Transmission performance of 20 × 10 Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on-off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor.The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems.The bit error rate (BER) for all channels observed is less than 10⁻¹⁰ up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.     

Improving channel capacity by nonlinearity compensation and noise suppression in high-speed multi-span optical transmission systems

In this paper, the channel capacity of 40 Gb/s multi-span nonlinear optical transmission systems with nonlinearity compensation and self-adapting Wiener filtering is studied by use of Finite State Machine (FSM) approach. The comparison of channel capacity of the system with differential phase shift keying (DPSK) and on–off keying (OOK) modulation is also investigated. The channel capacity increases monotonically with the input power for transmission systems with simultaneous compensation of dispersion and nonlinearity, which performs as well as linear system. DPSK shows a much better performance and the channel capacity has an improvement of at least 48 percent over that OOK modulation. A further reduction of the amplified spontaneous emission (ASE) noise accumulation is obtained by Wiener filtering, which improves the channel capacity considerably when the input peak power is less than 3 mW.     

40Gb/s差分相移键控格式抗偏振模色散的性能研究

研究了40Gb／s非归零或归零格式下,差分相移键控和开关键控信号对一阶偏振模色散的影响．比较分析了不同偏振模色散影响下的各种调制格式的眼开度．结果表明：使用非归零和归零格式,在一阶偏振模色散情况下,差分相移键控信号均比开关键控信号有更高的眼开度;与归零差分相移键控格式相比,非归零差分相移键控格式受偏振模色散影响眼开度要小;对于给定的比特率,载波抑制归零差分相移键控格式比归零差分相移键控格式有更好的抗偏振模色散能力．     

40 Gb/s差分相移键控格式抗偏振模色散的性能研究

研究了40Gb/s非归零或归零格式下,差分相移键控和开关键控信号对一阶偏振模色散的影响.比较分析了不同偏振模色散影响下的各种调制格式的眼开度.结果表明:使用非归零和归零格式,在一阶偏振模色散情况下,差分相移键控信号均比开关键控信号有更高的眼开度;与归零差分相移键控格式相比,非归零差分相移键控格式受偏振模色散影响眼开度要小;对于给定的比特率,载波抑制归零差分相移键控格式比归零差分相移键控格式有更好的抗偏振模色散能力.     

Orthogonal labelling scheme using inverted RZ as payload

In this paper, we present an orthogonal labelling scheme using inverted return-to-zero (IRZ) as payload and differential-phase-shift-keying (DPSK) as label. Transmission performances of orthogonal labelling with 40 Gb/s IRZ payload and 10 Gb/s label are evaluated. Simulation results show that orthogonal labelling using IRZ as payload exhibits a much larger extinction ratio margin than that of using return-to-zero (RZ) as payload. The asynchronous effect between payload and label on the transmission performances of orthogonal labelling using IRZ and RZ as payload is evaluated. Simulation results show that the degradation of asynchronous orthogonal labelling using IRZ as payload is relatively worse than that of using RZ as payload. The impact of optical filter bandwidth before receivers is also investigated. Results show that the receiver sensitivities of label for IRZ/DPSK and payloads for both IRZ/DPSK and RZ/DPSK are degraded with the reduction of the filter bandwidth, while the label of RZ/DPSK exhibits an opposite trend.     

All-optical wavelength conversion for 10-Gb/s NRZ payload and 2.5-Gb/s OFDM label in optical-packet-switched network

Simultaneous wavelength conversion based on four-wave mixing (FWM) for 10-Gb/s NRZ payload and 2.5-Gb/s OFDM label signals in optical switching network is experimentally demonstrated. The dual-pump scheme based on FWM in semiconductor optical amplifier (SOA) is employed and simultaneous wavelength conversion for optical packet with one optical payload of 10-Gb/s non-return-to-zero (NRZ) on-off keying (OOK) signals and one optical label of 2.5-Gb/s OFDM signals are realized. The bit-error-rate performance is evaluated for both payload and label after wavelength conversion.     

