All-optical Format Research Articles

Simultaneous multiple channel all-optical NRZ to CSRZ and RZ to CSRZ format conversion using an SOA-NOLM

The optical conversion bandwidth for an all-optical modulation format converter, based on a semiconductor laser amplifier in a nonlinear optical loop mirror (SOA-NOLM), is investigated. 4×10Gbit/s channels are all-optically converted between both non-return-to-zero (NRZ) and return-to-zero (RZ) format to carrier-suppressed return-to-zero (CSRZ). WDM transmission of the converted signals over a 194km fibre span is then demonstrated. The receiver sensitivity for the converted four wavelengths is measured and compared after transmission.

All-optical XOR logic gate using intersubband transition in III-V quantum well materials.

A monolithically integrated all-optical exclusive-OR (XOR) logic gate is experimentally demonstrated based on a Michelson interferometer (MI) gating device in InGaAs/AlAsSb coupled double quantum wells (CDQWs). The MI arms can convert the pump data with return-to-zero ON-OFF keying (RZ OOK) to binary phase-shift keying (BPSK) format, then two BPSK signals can interfere with each other for realizing a desired logical operation. All-optical format conversion from the RZ OOK to BPSK is based on the cross-phase modulation to the transverse electric (TE) probe wave, which is caused by the intersubband transition excited by the transverse magnetic (TM) pump light. Bit error rate measurements show that error free operation for both BPSK format conversion and XOR logical operation can be achieved.

Demonstration of all-optical RZ-to-NRZ format conversion based on self phase modulation in a dispersion flattened highly nonlinear photonic crystal fiber

We propose a novel all-optical format conversion scheme from the return-to-zero (RZ) to non-return-to-zero (NRZ) based on a single dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF) and an optical band-pass filter (OBPF). The polarity-preserved, 30Gbit/s RZ-to-NRZ format conversion with Q factor and extinction ration (ER) of 6.57 and 16.06dB is demonstrated by exploiting self-phase modulation (SPM) induced spectral broadening together with subsequent spectral tailoring in the DF-HNL-PCF. The experiments are carried out to investigate the wavelength tunability and the dynamic characteristics of the newly designed PCF-based format converter. Our results show that the designed format converter has a wide operating wavelength range of 24nm and higher tolerance to input signal power fluctuation. This is very useful and attractive for engineering applications of optical-fiber-based RZ-to-NRZ format converter in future ultra-high speed photonic networks.

Demonstration of 40 Gbit/s all-optical return-to-zero to nonreturn-to-zero format conversion with wavelength conversion and dual-channel multicasting based on multiple cross-phase modulation in a highly nonlinear fiber

Zhan-Qiang HuiXi’an University of Posts and TelecommunicationsSchool of Electronic EngineeringXi’an 710061, ChinaEmail: zhanqianghui@xupt.edu.cnJian-Guo ZhangLondon South Bank UniversityDepartment of Engineering and Design103 Borough RoadLondon SE1 0AA, United KingdomJia-Min GongMeng LiangMei-Zhi ZhangYi YangFeng-Tao HeJi-Hong LiuXi’an University of Posts and TelecommunicationsSchool of Electronic EngineeringXi’an 710061, ChinaAbstract. We propose and experimentally demonstrate all-optical return-to-zero (RZ) to nonreturn-to-zero (NRZ) format conversion by using multi-ple cross-phase modulation (MXPM) in a highly nonlinear fiber. The pro-posed all-optical format converter can perform simultaneously wavelengthconversionanddual-channelsignalmulticasting.Thisisachievedbyprop-erly filtering two broadened probe spectra induced by MXPM between theRZ signal and continuous-wave double probe lights. We also study exper-imentally wavelength tunability for the proposed format converter at40 Gbit∕s, which is feasibly achieved by varying the central wavelengthsof the double probe lights. Our results show that a wide operation wave-length range of 24 nm is obtained. By monitoring eye diagrams, the con-verted 40 Gbit∕s NRZ signals can have an extinction ratio of 10.9 dB andthe

An All-Optical Modulation Format Conversion for 8QAM Based on FWM in HNLF

In this letter, we propose and experimentally demonstrate an all-optical modulation format conversion scheme from amplitude shift keying (ASK) and quadrature phase shift keying (QPSK) to 8-ary quadrature amplitude modulation (8QAM), using four-wave mixing (FWM) effect in highly nonlinear fiber. In the FWM process, a 20-Gbits/s return-to-zero QPSK (RZ-QPSK) signal and a 10-Gbit/s ASK signal are utilized as probe light and pump light, respectively. A 30-Gbits/s RZ-8QAM signal, which is the idler light, is successfully obtained with optical signal-to-noise ratio larger than 30 dB and bit-error rate lower than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10^{-5}$</tex></formula> .

