WO2019056722A1

WO2019056722A1 - Fiber laser

Info

Publication number: WO2019056722A1
Application number: PCT/CN2018/080584
Authority: WO
Inventors: 李程; 郑渚; 杨彬; 徐飞; 丁庆
Original assignee: 深圳市太赫兹科技创新研究院; 深圳市太赫兹科技创新研究院有限公司
Priority date: 2017-09-19
Filing date: 2018-03-27
Publication date: 2019-03-28
Also published as: CN107453198A

Abstract

A fiber laser comprises a pump source (11), an annular optical path (10), a tuning device, and a current adjustment device. The pump source provides pump light for a resonant optical path. The tuning device is disposed on the annular optical path. The tuning device comprises a graphene film (263) and a first optical fiber (264), and the graphene film covers an end surface of a fiber core at one end of the first optical fiber. The current adjustment device is connected to the graphene film, and the current adjustment device is used to electrify the graphene film and adjust the current passing through the graphene film. By adjusting the current passing through the graphene film, the temperature of the graphene film is adjustable, and the modulation depth of the tuning device with respect to transmitted laser passing through the tuning device is modified, such that the performance of the fiber laser is adjustable. In addition, because the tuning device is an optical fiber device integrated by the first optical fiber and the graphene film, optical signal transmission loss via the tuning device is low, such that tuning performance of the fiber laser is improved.

Description

fiber-optic laser

Technical field

The present invention relates to the field of laser technology, and in particular to a fiber laser.

Background technique

At present, after the fiber laser is manufactured, the pulse laser outputted by the fiber laser is also determined. When performing processes such as microfabrication, the laser fiber of different pulse widths is required to perform operations such as cutting, thereby making the current fiber. The laser cannot meet the needs of the corresponding process.

Summary of the invention

Based on this, it is necessary to provide a fiber laser capable of outputting pulsed lasers of different pulse widths to meet the demand for various pulse width pulsed lasers in processes such as microfabrication.

A fiber laser, comprising a pump source and an annular light path, further comprising a doped fiber disposed on the annular optical path, a polarization control element, and a saturable absorber;

The pump light emitted by the pump source excites the doped fiber to radiate photons to form spontaneous radiation;

The saturable absorber has polarization characteristics for converting the received continuous laser light into a pulsed laser;

The polarization control element is configured to control a polarization state of light of the annular optical path to adjust a state of a pulsed laser light output by the annular optical path;

Among them, the pulse widths of the pulsed lasers in different states are different.

In the above fiber laser, the feedback state of the ring optical path is adjusted by the polarization control element based on the saturable absorber having the polarization characteristic disposed on the ring optical path, so that the fiber laser can output pulse lasers of different states, thereby satisfying, for example, fine The need for a variety of pulse width pulsed lasers in processes such as machining.

In one embodiment, the fiber laser may further include a first coupling element disposed on the annular optical path;

The first coupling element is configured to split a received pulsed laser into a feedback laser beam for feeding back to the doped fiber, and an outgoing laser beam for use as the fiber The output of the laser.

In one embodiment, the fiber laser may further include a second coupling element disposed on the annular optical path;

The second coupling element is configured to combine the received pump light with the feedback laser beam to form a combined optical signal and transmit the combined optical signal to the doped fiber.

In one embodiment, the fiber laser described above may further include an isolation element disposed on the annular optical path:

The isolation element is disposed on an optical path between the doped fiber and the saturable absorber to unidirectionally transmit the spontaneous radiation emitted by the doped fiber to the saturable absorber.

In one of the embodiments, the first coupling element is a coupler, the second coupling element is a wavelength division multiplexer, and the isolation element is a polarization independent fiber optic isolator.

In one embodiment, the fiber laser described above may further include a single mode fiber disposed on the annular optical path for enhancing a nonlinear polarization rotation effect of the annular optical path.

In one of these embodiments, the doped fiber is an erbium doped gain fiber.

In one embodiment, the polarization control element includes a first polarization controller and a second polarization controller, the saturable absorber being disposed at the first polarization controller and the second polarization controller The light path between.

In one embodiment, the saturable absorber in the fiber laser of any of the above may comprise:

a support rod, the outer surface of the support rod is covered with a graphene film;

A micro-nano fiber that is non-overlapping around the surface of the graphene film.

