In this letter, we use four-wave mixing in semiconductor optical amplifiers to obtain wavelength conversion of data stream at 10 Gb/s. The wavelength conversion is made independent of polarization and conversion shift by means of a polarization diversity scheme with the use of two pumps proposed in a previous work of ours. The penalty measured is of about 1.2 dB.

We investigate experimentally and numerically the gain recovery time and gain compression resulting from intraband effects induced by sub-picosecond optical pulses in bulk semiconductor optical amplifiers. With the help of data produced by pump-probe measurements, the dependence of the intraband gain dynamics on pulse energy, device bias current, and length is discussed. The simulation results show a good agreement with the experimental data.

We report material gain measurements of bulk 1.55 μm InGaAsP/InP performed at constant temperature and carried out over a large range of carrier densities and a large spectral region. In addition, a polynomial model for the material gain is proposed that not only fits the experimental data well over the whole measured range but also shows stable convergence in simulation tools when carrier densities exceed the usual range. To get reliable parameters for the model we eliminated temperature effects arising from different current biases and performed material-gain measurements over the largest possible carrier density range. The material-gain model realized is used in semiconductor optical amplifier simulation tools.

We show that four-wave mixing in semiconductor optical amplifiers with the use of two orthogonally polarized pumps offers the possibility of frequency conversion with constant efficiency over several terahertz, The same two-pump configuration permits one to convert the signal to lower or higher frequencies with the same efficiency.

We propose and demonstrate a method to obtain polarization-insensitive four-wave mixing in a semiconductor optical amplifier. The method makes use of two pumps with orthogonal polarization placed at the two sides of the signal spectrum. Unlike a previously proposed scheme, a large bandwidth of the signal does not set a lower limit to the degree of polarization insensitivity obtained. Using a commercially available pig-tailed semiconductor optical amplifier, we have obtained less than 0.4 dB of intensity variation of the conjugate field for arbitrary changes of the signal polarization.

Optical waveguide mode-combiners for fundamental and first-order modes, based on multimode interference (MMI) couplers are presented. These devices convert a fundamental mode into a transversal first-order mode and combine it in lossless fashion with a second fundamental mode. They can separate zero- and first-order modes in a common waveguide and allow the splitting and combining of zero- and first-order modes with nonuniform power splitting ratios. Realizations in InGaAsP-InP are demonstrated. These new components have successfully been integrated into all-optical switches and were found to have advantageous characteristics in all-optical devices.

Asymmetric Mach-Zehnder interferometer (MZI) configurations are proposed to build all-optical space switches with gain and principally ideal extinction ratios. Actually, three asymmetries in MZI configurations with semiconductor optical amplifiers (SOA's) on their arms are discussed. The asymmetries in the all-optical switches are necessary to overcome the extinction ratio limitations that are due to the disturbing gain changes that arise when control signals are introduced into the SOA's to induce the necessary refractive index change for switching. Starting from a generic MZI configuration with SOA's on the arms, a description in terms of transmission matrices is used and applied to identify 1/spl times/2 and 2/spl times/2 all-optical switch configurations with high on-state transmissions and close to ideally large extinction ratios. The theoretical predictions are verified and found to be in excellent agreement with experiments for a switch with symmetric MZI splitters in a monolithically integrated InP waveguide version that allows operation with equally or unequally biased SOA's.

We propose a method to obtain spectral inversion of a signal without shifting its frequency. We use four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) with two pumps of orthogonal polarization. A conjugate field is generated with a polarization orthogonal to that of the incoming signal and is selected at the amplifier output by a polarizer. Using a commercially available pig-tailed SOA of 1.5-mm length, we obtain after the polarizer 21.5 dB of intensity ratio between conjugate and amplified incoming signal.

We report on experimental investigation of the dependence on pump-wavelength of efficiency and signal to background ratio of a wavelength converter based on four-wave mixing in a semiconductor optical amplifier (SOA). The signal wavelength has been varied over a 60-nm range at fixed signal-converted detuning. Both efficiency and background level increase by moving the operation wavelength toward bandgap. Nevertheless, we observe a variation of the signal to background ratio of only 2 dB in a 40-nm range. A qualitative interpretation of the results is presented.

80 Gbit/s all-optical demultiplexing using a monolithically integrated Mach-Zehnder interferometer with semiconductor optical amplifers is demonstrated for the first time. BER assessment at 40 Gbit/s shows penalty-free demultiplexing.

Four-wave mixing in semiconductor optical amplifiers is used to produce wavelength conversion. We report an extended study on the dependence of efficiency and noise on device length, pump power, operation wavelength and conversion interval. The use of longer active regions is a good way to obtain performance as good as requested by the most advanced telecommunication systems.

Very high four-wave mixing (FWM) efficiency and signal-to-background ratio (SBR) are obtained in a 1.5-mm-long bulk semiconductor optical amplifier. The FWM efficiency is measured to be 5 dB at 1-THz pump-signal detuning, which is the highest value reported to date. With a pump power of -1.4 dBm, the SBR is in excess of 20 dB in a bandwidth of 12.5 GHz, for a pump-signal detuning range as large as 2 THz and the efficiency is under the same conditions larger than -1 dB for a pump-signal detuning range as large as 1 THz. These results make FWM an attractive method for practical wavelength conversion. Some low-detuning measurements show a maximum efficiency around 8 GHz.

Summary form only given. In conclusion, we have realized a novel monolithically integrated all-optical switch with 8 db fiber-fiber gain, that can be operated in counter- and copropagating direction at any wavelength within the semiconductor optical amplifier (SOA) bandwidth. Furthermore, using a new single order mode (SOMO) configuration, the control signal is intrinsically radiated out, avoiding the use of wavelength-filters.

In this article we report extended measurements of four-wave mixing in bulk-semiconductor amplifiers using continuous wave sources. We demonstrate that four-wave mixing in semiconductor amplifiers permits realizing in the practice frequency conversion in the spectral range of utility for optical telecommunications. Efficiency larger than 1 have been demonstrated up to 1 THz with a low level of background noise. In addition, this technique has allowed us to investigate the carrier dynamics down to an equivalent time resolution of the order of few tens of femtoseconds.

Using semiconductor optical amplifiers of different length, we show experimentally that the signal to noise ratio at the output of a WDM network wavelength converter based on four-wave mixing is larger for amplifiers with large unsaturated gain, and increases with gain saturation.

We present theory and experiments of four-wave mixing in bulk-semiconductor amplifiers. The theory includes bimolecular and auger recombinations. We show experimentally conversion efficiency larger than unit up to 2 THz frequency shift. We measure a signal-to- background ratio compatible with that required by practical applications as frequency converters. The high efficiency of the four-wave mixing process permits the investigation of the carrier dynamics down to an equivalent time resolution of the order of few tens of femtoseconds.

Spatial mode filters based on multimode interference couplers (MMI's) that offer the possibility of splitting off antisymmetric from symmetric modes are presented, and realizations of these filters in InGaAsP/InP are demonstrated. Measured suppression of the antisymmetric first-order modes at the output for the symmetric mode is better than 18 dB. Such MMI's are useful for monolithically integrating mode filters with all-optical devices, which are controlled through an antisymmetric first-order mode. The filtering out of optical control signals is necessary for cascading all-optical devices. Another application is the improvement of on-off ratios in optical switches.