CN102662290B - Self-phase modulation effect based transient signal light modulus conversion system - Google Patents
Self-phase modulation effect based transient signal light modulus conversion system Download PDFInfo
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Abstract
一种基于自相位调制效应的瞬态信号光模数转换系统，包括激光器，激光器的输出端经可调衰减器与第一环形器的输入端连接，第一环形器的第一输出端经第一色散介质和第一法拉第旋转镜连接，第一环形器的第二输出端经偏振控制器与双臂单端输出电光调制器的输入端连接，微波信号经混合耦合器分成两路后接双臂单端输出电光调制器，双臂单端输出电光调制器的输出端接第二环形器的输入端，第二环形器的第一输出端经第二色散介质和第二法拉第旋转镜连接，第二环形器的第二输出端依次经光纤放大器、光电探测器和电模数转换器相连。本发明可以节省色散介质的长度，降低成本，减少色散介质中的损耗。
A transient signal optical analog-to-digital conversion system based on self-phase modulation effect, including a laser, the output end of the laser is connected to the input end of a first circulator through an adjustable attenuator, and the first output end of the first circulator is connected through a second A dispersive medium is connected to the first Faraday rotating mirror, the second output end of the first circulator is connected to the input end of the dual-arm single-ended output electro-optic modulator through a polarization controller, and the microwave signal is divided into two paths by a hybrid coupler and then connected to a dual An arm single-ended output electro-optic modulator, an output end of the dual-arm single-end output electro-optic modulator is connected to an input end of the second circulator, and the first output end of the second circulator is connected to the second Faraday rotating mirror through the second dispersion medium, The second output end of the second circulator is sequentially connected through a fiber amplifier, a photodetector and an electrical analog-to-digital converter. The invention can save the length of the dispersion medium, reduce the cost and reduce the loss in the dispersion medium.
Description
技术领域 technical field
本发明涉及光模数转换技术领域，具体涉及的是一种基于自相位调制效应的瞬态信号光模数转换系统。The invention relates to the technical field of optical analog-to-digital conversion, in particular to a transient signal optical analog-to-digital conversion system based on self-phase modulation effect.
背景技术 Background technique
随着数字信号处理能力的不断提升，对模数转换器性能的要求越来越高，如今对于高采样率，高分辨率，高带宽模数转换器的需求越来越大，主要应用于先进的实验仪器，军事系统，生物医学成像系统，雷达系统和通信系统等重要领域。UCLA的Jalali教授实验组于1999年首先提出了利用时间拉伸的方法提高模数转换系统的采样率，它相对于传统的电模数转换系统有许多优点如光脉冲抖动较小，可测量的微波信号带宽范围较大等等。Jalali教授实验组并于2007年提出了10TSa/s的高速瞬态信号模数转换系统。With the continuous improvement of digital signal processing capabilities, the requirements for the performance of analog-to-digital converters are getting higher and higher. Today, there is an increasing demand for high-sampling rate, high-resolution, and high-bandwidth analog-to-digital converters, which are mainly used in advanced Important fields such as experimental instruments, military systems, biomedical imaging systems, radar systems and communication systems. The experimental group of Professor Jalali of UCLA first proposed the method of using time stretching to increase the sampling rate of the analog-to-digital conversion system in 1999. Compared with the traditional electrical analog-to-digital conversion system, it has many advantages such as small optical pulse jitter and measurable Microwave signals have a wide range of bandwidth and so on. Professor Jalali's experimental group proposed a 10TSa/s high-speed transient signal analog-to-digital conversion system in 2007.
