Phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing

Abstract

The present invention discloses a phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser is composed of a dual-wavelength single-frequency fiber laser seed source, a laser power amplifier, a nonlinear medium, and a filtering device. The dual-wavelength single-frequency fiber laser seed source is used to generate a dual-wavelength laser with high phase correlation; the laser power amplifier is used to amplify the power of the laser; the nonlinear medium is used to stimulate the four-wave mixing effect, thereby generating a multi-wavelength single-frequency fiber laser; and the filtering device is used to filter out a single wavelength of the multi-wavelength laser, the linewidth of which is measured and analyzed by a linewidth test system. The present invention has the characteristics of an all-fiber structure, a simple device, and strong resistance to environmental interference.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber lasers, in particular to a phase-correlated narrow-linewidth multi-wavelength single-frequency optical fiber laser based on four-wave mixing. Background Art

[0002] Multi-wavelength, single-frequency fiber lasers offer advantages such as narrow linewidth, low noise, and good coherence, and have broad application prospects in fiber-optic sensing, microwave photonics, terahertz technology, Doppler lidar, and other fields. In these applications, compared to arrays consisting of multiple lasers with different wavelengths, multi-wavelength, single-frequency fiber lasers are easy to integrate, compact, and low-cost, making them ideal detection light sources.

[0003] The main methods for preparing multi-wavelength lasers include: (1) generating multiple single-wavelength lasers from different resonant cavities, and then directly obtaining multi-wavelength laser output after beam combining; (2) generating multi-wavelength lasers through nonlinear effects, such as introducing a highly nonlinear optical fiber into the resonant cavity and using four-wave mixing to generate Stokes and anti-Stokes light to form multi-wavelength laser output; (3) inserting wavelength-selective elements into the resonant cavity to achieve multi-wavelength laser output, such as Fabry-Perot filters and Sagnac rings. Among them, the multi-wavelength lasers prepared based on nonlinear effects have higher phase correlation, narrower linewidths at each wavelength, and lower noise.

[0004] Dual-wavelength single-frequency fiber lasers and cascaded four-wave mixing based on high phase correlation are ideal ways to prepare phase-correlated narrow-linewidth multi-wavelength single-frequency fiber lasers. The generation of cascaded four-wave mixing requires strict phase matching conditions, and will also transfer the phase jitter of the dual-wavelength laser (pump light) to the high-order Stokes and anti-Stokes light, resulting in degradation of its laser linewidth and noise. Improving the phase correlation of the dual-wavelength laser will alleviate this degradation trend. Ideally, each wavelength component of the multi-wavelength laser can maintain the phase noise, linewidth, and coherence parameters of the pump light, thereby preparing a phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser.

[0005] In 2017, the University of Electronic Science and Technology of China disclosed a precisely tunable Brillouin multi-wavelength fiber laser (CN107768973A), which inserted a Leo filter as a wavelength selection element into the ring resonator to generate multi-wavelength lasers, and further increased the number of multi-wavelength lasers through highly nonlinear optical fibers and laser power amplifiers. However, the ring cavity structure is susceptible to interference from environmental factors such as vibration, which limits its application scenarios. In 2019, South China University of Technology disclosed a narrow-linewidth fiber laser (CN110544864A) based on frequency-modulated single-frequency seed source and four-wave mixing. The dual-wavelength single-frequency seed source is split into two different wavelengths by a polarization beam splitter, and its power intensity is increased by a laser power amplifier respectively. After combining, it enters the nonlinear optical fiber and generates a new frequency through the four-wave mixing effect. The above-mentioned prior art device has a complex structure and is difficult to control. After beam splitting, transmission through different optical fibers will reduce the phase correlation of the multi-wavelength laser, and the linewidth is prone to broadening. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and discloses a phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing.

[0007] The purpose of the present invention is achieved by at least one of the following technical solutions.

[0008] A phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing, comprising a highly phase-correlated dual-wavelength single-frequency fiber laser seed source, a laser power amplifier, a nonlinear medium, and a filter device connected in sequence;

[0009] The high phase correlation dual-wavelength single-frequency fiber laser seed source includes a high-reflectivity Bragg fiber grating, a multi-component highly doped gain fiber, a polarization-maintaining low-reflectivity Bragg fiber grating, a wavelength division multiplexer and a semiconductor laser pump source connected in sequence;

[0010] Among them, a high-reflectivity Bragg fiber grating, a multi-component highly doped gain fiber, and a polarization-maintaining low-reflectivity Bragg fiber grating constitute the resonant cavity; the seed laser generated by the resonant cavity is output through a wavelength division multiplexer, and a semiconductor laser pump source is injected into the resonant cavity through the wavelength division multiplexer to provide the pump light of the dual-wavelength fiber laser seed source. The effective cavity length corresponding to the fast and slow axis light of the dual wavelengths is basically the same, so that the two wavelength components separated by filtering have similar optical characteristic parameters, such as linewidth, phase noise, relative intensity noise, etc. Since the dual-wavelength laser is generated by the same resonant cavity and the equivalent cavity length is similar, the phases of the fast and slow axis light are highly correlated.

