Method for improving performance of erbium-doped optical fiber amplifier based on nonlinear Fourier transform

Abstract

The invention belongs to the field of optical fiber amplifiers, and particularly relates to a method for improving the performance of an erbium-doped optical fiber amplifier based on nonlinear Fourier transform, which comprises the following steps of: performing nonlinear Fourier transform on soliton pulses to obtain a nonlinear spectrum, and extracting eigenvalues and corresponding discrete spectrums from the nonlinear spectrum; identifying the eigenvalue according to the size of the eigenvalue imaginary part to obtain a discrete spectrum corresponding to the soliton pulse and the coherent sideband; the eigenvalue corresponding to the coherent sideband is removed, the eigenvalue corresponding to the soliton pulse is reserved, and a discrete spectrum corresponding to the pure soliton pulse is obtained; performing inverse nonlinear Fourier transform on the obtained nonlinear spectrum of the pure pulse to obtain a pure soliton pulse without a coherent sideband; pure soliton pulses are used for replacing original soliton pulses to be input into the erbium-doped optical fiber amplifier, higher gain and small pulse width broadening can be obtained, and small spectral distortion is generated. The performance of the erbium-doped optical fiber amplifier is improved, and meanwhile the high quality of soliton signals is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber amplifiers, and more specifically, relates to a method for improving the performance of erbium-doped fiber amplifiers based on non-linear Fourier transform. Background Art

[0002] In recent years, with the continuous emergence of new network applications, the global data traffic has grown exponentially, and the transmission capacity of optical fiber communication systems is facing continuous expansion pressure. In optical fiber communication systems, the main reasons for restricting the transmission distance and transmission capacity are the loss, dispersion, and non-linearity of optical fibers. With the development of optical fiber manufacturing technology, the loss of optical fibers has been reduced to an extent close to the theoretical limit value, and the problems of dispersion and non-linearity have become the main problems for realizing ultra-long-distance and ultra-large-capacity optical fiber communication. The dispersion of optical fibers broadens the pulses of optical signals, while non-linearity compresses and narrows the pulses. When the dispersion and non-linear effects cancel each other out, the optical pulses can remain unchanged during optical fiber transmission, achieving ultra-long-distance and ultra-large-capacity communication. Such optical pulses that remain unchanged during the transmission process are called optical solitons. It completely gets rid of the limitations of optical fiber dispersion and non-linearity on the transmission rate and communication capacity, and its transmission capacity is 1-2 orders of magnitude higher than that of the current best communication systems, and the relay distance can reach several hundred kilometers. It is considered to be one of the most promising transmission methods for the next generation.

[0003] As an optical amplification device, the erbium-doped fiber amplifier has become a core device of dense wavelength division multiplexing technology due to its characteristics such as wide bandwidth, high gain, low noise, high pump efficiency, and operating near 1550 nm. In addition to amplifying continuous optical signals, the erbium-doped fiber amplifier can also amplify pulse signals. However, when the erbium-doped fiber amplifier amplifies pulses, problems such as pulse broadening, limited gain, and pulse spectrum distortion are inevitable, making traditional pulsed erbium-doped fiber amplifiers have certain limitations. Summary of the Invention

[0004] In view of the defects and improvement requirements of the prior art, the present invention provides a method for improving the performance of erbium-doped fiber amplifiers based on non-linear Fourier transform, aiming to increase the gain of the erbium-doped fiber amplifier while reducing the broadening of the pulse width and the distortion of the spectrum.

[0005] To achieve the above object, the present invention provides a method for improving the performance of erbium-doped fiber amplifiers based on non-linear Fourier transform, including:

[0006] Collecting the full-time domain information of the soliton pulses output by an erbium-doped fiber laser;

[0007] After normalizing the intensity of the full-time domain information, performing non-linear Fourier transform to transform the full-time domain information to the non-linear frequency domain, obtaining a non-linear spectrum, and extracting each eigenvalue and its corresponding discrete spectrum from the non-linear spectrum;

[0008] Identify the eigenvalues corresponding to pure soliton pulses and coherent sidebands from the respective eigenvalues according to the magnitude of the imaginary part of the eigenvalue, remove the eigenvalues corresponding to the coherent sidebands, and retain the eigenvalues corresponding to the pure soliton pulses;

[0009] Perform an inverse non-linear Fourier transform on the eigenvalues to obtain pure soliton pulses;

[0010] Input the pure soliton pulses into an erbium-doped fiber amplifier to obtain higher gain and smaller pulse-width broadening, thereby improving the performance of the erbium-doped fiber amplifier.

