CN113258421B - Device and method for improving stability of chaotic fiber laser based on chaotic light injection - Google Patents

Abstract

The invention discloses a device and a method for improving the stability of a chaotic fiber laser based on chaotic light injection, which comprises a Master Laser (ML) and a Slave Laser (SL); the main laser includes: the device comprises a first semiconductor laser pumping source (LD1), a first wavelength division multiplexer (WDM1), a first erbium-doped fiber (EDF1), a first coupler (OC1), a polarization controller (PC1), a first polarization-independent optical isolator (ISO1) and a tunable optical Filter (Filter). The master laser is connected to the slave laser through an isolator (OC4) to form an injection structure. The master-slave laser works in a chaotic state, and the short-term time jitter of the chaotic fiber laser can be eliminated and the self-mode locking caused by long-term instability can be eliminated through the master-slave injection structure. Meanwhile, a method for evaluating the stability of the chaotic signal by using the standard deviation of the permutation entropy is provided.

Description

Device and method for improving stability of chaotic fiber laser based on chaotic light injection

Technical Field

The invention relates to the field of chaotic fiber lasers, in particular to a device and a method for improving the stability of a chaotic fiber laser based on chaotic light injection.

Background

Since the last 90 s, fiber lasers have been developed vigorously, and scientists have conducted a great deal of research on the chaotic behavior of fiber lasers. It is found that chaos can be formed by external cavity feedback, saturation absorption of erbium ion pair, additional modulator and special cavity structure, including 8-shaped cavity, 9-shaped cavity, and the fiber laser works in chaos state by means of nonlinear Kerr effect of fiber cavity. In the 21 st century, the research on the application of the chaotic fiber laser is more and more concerned. Chaotic secret communication research, chaotic optical fiber sensing research and chaotic radar research based on chaotic optical fiber lasers are greatly developed.

These studies do not rely on a highly complex and extremely stable source of chaos. However, a pure fiber laser is easy to generate time jitter, and the fiber laser is also easy to lose a chaotic state after long-term unstable accumulation, so that the invention aims to obtain a stable chaotic source. A large number of theories and experiments prove that the light injection technology can realize the functions of laser system stability, bandwidth modulation, wavelength selection, noise suppression and the like.

Disclosure of Invention

The invention solves the instability problems of the chaotic fiber laser during operation, including short-term time jitter and long-term self-mode locking. Meanwhile, the stability of the chaotic signal is described by the standard deviation of the permutation entropy of the chaotic signal. The chaotic signal generated by the master laser increases the degree of freedom of the slave laser when the low power is injected into the slave laser, and simultaneously, the frequency difference between the master laser and the slave laser is small, so that the locking can be realized, and the aim of stabilizing the output of the laser is fulfilled. Specifically, the time jitter on the chaotic signal is eliminated in a short term, and the self-pulse generated by the self-mode locking of the fiber laser can be inhibited in a long term.

A device for improving the stability of a chaotic fiber laser based on chaotic light injection comprises a Master Laser (ML) and a Slave Laser (SL); the main laser includes: a first semiconductor laser pump source (LD1), a first wavelength division multiplexer (WDM1), a first erbium doped fiber (EDF1), a first coupler (OC1), a polarization controller (PC1), a first polarization independent optical isolator (ISO1), a tunable optical Filter (Filter), the slave laser comprising: the laser comprises a second semiconductor laser pump source (LD2), a second wavelength division multiplexer (WDM2), a second erbium-doped fiber (EDF2), an output coupler (OC2), an input coupler (OC3), a polarization controller (PC2) and a second polarization-independent optical isolator (ISO2), wherein the master laser and the slave laser are connected between the fourth coupler (OC4) and the fourth isolator (ISO4) through flanges to form an injection structure.

In the device, 974nm pump light of a first semiconductor laser pumping source (LD1) enters a laser cavity through a first wavelength division multiplexer (WDM1), and the stimulated radiation is realized in a first erbium-doped fiber (EDF1) of 1m to generate 1550nm signal light; the 1550nm signal light passes through a first polarization-independent optical isolator (ISO1), then passes through a tunable optical Filter (Filter), enters a 1000m long single-mode optical fiber (SMF1), and passes through a 90: 10 first coupler (OC1), 10% output signal light, 90% re-enter loop; the main laser works in a chaotic state by adjusting a polarization controller (PC 1); the output signal light is divided into two paths through a third isolator (ISO3) and a fourth coupler (OC4), and an output spectrum is monitored by a 5% connection Optical Spectrum Analyzer (OSA); the slave laser is regulated by the fact that 95% of the optical signal enters the laser cavity through the fourth isolator (ISO4) and the input coupler (OC 3); 974nm pump light of a second semiconductor laser pump source (LD2) enters a laser cavity through a second wavelength division multiplexer (WDM2), and the generation of 1550nm signal light by stimulated radiation is realized in a second erbium-doped fiber (EDF2) of 1 m; the 1550nm signal light passes through a second isolator (ISO2) into a 1000m long single mode fibre (SMF2) and through a 90: 10 output coupler (OC2), 90% re-entering the loop via input coupler (OC 3); 10% of signal light is divided into two paths through a coupler (OC5), 95% of signal light is converted into an electric signal through PD and is connected into an Oscilloscope (OSC), a chaotic signal is collected from the OSC, and 5% of input Optical Spectrum Analyzer (OSA) monitors the spectrum signal.

