Electro-optically frequency-modulated self-injection-locked narrow-linewidth semiconductor laser and method of use thereof

Abstract

The application discloses an electro-optical frequency modulation self-injection locking narrow line width semiconductor laser and a use method thereof, and belongs to the technical field of semiconductor lasers. The laser comprises a distributed feedback semiconductor laser, a first temperature controller, a first aspheric mirror, a first electro-optical crystal, a second aspheric mirror, a first high reflection mirror, a second high reflection mirror, a third high reflection mirror, a second electro-optical crystal and a negative thermal expansion alloy bottom plate. The electro-optical crystal is arranged in the optical resonant cavity, the refractive index of the electro-optical crystal is modulated to realize fast electro-optical frequency modulation, the bottom plate of the resonant cavity is made of the negative thermal expansion alloy, the change of the optical path of the electro-optical crystal with temperature is compensated, the sensitivity of the overall optical path of the resonant cavity to the change of temperature is reduced, the resonant frequency of the resonant cavity and the stability of the output frequency of the laser are improved, and therefore the frequency stability of the laser is improved while the fast frequency modulation performance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology and relates to a semiconductor laser, specifically an electro-optic frequency-modulated self-injection locked narrow linewidth semiconductor laser and its usage method. This laser can be applied to fields such as optical coherent detection and sensing, coherent optical communication, microwave photonics and lidar. Background Technology

[0002] Self-injection locked lasers have advantages such as narrow linewidth, small size, and high efficiency. Improving the frequency stability of these lasers and enabling them to have fast frequency tuning performance has good potential application prospects in fields such as coherent optical communication, optical coherent detection and sensing, microwave photonics, and lidar.

[0003] The frequency of an injection-locked laser primarily depends on the resonant frequency of its optical resonator. A traditional method to improve frequency stability is to use a vacuum microcavity as the resonator. The spacers in this type of resonator are made of ultra-low expansion glass material with a near-zero coefficient of thermal expansion, thus ensuring the stability of the optical path length and resonant frequency, and simultaneously improving the laser's frequency stability. However, using this type of resonator makes laser frequency modulation, especially rapid frequency modulation, difficult.

[0004] To solve the problem of rapid frequency modulation, monolithic or waveguide optical resonant cavities can be made using electro-optic crystals such as LiTaO3 or LiNbO3. However, because these materials have a large thermo-optic coefficient, the laser frequency changes significantly with temperature, which makes the frequency stability of the laser worse.

[0005] To address the aforementioned issues, this invention proposes a self-injection locked narrow-linewidth semiconductor laser with electro-optic frequency modulation. An electro-optic crystal is placed within its optical resonant cavity, and rapid electro-optic frequency modulation is achieved by modulating the refractive index of the electro-optic crystal. Furthermore, the base plate of the resonant cavity is made of a negative thermal expansion alloy to compensate for temperature variations in the optical path length of the electro-optic crystal, reducing the overall optical path length sensitivity of the resonant cavity to temperature changes and improving the stability of the resonant frequency of the cavity and the laser output frequency. This achieves both rapid frequency modulation performance and improved laser frequency stability. Summary of the Invention

[0006] The purpose of this invention is to address the problem in the prior art where self-injection locked lasers cannot simultaneously achieve fast frequency modulation and high frequency stability. This invention proposes an electro-optically modulated self-injection locked narrow-linewidth semiconductor laser and its application method. By employing electro-optic frequency modulation and a negative thermal expansion alloy, fast frequency modulation and high frequency stability are achieved. The invention proposes placing an electro-optic crystal within the optical resonant cavity. Fast electro-optic frequency modulation is achieved by modulating the refractive index of the electro-optic crystal. Furthermore, the base plate of the resonant cavity uses a negative thermal expansion alloy to compensate for temperature variations in the optical path length of the electro-optic crystal, reducing the sensitivity of the overall optical path length of the resonant cavity to temperature changes and improving the stability of the resonant frequency of the cavity and the output frequency of the laser. Therefore, while achieving fast frequency modulation performance, the frequency stability of the laser is also improved.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser includes a distributed feedback semiconductor laser, a first aspherical mirror, a first electro-optic crystal, a second aspherical mirror, a first high-reflectivity mirror, a second high-reflectivity mirror, a third high-reflectivity mirror, and a second electro-optic crystal. The laser output from the distributed feedback semiconductor laser is collimated by a first aspherical mirror. The collimated parallel beam passes through a first electro-optic crystal and is then incident on a second aspherical mirror. The second aspherical mirror converges the beam, and the converged laser is coupled into a folded optical resonant cavity through a first high-reflectivity mirror, matching the laser mode within the cavity. The first, second, and third high-reflectivity mirrors form a folded optical resonant cavity. A second electro-optic crystal is placed inside the folded optical resonant cavity. The beam oscillating within the folded optical resonant cavity is coupled out through the first high-reflectivity mirror and then sequentially injected into the distributed feedback semiconductor laser through the second aspherical mirror, the first electro-optic crystal, and the first aspherical mirror, achieving linewidth compression through a self-injection locking effect.