[0011] Furthermore, the implementation method for identifying the eigenvalues corresponding to pure soliton pulses and coherent sidebands from the respective eigenvalues is as follows:

[0012] The non-linear spectrum of a soliton pulse contains the eigenvalue information of pure soliton pulses and coherent sidebands. Among them, the eigenvalue is a complex number, and the magnitudes of its real part and imaginary part correspond to the amplitude and frequency of the soliton pulse respectively. Generally, the imaginary part of the eigenvalue corresponding to a soliton pulse is significantly greater than the imaginary part of the eigenvalue corresponding to the coherent sideband, and the real part of the eigenvalue corresponding to the soliton pulse approaches 0, that is, it is closer to the center frequency.

[0013] According to the imaginary part values of the eigenvalues of the soliton and the coherent sideband, remove the eigenvalues corresponding to the coherent sideband from all the eigenvalues to obtain the eigenvalues corresponding to the pure soliton pulses.

[0014] Furthermore, the implementation method for performing an inverse non-linear Fourier transform on the discrete spectrum to obtain pure soliton pulses is as follows:

[0015] The imaginary part of the eigenvalue corresponding to a pure soliton pulse is greater than the imaginary part of the eigenvalue corresponding to the coherent sideband, and the absolute value of the real part of the eigenvalue corresponding to the pure soliton pulse is the smallest, that is, it is closest to the center frequency.

[0016] Furthermore, the pure soliton pulse is a hyperbolic secant soliton pulse.

[0017] Furthermore, since the pure soliton pulse is a hyperbolic secant soliton pulse with an ideal dispersionless wave background, the non-linear spectrum contains only a single eigenvalue, and the time-domain waveform of the pure soliton pulse is:

[0018]

[0019] where j is the imaginary unit, λ n is the eigenvalue corresponding to the pure soliton pulse, λ R and λ I are the real part and the imaginary part of the eigenvalue respectively, t0 is the central time of the time-domain waveform of the pure soliton pulse, and are the discrete spectra of the pure soliton pulse The amplitude and phase.

[0020] Furthermore, when generating a pure soliton pulse in the time domain by using the inverse nonlinear Fourier transform, it is implemented by the following formula:

[0021]

[0022] where λ i is the eigenvalue corresponding to the soliton pulse, i = 1, 2, ···, N, and N is the number of eigenvalues; λ n is the eigenvalue for the inverse nonlinear Fourier transform, that is, the eigenvalue corresponding to the pure soliton pulse; and are the conjugate complex numbers corresponding to the above eigenvalues; is the discrete spectrum corresponding to the eigenvalue; V(t, λ) is the solution of the linear equation system.

[0023] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0024] The present invention proposes a method for improving an erbium-doped fiber amplifier based on the nonlinear Fourier transform. By using the nonlinear Fourier transform technology, the corresponding eigenvalues and discrete spectra are generated through the amplitude, frequency, central time, and phase of the soliton pulse. After removing the eigenvalues corresponding to the coherent sidebands, the eigenvalues and discrete spectrum functions corresponding to the pure soliton pulse are subjected to the inverse nonlinear Fourier transform to obtain an ideal hyperbolic secant-shaped pure soliton pulse without a dispersion wave background. Inputting this pure pulse into an erbium-doped fiber amplifier, the output pulse obtains higher gain, smaller pulse width broadening, and smaller spectral distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flowchart of a method for improving the performance of an erbium-doped fiber amplifier based on the nonlinear Fourier transform provided by the present invention;

[0026] Figure 2 is the (a) time-domain waveform, (b) frequency-domain spectrum, and (c) eigenvalue distribution diagram of the soliton pulse provided by the present invention;

[0027] Figure 3 is the (a) time-domain waveform, (b) frequency-domain spectrum, and (c) eigenvalue distribution diagram of the pure soliton pulse provided by the present invention;

[0028] Figure 4 is the output spectrum of the soliton pulse at different gain fiber lengths, (a) the original soliton pulse; (b) the pure soliton pulse. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various implementation methods of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The present invention provides a method for improving the performance of an erbium-doped fiber amplifier based on nonlinear Fourier transform, including:

[0031] Collecting the full-time domain information of the soliton pulses output by an erbium-doped fiber laser;

[0032] After normalizing the intensity of the full-time domain information, performing nonlinear Fourier transform to transform the full-time domain information into the nonlinear frequency domain, obtaining a nonlinear spectrum, and extracting each eigenvalue and its corresponding discrete spectrum from the nonlinear spectrum;

[0033] According to the magnitude of the imaginary part of the eigenvalue, identifying the eigenvalues corresponding to pure soliton pulses and coherent sidebands from the eigenvalues, removing the eigenvalues corresponding to coherent sidebands, and retaining the eigenvalues corresponding to pure soliton pulses;

[0034] Performing inverse nonlinear Fourier transform on the eigenvalues to obtain pure soliton pulses;

[0035] Inputting the pure soliton pulses into an erbium-doped fiber amplifier, thereby obtaining higher gain and smaller pulse-width broadening, and improving the performance of the erbium-doped fiber amplifier.