传统的仅利用色散拉伸方法的高速瞬态信号光模数转换系统的工作原理是光脉冲先后经过第一、二段色散介质，假设光脉冲的带宽为Δλ（上下限波长分别为λ1、λ2），色散介质的色散系数为D(λ)，则经过第一段色散介质（长度为L1）后，脉冲宽度变为：The working principle of the traditional optical analog-to-digital conversion system for high-speed transient signals that only uses the dispersion stretching method is that the optical pulse passes through the first and second dispersive media successively, assuming that the bandwidth of the optical pulse is Δλ (the upper and lower wavelength limits are λ 1 , λ 2 ), the dispersion coefficient of the dispersive medium is D(λ), then after passing through the first dispersive medium (length L 1 ), the pulse width becomes:
t1＝L1×τ1(λ)(1)t 1 ＝L 1 ×τ 1 (λ)(1)
其中
t2＝L1×τ1(λ)+L2×τ2(λ) (2)t 2 =L 1 ×τ 1 (λ)+L 2 ×τ 2 (λ) (2)
若前后色散介质具有相同的色散特性，即τ1(λ)=τ2(λ)，则前后脉冲时间宽度之比（t2/t1）决定了时间拉伸倍数（即RF带宽压缩倍数）：If the front and rear dispersive media have the same dispersion characteristics, that is, τ 1 (λ)=τ 2 (λ), the ratio of the front and rear pulse time widths (t 2 /t 1 ) determines the time stretching factor (ie, the RF bandwidth compression factor) :
M＝(L1+L2)/L2 (3)M=(L 1 +L 2 )/L 2 (3)
这种仅依靠色散对光脉冲进行拉伸的方法在高速瞬态信号光模数转换系统中需要较大的色散量，对于色散系数一定的色散介质往往需要很长的光纤长度，光脉冲在较长色散介质中传输时损耗较大，系统信噪比和有效比特位不是很高。This method of stretching the optical pulse only by dispersion requires a large amount of dispersion in the high-speed transient signal optical analog-to-digital conversion system. For a dispersion medium with a certain dispersion coefficient, a long fiber length is often required. The transmission loss in the long dispersion medium is large, and the system signal-to-noise ratio and effective bits are not very high.
发明内容 Contents of the invention
本发明的目的在于针对上述现有技术的不足，提出一种基于自相位调制效应的瞬态信号光模数转换系统，通过可调衰减器调整被动锁模光纤激光器发出的光脉冲的峰值功率，从而使经过第一段色散介质的光脉冲在自相位调制效应和色散效应的共同作用下加速展宽，进而大大的减少所需色散介质长度。The purpose of the present invention is to address the above-mentioned deficiencies in the prior art, and propose a transient signal optical analog-to-digital conversion system based on self-phase modulation effect, adjust the peak power of the optical pulse sent by the passive mode-locked fiber laser through an adjustable attenuator, Therefore, the light pulse passing through the first section of the dispersive medium is accelerated and broadened under the joint action of the self-phase modulation effect and the dispersive effect, thereby greatly reducing the required length of the dispersive medium.
本发明的技术解决方案如下：Technical solution of the present invention is as follows:
一种基于自相位调制效应的瞬态信号光模数转换系统，其特点在于该系统的构成包括激光器，该激光器的输出端经可调衰减器与第一环形器的输入端连接，第一环形器的第一输出端经第一色散介质和第一法拉第旋转镜连接，第一环形器的第二输出端经偏振控制器与双臂单端输出电光调制器的输入端连接，微波信号经混合耦合器分成两路，一路信号输入到双臂单端输出电光调制器的一个臂上，另一路信号经过移相器进行90度的相移后输入到双臂单端输出电光调制器的另一个臂上，双臂单端输出电光调制器的输出端接第二环形器的输入端，第二环形器的第一输出端经第二色散介质和第二法拉第旋转镜连接，第二环形器的第二输出端依次经光纤放大器、光电探测器和电模数转换器相连。A transient signal optical analog-to-digital conversion system based on the self-phase modulation effect, which is characterized in that the system includes a laser, the output of the laser is connected to the input of the first circulator through an adjustable attenuator, and the first circulator The first output end of the circulator is connected with the first Faraday rotating mirror through the first dispersion medium, the second output end of the first circulator is connected with the input end of the dual-arm single-ended output electro-optic modulator through the polarization controller, and the microwave signal is mixed The coupler is divided into two circuits, one signal is input to one arm of the dual-arm single-ended output electro-optical modulator, and the other signal is input to the other arm of the dual-arm single-ended output electro-optic modulator after being shifted by a phase shifter for 90 degrees. On the arm, the output end of the double-arm single-ended output electro-optic modulator is connected to the input end of the second circulator, the first output end of the second circulator is connected with the second Faraday rotating mirror through the second dispersion medium, and the second circulator The second output end is sequentially connected through the optical fiber amplifier, the photodetector and the electric analog-to-digital converter.
所述的第一色散介质和第二色散介质为具有较高色散传输比的色散介质。The first dispersion medium and the second dispersion medium are dispersion mediums with relatively high dispersion transmission ratio.