In one embodiment, the pulsed laser light output by the annular optical path in the fiber laser according to any one of the above items may include a Q-switched pulsed laser and a rectangular-wave mode-locked pulsed laser.

DRAWINGS

1 is a block diagram of a fiber laser in an embodiment;

2 is a schematic structural view of a fiber laser in another embodiment;

Figure 3 is a schematic view showing the structure of the saturable absorber of Figure 2.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

1 is a block diagram of a fiber laser in an embodiment. As shown in FIG. 1, a fiber laser may include an annular optical path 10 and a pump source 11, and a doped fiber 13 disposed on the annular optical path 10, a saturable absorber 15 having polarization characteristics, and a polarization control element 16 and the like. component. The pump source 11 can be used to emit pump light into the annular optical path 10. The doped optical fiber 13 is excited by the pump light emitted by the pump source 11 to form a spontaneous radiation, that is, under the action of the pump light. The energy level of the rare earth ions in the hybrid optical fiber 13 is increased, and when the high-energy rare earth ions transition to the low-energy state, the photons are radiated outward, and then spontaneous radiation can be formed, and a continuous laser can be formed through the action of the resonant cavity; The saturable absorber 15 passes the mode-locking operation of the continuous laser light emitted by the doped fiber 13 to form a pulsed laser, and the polarization control element 16 can control the feedback state of the ring optical path 10, and the ring-shaped optical path in the positive feedback state or the negative feedback state. 10 The state of the pulsed laser light outputted is different; that is, by adjusting the polarization control element 16 so that the annular optical path as the resonant cavity is in a different feedback state, thereby adjusting the state of the pulsed laser light emitted from the annular optical path 10. For example, the polarization control element 16 can be adjusted such that the annular optical path 10 is in a different feedback state, thereby enabling the pulsed laser outputted by the fiber laser to switch between the Q-switched pulsed laser and the rectangular-mode mode-locked pulsed laser.

In the present embodiment, since the saturable absorber 15 having polarization characteristics on the annular optical path 10 can simultaneously perform two kinds of laser pulse state operations, the ring-shaped optical path 10 is placed in different feedback states by adjusting the polarization control element 16 to make the fiber laser. It is possible to output pulsed lasers of different states, and pulsed lasers in different states have different pulse widths from each other, that is, pulse lasers having different pulse widths are output through a fiber laser to satisfy different pulse widths in processes such as microfabrication. The demand for pulsed lasers.

Preferably, the pump source 11 may be a semiconductor pump source, such as a 980 nm semiconductor pump source or a 1480 nm semiconductor pump source, etc.; the doped fiber 13 may be an erbium-doped gain fiber such as OFS EDF80, corresponding to the doped A transition of germanium atoms in the hetero-fiber 13 can radiate photons to form a laser having a wavelength of 1550 nm.

In one of the embodiments, as shown in FIG. 1, the fiber laser described above may further include a first coupling element 18 for splitting the received pulsed laser light, such as a fiber coupling. A device such as a light beam splitting function. The first coupling element 18 can split the pulsed laser light modulated by the polarization control element 16 into an outgoing laser beam and a feedback laser beam; the outgoing laser beam is output through the first output port 181 of the first coupling element 18 as a fiber laser. The laser beam is output; the feedback laser beam is output to the doped fiber 13 via the second output port 182 of the first coupling element 18 to serve as an excitation source for the doped fiber 13, thereby improving the stability of the output laser of the fiber laser.

In one of the embodiments, as shown in FIG. 1, the fiber laser described above may further include a second coupling element 12 for combining the received optical signals, the second coupling element 12 may be such as a wave division. A device such as a multiplexer that has an optical signal combining function. The second coupling element 12 can combine the pump light emitted by the pump source 11 and the feedback laser beam emitted by the first coupling element 18 to form a combined optical signal, and send the combined optical signal to the blending The hybrid optical fiber 13, which in turn excites the doped fiber to radiate photons more efficiently, forms a more stable laser beam.

