CN109193326B

CN109193326B - Optical fiber microsphere cavity mode-locked laser based on graphene channel structure

Info

Publication number: CN109193326B
Application number: CN201811131814.3A
Authority: CN
Inventors: 谭腾; 袁中野; 姚佰承; 吴宇; 饶云江
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2018-09-27
Filing date: 2018-09-27
Publication date: 2021-03-30
Anticipated expiration: 2038-09-27
Also published as: CN109193326A

Abstract

The invention belongs to the technical field of information and science, and particularly relates to an optical fiber microsphere cavity mode-locked laser based on a graphene channel structure. According to the invention, two gold electrodes are arranged on the surface of the erbium-doped microsphere, and the multilayer graphene is attached between the two gold electrodes on the sphere to form a gold-graphene-gold heterostructure; the micro-nano optical fiber is vertically attached to the spherical center line between two gold electrodes of the surface erbium-doped microsphere to realize optical coupling with the microsphere cavity of the surface erbium-doped microsphere. The invention realizes the multiple characteristics of simple structure, low cost, large-range adjustability and stability of the mode-locked laser; the single longitudinal mode line width is 1kHz, and the threshold value is 20 microwatts; the repetition frequency of the output laser is widely adjustable from 100GHz to 1 THz.

Description

Optical fiber microsphere cavity mode-locked laser based on graphene channel structure

Technical Field

The invention belongs to the technical field of information and science, and particularly relates to an optical fiber microsphere cavity mode-locked laser based on a graphene channel structure.

Background

The mode-locked laser is widely applied to the fields of laser rapid prototyping, laser spectroscopy, nonlinear optics, condensed state physics, precise drilling, material processing, micromachining of optical crystals and the like due to the ultrashort pulse and ultrahigh peak power of the mode-locked laser. A free-running laser often has many laser pulses of different modes or frequencies simultaneously, and laser ultrashort pulses, or mode-locked pulses, can be generated only when the laser modes are phase-locked to each other. There are many ways to achieve mode locking, but they can be generally divided into two broad categories: namely active mode locking and passive mode locking.

At present, the active mode-locked laser periodically changes the gain or loss of the laser by providing a modulation signal to the laser from the outside, so as to achieve the purpose of mode locking, the repetition frequency of the active mode-locked laser is limited by the bandwidth of the modulation signal, and meanwhile, the active mode-locked laser has high requirements on the modulator, the unstable modulation can cause the loss of the lock of the laser, and the system structure of the mode-locked laser is complex and the price is high. Passive mode locking utilizes nonlinear absorption or nonlinear phase change characteristics of materials to generate laser ultrashort pulses, and compared with active mode locking, the passive mode locking pulse has narrower pulse width, simple system structure and no need of manual control, but the system has poor adjustability and poor laser output stability.

The mode-locked fiber laser has many advantages such as ultrashort pulse, ultrashort recovery time, ultrastrong peak power, and an excessive value, is convenient to integrate in the existing optical network, and is widely concerned, and becomes a research hotspot in the laser field. However, at present, there is no fiber mode-locked laser which has the advantages of simple structure, low cost, large-range adjustability and ultra-stability.

Disclosure of Invention

Aiming at the problems or the defects, the mode-locked laser aims to solve the problems that the existing mode-locked laser cannot give consideration to simple structure, low cost, large-range adjustability and stability; the invention provides an optical fiber microsphere cavity mode-locked laser based on a graphene channel structure, which integrates a gold-graphene-gold heterostructure in a system of the optical fiber microsphere mode-locked laser, and realizes stable ultrashort pulse output of repetition frequency large-range modulation under dynamic regulation and control of external voltage.

The optical fiber microsphere cavity mode-locked laser based on the graphene channel structure comprises surface erbium-doped microspheres, multiple layers of graphene and micro-nano optical fibers.

The surface erbium-doped microspheres are prepared by doping trivalent erbium ions Er on the surfaces of silicon dioxide microspheres prepared by optical fibers³⁺And (4) forming. Erbium ions on the surface of the microsphere jump to a high energy level after absorbing energy of pump photons to form population inversion, and a large number of coherent photons are obtained through stimulated radiation. Gold electrodes are arranged at the connecting end of the surface erbium-doped microsphere and the optical fiber and at the other end of the sphere corresponding to the connecting end, the multilayer graphene is attached between the two gold electrodes on the sphere, and the distance between the two gold electrodes is 1/4-1/3 of the diameter D of the microsphere. Section of two gold electrodes for coupling micro-nano optical fiber and sphereSymmetrical and form a gold-graphene-gold heterostructure.

The micro-nano optical fiber is vertically attached to the spherical center line between two gold electrodes of the surface erbium-doped microsphere, realizes optical coupling with the microsphere cavity of the surface erbium-doped microsphere, and is used for inputting pumping light and outputting laser.

