CN105337149A - Pulse narrow linewidth fiber laser based on graphene micro fiber ring modulation - Google Patents

Abstract

The invention relates to the technical fields of optical engineering, material engineering and fiber optics, in particular to a pulse-type narrow-linewidth fiber laser based on graphene micro-fiber ring modulation. Its structural features are: a micro-fiber ring resonator drawn and linked by a single-mode optical fiber in the 980-nanometer waveband and a gain-type distributed feedback Bragg fiber grating are cascaded, and a part of the micro-fiber ring resonator is made of a graphene film Cover it, and cover metal electrodes on both sides on the graphene film, and the entire micro-fiber ring resonant cavity is fixed on a silicon dioxide substrate. Pumped by a conventional 980-band continuous light source, the present invention can produce both a narrow linewidth and an adjustable pulse laser output; it also has strong practicability, its frequency domain linewidth is 2-3k Hz, and the maximum modulation speed is 10G Hz, the signal-to-noise ratio is 20 decibels, and can be widely and directly used in all-fiber sensing and communication systems.

Description

A Pulsed Narrow Linewidth Fiber Laser Based on Graphene Microfiber Ring Modulation

technical field

The invention relates to the technical fields of optical engineering, material engineering and fiber optics, in particular to fiber laser, modulation and sensing technologies.

Background technique

As an important optical device, pulsed lasers have important and extensive applications in both scientific research and industrial production, such as high-brightness light sources, optical signal generation sources, laser cutters, modulation and demodulation components, and so on. With the development of economy and technology, people put forward higher and higher demands on pulsed lasers, such as: ultra-fast, high-power, high-speed tunable, optical sensing and so on.

Especially in the field of long-distance optical sensing, pulsed lasers as light sources are required to have tunable pulse characteristics, narrow linewidth characteristics, and high peak power output, which is a huge challenge in theory and practice.

At present, pulsed lasers are generally divided into three categories in terms of working principles, namely: mode-locked pulsed lasers, Q-switched pulsed lasers and externally modulated pulsed lasers. Pure mode-locked, Q-switched and externally modulated pulsed lasers cannot meet the stringent requirements of low insertion loss, high-speed adjustable narrow-linewidth pulsed light output. Specifically, mode-locked lasers and Q-switched lasers are generally difficult to control repetition frequency and pulse width, and cannot achieve output with narrow linewidth in principle. Externally modulated pulsed lasers are subject to external modulators, with high insertion loss and low modulation rate (megahertz level).

In addition, traditional pulsed lasers are limited by materials, processes and costs, and more semiconductor structures are used. However, semiconductor pulsed lasers also have many limitations, and it is difficult to output pulses with wide range tunability and high peak power.

The development of fiber lasers provides a new solution to this problem. Laser devices based on all-fiber have the unique advantages of low cost, low loss, easy access, expandability and networking, and can output higher power, higher bandwidth and purer modes, and are widely used in modern optical communication and optical transmission. sense is playing an increasingly important role. Mode-locked, Q-switched and modulated pulsed lasers based on all-fiber have also been continuously invented and improved in recent years. Even so, it is difficult to use the fiber structure while taking into account the pulse characteristics and narrow linewidth characteristics. It often requires the combination of multiple components such as fiber lasers, fiber modulators, and fiber filters, which increases the complexity and complexity of the system. cost.

Contents of the invention

In view of the above existing problems or deficiencies, in order to solve the problem that traditional narrow-linewidth fiber lasers cannot achieve high-speed adjustable pulsed light output in the same device, the present invention provides a pulse-type narrow laser based on graphene micro-fiber ring modulation. Linewidth Fiber Lasers.

Its structural features are: a micro-fiber ring resonator (MFR) drawn and looped by a single-mode optical fiber in the 980-nanometer band and a gain-type distributed feedback Bragg fiber grating (DFB) are cascaded through a coupler; The optical fiber annular cavity is far from the position of the coupling area, covered with a rectangular graphene film with a width of 1 mm, and then a pair of electrodes are grown on the two ends of the graphene film that do not cover the micro-fiber annular cavity. The micro-fiber ring is placed on the silica substrate and fixed tightly by van der Waals force.

The specific parameters are: the diameter of the micro-fiber is 1 micron, the length is 1-2 cm, the diameter of the micro-fiber ring is 0.5 mm, the length of the knotted coupling area of the micro-fiber ring is 5-6 microns, and the graphene film is 0.38 nm thick and 1 mm wide. layers of graphene. The electrode material on the graphene film is gold, which is used to apply a modulation voltage of ±20 volts. The silicon dioxide substrate has an area of 1 square centimeter and a thickness of 3 millimeters. The used gain-type distributed feedback Bragg grating is written in the core of an erbium-ytterbium double-doped single-mode optical fiber with a core diameter of 6 microns and a grating length of 2 cm.

