CN110165541B

CN110165541B - Brillouin-erbium-doped fiber random laser with switchable wavelength intervals

Info

Publication number: CN110165541B
Application number: CN201910519403.XA
Authority: CN
Inventors: 张祖兴; 梅杰; 蒋奇; 孟爽; 周夏冰
Original assignee: Nanjing University of Posts and Telecommunications
Current assignee: Nanjing University of Posts and Telecommunications
Priority date: 2019-06-17
Filing date: 2019-06-17
Publication date: 2020-12-18
Anticipated expiration: 2039-06-17
Also published as: CN110165541A

Abstract

The invention discloses a Brillouin-erbium-doped fiber random fiber laser with switchable wavelength intervals, which is of a half-open cavity structure and comprises an open-loop part and a straight line part, wherein in the open-loop part, one end of a circulator is connected with the output end of a coupler, the other end of the circulator is connected with the input port of the coupler, the other input end of the coupler is connected with the output end of a Brillouin pump source, and the other output end of the coupler is connected with the input end of a spectrometer; the linear part comprises two connected linear units, and each linear unit comprises a pumping source, a wavelength division multiplexer, an erbium-doped fiber and a single-mode fiber; the output end of the pump source is connected with the input end of the wavelength division multiplexer, and the output end of the wavelength division multiplexer is connected with the erbium-doped optical fiber; the other side of the erbium-doped fiber is connected with one end of a single-mode fiber, and the other end of the single-mode fiber is connected with a second linear unit wavelength division multiplexer; the single mode fiber of the second linear element is connected to the isolator. The Brillouin Stokes light output with switchable wavelength intervals is realized by adjusting the switch and the power of the pumping source.

Description

Brillouin-erbium-doped fiber random laser with switchable wavelength intervals

Technical Field

The invention relates to a random laser, in particular to a Brillouin-erbium-doped fiber random laser with switchable wavelength intervals.

Background

The concept of random laser was first proposed by Ambartsumyan equal to 1966. Compared with the traditional laser, the random laser has no fixed optical resonant cavity, the optical feedback of the random laser is realized by the multiple scattering effect in disordered media, and the random laser output is realized by utilizing the interference effect of scattered light to generate a resonant mode with specific frequency. In recent decades, the potential applications of random lasers in the fields of fiber sensing, physical optical imaging, spectral measurements, microwave photonics, and biomedicine have attracted a great deal of enthusiasts.

Random laser does not have a fixed optical resonant cavity, the working principle is that light is scattered for multiple times in a disordered medium to realize feedback, and the interference effect of the scattered light generates a resonant mode under specific frequency to realize the generation of random laser. The random laser has the advantages of not requiring a strict optical resonant cavity, being capable of simultaneously generating a plurality of incoherent laser modes and the like, but has the disadvantages of high angle dependence of an emission spectrum, high threshold power and the like.

In recent years, random fiber lasers have received much attention since their first proposal in 2010 due to their great potential in optical communication and fiber sensing. Different from the traditional optical fiber laser with fixed cavity length, the random optical fiber laser provides random distribution feedback by virtue of Rayleigh scattering in the optical fiber, and has the advantages of simple structure, no need of fixed point feedback, incoherence, low relative intensity noise and the like. The gain mechanism of the random fiber laser is developed from stimulated raman scattering to stimulated brillouin scattering, stimulated emission of rare earth doped fiber, and the above-mentioned hybrid gain.

An optical fiber is selected as a waveguide with two-dimensional constraint performance to improve the random laser performance, Turitsyn and the like report a random optical fiber laser based on Rayleigh scattering random distribution feedback for the first time, and the stable random laser signal output is obtained by utilizing distributed Raman gain amplification in a conventional optical fiber with the total length of 83 kilometers. In 2011, Vatnik et al reported that a cascade random laser is generated based on Raman gain and Rayleigh scattering random distribution feedback, and a second-order Stokes random signal with the wavelength of 1.2 μm is obtained experimentally. In 2013, Zhang et al proposed a semi-open random laser cavity formed by mixing a dispersion compensation fiber and a single-mode fiber, and first-order and second-order Stokes random lasers were respectively obtained from a Raman random fiber laser. However, the generation of random laser based on Raman scattering cascade has obvious disadvantages of high threshold power (the threshold of the second-order Stokes line exceeds 1W), small number of generated Stokes lines (no more than 3-order Stokes line), large wavelength spacing of 100nm and the like.

