S. B. Jun

Enhanced performance of RSOA-based WDM PON by using Manchester coding

Feature Issue on Passive Optical Network Architectures and TechnologiesWe propose and demonstrate that the power budget and scalability of the wavelength-division-multiplexed passive optical network (WDM PON) implemented by using reflective semiconductor optical amplifiers (RSOAs) can be significantly improved by modulating the downstream signals in Manchester format instead of the conventional non-return-to-zero format. As an example, we experimentally show that the maximum transmission distance of the RSOA-based WDM PON can be increased by a factor of 2 by using the Manchester-encoded downstream signals.

Optical performance monitoring techniques based on pilot tones for WDM network applications

Feature Issue on Optical Performance Monitoring (OPM). We report on the pilot-tone-based optical performance monitoring techniques for use in the wavelength-division multiplexing (WDM) network. We first described the operating principle of the pilot-tone-based monitoring technique and estimated its scalability by analyzing potential problems. We then reviewed the techniques proposed for monitoring various optical parameters of WDM signals--such as optical power, wavelength, optical path, and cross talk--using pilot tones. We also presented examples of various network elements using the pilot-tone-based monitoring technique. In addition, we reviewed the pilot-tone-based monitoring techniques used in adaptive compensators for chromatic dispersion and polarization-mode dispersion, and we discussed their limitations and possible solutions. For example, we demonstrated a simple technique for monitoring the chromatic dispersion and polarization-mode dispersion simultaneously, without their affecting each other, by scrambling the state of polarization of the optical signal.

Pilot-tone-based WDM monitoring technique for DPSK systems

To evaluate the effectiveness of the pilot-tone-based monitoring technique in differential phase-shift keying (DPSK) systems, we measure the mutual interactions between the pilot tones and DPSK signals and compare the results with those of on-off keying (OOK) signals. The results show that, by using the DPSK format instead of OOK, it is possible to increase the number of wavelength-division-multiplexed channels that can be monitored simultaneously by using pilot tones without using optical demultiplexers by more than one hundred times

Reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based broadband source

We report on the reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based ASE source for injection locking to FPLD. The results show that, to suppress the polarization-induced Q penalty sufficiently less than 0.5 dB, the MQW-SLD output should be depolarized within the locking range of the wavelength-locked FPLD.

A Novel Four-Wave Mixing Compensator

We propose and demonstrate a novel four-wave-mixing (FWM) compensator made of a highly nonlinear fiber and a pump laser. This technique utilizes the additional pi/2 phase delay occurring in every FWM process. Thus, the FWM components generated in the transmission fiber can be cancelled out by the FWM components generated within the FWM compensator. We have experimentally confirmed that the proposed technique could effectively suppress the FWM crosstalk generated in the transmission fiber and improve the systems performance

Simultaneous monitoring technique for ASE and MPI noises in distributed Raman Amplified Systems.

We develop a new technique for simultaneously monitoring the amplified spontaneous emission (ASE) and multi-path interference (MPI) noises in distributed Raman amplified (DRA) systems. This technique utilizes the facts that the degree-of polarization (DOP) of the MPI noise is 1/9, while the ASE noise is unpolarized. The results show that the proposed technique can accurately monitor both of these noises regardless of the bit rates, modulation formats, and optical signal-to-noise ratio (OSNR) levels of the signals.

A novel chromatic dispersion monitoring technique using frequency-modulated and amplitude-modulated pilot tones

We propose and demonstrate a novel chromatic dispersion monitoring technique using frequency-modulated and amplitude-modulated pilot tones. Unlike the conventional pilot-tone-based monitoring techniques, the proposed technique could discriminate the sign of accumulated dispersion

Effects of downstream modulation formats on the performance of RSOA-based WDM PON

We evaluate the effects of the downstream modulation formats (such as NRZ, inverse RZ, and Manchester) on the performance of the WDM PON implemented by using the reflective semiconductor optical amplifiers (RSOAs). The results show that, when we modulate the downstream signals in Manchester format, the performance of the upstream signal becomes insensitive to the operating condition of the RSOA.

Ultra-fast Clock Recovery Based on Pre-embedded Sub-harmonic Clock in Optical Burst/Packet Networks

We propose an ultra-fast clock recovery technique for the use in the optical burst/packet networks, and evaluated its performance by using 40-Gb/s burst-mode NRZ and DPSK signals.

Temperature-independent fiber-based optical phase conjugation

We have investigated the effect of temperature variation on the performance of fiber-based optical phase conjugation (OPC) module. The results show that the bandwidth of the fiber-based OPC module could be reduced significantly by temperature variation. However, it would be difficult to control the temperature of bulky fiber spool precisely. To solve this problem, we have proposed and demonstrated a simple method to compensate the bandwidth reduction (caused by temperature variation) by adjusting the pump power. Using this method, we could maintain the 1-dB bandwidth of fiber-based OPC module within 5% even when the ambient temperature was varied as much as plusmn15 degC