CN111983871B - All-optical amplification method of optical soliton pulse train - Google Patents

Abstract

The invention provides an all-optical amplification method of an optical soliton pulse train, belongs to the technical field of optics, and aims to solve the problem that the existing mode for amplifying the optical soliton pulse train is limited by an amplifier and has certain limitation. The invention can realize the direct amplification of the optical soliton pulse train by utilizing the method of combining plane wave pumping and a frequency spectrum filter. The amplification process expressed by the amplification method is independent of factors such as the width, the central wavelength, the optical fiber doping concentration and the like of the optical soliton pulse, and the method is applicable to high-order models and optical fiber systems in different modes, and particularly can realize direct amplification of ultrashort optical soliton pulse strings. The amplification method of the invention is not limited by factors such as parameters of the amplifier, and the like, so the amplification mode is relatively flexible.

Description

All-optical Amplification Method of Soliton Pulse Train

technical field

The invention relates to the field of optical technology, in particular to an all-optical amplification method of an optical soliton pulse train.

Background technique

All-optical signal processing has higher speed, lower latency, and greater bandwidth than electrical signal processing. One of the goals of modern nonlinear optics is the development of ultrafast all-optical devices, of which all-optical amplifiers are an important part. Solitons are localized light waves propagating in optically nonlinear media that can travel long distances without changing their shape. Due to their potential applications in optical communication and optical signal processing systems, a large number of studies have been carried out on optical solitons in the past few decades, such as the existence and stability of solitons, soliton collisions and interactions, and higher-order solitons. With the emergence of the concept of optical soliton, in the early 1980s, Hasegawa and Kodama theoretically proposed the mechanism of soliton amplification, which can be realized by erbium-doped amplifiers, Raman amplifiers, parametric amplifiers and semiconductor amplifiers in practice.

At present, in soliton amplification, erbium-doped amplifiers and Raman amplifiers are used more. These amplifiers have their own limitations in practical use, especially for the amplification of ultra-short pulses in the femtosecond range, it is difficult to realize erbium-doped amplifiers and Raman amplifiers. For erbium-doped amplifiers, the amplification of ultrashort pulses is based on erbium doping with fairly high concentrations (between 1000 ppm and 2000 ppm). For Raman amplification, nonlinear effects such as stimulated Brillouin scattering, self-phase modulation, etc. can affect the performance of the amplifier, especially for ultrashort pulsed systems.

To sum up, the current way of amplifying the optical soliton pulse train has certain limitations due to the limitation of the amplifier.

SUMMARY OF THE INVENTION

In order to solve the technical problem that the current way of amplifying the optical soliton pulse train is limited by the amplifier, the present invention provides an all-optical amplifying method for the optical soliton pulse train.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

An all-optical amplification method for an optical soliton pulse train, comprising the following steps:

S1, generating an initial optical soliton pulse train, and injecting the initial optical soliton pulse train into a single-mode fiber for transmission;

S2, control the initial optical soliton pulse train to transmit z _A = 23.8095-34.5238km in the single-mode fiber, reduce the peak power P of the initial optical soliton pulse train to 2.5788-0.4293W, and obtain the attenuated optical soliton pulse train;

的混合波，并让混合波继续在单模光纤中传输；S3, inject a continuous plane wave with power P ₀ at z _A of the single-mode fiber, and mix it with the attenuated optical soliton pulse train, the composition form is

the mixed wave, and let the mixed wave continue to transmit in the single-mode fiber;

S4, under the action of the continuous plane wave, the attenuated optical soliton pulse train is gradually amplified, and continues to transmit in the single-mode fiber. When L _A = 0.2893-1.5381km, the attenuated pulse train is amplified to form an amplified optical soliton with a plane wave background pulse train;

S5, place a spectral filter at the position z _A +L _A of the single-mode fiber, and perform spectral filtering with the wavelength of the amplified optical soliton pulse train 1550 nm as the center and 0.2 nm as the width to obtain the amplified optical soliton pulse with zero background stable transmission At this time, the amplified optical soliton pulse train with zero background stable transmission has the same power as the initial optical soliton pulse train.

