CN102208736A - Tunable multi-wavelength fiber laser - Google Patents

Abstract

The invention provides a tunable multi-wavelength fiber laser based on piezoelectric ceramics, which solves the disadvantage of the existing lasers outputting a fixed single wavelength. The tunable multi-wavelength fiber laser includes a pump light source, a gain medium and a ring cavity, and a wavelength division multiplexer (WDM), a rare earth fiber, a first optical isolator, an optical coupler, and a tunable A multi-wavelength generating unit and a second optical isolator; the output end of the second optical isolator is connected to an input end of the wavelength division multiplexer, and the pumping light source is connected to the other input end of the wavelength division multiplexer; One output end of the coupler is connected with the input end of the tunable multi-wavelength generating unit, and the other output end of the optical coupler is used for laser output. The laser can provide the required light source for multiple channels at the same time, making the design of the transmitter more compact and economical.

Description

Tunable Multiwavelength Fiber Lasers

technical field

The invention relates to a tunable multi-wavelength fiber laser, in particular to a tunable multi-wavelength fiber laser based on piezoelectric ceramics.

Background technique

Fiber lasers are developed on the basis of doped fiber amplifier technology. The waveguide structure and strong light pumping characteristics of fiber lasers make them have many advantages such as high output power, good beam quality, high conversion efficiency, low threshold, narrow line width, multiple output wavelengths, good compatibility and simple structure. It has broad application prospects in the fields of optical fiber communication, optical fiber sensing, military, industrial processing, optical information processing and full-color display. In particular, tunable fiber lasers play an extremely important role in wavelength division multiplexing fiber optic communication and fiber optic sensing applications.

At present, lasers for communication are mainly semiconductor lasers, and their output wavelength is fixed and single. With the continuous development of optical fiber communication systems, modern optical fiber wavelength division multiplexing communication systems are developing towards more and more channels. The most direct way to provide multiple signals is to use multiple fixed-wavelength lasers. But this method has the following two obvious disadvantages:

1. With the development of dense wavelength division multiplexing (DWDM) technology, the number of wavelengths in the system has reached dozens or even hundreds. For occasions where protection is required, the backup of each wavelength must be provided by a laser with the same output wavelength, which leads to an increase in the number of backup lasers and an increase in cost.

2. Since fixed-wavelength lasers need to be distinguished by wavelength, the number and types of lasers continue to increase with the increase in the number of wavelengths. To support dynamic wavelength allocation in optical networks and improve network flexibility, a large number of fixed-wavelength lasers with different wavelengths need to be equipped, so the utilization rate of each laser is reduced, resulting in waste of resources.

Contents of the invention

The invention provides a tunable multi-wavelength fiber laser based on piezoelectric ceramics, which solves the shortcoming of a fixed single-wavelength output of the existing laser.

Technical solution of the present invention is:

The tunable multi-wavelength fiber laser includes a pump light source, a gain medium and a ring cavity. The gain medium is an optical fiber doped with rare earth elements; a wavelength division multiplexer (WDM), a rare earth optical fiber, a first optical isolator, an optical coupler, a tunable multi-wavelength generating unit, a second Two optical isolators; the output end of the second optical isolator is connected to an input end of the wavelength division multiplexer, and the pump light source is connected to the other input end of the wavelength division multiplexer; one of the optical couplers The output end is connected with the input end of the tunable multi-wavelength generating unit, and the other output end of the optical coupler is used for laser output.

The above-mentioned tunable multi-wavelength generating unit includes an optical splitter, at least two optical circulators, fiber Bragg gratings (FBGs) having the same number as the optical circulators, an optical coupler, and a period adjustment mechanism for adjusting the FBG period; One output end of the coupler is connected to one end of the optical splitter, the other end of the optical splitter is connected to the first ports of at least two optical circulators, the second ports of each optical circulator are respectively connected to the FBG, each optical circulator The third ports of the FBGs are respectively connected to the optical couplers; the FBGs are set on the period adjustment mechanism.

According to different situations, each FBG can be arranged on a separate period adjustment mechanism, each FBG corresponds to a period adjustment mechanism, or each FBG can be arranged on a period adjustment mechanism.

The above-mentioned adjustable FBG cycle mechanism is preferably piezoelectric ceramics, and the piezoelectric ceramics are connected to the piezoelectric ceramic drive power supply; it is better to arrange the above-mentioned FBGs in parallel, and the interval between the center wavelengths is preferably 0.2nm; the above-mentioned The rare earth fiber is preferably erbium-doped fiber.

