All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.      

WDM PON using 10-Gb/s DPSK downstream and re-modulated 10-Gb/s OOK upstream based on SOA

A signal remodulation scheme of 10-Gb/s differential phase-shift keying(DPSK) downstream and 10-Gb/s on-off keying(OOK) upstream using a semiconductor optical amplifier(SOA) and a Mach-Zehnder intensity modulator(MZ-IM) at the optical networking unit(ONU) side for wavelength division multiplexed passive optical network(WDM PON) is proposed.Simulation results indicate that error-free operation can be achieved in a 20-km transmission,and the receiver sensitivity of return-to-zero differential phase-shift keying(RZ-DPSK) is higher than nonreturn-to-zero differential phase-shift keying(NRZ-DPSK) in the proposed scheme.     

Joint Effect of MLSE and Receiver Filters Optimization on Dispersion Robustness of IMDD, DPSK, DQPSK, and Duobinary Modulation

We analyze the effectiveness of a 32-state maximum-likelihood sequence-estimation (MLSE) receiver on chromatic dispersion robustness of optical transmission based on several binary modulation formats: intensity modulation direct detection, differential phase-shift keying, and duobinary line coding. Multilevel differential quadrature phase-shift keying modulation is also analyzed using a four-state 2-bit/symbol joint MLSE processor. For all modulation formats, receiver filters are optimized together with the use of the MLSE technique.     

Rayleigh Backscattering Noise-Eliminated 115-km Long-Reach Bidirectional Centralized WDM-PON With 10-Gb/s DPSK Downstream and Remodulated 2.5-Gb/s OCS-SCM Upstream Signal

We propose a novel scheme of Rayleigh backscattering noise-eliminated, long-reach, single-fiber, full-duplex, centralized wavelength-division multiplexed passive optical network with differential quadrature phase-shift keying (DPSK) downstream and remodulated upstream using an optical carrier-suppressed subcarrier-modulation (OCS-SCM) technique and optical interleaver. The error-free transmissions of 10-Gb/s downstream and 2.5-Gb/s upstream signals are experimentally demonstrated over 115-km single-fiber bidirectional SMF-28 with less than 0.5 and 1.9 dB power penalties, respectively.      

Optical subcarrier labeling transparent to the payload format using carrier suppression technique

In this letter, we propose an optical subcarrier labeling technique that guarantees the transparency to the payload modulation format based on carrier suppression of the payload. We experimentally demonstrate transparent wavelength conversion based on four-wave mixing in a highly nonlinear fiber and subcarrier label insertion for a 10-Gb/s differential phase-shift keying payload and a 155-Mb/s amplitude shift keying subcarrier label with an overall penalty of 1.8 dB for the payload and 1.7 dB for the label.     

Theoretical and experimental analysis of the dependence of a signal's degree of polarization on the optical data spectrum

We show theoretically and experimentally the relationship between a signal's degree of polarization (DOP), all-order polarization mode dispersion (PMD), and the optical spectrum (and hence the data modulation format and pulse width), and that these effects must be taken into account when using the DOP for differential group delay (DGD) monitoring. We explain the theory behind how all-order PMD affects a signal's DOP, and observe the pulse-width dependence for 10-, 20-, and 40-Gb/s return-to-zero (RZ) systems as the duty cycle changes. We then analyze and show (via simulation and experimentation) the effects of different data modulation formats (RZ, carrier-suppressed RZ, alternate-chirped RZ, and differential phase-shift keying) on the DOP in a DGD monitor. We conclude that the measurable DGD range and DOP sensitivity in DOP-based DGD monitors are dependent on a signal's pulse width and the data modulation format. We also show the theory behind the effects of first- and second-order PMD on the maximum and minimum DOP.     

Amplitude Regeneration of RZ-DPSK Signals in Single-Pump Fiber-Optic Parametric Amplifiers

The input power tolerance of a single-pump fiber-optic parametric amplifier (FOPA) is experimentally shown to be enhanced for return-to-zero differential phase-shift keying (RZ-DPSK) modulation compared to RZ on–off keying modulation at 40 Gb/s. The improved nonlinear tolerance is exploited to demonstrate amplitude regeneration of a distorted RZ-DPSK signal in a gain-saturated FOPA. An optical signal-to-noise ratio penalty of 3.5 dB after amplitude distortion is shown to be reduced to 0.2 dB after the FOPA, thus clearly demonstrating the regenerative nature of saturated FOPAs for RZ-DPSK modulation.      

