A flat multi-wavelength vector vortex fiber laser

Abstract

This invention discloses a flat multi-wavelength vector vortex fiber laser, which utilizes a dual-injection recirculating frequency-shifting fiber cavity and a few-mode long-period fiber grating to achieve the generation of a flat multi-wavelength vector vortex beam. The laser mainly includes an injection seed source, a pump source, a wavelength division multiplexer, an erbium-doped fiber, an RF drive signal, a phase modulator, a few-mode long-period fiber grating, a partial mirror, a fiber delay unit, a fiber circulator, a polarization controller, and a fiber coupler. This laser uses a recirculating frequency-shifting fiber cavity to suppress mode competition in the erbium-doped fiber, achieving multi-wavelength oscillation. By injecting two seed lights externally, it generates complementary triangular spectral envelopes, achieving a flat multi-wavelength vector vortex beam output between the injected wavelengths. Since this laser does not use an interferometric filter as a multi-wavelength oscillation device, it exhibits excellent time stability.

Description

Technical Field

[0001] This invention belongs to the field of lasers, specifically relating to a flat multi-wavelength vector vortex fiber laser. Background Technology

[0002] Vector vortex beams, due to their unique axisymmetric polarization distribution, offer distinct advantages in laser processing, particle trapping, high-resolution imaging, and optical communication. Based on their polarization distribution, they can be categorized into radial vector vortex beams, angular vector vortex beams, and hybrid vector vortex beams. Due to the presence of polarization singularities, the intensity of a vector vortex beam exhibits a ring-like distribution. Multi-wavelength vector vortex beams, which simultaneously generate multiple wavelengths, have potential applications in optical communication and high-resolution imaging.

[0003] Most reported multi-wavelength vector vortex fiber lasers currently available only have a few wavelengths and exhibit poor power flatness, which is highly detrimental to many applications. Furthermore, the use of interferometric filters for multiple wavelength initiation and the strong mode competition in erbium-doped fibers further complicate the stability of these reported multi-wavelength vector vortex fiber lasers. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems described in the background art and to propose a flat multi-wavelength vector vortex fiber laser for generating a flat and stable multi-wavelength vector vortex beam. Furthermore, due to the broadband and efficient conversion efficiency of the few-mode long-period fiber grating, it achieves high-purity multi-wavelength vector vortex beam output.

[0005] The technical solution of this invention to solve its technical problem is as follows:

[0006] A flat multiwavelength vector vortex fiber laser includes a first injection seed source, a second injection seed source, a pump source, a wavelength division multiplexer, an erbium-doped fiber, a radio frequency drive signal, a phase modulator, a few-mode long-period fiber grating, a partial mirror, a fiber delayer, a fiber circulator, a first polarization controller, a second polarization controller, a third polarization controller, a first fiber coupler, and a second fiber coupler.

[0007] The first and second seed sources are injected into the recirculating frequency-shifting fiber optic ring cavity via the first and second fiber couplers, respectively. The pump source is connected to a wavelength division multiplexer and to one end of the erbium-doped fiber, providing pump energy to the erbium-doped fiber to achieve simultaneous oscillation of multiple wavelengths. The other end of the erbium-doped fiber is connected to the input end of the phase modulator, providing gain to the flat multi-wavelength vector vortex fiber laser by absorbing pump light. The radio frequency (RF) drive signal is connected to the electrodes of the phase modulator via an RF connection line, providing a sinusoidal drive signal. The output port of the phase modulator is connected to the first port of the fiber circulator. The second port of the fiber circulator is connected to a few-mode long-period fiber grating (LGF) via core-to-core fusion splicing. The LGF connects the LP (Long-Period Fiber) in the few-mode fiber. 01 Modular to LP 11 The system achieves high-purity vector vortex beam output by adjusting the first and second polarization controllers on both sides of the few-mode long-period fiber grating. The other end of the few-mode long-period fiber grating is connected to a partial mirror, through which part of the energy is output and the remaining energy is reflected back to the recirculating frequency-shifting fiber optic cavity. The third port of the fiber optic circulator is connected to a fiber delayer, and the other port of the fiber delayer is connected to a wavelength division multiplexer via a first and a second fiber coupler, forming a complete fiber optic loop.

[0008] Furthermore, the first and second injection seed sources are wavelength-tunable narrow-linewidth semiconductor lasers; when the injection wavelength is a resonant wavelength of the recirculating frequency-shifted fiber optic ring cavity, multiple amplifications and modulations of the seed light are achieved.

[0009] Furthermore, the pump source is a 980nm semiconductor pump laser.