Stimulated brillouin scattering SBS is widely used to implement multi-wavelength fiber lasers with precise and stable wavelength spacing and a large cascade of stokes lines. Based on random distributed feedback formed by rayleigh scattering, multi-wavelength brillouin-erbium doped fiber/raman random lasers have been reported by combining SBS gain with erbium doped fiber amplifier gain or stimulated raman scattering gain. For example, ping et al report a coherent brillouin random fiber laser, which uses rayleigh scattering in a section of non-uniform fiber as random distribution feedback, and brillouin scattering in a conventional single-mode fiber as gain, to obtain stable brillouin random laser output with a single peak and narrow linewidth. For the multi-wavelength fiber laser applied to the dense wavelength division multiplexing system, it is required that the output power of each channel is as much and flat as possible, and researchers have made efforts to reduce the peak power difference of the random multi-wavelength laser to improve the number of wavelengths and the power flatness, but it is still not ideal.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a Brillouin-erbium-doped fiber random laser with switchable wavelength intervals, which aims to solve the problems that the feedback of Brillouin signal light in the random fiber laser is weak, and the Brillouin order generated by cascade connection is small, and can realize the output with switchable wavelength intervals.

The technical scheme is as follows: the invention relates to a Brillouin-erbium-doped fiber random laser with switchable wavelength intervals, which is of a semi-open cavity structure and comprises an open loop part and a straight line part connected with the open loop part, wherein the open loop part is connected with the straight line part through a circulator;

in the open loop part, an A port of the circulator is connected with an output port of the 3-dB coupler, a C port of the circulator is connected with an input port of the 3-dB coupler, the other input port of the 3-dB coupler is connected with an output end of the Brillouin pump source, and the other output port of the 3-dB coupler is connected with an input port of the spectrometer;

the linear part comprises two linear units which are connected with each other, and each linear unit comprises a pumping source, a wavelength division multiplexer, an erbium-doped fiber and a single-mode fiber; the output end of the pumping source is connected with the input end of the wavelength division multiplexer, and the output end of the wavelength division multiplexer is connected with the erbium-doped optical fiber; the other side of the erbium-doped fiber is connected with one end of the single-mode fiber, and the other end of the single-mode fiber is connected with the wavelength division multiplexer of the second linear unit; the other end of the single-mode fiber of the last linear unit is connected with the isolator.

The circulator has A, B, C three ports, the circulator connects the open loop section through the A and C ports, and the circulator connects with the wavelength division multiplexer of the straight line section through the B port.

The erbium-doped fiber adopts a laser diode bidirectional pumping mode to amplify both reverse and forward brillouin signal light.

After the brillouin pump source passes through the 3-dB coupler, 50% of the power is injected into the B port through the a port of the circulator.

The Brillouin pump source is a tunable laser source with a tuning range of 970-1680 nm and an output power range of 7.4-12.4 dBm.

When the power of the Brillouin pump light is larger than the stimulated Brillouin scattering threshold value, first-order Brillouin Stokes light is generated, and Rayleigh scattering provides random distribution feedback; the backward propagating first-order stokes wave will be first amplified by the erbium doped fiber and 50% of the stokes light will be output from the output port of the 3-dB coupler.

