Lian-Kuan Chen

An optical network unit for WDM access networks with downstream DPSK and upstream remodulated OOK data using injection-locked FP laser

We investigate the use of optical differential phase-shift keying (DPSK) as the downstream modulation format in a low-cost upstream data remodulation scheme for a wavelength-division multiplexing (WDM)-based passive optical network. A 2.5-Gb/s upstream data transmitter is realized by directly modulating a Fabry-Perot (FP) laser, injection-locked with a 10-Gb/s downstream optical DPSK signal. A simple polarization-offset technique is proposed to largely minimize the induced power penalty.

An all-optical XOR logic gate for high-speed RZ-DPSK signals by FWM in semiconductor optical amplifier

All-optical exclusive-OR (XOR) logic gate is a basic and crucial element for optical signal processing. We propose and demonstrate a novel high-speed all-optical XOR gate based on four-wave mixing (FWM) in a semiconductor optical amplifier, with optical return-to-zero differential phase-shift keying (RZ-DPSK) input signals. With this constant-envelope modulation format, the patterning effect-induced signal degradation in semiconductor optical amplifier (SOA) is alleviated. The proposed XOR gate can accommodate both two-input and three-input logic operations, which offer better flexibility for cascaded all-optical processing. Experimental demonstrations at 10- and 20-Gb/s verified the logic integrity of the proposed XOR gate. In addition, the XOR output tolerance against temporal misalignment among the data inputs is also experimentally investigated

A novel centrally controlled protection scheme for traffic restoration in WDM passive optical networks

We propose and experimentally demonstrate a novel centrally controlled protection scheme for arrayed waveguide grating-based bidirectional wavelength-division-multiplexing passive optical networks which can provide automatic traffic restoration against fiber cut between remote node and optical network unit. Compared with the previous structures, its requirements on the network resources are greatly reduced with negligible protection performance degradation.

Fiber-fault identification for branched access networks using a wavelength-sweeping monitoring source

We propose and experimentally demonstrate a new fiber-fault identification scheme for optically amplified branched networks. The scheme makes use of fiber Bragg gratings and an internally generated light source from erbium-doped fiber amplifiers through an optical feedback loop, and no additional dedicated monitoring source is required. The monitoring technique invokes both frequency and time domain by sweeping the wavelength of the monitoring source. By combining with a conventional optical time-domain reflectometer technique, exact location in fiber cut in branched network can be identified readily.

A WDM Passive Optical Network With Centralized Light Sources and Multicast Overlay

We propose a novel wavelength-division-multiplexed passive optical network (WDM-PON) architecture to provide a downstream multicast overlay on the conventional point-to-point data service. The differential-phase-shift-keying multicast data is modulated on the same optical downstream carrier with the inverse return-to-zero point-to-point data signal, thus additional light sources are saved. Broadcast or multicast control is realized at the optical line terminal. For each WDM channel, part of the downstream power is re-used as the upstream data carrier, and thus realizes a colorless optical network unit. We successfully demonstrate the proposed WDM-PON with 10-Gb/s downstream point-to-point signals,10-Gb/s downstream multicast signals, and 2.5-Gb/s upstream signals.

A Multicast WDM-PON Architecture Using DPSK/NRZ Orthogonal Modulation

We propose a novel scheme to overlay multicast data on a wavelength-division-multiplexed passive optical network (WDM-PON) with point-to-point data delivery. The differential phase-shift keying multicast signal is superimposed onto all point-to-point nonreturn-to-zero (NRZ) signals. By adjusting the extinction ratios of the individual NRZ point-to-point signals, multicast can be realized and only the designated optical network units can properly receive the multicast data. We successfully demonstrated the proposed WDM-PON with 10-Gb/s downstream point-to-point signals and 10-Gb/s multicast signals.

A novel star-ring protection architecture scheme for WDM passive optical access networks

We propose and demonstrate a star-ring network architecture and wavelength assignment scheme for multi-wavelength passive optical networks with full path protection capability. Bi-directional traffic can be restored promptly for single/multiple link failure scenarios.

A practical passive surveillance scheme for optically amplified passive branched optical networks

We propose and experimentally demonstrate a novel and practical surveillance scheme for in-service fault identification in passive optically amplified branched networks. This scheme does not require any wavelength-tunable light source as used in multiwavelength optical time-domain reflectometer (OTDR). Fiber-Bragg gratings are placed at some strategic positions on different fiber branches to slice and reflect the optical amplifiers residual amplified spontaneous emission (ASE) power at some wavelengths other than the signal wavelengths. The conditions of the fiber link and optical amplifier at each branch can be monitored by constantly checking the reflected power level of the corresponding wavelength without suspending the in-service channels.

PMD-insensitive OSNR monitoring based on polarization-nulling with off-center narrow-band filtering

We propose and experimentally demonstrate the use of polarization-nulling with off-center narrow-band filtering to realize a new polarization-mode dispersion (PMD)-insensitive in-band optical signal-to-noise ratio monitoring scheme. When applied to a 39.81-Gb/s 2.5-ps full-width at half-maximum return-to-zero on-off keyed optical time-division-multiplexing system with 10and 20-ps differential group delay, the monitoring errors were reduced from >20 dB to <0.9 and <1.6 dB, respectively, hence demonstrating the feasibility of this scheme even under severe PMD degradation. This technique is simple and can be easily upgraded for use in higher data-rate optical systems.

A novel optical-path supervisory scheme for optical cross connects in all-optical transport networks

We propose and demonstrate a novel and effective supervisory scheme to monitor the optical-path routing at the optical cross connects in all-optical transport networks. Any error in optical-path routing due to failure in the cross connect can be detected without tapping off the power at the data wavelengths, and no dedicated monitoring light source is required. The scheme supports in-service surveillance. It can facilitate the network management in the optical layer of all-optical and reconfigurable transport networks.