RZ-DPSK Signals Research Articles

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 mixing (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 10Gbit/s RZ-DPSK signal with OSNR lower than 19dB.

Phase-preserving amplitude regeneration for a WDM RZ-DPSK signal using a nonlinear amplifying loop mirror

We propose a modified nonlinear amplifying loop mirror (NALM) for phase-preserving 2R regeneration of wavelength division multiplexed (WDM) return-to-zero differential phase-shift-keyed signals. As proof of principle the regeneration capability of this NALM setup has been investigated experimentally for two 10 Gbit/s wavelength channels. A significant eye-opening improvement and a negative power penalty of 1.2 dB have been observed in both channels.

Erratum to “Polarization-Insensitive Wavelength Conversion by FWM in a Highly Nonlinear PCF of Polarization-Scrambled 10-Gb/s RZ-OOK and RZ-DPSK Signals” [Oct 15 07 1676-1678

In the above titled paper (ibid., vol. 19, no. 20, pp. 1676-1678), a production error caused a greater-than sign to be changed to a less-than sign. The correct version of the sixth sentence in Section II is presented here.

Polarization-Insensitive Wavelength Conversion by FWM in a Highly Nonlinear PCF of Polarization-Scrambled 10-Gb/s RZ-OOK and RZ-DPSK Signals

Wavelength conversion of polarization-scrambled 10-Gb/s on-off keyed and differential phase-shift-keyed signals for which the pulse format was 33% return-to-zero, has been achieved by partially degenerate four-wave mixing in a record 20-m-short highly nonlinear photonic crystal fiber. It was found that a minimum pump-probe detuning of ~9 nm was required to achieve polarization-insensitive wavelength conversion of <1 dB, resulting in a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> -receiver sensitivity penalty of <1 dB, for both modulation formats.

2R-Regeneration of an RZ-DPSK Signal Using a Nonlinear Amplifying Loop Mirror

The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for return-to-zero differential-phase-shift-keyed signals has been investigated experimentally. The measured power characteristics and phase functions show that the signal amplitude is regenerated while the signal phase is preserved in the setup. A significant eye-opening improvement and a negative power penalty of about 1.5 dB were obtained

Amplitude regeneration of RZ-DPSK signals based on four-wave mixing in fibre

Amplitude regeneration of a differential phase-shift keying signal using four-wave mixing in an optical fibre is studied experimentally. The device removes amplified spontaneous emission amplitude noise without significant degradation of phase information. Performance is evaluated under different input noise conditions.

Suppression of XPM and XPM-induced nonlinear phase noise for RZ-DPSK signals in 40 Gbit/s WDM transmission systems with optimum dispersion mapping

We numerically investigate XPM effect and XPM-induced nonlinear phase noise in both RZ-DPSK and multi-format (RZ-DPSK and RZ-OOK) WDM systems operating at 40 Gbit/s with different dispersion maps. The relative strength of XPM effect and XPM-induced nonlinear phase noise is discussed for both RZ-DPSK and multi-format WDM transmission. With optimum dispersion mapping, XPM and XPM-induced nonlinear phase noise from neighboring channels carrying either OOK or DPSK signals can both be effectively suppressed.

RZ-DPSK signal regeneration based on dual-pump phase-sensitive amplification in fibers

All-optical regeneration of differential phase-shift keying signals by means of a phase-sensitive amplification scheme solely based on highly efficient four-wave mixing in fibers is theoretically and numerically studied. The analytical and numerical investigation demonstrates almost ideal phase regeneration accompanied with enhanced amplitude noise suppression in the regime of pump depletion

Simultaneous reshaping of OOK and DPSK signals by a fiber-based all-optical regenerator

Simultaneous reshaping of optically time-division-multiplexed RZ-OOK and RZ-DPSK signals by a fiber-based regenerator is numerically demonstrated. The regenerator utilizes the four-wave mixing (FWM) in a highly nonlinear fiber. A parametric amplifier configuration without wavelength conversion of the signal is assumed, in which ultra-fast saturation of the FWM interaction gives stabilization of signal amplitude with the signal phase principally maintained. The regenerator greatly improves the performance of OOK tributaries. Although the regenerator does not have the function of phase regeneration, it improves the DPSK signal quality when the signal power is relatively low where the amplitude noise is significant. Influence of the pump phase modulation on the regenerator performance is also examined.

8/spl times/160-Gb/s WDM field transmission experiment with single-polarization RZ-DPSK signals and PMD compensator

Single-polarization 160-Gb/s-based wavelength-division-multiplexing (WDM) field transmission has been successfully demonstrated. By using a return-to-zero differential phase-shift-keying modulation format and a simple polarization-mode dispersion compensator, we have successfully demonstrated single-polarization 8/spl times/160 Gb/s WDM transmission without the polarization demultiplexing.