Optionally, the S1 is implemented by the following process when generating the initial optical soliton pulse train:

The transmission of a picosecond light pulse in a single-mode fiber is described by the following nonlinear Schrödinger equation:

In formula (1), A=A(z, T) is the slow-varying envelope of the electromagnetic field, z is the transmission distance, T is the time measurement in the reference frame moving with the pulse at the group velocity v _g , T=tz/v _g , the coefficients β ₂ and γ are the second-order group velocity dispersion GVD and Kerr nonlinear parameters, respectively, and α > 0 is the fiber loss;

Regardless of fiber loss, under anomalous dispersion conditions, that is, β < 0 and α = 0, equation (1) has a solution of the form:

时间尺度T₀＝(|β₂|/γP₀)^1/2，这里z₀是一个实参数；ω为调制频率，

a为调制不稳定增益；

确定不稳定调制增长；当0＜a＜1/2时，公式(2)表示的解称为Akhmediev呼吸解；In formula (2), P ₀ is the average power of the incident field, time τ=T/T ₀ , distance Z=(zz ₀ )/L _NL , normalized nonlinear length

Time scale T ₀ =(|β ₂ |/γP ₀ ) ^1/2 , where z ₀ is a real parameter; ω is the modulation frequency,

a is the modulation instability gain;

Determine the unstable modulation growth; when 0 < a < 1/2, the solution expressed by formula (2) is called the Akhmediev breathing solution;

For the periodic solution (2) of the Schrödinger equation (1), its Fourier series expansion has the following form:

The forms of pump wave and sideband amplitude evolution are:

n=±1,±2,±3... is an integer

得到无背景的能够稳定传输的光孤子脉冲串；Filter out time-invariant in the frequency domain

A background-free optical soliton pulse train that can be transmitted stably is obtained;

If the fiber loss is not considered, that is, when α=0 in the formula (1), the zero-background pulse train represented by the formula (5) can be transmitted stably.

Optionally, the single-mode fiber is a silica SMF-28 fiber, the second-order group velocity dispersion GVD is β ₂ =-21.4ps ² km ^-1 , the Kerr nonlinear parameter γ=1.2W ^-1 km ^-1 , The fiber loss α=0.19dB/km, the center wavelength is 1550nm, and the incident power P ₀ =0.7W.

The beneficial effects of the present invention are:

The invention utilizes the method of combining plane wave pumping and spectrum filter, and can realize the direct amplification of the optical soliton pulse train. The amplification process represented by this amplification method has nothing to do with the width of the soliton pulse, the central wavelength, the fiber doping concentration and other factors, and can be applied to high-order models and fiber systems of different modes, especially for ultra-short soliton pulse trains. Achieving direct magnification. The amplification method of the present invention is relatively flexible because it is not restricted by factors such as parameters of the amplifier.

Description of drawings

Figure 1 is a schematic diagram of the stable transmission of an optical soliton pulse train.

FIG. 2 is an enlarged schematic diagram of an optical soliton pulse train.

FIG. 3 is a 4-stage enlarged schematic diagram of an optical soliton pulse train.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

An all-optical amplifying method for an optical soliton pulse train in an embodiment of the present invention includes the following steps:

S1, generating an initial optical soliton pulse train, and injecting the initial optical soliton pulse train into a single-mode fiber for transmission.

S2, control the initial optical soliton pulse train to transmit z _A = 23.8095-34.5238km in the single-mode fiber, and reduce the peak power P of the initial optical soliton pulse train to 2.5788-0.4293 W to obtain an attenuated optical soliton pulse train.

的混合波，并让混合波继续在单模光纤中传输。S3, inject a continuous plane wave with power P ₀ at z _A of the single-mode fiber, and mix it with the attenuated optical soliton pulse train, the composition form is

the mixed wave and let the mixed wave continue to propagate in the single-mode fiber.

S4, under the action of the continuous plane wave, the attenuated optical soliton pulse train is gradually amplified, and continues to transmit in the single-mode fiber. When L _A = 0.2893-1.5381km, the attenuated pulse train is amplified to form an amplified optical soliton with a plane wave background burst.