[0011] A high phase-correlation dual-wavelength single-frequency fiber laser seed source generates a dual-wavelength laser that is input into a laser power amplifier. After being amplified by the laser power amplifier to increase the output power, the dual-wavelength laser is injected into a nonlinear medium to generate cascade four-wave mixing, generating Stokes and anti-Stokes light, and producing a multi-wavelength single-frequency fiber laser output. The multi-wavelength single-frequency fiber laser is filtered out by a filtering device to obtain a single wavelength of the multi-wavelength laser, namely, each frequency component in the four-wave mixing, and its linewidth is measured and analyzed by a linewidth test system.

[0012] Furthermore, a semiconductor cooler is provided below the resonant cavity, and the temperature of the resonant cavity is controlled by the semiconductor cooler.

[0013] Furthermore, the high-reflectivity Bragg fiber grating is written once on a single-mode optical fiber and has a reflection peak, a reflectivity of >90%, a reflection bandwidth of >1nm, and a central wavelength that can be located at 1.0μm, 1.5μm or 2.0μm, covering the two reflection peaks of the polarization-maintaining low-reflectivity Bragg fiber grating.

[0014] Furthermore, the multi-component high-doped gain optical fiber doped ion components include lanthanide ions or one or more transition metal ions, and the doping concentration of the luminescent ions is greater than 6×10 19 ions / cm 3 , length is 5mm~15cm, and the core glass component is one or more of phosphate, silicate, germanate, fluoride, and quartz glass.

[0015] Furthermore, the polarization-maintaining fiber used in the polarization-maintaining low-reflectivity Bragg fiber grating can obtain two reflection peaks of different wavelengths in one writing due to the degeneration of the polarization eigenmode, corresponding to the fast and slow axes of the polarization-maintaining fiber, with a wavelength interval of 0.2 to 0.6 nm.

[0016] Furthermore, the two reflection peaks corresponding to the fast axis and the slow axis have the same reflectivity, the reflectivity is greater than 60%, the reflection bandwidth is less than 0.2 nm, and the central wavelength can be located at 1.0 μm, 1.5 μm or 2.0 μm.

[0017] Furthermore, the nonlinear medium may be a highly nonlinear optical fiber, a photonic crystal optical fiber, a semiconductor optical amplifier, a high-Q optical microcavity or a bulk material, for generating nonlinear gain.

[0018] Furthermore, in the filtering device, a multi-wavelength laser is input into the optical circulator from the first port a, reflected and filtered by a narrow-band high-reflectivity fiber Bragg grating at the second port b, and then output from the third port c to obtain a dual-wavelength single-frequency fiber laser seed source or a single wavelength component of a narrow-linewidth multi-wavelength single-frequency fiber laser.

[0019] Furthermore, the narrowband high-reflectivity fiber Bragg grating uses fiber Bragg gratings with multiple different central wavelengths, which are respectively fused on the second port b of the optical circulator to accurately filter out a single wavelength component, have a reflection peak, a reflectivity of >99%, a reflection bandwidth of <0.4nm, and the central wavelength can be 1.0μm, 1.5μm or 2.0μm.

[0020] Furthermore, the phase correlation coefficient ρ of the fast and slow axis light of the wavelength single-frequency fiber laser seed source is characterized by the broadening degree of the Stokes and anti-Stokes light generated by four-wave mixing, and the specific form is given by the following formula:

[0021]

[0022] Where Δv Pump-1 , Δv Pump-2 are the line widths of fast and slow axis light, Δv Stokes , Δv anti-Stokes are the linewidths of Stokes and anti-Stokes light generated by four-wave mixing;

[0023] When the absolute value of the phase correlation coefficient ρ approaches 1, it indicates that the dual-wavelength laser has a high phase correlation; when the absolute value of the phase correlation coefficient ρ approaches 0, it indicates that the dual-wavelength laser has a low phase correlation.

