All-optical multiple-channel logic XOR gate for NRZ-DPSK signals based on nondegenerate four-wave mixing in a silicon waveguide

We report an all-optical multiple-channel exclusive OR (XOR) gate for 10?Gbits/s non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals using nondegenerate four-wave mixing in a silicon waveguide. The function of the logic XOR gate is experimentally demonstrated using 40?bit DPSK sequences. Also, the eye diagram of the XOR signal is clearly observed as the incident signals are both modulated by DPSK sequences originating from 2(31)-1 pseudorandom binary sequences.     

Experimental demonstration on 40 Gbit/s all-optical multicasting logic XOR gate for NRZ-DPSK signals using four-wave mixing in highly nonlinear fiber

We propose and demonstrate all-optical multicasting logic XOR gate for non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals by using non-degenerate four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). Theoretical analysis regarding the operation principle of NRZ-DPSK logic XOR gate is clearly described by deriving an analytical solution under the non-depletion approximation. The NRZ-DPSK logic XOR operation is attributed to the linear relationship of complex amplitudes between converted idlers and input NRZ-DPSK signals. By using three non-degenerate FWM processes in an HNLF, 40 Gbit/s all-optical multicasting logic XOR gate for NRZ-DPSK signals are successfully demonstrated in the experiment.     

Ultrafast all-optical three-input Boolean XOR operation for differential phase-shift keying signals using periodically poled lithium niobate

We propose and demonstrate that periodically poled lithium niobate (PPLN) can act as an ultrafast three-input XOR gate for differential phase-shift keying (DPSK) signals based on cascaded sum- and difference-frequency generation. PPLN-based all-optical three-input Boolean XOR operations for 20 Gbits/s return-to-zero DPSK (RZ-DPSK), 40 Gbits/s RZ-DPSK, and 20 Gbits/s non-return-to-zero DPSK signals are all successfully verified in the experiment.     

Simultaneous demodulation and slow light of differential phase-shift keying signals using stimulated-Brillouin-scattering-based optical filtering in fiber

For the first time to our knowledge, we demonstrate simultaneous demodulation and slow-light delay of differential phase-shift keying (DPSK) signals at flexible bit rates using the stimulated-Brillouin-scattering-based optical filtering effect in optical fiber. Both 10 and 2.5 Gbit/s DPSK signals have been demodulated and delayed with excellent performances. In the case of the 10 Gbit/s DPSK signal, after demodulation the tunable delay range with error-free operation is about 50 ps, which we believe is the best result obtained for 10 Gbit/s slow-light demonstrations. For the 2.5 Gbit/s DPSK signal, the optimal sensitivity after demodulation is -36.5 dBm, which is comparable with the back-to-back sensitivity of a 2.5 Gbit/s nonreturn-to-zero signal.     

PPLN-based all-optical 40 Gbit/s ODB/AMI/FSK wavelength conversion and FSK logic NOT gate

We propose and demonstrate all-optical wavelength conversion for optical duobinary (ODB), alternate-mark inversion (AMI), and frequency-shift keying (FSK) signals and a logic NOT gate for a FSK signal based on cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) in a periodically poled lithium niobate (PPLN) waveguide. ODB/AMI/FSK are generated from the demodulation of differential phase-shift keying (DPSK) using one-bit-delay fiber delay interferometer (FDI). PPLN-based 40 Gbit/s ODB/AMI/FSK wavelength conversion and FSK logic NOT gate are simultaneously implemented in the experiment.     

Phase-erased wavelength/format conversion and demodulation of 40 Gbit/s DPSK assisted by periodically poled lithium niobate

We report a novel phase-erased demodulation of differential phase-shift keying (DPSK) by exploiting cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) in a periodically poled lithium niobate (PPLN) waveguide. Analytical solutions are derived to clearly describe the operation principle. The binary optical phase information carried by the conventional DPSK demodulation outputs is removed thanks to the cSHG/DFG in a PPLN waveguide. PPLN-assisted phase-erased wavelength conversion and demodulation of 40 Gbit/s non-return-to-zero DPSK (NRZ-DPSK), return-to-zero DPSK (RZ-DPSK), and carrier-suppressed return-to-zero DPSK (CSRZ-DPSK) are demonstrated in the experiment. Moreover, the accompanying all-optical format conversions from optical duobinary (ODB) to NRZ and from ODB/alternate-mark inversion (AMI) to RZ are also substantiated in the experiment. In addition, the calculated theoretical results including optical spectra, temporal waveforms, and phase diagrams also confirm the successful implementation of PPLN-assisted 40 Gbit/s NRZ-DPSK/RZ-DPSK/CSRZ-DPSK phase-erased wavelength conversion, demodulation, and ODB-to-NRZ and ODB/AMI-to-RZ format conversions.     