S5, place a spectral filter at the position z _A +L _A of the single-mode fiber, and perform spectral filtering with the wavelength of the amplified optical soliton pulse train 1550 nm as the center and 0.2 nm as the width to obtain the amplified optical soliton pulse with zero background stable transmission string. At this time, the zero-background amplified optical soliton pulse train has the same power as the initial optical soliton pulse train.

Optionally, the S1 is implemented by the following process when generating the initial optical soliton pulse train:

The transmission of a picosecond light pulse in a single-mode fiber is described by the following nonlinear Schrödinger equation:

In formula (1), A=A(z, T) is the slow-varying envelope of the electromagnetic field, z is the transmission distance, T is the time measurement in the reference frame moving with the pulse at the group velocity v _g , T=tz/v _g , the coefficients β ₂ and γ are the second-order group velocity dispersion GVD and Kerr nonlinear parameters, respectively, and α > 0 is the fiber loss.

Regardless of fiber loss, under anomalous dispersion conditions, that is, β < 0 and α = 0, equation (1) has a solution of the form:

时间尺度T₀＝(|β₂|/γP₀)^1/2，这里z₀是一个实参数。ω为调制频率，

a为调制不稳定增益。

确定不稳定调制增长。In formula (2), P ₀ is the average power of the incident field, time τ=T/T ₀ , and distance Z=(zz ₀ )/L _NL . normalized nonlinear length

Time scale T ₀ =(|β ₂ |/γP ₀ ) ^1/2 , where z ₀ is a real parameter. ω is the modulation frequency,

a is the modulation instability gain.

Determine unstable modulation growth.

When 0<a<1/2, the solution represented by formula (2) is called the Akhmediev breathing solution.

以上解成为怪波解，具有如下形式：when

The above solution becomes the strange wave solution, which has the following form:

The solution starts from a continuous plane wave with intensity |A(0,T)| ² =P ₀ at the initial moment. According to the modulation instability principle, due to the existence of the continuous plane wave, the initial optical soliton pulse train with small peaks, with the transmission With the evolution of distance, the pulse width gradually narrows, and the peak power gradually increases, and an amplified optical soliton pulse train is formed at z=ξ ₀ (ξ ₀ ≤z ₀ ). However, due to the existence of continuous plane waves, the formed amplified optical soliton pulse train cannot be transmitted stably. Therefore, the present invention can realize the stable transmission of the amplified optical soliton pulse train by using the spectrum filtering method to filter out the spectrum of the unstable continuous plane wave.

For the periodic solution (2) of the Schrödinger equation (1), its Fourier series expansion has the following form:

The forms of pump wave and sideband amplitude evolution are:

n=±1,±2,±3... is an integer

得到无背景的能够稳定传输的光孤子脉冲串。Filter out time-invariant in the frequency domain

A background-free optical soliton pulse train capable of stable transmission is obtained.

If the fiber loss is not considered, that is, when α=0 in the formula (1), the zero-background pulse train represented by the formula (5) can be transmitted stably. As shown in FIG. 1 , in the embodiment of the present invention, the single-mode fiber is a silica SMF-28 fiber, the second-order group velocity dispersion GVD is β ₂ =-21.4ps ² km ^-1 , and the Kerr nonlinear parameter γ=1.2W ^{− 1} km ^-1 , the fiber loss α=0.19dB/km, the center wavelength is 1550nm, and the incident power P ₀ =0.7W.

Figure 1 shows the transmission diagram of zero background burst transmission z _A = 95.2381 km, parameter a = 0.4. Picture a in Figure 1 is a zero-background pulse train. From Figure a in Figure 1, the full width at half maximum of the center pulse of the zero-background pulse train can be obtained Δτ=3.4045ps (FWHM). According to the formula, the number of solitons in the center pulse train can be calculated for:

where P is the peak power of the pulse train. According to the soliton theory, when the number of solitons is between 0.5<N<1.5, the pulse can oscillate and transmit stably, as shown in the b diagram in Fig. 1.