[0008] Furthermore, the light-transmitting end faces of the first and second electro-optic crystals are inclined planes with an angle of 5~10°.

[0009] Furthermore, the oblique angle of the light-transmitting end face of the first electro-optic crystal and the second electro-optic crystal is 8°.

[0010] Furthermore, the first high-reflectivity mirror is a plane mirror with an incident angle of 30~60°; the second high-reflectivity mirror is a curved mirror with an incident angle of 0°; and the third high-reflectivity mirror is a plane mirror with an incident angle of 0°.

[0011] Furthermore, the incident angle of the first highly reflective mirror is 45°.

[0012] Furthermore, it also includes a first temperature controller, which is in close thermal contact with the distributed feedback semiconductor laser to control the temperature of the distributed feedback semiconductor laser.

[0013] Furthermore, it also includes a negative thermal expansion alloy base plate, and a folded optical resonant cavity composed of a first high-reflectivity mirror, a second high-reflectivity mirror, and a third high-reflectivity mirror is mounted on the negative thermal expansion alloy base plate.

[0014] Furthermore, the length of the second electro-optic crystal The cavity length of the folded optical resonator satisfies the following relationship: ; in, This indicates the distance between the first and second high-reflectivity mirrors. This indicates the distance between the second and third high-reflectivity mirrors. Indicates the length of the second electro-optic crystal. This represents the thermo-optic coefficient of the second electro-optic crystal. This represents the refractive index of the second electro-optic crystal in the laser polarization direction. This represents the coefficient of thermal expansion of the second electro-optic crystal. This represents the coefficient of thermal expansion of the negative thermal expansion alloy base plate.

[0015] A method for using an electro-optically frequency-modulated self-injection-locked narrow-linewidth semiconductor laser, comprising the following steps: Step 1: Control the temperature of the distributed feedback semiconductor laser in the above-mentioned electro-optic frequency-modulated self-injection locked narrow linewidth semiconductor laser; Step 2: Adjust the driving voltage of the first electro-optic crystal until the laser output linewidth reaches the corresponding minimum value; Step 3: Adjust the temperature of the distributed feedback semiconductor laser until the laser output linewidth reaches the corresponding minimum value; Step 4: Place all the electro-optically modulated self-injection locked narrow linewidth semiconductor lasers in a temperature-controlled and vibration-isolated enclosed chassis.

[0016] It should be noted that the "laser output linewidth" in steps 2 and 3 refers to the linewidth reflected by the first high-reflectivity mirror 6, which is the output linewidth of the entire laser system. Figure 1 The line width at the "output" arrow in the middle.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In this invention, by setting an electro-optic crystal in the optical resonant cavity, rapid electro-optic frequency modulation can be achieved by modulating the refractive index of the electro-optic crystal; based on the realization of rapid photoelectric frequency modulation, the tuning rate of the laser can be significantly improved, ensuring the high coherence of the laser, which is suitable for long-term precision measurement.

[0018] 2. In this invention, the base plate of the resonant cavity is made of a negative thermal expansion alloy to compensate for the change in optical path length of the electro-optic crystal with temperature, reduce the sensitivity of the overall optical path length of the resonant cavity to temperature changes, and improve the stability of the resonant frequency of the resonant cavity and the output frequency of the laser, thereby improving the frequency stability of the laser while obtaining fast frequency modulation performance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention; In the attached figures, the following labels are used: 1 is a distributed feedback semiconductor laser, 2 is a first temperature controller, 3 is a first aspherical mirror, 4 is a first electro-optic crystal, 5 is a second aspherical mirror, 6 is a first high-reflectivity mirror, 7 is a second high-reflectivity mirror, 8 is a third high-reflectivity mirror, 9 is a second electro-optic crystal, and 10 is a negative thermal expansion alloy base plate. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0021] Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1 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.

