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.     

10 Gbit/s all-optical non-return to zero-return-to-zero data format conversion based on a backward dark-optical-comb injected semiconductor optical amplifier

By using a semiconductor optical amplifier backward injected by a dark-optical-comb pulse train at 10 GHz, we demonstrate a 10 Gbit/s all-optical nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion of an incoming optical pseudorandom binary sequence (PRBS) data stream. Both the polarity and the wavelength of data are conserved during format conversion. Without any pre-amplification, the extinction ratio of degraded optical NRZ PRBS data is greatly improved from 7.13 to 13.6 dB after NRZ-to-RZ conversion. An ultralow bit-error rate of 10(-12) at a data rate as high as 10 Gbits/s is obtained with a received optical power of -18.3 dBm. The converted RZ PRBS data exhibit a negative power penalty of >3.7 dB compared with the NRZ PRBS data at a bit-error rate of 10(-12).     

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。     

Analysis of 160 Gb/s all-optical NRZ-to-RZ data format conversion using quantum-dot semiconductor optical amplifiers assisted Mach-Zehnder interferometer

A scheme of all-optical data format conversion from nonreturn-to-zero to return-to-zero is proposed using quantum-dot semiconductor optical amplifiers (QD SOAs) assisted Mach-Zehnder interferometer (MZI). The proposed scheme has the potential to operate at much larger bit rate ∼160 Gb/s, and the converted signal has a lower frequency chirp. 160 Gb/s all-optical format conversion is verified through numerical simulations, and the output contrast ratio and Q-factor are analyzed to evaluate the system performance. With properly selected parameters, the converted signal with a contrast ratio over 8 dB and a Q-factor over 8 can be achieved.     

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.     

Nonlinear polarization rotation in a dispersion-flattened photonic-crystal fiber for ultrawideband (>100 nm) all-optical wavelength conversion of 10 Gbit/s nonreturn-to-zero signals

We study the conversion bandwidth of the cross-polarization-modulation (XPoIM)-based wavelength conversion scheme with a dispersion-flattened highly nonlinear photonic-crystal fiber for signals with a nonreturn-to-zero (NRZ) modulation format. Both theoretical and experimental results show that the conversion bandwidth can be extended to cover a very wide band, including S-, C-, and L-bands for 10 Gbit/s NRZ signals (a total bandwidth of 120 nm is experimentally demonstrated). We also study the theoretical bandwidth limit for 40 Gbit/s NRZ signals. A significant extension of the conversion bandwidth using the XPoIM approach compared with the four-wave mixing approach previously reported is demonstrated.     

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.     

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.     

Dynamic routing,modulation level and spectrum allocation (RMLSA) in FWDM with modulation format conversion

This paper proposes a dynamic routing, modulation level and spectrum allocation (RMLSA) scheme in the flexible optical wavelength-division multiplexing (FWDM) networks with modulation format conversion ability. The scheme considers the modulation format conversion at the intermediate nodes and addresses the fragmentation problem by avoiding appearance of them. The influence of routing to the emergence of the fragmentation is quantified, which is referenced to decide which one route of k-paths to use. Simulation results demonstrate efficient reductions in blocking rates and improvements in failure recovery rates for the scheme in the network.     

PDM RZ-to-NRZ and NRZ-to-PRZ format conversions using a variable DGD element inside a polarization-diversified loop

A novel scheme for bit-rate-variable polarization-division-multiplexed return-to-zero to nonreturn-to-zero and NRZ to pseudo-return-to-zero format conversions is proposed using a variable differential-group-delay element inside a polarization-diversified loop. Conversion for both 2×10 and 2×12.5 Gbit/s PDM signals are successfully demonstrated with approximately 1 dB additional power penalty by properly adjusting DGD values of the variable DGD element.     

All-optical error-bit amplitude monitor based on NOT and AND gates in cascaded semiconductor optical amplifiers

This paper proposes and simulates a novel all-optical error-bit amplitude monitor based on cross-gain modulation and four-wave mixing in cascaded semiconductor optical amplifiers （SOAs）, which function as logic NOT and logic AND, respectively. The proposed scheme is successfully simulated for 40 Gb/s return-to-zero （RZ） signal with different duty cycles. In the first stage, the SOA is followed by a detuning filter to accelerate the gain recovery as well as improve the extinction ratio. A clock probe signal is used to avoid the edge pulse-pairs in the output waveform. Among these RZ formats, 33% RZ format is preferred to obtain the largest eye opening. The normalized error amplitude, defined as error bit amplitude over the standard mark amplitude, has a dynamic range from 0.1 to 0.65 for all RZ formats. The simulations show small input power dynamic range because of the nonlinear gain variation in the first stage. This scheme is competent for nonreturn-to-zero format at 10Gb/s as well.     

QPSK wavelength multicasting based on four-wave mixing in semiconductor optical amplifier

We experimentally demonstrate one-to-five quadrature phase-shift keying（QPSK） wavelength multicasting based on four-wave mixing in bulk semiconductor optical amplifier. The input 25 Gb/s nonreturn-to-zero QPSK signal is successfully multicast to five new wavelengths with all information preserved. All the multicast channels are with a power penalty less than 1.1 d B at a bit error rate（BER） of 10-3. A characterization of the conversion efficiency in terms of pump and signal powers using the BER as figure of merit is also presented, the results indicate that the pump and signal powers should be optimized to eliminate the introduced deleterious nonlinear components.     

