A tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter

Abstract

The present invention discloses a tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter. The device includes: a semiconductor pump source, a single-mode wavelength division multiplexer, a polarization-maintaining doped fiber, a polarization-maintaining fiber circulator, a polarization-maintaining tunable fiber Bragg grating (FBG), first to third polarization-maintaining 2#imgabs0#2 output couplers, a polarization-maintaining 1#imgabs1#2 fiber coupler, and a TEC temperature-controlled heat sink. The first to third polarization-maintaining 2#imgabs2#2 output couplers together form the "8"-shaped composite ring cavity filter. This filter interacts with the polarization-maintaining tunable fiber Bragg grating (FBG) and the ring cavity structure to achieve laser mode selection. The polarization-maintaining tunable fiber Bragg grating (FBG) is controlled by voltage and temperature to achieve wavelength tuning. According to the technical solution of the present invention, high spectral purity operation of the laser can be achieved under different pump powers for each wavelength channel, and it can be applied to fiber lasers to achieve high-quality laser output.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber and laser technology, and in particular to a tunable single-frequency optical fiber laser based on an "8"-shaped composite ring cavity filter. Background Art

[0002] Tunable single-frequency fiber lasers have garnered widespread attention in recent laser technology developments due to their exceptional signal-to-noise ratio and tunable output wavelength. Fiber lasers, with their compact structure, easy thermal management, and excellent beam quality, have become a vital tool for scientific research and industrial applications. With the continuous advancement of laser technology, the linewidth, stability, and single-longitudinal-mode operation of narrowly tunable lasers have been significantly optimized. Applications include fiber-optic sensing, Doppler lidar, nonlinear frequency conversion, high-energy lasers, and laser spectroscopy.

[0003] At present, the realization of single-frequency laser output mainly relies on two structures: linear cavity and ring cavity. Due to the limitation of cavity length, the tuning means of linear cavity laser are relatively limited, and it is difficult to achieve laser output with a wide tuning range. In contrast, ring cavity lasers are more flexible in structural design and can effectively achieve the output of wide-tunable single-frequency fiber lasers by inserting appropriate mode selection elements and wavelength tuning devices. Although ring cavity lasers perform well in terms of tunability, their wavelength tuning range is still subject to certain limitations in applications in the 1.5-micron band. Since the absorption rate of ions is low in the short-wave and long-wave bands that deviate from the center wavelength near 1550nm, it is difficult to achieve efficient laser output. Therefore, the development of single-frequency fiber lasers with a wide spectral range in the 1.5-micron band has important application value. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter. 2. The output coupler builds an "8"-shaped resonant cavity as an ultra-narrow comb filter, which works together with the polarization-maintaining tunable fiber Bragg grating and the ring cavity structure to narrow the linewidth and achieve single-frequency laser output; by controlling the gain of erbium ions in various 1.5-micron bands and tuning the central wavelength of the polarization-maintaining tunable fiber Bragg grating by adjusting the control voltage and changing the heat sink temperature, the output of fiber laser with a wide spectral range is achieved.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: a tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter, comprising a semiconductor pump source, a single-mode wavelength division multiplexer, a polarization-maintaining doped fiber, a polarization-maintaining fiber circulator, a polarization-maintaining tunable fiber Bragg grating, a first polarization-maintaining 2 2 output coupler, second polarization maintaining 2 2 output coupler, third polarization maintaining 2 2 output coupler, polarization maintaining 1 2. Fiber optic coupler and TEC temperature controlled heat sink;

[0006] The connection relationship between each part is:

[0007] The semiconductor pump source is fused to the first end of the single-mode wavelength division multiplexer, the second end of the single-mode wavelength division multiplexer is fused to one end of the polarization-maintaining doped fiber, the other end of the polarization-maintaining doped fiber is fused to the first end of the polarization-maintaining fiber circulator, the second end of the polarization-maintaining fiber circulator is fused to the first end of the polarization-maintaining tunable fiber Bragg grating; the TEC temperature control heat sink controls the temperature of the polarization-maintaining tunable fiber Bragg grating; the third end of the polarization-maintaining fiber circulator is fused to the first end of the polarization-maintaining tunable fiber Bragg grating. 2 The first end of the output coupler is fused, the first polarization maintaining 2 2 The second end of the output coupler and the second polarization maintaining 2 2 The first end of the output coupler is fused, the first polarization maintaining 2 2 The third end of the output coupler and the second polarization maintaining 2 2 The fourth end of the output coupler is fused; the second polarization maintaining 2 2 The second end of the output coupler and the third polarization maintaining 2 2 The first end of the output coupler is fused, and the second end is polarization-maintaining 2 2 The third end of the output coupler and the third polarization maintaining 2 2 The fourth end of the output coupler is fused, and the third polarization maintaining 2 2 The third end of the output coupler is connected to the polarization maintaining 2. First end fusion splicing of fiber coupler; polarization maintaining 1 2. Connect the second end of the fiber coupler to the third end of the single-mode wavelength division multiplexer; polarization maintaining 1 2 The third end of the fiber coupler serves as the output port of the single-frequency fiber laser.