In one of the embodiments, as shown in FIG. 1, the fiber laser described above may further include an isolation element 14 for unidirectional transmission of the optical signal in the annular optical path 10, the isolation element 14 may be, for example, polarization independent. A type isolator or the like has a function of making a one-way transmission of an optical signal. The spacer element 14 can be disposed on the optical path between the doped fiber 13 and the saturable absorber 15, and the laser beam 13 is excited to generate laser light propagating in various directions, and the returning light is isolated by the spacer element 14. Then, the unidirectional propagation of the pulsed laser light can be ensured, that is, the isolation element 14 can cause the pulsed laser light emitted from the doped fiber 13 to propagate along the annular optical path 10 toward the saturable absorber 15 to enhance the optical performance of the fiber laser.

In one of the embodiments, as shown in FIG. 1, the fiber laser described above may further include a single mode fiber 17 for enhancing the nonlinear polarization rotation effect of the annular optical path 10. The polarization control element 14 may include a first polarization controller (not shown) and a second polarization controller (not shown), and the saturable absorber 15 is disposed on the first polarization controller and the second polarization controller. The annular optical path 10 is provided to improve the adjustment precision of the pulse width of the pulse laser of the fiber laser output by the polarization controller.

In one embodiment, as shown in FIG. 1, the saturable absorber 15 described above may include a support rod (not shown) having an outer surface covered with a graphene film and a non-overlapping wound on the surface of the graphene film. The micro-nano fiber (not shown), because graphene has a broad spectrum absorption characteristic, and the micro-nano fiber has a large evanescent field, the three-dimensional device can be made to have a polarization. Characteristic saturable absorber.

Referring to FIG. 1, based on the annular optical path 10 as a resonant cavity, the pump light emitted from the pump source 11 is transmitted to the doped fiber 13 via the second coupling element 12, and the doped fiber 13 is subjected to the pump light. The excitation radiation photons form spontaneous radiation, and the spontaneous radiation can form a continuous laser that propagates in a different direction after being operated by the cavity; the isolation element 14 isolates the laser light propagating in the opposite direction on the annular optical path 10, and forms an edge in the annular optical path 10. a unidirectional continuous laser that propagates the doped fiber 13 toward the saturable absorber 15; the saturable absorber 15 converts the incident unidirectional continuous laser into a pulsed laser, and since the saturable absorber 15 has a polarization characteristic, it can simultaneously Pulse lasers are formed in two mode-locking modes; the polarization control element 16 can be adjusted such that the annular optical path (ie, the resonant cavity) 10 is in a positive feedback state or a negative feedback state, and the corresponding pulsed laser light emitted from the doped fiber is converted into a tone. Q pulse or rectangular wave mode-locking pulse; the first coupling element 18 converts the above-mentioned pulsed laser into a Q-switched pulse and a rectangular wave-mode-locked pulse for splitting to form an outgoing laser and a counter The laser, the exiting laser is emitted to the outside through the first output port 181 as an output of the fiber laser, and the feedback laser is sent to the second coupling element 12 via the second output port 182; the second coupling element 12 will pump the source 11 The emitted pump light is combined with the feedback laser described above and emitted into the doped fiber 13, which can effectively improve the quality and efficiency of the spontaneously radiated light generated by the doped fiber 13 being excited. The nonlinear polarization rotation effect of the annular optical path can also be improved by providing the single mode fiber 17 on the annular optical path 10 to further improve the stability of the pulsed laser outputted by the fiber laser.

The following is a detailed description using a three-dimensional structure of a graphene-micro-nano fiber as a saturable absorber. 2 is a schematic structural view of a fiber laser in another embodiment; as shown in FIG. 2, a fiber laser includes a semiconductor pump source 21, a wavelength division multiplexer 22, an erbium-doped gain fiber 23, and an isolator 24; a first polarization controller 25, a three-dimensional structure of graphene-micro/nano fiber integrated device 26, a second polarization controller 27, a single mode fiber 28 and a coupler 29; the output terminal d of the coupler 29 is wavelength division multiplexed The device 22 is connected such that the wavelength division multiplexer 22, the erbium-doped gain fiber 23, the isolator 24, the first polarization controller 25, the three-dimensional structure of the graphene-micro/nano fiber integrated device 26 as a saturable absorber The two polarization controllers 27, the single mode fiber 28 and the coupler 29 together form an annular resonant cavity. The output c of the coupler 29 serves as a pulsed laser output port of the fiber laser.

