Enbo Zhou

Analysis on dynamic characteristics of semiconductor optical amplifiers with certain facet reflection based on detailed wideband model

Dynamic characteristics of semiconductor optical amplifiers (SOAs) with certain facet reflection in different operation conditions are theoretically investigated with a detailed wideband model. Influences of different facets reflectivities are numerically simulated for different lengths of active regions. The results indicate that the gain recovery time can be reduced to 50% of the initial value while the other related characteristics are optimized for appropriate facets reflections. A half reflective semiconductor optical amplifier (HR-SOA) with a cleaved facet on rear facet and an antireflection coating on front facet can speed up the gain recovery with easy realization and low cost. The related characteristics of this structure are evaluated. Its also indicated that the gain recovery has further potential to be reduced as low as twenties picoseconds for a long active region.

All-Optical Clock Recovery From NRZ Signals at Different Bit Rates via Preprocessing by an Optical Filter

We demonstrate a simple configuration for clock recovery from a nonreturn-to-zero signal, which is preprocessed by a narrowband filter. Evidently, the clock component is enhanced after the filter. Compared with previous preprocessing schemes, the single filter is simple and suitable for different bit rates. The output performances related to the bandwidth and the detuning of the filter are analyzed. By cascading a clock recovery unit with semiconductor optical amplifier based fiber ring laser, the clock signal can be extracted from the preprocessed signal, at 10 to 40 Gb/s. By simply using a filter with larger bandwidth, much higher operation can be achieved easily.

Photonic generation of ultrawideband monocycle and doublet pulses by using a semiconductor-optical-amplifier-based wavelength converter

Photonic generation of ultrawideband (UWB) monocycle and doublet pulses is experimentally demonstrated using a cascaded electroabsorption modulator (EAM) and semiconductor optical amplifier by exploiting a combination of cross-absorption modulation and cross-gain modulation. The polarities and shapes of UWB monocycle and doublet pulses can be simply controlled using an optical time-delay controller and the reverse voltage applied to the EAM. The corresponding measured rf spectra meet the UWB criteria.

Reduction of patterning effects in SOA-based wavelength converters by combining cross-gain and cross-absorption modulation.

A scheme for mitigating patterning effects in wavelength conversion by using a concatenated semiconductor optical amplifier (SOA) and electroabsorption modulator (EAM) is proposed. The optimization of the parameters of the semiconductor devices and receiver electronics is theoretically investigated. The bit error ratio (BER) of the output signals in both the co-propagating and the counter-propagating configurations is quantitatively evaluated. The simulation results indicate that the patterning effect in wavelength conversion due to the slow recovery of the carrier density in the SOA can be well compensated by a concatenated EAM. The simulation results are confirmed by preliminary pump-probe experiment using a 10Gb/s clock pulse train.

Evaluating characteristics of semiconductor optical amplifiers using optical pumping near the transparency

The improved characteristics of semiconductor optical amplifiers (SOAs) with optical pumping near the transparency (OPNT) are evaluated, and its improving mechanisms are analyzed. The characteristics of saturation behaviors, noise figures, signal-to-noise ratio, and gain recovery time are greatly improved by OPNT, especially for the counterpropagating scheme. The impacts of different wavelengths of a holding beam from absorption to the gain region are investigated contrastively. The maximum value of the small signal gain recovery time is obtained at the transparency wavelength. Also, the quality of the output eye patterns of a cross-gain modulation (XGM) system has been greatly improved by using OPNT, especially for the signal beyond 10 Gbit/s.

Photonic generation of UWB monocycle pulses using a cascaded semiconductor optical amplifier and electroabsorption modulator

Photonic generation of ultrawideband monocycle pulses is experimentally demonstrated by using a cascaded semiconductor optical amplifier and electroabsorption modulator. The polarity and the shape of the ultrawideband monocycle pulses can be electrically controlled and optimized.

Measurement of the carrier recovery time in SOA based on dual pump FWM

A measurement of carrier recovery time in semiconductor optical amplifiers (SOAs) based on dual pumps four-wave mixing (FWM) is presented. The results show the carrier time is 91 ps, 79 ps and 63 ps at 120 mA, 180 mA and 240 mA, respectively, which agree to our expectation. The experimental results show the conversion efficiency keeps constant when the spacing of the two pumps varies within a small range.

Photonic generation of ultra-wideband monocycle and doublet pulses using simplex semiconductor optical amplifier

We demonstrate two all-optical methods for UWB pulse generation based on various nonlinearities of the semiconductor optical amplifier (SOA), namely, self phase modulation (SPM), and cross gain modulation (XGM). In the first method, we present UWB doublet generation based on SPM. The monocycle pulse is generated from dark return-to-zero (RZ) signal, and then converted to doublet pulse by injecting an additional probe signal with the SMF transmission. For the first time to best of our knowledge, we report that the generated doublet pulses are transmitted over 5km SMF by proper dispersion compensation without distortion. Second, we present UWB doublet generation by XGM of two cascaded SOAs. The configuration of our all-optical methods is compact and simple.

Mitigation of Patterning Effect in Wavelength Conversion by Cascaded Semiconductor Optical Amplifier and Electroabsorption Modulator

A scheme for mitigating patterning effects in wavelength conversion by using a concatenated semiconductor optical amplifier (SOA) and electroabsorption modulator (EAM) is proposed. The scheme is investigated theoretically and experimentally. The bit error ratio and the power penalty of the converted output signal are estimated and compared with the results of wavelength conversion based on cross gain modulation in a single SOA.

Theoretical investigation and experimental demonstration of nonlinear patterning suppression in bulk semiconductor optical amplifiers for transient cross phase modulation

A numerical model for the investigation of ultrafast gain and phase dynamics in InGaAsP bulk semiconductor optical amplifiers for transient cross phase modulation is presented in considering non-equilibrium carrier distribution and carrier temperature dynamics for different probe wavelengths. Results indicate that the nonlinear patterning of transient cross phase modulation can be effectively suppressed by an assist light, especially for the up-conversion and the assist light in counter-propagating scheme.