Gold is excellent conductive material, also has very strong absorption to light simultaneously, and the mode volume of ordinary microballon echo wall resonant cavity is great, and its resonant mode quantity is more, through to the gold-plating of microballon surface, can reduce the mode volume of microballon greatly, restricts resonant mode quantity, can realize the electricity regulation and control to attached graphite alkene between simultaneously. Meanwhile, two ends of the whole mode-locked laser adopt common single-mode optical fiber joints, so that the whole structure can be conveniently and directly connected into an optical path formed by single-mode optical fibers.

Further, the surface erbium-doped microspheres have the following structure: controlling the discharge intensity of a common single-mode optical fiber to be 150-250 milliamperes through an optical fiber fusion splicer, and carrying out arc discharge for 2-5 times within 3-6 seconds of single discharge time to obtain silica microspheres with the diameters of 200-400 micrometers; and preparing an erbium chloride-silicon dioxide mixed solution, adding UV glue to enable bait ions to be coated on the surfaces of the microspheres, finally removing the UV glue through an oxyhydrogen flame degreasing process, and sintering through a welding machine to obtain the transparent erbium-doped microspheres, wherein the quality factor of the cavity of the microsphere reaches more than 3 million.

Graphene, which is a thin film material with a monolayer thickness of 0.38nm, has excellent photon-electron interaction capability. Due to the gapless symmetrical distribution of Dirac fermi of the graphene, the graphene has very high charge tunability and broadband nonlinear absorption. The broadband saturable absorption effect of 3-5 layers of multilayer graphene is utilized, and mode locking and Q-switching operations of the laser can be realized.

According to the invention, a 1480 nanometer pump light source signal is injected into the micro-nano optical fiber from one side through a common silicon dioxide single mode fiber. In the microsphere cavity area of the surface erbium-doped microsphere, the Q value of the formed resonant cavity reaches over 3 million due to the whispering gallery mode of the laser cavity, and laser lasing is formed through gain amplification of surface erbium ions. Due to the saturated absorption effect of the graphene integrated on the surface of the microsphere, the microsphere cavity laser gradually forms mode-locked pulses. When the bias voltage of the gold electrode is 0 volt, the mode locking frequency is 100GHz based on the repetition frequency of the ultrashort pulse; further adjusting the bias voltage to 20 volts with repetition frequency up to 1 THz; in order to avoid damage to the graphene thermal conductive structure due to an excessively high bias voltage, an upper limit of the applied voltage is set to 20 volts.

Compared with the prior art, the invention combines the technologies in the fields of optics, metamaterial science and micro-nano processing, obtains the microsphere echo wall resonant cavity with the quality factor of more than 3 million by a cheap and simple manufacturing process, and realizes laser emission with the single longitudinal mode line width of 1kHz and the threshold value of 20 microwatts. By adopting the process of mixing and sintering erbium chloride and silicon dioxide powder, the gain medium is added into the microsphere cavity under the condition of not increasing the volume. By combining with metamaterial graphene and using a multilayer graphene film as an electrically adjustable saturable absorber, the repetition frequency of output laser can be adjusted in a large range from 100GHz to 1THz, and the laser far exceeds the conventional optical fiber mode-locked laser. The device disclosed by the invention works based on an all-optical system, can realize on-chip integration, is convenient to access to the existing optical network, and has very outstanding application potential in the scientific fields of ultrahigh-speed optical communication, ultra-sensitive optical sensing, ultra-precise analytical measurement, large-range adjustable light sources and the like.

In conclusion, the invention realizes the multiple characteristics of simple structure, low cost, large-range adjustability and stability of the mode-locked laser.

Drawings

FIG. 1 is a schematic three-dimensional structure of the present invention;

FIG. 2 is a detailed view of the regulating structure of the present invention;

FIG. 3 is a diagram of a test system;

fig. 4 is a schematic diagram of the saturation absorption efficiency of the voltage-regulated graphene according to an embodiment;

FIG. 5 is a schematic diagram of an output repetition frequency of an embodiment of a voltage-regulated fiber microsphere cavity mode-locked laser;

FIG. 6 is a time domain diagram of an embodiment laser output pulse;

reference numerals: the device comprises microspheres- (1), gold electrodes- (2 and 3), multilayer graphene- (4), micro-nano optical fibers- (5), 1480 nano laser- (6), voltage regulation- (7), a 3dB coupler- (8), a spectrometer- (9), an oscilloscope- (10), a photoelectric detector- (11) and a vacuum cavity- (12).

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

An optical fiber microsphere cavity mode-locked laser based on a graphene channel structure is composed of micro-nano optical fibers and silica microspheres with erbium-doped surfaces. The micro-nano optical fiber is manufactured by optical fiber melting tapering equipment, is 3 cm long and 1 micron in diameter, and is efficiently coupled with the microsphere cavity; the method comprises the steps of carrying out arc discharge on a common single-mode optical fiber for 4 times through an optical fiber fusion splicer within the discharge intensity of 200 milliamperes and the single discharge time of 5 seconds, then preparing an erbium chloride-silicon dioxide mixed solution with the concentration of 1019/cm3, adding UV glue to enable bait ions to be coated on the surface of a microsphere, finally removing the UV glue through an oxyhydrogen flame degreasing process, sintering through the fusion splicer to obtain the erbium-doped microsphere with the surface of 300 micrometers, plating two gold electrodes with the thickness of 30 nanometers and the interval of 100 micrometers at one end and the other end of the microsphere, wherein the number of resonance modes of the gold-plated microsphere is 2, attaching a 4-layer graphene film with the length of 120 micrometers and the width of 100 micrometers between the gold electrodes, and connecting a device into an optical path system through the single-.

