Optical Demultiplexing Based on Four-Wave Mixing in Semiconductor Optical Amplifiers

We demonstrate equalization of the frequency-shift dependent conversion efficiency of four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs). The wavelength converter provides fixed input tunable output wavelength conversion for ten wavelength-division-multiplexing (WDM) channels with 100-GHz spacing. Equalization is achieved by using a fiber Bragg grating (FBG) at the output of the fixed input tunable output wavelength converter. This method provides constant conversion efficiency to within /spl plusmn/1.5 dB over all WDM channels and can be easily adapted to other types of wavelength conversion.

We investigate the phase-preserving amplitude regenerative characteristics of the return-to-zero (RZ) differential-phase-shift-keying (DPSK) wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). The Q-factor and the optical signal-to-noise ratio (OSNR) before and after conversion are experimentally obtained and analysed in different input noise power levels. In both the continuous-wave and synchronous clock pumping cases, we find that there is amplitude clamping in the FWM conversion due to the gain saturation of SOA, which can suppress the amplitude fluctuation of the converted DPSK signal before and after demodulation. We have achieved 2-dB Q penalty improvement in our experiment demonstration of 10Gbit/s RZ-DPSK signal with OSNR lower than 19dB.

Nondegenerate four-wave mixing in semiconductor optical amplifiers was studied both as a spectroscopic tool for probing semiconductor dynamics and as a wavelength conversion technique. Four-wave mixing spectra were measured at detuning frequencies ranging from GHz to THz rates and ultrasfast intraband mechanisms having relaxation time constants of 650 fs and less than 100 fs were revealed in the measurements. Cross-polarization four-wave mixing was also measured to study the inter quantum-well carrier transport process in quantum-well amplifiers. In addition, broadband wavelength conversion using four-wave mixing in semiconductor optical amplifiers was investigated. Results concerning the conversion efficiency over spans up to 65 nm, as well as a demonstration of wavelength conversion with gain are presented. The issue of converted signal-to-background noise in this process is also addressed.

We report interval-polarization-independent wavelength conversion at 2.5 Gb/s using four-wave mixing in a single semiconductor optical amplifier. These results have been obtained with a dual-pump configuration in a bidirectional geometry. Bit-error-rate (BER) curves are reported for a conversion shifts of -1 and +1 THz. The signal polarization was automatically scrambled during the BER measurement. The penalty with respect to the back-to-back line is 2.4 and 1.6 dB, respectively.

Polarization-insensitive wavelength conversion at 2.5 and 10 Gb/s using four-wave mixing in a bulk semiconductor optical amplifier is reported. At 10 Gb/s, a conversion range from 6.4-nm wavelength downshift to 4.8-nm upshift has been demonstrated. The conversion efficiency and signal-to-noise ratio versus conversion range are also characterized.

We investigated wavelength conversion for polarization multiplexing signal based on four-wave mixing in a semiconductor optical amplifier. We found that the converted signals endured crosstalk among the pol-muxed channels. We also proposed and demonstrated a wavelength conversion scheme with polarization diversity technique. By utilizing the technique, the converted polarization multiplexing signal can be received without crosstalk. In addition, the performance of the proposed system is numerically analyzed with respect to the bit error rate of the converted signal, different frequency spacing between signal and pump and modulated data rate. The simulation results show that the proposed scheme may be a promising method to realize transparent wavelength conversion for polarization multiplexing signals.

Experimental demonstration of optical phase conjugation using counter-propagating dual pumped four-wave mixing in semiconductor optical amplifier

In this paper, we propose a cost-efficient, polarization-insensitive and widely-tunable wavelength conversion scheme for orthogonal frequency division multiplexing (OFDM) signal based on four-wave mixing (FWM) in semiconductor optical amplifier (SOA). In this scheme, electrical OFDM signal directly drives directly modulated laser (DML) to achieve intensity modulation, then the modulated signal lightwave and pump are coupled and injected into a polarization-diversity structure for performing FWM in SOA. The analytical results show that the proposed scheme is polarization-insensitive and has a wider conversion range compared with the parallel pump scheme and orthogonal pump scheme. We have also numerically demonstrated wavelength conversion of 16QAM-OFDM signal by employing the proposed scheme. The results can be agreed with the theoretical analyses. In addition, the impact of input optical power, line-width of external cavity laser (ECL) and injection current of SOA on the system performance are also studied.