所述的第一色散介质和第二色散介质为色散补偿光纤。The first dispersion medium and the second dispersion medium are dispersion compensating optical fibers.
所述的第一法拉第旋转镜和第二法拉第旋转镜为保偏法拉第旋转镜，具有较低的插入损耗。The first Faraday rotating mirror and the second Faraday rotating mirror are polarization-maintaining Faraday rotating mirrors with low insertion loss.
所述的激光器为1540—1560nm的被动锁模光纤激光器。The laser is a 1540-1560nm passive mode-locked fiber laser.
本发明的技术原理如下：Technical principle of the present invention is as follows:
1.自相位调制技术1. Self-phase modulation technology
被动锁模光纤激光器发出的超短光脉冲通过第一段色散介质时，其传输方程满足非线性薛定谔方程：When the ultrashort optical pulse emitted by the passively mode-locked fiber laser passes through the first dispersive medium, its transmission equation satisfies the nonlinear Schrödinger equation:
其中，ξ＝L/LD表示归一化的距离变量，τ＝T/T0表示归一化的时间变量，LD表示色散长度，T0为光脉冲的3dB宽度。参量N定义为：Among them, ξ=L/L D represents the normalized distance variable, τ=T/T 0 represents the normalized time variable, L D represents the dispersion length, and T 0 is the 3dB width of the optical pulse. The parameter N is defined as:
其中，LNL为非线性长度，γ为色散介质的非线性系数，β2可以表示为：Among them, L NL is the nonlinear length, γ is the nonlinear coefficient of the dispersive medium, and β2 can be expressed as:
其中，D为色散介质的色散系数，λ为光波波长，c为光脉冲传输速度。Among them, D is the dispersion coefficient of the dispersive medium, λ is the wavelength of the light wave, and c is the transmission speed of the light pulse.
参量N决定着光脉冲在色散介质中传输时是由自相位调制还是色散效应起主要作用。当N<<1时，色散效应起主要作用；当N>>1时，自相位调制效应起重要作用；而当N=1时，色散和自相位调制效应起同样重要的作用。由（5）可知，对于固定脉宽的光脉冲，N与进入色散介质中的光脉冲峰值功率有关，因此可以通过可调衰减器来调整光脉冲的峰值功率，进而来控制光脉冲传输时自相位调制效应的大小。The parameter N determines whether the self-phase modulation or the dispersion effect plays the main role when the optical pulse is transmitted in the dispersive medium. When N<<1, the dispersion effect plays a major role; when N>>1, the self-phase modulation effect plays an important role; and when N=1, the dispersion and self-phase modulation effects play an equally important role. It can be seen from (5) that for an optical pulse with a fixed pulse width, N is related to the peak power of the optical pulse entering the dispersive medium, so the peak power of the optical pulse can be adjusted through an adjustable attenuator, and then the automatic transmission of the optical pulse can be controlled. The magnitude of the phase modulation effect.
在传统的色散拉伸方法中只利用色散效应来展宽光脉冲，该方法中的脉冲展宽倍数随传输距离的关系表示为：In the traditional dispersion stretching method, only the dispersion effect is used to broaden the optical pulse. The relationship between the pulse broadening factor and the transmission distance in this method is expressed as:
本发明中，通过可调衰减器来调整光脉冲的峰值功率，进而利用自相位调制效应来促进色散对光脉冲的展宽程度In the present invention, the peak power of the optical pulse is adjusted through an adjustable attenuator, and then the self-phase modulation effect is used to promote the broadening degree of the optical pulse due to dispersion
通过对（4）进行数值仿真，可以得到传输相同距离条件下(L=3LD)，光脉冲展宽的程度随N（对应光脉冲的峰值功率）不同的变化情况。图1为在传输相同距离条件下，仅有色散效应和自相位调制效应（N值为1和N值为3情况下）促进色散时，脉冲展宽的对比图。可以明显看出当有自相位调制效应促进色散时，脉冲展宽的更多。因为脉冲进入第二段色散介质时已经展的很宽，并且由于调制器的损耗，其峰值功率降得很低，不再产生非线性效应即自相位调制效应，因此系统拉伸倍数与仅有色散情况下相同，仍为M=1+L2/L1(L1为第一色散介质的长度，L2为第二色散介质的长度）。Through the numerical simulation of (4), it can be obtained that under the condition of the same transmission distance (L=3L D ), the degree of broadening of the optical pulse changes with different N (corresponding to the peak power of the optical pulse). Figure 1 is a comparison diagram of pulse broadening when only dispersion effect and self-phase modulation effect (
然而，当利用自相位调制效应时，会使光脉冲产生一定相移，可以表示为：However, when the self-phase modulation effect is used, the optical pulse will have a certain phase shift, which can be expressed as:
其中，Δλ为光脉冲的谱宽，M为系统的拉伸倍数。这种自相位调制产生的相移会使输入的微波信号频率受到更大的限制，利用单边带调制可以消除这种限制，下面对此方法进行介绍。Among them, Δλ is the spectral width of the optical pulse, and M is the stretching factor of the system. The phase shift generated by this self-phase modulation will make the frequency of the input microwave signal subject to a greater limitation, and the single sideband modulation can be used to eliminate this limitation, and this method will be introduced below.