[0010] Furthermore, the wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer, which multiplexes the pump light into a recirculating frequency-shifted fiber ring cavity to provide pump light for the erbium-doped fiber.

[0011] Furthermore, the radio frequency driving signal provides a sinusoidal driving signal to the phase modulator. The continuous light generates multiple sub-harmonics under the modulation of the sinusoidal driving signal, which is used to suppress mode competition in the erbium-doped fiber to achieve the generation of multiple wavelengths.

[0012] Furthermore, the phase modulator is a lithium niobate electro-optic modulator, which generates sub-harmonics under the modulation of the radio frequency drive signal to suppress mode competition in the erbium-doped fiber.

[0013] Furthermore, the few-mode long-period fiber grating is a long-period fiber grating etched on a two-mode fiber. The first polarization controller and the second polarization controller are used to control the polarization state of the input and output beams. When the grating period satisfies the phase-matching condition at the output wavelength, the LP in the fiber... 01 Forward coupling of the module is LP 11 Model; LP 11 The module is a degenerate module, denoted as HE. 21 even HE 21 odd TE 01 , and TM 01 Linear combination of precise moduli; TE 01 and TM 01 The precise modes correspond to the angular and radial vector vortex beams, respectively. The output of the angular and radial vector vortex beams is achieved by controlling the first polarization controller and the second polarization controller.

[0014] Furthermore, the partial reflector is made by depositing a thin metal film on the vertical end face of the two-mode fiber. Part of the light passes through the partial reflector as the output of the laser, and the other part is reflected back to the recirculating frequency-shifting fiber cavity to form a complete loop.

[0015] The fiber delayer is used to adjust the length of the recirculating frequency-shifting fiber optic cavity. By adjusting the length of the recirculating frequency-shifting fiber optic cavity, the free spectral width of the recirculating frequency-shifting fiber optic cavity is matched with the frequency of the radio frequency driving signal, so that the subharmonic generated by modulation exists stably in the recirculating frequency-shifting fiber optic cavity.

[0016] Furthermore, the fiber circulator is a 3-port fiber circulator, which connects the few-mode long-period fiber grating to the recirculating frequency-shifting fiber optic cavity, while also ensuring the unidirectional operation of the recirculating frequency-shifting fiber optic cavity.

[0017] The first, second, and third polarization controllers are three-ring polarization controllers, used to adjust the polarization direction of the beam in the fiber ring cavity to maximize the modulation efficiency of the phase modulation, as well as to input and output the polarization direction of the few-mode long-period fiber grating beam, and selectively output a vector vortex beam.

[0018] The first and second fiber couplers are 3dB fiber couplers, which couple the seed light emitted from the first and second injected seed sources into the recirculating frequency shift fiber ring cavity.

[0019] Furthermore, the synchronization condition is as follows: when the frequencies of the first and second injected seed sources are the resonant frequencies of the recirculating frequency-shifting fiber optic cavity, and the free spectrum width of the recirculating frequency-shifting fiber optic cavity is an integer multiple of the RF drive signal, the externally injected seed light and the subharmonics generated by the phase modulator modulation will exist stably in the recirculating frequency-shifting fiber optic cavity.

[0020] When only one of the first and second injection seed sources is injected and the above synchronization conditions are met, a triangular spectral envelope will be formed after multiple amplifications and modulations. The slope of the triangular envelope can be changed by altering the power of the first or second injection seed source and the pump power. The slope of the triangular spectral envelope increases with the increase of the power of the first or second injection seed source and decreases with the increase of the incident power.

[0021] When both the first and second seed sources are injected, two triangular envelopes are formed in the spectrum. By adjusting the wavelength interval, injection power, and pump power of the first and second seed sources, the two triangular envelopes complement each other, thereby producing a flat multi-wavelength output between the wavelengths of the first and second seed sources. Due to the broadband conversion characteristics of the few-mode long-period fiber grating, combined with the control of the first and second polarization controllers on both sides of the few-mode long-period fiber grating, high-purity multi-wavelength vector beam output is achieved.