Analysis of format conversion from optical 16QAM to QPSK based on cascaded four-wave mixing in semiconductor optical amplifier

A scheme of format conversion from optical 16-ary quadrature amplitude modulation (16QAM) to quadrature phase shift keying (QPSK) signal based on cascaded four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is proposed. Theoretical analysis and simulations of the format conversion scheme are conducted to validate the feasibility of the proposal. In this proposal, the phase conjugated of 16QAM signal is generated after the first FWM process in an SOA, and then the QPSK signal is converted due to the second non-degenerate FWM (ND-FWM) process in another SOA. The performance and the optimal design of the 10 Gbit/s format conversion system under various key parameters of SOAs are evaluated and discussed. Simulation results present useful to enable interconnection between backbone network and access network.     

40 Gb/s all-optical logic NOR and OR gates using a semiconductor optical amplifier: Experimental demonstration and theoretical analysis

We experimentally and theoretically demonstrate 40 Gb/s all-optical logic NOR and OR gates based on a semiconductor optical amplifier (SOA) and a blue shifted optical bandpass filter (OBF). Two kinds of data formats are discussed, namely return-to-zero (RZ) format and nonreturn-to-zero (NRZ) format. The logic NOR and OR functions of RZ format are realized at the OBF detuning of −0.22 nm and −0.44 nm, respectively. The logic NOR function of NRZ format is realized at the OBF detuning of −0.24 nm. The simulation is in good agreement with the experimental results when the linewidth enhancement factor is 5.5. The simulation also shows that the SOA with large linewidth enhancement factor is preferred to achieve NOR and OR functions with good performance. The input data signal is of good pulsewidth-tolerance for NOR function, whereas not for OR function. The high Q factor could be obtained at narrow pulses injection.     

Analysis modulation formats of DQPSK in WDM-PON system

In the modulation and demodulation methods of the optical differential quadrature phase shift key (DQPSK) and the different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CS-RZ) are introduced, studying the different optical signals in the 40 Gb/s high speed transmission system. The system is simulated in 200 km optical fiber by way of dispersion compensation. It is showed that the ability of anti-dispersion and anti-PMD (polarization mode dispersion) is better in the CS-RZ-DQPSK modulation format, and this format has the smallest eye-opening penalty (EOP) with a wider range of power into the optical fiber.     

Amplification assisted optical parametric oscillator in the mid-infrared region

We demonstrate a high efficiency mid-infrared laser source based on optical parametric oscillator (OPO) assisted by an intracavity optical parametric amplification (OPA). The OPA-assisted-OPO scheme was realized in one piece of commensurable dual-periodic superlattice in which the signal light generated from the OPO process serves as the pump light for the OPA process. A maximum output power of 508 mW at 3.92 μm was achieved under a pump power of 2.85 W at 1.064 μm. The pump-to-idler conversion efficiency is 17.8% and the slope efficiency is 23.8%, and the enhancements of them are 58.9% and 67.6%, respectively, comparing with the standard OPO scheme.     

Theoretical Analyzing of Optical Parametric Oscillation with Intracavity Sum Frequency Generation

A new scheme of optical parametric oscillator with intracavity sum frequency generation is proposed,and the operation characters such as threshold,conversion efficiency,etc.,are theoretically studied. The factor affecting conversion efficiency is discussed.     

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     

Optical phase erasure and its application to format conversion through cascaded second-order processes in periodically poled lithium niobate

We describe a new optical phase erasure characteristic of periodically poled lithium niobate (PPLN) by using cascaded second-harmonic generation and difference-frequency generation with the signal set at the quasi-phase-matching wavelength. A simple analytical expression is derived clearly explaining the operation principle. It is interesting that the optical phase erasure feature enables an all-optical format conversion from carrier-suppressed return to zero (CSRZ) to return to zero (RZ). We experimentally and theoretically demonstrate a PPLN-based 40 Gbits/s all-optical CSRZ-to-RZ format conversion. Moreover, tunable and multicasting CSRZ-to-RZ format conversions are also verified in the experiment.     

Experimental study of SOA-based NRZ-to-PRZ conversion and distortion elimination of amplified NRZ signal using spectral filtering

We experimentally study both reshaping of nonreturn-to-zero (NRZ) signal and NRZ to pseudoreturn-to-zero (PRZ) format conversion based on self-phase modulation of a semiconductor optical amplifier (SOA) and detuning an optical bandpass filter (OBF). When an OBF with 1 nm bandwidth is blue shifted by 0.8 nm, the distortion of the amplified NRZ signal at 10 Gbit/s is shown to be eliminated completely. When an OBF with 0.32 nm bandwidth is red shifted by 0.42 nm from the carrier frequency, NRZ-to-PRZ conversion at 10 Gbit/s is obtained. A holding beam is used to suppress the SOA noise and improve the output extinction ratio (ER). The output ER of both the reshaped NRZ and the converted PRZ is larger than 10 dB when the signal wavelength is longer than 1540 nm, and an input power dynamic range from −7 dBm to 2 dBm is obtained at a signal wavelength of 1563.6 nm. The average power of the reshaped NRZ signal is about 3 dBm at an input power dynamic range of 13 dB. The amplitude fluctuation of the converted PRZ signal is around 1.6 dB.