Cheolhwan Kim

Phase-and-amplitude regeneration of differential phase-shift keyed signals using a phase-sensitive amplifier

DPSK phase-and-amplitude regeneration with a NOLM-based phase-sensitive amplifier is demonstrated experimentally. For a highly degraded input signal, maximum differential phase errors were reduced from 82 degrees to 41 degrees , while the SNR was improved by more than 5-dB. Differential phase Q-factor improvement was better than 6-dB. The PSA was operated free of excess noise due to stimulated Brillouin scattering by using a binary phase modulated pulse train as the pump. The impact of pump fluctuations on regeneration performance is clarified. The regenerated signal was characterized by measurement of the constellation diagram by linear optical sampling, giving the first directly measured evidence of DPSK phase regeneration.

All-optical regeneration of differential phase-shift keying signals based on phase-sensitive amplification

All-optical regeneration of differential phase-shift keying signals based on phase-sensitive amplification is described. Nearly ideal phase regeneration can be achieved in the undepleted-pump regime, and simultaneous amplitude and phase regeneration can be realized in the depleted-pump regime.

Demonstration of phase-regeneration of DPSK signals based on phase-sensitive amplification

Amplification and simultaneous phase regeneration of DPSK signals is demonstrated using a phase-sensitive amplifier. Phase-sensitive gain is achieved in a Sagnac fiber interferometer comprised of nonpolarization maintaining, highly nonlinear fiber operating in the un-depleted pump regime. Both the pump and signal are RZ-DPSK pulse trains. The amplifier is capable of producing greater than 13 dB of phase-sensitive gain for an average pumping power of 100 mW, and easily reduces the BER of the regenerated DPSK signal by two orders of magnitude compared to the un-regenerated signal, corresponding to a negative power penalty of 2 dB. Careful optimization of the regenerator reveals much stronger BER Improvement.

Direct-detection optical differential 8-level phase-shift keying (OD8PSK) for spectrally efficient transmission

An implementation of optical differential 8-level phase-shift keying (OD8PSK) is proposed for spectrally efficient high capacity long-haul optical fiber transmission systems. Interferometric demodulation and direct detection at the receiver yield three output binary sequences identical to the three input binary sequences. This is accomplished by proper design of electrical encoding and optical encoding at the transmitter. Three optical encoding schemes are proposed with corresponding differential electrical encoding schemes. Numerical simulations are performed for a single channel transmission to evaluate the transmission performances of OD8PSK systems.

180-GHz clock recovery using a multisection gain-coupled distributed feedback laser

All-optical clock recovery from 180-Gb/s data streams has been demonstrated using a self-pulsing multisection gain-coupled distributed feedback laser. The laser produces self-pulsations with a tuning range of more than 230 GHz. The recovered clock has a jitter of less than 410 fs over a dynamic range of 7 dB.

Wavelength and polarization insensitive all-optical clock recovery from 96-Gb/s data by using a two-section gain-coupled DFB laser

Wavelength- and polarization-insensitive all-optical clock recovery from data streams up to 96 Gb/s has been demonstrated by using a self-pulsing two-section gain-coupled distributed feedback laser and a semiconductor optical amplifier as a wavelength converter. The sensitivity of the clock recovery scheme is less than -10 dBm.

Optical microwave/millimeter-wave links using direct modulation of two-section gain-coupled DFB lasers

Transmission of 155-Mb/s binary phase-shift-keying-modulated microwave/millimeter-wave (MMW) signal on an optical carrier over up to 80 km of standard single-mode fiber has been demonstrated experimentally using direct modulation of a two-section gain-coupled distributed feedback laser. Direct data modulation at an MMW carrier frequency of 25 GHz was enabled by on-chip optical injection locking.

Requirements for the sampling source in coherent linear sampling

Complex envelope measurement using coherent linear optical sampling with mode-locked sources is investigated. It is shown that reliable measurement of the phase requires that one of the optical modes of the mode-locked laser be locked to the optical carrier of the data signal to be measured. Carrier-envelope offset (CEO) is found to have negligible effect on the measurement. Measurement errors of the intensity profile and phase depend on the pulsewidth and chirp of the sampling pulses as well as the detuning between the carrier frequencies of the data signal and the center frequency of sampling source.

WDM Transmission over 320 km EDFA-Amplified SSMF Using 30 Gb/s Return-to-Zero Optical Differential 8-Level Phase-Shift Keying (OD8PSK)

Fiber transmission of optical differential 8-level phase-shift keying (OD8PSK) signals is demonstrated for the first time. Co-polarized 8 WDM channels of 10 Giga-symbol/s or 30 Gb/s return-to-zero (RZ) OD8PSK signals with a channel spacing of 50 GHz were transmitted over 320 km of standard single mode fiber (SSMF) with an EDFA spacing of 80 km. The BER of the worst WDM channel after transmission of 320 km was 2.3x10-5.

All-optical passive clock extraction of 40 Gbit/s NRZ data using narrow-band filtering

A passive all-optical scheme for clock extraction from non return-to- zero (NRZ) data has been proposed based on narrow-band filtering. Two equally effective embodiments of the proposed scheme have been demonstrated experimentally. A carrier-to-noise ratio (CNR) of 30 dB has been achieved at 40 Gbit/s using fiber Bragg gratings (FBG).