[0024] Compared with the prior art, the technical effects of the present invention are:

[0025] The fast and slow axis lights of the dual-wavelength single-frequency fiber laser seed source have a high phase correlation. After their power is amplified, they are injected into a nonlinear medium and produce a four-wave mixing effect, generating Stokes and anti-Stokes lights with significantly smaller linewidth broadening, forming a phase-correlated, narrow-linewidth multi-wavelength single-frequency fiber laser output. It has the characteristics of an all-fiber structure, simple device and strong resistance to environmental interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of the phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing of the present invention.

[0027] Figure 2 This is a principle diagram of linewidth broadening in the frequency domain of a phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing in the present invention.

[0028] Figure 3 Schematic diagram of the laser linewidth measurement results of four-wave mixing pump light, Stokes light and anti-Stokes light in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following description, combined with specific illustrations, illustrates the technical solutions for a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein. Any similar generalizations made by persons of ordinary skill in the art without inventive effort are also within the scope of protection of the present invention.

[0030] The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this specification. As used in one or more embodiments of this specification and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0031] Example:

[0032] Phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing, such as Figure 1 As shown, it includes a high phase correlation dual-wavelength single-frequency fiber laser seed source, a laser power amplifier 7, a nonlinear medium 8 and a filtering device connected in sequence;

[0033] The high phase correlation dual-wavelength single-frequency fiber laser seed source comprises a high reflectivity Bragg fiber grating 1, a multi-component highly doped gain fiber 2, a polarization-maintaining low reflectivity Bragg fiber grating 3, a wavelength division multiplexer 5 and a semiconductor laser pump source 6 connected in sequence;

[0034] The resonant cavity comprises a high-reflectivity fiber Bragg grating (FBG) 1, a multi-component, highly doped gain fiber 2, and a polarization-maintaining, low-reflectivity fiber Bragg grating (FBG) 3. The resonant cavity generates a seed laser that is output via a wavelength division multiplexer (WDM) 5. A semiconductor laser pump source 6 is injected into the resonant cavity via the WDM 5, providing pump light for the dual-wavelength fiber laser seed source. The effective cavity lengths corresponding to the fast and slow axis light of the dual wavelengths are essentially the same, resulting in the two wavelength components separated by filtering having similar optical characteristic parameters, such as linewidth, phase noise, and relative intensity noise. Because the dual-wavelength lasers are generated by the same resonant cavity with similar equivalent cavity lengths, the phases of the fast and slow axis light are highly correlated.

[0035] A high phase-correlation dual-wavelength single-frequency fiber laser seed source generates a dual-wavelength laser that is input into a laser power amplifier 7. After being amplified by the laser power amplifier 7 to increase the output power, the dual-wavelength laser is injected into a nonlinear medium 8 to cause cascade four-wave mixing, generating Stokes and anti-Stokes light, and generating a multi-wavelength single-frequency fiber laser output. The multi-wavelength single-frequency fiber laser is filtered out by a filtering device to obtain a single wavelength of the multi-wavelength laser, namely, each frequency component in the four-wave mixing, and its linewidth is measured and analyzed by a linewidth test system.

[0036] In one embodiment, Figure 1 As shown, a semiconductor cooler 4 is provided below the resonant cavity, and the temperature of the resonant cavity is controlled by the semiconductor cooler 4 .

[0037] In one embodiment, Figure 1 As shown, in the filtering device, the multi-wavelength laser is input into the circulator from the first port a of the optical circulator 9, reflected and filtered by the narrow-band high-reflectivity fiber Bragg grating 10 at the second port b, and then output from the third port c to obtain a dual-wavelength single-frequency fiber laser seed source or a single wavelength component of a narrow-linewidth multi-wavelength single-frequency fiber laser.

[0038] like Figure 2 As shown in Figure 1, the principle of a phase-correlated, narrow-linewidth, multi-wavelength, single-frequency fiber laser based on four-wave mixing (FWM) is as follows: A dual-wavelength, single-frequency fiber laser is injected into a nonlinear medium as pump light, causing four-wave mixing (FWM) and generating Stokes and anti-Stokes light. The pump light's phase jitter is then transferred to the Stokes and anti-Stokes light. If the phase jitter between the two-wavelength lasers is uncorrelated, the phase jitter transferred to the Stokes and anti-Stokes light during FWM will be further aggravated. If the phase jitter between the two-wavelength lasers is correlated, the phase jitter transferred to the Stokes and anti-Stokes light during FWM will not be significantly aggravated, and the linewidth broadening will be significantly reduced. Ideally, the absolute value of the phase correlation coefficient ρ is equal to 1, and the Stokes and anti-Stokes light linewidths will not be broadened.