[0022] Beneficial effects:

[0023] This invention utilizes a few-mode long-period fiber grating (FSB) as a mode conversion device. Benefiting from the FSB's broadband conversion characteristics, high-purity multi-wavelength vector vortex beams are generated. When the injected seed source frequency is the resonant frequency of the recirculating frequency-shifting fiber optic cavity, and the free spectral width of the recirculating frequency-shifting fiber optic cavity is an integer multiple of the RF drive signal, the externally injected seed light and the subharmonics generated by the phase modulator can stably exist within the recirculating frequency-shifting fiber optic cavity. When a single wavelength of seed light is injected, a triangular envelope spectrum is generated under the combined action of the erbium-doped fiber and the phase modulator. When two wavelengths of seed light are injected, two triangular envelopes are generated in the spectrum. By adjusting the interval between the injected wavelengths, the injection power, and the pump power, the two triangular envelopes can be made complementary, thereby generating a flat multi-wavelength output between the two injected wavelengths. Since no interferometric filter is used, the output multi-wavelength vector vortex beam exhibits excellent stability. Attached Figure Description

[0024] The accompanying drawings used in the proposed embodiments will be briefly described below to more clearly illustrate the technical solutions of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of the flat multi-wavelength vector vortex fiber laser of the present invention.

[0026] Figure 2 The following is an exemplary diagram of the output spectrum of a single seed source during injection as a function of injection power and pump power: (a) is the spectrum when the injection power is 0.5 mW and the pump power is 91.34 mW; (b) is the spectrum when the injection power is 1.5 mW and the pump power is 91.34 mW; (c) is the spectrum when the injection power is 2.5 mW and the pump power is 91.34 mW; (d) is the spectrum when the injection power is 4.3 mW and the pump power is 51.6 mW; (e) is the spectrum when the injection power is 4.3 mW and the pump power is 91.3 mW; and (f) is the spectrum when the injection power is 4.3 mW and the pump power is 172.5 mW.

[0027] Figure 3 The image shows a flat multi-wavelength spectrum generated between the injection wavelengths when two seed sources are injected, as exemplified by this invention.

[0028] Figure 4 The light intensity distribution and polarization detection diagram of the multi-wavelength vector vortex light generated by this invention are exemplary. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] like Figure 1As shown, a flat multiwavelength vector vortex fiber laser of the present invention includes a first injection seed source 1, a second injection seed source 2, a pump source 3, a wavelength division multiplexer 4, an erbium-doped fiber 5, an RF drive signal 6, a phase modulator 7, a fiber circulator 8, a first polarization controller 9, a few-mode long-period fiber grating 10, a second polarization controller 11, a partial reflector 12, a third polarization controller 13, a fiber delayer 14, a first fiber coupler 15, and a second fiber coupler 16. The first injection seed source 1 and the second injection seed source 2 are injected into the recirculating frequency-shifted fiber optic cavity through the first fiber coupler 15 and the second fiber coupler 16, respectively. The pump source 3 is connected to the wavelength division multiplexer 4 and connected to one end of the erbium-doped fiber 5 to provide pump energy to the erbium-doped fiber 5. The other end of the erbium-doped fiber 5 is connected to the input end of the phase modulator 7. The RF drive signal 6 is connected to the electrodes of the phase modulator 7 through an RF connection line to provide it with a sinusoidal drive signal. The output port of the phase modulator 7 is connected to the first port of the fiber circulator 8. The second port of the fiber optic circulator 8 is connected to the few-mode long-period fiber grating 10 via core-to-core fusion splicing. The few-mode long-period fiber grating 10 connects the LP in the few-mode fiber. 01 Modular to LP 11 By adjusting the first polarization controller 9 and the second polarization controller 11 on both sides of the few-mode long-period fiber grating 10, a high-purity vector vortex beam output can be achieved. The other end of the few-mode long-period fiber grating 10 is connected to a partial reflector 12. Part of the energy is output through the partial reflector 12, and the remaining energy is reflected back to the recirculating frequency-shifting fiber optic cavity. The third port of the fiber optic circulator 8 is connected to the fiber optic delayer 14, and the other port of the fiber optic delayer 14 is connected to the wavelength division multiplexer 4 via the first fiber coupler 15 and the second fiber coupler 16, forming a complete fiber optic loop.

[0031] The synchronization conditions for a flat multiwavelength vector vortex fiber laser are: the frequency of the injected seed source must be one of the resonant frequencies of the recirculating frequency-shifting fiber cavity (RFC), and the free spectral width of the RFC must be an integer multiple of the RF drive signal. When these synchronization conditions are met, the externally injected seed light and the subharmonics generated by the phase modulator can exist stably in the RFC. The injected RF frequency can be adjusted to the resonant frequency of the RFC by changing the wavelength of the seed source. The length of the RFC can be changed by adjusting the fiber delay, thus ensuring that the free spectral width of the RFC is an integer multiple of the RF drive signal.