[0036] Embodiment 1

[0037] A method for improving the performance of an erbium-doped fiber amplifier based on nonlinear Fourier transform, as Figure 1 shown, includes:

[0038] Collecting the full-time domain information of the soliton pulses output by a fiber laser;

[0039] After normalizing the intensity of the full-time domain information, performing nonlinear Fourier transform to transform the full-time domain information into the nonlinear frequency domain, obtaining a nonlinear spectrum, and extracting the eigenvalues and corresponding discrete spectra of pure soliton pulses and coherent sidebands from the nonlinear spectrum;

[0040] According to the magnitude of the imaginary part of the eigenvalue, identifying the eigenvalues corresponding to pure soliton pulses and coherent sidebands respectively from the eigenvalues, and removing the eigenvalues corresponding to coherent sidebands, thereby obtaining the discrete spectrum corresponding to pure soliton pulses;

[0041] Performing inverse nonlinear Fourier transform on the nonlinear spectrum of pure soliton pulses to obtain pure soliton pulses;

[0042] The obtained pure soliton pulse is input into an erbium-doped fiber amplifier to obtain higher gain, smaller pulse-width broadening, and smaller spectral distortion.

[0043] In the soliton pulse, the pure soliton pulse and the coherent sidebands correspond one-to-one to the respective eigenvalues in the nonlinear domain. Considering that the imaginary part of the eigenvalue is related to the intensity of the temporal soliton or coherent sideband, and the modulus value of the eigenvalue is related to the position (time center) of the temporal soliton, the eigenvalues corresponding to the pure soliton pulse and the coherent sidebands can be distinguished by the magnitude of the value of the imaginary part of the eigenvalue and the corresponding position of the real part.

[0044] After filtering the sidebands of the seed-source soliton pulse to be amplified to obtain a pure soliton pulse and then inputting it into the erbium-doped fiber amplifier, the performance of the erbium-doped fiber amplifier is improved, specifically manifested as increased gain, reduced pulse-width broadening, and reduced spectral distortion.

[0045] To verify the effectiveness of this embodiment, the following example is proposed in this embodiment:

[0046] The total cavity length of the fiber laser is 6 meters, including: two sections of single-mode fiber with a total length of 3 meters and one section of 3-meter erbium-doped fiber. The fiber dispersion parameter in the cavity is -23 ps 2 / km, and mode locking is achieved through the nonlinear polarization rotation technique. By adjusting the pump power, a stable soliton pulse output is obtained, which serves as the seed source of the erbium-doped fiber amplifier. Its energy is 7.61 pJ, and the full width at half maximum is 264 fs. As Figure 2 shown, it is the soliton pulse output of the fiber laser. Among them, Figure 2 in (a) is the temporal waveform, Figure 2 in (b) is the frequency-domain spectrum, Figure 2 in (c) are the eigenvalues corresponding to the soliton pulse. The imaginary part of the eigenvalue corresponds to the intensity of the pure soliton pulse and the coherent sidebands. As shown by Figure 2 in (c), it can be clearly found that the eigenvalue with a larger imaginary part is the one corresponding to the pure soliton pulse, and the eigenvalue with a smaller imaginary part is the one corresponding to the coherent sideband.

[0047] Eliminate Figure 2 the two eigenvalues corresponding to the coherent sidebands in (c), retain the eigenvalues corresponding to the pure soliton pulse, and perform inverse nonlinear Fourier transform on them, and a pure soliton pulse as shown in Figure 3 can be obtained. Among them, Figure 3 in (a) is the temporal waveform, Figure 3 in (b) is the frequency-domain spectrum, Figure 3 in (c) are the eigenvalues corresponding to the pure soliton pulse. It can be found that by this method based on nonlinear Fourier transform, the coherent sidebands of the soliton pulse can be effectively filtered out, and a pure soliton pulse without sidebands can be output.

[0048] The original soliton pulse in Figure 1 and the pure soliton pulse in Figure 2 are respectively input into erbium-doped fiber amplifiers with the same parameters, and the time-domain waveforms of the output pulses are compared. After the pure soliton pulse with the coherent sidebands filtered out is amplified by the erbium-doped fiber amplifier, the full width at half maximum is 381 ps, the output energy is 510.67 pJ, and the gain of the erbium-doped fiber amplifier for the pure soliton pulse is 39.0 dB. After the original soliton pulse is amplified by the erbium-doped fiber amplifier, the full width at half maximum is 410 ps, the output energy is 474.14 pJ, and the gain of the erbium-doped fiber amplifier for the original soliton pulse is 35.7 dB. Therefore, it can be found that the gain of the erbium-doped fiber amplifier for the pure soliton pulse is higher than that for the original soliton pulse, and the pulse width broadening of the erbium-doped fiber amplifier for the pure soliton pulse is less than that for the original soliton pulse.

