8-shaped cavity mode-locking neodymium-doped femtosecond fiber laser

Abstract

The utility model relates to a fiber laser, and discloses an 8-shaped cavity mode-locking neodymium-doped femtosecond fiber laser, which comprises a 3 * 3 fiber coupler, a pumping source, a wavelength division multiplexer, a chirped fiber Bragg grating, a neodymium-doped fiber and a fiber isolator, a first end of the wavelength division multiplexer is connected with the pumping source, pump light generated by the pumping source is coupled into a resonant cavity, and a second end of the wavelength division multiplexer is connected with the fiber isolator. The second end of the wavelength division multiplexer is connected with the first end of the optical fiber coupler, and the third end of the wavelength division multiplexer is connected with the chirp fiber Bragg grating; the first end of the optical fiber coupler is sequentially connected with the wavelength division multiplexer and the chirp fiber Bragg grating to form a linear end, the second end and the third end of the optical fiber coupler are connected with the optical fiber isolator to form a main ring, and light is transmitted in the main ring in a one-way mode; the fourth end and the fifth end of the optical fiber coupler are connected with the neodymium-doped optical fiber to form a nonlinear amplification annular mirror; and the sixth end of the optical fiber coupler is an optical fiber output end. The device is compact in structure, stable and reliable.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of laser, especially relates to a 8 -letter cavity mode -locked doped neodymium femtosecond fiber laser. BACKGROUND

[0002] In recent years, two-photon microscopic imaging develops rapidly, and it is urgent to need a stable portable femtosecond laser working at 0.9 μm as a light source to improve imaging quality.In addition, by frequency doubling technology, about 460 nm pure blue light is obtained, and 0.9 μm is the exclusive waveband of neodymium ion, so it is of great significance to develop a stable and compact structure mode-locked doped neodymium femtosecond fiber laser.

[0003] The traditional 8 -letter cavity structure is usually based on 2x2 fiber coupler, and it may suffer from high mode-locking threshold.A typical method to overcome this problem is to introduce a non-reciprocal phase shifter in the resonant cavity.However, this scheme utilizes a Faraday rotator and a wave plate, so that the phase shift element is not a complete fused fiber component, which may be sensitive to the ambient temperature. SUMMARY

[0004] The utility model aims at overcoming the insufficient of prior art, provide a compact structure, stable and reliable 8 -letter cavity mode -locked doped neodymium femtosecond fiber laser.

[0005] The 8 -letter cavity mode -locked doped neodymium femtosecond fiber laser provided by the utility model, including 3x3 fiber coupler, pump source, wavelength division multiplexer, chirped fiber bragg grating, doped neodymium fiber and fiber isolator,

[0006] The pump source is used for generating pump light;

[0007] The chirped fiber bragg grating is used for reflecting laser, reflecting laser back into the resonant cavity, and adjusting the dispersion in the resonant cavity, so that the total dispersion of the whole resonant cavity is about zero;

[0008] The first end of the wavelength division multiplexer is connected with the pump source, the pump light generated by the pump source is coupled into the resonant cavity, the second end of the wavelength division multiplexer is connected with the first end of the 3x3 fiber coupler, and the third end of the wavelength division multiplexer is connected with the chirped fiber bragg grating;

[0009] The first end of the 3x3 fiber coupler is sequentially connected with the wavelength division multiplexer and the chirped fiber bragg grating to form a linear end, the linear end is used for inputting pump light and reflecting laser;The second end and the third end of the 3x3 fiber coupler are connected with the fiber isolator to form a main ring, and light is unidirectionally transmitted in the main ring;The fourth end and the fifth end of the 3x3 fiber coupler are connected with the doped neodymium fiber to form a nonlinear amplification ring mirror;The sixth end of the 3x3 fiber coupler is a fiber output end;

[0010] The neodymium-doped fiber is excited by the pump light to generate laser signal light.

[0011] Further, the 3x3 fiber coupler is a 3x3 polarization maintaining fiber coupler.

[0012] Further, the splitting ratios of the 3x3 fiber coupler are uniform.

[0013] Further, the fourth end, the fifth end and the sixth end of the 3x3 fiber coupler have a 120° phase difference.