[0032] When only one seed source is injected and the synchronization condition is met, a triangular spectral envelope will be formed after multiple amplifications and modulations. The slope of the triangular envelope can be changed by changing the power of the injected seed source and the pump power. Figure 2(a), (b), and (c) are the spectra when the pump power is 91.34 mW and the injection power is 0.5 mW, 1.5 mW, and 2.5 mW, respectively. The slope of the triangular spectral envelope increases with the increase of the injected seed source power. Figure 2 (d), (e), and (f) are the spectra when the injection power is 4.3 mW and the pump power is 51.6 mW, 91.3 mW, and 172.5 mW, respectively. The slope of the triangular spectral envelope decreases with increasing incident power. When two seed sources are injected, two triangular envelopes are formed in the spectrum. By adjusting the wavelength spacing, injection power, and pump power of the two injected seed sources, the two triangular envelopes can be made to complement each other, thereby producing a flat multi-wavelength output between the two injected wavelengths, such as... Figure 3 As shown. Due to the broadband conversion characteristics of few-mode long-period fiber gratings, and with careful control of the polarization controllers on both sides of the few-mode long-period fiber grating, high-purity multi-wavelength vector beam output can be achieved. Figure 4 The intensity diagrams are shown for the angular and radial vector vortex beams. To verify the polarization distribution of the beam, the intensity distribution of the vector vortex beam after passing through a linear polarizer was collected. The polarization direction of the polarizer is marked with a white arrow, which is consistent with the theoretical results.

[0033] The innovation of this invention lies in the following: a few-mode long-period fiber grating is used as a broadband mode conversion device to achieve the generation of a high-purity vector vortex beam; a recirculating frequency-shifting fiber ring cavity is used to suppress mode competition in erbium-doped fiber, achieving multi-wavelength oscillation; and two seed lights are injected externally to generate complementary triangular spectral envelopes, thereby achieving the generation of a flat multi-wavelength vector vortex beam between the injected wavelengths.

[0034] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims. Furthermore, this application is not intended to be limited to the specific embodiments of the processes, equipment, manufactures, and material compositions, means, methods, and steps described in the specification. Those skilled in the art will readily recognize from the disclosure of this invention those existing or hereafter discovered processes, equipment, manufactures, material compositions, means, methods, or steps that perform substantially the same function or achieve substantially the same result as those described herein in their respective embodiments according to the invention. Therefore, it is intended that the appended claims include such processes, equipment, manufactures, material compositions, means, methods, or steps within their scope.

Claims

1. A flat multi-wavelength vector vortex fiber laser, characterized in that: It includes a first injection seed source, a second injection seed source, a pump source, a wavelength division multiplexer, an erbium-doped fiber, a radio frequency drive signal, a phase modulator, a few-mode long-period fiber grating, a partial reflector, a fiber delayer, a fiber circulator, a first polarization controller, a second polarization controller, a third polarization controller, a first fiber coupler, and a second fiber coupler. The first and second seed sources are injected into the recirculating frequency-shifting fiber optic ring cavity via the first and second fiber couplers, respectively. The pump source is connected to a wavelength division multiplexer and to one end of the erbium-doped fiber, providing pump energy to the erbium-doped fiber to achieve simultaneous oscillation of multiple wavelengths. The other end of the erbium-doped fiber is connected to the input end of the phase modulator, providing gain to the flat multi-wavelength vector vortex fiber laser by absorbing pump light. The radio frequency (RF) drive signal is connected to the electrodes of the phase modulator via an RF connection line, providing a sinusoidal drive signal. The output port of the phase modulator is connected to the first port of the fiber circulator. The second port of the fiber circulator is connected to a few-mode long-period fiber grating (LGF) via core-to-core fusion splicing. The LGF connects the LP (Long-Period Fiber) in the few-mode fiber. 01 Modular to LP 11 The system achieves high-purity vector vortex beam output by adjusting the first and second polarization controllers on both sides of the few-mode long-period fiber grating. The other end of the few-mode long-period fiber grating is connected to a partial mirror, through which part of the energy is output and the remaining energy is reflected back to the recirculating frequency-shifting fiber optic cavity. The third port of the fiber circulator is connected to a fiber delayer, and the other port of the fiber delayer is connected to a wavelength division multiplexer via a first and second fiber coupler, forming a complete fiber optic loop. The synchronization conditions for a flat multiwavelength vector vortex fiber laser are: the frequency of the injected seed source is one of the resonant frequencies of the recirculating frequency-shifting fiber cavity, and the free spectrum width of the recirculating frequency-shifting fiber cavity is an integer multiple of the RF drive signal; when the synchronization conditions are met, the externally injected seed light and the subharmonics generated by the phase modulator can exist stably in the recirculating frequency-shifting fiber cavity.

2. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The first and second injection seed sources are wavelength-tunable narrow-linewidth semiconductor lasers; when the injection wavelength is a resonant wavelength of the recirculating frequency-shifted fiber optic ring cavity, multiple amplifications and modulations of the seed light are achieved.

3. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The pump source is a 980nm semiconductor pump laser.

4. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer, which multiplexes the pump light into a recirculating frequency-shifted fiber ring cavity to provide pump light for the erbium-doped fiber.

5. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The radio frequency drive signal provides a sinusoidal drive signal to the phase modulator. The continuous light generates multiple sub-harmonics under the modulation of the sinusoidal drive signal, which is used to suppress mode competition in the erbium-doped fiber to achieve the generation of multiple wavelengths.

6. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The phase modulator is a lithium niobate electro-optic modulator, which generates sub-harmonics under the modulation of the radio frequency drive signal to suppress mode competition in the erbium-doped fiber.

7. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The few-mode long-period fiber grating is a long-period fiber grating etched onto a two-mode fiber. The first polarization controller and the second polarization controller are used to control the polarization state of the input and output beams. When the grating period satisfies the phase-matching condition at the output wavelength, the LP in the fiber... 01 Forward coupling of the module is LP 11 Model; LP 11 The module is a degenerate module, denoted as HE. 21 even HE 21 odd TE 01 , and TM 01 Linear combination of precise moduli; TE 01 and TM 01 The precise modes correspond to the angular and radial vector vortex beams, respectively. The output of the angular and radial vector vortex beams is achieved by controlling the first polarization controller and the second polarization controller.

8. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The partial reflector is made by depositing a thin metal film on the vertical end face of the two-mode fiber. Part of the light passes through the partial reflector as the output of the laser, and the other part is reflected back to the recirculating frequency-shifted fiber cavity to form a complete loop. The fiber delayer is used to adjust the length of the recirculating frequency-shifting fiber optic cavity. By adjusting the length of the recirculating frequency-shifting fiber optic cavity, the free spectral width of the recirculating frequency-shifting fiber optic cavity is matched with the frequency of the radio frequency driving signal, so that the subharmonic generated by modulation exists stably in the recirculating frequency-shifting fiber optic cavity.

9. A flat multi-wavelength vector vortex fiber laser according to claim 1, characterized in that: The fiber circulator is a 3-port fiber circulator that connects the few-mode long-period fiber grating to the recirculating frequency-shifting fiber circulator cavity, while also ensuring the unidirectional operation of the recirculating frequency-shifting fiber circulator cavity. The first, second, and third polarization controllers are three-ring polarization controllers, used to adjust the polarization direction of the beam in the recirculating frequency-shifting fiber ring cavity to maximize the modulation efficiency of the phase modulation, and to input and output the polarization direction of the few-mode long-period fiber grating beam, selectively outputting a vector vortex beam. The first and second fiber couplers are 3dB fiber couplers, which couple the seed light emitted from the first and second injected seed sources into the recirculating frequency shift fiber ring cavity.

10. A flat multi-wavelength vector vortex fiber laser according to any one of claims 1-9, characterized in that: The synchronization condition is as follows: when the frequencies of the first and second injected seed sources are the resonant frequencies of the recirculating frequency-shifting fiber optic cavity, and the free spectrum width of the recirculating frequency-shifting fiber optic cavity is an integer multiple of the RF drive signal, the externally injected seed light and the sub-harmonics generated by the phase modulator modulation will exist stably in the recirculating frequency-shifting fiber optic cavity. When only one of the first and second injection seed sources is injected and the above synchronization conditions are met, a triangular spectral envelope will be formed after multiple amplifications and modulations. The slope of the triangular envelope can be changed by altering the power of the first or second injection seed source and the pump power. The slope of the triangular spectral envelope increases with the increase of the power of the first or second injection seed source and decreases with the increase of the incident power. When both the first and second seed sources are injected, two triangular envelopes are formed in the spectrum. By adjusting the wavelength interval, injection power, and pump power of the first and second seed sources, the two triangular envelopes complement each other, thereby producing a flat multi-wavelength output between the wavelengths of the first and second seed sources. Due to the broadband conversion characteristics of the few-mode long-period fiber grating, combined with the control of the first and second polarization controllers on both sides of the few-mode long-period fiber grating, high-purity multi-wavelength vector beam output is achieved.

Images