It should be noted that the connections between the various components in the fiber laser of the embodiment of the present invention may be directly connected through a port or connected through a single mode fiber to realize an all-fiber structure for optical signal transmission. At the same time, the components in the fiber laser can be connected by splicing the optical fiber to effectively avoid the reflected light in the ring optical path, thereby further improving the optical performance of the fiber laser.

Figure 3 is a schematic view showing the structure of the saturable absorber of Figure 2. As shown in FIG. 2, the three-dimensional structure graphene-micro/nano fiber integrated device 26 may include a support rod 216, a Teflon polymer film 262, a graphene film 263, and a micro/nano fiber 264; the Teflon polymer film 262 is covered. The outer surface of the support rod 261 is formed on the exposed surface of the Teflon polymer film 262 by transfer to form a graphene film 263, and the Wiener fiber 264 is wound on the surface of the above graphene film 263; The material is a support rod 261 of polymethyl methacrylate. Since the microfiber 264 is wound on the support rod 261 on which the graphene film 263 is transferred, the interaction distance between the graphene and the light field can be effectively increased, thereby improving the optical performance of the fiber laser.

In addition, since the micro/nano fiber 264 has a strong evanescent field, and the direction of one of the two electric fields in the micro/nano fiber 264 is parallel to the extending direction of the graphene film 263, the direction of the other electric field is perpendicular to the graphene. The transmission and the direction of action, in turn, cause the transmission loss of the laser of the micro-nano fiber 264 to be different in the direction of the two electric fields, thereby producing a sharp extinction ratio. Meanwhile, since the graphene film 263 has a preferable broad-spectrum absorption property and excellent saturable absorption characteristics, the three-dimensional structure of the graphene-micro/nano fiber integrated device 26 can be regarded as a saturable absorption device having polarization characteristics.

In an alternative embodiment, as shown in Figures 2-3, the length of the erbium-doped gain fiber 23 can be about 7 m, while ensuring better stability of the fiber laser, the length of the erbium-doped gain fiber 23 is taken. The difference between the two extreme values of the range of values does not exceed 2 m; for example, the length of the erbium-doped gain fiber 23 may range from 6.5 to 7.5 m, that is, the length of the erbium-doped gain fiber 23 may be 6.5 m. , 6.8m, 7m, 7.3m or 7.5m, etc. The length of the single-mode fiber 28 may be about 220 m. Also, in order to ensure better stability of the fiber laser, the difference between the two extreme values of the length range of the single-mode fiber 28 is not more than 2 m; for example, The length of the single-mode fiber 28 may range from 219.5 m to 220.5 m, that is, the length of the single-mode fiber 28 may be 219.5 m, 219.8 m, 220 m, 220.3 m, or 220.5 m, or the like. The coupler 29 may be a fiber coupler having an output ratio of 10%, that is, a ratio of a pulsed laser power outputted from the output terminal c of the coupler 29 to a pulsed laser power outputted from the output terminal d of the coupler 29 is 1: 9. It can also be understood that the ratio between the power of the outgoing laser beam formed by the splitting of the coupler 29 and the power of the feedback laser beam is 1:9. In another alternative embodiment, the coupler 29 may be a fiber coupler having an output ratio of 30%, that is, the pulsed laser power output from the output c of the coupler 29 and the output d of the coupler 29 are output. The ratio between the pulsed laser powers is 3:7, and it can also be understood that the ratio between the power of the outgoing laser beam formed by the splitting of the coupler 29 and the power of the feedback laser beam is 3:7.

Specifically, in a fiber laser, the transmission coefficient formula of nonlinear polarization rotation can be expressed as:

Where Δφ=Δφ _PC +Δφ _LB +Δφ _NL is the total phase delay between the fast and slow axes of the fiber, Δφ _PC is the delay introduced by the polarization controller, Δφ _NL =-2γLPcos(2θ)/3 is due to the fiber optic Linearly introduced nonlinear phase change, Δφ _LB = 2πLB _m /λ is the linear phase shift introduced by fiber birefringence, θ and

It is the angle between the polarizer and the analyzer and the fast axis of the fiber.

When the optical path of the fiber laser is completed, θ and

Can be considered as a constant. Therefore, the above-mentioned transmission coefficient formula for nonlinear polarization rotation can be reduced to:

|T| ² to cos(Δφ _PC +Δφ _LB +Δφ _NL )

That is, when the optical signal is transmitted in a laser cavity based on a nonlinear polarization rotating structure, the loss of the cavity has a very large relationship with the phase delay.