The working principle is as follows: in the fiber, the position of erbium-doped fiber amplification is crucial to improving the performance of random fiber lasers with weak distributed feedback in the fiber. After the erbium-doped fiber is added into the double-pass port, the erbium-doped fiber gain can provide effective and sufficient amplification for Stokes light generated by double-pass amplification, and the performance of the random fiber laser is greatly improved. The invention provides an erbium-doped fiber linear gain introduced into a double-pass port of a circulator, so that brillouin signal light is subjected to double-pass amplification while brillouin pump light is amplified, and multi-order brillouin wavelengths are generated through multiple cascading. The erbium-doped fiber adopts a bidirectional pumping mode, so that reverse and forward Brillouin signal light can be effectively amplified. When the power of the brillouin pumping light exceeds the stimulated brillouin scattering threshold value, first-order brillouin stokes light is generated, and rayleigh scattering provides random distribution feedback. The backward propagating first-order stokes wave will be first amplified by the erbium doped fiber and 50% of the stokes light will be output from the output port of the 3-dB coupler. The other light passes through the left open loop, enters the erbium-doped fiber again for amplification, and then enters the single-mode fiber again as new pump light. With the cascade of this process, higher order brillouin stokes light can be generated. Finally, the multi-order Stokes light oscillation is realized in the laser cavity by using the Brillouin-erbium-doped mixed gain, and the wavelength adjustability can be realized by changing the Brillouin pumping wavelength. In this semi-open cavity design, a tunable multi-wavelength brillouin-erbium doped random laser can be realized.

The linear gain of the erbium-doped fiber is introduced into a double-pass port of the circulator, and the Brillouin pump light is injected into a left open loop through the 3-dB coupler, reaches a B port of the circulator, is amplified and then is injected into the long single-mode fiber. Backward Stokes signals generated by stimulated Brillouin scattering in the single-mode optical fiber are amplified in the erbium-doped optical fiber and then enter the left half open loop, and after partial output, the backward Stokes signals enter the erbium-doped optical fiber through the port B of the circulator again for amplification to generate next-stage stimulated Brillouin scattering.

Has the advantages that: compared with the prior art, the invention has the following advantages:

(1) all devices of the invention adopt an all-fiber coupling mode, are not interfered by external factors and can continuously and stably work;

(2) the erbium-doped fiber linear gain is introduced into the double-pass port of the circulator, and the Brillouin pumping light is amplified, so that the Brillouin signal light is subjected to double-pass amplification, and multiple cascade connection is performed to generate multi-order Brillouin wavelengths; the switching between the single interval and the double interval of the output wavelength can be realized by controlling the switches of the two pumping sources and the power;

(3) the Brillouin signal light of the invention obtains larger gain and can generate higher-order Brillouin Stokes light;

(4) the power difference between the multiple-order brillouin stokes lights is smaller, and flat multiple-order brillouin wavelengths can be generated.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a random laser output spectrum with a 20-order Brillouin Stokes light;

FIG. 3 is a single wavelength interval output spectrum with only the first 980nm erbium doped fiber pump source turned on;

fig. 4 is a double wavelength interval output spectrum with only the second 980nm erbium doped fiber pump source switched on.

Detailed Description

As shown in fig. 1, the half-open cavity multi-wavelength brillouin-erbium-doped fiber random laser includes two pump sources 1, two wavelength division multiplexers 2, two sections of erbium-doped fibers 3, two sections of single-mode fibers 4, an isolator 5, a circulator 6, a 3-dB coupler 7, a brillouin pump source 8, and a spectrometer 9. The random laser has a semi-open cavity structure comprising a left open loop section and a right straight section connected by a circulator 6, wherein the circulator 6 has A, B, C three ports.