[0039] The specific implementation of the example is described below with reference to specific parameters. First, in one embodiment, a dual-wavelength single-frequency fiber laser seed source is constructed based on the birefringence characteristics of the polarization-maintaining fiber Bragg grating. The resonant cavity is composed of a broadband high-reflectivity Bragg fiber grating 1, a 20mm multi-component high-doped gain fiber 2, i.e., a high-gain erbium-ytterbium co-doped phosphate fiber, and a narrowband polarization-maintaining low-reflectivity Bragg fiber grating 3. The resonant cavity is placed in an aluminum tank, and the temperature of the resonant cavity is precisely controlled by a semiconductor cooler 4 to prevent mode hopping. The 3dB reflection bandwidth of the broadband high-reflectivity Bragg fiber grating 1 is 2nm, and the reflectivity is greater than 99%; the 3dB reflection bandwidth of the narrowband polarization-maintaining low-reflectivity Bragg fiber grating 3 is 0.08nm, and the reflectivity is greater than 60%. The pigtail of the broadband high-reflectivity Bragg fiber grating 1 is cut at an 8° angle to prevent scattered light from affecting the stability of the laser. Polarization-maintaining wavelength division multiplexer 5 operates in dual-axis mode, with backward pumping used for the resonant cavity. Semiconductor laser pump source 6 utilizes a 976nm single-mode semiconductor laser with a maximum output power of 250mW. The dual-wavelength laser is amplified to 120mW by laser power amplifier 7, an erbium-doped fiber amplifier, and four-wave mixing (FWM) occurs in a 250m-long nonlinear medium 8, a highly nonlinear fiber. The fast and slow axis beams of the dual-wavelength laser serve as pump beams (Pump-1 and Pump-2) for FWM, generating a pair of Stokes and anti-Stokes beams, as shown in Figure 1. Figure 2 To filter out a single frequency component for analysis, a narrowband, high-reflectivity fiber Bragg grating (FBG) 10 with a 3dB bandwidth of 0.2nm and a reflectivity greater than 99% is fused to the second port b of the circulator 9. The filtered single frequency component is input into the linewidth measurement system through the third port c, where the laser linewidth is analyzed using the delayed self-heterodyne method. The delay fiber length is 50km.

[0040] The dual-wavelength laser and the multi-wavelength laser generated by four-wave mixing are input into the circulator from the first port a of the optical circulator 9. After being reflected and filtered by the narrow-band high-reflectivity fiber Bragg grating 10 at the second port b, they are input into the linewidth test system from the third port c. The linewidth measurement results of each frequency component are shown in the figure below. Figure 3 The results show that the line widths of the pump light, Stokes light and anti-Stokes light have similar line shapes. The results of Lorentz fitting show that the fast and slow axis line widths of the pump light are converted into 3dB line widths of 0.84kHz and 0.89kHz respectively, as shown in Figure 3 The generated Stokes and anti-Stokes light widths are only slightly broadened, both at 1.4kHz, as shown in Figures a and b. Figure 3As shown in Figures c and d, these results demonstrate that the multi-wavelength laser generated by four-wave mixing still exhibits narrow linewidth characteristics. The calculated phase correlation coefficient ρ between the fast and slow axis beams of the dual-wavelength, single-frequency fiber laser seed source is 0.81, indicating that the dual-wavelength, single-frequency fiber laser seed source has high phase correlation, and the multi-wavelength laser generated by four-wave mixing also exhibits good phase correlation.

[0041] The preferred embodiments of the present application disclosed above are intended only to facilitate understanding of the present invention and its core concepts. Those skilled in the art will appreciate that specific application scenarios and implementations may vary based on the principles of the present invention, and this description should not be construed as limiting the present invention. The present invention is intended to be limited only by the claims and their full scope and equivalents.

