基于光子晶体光纤中四波混频效应的单到双非归零到归零码型转换

归零(RZ)码与非归零(NRZ)码是波分复用和时分复用系统中广泛采用的两种码型, 全光NRZ到RZ码型转换能完成从波分复用到时分复用的网络接口功能, 是未来透明光子网络中一项重要的全光信号处理技术. 提出并实验证实了一种基于色散平坦高非线性光子晶体光纤中四波混频效应的单到双NRZ到RZ码型转换方法, 将一束信号光与同步时钟脉冲同时输入色散平坦高非线性光子晶体光纤中, 通过四波混频过程, 产生两个携带该数据信息的闲频光, 从而实现了单到双的NRZ到RZ码型转换功能, 码型转换器工作波长在193 nm范围可调谐, 最大转换效率为-21 dB, 最优消光比和品质因子分别为11.9 dB和7.2. 该方法的特点在于基于光纤中的四波混频效应工作, 因而具有对调制格式和比特率透明的优点, 同时, 光子晶体光纤特有的高非线与色散平坦性, 既避免了使用传统光纤需要较长的长度, 又避免了波长设置不灵活的弊端, 并具备可进一步增加带宽的能力, 且在码型转换的同时, 实现了波长转换, 完成了双通道波长组播功能. 整个系统为全光纤设计, 结构简单, 性能可靠, 并易于与现有的光纤通信系统相容, 对促进超高速大容量光子网络的发展具有重要意义. 关键词： 码型转换 四波混频 光子晶体光纤     

All-Optical RZ to NRZ Format Conversion Using Single SOA Assisted by Optical Band-Pass Filter

We propose a novel all-optical format conversion from the return-to-zero （RZ） to the non-return-to-zero （NRZ） based on single semiconductor optical amplifier （SOA） and optical band-pass filter （OBE）. We demonstrate the proof of the principle experiment at 10 Gbps by using the test SOA and OBF converter. The format conversion can be achieved with output extinction ratio of 11.51 dB. The BER is 5.5×10^-9 when the power of NRZ is - 10 dBm. The proposed scheme is robust and potential for applications in optical networks.     

自启动的非归零/归零码和光电时钟信号发生器及码型转换

采用双波长注入一包含伪随机码发生器与相位调制器的光电振荡器可以同时得到非归零(NRZ)码,归零(RZ)码以及光,电时钟信号输出。该方案使用了光域耦合的双环路结构,在不增加有源器件的条件下实现边模抑制。相位调制器用于反馈调制并同时实现占空比可调的非归零码到归零码的转换。双波长的注入排除了编码信号在振荡器中引入的非时钟频率成分。实验给出了10 Gb/s工作速率下的结果,得到了抖动为637 fs的光信号输出。转换得到的归零码信号占空比约为33%。输出电时钟信号的相位噪声在频偏10 kHz处为-109 dBc/Hz,边模抑制比为58 dB。     

All-optical NRZ-to-RZ format conversion with dual channel wavelength multicasting functions exploiting cross-phase modulation in a dispersion-flattened nonlinear photonic crystal fiber

All-optical single-to-dual channel format conversion from NRZ to RZ at 10 Gbit/s using cross phase modulation (XPM) in dispersion flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF) is demonstrated. Format conversion with dual channels signal multicasting function is achieved by filtering simultaneously the blue- and red-chirped components of broadened optical spectrum induced by XPM between NRZ signal and clock light. Moreover, the wavelength tunability and dynamics characteristics of proposed format converter are also exploited experimentally by using NRZ signal light with different central wavelength and varying input power. Our results show that a wide wavelength operation range of 21.2 nm, extinction ratio (ER) and Q factor of over 10.9 dB and 6.1 are obtained. Furthermore, the influence of central wavelength offset of optical bandpass filter on converted RZ signal quality is investigated. The proposed scheme is simple, robust, and transparent to bit rate, which makes it very potential for application in future photonic networks.     