In the device, the erbium-doped fibers in the master laser and the slave laser are both 1m high-doped fibers, and the absorption at 1530nm is 50 dB/m.

In the device, single-mode fibers of a master laser and a slave laser are 1000m SMF-28e fibers.

In the device, the filtering bandwidth of the optical filter is 50 dB.

In the device, the isolators all adopt polarization-independent isolators.

The device can realize the injection power ratio of the master laser and the slave laser from 0.04 to 0.14.

The frequency difference of the master laser and the slave laser can be realized in the range of-0.3 nm to +0.3 nm.

According to any method for improving the stability of the erbium-doped fiber laser, the master laser works in a chaotic state and is injected into the slave laser with low power, so that the slave laser is modulated.

A method of characterizing the stability of a chaotic signal obtained according to the method, characterized by using a plurality of sets of standard deviations of time series permutation entropies, permutation entropy Standard Deviation (SDOPE), whose expression is as follows:

in the formula H_iRepresenting the permutation entropy of the ith set of chaotic signals,

represents the average of N sets of permutation entropies.

The invention has the beneficial effects that: (1) the master-slave injection structure can induce the generation of chaos; (2) the chaotic light injection can realize the time jitter of the chaotic signal; (3) the self-locking mode of the chaotic system can be prevented through chaotic light injection; (4) the implementation method is simple, and the complexity of the chaotic signal is ensured on the basis of improving the stability of the chaotic system.

Drawings

FIG. 1 is a schematic structural diagram of an experimental apparatus for injecting a chaotic light into an erbium-doped fiber laser adopted by the present invention;

FIG. 2 is a P-I plot of master and slave laser outputs; (a) and (b) the graphs are output power graphs of the master laser and the slave laser respectively;

FIG. 3 is a timing diagram (a), a spectrogram (b), an autocorrelation chart (c), and a spectrogram (d) of the output of the master laser at 400mA pump;

FIG. 4 is an output spectrum of a laser system with different wavelength detunes of the master and slave lasers;

FIG. 5 is a timing diagram, a frequency spectrum diagram, an autocorrelation diagram and a spectrum diagram of a chaotic signal with an injection power ratio of 0.15;

FIG. 6 is a graph of the variation of the chaotic signals PE and SDOPE output from the laser with different injection power ratios;

FIG. 7 is a timing diagram of the output self-pulses when pumped from laser 400 mA;

fig. 8 is a timing chart a of laser output signals in different output states: 113mA from: 400 mA; b, main: 113.4mA from: 400 mA; c, main: 113.7mA from: 400 mA; d, main: 116.5mA from: 400 mA;

FIG. 9 shows the arrangement entropy and standard deviation of the chaos signal output by the injection slave laser under different pumping conditions of the master laser;

in the figure, LD: semiconductor laser, WDM: wavelength division multiplexer, EDF: erbium-doped fiber, SMF: single mode fiber, Filter: tunable optical filter, OC: optical coupler, PC: polarization controller, ISO: optical isolator, PD: photodetector, OSC: oscilloscope, OSA: spectrum analyzer, PE: permutation entropy, SDOPE: and arranging standard deviation of entropy.

Detailed Description

The present invention will be described in detail with reference to specific examples.