[0023] Example An electro-optic frequency-modulated self-injection locked narrow linewidth semiconductor laser includes a distributed feedback semiconductor laser 1, a first temperature controller 2, a first aspherical mirror 3, a first electro-optic crystal 4, a second aspherical mirror 5, a first high-reflectivity mirror 6, a second high-reflectivity mirror 7, a third high-reflectivity mirror 8, a second electro-optic crystal 9, and a negative thermal expansion alloy base plate 10. The light-transmitting end face of the first electro-optic crystal 4 and the second electro-optic crystal 9 is an inclined surface with an angle of 8°; The first high-reflection mirror 6 is a plane mirror with an incident angle of 45°; the second high-reflection mirror 7 is a curved mirror with an incident angle of 0°; and the third high-reflection mirror 8 is a plane mirror with an incident angle of 0°. The first temperature controller 2 is in close thermal contact with the distributed feedback semiconductor laser 1 to control the temperature of the distributed feedback semiconductor laser 1. The laser output from the distributed feedback semiconductor laser 1 is collimated by the first aspherical mirror 3, and the collimated parallel beam passes through the first electro-optic crystal 4 and then enters the second aspherical mirror 5. The second aspherical mirror 5 focuses the beam, and the focused laser is coupled into the resonant cavity through the first high-reflectivity mirror 6, matching the laser mode within the cavity. The first high-reflectivity mirror 6, the second high-reflectivity mirror 7, and the third high-reflectivity mirror 8 form a folded optical resonant cavity. The second electro-optic crystal 9 is placed inside the resonant cavity. The transmission of the laser between the three mirrors in the resonant cavity is existing technology, except that a second electro-optic crystal 9 is set in the optical path from the first high-reflectivity mirror 6 to the third high-reflectivity mirror 8. The laser beam emitted from the first high-reflectivity mirror 6 is fed into the third high-reflectivity mirror 8 via the second electro-optic crystal 9. The reflected laser beam from the third high-reflectivity mirror 8 is then fed back into the first high-reflectivity mirror 6 via the second electro-optic crystal 9. The entire resonant cavity is mounted on a negative thermal expansion alloy base plate 10. A portion of the oscillating laser beam within the resonant cavity is coupled out through the first high-reflectivity mirror 6 and then sequentially injected into the distributed feedback semiconductor laser 1 via the second aspherical mirror 5, the first electro-optic crystal 4, and the first aspherical mirror 3, achieving linewidth compression through a self-injection locking effect. The other portion of the beam is reflected out by the first high-reflectivity mirror 6. By adjusting the driving voltage of the first electro-optic crystal 4 and the temperature of the distributed feedback semiconductor laser 1, the beam is further reflected out by the first high-reflectivity mirror 6 (i.e.,...). Figure 1 The line width (as shown in the "Output") reaches the corresponding minimum value.

[0024] The specific steps for using the self-injection locked laser in this embodiment are as follows: 1. The first temperature controller 2 is brought into close thermal contact with the distributed feedback semiconductor laser 1 to control the temperature of the distributed feedback semiconductor laser 1. The wavelength of the distributed feedback semiconductor laser 1 is 1550nm, and the temperature is controlled according to... Figure 1 Connect all the components in sequence.

[0025] 2. The first electro-optic crystal 4 is used to adjust the circular optical path between the distributed feedback semiconductor laser 1 and the first high-reflectivity mirror 6. When the circular optical path is an integer multiple of the wavelength, the optimal linewidth compression effect can be obtained. Adjust the driving voltage of the first electro-optic crystal 4 until the laser output linewidth reaches the corresponding minimum value.

[0026] 3. Adjusting the temperature of the distributed feedback semiconductor laser 1 controls its free oscillation frequency. When the free oscillation frequency of the distributed feedback semiconductor laser 1 matches the resonant frequency of the folded optical resonator, the optimal linewidth compression effect can be obtained. Adjust the temperature of the distributed feedback semiconductor laser 1 until the laser output linewidth reaches the corresponding minimum value.

[0027] 4. 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.

[0028] In this embodiment, when the cavity length (L1+L2) is equal to the length of the second electro-optic crystal 9... Optimal frequency stabilization can be achieved when the following relationship is satisfied: (1) in, The distance between the first high-reflectivity mirror 6 and the second high-reflectivity mirror 7. The distance between the second high-reflectivity mirror 7 and the third high-reflectivity mirror 8. The length of the second electro-optic crystal 9, The thermo-optic coefficient of the second electro-optic crystal 9. Let be the refractive index of the second electro-optic crystal 9 in the laser polarization direction. The coefficient of thermal expansion of the second electro-optic crystal 9 is given. The coefficient of thermal expansion of the negative thermal expansion alloy base plate 10 is given. If the second electro-optic crystal 9 is taken as LiTaO3 crystal, the type of the negative thermal expansion alloy is ALLVAR Alloy 15, i.e. K represents absolute temperature; substituting the relevant material parameters into equation (1), we can obtain: .

