CN106654832B

CN106654832B - Dual-wavelength synchronous Q-switched optical fiber laser based on graphene

Info

Publication number: CN106654832B
Application number: CN201710139698.9A
Authority: CN
Inventors: 冯鸣; 任爱兵; 杨洁
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2017-03-08
Filing date: 2017-03-08
Publication date: 2020-05-26
Anticipated expiration: 2037-03-08
Also published as: CN106654832A

Abstract

The present invention relates to fiber lasers. The all-fiber double-ring laser is composed of a semiconductor laser, an active optical fiber, a wavelength division multiplexer, a polarization controller, an optical fiber isolator and a saturable absorber based on graphene. The innovation of the method is that a saturable absorber is shared to realize the output of the synchronous Q-switched pulse with double wavelengths. The invention has the advantages of small energy loss, compact and simple structure, simple and convenient operation and strong application advantages in optical fiber communication, nonlinear frequency conversion, multi-wavelength pump detection spectrum and Raman scattering spectrum.

Description

Dual-wavelength synchronous Q-switched optical fiber laser based on graphene

Technical Field

The invention relates to a laser, in particular to a graphene-based dual-wavelength synchronous Q-switched fiber laser.

Background

The fiber laser has the characteristics of high conversion efficiency, high output power, high beam quality, high stability, broadband adjustability, easiness in miniaturization, no need of refrigeration, simplicity in maintenance and the like which cannot be compared with other traditional lasers.

The dual-wavelength synchronous Q-switched pulse laser source has huge potential application in the fields of wavelength division multiplexing systems, photonic microwave signal processing, terahertz generation sources and the like, and has attracted wide interest of laser scientists at home and abroad. However, most of the present Q-switched fiber lasers only perform single-wavelength lasing, and there are still few reports on the realization of dual-wavelength synchronous Q-switched laser pulses. Therefore, it is necessary to develop a low-cost dual-wavelength synchronous Q-switched fiber laser.

Graphene was awarded to the nobel prize in physics since 2004 to 2010, and has become a hotspot of international research and widely accepted by academia in as little as 6 years. Graphene is a zero-band-gap semiconductor material, the energy band structure of the graphene is in a double-cone shape with opposite tops in a K space, and the Fermi level is above the Dirac point. The unique energy band structure of the graphene enables the graphene to have interaction of a wide light band and can cover visible light and near infrared light. In addition, due to the existence of the blocking phenomenon in the bubbles, the saturable absorption phenomenon exists in the graphene. There are two characteristic relaxation times in the saturable absorption process of graphene: the thermal balance of the in-band carriers by carrier-carrier scattering, and the subsequent carrier-phonon scattering and interband carrier recombination processes. The thermal equilibrium time of the in-band carriers is very short and is in the range of 10-107 fs. The time for the thermal equilibrium of the carriers between the bands is long, and is about 0.4-1.7 ps. It can be seen that the time response capability of the saturable absorption characteristic of graphene is extremely fast. Due to the blocking effect in the bubbles of graphene, cross-absorption modulation occurs when two beams of light interact with graphene. Based on the cross-absorption modulation characteristics of graphene, graphene can serve as a saturable absorber of the multi-wavelength synchronous Q-switched laser.

Disclosure of Invention

The invention aims to provide a graphene-based dual-wavelength synchronous Q-switched optical fiber laser.

The invention is provided with a wavelength division multiplexer, a gain optical fiber, an optical isolator, an output optical coupler, a pumping source, a polarization controller and a saturable absorber based on graphene.

The dual-wavelength synchronous Q-switched fiber laser is composed of two annular cavities, and the two annular cavities are used as resonant cavities for lasers with 1550nm wavelength and 1060nm wavelength respectively. The pump light output by the pump source is injected into the common part of the two annular cavities through the pump input end of the wavelength division multiplexer, and the output end of the optical coupler is used for outputting synchronous Q-switched pulses generated by oscillation in the cavities.

The dual-wavelength passive Q-switch is constructed by attaching a graphene material to an evanescent field of a micro-nano optical fiber. The graphene is transferred by taking PDMS as a substrate, and forms a passive Q-switch together with the magnesium fluoride crystal.

According to the invention, the strong saturable absorption characteristic of the graphene material is utilized, and the cross absorption modulation characteristic of the graphene to two beams of light is also utilized, so that the dual-wavelength Q-switched laser pulse formed by the two annular cavities can be synchronously output.