Comparison of polarization-mode dispersion tolerances in polarization-multiplexing systems with different modulation formats

The polarization-mode dispersion (PMD) tolerance of 10 Gb/s polarization-multiplexing (PM) system is investigated. Using the importance sampling (IS) method, the outage probabilities of the PM systems with three modulation formats, including on-off keying (OOK), differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK), are quantified. When the amplified spontaneous emission (ASE) noise is assumed to be dominant, we evaluate the optical power penalties caused by the PMD effect at bit error rate (BER) of 10⁻¹². The performance of compensated PM systems with variable optical delay line is also described. The simulation results indicate that the OOK signal with higher duty cycle (DC) performs better in the PM systems with PMD compensation. It is found that the higher-order PMD impairs seriously the performance of the PM system, and phase-keying formats are more sensitive to the PMD than the OOK.     

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.     

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.     

80Gbits/s DPSK receiver-sensitivity improvement using balanced gain-compression and amplification inside an SOA balanced-receiver

A novel technique for 2R-regeneration (re-shaping and re-amplification) of received RZ or NRZ 80 Gbit/s DPSK data is demonstrated using numerical simulations. The technique is based on using a single SOA balanced-receiver for balanced gain-compression and balanced amplification of demodulated DPSK (OOK) data. The utilized SOA is polarization-insensitive with 100 ps recovery time, and the tested data is 2²³-1 PRBS long. The balanced configuration of co-propagating orthogonally-polarized and complementary OOK streams inside SOA introduce a negligible pattern-dependence at system output. The receiver has been tested by wide-range of input random phase and amplitude-noise showing a remarkable improvement in data quality-factor. The BER demonstrates a receiver-sensitivity improvement by more than 4 dB in both cases of single-ended and balanced-detected signals.     

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.     

Optical label switching of DRZ/DPSK orthogonal signal generated by photonic-crystal fiber

We demonstrate orthogonal label switching by using a dark-return-to-zero (DRZ) payload and differential phase-shift keying (DPSK) label generated by a dispersion-flattened photonic-crystal fiber. The high extinction ratio of both the payload and label improves the receiver margin. The DRZ payload introduces little cross talk to the DPSK label due to the RZ-like output of the demodulated DPSK. Simulations are performed to study the eye-closure penalty of the payload and label at different DRZ pulse widths. We compare the DRZ/DPSK with the RZ and DPSK signals numerically at the same data rate and show that the DRZ/DPSK has a strong tolerance to the polarization-mode dispersion. The DRZ/DPSK has a more compact spectrum suitable for the strong filtering requirements in WDM systems.     

All-optical demultiplexing of 4-ASK optical signals with four-wave mixing optical gates

A new all-optical technique to demultiplex quaternary-amplitude-shift keying (4-ASK) signals into two on-off keying (OOK) signals is proposed. We show that such quaternary-to-binary conversion may be performed with two types of optical gates (OGs); a first one that implements an S-shaped optical power transfer function (TF), which is also the characteristic TF of optical pulse reshaping devices, and a second type that implements a U-shaped TF. Furthermore, we describe a heuristic approach to design such OGs by using the fiber four-wave mixing effect in highly non-linear dispersion-shifted fibers. The performance of the technique is evaluated by simulating the demultiplexing of 4-ASK signals with these OGs. Results indicate that the proposed devices are able to provide binary signals with acceptable BERs even after the 4-ASK signals are propagated through a cascade of eight fiber links of 50 km followed by optical amplifiers with a 4.5-dB noise figure.     

Novel optical packet switching scheme using OFDM label with one core router and two edge routers

In this paper, we propose and experimentally demonstrate a novel optical packet switching scheme with one core router and two edge routers, in which an orthogonal frequency division multiplexing (OFDM) signal is generated as a label. In this experiment there are two transmission spans, each span consists of 50-km SMF-28 and an erbium-doped optical fiber amplifier (EDFA) without dispersion management. A 10 Gb/s on-off keying (OOK) optical payload and a 2.5 Gb/s OFDM optical label are generated, encapsulated, and transmitted in the first span. And then old label is replaced by new label, the generated new optical packet after transmission over the second span is detached and detected. The transmission performance of the optical label and payload is experimentally investigated at the ingress router, core router and egress router.     