The pulse-type narrow-linewidth fiber laser based on graphene micro-fiber ring modulation is characterized in that: a 980-nanometer waveband laser is used as a pumping light source, and its output is a narrow-linewidth adjustable pulse in a 1550-1560-nanometer waveband. 0.5% to 1%, the output signal is an adjustable pulse in the 1550-1560 nanometer band, its frequency domain line width is 2-3k Hz, the maximum modulation speed is 10G Hz, and the signal-to-noise ratio is 20 decibels.

In this invention, single-layer graphene plays an important role to achieve pulsed modulation of the pump injected into the gain medium. Single-layer graphene, with a thickness of 0.38nm, as a two-dimensional material, is the thin film material with the largest surface area/volume ratio reported so far. It has unique physical and chemical properties, and one of the most typical ones is based on the Fermi level With the photoelectric tunable effect, by adjusting the carrier concentration of graphene with an applied voltage, its optical transmission loss can be significantly adjusted, and then the whole of the micro-fiber ring in the present invention can be adjusted in a specific wavelength band, thereby forming a time-domain pulse. In addition, in this invention, the gain-type distributed feedback Bragg fiber grating serves as a laser generating element and a narrow-linewidth filter device at the same time, and outputs laser light with a narrow linewidth at the reflection end. Excited by pulsed pumping modulated by graphene, its output is also pulsed.

The working process of the present invention is as follows: through the single-mode optical fiber of the 980 nanometer band, the 980 nanometer continuous optical pump is injected into the fiber ring resonant cavity, and interference is formed, and the interference extinction point (ResonantDip) is located at 980 nanometers. At the same time, a periodically changing modulation voltage is connected through the electrodes on the graphene to adjust the light attenuation of the graphene-covered area. When the attenuation of the graphene-covered area is strong, it is more difficult for the optical signal to be coupled into the ring resonator, thus showing a strong output, that is, the interference phase weakens. When the attenuation of the graphene-covered area is weak, the ring resonator has high Q characteristics, and the optical signal is stronger. Most of them remain in the ring resonant cavity, which shows weak output, that is, strong interference and destructive phase. At the output end, a pulsed pump modulated by electricity is formed. The pump is injected into the gain-type distributed feedback fiber Bragg grating to generate laser light in the 1550nm band and output it through the reflection end. The time-domain characteristics of this laser are consistent with that of the pump, and it is a pulsed laser based on graphene modulation. At the same time, the distributed feedback fiber Bragg grating itself has narrow linewidth filtering characteristics, so the output pulse laser also has narrow linewidth characteristics.

In summary, the present invention has the characteristics of low cost, low loss, small volume, simple and compact structure and simple manufacture, and is convenient for application; pumped by a conventional 980-band continuous light source, it can generate both narrow line width and adjustable pulse It also has strong practicability, its frequency domain line width is 2-3k Hz, the maximum modulation speed is 10G Hz, and the signal-to-noise ratio is 20 dB, which can be widely used directly in all-fiber sensing and in the communication system.

Description of drawings

Fig. 1 is the three-dimensional structure schematic diagram of the present invention;

Fig. 2 is the micrograph of graphene covering microfiber ring structure of the present invention;

Fig. 3 is the embodiment system diagram of the present invention;

Fig. 4 is a schematic diagram of the modulation result of the application of the present invention;

Reference signs: 1-ring resonant cavity formed by structuring micro-nano optical fiber, 2-single-layer graphene film, 3-gold electrode, 4-980 nanometer band single-mode optical fiber, 5-1550 nanometer band single-mode optical fiber, 6- Distributed feedback fiber Bragg grating, 7-silica substrate, 8-980nm continuous optical pump, 9-wavelength division multiplexing coupler.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, Figure 2, Figure 3, and Figure 4, the single-mode optical fiber in the 980-nanometer waveband is prepared into a micro-optical fiber with a diameter of 1 micron and a length of 2 cm by the fusion tapered method, and is drawn into a knot by a probe. Knot ring, the diameter of the micro-fiber ring is 0.5 mm, and the length of the knotted coupling area of the micro-fiber ring is 5 microns. The micro-fiber ring is placed on a silica substrate and fixed tightly by van der Waals force. A single-layer graphene film with a thickness of 0.38 nm and a width of 1 mm is covered at the position of the micro-fiber ring cavity away from the coupling area by CVD method and wet transfer technology. Then, through the magnetron sputtering technique, a pair of gold electrodes are grown on the two ends of the graphene film that do not cover the micro-fiber ring. The gold electrode covers an area of 1mm*0.5mm, and the electrode thickness is 130nm. The output end of the microfiber ring resonant cavity is coupled to a 3 decibel wavelength division multiplexing coupler, and the other end of the wavelength division multiplexing coupler is connected to a gain-type distributed feedback fiber Bragg grating, and the distributed feedback fiber Bragg grating is written on the Erbium Ytterbium double In the doped single-mode fiber core, the core diameter is 6 μm and the grating length is 2 cm.