Referring to fig. 1 and 2, a common single-mode optical fiber was subjected to arc discharge by an optical fiber fusion splicer to obtain microspheres (1) having a diameter of 300 μm. Pump light with the wavelength of 1480 nanometers is coupled into the microsphere resonant cavity along the micro-nano optical fiber (5), trivalent erbium ions doped on the surface of the microsphere can absorb pump photons to form population inversion, and the light with the wavelength meeting the resonance condition of the microsphere cavity can be amplified in the cavity to form stimulated radiation. By adjusting the two gold electrodes, the saturation absorption effect of the multilayer graphene is tuned, and the mode-locked pulse laser is emitted.

With reference to fig. 3, 4, 5 and 6, 1480 nm pump laser (6) is input from one side of the micro-nano fiber and coupled into the erbium-doped micro-sphere cavity, and laser is output from the other side of the micro-nano fiber and divided into two paths at the output end by a 3dB coupler (8). One path is connected with a spectrometer (9) to obtain the repetition frequency data of the output laser, as shown in fig. 5. One path is connected with a photoelectric detector (11) and then connected with an oscilloscope (10) to obtain a time domain pulse signal of output laser, as shown in fig. 6. The whole device is arranged in a vacuum cavity (12) to prevent the influence caused by the adsorption of gas molecules by graphene.

According to the invention, the current carrier concentration of the multilayer graphene is modulated by regulating and controlling the voltage of the two gold electrodes (7), so that the saturation absorption efficiency of the multilayer graphene is changed (figure 4). The embodiment obtains the microsphere echo wall resonant cavity with the quality factor as high as 3 million, and realizes the stable laser emission with the single longitudinal mode line width of 1kHz and the threshold value of 20 microwatts. By adopting the process of mixing and sintering erbium chloride and silicon dioxide powder, the gain medium is added on the surface of the microsphere cavity under the condition of not increasing the volume. By combining with metamaterial graphene, the multilayer graphene film is used as an electrically adjustable saturable absorber, different bias voltages are added, the repetition frequency of output laser can be adjusted in a large range from 100GHz to 1THz, and the laser far exceeds the conventional optical fiber mode-locked laser.

In conclusion, the invention realizes the mode-locked laser with the characteristics of simple structure, low cost, large-range adjustability and stability.

Claims

1. The utility model provides an optic fibre microballon chamber mode-locked laser based on graphite alkene channel structure which characterized in that:

the optical fiber comprises surface erbium-doped microspheres, multilayer graphene and micro-nano optical fibers;

the surface erbium-doped microspheres are prepared by doping trivalent erbium ions Er on the surfaces of silicon dioxide microspheres prepared by optical fibers³⁺Forming; gold electrodes are arranged at the connecting end of the surface erbium-doped microsphere and the optical fiber and at the other end of the sphere corresponding to the connecting end, the multilayer graphene is attached between the two gold electrodes on the sphere, and the distance between the two gold electrodes is 1/4-1/3 of the diameter D of the microsphere; the two gold electrodes are symmetrical about the coupling tangent plane of the micro-nano optical fiber and the sphere and form a gold-graphene-gold heterostructure;

the micro-nano optical fiber is vertically attached to the spherical center line between two gold electrodes of the surface erbium-doped microsphere, realizes optical coupling with the microsphere cavity of the surface erbium-doped microsphere, and is used for inputting pump light and outputting laser;

the working mechanism of the optical fiber microsphere cavity mode-locked laser is as follows: pumping light source signals are injected into the micro-nano optical fiber from one side, and laser lasing is formed in a micro-sphere cavity area with erbium ions on the surface through gain amplification of the erbium ions on the surface; due to the saturated absorption effect of the graphene integrated on the surface of the microsphere, the microsphere cavity laser gradually forms mode-locked pulses; and applying a bias voltage of 0-20 volts to the gold electrode to realize a pulse repetition frequency regulation range of 100GHz-1 THz.

2. The graphene channel structure-based fiber microsphere cavity mode-locked laser of claim 1, wherein:

the surface erbium-doped microsphere comprises: controlling the discharge intensity of a common single-mode optical fiber to be 150-250 milliamperes through an optical fiber fusion splicer, and carrying out arc discharge for 2-5 times within 3-6 seconds of single discharge time to obtain silica microspheres with the diameters of 200-400 micrometers; and preparing an erbium chloride-silicon dioxide mixed solution, adding UV glue to enable bait ions to be coated on the surfaces of the microspheres, finally removing the UV glue through an oxyhydrogen flame degreasing process, and sintering through a welding machine to obtain the transparent erbium-doped microspheres, wherein the quality factor of the cavity of each microsphere is more than 3 million.