[0049] The original soliton pulse in Figure 1 and the pure soliton pulse in Figure 2 are respectively input into erbium-doped fiber amplifiers using erbium-doped fibers of different lengths, and the frequency-domain spectra of the output pulses are compared, as shown in Figure 4 . In order to better compare the changes in the spectral shape, the intensity is normalized. Among them, Figure 4 (a) shows the spectral outputs of the original soliton pulse after passing through erbium-doped fibers of 6 m, 7 m, 8 m, and 9 m respectively, Figure 4 (b) shows the spectral outputs of the pure soliton pulse after passing through erbium-doped fibers of 6 m, 7 m, 8 m, and 9 m respectively. As the length of the erbium-doped fiber gradually increases, the shapes of the spectra of both the pure soliton pulse and the original soliton pulse are gradually distorted, but it can be found that the distortion of the spectrum of the pure soliton pulse with the increase of the erbium-doped fiber length is significantly less than that of the spectrum of the original soliton pulse. Therefore, the erbium-doped fiber amplifier has a better effect on the spectral output of the pure soliton pulse compared to the original soliton pulse.

[0050] Generally speaking, this embodiment uses the nonlinear Fourier transform technology to provide a method for improving the performance of erbium-doped fiber amplifiers. After collecting the full-field information of the soliton pulse seed source, the pulse intensity is normalized, and then through the nonlinear Fourier transform, the time-domain pulse is transformed into the nonlinear domain to obtain its eigenvalues and discrete spectrum. Then, the eigenvalues of the coherent sidebands are removed, and the inverse nonlinear Fourier transform is performed on the discrete spectrum corresponding to the pure soliton pulse to obtain a pure soliton pulse without sidebands. Finally, this pure soliton pulse is input into the erbium-doped fiber amplifier. Compared with the original soliton pulse, the erbium-doped fiber amplifier has better performance for the pure soliton pulse. This embodiment provides a method for improving the performance of erbium-doped fiber amplifiers in the field of fiber amplifiers, which can directly improve the gain of the erbium-doped fiber amplifier and the quality of the output signal, and better meet the requirements of the soliton communication system.

[0051] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the performance of an erbium-doped fiber amplifier based on non-linear Fourier transform, characterized in that Including: Collecting the time-domain full-field information of the soliton pulses output by the fiber laser; After performing intensity normalization on the full-field information, performing a non-linear Fourier transform to transform the time-domain full-field information into the non-linear frequency domain, obtaining a non-linear spectrum, and extracting the eigenvalues corresponding to the pure soliton pulses and coherent sidebands and their corresponding discrete spectra from the non-linear spectrum; According to the magnitude of the imaginary part of the eigenvalue, identifying the eigenvalues corresponding to the pure soliton pulses and coherent sidebands respectively from the eigenvalues, removing the eigenvalues corresponding to the coherent sidebands, and retaining the eigenvalues corresponding to the pure soliton pulses; Performing an inverse non-linear Fourier transform on the eigenvalues corresponding to the pure soliton pulses to obtain pure soliton pulses; Inputting the pure soliton pulses into an erbium-doped fiber amplifier to increase the gain of the erbium-doped fiber amplifier and reduce the pulse-width broadening.

2. The method for improving the performance of an erbium-doped fiber amplifier based on non-linear Fourier transform according to claim 1, characterized in that, The implementation manner of identifying the eigenvalues corresponding to the pure soliton pulses from the eigenvalues is as follows: The imaginary part of the eigenvalue corresponding to the pure soliton pulse is greater than the imaginary part of the eigenvalue corresponding to the coherent sideband, and the absolute value of the real part of the eigenvalue corresponding to the pure soliton pulse is the smallest, that is, closest to the center frequency.

3. The method for improving the performance of an erbium-doped fiber amplifier based on non-linear Fourier transform according to claim 1, characterized in that, The pure soliton pulse is a hyperbolic secant-shaped soliton pulse.

4. The method for improving the performance of an erbium-doped fiber amplifier based on non-linear Fourier transform according to claim 3, characterized in that, The time-domain waveform of the pure soliton pulse is: where j is the imaginary unit, and λ n is the eigenvalue corresponding to the pure soliton pulse, λ R and λ I are the real and imaginary parts of the eigenvalue respectively, and t0 is the central time of the time domain waveform of the pure soliton pulse.

5. An electronic device, characterized in that, Including: A computer-readable storage medium and a processor; The computer-readable storage medium is used for storing executable instructions; The processor is used for reading the executable instructions stored in the computer-readable storage medium and executing the method according to any one of claims 1-4.

6. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, and the computer instructions are used for causing the processor to execute the method according to any one of claims 1-4.

7. A computer program product, comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed by the processor, the method according to any one of claims 1-4 is implemented.

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