Amplitude Regenerative Characteristics of RZ-DPSK Wavelength Converter Based on Four-Wave Mixing in SOA

We investigate the phase-preserving amplitude regenerative characteristics of the return-to-zero （RZ） differential- phase-shift-keying （DPSK） wavelength conversion based on four-wave m/xing （FWM） in a semiconductor optical amplifier （SOA）. The Q-factor and the optical signal-to-noise ratio （OSNR） before and after conversion are experimentally obtained and analysed in different input noise power levels. In both the continuous-wave and synchronous clock pumping cases, we find that there is amplitude clamping in the FWM conversion due to the gain saturation of SOA, which can suppress the amplitude fluctuation of the converted DPSK signal before and after demodulation. We have achieved 2-dB Q penalty improvement in our experiment demonstration of lOGbit/s RZ-DPSK signal with OSNR lower than 19dB.     

Robust optical signal-to-noise ratio monitoring scheme using a phase-modulator-embedded fiber loop mirror

We propose and experimentally demonstrate a novel in-band optical signal-to-noise ratio (OSNR) monitoring technique using a phase-modulator-embedded fiber loop mirror. This technique measures the in-band OSNR accurately by observing the output power of a fiber loop mirror filter, where the transmittance is adjusted by an embedded phase modulator driven by a low-frequency periodic signal. The measurement errors are less than 0.5 dB for an OSNR between 0 and 40 dB in a 10 Gbit/s non-return-to-zero system. This technique was also shown experimentally to have high robustness against various system impairments and high feasibility to be deployed in practical implementation.     

产生暗归零码光标记信号的新方案

在对预编码、调制和编码过程进行改进的基础上,提出了一种利用一个双臂马赫-曾德尔铌酸锂调制器和一个电信号时延器产生可调占空比和消光比的光暗脉冲归零码二进制信号的新方案。实验证明这种信号能用传统的二进制强度调制-直接检测系统的接收机进行检测。实验得到了在调节电信号时延器时速率为2.5 Gbit/s的光暗脉冲归零码二进制信号的频谱变化规律,以及占空比分别为0.25,0.35,0.60和0.80时光暗脉冲归零码二进制信号的误码率和眼图。此外,利用该方案产生的光暗脉冲归零码二进制信号可以作为标记在光标记交换网络中得到应用。     

All-optical clock recovery of 20 Gbit/s NRZ-DPSK signals using polarization-maintaining fiber loop mirror filter and semiconductor optical amplifier fiber ring laser

All-optical clock recovery (CR) from 20 Gbit/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signals are demonstrated experimentally by using a polarization-maintaining fiber loop mirror filter (PMF-LMF) and a semiconductor optical amplifier (SOA) fiber ring laser. Only by adjusting polarization controller (PC), NRZ-DPSK signals were conveniently and fast converted to pseudo return-to-zero (PRZ) signal via PMF-LMF. Then the PRZ signals are injected into the SOA fiber laser for CR. The recovered clock signals is with the extinction ratio (ER) of 10 dB and the root-mean-square (RMS) timing jitter of 750 fs in 2³¹ − 1 long pseudorandom binary sequence (PRBS) NRZ-DPSK signals measurement. Moreover, the broad wavelength tunability of recovered clock stemmed from the use of SOAs as modulator and the gain medium are shown too.     

Wideband tunable wavelength conversion of 10-Gbit/s return-to-zero signals by optical time gating of a highly chirped rectangular supercontinuum light source

We propose a novel technique for wideband tunable wavelength conversion of return-to-zero signals by optical time gating of a supercontinuum (SC) light source. A SC pulse generated by nonlinear propagation in a normal-dispersion fiber has a rectangular shape with highly linear upchirping. By control of the optical time-gating position, the center wavelength of time-gated SC pulse can be precisely tuned. Error-free 10-Gbit/s wavelength conversion with a tuning range of 27.1 nm is experimentally demonstrated.     