All-optical simultaneous drop and wavelength conversion of DPSK data

We demonstrate an all-optical scheme for the simultaneous drop and wavelength conversion of bursts of data from a continuous stream of differential phase-shift keyed (DPSK) signals. This function is obtained in a single semiconductor optical amplifier Mach-Zehnder interferometer thanks to proper nonlinear interaction of the data stream and an optical gate signal at different wavelength. Fast switching-time enabling wavelength shifting operation on continuous DPSK data stream at 10 and 40 Gb/s without any bit loss is reported. Corresponding measured power penalties are negligible at 10 Gb/s and about 1.7 dB at 40 Gb/s.     

Demultiplexing of OTDM-DPSK signals based on a single semiconductor optical amplifier and optical filtering

We propose and demonstrate the use of a single semiconductor optical amplifier (SOA) and optical filtering to time demultiplex tributaries from an optical time division multiplexing-differential phase shift keying (OTDM-DPSK) signal. The scheme takes advantage of the fact that phase variations added to the target channel by cross-phase modulation from the control signal are effectively subtracted in the differential demodulation scheme employed for DPSK signals. Demultiplexing from 80 to 40 Gbit/s is demonstrated with moderate power penalty using an SOA with recovery time twice as long as the bit period at 80 Gbit/s. Large dynamic ranges for the input power and SOA current are experimentally demonstrated. The scheme is expected to be scalable toward higher bit rates.     

Optical 3R regeneration of 40 Gbit/s degraded data signals

A 40 Gbit/s optical 3R regenerator is proposed and demonstrated. The 3R regenerator consists of a dual-ring injection mode-locked fiber ring laser as the clock recovery module and an electroabsorption modulator (EAM) as the decision gate. The clock recovery module extracts the optical short pulse clock with low timing jitter from degraded 40 Gbit/s optical data streams, while the decision gate restores their signal quality. A numerical model describing the cross-absorption modulation effect in a bulk EAM is developed to explore the operating conditions, such as bias voltage, pump signal power. The timing jitter tolerance for the EAM optical gate is also investigated. Significantly improvement of BER is obtained from 40 Gbit/s RZ signals which are degraded by polarization mode dispersion or chromatic dispersion.     

基于线性光放大器的全光逻辑异或门理论分析

基于速率方程建立了线性光放大器(LOA)的数值模型,模拟了线性光放大器的增益钳制特性。与对称结构马赫曾德尔干涉仪(MZI)的传输矩阵相结合,构建了线性光放大器马赫曾德尔干涉仪全光逻辑异或门模型,实现了两路40Gbit/s信号的异或运算。与传统的半导体光放大器(SOA)构成的马赫曾德尔干涉仪型异或门进行了比较,从器件结构上对两种异或门运算结果的差异给出了解释。结果表明,线性光放大器具有平坦的增益特性,对输入信号的扰动具有不敏感性,垂直光场缩短了载流子恢复时间;线性光放大器马赫曾德尔干涉仪结构可以实现异或运算;利用差分相位法可以解决载流子恢复时间对信号处理速度的限制,合理地选择延迟时间能获得较好的运算结果;输出信号具有眼图张开度大、消光比高、峰值啁啾小、对波长变化不敏感等优点。     

Ultrafast all-optical XOR logic gate based on a symmetrical Mach-Zehnder interferometer employing SOI waveguides

We present an integrated Silicon-on-Insulator (SOI) based Mach-Zehnder interferometer (MZI) in order to perform ultrafast all-optical XOR logic gate operation with a bit rate of ∼ 0.33 Tb/s. A numerical simulation is carried out in order to study various parameters such as extinction ratio and eye-opening parameters, characterizing the performance of the XOR logic gate. The output XOR logic gate signal can have improved extinction and eye margin if the initial powers of primary signals and the probe continuous-wave (CW), and SOI waveguide length are judiciously adjusted.     

Three-chip differential phase-shift keying maximum likelihood sequence estimation for chromatic-dispersion and polarization-mode-dispersion compensation

We propose a novel three-chip differential phase-shift keying (DPSK) maximum likelihood sequence estimation (MLSE) for chromatic-dispersion (CD) and first-order polarization-mode-dispersion (PMD) compensation to extend the transmission reach of the DPSK signal. Such a technique searches the most probable path through the trellis for DPSK data sequence estimation by exploiting the phase difference between not only the adjacent optical bits but also the bits that are one bit slot apart. The proposed scheme significantly outperforms conventional two-chip DPSK MLSE in CD and PMD compensation. We show that the proposed three-chip DPSK MLSE can enhance the CD tolerance of 10 Gbit/s DPSK signal to 2.5 times of that by using two-chip DPSK MLSE and can bound the penalty for 100 ps differential group delay by 1.4 dB.     

