We proposed and experimental demonstrated all-optical two line-four line encoder and two bit-wise comparator of RZ data streams at 40Gb/s based on cross gain modulation (XGM) and four wave mixing (FWM) in three parallel SOAs. Five logic functions for digital encoder and comparator between two signals A and B: AB, AB, AB, AB and AOmicronB, were achieved simultaneously. The first three optical logics are realized based on XGM in SOAs, the fourth is realized with FWM, and the fifth is the mixing result of the first and the fourth. A detuning filter is employed to improve the output performance. The output extinction ratio (ER) for the XGM operation is above 10dB, and the ER for FWM operation is around 8 dB. Wide and clear eye patterns for the five logic outputs can be observed.

Simultaneous demonstration on all-optical digital encoder and comparator at 40 Gb/s with semiconductor optical amplifiers.

This paper presents a detailed theoretical and experimental study of the impact of amplified spontaneous emission (ASE) on self-phase modulation in semiconductor optical amplifiers (SOAs). A theoretical model of pulse propagation in SOAs is developed that includes the ASE power and its effect on gain-saturation and gain-recovery. We study the impact of ASE on the nonlinear phase shift, frequency chirp, spectrum, and shape of amplified picosecond pulses at a range of drive currents. We verify our predictions experimentally by launching gain-switched picosecond pulses with 3-mW peak power into a commercial SOA exhibiting 9-ps gain-recovery time at a current of 500 mA. Understanding the impact of ASE on SOAs is important for applications that employs SOAs for all-optical signal processing and as data-network amplifiers.

Self-Phase Modulation in Semiconductor Optical Amplifiers: Impact of Amplified Spontaneous Emission

We propose a novel all-optical format conversion from nonreturn-to-zero (NRZ) to return-to-zero (RZ) based on single semiconductor optical amplifier (SOA) and a detuning optical bandpass filter (OBF). By adopting the ultrafast SOA model associated with intraband mechanism, the 40Gb/s NRZ-to-RZ format conversion is successfully demonstrated with numerical simulation. We investigate the influence of the filter detuning, extinction ratio, conversion efficiency, output pulsewidth, and filter bandwidth. These simulation results confirm the feasibility of our scheme. The proposed scheme is robust and potential for applications in future optical networks.

40 Gb/s all-optical NRZ to RZ format conversion using single SOA assisted by optical bandpass filter

As wavelength converters based on four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) attract more attention, dynamic effects and wavelength dependent performance become key aspects to be investigated. Such issues are particularly important, as complex configurations are likely to be used to overcome challenges like tunability and polarization dependence. In this paper a numerical model is used to predict the dynamic performance of three FWM configurations and an analytical model is used to derive design rules. First, the wavelength dependent behavior of a wavelength converter is investigated and the requirement for a widely tunable converter is identified. Secondly, a configuration for extinction ratio (ER) improvement is studied and novel design rules are obtained analytically, tested experimentally and explained by the numerical model; experimental results with ER improvement at 10 Gb/s were achieved for the first time. The third configuration studied is a dual-pump arrangement enabling wide tunability. Fixed input/tunable output and tunable input/fixed output configurations are discussed in terms of optical signal-to-noise ratio and tunability. Design rules are extracted and verified for all three configurations that are likely to be deployed: simple wavelength converters, regenerating converters and tunable wavelength converters.

Dynamic behavior of wavelength converters based on FWM in SOAs

On the amplified spontaneous emission noise modeling of semiconductor optical amplifiers

We investigate theoretically and experimentally the dynamic characteristics of the wavelength conversion that is based on four-wave mixing (FWM) in a light-holding semiconductor optical amplifier (LHSOA). Two FWM conversion techniques, including the single-pump (SP) and two orthogonal-polarized pumps (OPP) schemes, are investigated using a sophisticated time-domain simulation model. The simulation indicates that the holding light gives an improved eye opening and signal-to-noise ratio for both the SP and OPP schemes. The chirp response for both schemes are also presented. The performance improvement are verified from dynamic measurements such as eye diagram and bit-error-rate (BER) tests. Clearer eye openings and reduced power penalties are obtained with the injection of a holding light. By comparing to the experimental results, we also prove that our numerical modeling can predict the device performance and can be used for optimizing the wavelength conversion process.