Pulse-width tunable multi-channel NRZ-to-RZ conversion with duplicate output

We demonstrate multi-channel non-return-to-zero (NRZ) to return-to-zero (RZ) conversions with tunable output pulse-width and single-to-dual function, using a phase modulator and an array waveguide grating (AWG), which acts both detuned multi-channel filter and demultiplexer. Four-channel NRZ signals after transmission can be converted to eight-channel RZ signals with timing jitter and extinction ratio improvement. Further transmission and bit error ratio (BER) measurements for the converted RZ signal show a good performance compared with conventional one.     

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.     

New trend for optical signal-to-noise ratio of disturbed Raman fiber amplifier

In a distributed Raman fiber amplifier (DRFA), Raman amplification allows a lower signal launch powers to transverse the span above the noise floor while still increasing the optical signal-to-noise ratio (OSNR). It improves the noise figure and reduces the nonlinear penalty of fiber systems. In this paper, we demonstrate a new trend of OSNR at different pump configurations: forward, backward and bidirectional pumping for DRFAs as a function of fiber length. We also present the variation of OSNR with both input pump power and input signal power. It is found that forward pumping provides the highest OSNR, reaching its maximum value of 37 dB. However, backward pumping provides the smallest OSNR that has its maximum of 22 dB and the bidirectional pumping provides the moderate OSNR between the others having its peak of 26 dB.     

Cascaded SOA configuration for NRZ-OOK to RZ-QPSK format conversion

We propose and experimentally demonstrate an all-optical format conversion from two independent non-return-to-zero on-off keying (NRZ-OOK) signals to a return-to-zero quadrature phase shift keying (RZ-QPSK) signal using two cascaded SOAs. Within each SOA, the cross phase modulation (XPM) process is properly controlled by an assistant light. After evaluating its effect on XPM, a suitable power range of assistant light is chosen for the NRZ-OOK to RZ-QPSK format conversion. In the experiment, a RZ-QPSK signal is successfully obtained with opened demodulation eye-diagrams.     

光网络节点设备信噪比恶化的测量

从理论与实验两方面分析了光网络节点设备光信噪比（OSNR）恶化量的测量,导出了单节点设备输出,输入侧光信噪比之差的公式。理论分析表明：节点设备输出,输入侧光信噪比之差值在一般测试条件下不能反映节点设备对光信号的影响,能作为节点设备光信噪比的恶化量来衡量设备对光信号的影响;为使测量结果能反映光节点参数对光信号的综合影响,测试系统应当满足文中给出的增益条件C＝1。实验结果支持了理论分析,实验结果表明,对于C＝1时光信噪比恶化量为4.5dB的光点设备,当C从3变化与0.16时,其输入、输出侧光信噪比之差从1．8dB变化到11．3dB.     

Simultaneous all-optical multi-channel RZ and CSRZ to NRZ format conversion

We propose and demonstrate multi-channel all-optical return-to-zero (RZ) and carrier-suppressed RZ (CSRZ) to non-return-to-zero (NRZ) format conversions using a same fiber delay-interferometer (DI). The conversions are based on simultaneous constructive interference induced by the periodical comb-like filtering characteristic of the DI. By using a DI with free spectral range of 40 GHz, 8 channel RZ and CSRZ signals at 20 Gb/s can be converted to corresponding NRZ signals at the same time. Furthermore, a duplicate output can be obtained for multi-channel CSRZ input. Bit error ratio measurements show 4 and 3.5 dB penalties for the proposed multi-channel RZ and CSRZ to NRZ conversions respectively. Further transmission for the converted NRZ signals verifies the good performance of the proposed all-passive multi-channel format converter. The potential of multi-channel RZ signals with mixed duty-cycle to NRZ conversions is also investigated.     