2.单边带调制技术2. Single sideband modulation technology
微波信号输入到混合耦合器中，并且分成两路，其中一路从混合耦合器的一个端口输出，另一路从混合耦合器的另一个端口输出后，通过移相器使其产生90度的相移。再将两个路微波信号加载到双臂单端输出电光调制器的两个臂上，再利用单边带调制将其调制到光脉冲上，经过第二段色散介质后，光电探测器检测到的输出信号电流表示为：The microwave signal is input into the hybrid coupler and divided into two paths, one of which is output from one port of the hybrid coupler, and the other is output from the other port of the hybrid coupler, which is then passed through a phase shifter to generate a phase shift of 90 degrees . Then load two microwave signals to the two arms of the dual-arm single-ended output electro-optic modulator, and then use single-sideband modulation to modulate it onto the optical pulse. After passing through the second dispersive medium, the photodetector detects The output signal current is expressed as:
其中，a为调制系数，
3.自变陡效应3. Self-steepening effect
当光脉冲在色散介质中传输时，若通过调整其峰值功率产生自相位调制效应，则相应的也会产生高阶非线性效应，在该系统中，此高阶非线性效应主要是脉冲自变陡效应。当光脉冲宽度一定时，光功率不能无限制的增大，它的上限应受到产生自变陡效应时临界阈值的限制。若考虑光纤中的高阶非线性效应，光脉冲传输方程应满足广义非线性薛定谔方程，假若只研究自变陡效应，设自相位调制，色散的影响不存在以及光纤损耗值为零，则该化简的广义非线性薛定谔方程为：When the optical pulse is transmitted in the dispersive medium, if the self-phase modulation effect is generated by adjusting its peak power, the corresponding high-order nonlinear effect will also be generated. In this system, the high-order nonlinear effect is mainly the pulse self-variation steep effect. When the optical pulse width is constant, the optical power cannot be increased without limit, and its upper limit should be limited by the critical threshold when the self-steepening effect occurs. Considering the high-order nonlinear effects in the optical fiber, the optical pulse transmission equation should satisfy the generalized nonlinear Schrödinger equation. If only the self-steepening effect is studied, the self-phase modulation, the influence of dispersion does not exist, and the fiber loss value is zero, then the The simplified generalized nonlinear Schrödinger equation is:
其中U为光脉冲的包络函数，用以描述自变陡效应，对（10）进行求解，可以得到在传输距离Z处的脉冲形状表达式为：where U is the envelope function of the light pulse, To describe the self-steepening effect, solve (10), and the pulse shape expression at the transmission distance Z can be obtained as:
I(Z,T)＝exp[-(T-3sI(Z,T)Z)2]（11）I(Z,T)=exp[-(T-3sI(Z,T)Z) 2 ] (11)
其中
图2为同一个脉冲，在传输不同距离时（对应不同的Z值）其自变陡的不同程度的仿真图。从图中可见当s*Z=0.025时自变陡程度较小，此时的Z值对应的光功率值应成为光脉冲峰值功率的阈值。Figure 2 is the simulation diagram of different degrees of self-steeping of the same pulse when it travels different distances (corresponding to different Z values). It can be seen from the figure that when s*Z=0.025, the degree of self-steepness is small, and the optical power value corresponding to the Z value at this time should become the threshold value of the peak power of the optical pulse.