[0029] In summary, this invention proposes a self-injection locked narrow-linewidth semiconductor laser with electro-optic frequency modulation. An electro-optic crystal is placed within the proposed optical resonant cavity, and rapid electro-optic frequency modulation is achieved by modulating the refractive index of the electro-optic crystal. Furthermore, the base plate of the resonant cavity is made of a negative thermal expansion alloy to compensate for the change in the optical path length of the electro-optic crystal with temperature, reducing the sensitivity of the overall optical path length of the resonant cavity to temperature changes and improving the stability of the resonant frequency of the resonant cavity and the output frequency of the laser. Thus, while achieving rapid frequency modulation performance, the frequency stability of the laser is also improved.

Claims

1. A self-injection-locked narrow-linewidth semiconductor laser with electro-optic frequency modulation, characterized in that: It includes a distributed feedback semiconductor laser (1), a first aspherical mirror (3), a first electro-optic crystal (4), a second aspherical mirror (5), a first high-reflectivity mirror (6), a second high-reflectivity mirror (7), a third high-reflectivity mirror (8), and a second electro-optic crystal (9). The laser output from the distributed feedback semiconductor laser (1) is collimated by the first aspherical mirror (3). The collimated parallel beam passes through the first electro-optic crystal (4) and is then incident on the second aspherical mirror (5). The second aspherical mirror (5) converges the beam, and the converged laser is coupled into the folded optical resonant cavity through the first high-reflectivity mirror (6) and matched with the laser mode in the cavity. The first high-reflectivity mirror (6), the second high-reflectivity mirror (7), and the third high-reflectivity mirror (8) form the folded optical resonant cavity. The second electro-optic crystal (9) is placed in the folded optical resonant cavity. The beam oscillating in the folded optical resonant cavity is coupled out through the first high-reflectivity mirror (6) and then injected into the distributed feedback semiconductor laser (1) in sequence through the second aspherical mirror (5), the first electro-optic crystal (4), and the first aspherical mirror (3), thereby achieving linewidth compression through the self-injection locking effect.

2. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 1, characterized in that: The light-transmitting end faces of the first electro-optic crystal (4) and the second electro-optic crystal (9) are inclined planes with an angle of 5~10°.

3. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 2, characterized in that: The oblique angle of the light-transmitting end face of the first electro-optic crystal (4) and the second electro-optic crystal (9) is 8°.

4. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 1, characterized in that: The first high-reflection mirror (6) is a plane mirror with an incident angle of 30~60°; the second high-reflection mirror (7) is a curved mirror with an incident angle of 0°; and the third high-reflection mirror (8) is a plane mirror with an incident angle of 0°.

5. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 4, characterized in that: The incident angle of the first high-reflectivity mirror (6) is 45°.

6. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 1, characterized in that: It also includes a first temperature controller (2), which is in close thermal contact with the distributed feedback semiconductor laser (1) to control the temperature of the distributed feedback semiconductor laser (1).

7. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 1, characterized in that: It also includes a negative thermal expansion alloy base plate (10), and a folded optical resonant cavity composed of a first high reflective mirror (6), a second high reflective mirror (7) and a third high reflective mirror (8) is mounted on the negative thermal expansion alloy base plate (10).

8. The electro-optic frequency-modulated self-injection locked narrow-linewidth semiconductor laser as described in claim 7, characterized in that: Length of the second electro-optic crystal (9) The cavity length of the folded optical resonator satisfies the following relationship: ； in, This indicates the distance between the first high-reflectivity mirror (6) and the second high-reflectivity mirror (7). This indicates the distance between the second high-reflectivity mirror (7) and the third high-reflectivity mirror (8). This indicates the length of the second electro-optic crystal (9). This represents the thermo-optic coefficient of the second electro-optic crystal (9). This represents the refractive index of the second electro-optic crystal (9) in the laser polarization direction. Indicates the coefficient of thermal expansion of the second electro-optic crystal (9). The coefficient of thermal expansion of the negative thermal expansion alloy base plate (10) is indicated.

9. A method of using an electro-optically frequency-modulated self-injection-locked narrow-linewidth semiconductor laser, characterized in that, The usage steps are as follows: Step 1: Control the temperature of the distributed feedback semiconductor laser (1) in the electro-optic frequency-modulated self-injection locked narrow linewidth semiconductor laser according to any one of claims 1-8; Step 2: Adjust the driving voltage of the first electro-optic crystal (4) until the laser output linewidth reaches the corresponding minimum value; Step 3: Adjust the temperature of the distributed feedback semiconductor laser (1) until the laser output linewidth reaches the corresponding minimum value; Step 4: Place all the electro-optically modulated self-injection locked narrow linewidth semiconductor lasers in a temperature-controlled and vibration-isolated enclosed chassis.

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