[0008] Compared with the prior art, the present invention has significant advantages and beneficial effects, which are specifically reflected in the following aspects:

[0009] The present invention uses a full polarization-maintaining fiber ring cavity structure, which can effectively suppress the spatial hole burning effect in the traveling wave cavity structure. At the same time, the ring cavity structure is not limited by the cavity length, which makes it easy to insert mode selection components and wavelength tuning devices to achieve single-mode operation of the laser. 2. The output coupler is used to build an ultra-narrow comb filter to build a single longitudinal mode selector for the ring fiber laser. The free spectral range and passband of the comb filter must be greater than 0.5 times the reflection bandwidth of the polarization-maintaining tunable fiber Bragg grating and less than 2 times the longitudinal mode spacing of the ring cavity, respectively.

[0010] The present invention utilizes a tunable fiber Bragg grating (FBG) as a wavelength tuning device and a narrowband filter device, combining the tunable and filter devices without separately adding the tunable filter and narrowband filter devices into the cavity. This simplifies the optical path structure and can also achieve single-frequency laser output that is continuously tunable over a wide spectral range. At the same time, the polarization-maintaining tunable fiber Bragg grating is temperature-controlled to further enhance the tuning range of the output wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of the structure of a tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter in an embodiment of the present invention;

[0012] Figure 2 This is the simulated transmission spectrum of the "8"-shaped composite ring cavity filter in the embodiment of the present invention with a wavelength range of 1550-1555nm;

[0013] Figure 3 This is the simulated transmission spectrum of the "8"-shaped composite ring cavity filter in the wavelength range of 1550.06-1550.25 nm according to the embodiment of the present invention. The inset inside is the transmission spectrum of a single peak (1550.1582-1550.15858 nm).

[0014] Reference numerals: 1-semiconductor pump source; 2-single-mode wavelength division multiplexer; 3-polarization-maintaining doped fiber; 4-polarization-maintaining fiber circulator; 5-polarization-maintaining tunable fiber Bragg grating; 6-first polarization-maintaining 2 2 output coupler; 7- second polarization maintaining 2 2 output couplers; 8-third polarization maintaining 2 2 output couplers; 9-polarization maintaining 1 2 fiber couplers; 10-TEC temperature-controlled heat sink. DETAILED DESCRIPTION

[0015] In order to make the purpose and technical solution of this application clearer, the present invention is further described below with reference to the accompanying drawings and specific implementations. It should be understood that the specific embodiments described herein are only used to illustrate the present invention and should not be used to limit the scope of protection of the present invention.

[0016] In the description of the present invention, if there is a description of first and second, it is only for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0017] like Figure 1As shown, this embodiment provides a tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter. The single-frequency fiber laser generating device includes the following components: a semiconductor pump source 1, a single-mode wavelength division multiplexer 2, a polarization-maintaining doped fiber 3, a polarization-maintaining fiber circulator 4, a polarization-maintaining tunable fiber Bragg grating 5, a first polarization-maintaining 2 2 output coupler 6, second polarization maintaining 2 2 output coupler 7, third polarization maintaining 2 2 output coupler 8, polarization maintaining 1 2 Fiber optic coupler 9 and TEC temperature control heat sink 10.

[0018] The connection relationship between each component is as follows:

[0019] The semiconductor pump source 1 is fused to the first end of the single-mode wavelength division multiplexer 2, the second end of the single-mode wavelength division multiplexer 2 is fused to one end of the polarization-maintaining doped fiber 3, the other end of the polarization-maintaining doped fiber 3 is fused to the first end of the polarization-maintaining fiber circulator 4, the second end of the polarization-maintaining fiber circulator 4 is fused to the first end of the polarization-maintaining tunable fiber Bragg grating 5; the TEC temperature control heat sink 10 controls the temperature of the polarization-maintaining tunable fiber Bragg grating 5; the third end of the polarization-maintaining fiber circulator 4 is fused to the first end of the polarization-maintaining tunable fiber Bragg grating 5. 2 The first end of the output coupler 6 is fused, and the first polarization maintaining 2 2 The second end of the output coupler 6 and the second polarization maintaining 2 2 The first end of the output coupler 7 is fused, and the first polarization maintaining 2 2 The third end of the output coupler 6 and the second polarization maintaining 2 2 The fourth end of the output coupler 7 is fused; the second polarization maintaining 2 2 The second end of the output coupler 7 and the third polarization maintaining 2 2 The first end of the output coupler 8 is fused, and the second end of the polarization maintaining 2 The third end of the output coupler 7 and the third polarization maintaining 2 2 The fourth end of the output coupler 8 is fused, and the third polarization maintaining 2 2 The third end of the output coupler 8 is connected to the polarization maintaining 1 2 The first end of the optical fiber coupler 9 is fused; polarization maintaining 1 2 The second end of the optical fiber coupler 9 is connected to the third end of the single-mode wavelength division multiplexer 2; The third end of the fiber coupler 9 serves as the output port of the single-frequency fiber laser.

[0020] The above-mentioned single-frequency fiber laser is explained in detail below with reference to specific embodiments.

[0021] In one embodiment, the semiconductor pump source 1 is a single-mode linearly polarized laser pump source with a maximum output power of 600 mW at 976 nm. The wavelength division multiplexer 2 is a 976 / 1550 nm wavelength division multiplexer, wherein the first end is a 976 nm port, the second end is a 1550 nm port, and the third end is a common port. The semiconductor pump source 1 provides a 976 nm pump light signal to the single-frequency fiber laser through the wavelength division multiplexer 2. The polarization-maintaining doped fiber 3 is a rare-earth-doped single-mode glass fiber. The matrix materials of the core and cladding of the doped fiber are one or a combination of two of phosphate glass, germanate glass, tellurite glass, and silicate glass. The rare-earth doping ions in the core of the doped fiber are erbium ions. The peak absorption at 1530 nm reaches 55 dB / m. The length used is 1.5 m. The polarization-maintaining fiber circulator 4 is a three-port fiber device, and the polarization-maintaining tunable fiber Bragg grating 5 is a wavelength tunable filter with a tuning range of 1540-1570nm, a 3dB bandwidth of 0.2nm, and a reflectivity of 90%. On the one hand, its function is to change the central wavelength of the output laser to achieve laser tuning, and on the other hand, it serves as a narrowband filter device for the laser, which is conducive to achieving single-frequency operation. 2 The first and second ends of the output coupler are optical energy input ports. The first polarization maintaining 2 The third end of the output coupler is the 90% light energy output port, the first polarization maintaining 2 The fourth end of the output coupler is the 10% light energy output port. 2 The first and second ends of the output coupler are optical energy input ports, and the second polarization maintaining 2 The third end of the output coupler is the 99% light energy output port, the second polarization maintaining 2 The fourth end of the output coupler is the 1% light energy output port. 2 The first and second ends of the output coupler are optical energy input ports, and the third end is polarization maintaining 2 2 The third end of the output coupler is the 70% light energy output port, the third polarization maintaining 2 2 The fourth end of the output coupler is the 30% light energy output port. 2 The second end of the fiber coupler 9 is the 80% optical energy output port, maintaining polarization 1 2 The third end of the fiber coupler is the 20% optical energy output port. The splitting ratio between the third end and the second end of the optical fiber coupler 9 is 20:80.

[0022] The polarization-maintaining tunable fiber Bragg grating 5 has a 3 dB bandwidth of 0.2 nm and a reflectivity of 90% within a tuning range of approximately 30 nm near 1560 nm. A TEC temperature-controlled heat sink 10 is used to improve the anti-interference ability of the polarization-maintaining tunable fiber Bragg grating 5 to the environment, and its wavelength tuning range can be further enhanced by adjusting the temperature.

[0023] This example uses a laser ring cavity structure, a single-mode wavelength division multiplexer, a polarization-maintaining doped fiber, a polarization-maintaining fiber circulator, a first polarization-maintaining 2 output coupler, second polarization maintaining 2 2 output coupler, third polarization maintaining 2 2 output coupler, polarization maintaining 1 2 fiber couplers together form a ring cavity of a wide spectral range single-frequency fiber laser generating device.