Multi-Channel NRZ/RZ-DPSK to CSRZ-DPSK Format Conversion Based on Nonlinear Polarization Rotation of SOA

We present an all-optical nonreturn-to-zero/return-to-zero(NRZ/RZ) to carrier-suppressed return-to-zero(CSRZ)format conversion scheme for differential phase-shift ke.ying(DPSK) signals. The conversion is based on nonlinear polarization rotation of a semiconductor optical amplifier(SOA). The 4-channel NRZ-DPSK or RZ-DPSK signals at 10 Gb/s are simultaneously converted to the corresponding CSRZ-DPSK signals, with-0.8 and 1.4 dB average power penalties, respectively. Additionall.y, high quality format conversion performanes are shown with the optical spectra and eye diagrams.     

All-optical polarization-insensitive non-return-to-zero-to-pulsewidth tunable return-to-zero conversion

We demonstrate polarization-insensitive non-return-to-zero (NRZ)-to-pulsewidth tunable return-to-zero (RZ) conversion based on a Raman amplifier (RA)-based pulse compressor and a fiber-based NRZ-to-RZ converter, which consists of a polarization diversity loop. We measure the bit-error rate (BER) characteristics of the input NRZ signal and the converted RZ signals. The power penalty of less than 0.2 dB between the converted RZ signals with different power ratios proved the polarization insensitivity. Moreover, by changing the Raman pump power of the RA-based pulse compressor, the pulsewidths of the converted RZ signals were flexibly tuned from 10 to 2 ps, which proved NRZto-RZ conversion with pulsewidth tunability. In all cases, clear eye diagrams were obtained.     

基于半导体光放大器和光滤波器的全光非归零码到归零码的转换

利用半导体光放大器模型和仿真软件对全光非归零码到归零码的变换进行了数值仿真.在仿真结果的基础上,实现了基于半导体光放大器和光滤波器的10 Gbps的全光非归零码到归零码的变换试验.试验结果显示在RZ码输入功率为－15 dBm时,该变换的误码率为1.0×10－9.     

基于半导体光放大器四波混频效应的多种调制格式的波长转换实验

实验报道了利用半导体光放大器(SOA)的四波混频(FWM)效应实现多种码型的波长转换.其中对于非归零(NRZ)信号实现了从单信道到三信道的多波长转换.调制速率从10 Gb/s到40 Gb/s均实现多波长转换.对于归零(RZ)信号分别实现了20 Gb/s和40 Gb/s的RZ格式的波长转换和40 Gb/s的载波抑制归零(CSRZ)格式的波长转换,利用光纤布拉格光栅(FBG)作为带陷滤波器消除共轭光和抽运光之间的串扰.对于非归零差分相移键控(NRZ_DPSK)信号分别实现了20 Gb/s和40 Gb/s的波长转换,利用实验室自制的光纤延时干涉仪进行NRZ-DPSK信号的解调.基于FWM效应的转换光的输出消光比大于7 dB,转换后消光比退化约为3 dB.     

All-optical NRZ-OOK-to-RZ-OOK format conversions with tunable duty cycles using nonlinear polarization rotation of a semiconductor optical amplifier

We experimentally demonstrate an all-optical 10 Gb/s format conversion from non-return-to-zero (NRZ) on-off-keying (OOK) to return-to-zero (RZ)-OOK with tunable duty cycle in the whole C-band using nonlinear polarization rotation (NPR) arising in an semiconductor optical amplifier (SOA). The experimental results show that, by tuning the polarizer at the SOA output, an RZ signal with tunable duty cycle from 33% to 66% could be obtained with an extinction ratio(ER) over 10 dB. In addition, we show that the NRZ-to-RZ conversion with duty cycle of 33-66% can be obtained with less than 1 dB power penalty at the bit error ratio (BER) of 10⁻⁹. The device can facilitate the cross-connection between optical transmission networks employing different modulation formats.     

All-Optical RZ-to-NRZ Format Conversion with a Tunable Fibre Based Delay Interferometer

All-optical format conversion from return-to-zero （RZ） to non-return-to-zero （NRZ） is demonstrated with temperaturecontrolled all-fibre delay interferometer （DI） at 20 Gb/s. The operation principle is theoretical analysed with the help of numerical simulation and spectra analysis. Theoretical analysis results are consistent well with the experimental results. The format conversion can be achieved with power penalty of 0.54 dB and with output extinction ratio 20 dB.     

