Inwoong Kim

Electronic post-compensation of WDM transmission impairments using coherent detection and digital signal processing.

A universal post-compensation scheme for fiber impairments in wavelength-division multiplexing (WDM) systems is proposed based on coherent detection and digital signal processing (DSP). Transmission of 10 x 10 Gbit/s binary-phase-shift-keying (BPSK) signals at a channel spacing of 20 GHz over 800 km dispersion shifted fiber (DSF) has been demonstrated numerically.

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.

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.

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.

All-Optical Carrier Synchronization Using a Phase-Sensitive Oscillator

An all-optical carrier synchronization (carrier-phase and polarization recovery) scheme from binary phase-shift keying signals is proposed and demonstrated for the first time. The proposed scheme uses a degenerate optical parametric oscillator which has a phase-sensitive amplifier as a gain block.

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.

Dynamics of all-optical clock recovery using two-section index- and gain-coupled DFB lasers

The dynamics of coherent clock recovery (CR) using self-pulsing two-section distributed feedback (TS-DFB) lasers have been investigated. Both simulation and experimental results indicate fast lockup and walk-off of the clock-recovery process on the order of nanoseconds. Phase stability of the recovered clock from a pseudorandom bit sequence (PRBS) signal can be achieved by limiting the detuning between the frequency of free-running self-pulsation and the input bit rate. The simulation results show that all-optical clock recovery using TS-DFB lasers can maintain a better than 5% clock phase stability for large variations in power, bit rate, and optical carrier frequency of the input data and therefore is suitable for applications in optical packet switching.

All-Optical Carrier Phase and Polarization Recovery Using a Phase-Sensitive Oscillator

An all-optical carrier phase and polarization recovery scheme from PSK signals is proposed and demonstrated for the first time. The scheme uses a phase-sensitive optical oscillator with a phase sensitive amplifier as the gain block.

Coherent Detection Using Optical Time-Domain Sampling

Coherent optical time-domain sampling (COTDS) is proposed to relax the requirement for photodetector bandwidth and the speed of ADC and DSP. Transmission of 10-Gb/s BPSK signals over 220-km SSMF was demonstrated using 10-Gsa/s ADCs.