As shown in fig. 1, the master and slave fiber lasers both adopt a ring cavity structure, and generate chaotic laser by using the nonlinear kerr effect of the fiber. The pumping sources (LD1 and LD2) are semiconductor lasers with the wavelength of 974 nm; the erbium-doped fiber (EDF1, EDF2) is 1m long; the single-mode optical fiber (SMF1, SMF2) is 1000m in length; wavelength division multiplexers (WDM1, WDM2) for coupling 974nm pump light with 1550nm stimulated emission light; the isolator (ISO1, ISO2) ensures the unidirectional transmission of laser in the optical fiber cavity and removes redundant pump light; the polarization controllers (PC1 and PC2) adjust polarization and loss in the optical fiber cavity; the tunable optical Filter (Filter) ensures that the laser works near 1550nm, and controls the output line width of the main laser, wherein the tuning range is 1530-1570 nm; the splitting ratios of the output couplers (OC1 and OC2) are both 90: 10, 10% end outputs signal, 90% end enters into intracavity to circulate; the input coupler (OC3) split ratio was 95: 5, 5% end is used as input port, 95% end is connected to slave laser; isolator 3(ISO3) prevents reflected light from entering the main laser and affecting it; coupler 4(OC4) facilitates monitoring of the master laser; the master and slave lasers are connected by isolator 4(ISO4) forming an injection structure. As shown with reference to fig. 2, is a graph of the output power of the master and slave lasers.

974nm pump light of a semiconductor laser (LD1) enters a laser cavity through a wavelength division multiplexer (WDM1), and the generation of 1550nm signal light by stimulated radiation is realized in a 1m erbium-doped fiber (EDF 1). The 1550nm signal light passes through an isolator (ISO1), then passes through a tunable optical Filter (Filter), enters a 1000m long single-mode optical fiber (SMF1), and passes through a 90: 10 coupler 1(OC1), 10% of the output signal light, 90% re-enters the loop. The master laser is operated in a chaotic state by adjusting a polarization controller (PC 1). The output signal light is divided into two paths by an isolator 3(ISO3) and a coupler 4(OC4), and a 5% connection Optical Spectrum Analyzer (OSA) monitors an output spectrum. The slave laser is conditioned by the 95% optical signal entering the laser cavity through isolator 4(ISO4) and input coupler 3(OC 3). 974nm pump light of a semiconductor laser (LD2) enters a laser cavity through a wavelength division multiplexer (WDM2), and the generation of 1550nm signal light by stimulated radiation is realized in a 1m erbium-doped fiber (EDF 2). The 1550nm signal light enters a 1000m long single mode fiber (SMF2) through an isolator (ISO2), and passes through a 90: 10 output coupler 2(OC2), 90% re-enters the loop via input coupler (OC 3). 10% of signal light is divided into two paths through a coupler 5(OC5), 95% of signal light is converted into an electric signal through a PD and is connected into an Oscilloscope (OSC), a chaotic signal is collected from the OSC, and 5% of input Optical Spectrum Analyzer (OSA) monitors the spectrum signal.

The master laser is operated in a chaotic state by tuning a polarization controller (PC 1). The coupler 4(OC4) outputs a main laser signal at the 5% end, the main laser spectral information is observed and collected through an Optical Spectrum Analyzer (OSA), and an optical signal output at the 95% end is converted into an electric signal through a PD and is observed and collected through an Oscilloscope (OSC). And carrying out FFT (fast Fourier transform) on the acquired time sequence to obtain a spectrogram, and carrying out correlation operation on the acquired time sequence to obtain an autocorrelation graph. Refer to fig. 3.

Since there is no filter from the laser, there are more operating states. And adjusting the pumping current of the polarization controller and the LD2 to make the slave laser work in a chaotic state. Meanwhile, in order to ensure that the master laser exerts influence on the slave laser, the frequency detuning range of the master laser and the slave laser needs to be determined, referring to fig. 4, the output spectra of the laser system under different wavelength detuning conditions, and the detuning range of chaotic injection is determined to be in the range of-0.3 nm to +0.3 nm.

There is a short period of time jitter in the chaotic state output from the laser. The master laser is connected with the slave laser, so that the chaotic light output by the master laser is injected into the slave laser in a certain proportion, and then the chaotic signal is observed and output by an oscilloscope. Referring to fig. 5, a timing diagram, a frequency spectrum diagram, an autocorrelation diagram, and a spectrum diagram of the chaotic signal output when the injection power ratio is 0.15.

The method is characterized in that besides the method, the chaotic signal complexity is also used as an index for representing the stability of the chaotic fiber laser. Therefore, standard deviation analysis is performed on the arrangement entropy of the N groups of data under the same state to obtain the arrangement entropy Standard Deviation (SDOPE), and the expression is as follows:

in the formula H_iRepresenting the permutation entropy of the ith set of chaotic signals,

represents the average of N sets of permutation entropies.

In order to describe the stability of the injected chaotic signal, the chaotic signal under different injection power ratios is subjected to permutation entropy standard deviation analysis, and referring to fig. 6, it can be seen from the figure that the injected chaotic signal has higher stability and eliminates time jitter to a certain extent on the basis of higher complexity.

