CN2638081Y - Ultra narrow regulatable optical fibre laser used for concentrated wave multiplexing system - Google Patents

Abstract

It relates to ultra-narrow linewidth tunable fiber lasers for dense wavelength division multiplexing systems. It is equipped with a pump source, a rare earth-doped fiber, an isolator, a fiber coupler, and a comb filter composed of a high birefringence polarization-maintaining fiber and a 3dB coupler. The fiber is connected to one end of the isolator ISO2, and the other end of the isolator ISO2 Connect the coupler, the port of the coupler is connected to one end of another isolator ISO1, the other end of the isolator ISO1 is connected to the comb filter, the comb filter is connected to the pump source, the port of the coupler is the laser output, the reflection of the coupler The port is connected with a tunable fiber grating. Its output power is stable; the laser line width is narrow, which can be less than 0.01nm; the wavelength drift can be less than 0.01nm, and the filter design is simple. Just change the length of the polarization-maintaining fiber on the filter to change the wavelength interval of the laser to meet the standard , suitable for DWDM communication systems; all-fiber design, low insertion loss and threshold, easy to use and install.

Description

Ultra-narrow linewidth tunable fiber lasers for dense wavelength division multiplexing systems

(1) Technical field

The utility model relates to an optical fiber laser, in particular to an ultra-narrow line-width adjustable optical fiber laser used in a Dense Wavelength Division Multiplexing (DWDM) system.

(2) Background technology

At present, the rapid growth of the global communication traffic, especially the Internet, has higher and higher requirements on the transmission capacity of the communication system. The ways to increase the transmission capacity of an optical fiber communication system include: 1) increasing the bit rate of a single channel; 2) increasing the number of channels of a single-core optical fiber; 3) increasing the number of optical fiber cores in an optical cable. Among the above-mentioned solutions, adopting DWDM technology is the best way to increase the transmission capacity of the communication system at present, and it is also a method commonly used at present. Since in the DWDM system, the interval between different channels is very small (for example, the channel interval of 100MHz system is 0.8nm), so in order to avoid serious inter-channel crosstalk in transmission, the spectral width of the laser light source required by DWDM is very narrow, and requires The working wavelength of the laser is stable, the frequency drift is small, and the working frequency of the laser required by DWDM is at the working frequency of the DWDM system recommended by the International Telecommunication Union (ITU-T), that is, lasers with uniform frequency spacing are required. At present, there are mainly distributed feedback (DFB) semiconductor lasers that can be used as light sources for DWDM, but these lasers have disadvantages such as complex process, high price, and difficult wavelength adjustment.

(3) Contents of the invention

The utility model aims to provide an ultra-narrow line-width adjustable fiber laser used in a DWDM system, which is simple in design, stable in output light intensity, adjustable in output laser wavelength and oscillates at a given wavelength, and small in line width.

In order to achieve the above object, the utility model utilizes the rare earth doped fiber as the gain medium, and the Sagnac loop and the ring cavity containing the high birefringence polarization-maintaining fiber cooperate with the large-scale linear tunable fiber grating to realize, and can be realized according to ITU -T Suggested wavelength-spaced output lasing tunable narrow-linewidth fiber lasers for DWDM systems.

The utility model is provided with a pumping source, a rare earth element-doped optical fiber, two optical fiber isolators, an optical fiber coupler and a comb filter.

After the pump source excites the rare earth element-doped fiber, the stimulated radiation is transmitted in the fiber loop and is amplified to form a laser. The rare earth element-doped fiber is connected to one end of the isolator ISO2, and the other end of the isolator ISO2 is connected to the fiber coupler. The stimulated radiation enters the fiber coupler through the isolator ISO2, the reflected light port of the fiber coupler is connected to one end of another isolator ISO1, the other end of the isolator ISO1 is connected to a comb filter, and the comb filter is connected to the pump source. One end of the fiber coupler is used as a laser output, and the other end is connected to a tunable fiber grating.

Said isolator adopts polarization-independent optical fiber isolator.

Said comb filter is composed of polarization maintaining fiber and 3dB coupler.

The utility model utilizes the action of an external mechanism to make the Bragg wavelength of the fiber grating move linearly, then every time a cycle of a comb filter is passed, that is, when the Bragg wavelength of the fiber grating matches the transmission maximum of the comb filter, a The laser with strong power and extremely narrow line width, and there is basically no laser output between two adjacent lasers, that is, the laser output with a wavelength at a certain discrete point is realized, and the interval between adjacent laser wavelengths and The period of the designed comb filter is consistent. According to the birefringence of the polarization-maintaining fiber, the period of the comb filter can be changed by selecting different fiber lengths to make it conform to the wavelength interval of the DWDM system recommended by ITU-T. Then, the fiber laser realized by this scheme can be applied to the DWDM system. middle. This rare-earth-doped fiber laser with uniform wavelength intervals uses a Sagnac comb filter composed of polarization-maintaining fibers and a rare-earth-doped fiber amplifier in structure, and realizes lasing with uniform wavelength intervals through linear tuning of fiber gratings. Compared with traditional fiber lasers, its advantages are: 1) The output power of fiber lasers is stable; 2) The laser line width is narrow, which can be less than 0.01nm; 3) In the case of tuning fiber gratings and appropriate stabilization measures, the wavelength The drift can be less than 0.01nm, or even lower; 4) The design of the comb filter is simple, and the wavelength interval of the lasing can be changed by changing the length of the polarization-maintaining fiber on the filter to meet the ITU-T standard, which is suitable for DWDM Communication system; 5) All-fiber design, low insertion loss, low laser threshold, easier to use and install in the system. Therefore, this tunable fiber laser with all-fiber structure can be conveniently applied to fields such as wavelength division multiplexer (WDM) and dense wavelength division multiplexer (DWDM), and has broad application prospects.