In the actual transmission process of the pulse train, the amplitude of the pulse train gradually decreases with the increase of the transmission distance due to the influence of loss, so it needs to be amplified. The combination of plane wave pumping and spectral filter, placed in the appropriate position of the fiber, can realize the amplification of the optical pulse train, as shown in Figure 2.

由于连续平面波的在，在L_A＝0.8821km处衰减的脉冲串被放大，具有与初始光孤子脉冲串相同的功率。但是由于连续平面波背景的存在，放大的光孤子脉冲串不能稳定传输。因此，本发明在单模光纤的z_A+L_A位置处放置频谱过滤器来滤除平面波背景。根据本发明实施例中所取参数，过滤掉中心频谱1550nm附近大约0.2nm的频谱，可以获得稳定传输的零背景放大脉冲串，如图2中的c图所示。z_A是初始光孤子脉冲串衰减到小振幅脉冲串的传输距离，也是连续波泵浦放置的位置。L_A是放大器长度，z_A+L_A是频谱过滤器放置的位置。z_A处注入连续平面波，经过L_A衰减脉冲串被放大到初始入射光孤子脉冲串的功率，在单模光纤的位置z_A+L_A处通过频谱过滤器获得零背景稳定传输的放大光孤子脉冲串。Figure a in Figure 2 is the distribution of the initial optical soliton pulse train represented by formula (5), its peak power P=8.96W, and after transmission z _A =33.33km, due to the existence of loss, the peak power of the optical soliton pulse train decreases to 0.7041W, as shown in panel b in Figure 2. In order to amplify the attenuated optical soliton pulse train, a continuous plane wave with power P ₀ is injected at z _A to form a mixed wave with the attenuated optical soliton pulse train

Due to the presence of the continuous plane wave, the decaying pulse train at LA = _0.8821 km is amplified with the same power as the original optical soliton pulse train. However, due to the existence of the continuous plane wave background, the amplified optical soliton pulse train cannot be transmitted stably. Therefore, the present invention places a spectral filter at the z _A + L _A position of the single mode fiber to filter out the plane wave background. According to the parameters taken in the embodiment of the present invention, a spectrum of about 0.2 nm near the center spectrum of 1550 nm can be filtered out, and a zero-background amplified pulse train of stable transmission can be obtained, as shown in Figure c in FIG. 2 . z _A is the transmission distance of the initial optical soliton pulse train decaying to a small amplitude pulse train, and it is also the position where the continuous wave pump is placed. L _A is the amplifier length and z _A + L _A is where the spectral filter is placed. The continuous plane wave is injected at z _A , and the attenuation pulse train is amplified to the power of the initial incident optical soliton pulse train after L _A , and the amplified optical soliton with zero background and stable transmission is obtained by the spectral filter at the position of z _A + L _A of the single-mode fiber burst.

In order to realize the long-distance transmission of the optical soliton pulse train, the period amplification of the optical soliton pulse train is necessary. Figure 3 shows the periodic amplification process of the optical soliton pulse train by taking the 4-stage amplification of the optical soliton pulse train as an example.

The above amplification is divided into two processes, and the first-stage amplification is taken as an example to illustrate the process. Figure a1 in Figure 3 is the initial soliton pulse train, which is attenuated to an optical soliton pulse train with a peak power of 1.7179W after transmission z _A = 23.8095km, as shown in Figure b1 in Figure 3 . A continuous plane wave is injected at z _A , and after L _A =0.4310km, the attenuated pulse train is amplified and restored to the power of the original incident optical soliton pulse train, as shown in the c1 diagram in Fig. 3 . The solid line in Fig. 3c1 is the initial incident optical soliton pulse train represented by formula (5), and the dashed line represents the amplified optical soliton pulse train. The results show that the two are in good agreement. The initial optical soliton pulse train of the second stage is the amplified optical soliton pulse train of the first stage, as shown in figure a2 in FIG. 3 , and the rest of the process is exactly the same. In the above embodiment, the parameter a=0.45. In the 4-stage amplification process, z _A =23.8095km, and the amplifier lengths LA are 0.4310km, 0.3905km, 0.3845km and _1.0119km respectively.