The advantages of the present invention are:

1. The fiber laser is an efficient wavelength converter, that is, the wavelength of the pump laser is converted to the lasing wavelength of the doped erbium ions. Just because the lasing wavelength of the fiber laser is determined by the erbium ion and is not controlled by the pump wavelength, it can be pumped by an inexpensive short-wavelength, high-power semiconductor laser corresponding to the absorption spectrum of the erbium ion to obtain a low-loss window for optical fiber communication. C-band (near 1550nm) laser output.

2. Due to the cylindrical geometry of the fiber laser, on the one hand, it is easy to couple into the transmission fiber of the system, which greatly simplifies the design and manufacture of the fiber laser, and the fiber has excellent flexibility, making the laser quite small and flexible. It is easy to use and cost-effective; on the other hand, it has a high "surface area/volume" ratio, fast heat dissipation, small heat load on the working substance, no need for a cooling system, and can produce high brightness and high peak power.

3. The tunable multi-wavelength fiber laser can effectively solve the shortcomings of fixed-wavelength lasers. It can not only provide the required light source for multiple channels at the same time, but also make the design of the transmitting end more compact and economical; and the output wavelength of the laser can also be adjusted. Tuning is suitable for the dynamic allocation of wavelengths in optical fiber communication networks, which can improve the flexibility of the network.

4. Capable of harsh working environment, with high tolerance to dust, vibration, shock, humidity and temperature.

5. Since the voltage adjustment range of the piezoelectric ceramic driving power is 0-150V, the single independent wavelength tuning accuracy of the laser is 0.00495nm/V, and the tuning range is 0.7425nm.

Description of drawings

Fig. 1 is a structural schematic diagram of a tunable multi-wavelength fiber laser;

Fig. 2 is a schematic structural diagram of a tunable multi-wavelength generating unit.

Detailed ways

The principle behind the tuning performance of this multi-wavelength fiber laser is as follows:

1. Coupling the pump light output from the pump light source in the first band with the signal light in the second band and then transporting them to step 2 for processing;

2. Input the light output in step 1 into the erbium-doped optical fiber for processing, the pump light in the first wave band reverses the particle number of erbium ions, and spontaneous amplified emission (ASE) occurs, forming the same spontaneous wave band as the signal light Radiant light. Spontaneous emission light amplifies the signal light of the second waveband described in step 1 to generate stimulated emission light; the stimulated emission light is unidirectionally transmitted to step 3; the signal light amplification of the second waveband is specifically at the ground state energy level The erbium ion transitions to a high energy level under the action of the pump light near the first wave band, and after about 1 μs delays to the metastable energy level, then transitions from the metastable energy level to the ground state, and emits the same energy as the second wave band Photons with the same wavelength and direction as the signal light realize the signal light amplification in the second band;

3. Split the light processed in step 2, a part of the light provides laser output, and the other part of light is fed back to step 4, after processing, it will be used as laser output after meeting the conditions;

4. Split the light fed back in step 3, and divide it into at least two groups of the same light;

5. Make each path of light processed in step 4 enter into corresponding optical circulators;

6. After passing through the optical circulator, each path of light enters into the corresponding FBG respectively. By adjusting the length of each FBG to change the period of each FBG and the fiber Bragg wavelength, the FBG will reflect the same light as its Bragg wavelength, and transmit the light of different wavelengths out of the FBG; the light reflected by the FBG returns to the optical circulator;

7. Coupling each path of light processed in step 6 and outputting it to step 1 in one direction, the wavelengths of each path of light are within the second wave band.

The tunable multi-wavelength fiber laser includes a pump light source, a gain medium and a ring cavity. The gain medium is an optical fiber doped with rare earth elements; a WDM, a rare earth optical fiber, a first optical isolator, an optical coupler, a tunable multi-wavelength generating unit, and a second optical isolator are sequentially arranged in series in the annular cavity; the The output end of the second optical isolator is connected with an input end of the wavelength division multiplexer, and the pump light source is connected with the other input end of the wavelength division multiplexer; an output end of the optical coupler is connected with the tunable multi-wavelength The input end of the generating unit is connected, and the other output end of the optical coupler is used for laser output.

The above-mentioned tunable multi-wavelength generation unit includes an optical splitter, at least two optical circulators, FBGs with the same number as the optical circulators, an optical coupler and a period adjustment mechanism for adjusting the FBG cycle; an output of the optical coupler One end of the optical splitter is connected to one end of the optical splitter, the other end of the optical splitter is connected to the first port of at least two optical circulators, the second port of each optical circulator is connected to the FBG respectively, and the third port of each optical circulator is respectively It is connected with an optical coupler; the FBGs are set on the period adjustment mechanism.