During the laser working process, the continuous optical pumping in the 980 nanometer band is injected from the input end of the ring resonant cavity, and at the same time, a rapidly modulated ±20 volt modulation voltage is applied to the gold electrode. At the output of the ring resonator, the output is pumped with rapidly modulated pulses. In the gain-type distributed feedback fiber Bragg grating, it is pumped to generate laser light in the 1550nm band, which is output backward and separated into pure modulated pulsed laser light in the 1550nm band by the wavelength division multiplexing coupler. The laser exhibits narrow linewidth characteristics due to the filtering characteristics of distributed feedback fiber Bragg gratings.

The above specific implementation methods are used to explain the device of the present invention, rather than to limit the present invention. Within the spirit of the present invention and the protection scope of the rights specification, any changes and variations of the present invention fall within the protection scope of the present invention.

Claims (4)

1. A pulse-type narrow-linewidth fiber laser based on graphene micro-fiber ring modulation. Its structural features are: a micro-fiber ring resonator MFR and a gain-type micro-fiber ring resonator drawn and looped by a single-mode fiber in the 980-nanometer waveband The distributed feedback fiber Bragg grating DFB is formed by cascading couplers; the microfiber ring resonator is far away from the coupling area, covered with a layer of 1 mm wide graphene film, and then the two sides of the microfiber ring cavity are not covered by the graphene film. A pair of electrodes are grown on the upper side of the end, so that the micro-fiber ring resonant cavity is placed on the silicon dioxide substrate, and is fixed and adhered to by van der Waals force. The graphene film is a single-layer rectangular graphene with a thickness of 0.38 nanometers. 2. The pulse-type narrow-linewidth fiber laser based on graphene micro-fiber ring modulation as claimed in claim 1, wherein: the micro-fiber has a diameter of 1 micron, a length of 1 to 2 cm, a micro-fiber ring diameter of 0.5 mm, and a micro-fiber diameter of 1 micron. The length of the fiber ring knotted coupling region is 5-6 microns; the electrode material on the graphene film is gold, which is used to apply a modulation voltage of ± 20 volts; the silicon dioxide substrate has an area of 1 square centimeter and a thickness of 3 mm; the used gain-type distributed feedback Bragg grating is written in the core of an erbium-ytterbium double-doped single-mode fiber, the core diameter is 6 microns, and the grating length is 2 cm. 3. As claimed in claim 1 or 2, the pulse-type narrow-linewidth fiber laser based on graphene micro-fiber ring modulation is characterized in that: the 980-nm band laser is used as the pump light source, and its output is a narrow band of 1550-1560 nm. Line width adjustable pulse, the lasing efficiency is 0.5% ~ 1%, the output signal is an adjustable pulse in the 1550 ~ 1560 nanometer band, its frequency domain line width is 2 ~ 3k Hz, the maximum modulation speed is 10G Hz, the signal to noise ratio is 20 dB. 4. as claimed in claim 1 or 2, based on the pulse type narrow-linewidth fiber laser modulated by the graphene micro-fiber ring, its working process is: Through a single-mode optical fiber with a wavelength of 980 nanometers, the 980-nanometer continuous optical pump is injected into the fiber ring resonator, and interference is formed, and the interference extinction point ResonantDip is located at 980 nanometers; at the same time, through the electrodes on the graphene. Periodically varying modulation voltages to tune light attenuation in graphene-covered regions; When the attenuation of the graphene-covered area is strong, it is more difficult for the optical signal to be coupled into the ring resonator, thus showing a strong output, that is, the interference phase weakens. When the attenuation of the graphene-covered area is weak, the ring resonator has high Q characteristics, and the optical signal is stronger. Most of them remain in the ring resonant cavity, which shows weak output, that is, strong interference and destructive phase; at the output end, it forms a pulse pump modulated by electricity; this pump is injected into the gain-type distributed feedback fiber Bragg grating to generate a 1550-nanometer The laser in the wavelength band is output through the reflection end.