At the same time, since the three-dimensional structure of the graphene-micro/nano fiber integrated device 26 has both saturable absorption characteristics and polarization characteristics, that is, two kinds of mode-locking modes can be simultaneously generated in the fiber laser shown in FIG.

Therefore, by adjusting the first polarization controller 25 and/or the second polarizer 27 shown in FIG. 2, it is possible to realize that the laser cavity (ie, the ring light path) operates in a positive feedback or negative feedback region, that is, can be modulated. The polarization controller changes the feedback state in the fiber laser, and then on the basis of the three-dimensional structure-based graphene-micro-fiber device 26, the pulse laser outputted by the fiber laser can be performed between the Q-switched pulse laser and the rectangular wave-mode-locked pulse laser. Switch.

In addition, due to the certain degree of actual polarization contrast between the graphene-micro/nano fibers in the fiber laser, the effect of nonlinear polarization rotation in the laser can be enhanced by increasing the length of the single mode fiber. For example, when the graphene-micro/nano fiber integrated device 26 of the three-dimensional structure shown in FIG. 2 has an actual polarization contrast of about 2 dB, a single mode fiber 28 such as a length of about 220 m can be used to further enhance the fiber laser. The effect of nonlinear polarization rotation, which in turn improves the stability of the fiber laser.

In summary, the fiber laser in the embodiment of the present invention adjusts the laser pulse width emitted by the fiber laser through a saturable absorber having polarization characteristics and a polarization control element disposed in the annular optical path, thereby satisfying, for example, a biological The need for different pulse width pulsed lasers in various fields such as medicine, communications, micromachining, remote sensing, and military.

The technical features of the above-described embodiments may be arbitrarily combined. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be considered as the scope of this manual.

The above-described embodiments are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but is not to be construed as limiting the scope of the invention. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the appended claims.

Claims

A fiber laser, comprising a pump source and an annular optical path, wherein the fiber laser further comprises a doped fiber disposed on the annular optical path, a polarization control element, and a saturable absorber;

The pump light emitted by the pump source excites the doped fiber to radiate photons to form spontaneous radiation;

The saturable absorber has polarization characteristics for converting the received continuous laser light into a pulsed laser;

The polarization control element is configured to control a polarization state of light of the annular optical path to adjust a state of a pulsed laser light output by the annular optical path;

Among them, the pulse widths of the pulsed lasers in different states are different.
The fiber laser of claim 1 further comprising a first coupling element disposed on said annular optical path;

The first coupling element is configured to split a received pulsed laser into a feedback laser beam for feeding back to the doped fiber, and an outgoing laser beam for use as the fiber The output of the laser.
The fiber laser according to claim 2, further comprising a second coupling element disposed on said annular optical path;

The second coupling element is configured to combine the received pump light with the feedback laser beam to form a combined optical signal and transmit the combined optical signal to the doped fiber.
A fiber laser according to claim 3, further comprising an isolation element disposed on said annular optical path:

The isolation element is disposed on an optical path between the doped fiber and the saturable absorber to unidirectionally transmit the spontaneous radiation emitted by the doped fiber to the saturable absorber.
The fiber laser according to claim 4, wherein the first coupling element is a coupler, the second coupling element is a wavelength division multiplexer, and the isolation element is a polarization-independent fiber isolator.
The fiber laser of claim 1 further comprising a single mode fiber disposed on said annular optical path, said single mode fiber for enhancing a nonlinear polarization rotation effect of said annular path.
The fiber laser of claim 1 wherein said doped fiber is an erbium doped gain fiber.
The fiber laser according to claim 1, wherein said polarization control element comprises a first polarization controller and a second polarization controller, said saturable absorber being disposed in said first polarization controller and said The optical path between the second polarization controllers.
The fiber laser according to any one of claims 1 to 8, wherein the saturable absorber comprises:

a support rod, the outer surface of the support rod is covered with a graphene film;

A micro-nano fiber that is non-overlapping around the surface of the graphene film.
The fiber laser according to any one of claims 1 to 8, characterized in that the pulsed laser light output from the annular optical path comprises a Q-switched pulsed laser and a rectangular-wave mode-locked pulsed laser.