All-Optical Format Conversion for Multichannel QPSK Signals

All-optical format conversion is a key function in providing flexible management and interface for optical networks with different formats. In this paper, we propose and demonstrate multichannel mutual format conversions between the nonreturn-to-zero quadrature phase-shift keying (NRZ-QPSK) and the return-to-zero QPSK (RZ-QPSK) signals using a single semiconductor optical amplifier and/or a delay interferometer (DI). The conversion from the NRZ-QPSK to RZ-QPSK is based on the cross phase modulation (XPM) effect, which is introduced by a synchronous optical clock signal with high input power, and subsequent detuned filtering. The amplitude of the NRZ-QPSK signal is converted to the RZ-QPSK signal with identical phase shift onto every input bit by the XPM effect. The conversion from the RZ-QPSK to NRZ-QPSK is based on the constructive interference in a single DI with a half-bit delay. The principle for the mutual conversions is analyzed theoretically, and simulations validate the feasibility of the proposed schemes. Parallel 4 channels format conversions between the NRZ-QPSK and the RZ-QPSK signals are experimentally achieved well with small Q penalty less than 2 dB.

Combining DPSK and duobinary for the downstream in 40-Gb/s long-reach WDM-PONs

We propose and demonstrate combining differential phase-shift keying (DPSK) and duobinary transmission for the downstream in 40-Gb/s long-reach wavelength division multiplexed-passive optical networks (WDM-PONs) in order to provide robust transmission performance in the backhaul section and simple detection at the ONUs. DPSK is deployed in the trunk span as it provides stronger robustness to fiber nonlinearity. Duobinary is used in the access span where its higher chromatic dispersion tolerance relieves the need for dispersion compensation. All-optical multichannel modulation format conversion from DPSK to duobinary is realized in the local exchange in a single delay interferometer to reduce system cost. Single and multi-channel 80-km long-reach DPSK transmission and up to 5-km duobinary access transmission are experimentally demonstrated at 40Gb/s. The proposed approach shows great potential for future high data rate optical access networks.

All-optical format conversion of NRZ-OOK to QPSK and 16QAM signals via XPM in a SOA-MZI

This letter proposes a scheme for the format conversion of on-off keying (OOK) signal to quadrature phase-shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM) signals via cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA). Theoretical and experimental analyses of the format conversion scheme are conducted to validate its feasibility. The phase changing is obtained because of the XPM in the SOA. The QPSK and 16QAM signals are converted from the OOK signal. The performance of the 10 Gb/s format conversion system is evaluated and discussed. The receiver sensitivities of the converted QPSK and 16QAM signals after detection are -27.25 and -23.5 dBm, respectively, at a bit error rate (BER) of 10-9.

All-optical format conversion from non-return-to-zero to return-to-zero based on dual-pump four-wave mixing in photonic crystal fiber

A novel all-optical format conversion scheme based on dual-pump four-wave-mixing (DP-FWM) in dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF) is proposed and experimentally demonstrated. The original non-return-to-zero (NRZ) format is converted into double return-to-zero (RZ) format by injecting NRZ signal and double synchronized clock signals into the DF-HNL-PCF. The DP-FWM effect generates two sideband components, which carry the same data information as the original NRZ signal with RZ format. The wavelength tunability and dynamic range of format converter are investigated. The optimum extinct ratio and Q factor of converted signals are 15 dB and 5.4, respectively. The advantages of this scheme are that the each wavelength of double channel multicasting signals is dependent and flexible. Moreover, the system is transparent to bit rate as well as modulation format, and achieves all-optical wavelength conversion and wavelength multicasting.