Optical buffer is a key component in all-optical information processing systems. Slow light at room temperature via four-wave mixing in semiconductor an optical amplifier (SOA) is experimentally investigated. Time delay of 0.4 ns is achieved for a sinusoidal modulation signal at 0.1GHz, corresponding to a delay-bandwidth product (DBP) of 0.04. Factors that affect the experimental results are discussed. It is found out that the variable optical delay via four-wave mixing in SOA can be controlled either electrically by changing the SOA bias, or optically by varying the pump power or pump-probe detuning.

A reconfigurable and wideband photonic method is proposed for microwave photonic harmonic down-conversion based on cascaded four-wave mixing in a semiconductor optical amplifier (SOA). The cascaded four-wave mixing in SOA triggers high-order harmonics generation of local oscillator (LO) in the optical domain, and enables microwave down-conversion in the electrical domain with a low-frequency electrical LO. Compared with the conventional photonic method, ours allows microwave down-conversion operation for wide frequency range RF signal with a low-frequency electrical LO, and at the same time it avoids the requirement of complex phase control and heavy driving for the electrical LO. Moreover, it enables reconfigurable down-conversion with frequency tunability. In the demonstration, the 3~40 GHz RF signals are experimentally down-converted to IF signals below 2 GHz with a low-frequency electrical LO within the range of 5 GHz.

All-optical switching and wide-range wavelength conversion have been demonstrated at 160 Gbit/s using four-wave mixing in a semiconductor optical amplifier. We used the asymmetrical multiple-quantum-well semiconductor optical amplifier which allows for a wide 3 dB gain-bandwidth. The cross-correlation measurements show the high-speed switching capability for wavelength routing in optical time division multiplexing networks.

Numerically, we have analyzed the basic characteristics of all-optical demultiplexing based on four-wave mixing in semiconductor optical amplifiers by solving a modified nonlinear Schrodinger equation using the finite-difference beam propagation method. For high on-off ratio, the optimum input pump pulsewidth is 1~3 ps for 1 ps, 250 Gbit/s probe pulse. From the simulation results, it is clear that for the faster demultiplexing operation, semiconductor optical amplifiers with wider gain bandwidth are required. We have simulated pattern effects in the FWM signal. We have also obtained demultiplexing from the time-multiplexed signals by repetitive pump pulses

We present a theoretical analysis of the noise properties in a nonlinear semiconductor optical amplifier. We concentrate on amplifiers operating as nonlinear media mediating four-wave mixing processes. We calculate error probabilities for different configurations that use four-wave mixing in all-optical signal manipulation such as frequency conversion and time domain demultiplexing. We identify a data induced nonlinear interference process as having a major adverse impact on the performance of nonlinear semiconductor optical amplifiers and propose the use of a variable decision threshold to overcome it. We compare the performance of the variable threshold to that using an optimal fixed threshold and show significant improvement in performance. We treat the cases of NRZ modulated data as well as the case of short optical pulses and demonstrate a vast advantage for the short pulses in terms of the required input field intensities and the achievable bit error rates.

A major advantage of the Four Wave Mixing technique for wavelength conversion is its transparency to modulation format. This advantage becomes important for some IP over WDM network realizations where part of the signaling information is an analog or subcarrier modulation approach. In such applications the phase noise characteristics of the conversion process are very important. In this work, a detailed theoretical and experimental study of the additional phase noise induced by the FWM process is presented. The nonlinear elements used in the experiments are semiconductor optical amplifiers as well as dispersion shifted fibers. Two linewidth measuring techniques have been used, the self-homodyne and the beating with a laser source with already known linewidth. The measurements are carried out for different operating conditions (wavelength, pumping level of the nonlinear elements, input power, input signals with different phase noise characteristics, etc). The theoretical interpretation of the above results is based on a modification (inclusion of the influence of the amplified spontaneous emission noise) of an already presented approach which has focused on the mixing process in a resonant optical cavity.

All- optical phase encoded 4-to-1 phase multiplexer using four wave mixing in semiconductor optical amplifier