Yizhi Gao

Clock extraction using an optoelectronic oscillator from high-speed NRZ signal and NRZ-to-RZ format transformation

A clock extraction scheme was demonstrated using an optoelectronic oscillator from high-speed nonreturn-to-zero (NRZ) signal. A theoretical model on the locking range of the oscillator was presented. A 10-GHz clock with a timing jitter of 0.4 ps was extracted from 10-Gb/s NRZ signal and a locking range of 800 kHz was achieved. NRZ to return-to-zero (RZ) data format conversion was also performed simultaneously with the NRZ clock extraction.

Theoretical and experimental study of pulse-amplitude-equalization in a rational harmonic mode-locked fiber ring laser

A simple technique, based on nonlinear polarization rotation, for the amplitude equalization of high repetition rate pulses generated from a rational harmonic mode-locked fiber ring laser was demonstrated. Amplitude equalized pulses at 10 GHz (the fourth rational harmonic) were obtained with a harmonic component suppression ratio up to 30 dB. A theoretical explanation was given in detail, which indicates that, after pulse amplitude equalization, the situation of unequal pulse spacing can be improved to a certain extend.

A study on the wavelength conversion and all-optical 3R regeneration using cross-absorption modulation in a bulk electroabsorption modulator

A 40-Gb/s 3R regenerator with a two-ring injection mode-locked fiber laser as the clock recovery and an electroabsorption modulator (EAM) as the reshaping optical decision gate is proposed and demonstrated. The cross-absorption modulation effect in a bulk EAM was also numerically modeled. Using this model, both the shape and the extinction ratio of the optical decision gate are optimized. The model is also employed to investigate the tolerance of the timing jitter, the chromatic dispersion, and the polarization mode dispersion of an all-optical 3R regenerator based on a bulk EAM decision gate. The operation margin of the 3R regenerator is presented. The theoretical results agree well with the experimental results

Comb-like filter preprocessing to reduce the pattern effect in the clock recovery based on SOA

A novel approach is proposed to reduce the amplitude fluctuation and timing jitter of clock pulses recovered from an injection mode-locked laser based on the semiconductor optical amplifier (SOA) caused by the pattern effect. A comb-like filter is used to preprocess the data pulses that are then injected into the injection mode-locked laser to recovery the clock. Numerical calculation for 40-Gb/s clock recovery demonstrates that this method is very effective for high-speed clock recovery based on the SOA.

A novel approach for clock recovery without pattern effect from degraded signal

Abstract A novel clock recovery scheme using two-ring injection mode-locked fiber ring laser based on all 10 GHz bandwidth components was demonstrated. With this scheme, the clock with low timing jitter was obtained from a degraded 10 Gb/s optical data stream. Optical clock recovery was also achieved from a degraded 20 Gb/s optical data train when the clock division technique in the opto-electronic oscillator (OEO) and the rational harmonic mode-locking technique in the fiber ring laser were applied. No pattern effect was observed in the experiments.

Combination of comb-like filter and SOA for preprocessing to reduce the pattern effect in the clock recovery

A comb-like filter and a semiconductor optical amplifier (SOA) were combined to preprocess the data signals before clock recovery utilizing injection mode-locked laser based on SOA. The amplitude fluctuation and timing jitters caused by the pattern effect in clock pulses were greatly reduced experimentally with this technology. Furthermore, it also demonstrated that clock could be recovered from the very degraded signals.

A dual-wavelength and dual-repetition-rate actively mode-locked fiber ring laser

A novel configuration was demonstrated to realize dual-wavelength operation in an erbium-doped fiber ring laser by incorporating a pair of multiplexer/demultiplexer. The repetition rate of each channel can be separately changed by adjusting a delay line associated with that channel in the cavity without changing the radio frequency. Dual-wavelength pulses at 2.5 and 5 GHz respectively were simultaneously obtained with pulse widths of 17.7 and 13 ps.

Interferometric noise in optical time division multiplexing transmission system

A theoretical assessment of the interferometric noise in the optical time division multiplexing (OTDM) transmission system is presented. The impact of such noise on the system performance were investigated in detail. The corresponding system requirements were also revealed by the calculation results. Recommendations on the use of prechirping to reduce the interferometric noise in the OTDM system are given.

Bit error rate analysis of OTDM system based on moment generation function

The performance of optical time division multiplexing (OTDM) system is limited by a complex combination of noise. In this paper we present a theoretical framework for the optical receiver in OTDM system based on the moment generation function. The proposed receiver model is showed to be more accurate in predicting the bit error rate (BER) performance than the former ones. Its validity is also verified by the experimental results.

Simple pulse compression scheme based on filtering self-phase modulation-broadened spectrum and its application in an optical time-division multiplexing system

We propose a simple and stable pulse compression scheme based on a filtering self-phase modulation broadened spectrum in a highly nonlinear fiber. It is found experimentally that under offset filtering the compressed pulse has a better quality compared with center filtering, such as a no pulse pedestal. Furthermore, numerical simulations reveal that the scheme has the potential to improve the pulse extinction ratio during compression. Finally, based on the obtained pulse train the 4 x 10 Gbits/s optical time-division multiplexing system is studied for verification of the high pulse quality. The compression scheme has the advantages of simple configuration, being pedestal-free, and having a high pulse extinction ratio.