According to different situations, each FBG can be arranged on a separate period adjustment mechanism, each FBG corresponds to a period adjustment mechanism, or each FBG can be arranged on a period adjustment mechanism.

The above-mentioned adjustable FBG cycle mechanism is preferably piezoelectric ceramics, and the piezoelectric ceramics are connected to the piezoelectric ceramic drive power supply; it is better to arrange the above-mentioned FBGs in parallel, and the interval between the center wavelengths is preferably 0.2nm; the above-mentioned The rare earth fiber is preferably erbium-doped fiber.

Example 1

The tunable multi-wavelength fiber laser uses a laser diode near 980nm as the pump source, and uses an erbium-doped fiber as the gain medium of the laser. The fluorescence spectrum of the erbium-doped fiber is broadband light in the band of 1530nm to 1560nm; the resonant cavity structure of the ring cavity is adopted , its resonant cavity includes tunable multi-wavelength generation unit, optical isolator, 980/1550nm WDM, erbium-doped fiber and optical coupler, etc.; FBG is used as filtering and wavelength selection device to select the specific wavelength required, and multiple The FBG is pasted on the piezoelectric ceramic, and the piezoelectric ceramic drive power is used to change the elongation of the piezoelectric ceramic to adjust the filtering and wavelength selection characteristics of multiple FBGs, so that the laser can output tunable multi-wavelength laser.

The above-mentioned erbium-doped optical fiber is doped with erbium ions in the rare earth ions into the fiber core at a certain concentration. Erbium-doped fiber is a laser-stimulated fiber with a three-level system. Erbium ions can realize light amplification in the C-band (near 1550nm) of the low-loss window of optical fiber communication, and the signal light near 1550nm can induce the erbium ions to produce stimulated radiation. The erbium ion in the ground state energy level transitions to a high energy level under the action of pump light near 980nm, and after about 1μs delays to the metastable energy level, then transitions from the metastable energy level to the ground state, and emits a signal light Photons with the same wavelength and direction can achieve light amplification near 1550nm.

The above annular cavity is composed of the following components: 980/1550nm WDM, erbium-doped optical fiber, optical isolator 1, optical coupler, tunable multi-wavelength generating unit and optical isolator 2. The WDM couples the pump light near 980nm and the light with a wavelength near 1550nm into the erbium-doped fiber. Erbium-doped fiber is the gain medium, in which the population inversion is formed to generate ASE. Then the spontaneously radiated light enters the input port of the optical isolator 1 , and the optical isolator 1 promotes the unidirectional transmission of light in the annular cavity, and then the light is output from the output port of the optical isolator 1 . The light enters the input port of the optical coupler, and the optical coupler splits the light into two beams of 20%:80%. The light output from 20% ports provides laser output; the light output from 80% ports feeds back into the ring cavity and enters the input port of the tunable multi-wavelength generating unit. The light is filtered and wavelength selected in this unit, and the light satisfying the FBG Bragg reflection condition is selected, output from the output port of the tunable multi-wavelength generating unit, and enter the input port of the optical isolator 2 . The optical isolator 2 also promotes the unidirectional transmission of light in the annular cavity. After the light is output from the output port of the optical isolator 2, it enters into the WDM. This forms the annular cavity.

As shown in Figure 1: the pump light with a pump wavelength near 980nm is first coupled into the 980nm port of the 980/1550nm WDM through the pigtail. Then it enters the erbium-doped fiber through the WDM output port. The erbium-doped fiber is the gain medium. If it is pumped, the number of particles will be reversed in the erbium-doped fiber, and ASE will appear. The spontaneously radiated light enters the input port of the optical isolator 1, and the optical isolator 1 promotes the unidirectional transmission of light in the annular cavity. The light is then output from the output port of the optical isolator 1 . The light enters the input port of the optical coupler, and the optical coupler splits the light into two beams of 20%:80%. The light output from 20% ports provides laser output; the light output from 80% ports feeds back into the ring cavity and enters the input port of the tunable multi-wavelength generating unit. The light is filtered and wavelength selected in this unit, and the light satisfying the FBG Bragg reflection condition is selected, output from the output port of the tunable multi-wavelength generating unit, and enter the input port of the optical isolator 2 . The optical isolator 2 also promotes the unidirectional transmission of light in the annular cavity. After the light is output from the output port of the optical isolator 2, it enters the 1550nm port of the WDM. The radiated light is recoupled into the erbium-doped fiber, completing a cycle. During each cycle, the radiated light energy of those wavelengths that meet the fiber Bragg conditions are amplified. When the gain is greater than the transmission loss of the radiated light in the loop, the entire laser ring resonator forms an oscillation, thereby realizing the fiber Bragg condition. laser output at those wavelengths.