All-optical processing of RZ-DPSK signals using counter-propagating pulses in a saturated SOA

We demonstrate three novel all-optical signal processing methods for RZ-DPSK signals using a saturated SOA. The two logically opposite pulse streams from a demodulated noisy RZ-DPSK signal counter-propagate in the SOA. This configuration decreases the fluctuations in the demodulated marks while preventing the spaces from getting amplified. Photonic balancing provides functionality analogous to electrical balanced detection by reducing the required OSNR, and saturated asymmetric filtering removes the in-band ASE noise before detection. These methods are demonstrated experimentally by observing eye diagrams and BER measurements at 10.7 Gb/s and 22.3 Gb/s.     

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 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.     

基于自相位调制和偏移滤波的全光2R再生

理论和实验研究了基于光纤中自相位调制效应和偏移滤波的全光2R再生,实现了因放大的自发辐射噪音而恶化的数据信号的再生.数值研究了输入平均功率对信号再生的影响,结果表明,通过控制输入光纤的平均功率,Q值在5到12的40 Gb/s归零码信号再生后均可实现Q值和幅度抖动的改善.最后进行了基于高非线性色散位移光纤的10 Gb/s归零码ASE恶化数据信号的再生实验,误码率为10－9时标准时的再生功率代价仅为0.1 dB.     

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     

基于高非线性光纤中四波混频饱和效应的NRZ-DPSK和RZ-DPSK信号幅度再生实验

利用高非线性光纤中的四波混频饱和效应,实验展示了42.8 Gbit/s非归零差分相移键控（NRZ-DPSK）信号和归零差分相移键控（RZ-DPSK）信号的全光幅度再生.测量了NRZ-DPSK信号和RZ-DPSK信号经过高非线性光纤的功率传递曲线.在平均输入功率均为16 dBm的条件下,对两种调制格式的再生性能进行了比较.实验结果显示RZ-DPSK信号具有更好的幅度再生性能.     

Pulsewidth-tunable CSRZ-DQPSK signal generation using DPMZMs

This letter proposes and experimentally demonstrates a simple scheme for generating 40-GBaud carriersuppressed return-to-zero differential quadrature phase shift keying(CSRZ-DQPSK) modulation signals with tunable pulsewidths using two dual-parallel Mach-Zehnder modulators(DPMZMs).The duty cycle of the generated 40-GHz CSRZ-DQPSK pulse train is continuously tuned from 31% to 62%,with the full-width at half-maximum tuned from 7.8 to 15.5 ps,by electrically tuning the delay between the two sine-clock signals in one of the DPMZMs.Error-free performance is achieved after 320-km transmission.     

Impact of chromatic dispersion and group delay ripple on self-phase modulation based optical regenerators

We demonstrate that chromatic dispersion and group delay ripple limit the performance of all-optical regeneration based on self-phase modulation. The level of degradation depends in detail on the type of phase distortions introduced. The regenerator performance is measured using the optical signal to noise ratio (OSNR) margin provided to the system for a given bit error ratio. The addition of chromatic dispersion and group delay ripple induces a significant reduction in this OSNR margin.     

基于ROADM级联的概率成型光传输方法北大核心CSCD

针对概率成型双偏振64-正交幅度调制相干光传输系统,实验研究了可重构光分插复用器(reconfigurable optical add-drop multiplexer,ROADM)级联引起的带宽变窄对系统比特级可实现信息速率(bit-wise achievable information rate,BW AIR)的影响。发射端采用基于麦克斯韦玻尔兹曼分布的3个概率成型分布信号。实验装置包括概率成型符号序列的产生、模拟ROADM级联引起整体频率响应带宽变窄的可变带宽光滤波器、简化检测和BW AIR计算。结果表明:对于不同的星座熵,带宽变窄的影响是相似的;对于给定光信噪比,产生最大BW AIR的星座熵取决于ROADM级联导致带宽变窄的程度。通过选择合适的概率成型星座分布,系统可获得最大化BW AIR。