Claims

1. Phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing, characterized by: It includes a high phase correlation dual-wavelength single-frequency fiber laser seed source, a laser power amplifier (7), a nonlinear medium (8) and a filtering device connected in sequence; A high phase correlation dual-wavelength single-frequency fiber laser seed source comprises a high reflectivity Bragg fiber grating (1), a multi-component highly doped gain fiber (2), a polarization-maintaining low reflectivity Bragg fiber grating (3), a wavelength division multiplexer (5), and a semiconductor laser pump source (6) connected in sequence; Wherein, a high reflectivity Bragg fiber grating (1), a multi-component high-doped gain fiber (2) and a polarization-maintaining low reflectivity Bragg fiber grating (3) constitute a resonant cavity; the resonant cavity generates a seed laser which is outputted through a wavelength division multiplexer (5), and a semiconductor laser pump source (6) is injected into the resonant cavity through the wavelength division multiplexer (5) to provide pump light of a dual-wavelength fiber laser seed source. Since the dual-wavelength lasers are generated by the same resonant cavity and have similar equivalent cavity lengths, the phases of the fast-axis light and the slow-axis light have a high correlation; A high phase correlation dual-wavelength single-frequency fiber laser seed source generates a dual-wavelength laser which is input into a laser power amplifier (7); the dual-wavelength laser is amplified by the laser power amplifier (7) to increase the output power and then injected into a nonlinear medium (8) to generate cascade four-wave mixing, thereby generating Stokes and anti-Stokes light and generating a multi-wavelength single-frequency fiber laser output; the multi-wavelength single-frequency fiber laser is filtered out by a filtering device to obtain a single wavelength of the multi-wavelength laser, i.e., each frequency component in the four-wave mixing, and its line width is measured and analyzed by a line width test system.

2. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: A semiconductor cooler (4) is provided below the resonant cavity, and the temperature of the resonant cavity is controlled by the semiconductor cooler (4).

3. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: The high-reflectivity Bragg fiber grating (1) is written once on a single-mode optical fiber and has a reflection peak with a reflectivity greater than 90%, a reflection bandwidth greater than 1 nm, a central wavelength at 1.0 μm, 1.5 μm or 2.0 μm, and covers the two reflection peaks of the polarization-maintaining low-reflectivity Bragg fiber grating (3).

4. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: The multi-component high-doped gain optical fiber (2) is doped with ion components including lanthanide ions or one or more transition metal ions, and the doping concentration of the luminescent ions is greater than 6×10 19 ions / cm 3 , length is 5 mm~15 cm, and the core glass component is one or more of phosphate, silicate, germanate, fluoride, and quartz glass.

5. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: The polarization-maintaining optical fiber used in the polarization-maintaining low-reflectivity Bragg fiber grating (3) can obtain two reflection peaks of different wavelengths by one writing due to the degeneration of the polarization eigenmode, corresponding to the fast and slow axes of the polarization-maintaining optical fiber, with a wavelength interval of 0.2-0.6 nm.

6. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 5, characterized in that: The two reflection peaks corresponding to the fast and slow axes have the same reflectivity, the reflectivity is >60%, the reflection bandwidth is <0.2 nm, and the central wavelength is at 1.0 μm, 1.5 μm or 2.0 μm.

7. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: The nonlinear medium (8) adopts a high nonlinear optical fiber, a photonic crystal optical fiber, a semiconductor optical amplifier, a high Q value optical microcavity or a bulk material, and is used to generate nonlinear gain.

8. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: In the filtering device, a multi-wavelength laser is input into the optical circulator (9) from a first port a thereof, is reflected and filtered by a narrowband high-reflectivity fiber grating (10) at a second port b, and is output from a third port c to obtain a dual-wavelength single-frequency fiber laser seed source or a single wavelength component of a narrow-linewidth multi-wavelength single-frequency fiber laser.

9. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 8, characterized in that: The narrowband high-reflectivity fiber Bragg grating (10) uses a variety of fiber Bragg gratings with different central wavelengths, which are respectively fused onto the second port b of the optical circulator (9) to accurately filter out a single wavelength component, have a reflection peak, a reflectivity greater than 99%, a reflection bandwidth less than 0.4 nm, and a central wavelength at 1.0 μm, 1.5 μm or 2.0 μm.

10. The phase-correlated narrow-linewidth multi-wavelength single-frequency fiber laser based on four-wave mixing according to claim 1, characterized in that: Phase correlation coefficient of fast-axis and slow-axis light of wavelength single-frequency fiber laser seed source ρ It is characterized by the broadening degree of the Stokes and anti-Stokes light generated by four-wave mixing, and the specific form is given by the following formula: (1) Among them, ∆ v Pump-1 ,∆ v Pump-2 are the line widths of the fast and slow axis light, ∆ v Stokes ,∆ v anti-Stokes are the linewidths of Stokes and anti-Stokes light generated by four-wave mixing; When the phase correlation coefficient ρ When the absolute value of approaches 1, it indicates that the dual-wavelength laser has a high phase correlation; when the phase correlation coefficient ρ When the absolute value of approaches 0, it indicates that the dual-wavelength laser has low phase correlation.

Images