Performance analysis of NRZ, RZ, CRZ and CSRZ data formats in 10 Gb/s optical soliton transmission link under the impact of chirp and TOD

This paper presents the performance analysis of non-return-to-zero (NRZ), return-to-zero (RZ), chirped return-to-zero (CRZ) and carrier suppressed return-to-zero (CSRZ) data formats in optical soliton transmission link under the impact of chirp and third-order dispersion (TOD). The performance of these data formats has been analyzed on the basis of certain performance metrics, viz, bit error rate (BER), Q² (dB), OSNR, eye opening, etc. It has been reported here that the performance of CRZ and CSRZ modulation format is better as compared to NRZ and RZ in a soliton transmission link. Further, CSRZ modulation format has been found to deliver optimum performance on the basis of performance evaluation metrics reported in this paper. In case of NRZ and CSRZ, comparatively narrow power spectrum has been observed. Best eye opening, highest value of Q² (dB) of 18 dB and lowest value of BER of the order of 10⁻¹⁶ has been reported in case of CSRZ among the considered data formats. The results have been obtained by varying noise figure from 3.0 to 9.0. No considerable effect of noise was observed. It was observed that at very narrow and ultra short pulse width, OSNR value suffers heavily and reduced to even negative values in dB, thus inducing a high degree of OSNR power penalty. The results were obtained by varying chirp factor from −0.6 to +0.6. Negative chirp resulted in improved OSNR as compared to positive chirp. RZ data format yielded a broader optical spectrum, comparatively low spectral efficiency and poor OSNR thus it was found that RZ format is not suitable for optical soliton transmission under the impact of chirp and TOD.     

Investigation of data format conversions based on MZI-SOA

Employing a Mach-Zehnder Interferometer (MZI), this paper describes simulation demonstration of an all-optical scheme for data format conversion between non-return-to-zero (NRZ) and return-to-zero (RZ). Data format conversion between NRZ and RZ at 120 Gb/s has been simulated for the first time using an MZI. In addition, we have proposed for the first time data format conversion from NRZ to RZ by using a single SOA in an MZI.     

基于光子晶体光纤中双抽运四波混频效应的非归零到归零码型转换实验研究

提出并实验证实了利用色散平坦高非线性光子晶体光纤中双抽运四波混频效应实现非归零 (NRZ)到归零(RZ)码型转换的新方案, 将一束NRZ信号光与两束同步时钟脉冲光同时注入光子晶体光纤, 通过双抽运四波混频效应产生两个闲频光, 经过光学滤波后即可完成单到双全光NRZ-RZ码型转换. 与基于常规单抽运四波混频效应的码型转换方式相比, 本设计方案由于采用了双抽运四波混频效应, 因此具有双路组播信号波长可彼此独立选取的优点. 分析了码型转换器的波长调谐性及对输入光功率波动的容忍性, 得到转换信号的最优消光比和Q 因子分别为15 dB和5.4. 研究结果表明, 本方案既具有对比特率和调制格式透明的优点, 又避免了使用单抽运四波混频效应进行码型转换时两路组播信号波长相互制约的弊端, 且实现了全光波长转换和波长组播功能. 关键词： 码型转换 四波混频 双抽运 光子晶体光纤     

Theoretical study of all-optical RZ to NRZ format conversion based on cascaded nanoporous silicon waveguides

In this paper, we present that the strong free carrier absorption and short carrier lifetime in nanoporous silicon waveguide can perform effectively the return-to-zero (RZ) to non-return-to zero (NRZ) format conversion. The project presented consisting of two cascaded millimeters long nanoporous silicon waveguides is numerically simulated and investigated at 5 Gbit/s. Numerical results clearly show that the outcome converted signal (NRZ) at the end of proposed device can be effectively optimized (e.g. clearer extinction ratio – ER, higher Q-factor, and lower bit-error rate – BER) by means of suitably choosing the system parameters such as initial RZ peak level and nanoporous silicon waveguide length.     