A detailed analysis of cross-phase modulation effects on OOK and dpsk optical WDM transmission systems in the presence of GVD,SPM, and ASE noise

A performance analysis is carried out to evaluate the effect of cross-phase modulation (XPM) on a dispersion-managed 20 Gb/s optical wavelength-division multiplexing (WDM) transmission system using either the on-off keying (OOK) or the different-phase-shifting keying (DPSK) modulation, in the presence of the group-velocity dispersion (GVD), self-phase modulation (SPM), and amplified spontaneous emission (ASE). It is found that to achieve a bit error rate (BER) of 10⁻⁹ at a distance of 160 km, a 1.0 dB XPM power penalty is incurred for input channel power of 3 dBm in the OOK transmission and 7 dBm in the DPSK transmission. The power penalty increases with input channel powers and is inversely proportional and exhibits oscillations with respect to the channel separation. The oscillation is evenly spaced for the DPSK but not for the OOK and suggests the presence of optimum separation values. The XPM penalty decreases when a high dispersion fiber is used and increases linearly with increasing dispersion slope. Small residual dispersion can reduce the penalty of nonlinear effects.     

Polarization insensitive wavelength multicasting of DPSK signal using four-wave mixing in a birefringent photonic crystal fiber

We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal.     

100 Gb/s RZ-OOK transmission through 212 km deployed SSMF using monolithically integrated ETDM receiver module

100 Gb/s on-off keying (OOK) transmission over 212 km installed standard single-mode fibers using an Indium Phosphide (InP)-based electrical clock-data-recovery (CDR) and demultiplexer module was demonstrated. 5.5 × 10^− 11 bit error rate (BER) performance was achieved and 1.1-dB optical signal-to-noise ratio (OSNR) penalty was required at 10^− 9 BER after transmission.     

Optical amplitude multiplexing through parametric amplification in optical fibers

We propose a new technique that uses parametric amplification in optical fibers to combine two binary signals into a single quaternary amplitude-shift keying (4-ASK) signal. We develop a theoretical model to predict the power level distribution of the 4-ASK signals as a function of the extinction ratios of the input binary signals. Computer simulation results agree with the predictions of this theoretical model within a 0.9 dB margin. We also analyze the application of this technique to the generation of quaternary-amplitude optical packets, which are attractive for allowing the label to be transmitted in the same bandwidth and simultaneously to the payload. Our results indicate that such optical packets may be propagated through lengths comparable to those involved in metropolitan area networks.     

Proposal and simulation for all-optical format conversion between differential phase-shift keying signals based on cascaded second-order nonlinearities

We propose and simulate simple realizations of all-optical format conversion between differential phase-shift keying (DPSK) signals based on cascaded second-order nonlinearities in a periodically poled lithium niobate (PPLN) waveguide. Four kinds of 40 Gb/s all-optical format conversion from non-return-to-zero differential phase-shift keying (NRZ-DPSK) to return-to-zero differential phase-shift keying (RZ-DPSK) are investigated based on cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) or cascaded sum- and difference-frequency generation (cSFG/DFG). The optical spectra, temporal waveforms, eye diagrams, constellation diagrams, and time-related phase distribution are analyzed, which indicate successful implementation of NRZ-DPSK-to-RZ-DPSK format conversion. The obtained results also confirm the phase preservation characteristic of PPLN.     

Optical millimeter-wave generation and transmission system for 1.25 Gbit/s downstream link using a gain switched laser

In this paper, we propose a novel and cost effective system for optical millimeter-wave (mm-wave) generation and transmission of downstream data based on a gain switched laser (GSL). The GSL produces an optical comb spectrum that can be appropriately filtered to generate two optical sidebands spaced by more than 4 times the repetition rate of the GSL. These sidebands are modulated by baseband data and then transmitted via optical fiber to the remote antenna unit (RAU). At the RAU, the two sidebands are heterodyned using a photodetector to generate the electrical modulated mm-wave signal, before demodulation using self mixing. We demonstrate the distribution of 1.25 Gbit/s data OOK modulated onto a 60 GHz carrier, similar to that used in the IEEE 802.15.3c draft standard, over fiber lengths up to 62 km.