Athermal optical demodulator for OC-768 DPSK and RZ-DPSK signals

We report an athermal optical delay-interferometer capable of demodulating any OC-768 differential phase-shift keying (DPSK) signal on the ITU 50-GHz grid over the C+L-band. The demodulator is based on a free-space Michelson interferometer. Experiments are performed with a 42.7-Gb/s nonreturn-to-zero DPSK signal and a 42.7-Gb/s return-to-zero DPSK signal with 67% duty cycle. Receiver sensitivity (at a bit error rate of 10/sup -9/) of better than /spl sim/35.5 dBm is achieved for both signals. Negligible temperature-induced penalty is observed over an operational temperature range between 0/spl deg/C and 70/spl deg/C. The penalty associated with laser frequency offset (from the ITU grid) is also investigated.

Single-span transmission of WDM RZ-DPSK signal over 310-km standard SMF without using FEC and remote-pumping

To avoid significant stimulated Brillouin scattering (SBS) generation in a bidirectional Raman-pumped long single-span transmission system, the SBS threshold is studied in both return-to-zero on-off -keying (RZ-OOK) and RZ differential phase-shift keying (DPSK) systems. It shows that SBS threshold in an RZ-DPSK system is more than 10 dB higher than that in an RZ-OOK system, and SBS reflection is dominated by copumping, while counterpumping has minor effect. Error-free eight-channel single-span transmission is demonstrated over 310-km standard single-mode fiber using RZ-DPSK format and bidirectional Raman pumping, without applying forward-error correction and remote-pumping techniques.

Wavelength conversion of a 40-Gb/s RZ-DPSK signal using four-wave mixing in a dispersion-flattened highly nonlinear photonic crystal fiber

Wavelength conversion of a 40-Gb/s return-to-zero differential phase-shift keying signal is demonstrated in a highly nonlinear photonic crystal fiber (HNL-PCF) for the first time. A conversion efficiency of -20 dB for a pump power of 23 dBm and a conversion bandwidth of 31 nm, essentially limited by the gain bandwidth of erbium-doped fiber amplifiers, are obtained in only 50-m dispersion-flattened HNL-PCF with nonlinear coefficient equal to 11 W/sup -1//spl middot/km/sup -1/. This experiment demonstrates the potential of four-wave mixing in HNL-PCF as a modulation format and bit rate transparent wavelength conversion mechanism in future high-speed systems.

Comparison of nonlinear phase noise and intrachannel four-wave mixing for RZ-DPSK signals in dispersive transmission systems

Self-phase modulation induced nonlinear phase noise is reduced with the increase of fiber dispersion but intrachannel four-wave-mixing (IFWM) is increased with dispersion. Both degrading DPSK signals, the standard deviation of nonlinear phase noise induced differential phase is about three times that from IFWM even in highly dispersive transmission systems.

NOLM-based RZ-DPSK signal regeneration

We present a nonlinear optical loop mirror (NOLM)-based 2R-regenerator setup, which is capable of regenerating signals modulated in phase-sensitive modulation formats. In a conventional NOLM, fluctuations of the signal amplitude are converted into phase fluctuations. Therefore, it is not suitable for regeneration of signals, modulated in formats such as differential phase-shift keying (DPSK) or duobinary. In this letter, we present a modified NOLM setup for 2R-regeneration taking return-to-zero DPSK as an example.

RZ/CSRZ-DPSK and Chirped NRZ Signal Generation Using a Single-Stage Dual-Electrode Mach-Zehnder Modulator

This letter presents a novel configuration for return-to-zero (RZ) differential phase-shift keyed (DPSK), carrier-suppressed (CS) RZ DPSK, and chirped nonreturn-to-zero (CNRZ) signal generation, which only requires a single-stage dual-electrode Mach-Zehnder modulator (DE-MZM). RZ-DPSK, CSRZ-DPSK, or CNRZ signals can be generated via the same configuration by changing the DE-MZM operating conditions. Analytical derivation and simulation on signal generation and wavelength-division-multiplexed transmission was also carried out to justify the equivalence of the proposed scheme and conventional methods. The proposed scheme is expected to be more cost-effective due to the reduction in required modulator number.

Non-magnetic 30 dB integrated optical isolator in III/V material

Travelling electrical waves make the transmission direction-dependent in a single-sideband electro-optic modulator. Isolation is 30 dB; excess insertion loss is 8 dB. Residual r.m.s. ripple is 7% for RF driving amplitudes of 3.5 Vpp at 4.0 GHz. Transmission penalty for 40 Gbit/s RZ-DPSK signals is 0.2 dB estimated, 0 dB measured.

Transmission of an ASK-Labeled RZ-DPSK Signal and Label Erasure Using a Saturated SOA

We demonstrate an optically labeled signal based on return-to-zero differential phase-shift keying for payload at 10-Gb/s and amplitude-shift keying for label at 622-Mb/s. Receiver sensitivity of /spl sim/-36 dBm and penalty-free transmission over 80-km standard single-mode fiber are achieved for both the payload (with dispersion compensation) and the label. This labeling scheme allows the use of a deeply saturated semiconductor optical amplifier to perform polarization-insensitive label erasure. Label swapping is demonstrated with moderate penalty.