Limited-range wavelength translation in all-optical networks

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) has several important features, such as, high speed and high FWM conversion efficiency as well as optical demultiplexing (DEMUX) (Mecozzi et al., 1995; Mecozzi & Mrk, 1997; Das et al., 2000). The are several applications of FWM in SOAs for all-optical devices, such as, wavelength converters (Vahala et al., 1996), optical samplers (Inoue & Kawaguchi, 1998), optical phase conjugators (Kikuchi & Matsumura, 1998) and optical multiplexers/demultiplexers (Kawanishi et al., 1997; Kawanishi et al., 1994; Morioka et al., 1996; Uchiyama et al., 1998; Tomkos et al., 1999; Kirita et al., 1998; Buxens et al., 2000) have been demonstrated for optical communication systems. When a pulse of a time-multiplexed signal train (for example, a probe pulse) and a pump pulse are injected simultaneously into an SOA, gain and refractive index in the SOA are modulated and an FWM signal is generated by the modulations. Thus, we can obtain a demultiplexed signal as an FWM signal at the output of SOA. All-optical demultiplexing has been experimentally demonstrated up to 200 Gbit/s (Morioka et al., 1996). Tomkos et al., (Tomkos et al., 1999) suggested a number of ways to improve the performance of the dual-pump demultiplexer at 40 Gbit/s as follows; adjustment of the input wavelengths at the peak gain wavelength of the SOA under saturation conditions, the use of higher pump power at the input of the device, or/and the use of pulsed pumps with short pulsewidths. For the higher bit-rate, the overlap of the input to the FWM signal pulses may appear both in the time and spectral domain. The pattern effect may also appear in the FWM signal due to the slow components of the optical nonlinearities in SOAs (Saleh & Habbab, 1990). These effects degrade the usefulness of the FWM in SOAs as a practical DEMUX device in optical network/ communication systems. Therefore, it is very important to analysis the optical DEMUX characteristics based on FWM in SOAs for the ultrafast multi-bit input optical pulses.

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.

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 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.

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.

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 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.

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.

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

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

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 have proposed a scheme of radio-over-fiber (RoF) system employing a dual-parallel Mach–Zehnder modulator (DP-MZM) based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). In this scheme, the pump and the signal are generated by properly adjusting the direct current bias, modulation index of the DP-MZM, and the phase difference between the sub-MZMs. Because of the pump and the signal deriving from the same optical wave, the polarization states of the two lightwaves are copolarized. The single-pump FWM is polarization insensitive. After FWM and optical filtering, the optical millimeter-wave with octuple frequency is generated. About 40-GHz RoF system with a 2.5-Gbit / s signal is implemented by numerical simulation; the result shows that it has a good performance after the signal is transmitted over 40-km single-mode fiber. Then, the effects of the SOA’s injection current and the carrier-to-sideband ratio on the system performance are discussed by simulation, and the optimum value for the system is obtained.

Hybrid encoding technique for the representation of the binary states of information, four-wave mixing in semiconductor optical amplifier (SOA) as frequency generator and cross-polarization rotation effect in semiconductor optical amplifier as a frequency converter are used to design all-optical universal logic gate NAND. The devices can perform ultrafast operation and easily integrable. The simulated results of the proposed logic gate ensure feasibility of the proposals.

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.

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.