[0024] First polarization maintaining 2 2 The second end of the output coupler 6 and the second polarization maintaining 2 2 The first end of the output coupler 7 is connected to the first polarization maintaining 2 2 Output coupler 6 third end and second polarization maintaining 2 2 The fourth end of the output coupler 7 is connected to the second polarization maintaining 2 2 The second end of the output coupler 7 and the third polarization maintaining 2 2 output coupler 8 first end connected to the second polarization maintaining 2 2 The third end of the output coupler 7 and the third polarization maintaining 2 2 The fourth end of the output coupler 8 is connected to form an "8"-shaped composite ring cavity filter, which acts as a comb filter and works together with the polarization-maintaining tunable fiber Bragg grating and the ring cavity structure to achieve single-frequency laser output.

[0025] The comb filter composed of the "8"-shaped resonant cavity must meet two requirements: 1. Its free spectral range (FSR) must be greater than 0.5 times the reflection bandwidth of the polarization-maintaining tunable fiber Bragg grating 5; 2. Its passband must be less than 2 times the longitudinal mode spacing of the ring cavity.

[0026] This embodiment uses a tunable fiber Bragg grating to achieve output wavelength tuning. By adjusting the voltage value input to the tunable fiber Bragg grating, the central wavelength value of the fiber Bragg grating is changed, thereby changing the output laser wavelength of the laser, thereby achieving tunable laser wavelength.

[0027] In this embodiment, the temperature control accuracy of the TEC temperature control heat sink 10 is ±0.01°C, and the temperature adjustment range is 20-70°C. By accurately controlling the temperature of the tunable fiber Bragg grating, the stability of the system can be improved, and the tuning range of the system can also be increased.

[0028] Semiconductor pump source 1, single-mode wavelength division multiplexer 2, polarization-maintaining doped fiber 3, polarization-maintaining fiber circulator 4, polarization-maintaining tunable fiber Bragg grating 5, first polarization-maintaining 2 2 output coupler 6, second polarization maintaining 2 2 output coupler 7, third polarization maintaining 2 2 output coupler 8 polarization maintaining 1 2 The optical fiber couplers 9 are all polarization-maintaining structures and use slow-axis alignment fusion to achieve linearly polarized light output.

[0029] In this embodiment, the first polarization maintaining 2 The second end of the output coupler 6 and the second polarization maintaining 2 2 The length of the optical fiber at the first end of the output coupler 7 is 0.36m, and the first polarization maintaining 2 Output coupler 6 third end and second polarization maintaining 2 2 The length of the optical fiber at the fourth end of the output coupler 7 is 0.27m, and the second polarization maintaining 2 The second end of the output coupler 7 and the third polarization maintaining 2 2 The optical fiber length of the first end of the output coupler 8 is 0.7m, and the second polarization maintaining 2 The third end of the output coupler 7 and the third polarization maintaining 2 The length of the optical fiber at the fourth end of the output coupler 8 is 0.25m. The transmission spectrum of the simulated "8" shaped composite ring cavity filter is as follows: Figure 2 and Figure 3 shown.

[0030] The simulated transmission spectrum of the "8"-shaped composite ring cavity filter in the 1550-1555nm band in this embodiment is as follows: Figure 2 The interval between adjacent transmission peaks is 0.16 nm, corresponding to a free spectrum range of 19.98 GHz. Figure 3 The illustration shows that the passband bandwidth of the "8"-shaped composite ring cavity filter is 18 MHz, the ring cavity length is 10.5 m, the corresponding longitudinal mode spacing is 19.43 MHz, and the free spectral range corresponding to the 3 dB bandwidth of the tunable fiber Bragg grating is 24.97 GHz, which meets the requirements that the free spectral range and passband of the comb filter must be greater than 0.5 times the reflection bandwidth of the tunable fiber Bragg grating and less than 2 times the longitudinal mode spacing of the ring cavity, respectively, and single-frequency laser output can be achieved.

[0031] The contents not described in detail in the present invention belong to the prior art known to professionals in this field.

[0032] The above embodiments are provided for the purpose of describing the present invention only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the present invention are intended to be within the scope of the present invention.