One side of the erbium-doped fiber 3 is provided with a pumping source 1 and a wavelength division multiplexer 2; the output ends of the two pumping sources 1 are respectively connected with one input end of a wavelength division multiplexer 2, and the output end of the wavelength division multiplexer 2 is connected with one end of an erbium-doped fiber 3; the other side of the erbium-doped fiber 3 is connected with one end of a long-distance single-mode fiber 4, the other end of the first long-distance single-mode fiber 4 is connected with the input end of a second wavelength division multiplexer 2, and the other end of the second long-distance single-mode fiber 4 is connected with an isolator 5; the signal input end of the first wavelength division multiplexer 2 is connected with the port B of the circulator 6; the port A and the port C of the circulator 6 are respectively connected with a first output port and a first input port of the 3-dB coupler 7; a second input port of the 3-dB coupler 7 is connected to an output port of the brillouin pump source 8, and a second output port of the 3-dB coupler 7 is connected to an input port of the spectrometer 9.

The left open loop, which is a single-sided feedback, consists of a 3-dB coupler 7 for brillouin pump injection and laser output. A tunable laser source with a tuning range of 970nm to 1680nm and an output power range of 7.4dBm to 12.4dBm was used as the brillouin pump source 8.

The right straight part is mainly two rolls of 10km single mode fiber 4(SMF) which is used as a Brillouin gain medium and has randomly distributed Rayleigh feedback, and the rightmost end is provided with an isolator to avoid Fresnel reflection and ensure stable random laser output. The circulator 6 connects the left open loop through the a port and the C port, and connects the right straight portion through the B port. After the brillouin pump passes through the 3-dB coupler 7, 50% of the power is injected into the B port through the a port of the circulator 6. To compensate for the lower brillouin gain, as with a conventional brillouin erbium-doped laser, a 1.3 meter length of erbium doped fiber 3 is bi-directionally pumped by two 980nm laser diodes LD, each with a maximum output power of 500 milliwatts, WDM-coupled into the erbium doped fiber 3 by two wavelength division multiplexers 2. An optical spectrum analyzer 9, model OSA or AQ-6370D, with a resolution of 0.02nm, monitors the output from the output port of the 3-dB coupler 7.

After the brillouin pump source 8 passes through the 3-dB coupler 7, 50% of the power is injected into the B port through the a port of the circulator 6. When only the second 980nm laser diode pump on the right is turned on, the brillouin pump light is amplified in the second erbium-doped fiber section 3 on the right and propagates forward in the single-mode fiber SMF of the second 10km section on the right. When the power of the brillouin pumping light exceeds the stimulated brillouin scattering threshold value, first-order brillouin stokes light is generated, and rayleigh scattering provides random distribution feedback. The backward propagating first order stokes wave will be first amplified by the erbium doped

fiber

3 and 50% stokes light will be output from the output port of the 3-dB coupler 7. The other light enters the second erbium-doped fiber section 3 on the right through the left open loop, is amplified and then enters the single-mode fiber 4 on the right as new pump light again. With the cascade of this process, higher order brillouin stokes light can be generated. Finally, the multiple-order Stokes light oscillation is realized in the laser cavity by using the Brillouin-erbium-doped mixed gain, and the output of the high-order Brillouin Stokes light with double wavelength intervals can be observed at the port on the right side of the isolator 5.

When only the first 980nm pump source on the left side is switched on, brillouin pump light is amplified in the first erbium-doped fiber section 3 on the right side and propagates forwards in the first single-mode fiber SMF of 10km on the right side, similarly, when the brillouin pump light power exceeds the stimulated brillouin scattering threshold value, backward-propagating first-order brillouin stokes light is also generated, 50% of the stokes light is output from the output port after passing through the 3-dB coupler 7, the rest enters the first erbium-doped fiber section 3 on the right side again through the left open loop to be amplified to generate brillouin stokes light, and finally, high-order brillouin stokes light output at intervals of wavelengths can be observed in the spectrometer 9.

The linear gain of the erbium-doped fiber 3 is introduced into a double-pass port of the circulator 6, the Brillouin pump light is injected through the 3-dB coupler 7, and the B port reaching the circulator 6 is amplified and then injected into the long single-mode fiber 4. Backward stokes signals generated by stimulated Brillouin scattering in the single-mode optical fiber 4 are amplified in the erbium-doped optical fiber 3 and then enter the circulator 6, and after part of the backward stokes signals are output, the backward stokes signals enter the erbium-doped optical fiber 3 through the port B of the circulator 6 again for amplification, and then next-stage stimulated Brillouin scattering is generated. The switching between single and double wavelength interval outputs can be realized by controlling the switching of the two 980nm pump lasers and the power.