[0014] Further, the neodymium-doped fiber is a polarization maintaining neodymium-doped fiber.

[0015] Further, the neodymium-doped fiber is arranged close to the 3x3 fiber coupler.

[0016] Further, the wavelength division multiplexer is a polarization maintaining wavelength division multiplexer.

[0017] Further, the 3x3 fiber coupler splits light into two paths, the clockwise transmitted light is first amplified by the neodymium-doped fiber, and then accumulates nonlinear phase shift in the nonlinear amplification ring mirror; the counterclockwise transmitted light first accumulates nonlinear phase shift, and then is amplified by the neodymium-doped fiber; the two paths of light accumulate different nonlinear phase shifts related to pulse intensity, and interfere at the 3x3 fiber coupler, so that the pulse center with higher energy is transmitted and the pulse edges with lower energy are reflected, thereby realizing mode locking.

[0018] Further, the two beams of light enter the linear end and the main ring after converging and interfering at the 3x3 fiber coupler; the fiber isolator in the main ring enables the input light to be unidirectionally transmitted in the main ring back to the 3x3 fiber coupler; the chirped fiber Bragg grating of the linear end reflects the light back to the 3x3 fiber coupler, while compensating for the dispersion to further narrow the pulse; the laser reflected and unidirectionally transmitted back to the 3x3 fiber coupler enters the nonlinear amplification ring mirror again, thereby reciprocating, and the laser is transmitted and oscillated in the resonant cavity, and finally output through the fiber output end of the 3x3 fiber coupler.

[0019] Further, the dispersion parameter of the chirped fiber Bragg grating can be selected to compensate for the total dispersion of the entire resonant cavity.

[0020] Compared with the prior art, the laser device has the advantages that: the laser device has compact structure, is stable and reliable, has low cost and high operation efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical scheme in the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings.

[0022] Figure 1 The present application provides a structure diagram of the 8-shaped cavity mode-locked neodymium-doped femtosecond fiber laser.

[0023] The meanings of the various reference numerals in the drawings are as follows:

[0024] 1-pump source, 2-wavelength division multiplexer, 3-chirped fiber Bragg grating, 4-3x3 fiber coupler, 5-neodymium-doped fiber, 6-fiber isolator. DETAILED DESCRIPTION

[0025] The technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0026] Please refer to Figure 1 The present application provides an 8-shaped cavity mode-locked neodymium-doped femtosecond fiber laser, which comprises a 3x3 fiber coupler 4, a pump source 1, a wavelength division multiplexer 2, a chirped fiber Bragg grating 3, a neodymium-doped fiber 5 and a fiber isolator 6.

[0027] The pump source 1 provides a pump light source for generating pump light to realize particle inversion of neodymium ions in the neodymium-doped fiber 5, which is a necessary condition for laser output.

[0028] The chirped fiber Bragg grating 3 serves as one cavity mirror of the resonant cavity for reflecting laser light back into the resonant cavity. The dispersion parameter of the chirped fiber Bragg grating 3 can be selected to compensate for the total dispersion of the entire resonant cavity, adjust the dispersion in the resonant cavity, and make the total dispersion of the entire resonant cavity approximately zero, so that the pulse is not broadened due to dispersion, and femtosecond pulse laser is output. The chirped fiber Bragg grating 3 can also define the oscillator starting wavelength, effectively suppress the four-level radiation transition in the neodymium-doped fiber 5, and realize stable three-level system operation.

[0029] The first end of the wavelength division multiplexer 2 is connected with the pump source 1 to couple the pump light generated by the pump source into the resonant cavity; the second end of the wavelength division multiplexer 2 is connected with the first end of the 3×3 optical fiber coupler 4 to transmit the pump light and the signal light; and the third end of the wavelength division multiplexer 2 is connected with the chirped fiber Bragg grating 3 to transmit the signal light.

