Guo-Wei Lu

40-Gbaud 16-QAM transmitter using tandem IQ modulators with binary driving electronic signals

We propose a novel 16-quadrature amplitude modulation (QAM) transmitter based on two cascaded IQ modulators driven by four separate binary electrical signals. The proposed 16-QAM transmitter features scalable configuration and stable performance with simple bias-control. Generation of 16-QAM signals at 40 Gbaud is experimentally demonstrated for the first time and visualized with a high speed constellation analyzer. The proposed modulator is also compared to two other schemes. We investigate the modulator bandwidth requirements and tolerance to accumulated chromatic dispersion through numerical simulations, and the minimum theoretical insertion attenuation is calculated analytically.

Format Conversion of Optical Multilevel Signals Using FWM-Based Optical Phase Erasure

An optical format conversion scheme of multilevel phase-shift keying (M-ary PSK) signals using the four-wave mixing based optical phase erasure is discussed in this paper. The conversion from differential quadrature phase-shift keying (DQPSK) to differential phase shift keying at 10 and 160 Gbaud, and the conversion from differential eight-ary phase-shift keying to DQPSK at 40 Gbaud have been experimentally demonstrated. The proposed scheme could be used as a phase erasure, in which a redundant tributary of the M-ary PSK signal is removed, or as an “updater” where the unwanted phase pattern is replaced with the new pattern.

Optical phase erasure based on FWM in HNLF enabling format conversion from 320-Gb/s RZDQPSK to 160-Gb/s RZ-DPSK.

Through four-wave mixing (FWM) process in highly-nonlinear fiber (HNLF) or semiconductor device, the phase-modulation depth of one converted FWM component could be doubled compared with that of the original input signal. Therefore, with a multilevel phase-modulated signal and a CW light as inputs, after FWM process in a nonlinear media, phase pattern (0, pi) carried in the input multilevel phase-modulated signal will not be transferred to one converted FWM component, which could be referred to as an optical phase erasure process. We experimentally demonstrated format conversion from 320-Gb/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) to 160-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) through the proposed all-optical phase erasure scheme. The phase information carried in the converted binary RZ-DPSK is logically equal to the input Q-component, or a logical XOR operation result between I and Q components of the input RZ-DQPSK, which correspond to a serial or parallel DQPSK transmitter for the input RZ-DQPSK signal. It can be applied to erase a binary tributary from a multilevel modulation format.

DPSK multicast using multiple-pump FWM in Bismuths highly nonlinear fiber with high multicast efficiency.

In this paper, we discuss the multicast efficiency issue in the optical layer multicast. A 1-to-8 phase-preserved different phase-shifted keying (DPSK) wavelength multicast is experimentally demonstrated using four-wave mixing (FWM) in a piece of Bismuth highly nonlinear fiber (Bi- HNLF). DPSK signal is successfully delivered from one wavelength to up to eight different wavelengths using only three pumps. Compared with the existing schemes, the multicast efficiency is greatly improved by delivering the phase information to more destination wavelengths.

Wavelength conversion of optical 64QAM through FWM in HNLF and its performance optimization by constellation monitoring

All-optical wavelength conversion (AOWC) plays an important role in the future transparent optical networks, in order to enhance the re-configurability and non-blocking capacity. On the other hand, high-order quadrature amplitude modulations (QAMs) have been extensively studied for achieving the high-speed and high-spectral-efficiency optical transmission. Since high-order QAMs are more sensitive to phase and amplitude noise, to implement an AOWC sub-system suitable for high-order QAM signals with minimized power penalty, it is important to optimize the operation conditions in order to avoid extra nonlinear distortions co-existed in the AOWC process. Our experimental results show that, constellation monitoring provides a more intuitive and accurate approach to monitor the converted high-order QAM signals, especially in presence of nonlinear phase noise such as self-phase modulation (SPM). We experimentally demonstrate an AOWC of 64QAM signal through four-wave mixing (FWM) in highly-nonlinear (HNLF). The performance of the AOWC is optimized through the constellation monitoring of the converted signal, achieving a negligible power penalty (<0.3 dB at BER of 10(-3)) for 60-Gbps 64QAM after conversion.

Experimental Demonstrations of All-Optical Phase-Multiplexing Using FWM-Based Phase Interleaving in Silica and Bismuth-Oxide HNLFs

We propose an all-optical phase-interleaving technology based on dual-pump four-wave mixing (FWM) in highly nonlinear fiber (HNLF). The proposed all-optical phase-interleaving technology is applied in an all-optical phase-multiplexing scheme to successfully phase-multiplex 2times or 3 times 10-Gb/s DPSK-WDM signals to a 20- or 30-Gb/s DPSK in non-return-to-zero (NRZ) formats. The proposed all-optical phase multiplexing scheme is demonstrated using dual-pump FWM in highly nonlinear silica and bismuth fibers. In contrast with optical time-division multiplexing technology, the proposed all-optical phase-multiplexing technology does not require pulse-carving, thus offering a high spectral-efficiency. Differential precoder for each input tributary is operated independently, and no additional encoder or postcoder is required to recover the original data after demodulation on the receiver side.

Use of downstream inverse-RZ signal for upstream data re-modulation in a WDM passive optical network

We propose and experimentally investigate a novel WDM-PON architecture using inverse-RZ modulated centralized light sources. The finite optical power in each bit of the downstream IRZ signal can greatly facilitate the upstream data re-modulation.

160-Gb/s all-optical phase-transparent wavelength conversion through cascaded SFG-DFG in a broadband linear-chirped PPLN waveguide.

We experimentally demonstrated ultra-fast phase-transparent wavelength conversion using cascaded sum- and difference-frequency generation (cSFG-DFG) in linear-chirped periodically poled lithium niobate (PPLN). Error-free wavelength conversion of a 160-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) signal was successfully achieved. Thanks to the enhanced conversion bandwidth in the PPLN with linear-chirped periods, no optical equalizer was required to compensate the spectrum distortion after conversion, unlike a previous demonstration of 160-Gb/s RZ on-off keying (OOK) using fixed-period PPLN.

Simultaneous PMD and OSNR monitoring by enhanced RF spectral dip analysis assisted with a local large-DGD element

In this letter, we propose and experimentally demonstrate an enhanced radio-frequency (RF) spectrum analysis technique to simultaneously monitor optical signal-to-noise ratio (OSNR) and polarization-mode dispersion (PMD) for return-to-zero ON- OFF keying (RZ-OOK) systems. In this method, by cascading a large differential group delay element at the monitoring module, the PMD and OSNR parameters can be derived from the analysis of the position shift and the minimum power of the RF spectral dip, respectively. Experimental results show that this scheme can monitor PMD from 0 to 90 ps with less than 2-ps error and OSNR from 16 to 35 dB with less than 1-dB error in a 10-Gb/s RZ-OOK transmission system with a pulsewidth of 2.5 ps. The scheme possesses the advantages of simple implementation, large monitoring range, and high PMD monitoring sensitivity by using the RF spectrum analysis only at low-frequency range.

Filter Optimization for Self-Homodyne Coherent WDM Systems Using Interleaved Polarization Division Multiplexing

We examine the impact of filtering on self-homodyne coherent WDM systems using the interleaved polarization division-multiplexing scheme. To investigate the performance limit and to provide more insight into previously obtained experimental results, we perform numerical simulations in which different filter shapes and filter bandwidths are used. It is shown that with proper prefiltering of the data and filtering of the pilot tone in the receiver, performance can approach that of an intradyne system. This would make it possible to implement coherent systems with high spectral efficiency without any digital signal processing in the receiver.