4.环形器配合法拉第旋转镜结构4. Circulator with Faraday rotating mirror structure
将系统设计成为环形器接色散介质，色散介质输出端接法拉第旋转镜的结构，可以使光脉冲首先通过环形器进入到色散介质中，然后经过法拉第旋转镜反射，光脉冲再次进入色散介质中进行色散拉伸，最终返回到环形器。这种使光脉冲完成一去一回的传输结构，可以使所需的光纤长度减少一半，从而大大的节省成本。The system is designed as a structure in which the circulator is connected to the dispersive medium, and the output terminal of the dispersive medium is connected to the Faraday rotator mirror, so that the light pulse first enters the dispersive medium through the circulator, and then is reflected by the Faraday rotator mirror, and the light pulse enters the dispersive medium again for further processing. Dispersion stretches and eventually returns to the circulator. This kind of transmission structure, which enables optical pulses to go back and forth, can reduce the required fiber length by half, thereby greatly saving costs.
与现有技术相比，本发明的有益效果如下：Compared with the prior art, the beneficial effects of the present invention are as follows:
1.当光脉冲在第一段色散介质中传输时，通过调整其峰值功率产生自相位调制效应，它能促使色散加速光脉冲的展宽，可以明显减少所需的第一段色散介质长度来达到脉冲需要展宽的倍数。1. When the optical pulse is transmitted in the first dispersive medium, by adjusting its peak power to produce a self-phase modulation effect, it can promote dispersion and accelerate the broadening of the optical pulse, which can significantly reduce the length of the first dispersive medium required to achieve The multiple by which the pulse needs to be stretched.
2.由于通过第二段色散介质时，自相位调制效应较弱，仅有色散发挥作用，系统拉伸倍数仍表示为M=1+L2/L1，因此可大幅减少光纤长度、降低成本，并且色散介质中损耗减少，系统信噪比和有效比特位得到提升。2. Since the self-phase modulation effect is weak when passing through the second dispersive medium, only dispersion plays a role, and the system stretching factor is still expressed as M=1+L 2 /L 1 , so the length of the fiber can be greatly reduced and the cost can be reduced , and the loss in the dispersion medium is reduced, and the system signal-to-noise ratio and effective bits are improved.
3.电光调制器选用双臂单端输出马赫—曾德（Mach-Zehnder）电光调制器，利用单边带调制，可以去除由于色散和自相位调制引起的微波信号功率周期性衰落的问题。3. The electro-optic modulator uses a dual-arm single-ended output Mach-Zehnder (Mach-Zehnder) electro-optic modulator. Using single-sideband modulation, the problem of periodic power fading of microwave signals caused by dispersion and self-phase modulation can be eliminated.
4.采用环形器和法拉第旋转镜结构可以使光脉冲在色散介质中完成往还的两次传输过程，所需的色散总量降低一倍，因此色散介质长度减少一半，从而达到降低成本的目的。4. The structure of the circulator and the Faraday rotating mirror can make the light pulse complete the two transmission processes back and forth in the dispersive medium, and the total amount of dispersion required is doubled, so the length of the dispersive medium is reduced by half, thereby achieving the purpose of reducing costs .
附图说明 Description of drawings
图1a为原始的高斯脉冲，在相同传输距离条件下（L=3LD）；Figure 1a is the original Gaussian pulse under the same transmission distance (L=3L D );
图1b为在仅有色散时脉冲的展宽；Figure 1b shows the broadening of the pulse when there is only dispersion;
图1c为在自相位调制（N=1）情况下，促进色散对脉冲的展宽；Figure 1c shows the broadening of the pulse by promoting dispersion in the case of self-phase modulation (N=1);
图1d为在自相位调制（N=3）情况下，促进色散对脉冲的展宽。Figure 1d shows the promotion of dispersion on pulse broadening in the case of self-phase modulation (N=3).
图2为对于脉宽相同的高斯脉冲，存在自变陡效应时，脉冲的形状随Z值的变化情况。Figure 2 shows how the shape of the pulse changes with the Z value when there is a self-steepening effect for a Gaussian pulse with the same pulse width.
图3为本发明基于自相位调制效应的瞬态信号光模数转换系统的结构示意图。Fig. 3 is a schematic structural diagram of the transient signal optical analog-to-digital conversion system based on the self-phase modulation effect of the present invention.