Claims

1. A tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter, characterized in that: It includes a semiconductor pump source (1), a single-mode wavelength division multiplexer (2), a polarization-maintaining doped fiber (3), a polarization-maintaining fiber circulator (4), a polarization-maintaining tunable fiber Bragg grating (5), a first polarization-maintaining 2 2 output coupler (6), second polarization maintaining 2 2 output coupler (7), third polarization maintaining 2 2 output coupler (8), polarization maintaining 1 2. Fiber optic coupler (9) and TEC temperature control heat sink (10); The connection relationship between each component is: The semiconductor pump source (1) is fused to the first end of the single-mode wavelength division multiplexer (2), the second end of the single-mode wavelength division multiplexer (2) is fused to one end of the polarization-maintaining doped fiber (3), the other end of the polarization-maintaining doped fiber (3) is fused to the first end of the polarization-maintaining fiber circulator (4), the second end of the polarization-maintaining fiber circulator (4) is fused to the first end of the polarization-maintaining tunable fiber Bragg grating (5); the TEC temperature control heat sink (10) controls the temperature of the polarization-maintaining tunable fiber Bragg grating (5); the third end of the polarization-maintaining fiber circulator (4) is fused to the first end of the polarization-maintaining tunable fiber Bragg grating (5); 2 The first end of the output coupler (6) is fused, and the first polarization maintaining 2 The second end of the output coupler (6) and the second polarization maintaining 2 2 The first end of the output coupler (7) is fused, and the first polarization maintaining 2 2 The third end of the output coupler (6) and the second polarization maintaining 2 2 The fourth end of the output coupler (7) is fused; the second polarization maintaining 2 2 The second end of the output coupler (7) and the third polarization maintaining 2 2 The first end of the output coupler (8) is fused, and the second end is polarization-maintaining 2 2 The third end of the output coupler (7) and the third polarization maintaining 2 2 The fourth end of the output coupler (8) is fused, and the third polarization maintaining 2 2 The third end of the output coupler (8) is connected to the polarization maintaining 2. The first end of the optical fiber coupler (9) is fused; polarization maintaining 1 2 The second end of the optical fiber coupler (9) is connected to the third end of the single-mode wavelength division multiplexer (2); polarization maintaining 1 The third end of the fiber coupler (9) serves as the output port of the single-frequency fiber laser.

2. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 1 is characterized in that: The single-mode wavelength division multiplexer (2), the polarization-maintaining doped optical fiber (3), the polarization-maintaining optical fiber circulator (4), the first polarization-maintaining 2 2 output coupler (6), second polarization maintaining 2 2 output coupler (7), third polarization maintaining 2 2 output coupler (8), polarization maintaining 1 2 fiber couplers (9) together form a ring cavity of a tunable single-frequency fiber laser based on an "8"-shaped composite ring cavity filter.

3. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 2, characterized in that: First polarization maintaining 2 2 output coupler (6), second polarization maintaining 2 2 output coupler (7), third polarization maintaining 2 2 output couplers (8) form an "8"-shaped composite ring cavity filter, which acts as a comb filter to achieve mode selection.

4. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 3 is characterized in that: The "8"-shaped resonant cavity, the polarization-maintaining tunable fiber grating (5), and the ring cavity structure work together to realize single-frequency laser output.

5. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 3 is characterized in that: The comb filter composed of the "8"-shaped resonant cavity must meet two requirements: first, its free spectral range must be greater than 0.5 times the reflection bandwidth of the polarization-maintaining tunable fiber Bragg grating (5); second, its passband must be less than 2 times the longitudinal mode spacing of the ring cavity.

6. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 1, characterized in that: Semiconductor pump source (1), single-mode wavelength division multiplexer (2), polarization-maintaining doped fiber (3), polarization-maintaining fiber circulator (4), polarization-maintaining tunable fiber Bragg grating (5), first polarization-maintaining 2 2 output coupler (6), second polarization maintaining 2 2 output coupler (7), third polarization maintaining 2 2 Output coupler (8) polarization maintaining 1 2 The optical fiber couplers (9) are all polarization-maintaining structures and are all spliced ​​by slow axis alignment to achieve linearly polarized light output.

7. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 1, characterized in that: The semiconductor pump source (1) is a single-mode linearly polarized laser with a maximum output power of 600 mW at 976 nm.

8. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 1 is characterized in that: The first polarization-maintaining doped optical fiber (3) is a rare-earth doped single-mode glass optical fiber, the matrix materials of the core and cladding of the doped optical fiber are one or a combination of two of phosphate glass, germanate glass, tellurite glass, and silicate glass, and the rare-earth doping ions in the core of the doped optical fiber are erbium ions.

9. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 1, characterized in that: The polarization-maintaining tunable fiber Bragg grating (5) has a 3 dB bandwidth of 0.2 nm and a reflectivity of 90% within a tuning range of about 30 nm near 1560 nm, and a TEC temperature-controlled heat sink (10) is used to improve the anti-interference ability of the polarization-maintaining tunable fiber Bragg grating (5) to the environment, while further enhancing its wavelength tuning range by adjusting the temperature.

10. The tunable single-frequency fiber laser based on the "8"-shaped composite ring cavity filter according to claim 1, characterized in that: Polarization Maintaining 1 The splitting ratio between the third end and the second end of the optical fiber coupler (9) is 20:80.

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