In conclusion, based on the modulation instability principle, the present invention can realize the direct amplification of the optical soliton pulse train by using the method of combining plane wave pumping and spectral filter. The amplification process represented by this amplification method has nothing to do with the width, center wavelength, fiber doping concentration and other factors of the optical soliton pulse. Zoom in directly. The invention also takes the 4-stage amplification as an example to realize the periodic amplification of the optical soliton pulse train, so as to realize the long-distance transmission of the optical soliton pulse train.

It can be understood that the above embodiments are only exemplary embodiments adopted to illustrate the principle of the present invention, but the present invention is not limited thereto. For those skilled in the art, without departing from the spirit and essence of the present invention, various modifications and improvements can be made, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims (1)

1. An all-optical amplification method of an optical soliton pulse train is characterized by comprising the following steps:

s1, generating an initial optical soliton pulse train, and injecting the initial optical soliton pulse train into a single mode fiber for transmission;

s2, controlling the transmission z of the initial optical soliton pulse train in the single-mode optical fiber_ALowering the peak power P of the initial optical soliton pulse train to 2.5788-0.4293W to obtain an attenuated optical soliton pulse train, wherein the peak power P is 23.8095-34.5238 km;

s3, in z of single mode fiber_AAt an injection power of P₀Is mixed with the attenuated optical soliton pulse train in the form of

And allowing the mixed wave to continue to propagate in the single mode fiber;

s4, under the action of continuous plane wave, the attenuated optical soliton pulse train is gradually amplified and continues to transmit L in single-mode optical fiber_AAt 0.2893-1.5381km, the attenuated burst is amplified to form an amplified optical soliton burst with a plane wave background;

S5，at position z of the single-mode fibre_A+L_APlacing a spectrum filter, and performing spectrum filtering by taking the wavelength of 1550nm of the amplified optical soliton pulse train as a center and 0.2nm as a width to obtain the amplified optical soliton pulse train stably transmitted in the zero background, wherein the amplified optical soliton pulse train stably transmitted in the zero background and the initial optical soliton pulse train have the same power;

wherein, when generating the initial optical soliton pulse train, the S1 is implemented by the following processes:

the transmission of picosecond optical pulses in a single-mode fiber is described by the nonlinear schrodinger equation:

in the formula (1), A is A (z, T) is the electromagnetic field slow-changing envelope, z is the transmission distance, and T is the group velocity v with the pulse_gTime measurement in a moving reference frame, T-T-z/v_gCoefficient of beta₂And gamma are second-order group velocity dispersion GVD and Kerr nonlinear parameters respectively, and alpha is more than 0, and is optical fiber loss;

regardless of fiber loss, under anomalous dispersion conditions, i.e., β < 0 and α ═ 0, equation (1) has a solution of the form:

in the formula (2), P₀For the average power of the incident field, time τ is T/T₀Distance Z ═ Z (Z-Z)₀)/L_NLNormalized nonlinear length L_NL＝T₀ ²/|β₂L, time scale T₀＝(|β₂|/γP₀)^1/2Where z is₀Is a real parameter; omega is the frequency of the modulation and is,

a is modulation instability gain;

determining an unstable modulation growth; when 0 < a < 1/2, the solution represented by formula (2) is called Akhmedeev respiratory solution;

for the periodic solution (2) of schrodinger equation (1), the fourier series expansion has the form:

the forms of pump wave and sideband amplitude evolution are respectively:

n ± 1, ± 2, ± 3

Filtering in the frequency domain to be invariant over time

Obtaining a background-free optical soliton pulse train capable of being stably transmitted;

if the fiber loss is not considered, that is, if α in formula (1) is 0, the zero background burst represented by formula (5) can be stably transmitted;

the single-mode fiber is quartz SMF-28 fiber, and the second-order group velocity dispersion GVD is beta₂＝-21.4ps²km^-1The Kerr nonlinearity parameter γ is 1.2W^-1km^-1The optical fiber loss alpha is 0.19dB/km, the central wavelength is 1550nm, and the incident power P is₀＝0.7W。

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