As shown in Figure 2: the light is output from 80% of the ports of the optical coupler in the ring cavity, and enters the input port of the 1×N optical splitter. The 1×N optical splitter splits the incident light into N paths, and the N paths of light are respectively output from N output ports of the 1×N optical splitter. Then N paths of light enter the Port 1 ports of the corresponding optical circulators 1~N respectively, and the N paths of light respectively pass through the circulators 1~N, output from the Port 2 ports of the optical circulators 1~N, and enter the corresponding N The root center wavelength is around 1550nm, and the center wavelength interval is about 0.2nm in the FBG. N FBGs are pasted on the same piezoelectric ceramics in parallel, or respectively pasted on the corresponding N piezoelectric ceramics, and the voltage is applied to the piezoelectric ceramics along the length direction of the FBG, and the piezoelectric ceramic driving power is adjusted to change the piezoelectric ceramics. The length of the FBG grating pasted on the piezoelectric ceramic is changed; according to the fiber Bragg reflection condition, the central wavelength of the reflected light also changes; any light that meets the FBG Bragg reflection condition will be reflected. The reflected light enters the Port 2 ports of the corresponding optical circulators 1~N respectively, passes through the optical circulators 1~N again, and is output from the Port 3 ports of the optical circulators 1~N; the light from the optical circulators 1~N After the output of the Port 3 port, it enters the N input ports of the corresponding N×1 optocoupler. The N×1 optical coupler couples N paths of light into one path of light, and then the combined light is output from the output port of the N×1 optical coupler and enters the input port of the optical isolator 2 in the ring cavity. In this way, the oscillation of light with N wavelengths in the resonant cavity is formed.

Paste N FBGs with a center wavelength around 1550nm and a center wavelength interval of about 0.2nm on the same piezoelectric ceramic in parallel, or respectively paste them on N corresponding piezoelectric ceramics, along the length direction of the FBG Apply voltage to the piezoelectric ceramics, adjust the piezoelectric ceramic drive power to change the length of the piezoelectric ceramics, thereby changing the period of the FBG grating pasted on the piezoelectric ceramics, to achieve the purpose of adjusting the filtering and wavelength selection characteristics of each FBG, and finally realize the Tuned multi-wavelength (N-wavelength) fiber laser output.

Claims (8)

1. A tunable multi-wavelength fiber laser, comprising a pump light source, a gain medium and an annular cavity, is characterized in that: the gain medium is an optical fiber doped with rare earth elements; in the annular cavity, wavelength division multiplexing is arranged in series successively device (WDM), rare earth optical fiber, first optical isolator, optical coupler, tunable multi-wavelength generating unit, second optical isolator; the output end of the second optical isolator and an input of the wavelength division multiplexer The pump light source is connected to the other input end of the wavelength division multiplexer; one output end of the optical coupler is connected to the input end of the tunable multi-wavelength generating unit, and the other output end of the optical coupler is used for Laser output. 2. The tunable multi-wavelength fiber laser according to claim 1, characterized in that: the tunable multi-wavelength generating unit comprises an optical splitter, at least two optical circulators, and optical fibers with the same number as the optical circulators A Bragg grating (FBG), an optical coupler and a period adjustment mechanism for adjusting the period of the FBG; an output end of the optical coupler is connected to one end of an optical splitter, and the other end of the optical splitter is connected to the first end of at least two optical circulators. One port is connected, the second port of each optical circulator is respectively connected with the FBG, and the third port of each optical circulator is respectively connected with the optical coupler; each FBG is arranged on the period adjustment mechanism. 3. The tunable multi-wavelength fiber laser according to claim 2, characterized in that: the FBGs are respectively arranged on the period adjustment mechanism. 4. The tunable multi-wavelength fiber laser according to claim 2, characterized in that: each of the FBGs is arranged on a period adjustment mechanism. 5. The tunable multi-wavelength fiber laser according to any one of claims 1 to 4, characterized in that: the mechanism for adjusting the period of the FBG is a piezoelectric ceramic, and the piezoelectric ceramic is connected to a driving power supply of the piezoelectric ceramic . 6. The tunable multi-wavelength fiber laser according to claim 5, wherein the rare earth fiber is an erbium-doped fiber. 7. The tunable multi-wavelength fiber laser according to claim 6, characterized in that: the mechanism for adjusting the period of the FBG is a piezoelectric ceramic, and the piezoelectric ceramic is connected to a driving power supply of the piezoelectric ceramic. 8. The tunable multi-wavelength fiber laser according to claim 7, characterized in that: the FBGs are arranged in parallel, and the interval between their center wavelengths is 0.2 nm.

Images