Theoretical Study of SOA-Based Wavelength Conversion with NRZ and RZ Format at 40 Gb/s

We theoretically discuss 40 Gb/s semiconductor optical amplifier （SOA）-based wavelength conversion （WC） using a detuning optical bandpass Jilter based on ultrafast dynamic characteristics of SOA. Both the inverted and noninverted WCs are obtained by shifting the filter central wavelength with respect to the probe wavelength when input data signal is in return-to-zero （RZ） format. However, we can obtain format conversion from nonreturn- to-zero （NRZ） to pseudo-return-to-zero （PRZ） and inverted WC when the input signal is in NRZ format.     

双抽运光纤光参变放大的全光多波长变换与码型转换

利用强度调制的数据信号光作为一路抽运光,与另一路直流或者正弦强度调制抽运光组合可以在双抽运光纤光参变放大过程中实现全光多波长变换或者在全光多波长变换的同时实现码型转换.理论上,从信号增益的角度分析了波长转换与码型转换的原理.实验上演示了2.5Gb/s的非归零(NRZ)码信号的全光多波长转换与到归零(RZ)码信号的转换.多波长转换实验表明:双抽运条件下的光参变过程可以实现多波长转换并得到正、反码的输出,还同时对信号有一定的再生作用.码型转换后信号的占空比为30%,消光比也得到提高.     

Experimental observation of all-optical non-return-to-zero-to-return-to-zero format conversion based on cascaded second-order nonlinearity assisted by active mode-locking

We report the experimental demonstration of all-optical format conversion by exploiting the cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) in a periodically poled lithium niobate (PPLN) waveguide assisted by the reflective semiconductor optical amplifier (RSOA)-based active mode-locking. 10 and 20 Gbit/s format conversions from non-return-to-zero (NRZ) to return-to-zero (RZ) are successfully observed. Two schemes with either the NRZ signal or the pump optical clock set at the quasi-phase matching (QPM) wavelength are both verified in the experiment.     

基于光信号偏振度的偏振模色散补偿系统的研究

偏振模色散已成为当前发展高速长距离光纤传输系统的主要限制因素。理论上分析了光纤一阶偏振膜色散效应对高速伪随机非归零码／归零码光信号偏振度的影响，并利用数值模拟的方法分析了信号不同输入偏振态以及高阶偏振膜色散效应对非归零码光信号偏振度的影响。最后对利用信号偏振度作为反馈控制信号的自适应偏振膜色散补偿系统的补偿性能进行了分析，大量统计分析结果表明对于10Gbit／s的非归零码光纤传输系统，当传输线路的平均偏振膜色散值小于43ps时，利用极大化输出信号偏振度的偏振膜色散补偿系统对信号眼图的补偿概率可以达到99．99％．     

A novel approach to all-optical wavelength conversion by utilizing a reflective semiconductor optical amplifier in a co-propagation scheme

Nonlinear optical gain modulation in an InGaAsP/InP bulk reflective semiconductor optical amplifier (RSOA) is studied. The differences of the optical properties between RSOAs and conventional SOAs are initially investigated. All-optical wavelength conversion based on nonlinear gain modulation in RSOAs is demonstrated at a bit rate of 2.488 Gbit/s. It is shown that a bit-error-rate of <10⁻⁹ can be achieved and an extinction ratio of >9 dB can be obtained at a bit rate of 2.488 Gbit/s with a 2³¹-1 non-return-to-zero (NRZ) pseudorandom bit sequence (PRBS). In comparison with conventional SOAs, wavelength conversion by RSOAs shows much improved performances in high-speed all-optical wavelength conversions.     

10Gbps-RZ光信号在光纤光栅色散补偿的2500km无电中继系统中的传输

全部利用线性啁啾光纤布拉格光栅(CBG)作色散补偿模块和在线通道滤波器,在2500km G.652光纤上实现10Gbps-RZ光信号的超长距离无电中继传输。在2081km处,功率代价~3dBm(RZ码,BER=10-12,PRBS=1023-1);在2560km处,功率代价~5dBm,远优于相同系统平台下NRZ无误码传输时的性能。