The manufacturing method of the graphene-based dual-wavelength synchronous Q-switched fiber laser comprises the following steps:

1) firstly, carrying out tapering treatment on a single-film optical fiber with the diameter of about 125 mu m, wherein the diameter of the tapered fiber is about 1-10 mu m;

2) laying the tapered micro-nano optical fiber on a flat substrate of a magnesium fluoride crystal, and fixing the micro-nano optical fiber by using glue;

3) transferring the graphene grown by CVD by taking PDMS as a substrate, and attaching a single layer of graphene to the tapered part of the micro-nano optical fiber;

4) the optical elements are welded with reference to the optical path diagram.

Compared with the prior art, the invention has the following beneficial effects: according to the invention, the strong saturable absorption characteristic of the graphene material is utilized, and the cross absorption modulation characteristic of the graphene to two beams of light is also utilized, so that the dual-wavelength Q-switched laser pulse formed by the two annular cavities can be synchronously output. The optical transmission characteristics of graphene can be modulated by long-wavelength light, and in the invention, a passive synchronous Q-switched fiber laser which works at 1060/1550nm and is realized by the same graphene saturable absorber is manufactured. In the synchronous process, the pulse formation and the influence of 1550nm laser pulse on 1060nm continuous wave in the graphene saturable absorber are studied. Research results can show that laser pulses of 1550nm can induce Q-switched laser pulses of 1060nm, and synchronization of the laser pulses can be achieved through a cross-absorption modulation effect of a graphene saturable absorber.

Drawings

Fig. 1 is a schematic diagram of an optical path of a graphene-based dual-wavelength synchronous Q-switched fiber laser according to the present invention.

Fig. 2 is a graph of the output spectrum of a two-wavelength synchronous laser.

Fig. 3 is a pulse sequence diagram for a pump power of 430 mw.

FIG. 4 is a graph showing the variation of repetition frequency, output pulse power and pulse width of 1550nm and 1060nm laser pulses with the pump power gradually increased while keeping the bias PC state constant.

Detailed Description

As shown in FIG. 1, the graphene-based dual-wavelength synchronous Q-switched optical fiber laser comprises a pumping source 1, a 980nm/1060nm wavelength division multiplexer 2, a 1550nm/1060nm wavelength division multiplexer 3, a polarization controller 4, a high-gain erbium-doped optical fiber 5, a high-gain ytterbium-doped optical fiber 6, a graphene-based saturable absorber 7, a 1550nm/1060nm wavelength division multiplexer 8, a 1550nm 2: 8 coupling output device 9, a 1550nm isolator 10, a 1060nm 2: 8 coupling output device 11 and a 1060nm isolator 12. The graphene-based saturable absorber 7 is formed by attaching single-layer graphene to the side face of an optical fiber with the diameter of about 8 mu m, supporting the single-layer graphene by magnesium fluoride, respectively belonging to an erbium-doped fiber laser and an ytterbium-doped fiber laser in an upper ring and a lower ring, and connecting the upper ring and the lower ring by 3 and 8 1550nm/1060nm wavelength division multiplexers; in the 1550nm loop, a 1550nm isolator 10(ISO) is added to allow the laser to propagate unidirectionally, with the light passing from the 1550nm cavity through a coupler 9 with 20% output. Similarly in the 1060nm loop there is a 1060nm isolator 12(ISO) and a 20% output coupler 11.

1) firstly, carrying out tapering treatment on a single-film optical fiber with the diameter of about 125 mu m, wherein the diameter of the tapered fiber is about 8 mu m;

4) the optical elements are welded with reference to the optical path diagram.

The principle of the invention is as follows:

the optical paths are connected with reference to a schematic diagram of the optical paths as shown in fig. 1. When pump light emitted by a 980nm semiconductor laser enters the erbium-doped optical fiber and the ytterbium-doped optical fiber from 980/1060WDM and 1550/1060WDM, erbium ions and ytterbium ions in the optical fiber are excited respectively to generate spontaneous radiation with 1550nm and 1060nm as central wavelengths. Wherein the weak forward spontaneous radiation light can be intercepted by an isolator arranged in the reverse direction after passing through a saturable absorber (GSA) based on graphene, 1550/1060WDM and a 2: 8 coupler, and can not play a role in laser generation. And the stronger reverse spontaneous radiation light enters 1060/1550WDM after passing through the polarization controller. Under the action of WDM, spontaneous emission lights centering on 1550nm and 1060nm respectively enter an upper optical path and a lower optical path, respectively pass through an isolator and an output coupler, then pass through 1550/1060WDM to be recombined together, and jointly enter a saturable absorber (GSA) based on graphene. In the GSA, spontaneous radiation light generates evanescent waves through the tapered optical fiber to interact with graphene on the surface of the optical fiber taper area, and a plurality of light pulses are formed under the effect of the saturable absorption characteristic of the graphene. Meanwhile, the 1550nm and 1060nm lights can jointly excite electrons in the graphene, so that a stronger saturable absorption effect is caused. Therefore, when the spontaneous radiation light of 1550nm and 1060nm is strongest, the light pulse can obtain the highest transmittance in the action with the graphene, and therefore the synchronous generation of the light pulse of 1550nm and 1060nm is achieved. And then, the generated synchronous light pulse passes through the ytterbium-doped optical fiber and the erbium-doped optical fiber, the amplification of the light pulse is realized under the action of pump light, and the generated synchronous light pulse respectively passes through 1550 and 1060 optical loops and keeps and strengthens the synchronism of the 1550nm and 1060nm light pulse through the saturable absorption effect of graphene. Therefore, in the structure proposed in this patent, the 1550nm and 1060nm optical pulses realize the generation and pulse synchronization of pulses due to the saturable absorption effect of graphene, and the amplification of energy is realized in erbium-doped and ytterbium-doped fibers, and finally the synchronous output of Q-switched laser pulses is realized.

Fig. 2 shows the output spectrum of the laser in normal operation. It can be seen that lasers centered around 1550nm and 1060nm, respectively, are simultaneously generated and appear in the spectrum, indicating that the laser is simultaneously generating laser light at two wavelengths. Fig. 3 shows the results of time domain measurements performed on two wavelengths of laser pulses, respectively. The results show that the lasers at 1550nm and 1060nm are pulsed out and have the same repetition period and frequency, indicating that a two-wavelength synchrotron Q-pulse has been formed. The two columns of pulses are not completely overlapped because the lengths of the paths through which the two pulses reach the detector after being output are different, and the two columns of pulses can be easily realized through the compensation of an optical path. Fig. 4 shows the average output power, peak power, repetition frequency and pulse width of two laser pulses as a function of pump power. It can be seen that the repetition frequency of the two columns of pulses can be kept the same within a large range of pump power, which illustrates the stability of the device, and has a large working range and a wide application prospect.

Claims

1. A dual-wavelength synchronous Q-switched optical fiber laser based on graphene is characterized in that a double-ring cavity is formed by connecting a pumping source with an erbium-doped optical fiber, an ytterbium-doped optical fiber, a 980nm/1060nm wavelength division multiplexer, a 1550nm/1060nm wavelength division multiplexer, a polarization controller, a 1550nm isolator, a 1060nm optical isolator and a saturable absorber based on graphene, and the double-ring cavity is respectively a ring resonant cavity of laser with 1550nm wavelength and a ring resonant cavity of laser with 1060nm wavelength, and the 1550nm ring cavity is formed by the erbium-doped optical fiber, a 2: 8 coupling output device of 1550nm and a 1550nm isolator; the 1060nm ring cavity consists of ytterbium doped fiber, 1060nm 2: 8 coupling output device and 1060nm optical isolator; the pumping source is fused with the cavity through a 980nm/1060nm wavelength division multiplexer; the two cavities are subjected to common-cavity fusion through a pair of inverted 1550nm/1060nm wavelength division multiplexers, and sharing of the polarization controller, the saturable absorber of the graphene and the two cavities of the pumping source is achieved;

the graphene saturable absorber is a saturable absorber formed by graphene, a micro-nano optical fiber and a magnesium fluoride crystal;

the 1550nm laser formed by the 1550nm annular cavity and the 1060nm laser formed by the 1060nm annular cavity are transmitted in the same direction by a 1550nm/1060nm wavelength division multiplexer to be interacted with the saturable absorber together;

the 1550nm laser and the 1060nm laser are mutually separated through a 1550nm/1060nm wavelength division multiplexer after interacting with the saturable absorber, and are respectively coupled into respective annular cavities.