second polarizing beam splitter 7, an electro-optic crystal 8, a second aspherical mirror 9, an FP cavity 10, a second temperature controller 11, an optical amplifier 12, a fiber coupler 13, a fiber laser 14, a fiber coupler 15, a photoelectric balance detector 16, a spectrum analyzer 17, a signal generator 18, a first voltage amplifier 19, a second voltage amplifier 20, and a third voltage amplifier 21.

[0033] The FP cavity 10 is a confocal cavity, placed at a 15° tilt angle; both the electro-optic crystal 8 and the FP cavity 10 are made of lithium tantalate (TaLiO3).

[0034] The output of the first temperature controller 2 is connected to the temperature control input of the distributed feedback semiconductor laser 1, and the output of the current driver 3 is connected to the current input of the distributed feedback semiconductor laser 1, respectively controlling the temperature and operating current of the distributed feedback semiconductor laser 1. The laser output from the distributed feedback semiconductor laser 1 is collimated by the first aspherical mirror 4, and the collimated parallel beam passes sequentially through the first polarizing beam splitter 5, the half-wave plate 6, and the second polarizing beam splitter 7, thereby controlling the polarization direction and optical power of the entire optical path. The laser output from the second polarizing beam splitter 7 then passes through the electro-optic crystal 8 and is focused by the second aspherical mirror 9. The focused laser is then incident on... The FP cavity 10 achieves matching between the incident laser's optical field distribution and the resonant optical field distribution within the FP cavity; the second temperature controller 11 controls the temperature of the FP cavity 10 to ensure its stable operation; part of the resonant light within the FP cavity 10 returns along its original path to be injected into the distributed feedback semiconductor laser 1, part is emitted along the incident direction and amplified by the optical amplifier 12 before being output, and the other part is emitted along the FP cavity's output direction and coupled into the fiber coupler 13. The laser coupled into the fiber coupler 13 and the reference laser output from the fiber laser 14 are coupled through the fiber coupler 15 and then input to the photoelectric balance detector 16 for mixing, and then the beat frequency signal is obtained through the spectrum analyzer 17;

[0035] Based on the beat frequency signal from the spectrum analyzer 17, the amplification factors of the first voltage amplifier 19, the second voltage amplifier 20, and the third voltage amplifier 21 are set. The DC component signal output by the signal generator 18 is amplified by the first voltage amplifier 19, the second voltage amplifier 20, and the third voltage amplifier 21, and then injected into the current driver 3, the electro-optic crystal 8, and the FP cavity 10, respectively. The first voltage amplifier 19 applies a voltage control signal to the current driver 3, thereby changing the operating current of the distributed feedback semiconductor laser 1 to regulate the resonant frequency of the semiconductor laser resonator. The second voltage amplifier 20 applies a voltage control signal to the electro-optic crystal 8, thereby controlling the refractive index of the electro-optic crystal 8 through the electro-optic effect to regulate the phase of the feedback light. The third voltage amplifier 21 applies a voltage control signal to the FP cavity 10, thereby changing the refractive index of the FP cavity through the electro-optic effect to regulate the resonant frequency of the FP cavity 10.

[0036] The specific steps for using the tunable injection-locked narrow linewidth laser in this embodiment are as follows:

[0037] 1. Connect the output terminals of the current driver 3 and the first temperature controller 2 to the input terminal of the distributed feedback semiconductor laser 1. Control the temperature between 25 and 85°C, and adjust the current of the semiconductor laser within the range of 70 to 100 mA. The distributed feedback semiconductor laser used is a Thorlabs L1550P5DFB DFB laser diode. Figure 1Connect all components in sequence, and adjust the first temperature controller 2 and the second temperature controller 11 to control the temperature of the distributed feedback semiconductor laser 1 and the FP cavity 10 respectively.

[0038] 2. The laser output from the optical amplifier 12 is coupled through a prism and connected to a linewidth measurement device to measure the linewidth of the output laser. By changing the DC component signal output from the signal generator 18, and simultaneously adjusting the operating current of the distributed feedback semiconductor laser 1, the resonant frequency of the FP cavity 10, and the control voltage of the electro-optic crystal 8, simultaneous control of the resonant frequency of the distributed feedback semiconductor laser 1, the resonant frequency of the FP cavity 10, and the phase of the feedback light is achieved. The spectrum analyzer is observed until the linewidth of the laser system spectrum is significantly compressed and more stable compared to the linewidth during free operation, achieving laser self-injection locking and linewidth compression. By superimposing a sawtooth wave signal onto the output DC signal, the signal generator 18 can achieve broadband tuning of the laser system.

[0039] 3. Place the entire laser system in a temperature-controlled and vibration-isolated enclosed chassis to reduce the impact of the external environment on the feedback optical path.