[0030] The 3×3 optical fiber coupler 4 constitutes the entire eight-shaped cavity structure. The first end of the 3×3 optical fiber coupler 4 is connected with the wavelength division multiplexer 2 and the chirped fiber Bragg grating 3 in sequence to constitute a linear end, and the linear end is used for inputting the pump light and reflecting the laser light; the second end and the third end of the 3×3 optical fiber coupler 4 are connected with the optical fiber isolator 6 to constitute a main ring, and the light is transmitted in one direction in the main ring; the fourth end and the fifth end of the 3×3 optical fiber coupler 4 are connected with the neodymium-doped optical fiber 5 to constitute a nonlinear amplification ring mirror, and the nonlinear amplification ring mirror is a key structure for realizing mode locking; and the sixth end of the 3×3 optical fiber coupler 4 is an optical fiber output end. In the embodiment, the splitting ratios of the 3×3 optical fiber coupler are uniform.

[0031] Preferably, the fourth end, the fifth end and the sixth end of the 3×3 optical fiber coupler 4 have a phase difference of 120° with respect to each other, which provides a linear phase shift for the nonlinear amplification ring mirror mode locking.

[0032] The neodymium-doped optical fiber 5 is an optical fiber doped with rare earth ions neodymium ions, and the optical amplification is realized by using the gain mechanism caused by the neodymium ions in the optical fiber. The condition for realizing the optical amplification is the population inversion of the neodymium ions in the active optical fiber. When the neodymium-doped optical fiber is supplied with energy from the outside (referred to as excitation or pumping process) to make the neodymium ions in the optical fiber in a non-thermal equilibrium state, the population inversion can be realized, and thus the pumping process is a necessary condition for the optical amplification. The neodymium-doped optical fiber 5 is excited by the pump light to generate laser signal light. The neodymium-doped optical fiber 5 is arranged close to the 3×3 optical fiber coupler 4 to make the nonlinear phase shifts accumulated by the two light beams in the nonlinear amplification ring mirror loop different, which is more conducive to the mode locking.

[0033] The optical fiber isolator 6 enables the light to be transmitted in one direction in the main ring.

[0034] The laser of the embodiment adopts a full polarization maintaining structure, the 3×3 optical fiber coupler is a 3×3 polarization maintaining optical fiber coupler, the neodymium-doped optical fiber is a polarization maintaining neodymium-doped optical fiber, and the wavelength division multiplexer is a polarization maintaining wavelength division multiplexer.

[0035] The working principle of the laser provided by the embodiment is as follows: pump light is output from a pump source 1, coupled into a resonant cavity by a wavelength division multiplexer 2, enters a nonlinear amplification ring mirror through a fiber coupler 4 by a common port (second end) of the wavelength division multiplexer 2, and provides energy for a neodymium-doped optical fiber 5 to achieve the particle number inversion condition of laser output. This cavity-pumped mode is different from the direct pumping mode in which the pump source connected with the wavelength division multiplexer is directly fused with the neodymium-doped optical fiber, and is more effective in the laser in which the wavelength of the pump light is relatively close to that of the signal light. The light is divided into two paths by the fiber coupler 4, the clockwise transmitted light first passes through the neodymium-doped optical fiber 5 for amplification, and then accumulates a nonlinear phase shift in the nonlinear amplification ring mirror; the counterclockwise transmitted light first accumulates a nonlinear phase shift, and then passes through the neodymium-doped optical fiber 5 for amplification; the two paths of light accumulate different nonlinear phase shifts related to the pulse intensity, interfere at the fiber coupler 4, the pulse center with higher energy is transmitted and the pulse edges with lower energy are reflected, thereby realizing mode locking. In addition, the fiber coupler 4 provides an additional linear phase shift of 120°, which is more conducive to the self-starting of the nonlinear amplification ring mirror mode locking.

[0036] The two beams of light converge and interfere at the fiber coupler 4 and then enter the linear end and the main ring; the optical fiber isolator in the main ring enables the input light to be transmitted unidirectionally in the main ring back to the fiber coupler 4; the chirped fiber Bragg grating 3 in the linear end acts as a cavity mirror to reflect the light back to the fiber coupler 4, while compensating for the dispersion to further narrow the pulses; the laser reflected and unidirectionally transmitted back to the fiber coupler 4 enters the nonlinear amplification ring mirror again, thereby reciprocating, and the laser is transmitted and oscillated in the resonant cavity, and finally output through the fiber output end of the fiber coupler 4.