Fig. 2 is a random laser output spectrum with 20-order brillouin stokes light. Fig. 3 shows a single wavelength interval output spectrum when only the first 980nm erbium-doped fiber is pumped, where more orders are generated when bp pumping power is the lowest, only few orders of brillouin stokes light can be generated when 980nm pumping power is lower, and the orders of the generated brillouin stokes light are gradually increased as the 980nm pumping power is increased.

Fig. 4 is a double wavelength interval output spectrum when only the second 980nm erbium-doped fiber pump is switched on, it is observed that more orders are generated when bp pump power is larger, the generated brillouin stokes optical order increases with the increase of the power of the second 980nm pump on the right side, and it is found that the output of brillouin stokes light of even orders in the output spectrum is suppressed and the output of odd orders is unchanged when viewed from the right port of the isolator, so that the output spectrum of double wavelength interval is finally formed.

Claims

1. A Brillouin-erbium-doped fiber random laser with switchable wavelength intervals is characterized in that: the laser is of a semi-open cavity structure and comprises an open loop part and a linear part connected with the open loop part, wherein the open loop part is connected with the linear part through a circulator (6);

in the open loop part, an A port of a circulator (6) is connected with an output port of a 3-dB coupler (7), a C port of the circulator (6) is connected with an input port of the 3-dB coupler (7), the other input port of the 3-dB coupler (7) is connected with an output end of a Brillouin pump source (8), and the other output port of the 3-dB coupler (7) is connected with an input port of a spectrometer (9);

the linear part comprises two linear units which are connected with each other, and each linear unit comprises a pumping source (1), a wavelength division multiplexer (2), an erbium-doped fiber (3) and a single-mode fiber (4); the output end of the pumping source (1) is connected with the input end of the wavelength division multiplexer (2), and the output end of the wavelength division multiplexer (2) is connected with the erbium-doped optical fiber (3); the other side of the erbium-doped fiber (3) is connected with one end of a single-mode fiber (4), and the other end of the single-mode fiber (4) is connected with the wavelength division multiplexer (2) of the second linear unit; the other end of the single-mode fiber (4) of the second linear unit is connected with an isolator (5);

the circulator (6) is connected with the wavelength division multiplexer (2) of the straight line part through a port B; the B port is a bi-pass port.

2. A wavelength-spaced switchable brillouin-erbium doped fiber random laser according to claim 1, wherein: the erbium-doped fiber adopts a laser diode bidirectional pumping mode to amplify both reverse and forward Brillouin signal light.

3. A wavelength-spaced switchable brillouin-erbium doped fiber random laser according to claim 1, wherein: after the Brillouin pump source (8) passes through the 3-dB coupler (7), 50% of power is injected into a port B through an port A of the circulator (6).

4. A wavelength-spaced switchable brillouin-erbium doped fiber random laser according to claim 1, wherein: the Brillouin pump source (8) is a tunable laser source with a tuning range of 970-1680 nm and an output power range of 7.4-12.4 dBm.

5. A wavelength-spaced switchable brillouin-erbium doped fiber random laser according to claim 1, wherein: when the power of the Brillouin pumping source is larger than the stimulated Brillouin scattering threshold value, first-order Brillouin Stokes light is generated, and Rayleigh scattering provides random distribution feedback; the backward propagating first-order stokes wave will be amplified for the first time by the erbium doped fiber (3), and 50% of the stokes light is output from the output port of the 3-dB coupler (7).

6. A wavelength-spaced switchable Brillouin-erbium doped fiber random laser according to any one of claims 1 to 5, characterized in that: the pumping source (1) is a laser diode.