[0040] In this embodiment, the relationship between the resonant frequency of the distributed feedback semiconductor laser 1 resonant cavity and the output frequency of the laser system is as follows: Figure 2 As shown, the laser frequency is taken as ν = 193 THz, and the free spectral range (FSR) of the FP cavity is 5.74 × 10⁻⁶. 9 HZ, the fineness of the FP cavity F cfp =1.57×10 3 The precision F of the resonant cavity of a semiconductor laser d =4.44, longitudinal mode spacing Δv of distributed feedback semiconductor laser d =c / 2ηl d The linewidth coupling factor α = 0.1, the injected feedback amount is -40dB, and the feedback efficiency κ = 0.0001.

[0041] Simulation results are as follows Figure 2 As shown, the curve exhibits an S-shaped hysteresis curve similar to the hysteresis loop of an electromagnetic field. The horizontal axis represents the resonant frequency of the semiconductor laser cavity, and the vertical axis represents the output laser frequency of the laser system. The relatively flat region of the curve corresponds to the frequency of the FP cavity resonant frequency on the vertical axis, and the frequency range on the horizontal axis corresponds exactly to the frequency locking range of the self-injection lock, verifying that the laser system frequency is mainly determined by the FP cavity resonant frequency.

[0042] In summary, this invention proposes a tunable self-injection locked narrow-linewidth semiconductor laser based on a FP cavity. It utilizes a V-type confocal FP cavity as the external resonant cavity of the laser. By feeding a portion of the resonant light from the FP cavity back into a distributed feedback semiconductor laser, and by simultaneously adjusting the driving current of the distributed feedback semiconductor laser, the driving voltage of the FP cavity, and the driving voltage of the electro-optic crystal, it achieves simultaneous control of the resonant frequency of the distributed feedback semiconductor laser cavity, the resonant frequency of the FP cavity, and the phase of the feedback light. This enables self-injection locked linewidth compression and wide-range tuning of the output laser frequency.

Claims

1. A tunable self-injection locked narrow-linewidth semiconductor laser based on an FP cavity, characterized in that, The system includes a distributed feedback semiconductor laser (1), a first temperature controller (2), a current driver (3), a first aspherical mirror (4), a first polarizing beam splitter (5), a half-wave plate (6), a second polarizing beam splitter (7), an electro-optic crystal (8), a second aspherical mirror (9), an FP cavity (10), a second temperature controller (11), an optical amplifier (12), a fiber optic coupler (13), a fiber laser (14), a fiber optic coupler (15), an optoelectronic balance detector (16), a spectrum analyzer (17), a signal generator (18), a first voltage amplifier (19), a second voltage amplifier (20), and a third voltage amplifier (21). The FP cavity (10) is a confocal cavity, placed at a 15° tilt angle; the materials of the electro-optic crystal (8) and the FP cavity (10) are both lithium tantalate; The output of the first temperature controller is connected to the temperature control input of the distributed feedback semiconductor laser, and the output of the current driver is connected to the current input of the distributed feedback semiconductor laser, thereby controlling the temperature and operating current of the distributed feedback semiconductor laser, respectively. The laser output from the distributed feedback semiconductor laser is collimated by the first aspherical mirror, and the collimated parallel beam passes sequentially through the first polarizing beam splitter, the half-wave plate, and the second polarizing beam splitter to control the polarization direction and optical power of the entire optical path. The laser output from the second polarizing beam splitter then passes through an electro-optic crystal and is collected by the second aspherical mirror. The focused laser beam is incident into the FP cavity, achieving matching between the incident laser's optical field distribution and the resonant optical field distribution within the FP cavity. A second temperature controller controls the temperature of the FP cavity. Part of the resonant light within the FP cavity returns along its original path to be injected into the distributed feedback semiconductor laser, part exits along the incident direction and is amplified by an optical amplifier before being output, and the remaining part exits along the FP cavity's exit direction and is coupled into a fiber coupler. The laser beam coupled into the fiber coupler is coupled with the reference laser output from the fiber laser through a fiber coupler and then input to a photoelectric balance detector for mixing. Finally, a beat frequency signal is obtained through a spectrum analyzer. Based on the beat frequency signal from the spectrum analyzer, the amplification factors of the first, second, and third voltage amplifiers are set. The DC component signal output by the signal generator is amplified by the first, second, and third voltage amplifiers and then injected into the current driver, electro-optic crystal, and FP cavity, respectively. The first voltage amplifier applies a voltage control signal to the current driver, thereby changing the operating current of the distributed feedback semiconductor laser to regulate the resonant frequency of the semiconductor laser cavity. The second voltage amplifier applies a voltage control signal to the electro-optic crystal, thereby controlling the refractive index of the electro-optic crystal through the electro-optic effect to regulate the phase of the feedback light. The third voltage amplifier applies a voltage control signal to the FP cavity, thereby changing the refractive index of the FP cavity through the electro-optic effect to regulate the resonant frequency of the FP cavity.

2. The tunable self-injection locked narrow-linewidth semiconductor laser based on an FP cavity according to claim 1, characterized in that, Self-injection locking of the semiconductor laser is achieved by adjusting the resonant frequency of the distributed feedback semiconductor laser resonator, the resonant frequency of the FP external cavity, and the phase of the feedback light; broadband tuning of the laser is achieved by superimposing a sawtooth wave signal on the DC component signal output by the signal generator.

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