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.     

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.     

All-optical phase and amplitude regeneration of return-to-zero differential phase shift keying data

We report a novel implementation of an all-optical rephasing, reshaping, and reamplification differential phase shift keying (DPSK) regenerator. The rephasing is based on converting phase noise into amplitude noise by using an interferometric configuration and then eliminating the amplitude noise by using a semiconductor optical amplifier (SOA). The reshaping is performed using gain competition and gain compression in a saturated SOA. The scheme was tested using 10Gbit/s, 2(23)-1 pseudorandom bit sequence return-to-zero DPSK data. The measurement shows removal of the degraded data error floor with a 6 order-of-magnitude improvement in bit-error rate. The measured negative power penalty is about 4dB. Mathematical analysis shows a reduction in DPSK phase-noise power by half.     

10 Gbit/s tributary channel exchange of 160 Gbit/ssignals using periodically poled lithium niobate

We propose and demonstrate data exchange in both the wavelength and time domains at a fine granularity, i.e., low-speed tributary channel exchange of wavelength-division multiplexed high-speed optical time-division multiplexed signals. Using the parametric depletion effect of cascaded second-order nonlinear interactions in a periodically poled lithium niobate (PPLN) waveguide, we experimentally implement 10?Gbit/s tributary channel exchange between two 160?Gbit/s signals with a power penalty of less than 4?dB at a bit-error rate of 10(-9). Moreover, taking into account the waveguide propagation loss, we derive analytical solutions to investigate the signal depletion (SD) and extinction ratio (ER) performance of the PPLN-based data exchange. The theoretical analyses indicate that low waveguide propagation loss benefits large achievable SD and ER.     

Design and demonstration of a novel optical CDMA platform for use in avionics applications

We designed, built, and demonstrated a highly scalable incoherent optical CDMA platform under DARPA contract which was delivered to Lockheed Martin for additional testing in avionic applications. The platform enables users to communicate with each other at ∼1.25 Gbit/s per user with raw BER of less than 10⁻¹². The system architecture uses (3, 11) fast wavelength-hopping, time-spreading prime codes with a chip size of 73 ps utilizing picosecond optical pulses allocated in the time and wavelength domains. A novel design of a “dual code” optical encoder and decoder realized a novel optical layer implementation of an XOR gate and enabled secure network connectivity using a “One-time pad” encryption approach. The testbed is also designed to conduct eavesdropping studies on testbed users. The incoherent OCDMA approach is compatible with existing DWDM optical networks and uses off-the-shelf components.     

Experimental observation of a 1.5 microm band wavelength conversion and logic NOT gate at 40 Gbit/s based on sum-frequency generation

We have experimentally verified a new idea for 40 Gbit/s wavelength conversion within the 1.5 microm band based on sum-frequency generation (SFG) in a periodically poled LiNbO3 waveguide. The spectrum and the temporal waveform of the output pump reveal that the input cw pump is converted to an optical pulse during SFG. Not only wavelength conversion but also a logic NOT gate at 40 Gbit/s are experimentally observed.     

Multi-parametric optimized design of FWM-based tunable all-optical wavelength converters for 40 Gbit/s ASK and DPSK signals

A full numerical optimization method for the design of FWM-based frequency converters for WDM systems is presented, taking into account specific system constraints set by the designer. The method is illustrated with the design of separate transparent frequency converters for 40 Gbit/s ASK and DPSK signals using Truewave fiber.     

Turbo-switched Mach-Zehnder interferometer performance as all-optical signal processing element at 160 Gb/s

Two variations of the active Mach-Zehnder interferometer (MZI) that incorporate the recently proposed turbo-switch effect are introduced to carry out three key functionalities in forthcoming high-speed optical telecommunication networks, namely, all-optical wavelength conversion, photonic XOR gating and optical time-division demultiplexing. Their performance is numerically investigated at 160 Gb/s using a sophisticated semiconductor optical amplifier (SOA) model. The more practical of the two proposed geometries shows error-free operation as XOR Boolean gate, low patterning as wavelength converter, and poor performance as demultiplexer. For comparison, results derived from well-accepted (or typical) schemes are also presented, and the role of the required extra SOAs as distinguishing elements of the new architectures is investigated.