图中：1-激光器，2-可调衰减器，3-第一环形器，4-第一色散介质，5-第一接法拉第旋转镜，6-偏振控制器，7-双臂单端输出电光调制器。8-混合耦合器，9-第二环形器，10-第二色散介质，11-第二法拉第旋转镜，12-光纤放大器，13-光电探测器，14-电模数转换器，15-微波信号，16-移相器。In the figure: 1-laser, 2-adjustable attenuator, 3-first circulator, 4-first dispersive medium, 5-first connection to Faraday rotating mirror, 6-polarization controller, 7-double-arm single-ended output electro-optic modulator. 8-hybrid coupler, 9-second circulator, 10-second dispersive medium, 11-second Faraday rotating mirror, 12-fiber amplifier, 13-photodetector, 14-electrical analog-to-digital converter, 15-microwave signal, 16-phaser.
图4为色散介质长度随光功率的变化关系（左纵坐标），以及系统有效比特位的提高值随光功率的变化关系（右纵坐标）。Figure 4 shows the relationship between the length of the dispersive medium and the variation of optical power (left ordinate), and the relationship between the increase of the effective bit of the system and the variation of optical power (right ordinate).
具体实施方式 Detailed ways
下面结合实施方式和附图对本发明作进一步说明，但是不应以此限制本发明的保护范围。The present invention will be further described below in conjunction with the embodiments and drawings, but the protection scope of the present invention should not be limited by this.
请先参阅图3，图3为本发明基于自相位调制效应的瞬态信号光模数转换系统的结构示意图。如图所示，一种基于自相位调制效应的瞬态信号光模数转换系统，该系统的构成包括激光器1，本实施例中采用被动锁模光纤激光器，激光器的输出端经可调衰减器2接第一环形器3的输入端，第一环形器3的第一输出端经第一色散介质4，接第一法拉第旋转镜5，第一环形器3的第二输出端经偏振控制器6接双臂单端输出电光调制器7的输入端。微波RF信号15经混合耦合器8后分为两路，一路接双臂单端输出电光调制器7的一臂，另一路经移相器16进行90度的相移后接到双臂单端输出电光调制器7的另一臂。双臂单端输出电光调制器7的输出端接第二环形器9的输入端，第二环形器9的第一输出端经第二色散介质10与第二法拉第旋转镜11连接，第二环形器9的第二输出端依次经过光纤放大器12、光电探测器13和电模数转换器14连接。Please refer to FIG. 3 first. FIG. 3 is a schematic structural diagram of the transient signal optical analog-to-digital conversion system based on the self-phase modulation effect of the present invention. As shown in the figure, a transient signal optical analog-to-digital conversion system based on the self-phase modulation effect. The system includes a
第一色散介质4具有较大的非线性系数，第一色散介质4和第二色散介质10具有较大的色散系数。本实施例选用色散补偿光纤。第一法拉第旋转镜5和第二法拉第旋转镜11为保偏法拉第旋转镜并且具有较低的插入损耗。The first dispersion medium 4 has a relatively large nonlinear coefficient, and the first dispersion medium 4 and the
图4为色散介质色散系数为-120ps/nm.km，非线性系数4.5/w.km，损耗0.4dB/km。输入脉冲脉宽为1.5ps,重复频率为37MHz，过第一色散光纤脉宽展宽为450ps，拉伸倍数为50,若后端电模数转换器的采样率为20GSample/s,则总采样率为1TSample/s的超高速瞬态信号光模数转换系统所需的色散介质长度随光功率变化关系（左纵坐标），以及系统有效比特位的提高值随光功率的变化关系（右纵坐标）。Figure 4 shows that the dispersion coefficient of the dispersion medium is -120ps/nm.km, the nonlinear coefficient is 4.5/w.km, and the loss is 0.4dB/km. The pulse width of the input pulse is 1.5ps, the repetition frequency is 37MHz, the pulse width of the first dispersion fiber is extended to 450ps, and the stretching factor is 50. If the sampling rate of the back-end electrical analog-to-digital converter is 20GSample/s, the total sampling rate The relationship between the length of the dispersion medium and the optical power required by the ultra-high-speed transient signal optical analog-to-digital conversion system of 1TSample/s (left vertical axis), and the relationship between the increase value of the effective bit of the system and the optical power (right vertical axis ).