Wavelength Remodulation Using DPSK Down-and-Upstream With High Extinction Ratio for 10-Gb/s DWDM-Passive Optical Networks

We propose and demonstrate a novel wavelength remodulation scheme using differential phase-shift keying (DPSK) modulation format in both downstream and upstream signals for ldquocolorlessrdquo dense wavelength-division-multiplexed (DWDM) passive optical networks (PONs). The scheme enables high extinction ratio in both downstream and upstream remodulated signals. Error-free operation was achieved in a 20-km-reach 10-Gb/s DWDM-PON without dispersion compensation. Timing misalignment tolerance between downstream and upstream remodulated signals and maximum launched optical power for the proposed scheme are studied. Comparison with other wavelength remodulation schemes for DWDM-PONs is also performed, showing the proposed scheme can be a potential candidate for next-generation wavelength reuse DWDM-PONs.     

A comparative study of DPSK and OOK WDM transmission over transoceanic distances and their performance degradations due to nonlinear phase noise

We have compared experimentally the transmission performance of return-to-zero differential phase-shift keying (RZ-DPSK) with RZ-ON-OFF keying (OOK), nonreturn-to-zero differential phase-shift keying (NRZ-DPSK), and NRZ-OOK for 100/spl times/10-Gb/s transmission with a spectral efficiency of 0.22 b/s/Hz over transoceanic distances. The Q degradation of the RZ-DPSK after transmission over 9180 km was 3 dB greater than that of RZ-OOK. The experimental results clearly showed the major cause of degradation for DPSK is not cross-phase modulation but self-phase modulation. The calculated nonlinear phase noise, i.e., the Gordon-Mollenauer effect, agreed with the experimental results. A distributed-Raman-amplifier assisted erbium-doped-fiber-amplified transmission line acted well in reducing the nonlinear phase noise.     

Comparison of 112-Gb/s PM-RZ-DQPSK and PM-RZ-D8PSK in Terms of OSNR Requirement and Transmission Impairments

We have, for the first time, experimentally investigated 112-Gb/s polarization-multiplexed return-to-zero differential 8-ary phase-shift keying (PM-RZ-D8PSK) with differential detection in terms of optical signal-to-noise ratio requirement, group velocity dispersion (GVD), and differential group delay (DGD) tolerances, together with a direct comparison with PM-RZ differential quadrature phase-shift keying at equivalent bit rate. The results indicate higher tolerances with respect to GVD and DGD but lower receiver sensitivity in the case of PM-RZ-D8PSK.      

Mitigation of XPM Penalty in 10-Gb/s OOK/DBPSK Mixed Modulation Format 50-GHz-Spaced WDM Transmission by Conversion of OOK to BPSK Using an SOA

Copropagation of return-to-zero differential binary phase-shift keying (RZ-DBPSK) with RZ on–off keying (RZ-OOK) in wavelength-division-multiplexed (WDM) transmission has been found to be detrimental to RZ-DBPSK due to cross-phase modulation (XPM) degradations induced by pattern-dependent RZ-OOK. A method is proposed at the optical cross-connect (not at the transmitter end) to alleviate this degradation, in which the impairing RZ-OOK channel is converted to RZ binary phase-shift keying (RZ-BPSK) in a semiconductor optical amplifier (SOA) prior to 50-GHz-spaced WDM transmission. The data format conversion completely compensates for the XPM degradation, while resulting in an optical signal-to-noise ratio transmission penalty of ${≪}$ 2 dB for converted RZ-BPSK relative to RZ-OOK. Moreover, the wavelength conversion may be used to address contention resolution at the cross-connects.      

Proposal for Beyond 100-Gb/s Optical Transmission Based on Bit-Interleaved LDPC-Coded Modulation

An iterative bandwidth-efficient coded modulation scheme based on bit-interleaving low-density parity-check (LDPC) codes, and M-ary differential phase-shift keying is proposed. A bit-interleaved LDPC-coded scheme, carrying 3 bits/symbol, provides the coding gain of 8.3 dB at a bit-error rate (BER) of 10^-7. The expected coding gain at BER of 10^-12 is 12.8 dB. Possible applications include 100G Ethernet, and high-speed (>100 Gb/s) long-haul transmission     

Study on the PMD impairment of optical multilevel DPSK systems and its mitigation methods

We examine the polarization-mode dispersion (PMD) impairment of optical multilevel differential phase-shift keying systems, and also its mitigation method by comparing the electrical equalization technique and the receiver bandwidth optimization. Analysis has been carried out with 40-Gb/s systems experiencing 0/spl sim/60 ps of instantaneous differential group delay, corresponding up to 240%/80% of bit/symbol transmission rate. Results show considerable improvement in the PMD tolerance for return-to-zero format for the optimized receiver bandwidth either with or without the electrical equalization. For nonreturn-to-zero, the bandwidth optimization alone does not significantly improve the system's PMD tolerances.     