Improved dynamic characteristics on four-wave mixing wavelength conversion in light-holding SOAs

Wavelength conversion with a high efficiency and wide conversion range can easily be realized by applying an assist beam of short wavelength to a dual-pumped semiconductor optical amplifier (SOA). Experimental results reveal that an assist beam can improve the conversion efficiency and signal-to-background ratio by up to 8.5 and 4.1 dB, respectively, when the SOA is biased at the current that makes the SOA transparent to the assist beam. The efficiency can exceed -10 dB over an 80-nm wavelength conversion range using a 23-dB gain SOA. The assist beam increases the system power budget because it simultaneously improves the conversion efficiency and reduces the receiver power penalty. The power penalties for up-converting and down-converting 10-Gb/s signals to 25 nm of wavelength range are less than 0.5 and 2.5 dB, respectively.

https://ir.nctu.edu.tw:443/bitstream/11536/26530/1/000222884300037.pdf

High-efficiency wide-band SOA-based wavelength converters by using dual-pumped four-wave mixing and an assist beam

We propose to use an additional injection beam of short wavelength to enhance the wavelength conversion that utilizes the four-wave-mixing (FWM) effect in a semiconductor optical amplifier (SOA). With this scheme, the assist light can increase the saturation intensity without sacrificing the gain of an SOA, and this leads to an increase in conversion efficiency. A numerical method dealing with various FWM mechanisms, such as amplified spontaneous emission (ASE) noise, longitudinal spatial hole burning, and wavelength-dependent gain spectrum, is developed to predict the static characteristics of our scheme. The carrier densities are nonuniformly distributed along the longitudinal direction of the SOA as a result of the ASE effect, which affects the measurement of the wavelength-dependent transparent current. The effects of an assist light on saturation output power and conversion efficiency are analyzed in detail. The analysis shows that using an assist light can improve both the conversion efficiency and signal-to-background-noise ratio (SBR) for SOAs of different lengths. The degree of improvement depends on the bias condition, assist light wavelength, and the device geometry. The study for the device optimization reveals that a compromise between conversion efficiency and SBR must be made to choose the device length.

Theoretical analysis of wavelength conversion based on four-wave mixing in light-holding SOAs

We propose to use an additional injection beam of short wavelength to enhance the wavelength conversion that utilizes the four-wave-mixing effect in a semiconductor optical amplifier (SOA) The experiments demonstrated larger than 5-dB improvement on conversion efficiency, as the SOA is biased at the corresponding transparent condition for the assisted beam At such a condition, an assisted beam can increase the saturation intensity without sacrificing the gain of an SOA, and this leads to an increase in conversion efficiency The assisted beam also improves the signal-to-background-noise ratio in wavelength conversion The effects of different assisted wavelengths and the measures for further improvement are discussed

http://ieeexplore.ieee.org/iel5/68/22805/01058261.pdf

Performance enhancement on SOA-based four-wave-mixing wavelength conversion using an assisted beam

The present invention provides a wavelength converter with wideband four-wave-mixing, which includes a laser diode, an optical modulator, a first and a second polarization controllers, a first, a second and a third tunable lasers, an optical coupler, a semiconductor optical amplifier (SOA) and a multiplexer. The present invention utilizes an assist beam that can improve the recovery rate and saturation power of the SOA. While the SOA is operated at a bias current close to the transparent condition for the assist beam, it does not influence the gain of the SOA wavelength converter.

Pei-Miin Gong

Papers

Improved dynamic characteristics on four-wave mixing wavelength conversion in light-holding SOAs

High-efficiency wide-band SOA-based wavelength converters by using dual-pumped four-wave mixing and an assist beam

Theoretical analysis of wavelength conversion based on four-wave mixing in light-holding SOAs

Performance enhancement on SOA-based four-wave-mixing wavelength conversion using an assisted beam

Wideband four-wave-mixing wavelength converter