There is also long term instability of the slave laser, referred to as self-pulsing due to self-mode locking as shown in fig. 7. The master laser is connected with the slave laser, so that the chaotic light output by the master laser is injected into the slave laser, then the chaotic signal is observed and output by an oscilloscope, and the output spectrum is observed by an Optical Spectrum Analyzer (OSA). Referring to fig. 8, the time sequence evolution of the master laser low-power injection slave laser, it can be seen that as the power of the master laser increases, the self-pulse is suppressed, and the system works in the chaotic state again. The standard deviation analysis of permutation entropy is performed on the chaotic signals under different injection power ratios, and referring to fig. 9, it can be seen from the figure that as the self-pulse is suppressed, the signal complexity is improved and stabilized at a higher level, and at the same time, the stability is enhanced. Therefore, the chaotic light injection can eliminate the self-pulse caused by long-term unstable accumulation of the fiber laser and improve the stability of the chaotic fiber laser.

It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.

Claims (9)

1. A device for improving the stability of a chaotic fiber laser based on chaotic light injection is characterized by comprising a Master Laser (ML) and a Slave Laser (SL); the main laser includes: a first semiconductor laser pump source (LD1), a first wavelength division multiplexer (WDM1), a first erbium doped fiber (EDF1), a first coupler (OC1), a polarization controller (PC1), a first polarization independent optical isolator (ISO1), a tunable optical Filter (Filter), the slave laser comprising: the laser comprises a second semiconductor laser pump source (LD2), a second wavelength division multiplexer (WDM2), a second erbium-doped fiber (EDF2), an output coupler (OC2), an input coupler (OC3), a polarization controller (PC2) and a second polarization-independent optical isolator (ISO2), wherein the master laser and the slave laser are connected between the fourth coupler (OC4) and the fourth isolator (ISO4) through flanges to form an injection structure; 974nm pump light of a first semiconductor laser pumping source (LD1) enters a laser cavity through a first wavelength division multiplexer (WDM1), and the generation of 1550nm signal light by stimulated radiation is realized in a first erbium-doped fiber (EDF1) of 1 m; the 1550nm signal light passes through a first polarization-independent optical isolator (ISO1), then passes through a tunable optical Filter (Filter), enters a 1000m long single-mode optical fiber (SMF1), and passes through a 90: 10 first coupler (OC1), 10% output signal light, 90% re-enter loop; the main laser works in a chaotic state by adjusting a polarization controller (PC 1); the output signal light is divided into two paths through a third isolator (ISO3) and a fourth coupler (OC4), and an output spectrum is monitored by a 5% connection Optical Spectrum Analyzer (OSA); the slave laser is regulated by the fact that 95% of the optical signal enters the laser cavity through the fourth isolator (ISO4) and the input coupler (OC 3); 974nm pump light of a second semiconductor laser pump source (LD2) enters a laser cavity through a second wavelength division multiplexer (WDM2), and the generation of 1550nm signal light by stimulated radiation is realized in a second erbium-doped fiber (EDF2) of 1 m; the 1550nm signal light was passed through a second polarization independent optical isolator (ISO2) into a 1000m long single mode optical fibre (SMF2) and through a 90: 10 output coupler (OC2), 90% re-entering the loop via input coupler (OC 3); 10% of signal light is divided into two paths through a coupler (OC5), 95% of signal light is converted into an electric signal through PD and is connected into an Oscilloscope (OSC), a chaotic signal is collected from the OSC, and 5% of input Optical Spectrum Analyzer (OSA) monitors the spectrum signal.

2. The apparatus of claim 1, wherein the erbium doped fibers of the master and slave lasers are both 1m high doped fibers and have an absorption of 50dB/m at 1530 nm.

3. The apparatus of claim 1, wherein the single mode fibers in both the master and slave lasers are 1000m SMF-28e fibers.

4. The apparatus of claim 1, wherein the filter bandwidth of the optical filter is 50 dB.

5. The apparatus of claim 1, wherein the isolators are polarization independent isolators.

6. The apparatus of claim 1 wherein the master-to-slave laser injection power ratio is achievable in the range of from 0.04 to 0.14.

7. The apparatus of claim 1, wherein the master and slave laser frequency differences are achievable in the range of-0.3 nm to +0.3 nm.

8. A method for improving the stability of an erbium-doped fiber laser according to any one of claims 1-7, wherein the master laser is operated in a chaotic state and injected with low power into the slave laser to modulate the slave laser.

9. A method of characterizing the stability of a chaotic signal obtained by the method of claim 8, wherein a plurality of sets of standard deviations of time-series permutation entropies, permutation entropy Standard Deviations (SDOPE), are used, and the expression:

in the formula H_iRepresenting the permutation entropy of the ith set of chaotic signals,

represents the average of N sets of permutation entropies.

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