本发明基于自相位调制效应的瞬态信号光模数转换系统的工作方法如下：The working method of the transient signal optical analog-to-digital conversion system based on the self-phase modulation effect of the present invention is as follows:
1.激光器发出的超短光脉冲经过可调衰减器对其峰值功率进行调节，从而控制光脉冲经过第一色散介质时自相位调制效应的大小。1. The peak power of the ultrashort optical pulse emitted by the laser is adjusted through an adjustable attenuator, so as to control the magnitude of the self-phase modulation effect when the optical pulse passes through the first dispersive medium.
2.峰值功率调整后的光脉冲经过第一环形器进入第一色散介质，并且产生自相位调制效应，它能加速色散对脉冲的展宽，最后通过第一法拉第旋转镜，再次经过第一色散介质返回到第一环形器。2. The light pulse after peak power adjustment enters the first dispersive medium through the first circulator, and produces a self-phase modulation effect, which can accelerate the broadening of the pulse by dispersion, and finally passes through the first Faraday rotating mirror, and then passes through the first dispersive medium again Return to the first circulator.
3.第一环形器输出的啁啾光脉冲经过偏振控制器调整其偏振态，保证调制深度可以达到较大值。3. The polarization state of the chirped optical pulse output by the first circulator is adjusted by the polarization controller to ensure that the modulation depth can reach a larger value.
4.微波信号输入到混合耦合器后分成两路，其中一路微波信号从其中一个端口输出，另一路微波信号从混合耦合器的另一个端口输出后通过移相器进行90度的相移。将两路微波信号加载到调制器的两个臂上，进而调制到啁啾光脉冲上。4. After the microwave signal is input into the hybrid coupler, it is divided into two channels, one of which is output from one port, and the other microwave signal is output from the other port of the hybrid coupler and then shifted by 90 degrees through the phase shifter. Two microwave signals are loaded on the two arms of the modulator, and then modulated onto the chirped optical pulse.
5.调制后的光波信号通过第二环形器进入第二色散介质，由于此时光波峰值功率较低，因此自相位调制效应较弱，仅有色散作用，因此系统的拉伸倍数仍为M=1+L2/L1，若M不变，由于L1长度大大减小，则L2也大大减小。光波信号经第二法拉第旋转镜重新返回第二环形器。5. The modulated light wave signal enters the second dispersive medium through the second circulator. Since the peak power of the light wave is low at this time, the self-phase modulation effect is weak, and only the dispersion effect, so the stretching factor of the system is still M= 1+L 2 /L 1 , if M remains unchanged, since the length of L 1 is greatly reduced, L 2 is also greatly reduced. The light wave signal returns to the second circulator through the second Faraday rotating mirror.
6.第二环形器输出的光波信号通过光纤放大器来补偿光波功率的损耗，再通过光电探测器检出微波信号，送至电模数转换器进行采样，量化处理。6. The light wave signal output by the second circulator compensates the loss of light wave power through the fiber amplifier, and then detects the microwave signal through the photoelectric detector, and sends it to the electric analog-to-digital converter for sampling and quantization processing.
经试验表明，本发明利用第一色散介质中自相位调制效应，进一步增强色散对光脉冲的展宽效应，相比于传统的仅依靠色散对脉冲展宽的方法，大大的节省色散介质的长度。降低成本的同时减少色散介质中的损耗，进而明显的提高系统的信噪比和有效比特位。此外，利用环形器配合法拉第旋转镜结构，使色散介质长度减少一半，进一步降低系统成本。可望在超高速瞬态信号光模数转换系统制备领域获得广泛应用。Experiments show that the present invention utilizes the self-phase modulation effect in the first dispersive medium to further enhance the broadening effect of dispersion on optical pulses, and greatly saves the length of the dispersive medium compared to the traditional method of only relying on dispersion to broaden the pulse. While reducing the cost, the loss in the dispersion medium is reduced, thereby significantly improving the signal-to-noise ratio and effective bits of the system. In addition, the use of the circulator and the Faraday rotating mirror structure reduces the length of the dispersion medium by half, further reducing the system cost. It is expected to be widely used in the field of preparation of ultra-high-speed transient signal optical analog-to-digital conversion systems.
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