Novel Optical Vector Signal Generation With Carrier Suppression and Frequency Multiplication Based on a Single-Electrode Mach–Zehnder Modulator

This investigation presents a novel modulation approach for generating optical vector signals using frequency multiplication based on double sideband with carrier suppression. A single-electrode Mach–Zehnder modulator is biased at null point with a driving signal consisting of a 10-GHz sinusoidal signal and a 5-GHz sinusoidal signal modulated with 1.25-Gb/s on–off keying, 1.25-Gb/s binary phase-shift keying data, or 625-MSym/s quadruple phase-shift keying data. After square-law photodetection, a 1.25-Gb/s radio-frequency signal at a sum frequency of 15 GHz is generated. After transmission over 50-km single-mode fiber, the power penalty of all three modulation formats is under 0.2 dB.      

111-Gb/s Transmission Over 1040-km Field-Deployed Fiber With 10G/40G Neighbors

We demonstrate transmission of a 111-Gb/s coherent polarization-multiplexed return-to-zero differential quadrature phase-shift keying signal over 1040-km field-deployed fiber together with different types of neighboring channels, and with a cascade of 50-GHz reconfigerable optical add-drop multiplexers. Our transmission experiment proves the feasibility of transmitting a 111-Gb/s phase-modulated channel with 10 times 10.7-Gb/s on-off keying neighboring channels on a 50-GHz grid, despite the presence of strong cross-phase modulation.     

Coherent detection of optical quadrature phase-shift keying signals with carrier phase estimation

This paper describes a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals. At the receiver, a phase-diversity homodyne detection scheme is employed without locking the phase of the local oscillator (LO). To handle the carrier phase drift, the carrier phase is estimated with digital signal processing (DSP) on the homodyne-detected signal. Such a scheme presents the following major advantages over the conventional optical differential detection. First, its bit error rate (BER) performance is better than that of differential detection. This higher sensitivity can extend the reach of unrepeated transmission systems and reduce crosstalk between multiwavelength channels. Second, the optoelectronic conversion process is linear, so that the whole optical signal information can be postprocessed in the electrical domain. Third, this scheme is applicable to multilevel modulation formats such as M-array PSK and quadrature amplitude modulation (QAM). The performance of the receiver is evaluated through various simulations and experiments. As a result, an unrepeated transmission over 210 km with a 20-Gb/s optical QPSK signal is achieved. Moreover, in wavelength-division multiplexing (WDM) environment, coherent detection allows the filtering of a desired wavelength channel to reside entirely in the electrical domain, taking advantage of the sharp cutoff characteristics of electrical filters. The experiments show the feasibility to transmit polarization-multiplexed 40-Gb/s QPSK signals over 200 km with channel spacing of 16 GHz, leading to a spectral efficiency as high as 2.5 b/s/Hz.     

Experimental Investigation of Delay-Tap Sampling Technique for Online Monitoring of RZ-DQPSK Signals

We experimentally demonstrate optical performance monitoring of 20-Gb/s return-to-zero differential quadrature phase-shift keying signals using an asynchronous delay-tap sampling technique. This method allows online monitoring of accumulated chromatic dispersion in the range from $-$600 to $+$600 ps/nm. We also show evaluation of optical signal-to-noise ratio at a level of 6.7 dB and monitor operation at input power of $-$ 16 dBm.      

Impact of filtering on RZ-DPSK reception

We discuss the influence of optical and electrical filtering on the performance of beat-noise limited balanced and single-ended direct detection of return-to-zero differential phase-shift keying (DPSK). Our simulations, supported by 40-Gb/s measurements, show that balanced DPSK detection outperforms both its single-ended equivalent and ON-OFF keying by /spl sim/2.7 dB, with higher gains at narrower optical filter bandwidths.     

FSK Modulation Scheme for High-Speed Optical Transmission

In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.     

一种基于D8PSK／ASK正交调制的新型光标记方案研究

深入研究了差分八相移键控（I）8PSK）j幅移键控（AsK）正交调制格式的机理,提出了一种基于D8PsKjASK正交调制的新型光标记方案,利用D8PSK作为载荷的调制方式,ASK作为标记的调制方式,仿真实现了载荷120Gb／s、标记10Gb／s的传输速率。分析了信号的消光比（ER）对误码率（BER）的影响,仿真结果表明...