(4) Description of drawings

Fig. 1 is a structural block diagram of the utility model.

Fig. 2 is the output spectrogram of the utility model embodiment.

(5) specific implementation

The following embodiments will further illustrate the utility model in conjunction with the accompanying drawings.

As shown in Figure 1, the pump source (Pump) excites the rare earth doped fiber (REDF) to generate stimulated radiation light with a certain wavelength bandwidth and enters the fiber coupler (Fiber Coupler) through the isolator ISO2. Through the coupler, a part of the light is coupled to port 1. Due to the wavelength selection effect of the fiber grating, the light at the Bragg wavelength corresponding to the grating is almost completely reflected back. The Sagnac ring composed of optical fiber and 3dB coupler (3dB Coupler), because the birefringence of polarization-maintaining fiber is related to wavelength, this device composed of high birefringent fiber and 3dB coupler has comb filter characteristics, that is, the transmission of the filter It has an approximately uniform periodic relationship with the wavelength. If the Bragg wavelength of the grating corresponds to the smaller part of the comb filter transmission, then the gain of the entire loop is small and cannot form laser light; when the Bragg wavelength of the grating is very consistent with the transmission of the comb filter, the entire loop The transmission loss of the wavelength is the smallest, and the light of this wavelength can generate laser light through the coupler and output from port 2 when the gain is large enough during the loop transmission. The laser center wavelength is consistent with the Bragg wavelength of the grating at this time. To sum up, only when the Bragg wavelength corresponds to the transmission maximum point of the comb filter, the laser output can be formed, while the light of other wavelengths cannot form the laser output due to the effect of the comb filter. It can be seen that the output lasing wavelength interval is determined by the comb filter, and its wavelength interval can be adjusted conveniently by changing the comb filter, which is very simple in design.

In Figure 1, Fiber Coupler is an ordinary 50:50 coupler, ISO1 and ISO2 are polarization-independent isolators, ISO1 can overcome the signal interference due to the reflection of the comb filter, and ISO2 avoids the light reflected by the fiber grating Noise generated by oscillation between the coupler and the comb filter. High birefringence polarization-maintaining fiber (Hi-Bi Fiber) and 3dBCoupler form a Sagnac ring to form a comb filter, where the length of the polarization-maintaining fiber is inversely proportional to the period of the comb filter, which determines the laser wavelength of the fiber laser output interval. Pump is a high-power pumping source, and REDF is a section of rare earth-doped optical fiber. Tunable FBG is a large-scale linear tunable fiber grating. By tuning the fiber grating, it plays the role of selecting the lasing wavelength of the fiber laser, and the emitted laser is output from the OUTPUT port.

Fig. 2 is an embodiment of the output spectrum of the narrow linewidth tunable laser realized by the scheme in Fig. 1 . The pump source is a 980nm wavelength laser, REDF is an erbium (Er)-doped fiber, the abscissa is the wavelength (nm), and the ordinate is the output light intensity (dBm). It can be seen from Fig. 2 that the laser wavelength interval between two adjacent wavelengths is basically equal, and this interval is determined by the period of the comb filter, which is 0.51nm. The output laser extinction ratio is greater than 35dB. The spectrogram shown in Figure 2 is scanned when the resolution of the spectrometer is set to 0.01nm. At this time, the 3dB line width of the laser obtained is extremely narrow, all of which are less than 0.015nm.

Claims (1)

1. An ultra-narrow linewidth tunable fiber laser for dense wavelength division multiplexing systems, characterized in that it is equipped with a pump source, a rare earth-doped fiber, 2 isolators, a fiber coupler, and a high birefringence polarization-maintaining fiber A comb filter composed of a 3dB coupler, a rare earth-doped fiber connected to one end of the isolator ISO2, the other end of the isolator ISO2 connected to a fiber coupler, the port of the fiber coupler connected to one end of another isolator ISO1, and the isolator ISO1 The other end of the fiber coupler is connected to the comb filter, the comb filter is connected to the pump source, the port of the fiber coupler is the laser output, and the reflection port of the fiber coupler is connected to the tunable fiber grating.

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