[0037] The 8-shaped cavity mode-locked neodymium-doped femtosecond fiber laser designed in the embodiment is more simple, stable and low in cost.

[0038] The 8-shaped cavity mode-locked neodymium-doped femtosecond fiber laser disclosed in the embodiment of the utility model is described in detail, the principle and implementation mode of the utility model are described by applying specific examples in this paper, and the description of the above embodiments is only used to help understand the core idea of the utility model; meanwhile, according to the idea of the utility model, the specific implementation mode and application range will be changed by the general technical personnel in the field, and according to the above, the content of the specification should not be understood as the limitation of the utility model.

Claims

1. An 8-word cavity mode-locked neodymium-doped femtosecond fiber laser characterized by, The 3×3 fiber coupler, the pump source, the wavelength division multiplexer, the chirped fiber Bragg grating, the neodymium-doped fiber and the fiber isolator, The pump source is used for generating pump light; The chirped fiber Bragg grating is used for reflecting laser light, reflecting the laser light back into the resonant cavity, and adjusting the dispersion in the resonant cavity so that the total dispersion of the entire resonant cavity is about zero; The first end of the wavelength division multiplexer is connected with the pump source, and the pump light generated by the pump source is coupled into the resonant cavity; the second end of the wavelength division multiplexer is connected with the first end of the 3×3 fiber coupler; and the third end of the wavelength division multiplexer is connected with the chirped fiber Bragg grating; The first end of the 3×3 fiber coupler is sequentially connected with the wavelength division multiplexer and the chirped fiber Bragg grating to form a linear end, and the linear end is used for inputting pump light and reflected laser light; the second end and the third end of the 3×3 fiber coupler are connected with the fiber isolator to form a main ring, and light is unidirectionally transmitted in the main ring; the fourth end and the fifth end of the 3×3 fiber coupler are connected with the neodymium-doped fiber to form a nonlinear amplification ring mirror; and the sixth end of the 3×3 fiber coupler is a fiber output end; The neodymium-doped fiber is excited by the pump light to generate laser signal light.

2. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The 3×3 fiber coupler is a 3×3 polarization maintaining fiber coupler.

3. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The splitting ratios of the 3×3 fiber coupler are uniform.

4. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The fourth end, the fifth end and the sixth end of the 3×3 fiber coupler have a phase difference of 120°.

5. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The neodymium-doped fiber is a polarization maintaining neodymium-doped fiber.

6. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The neodymium-doped fiber is arranged close to the 3×3 fiber coupler.

7. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The wavelength division multiplexer is a polarization maintaining wavelength division multiplexer.

8. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The 3×3 fiber coupler divides light into two paths, the clockwise transmitted light is first amplified by the neodymium-doped fiber, and then accumulates nonlinear phase shift in the nonlinear amplification ring mirror; The counterclockwise transmitted light first accumulates nonlinear phase shift, and then is amplified by the neodymium-doped fiber; The two paths of light accumulate different nonlinear phase shifts related to pulse intensity, interfere at the 3×3 fiber coupler, the pulse center with higher energy is transmitted, and the pulse edges with lower energy are reflected, thereby realizing mode locking.

9. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 8, wherein, The two beams of light converge and interfere at the 3×3 fiber coupler, and then enter the linear end and the main ring; the fiber isolator in the main ring enables the input light to be unidirectionally transmitted in the main ring back to the 3×3 fiber coupler; the chirped fiber Bragg grating in the linear end reflects the light back to the 3×3 fiber coupler, while compensating the dispersion to further narrow the pulse; the laser light reflected and unidirectionally transmitted back to the 3×3 fiber coupler enters the nonlinear amplification ring mirror again, and thus reciprocates, the laser light is transmitted and oscillated in the resonant cavity, and finally is output through the fiber output end of the 3×3 fiber coupler.

10. The figure-8 cavity mode-locked neodymium-doped femtosecond fiber laser of claim 1, wherein, The dispersion parameter of the chirped fiber Bragg grating can be selected to compensate the total dispersion of the entire resonant cavity.

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