All-Optical Format Conversion for Polarization and Wavelength Division Multiplexed System

All-optical return-to-zero (RZ) to nonreturn-to-zero (NRZ) format conversions for polarization division and wavelength division multiplexed on-off keying (OOK), differential phase-shift keying (DPSK), and quadrature phase-shift keying (QPSK) signals are proposed and demonstrated using a single delay interferometer (DI). Because of the periodical filtering property and the polarization insensitive characteristic of the free space-based DI, four wavelength division multiplexed and polarization division multiplexed RZ-OOK to NRZ-OOK, RZ-DPSK to NRZ-DPSK, and RZ-QPSK to NRZ-QPSK conversions have been achieved using the constructive interference. An average power penalty of 1.5 dB can be achieved. The proposed scheme can well accommodate the future transmission system with multiple modulation formats and multidimensional multiplexed techniques.

All-optical format conversion from RZ-QPSK to NRZ-QPSK

We proposed and demonstrated an all-optical format conversion from return-to-zero quadrature phase shift keying (RZ-QPSK) to non-return-to-zero QPSK (NRZ-QPSK) at 40 Gb/s using a half bit delay interferometer (DI). Due to the constructive interference in the DI, the format conversion was achieved with the phase information preserved. Q penalty for the format conversion was less than 1.8 dB for I and Q data.

High-Speed All-Optical Generation of Advanced Modulation Formats Using Photonic-Integrated All-Optical Format Converter

We propose and demonstrate all-optical method for generating advanced modulation formats with high-spectral efficiency. The proposed method is based on all-optical format conversion using photonic-integrated semiconductor optical amplifier-Mach-Zehnder interferometers. It enables application of advanced modulation formats at data rates not directly accessible using electronic means only. We demonstrate generation of single-polarization 86.4-Gb/s binary phase-shift keying and 173-Gb/s quadrature phase-shift keying optical signals.

Reconfigurable All-Optical OTDM-to-WDM Conversion Using a Multiwavelength Ultrashort Pulse Source Based on Raman Compression

We propose and demonstrate a reconfigurable all-optical format conversion from optical time-division multiplexing (OTDM) to wavelength division multiplexing (WDM) providing full flexibility in terms of channel spacing and wavelength allocation. The system consists of a Raman amplification-based multiwavelength pulse compressor and a parametric sampling gate. Four conventionally generated WDM 10 GHz pulse trains are compressed at the same time to around 2.5 ps and, then, used for multiwavelength sampling of a 40 Gb/s 3.49 ps OTDM signal. Simultaneous extraction of all four 10 Gb/s tributaries to WDM channels in WDM grid with tunable channel spacing is demonstrated. Controlling time delays among the WDM clock channels makes it flexible to map OTDM tributaries onto any desired wavelength order, which is also called wavelength- and time-selective function. The reconfigurable functions can be realized independently on the coming OTDM signal by simply setting corresponding parameters of the WDM synchronous pulse trains at the terminals. This is also the key for the good overall performance obtained for all demultiplexed channels. Low power penalties below 1.9 and 2.1 dB are achieved with small penalty variations, 0.3 and 0.5 dB, among channels as the OTDM tributaries are converted to WDM grid with spacing of 400 and 200 GHz, respectively.

All-optical modulation format conversion from NRZ-OOK to PSK-Manchester using SOA-MZI

Proposed and demonstrated is an all-optical modulation format conversion from a non-return-to-zero on-off keying (NRZ-OOK) signal to a phase-shift keying (PSK)-Manchester format signal using a semiconductor optical amplifier based Mach-Zehnder interferometer (SOA-MZI). In the experiment, a 2.5 Gbit/s PSK-Manchester format signal was obtained from a NRZ-OOK signal and a 50 km error-free transmission of the converted PSK-Manchester format signal was achieved. In addition, the feasibility of the conversion at a higher data rate using SOAs with fast phase recovery was investigaged.

Theoretical study of all-optical NRZ to RZ format conversion with tunable pulse width based on XPM in a silicon waveguide

An all-optical format conversion from non-return-to-zero (NRZ) to return-to-zero (RZ) is presented based on cross-phase modulation (XPM) in a silicon waveguide with a detuned optical bandpass filter (OBPF). The simulation results show that the tunable bandwidth of the OBPF leads to RZ signals with tunable pulse width. The conversion efficiency (CE) and the pattern effect of the RZ signal are attributed to the parameters of the pump pulse and the OBPF. The converted RZ signal exhibits lower timing jitter than the NRZ signal.

All-optical format conversion from non-return-to-zero to return-to-zero based on four-wave mixing in photonic crystal fiber

The conversion from all-optical non-return-to-zero (NRZ) to return-to-zero (RZ) format is a crucial technology in interfacing WDM and OTDM of future transparent photonic network. The conversion from all-optical single-to-dual NRZ to RZ format conversion is presented and experimentally demonstrated based on four-wave mixing (FWM) in a 50 m dispersion-flattened highly-nonlinear photon crystal fiber (DF-HNL-PCF). The original NRZ format is converted into RZ format by injecting synchronized clock signal into the DF-HNL-PCF. The FWM effect generates two sideband components, which carry the same data information as the original NRZ signal with RZ format. The proposed format converter has a wide and tunable operation wavelength range of 19.3 nm. The optimum conversion efficiency, extinct ratio and Q factor are -21 dB, 11.9 dB and 7.2, respectively. The system is transparent to both bit rate and modulation format. The advantage of this scheme consists in the ability of bandwidth scalable due to the fact that the dispersion flattening of HNL - PCF is used. Furthermore, it is all optical fiber, compact and robust, which makes it more competitive as well as easily accessible for use in practical optical communication systems.

Simulation for all-optical format conversion from NRZ-DPSK to RZ-DPSK

We propose and simulate a simple scheme of all-optical format conversion from non-return-to-zero differential phase-shift keying (NRZ-DPSK) to return-tozero differential phase-shift keying (RZ-DPSK) by using phase modulators and detuning filters. The operation principle is theoretically analyzed and simulated by exploiting spectra, temporal waveform and eye diagram with commerical optical design software VPI Transmission Maker 8.5. The use of electrical clock recovery and linear phase modulation in the conversion scheme may be potiental in practise use.

Simultaneous all-optical demodulation and format conversion for multi-channel (CS)RZ-DPSK signals

We proposed and demonstrate an all-optical demodulation and format conversion scheme for multi-channel (carrier suppressed) return-to-zero differential phase shift keying ((CS)RZ-DPSK) signals. By utilizing a single delay interferometer (DI) with half bit delay, multi-channel (CS)RZ-DPSK signals can be demodulated simultaneously at the destructive port of the DI, with the corresponding converted nonreturn-to-zero differential phase shift keying (NRZ-DPSK) signals obtained at the constructive port. The proposed multi-channel operation has been demonstrated for 6*20 Gb/s RZ-DPSK and 6*40 Gb/s CSRZ-DPSK signals, with ~0.8 and 1.2 dB average power penalties for the format conversions respectively.

All-Optical Format Conversion from RZ-DPSK to NRZ-DPSK at 40 Gbit/s

All-optical format conversion from return-to-zero differential phase shift keying (RZ-DPSK) to non-return-to-zero DPSK (NRZ-DPSK) is demonstrated by using a delay interferometer and a 1-nm-bandwidth filter at 40 Gbit/s. The operation principle is theoretically analyzed and numerically simulated with the help of VPI Transmission Maker 8.5. The simulated results are in agreement well with the experimental results. The conversion can be achieved with power penalty of 0.7dB.

Ultrahigh-speed all-optical wavelength conversion and format conversion for polarisation-shift-keying signal based on four-wave mixing in light-holding semiconductor optical amplifier

An ultrahigh-speed all-optical module, which can realise both the wavelength conversion of polarisation-shift-keying (PolSK) signal and the format conversion from non-return-to-zero (NRZ)-PolSK to return-to-zero (RZ)-PolSK, is proposed based on four-wave mixing (FWM) in light-holding semiconductor optical amplifier (SOA). This scheme is simple and free of pattern effect. The conversion efficiencies are improved by utilising a holding light. Using the polarisation-dependent broadband model, wavelength conversion and format conversion for PolSK signal are theoretically realised at 40 Gbit/s. Moreover, the effects of holding light, polarisation dependence of SOA and polarisation angle between input pump light and PolSK signal on the output performance of wavelength conversion and format conversion for PolSK signal are theoretically investigated in detail.