A. D’Ottavi

VERY HIGH EFFICIENCY FOUR-WAVE MIXING IN A SINGLE SEMICONDUCTOR TRAVELING-WAVE AMPLIFIER

We report on high efficiency frequency‐conversion obtained by four‐wave mixing in a single traveling‐wave semiconductor optical amplifier. Efficiency in excess of 0 dB is demonstrated for frequency conversion up to 2 THz. Measurements of the signal to the amplified spontaneous emission background ratio are also presented.

4.3 terahertz four‐wave mixing spectroscopy of InGaAsP semiconductor amplfiers

A four‐wave mixing experiment in a bulk InGaAsP traveling‐wave semiconductor amplifier is reported. The maximum pump‐probe detuning is 4.3 THz. The equivalent time resolution of 37 fs is high enough to measure with good accuracy the time constant of spectral‐hole burning (100 fs in our case). The simultaneous presence of spectral‐hole burning and of an instantaneous, within our time resolution, saturation process is clearly displayed.

Experimental observation of time jitter in semiconductor laser turn‐on

We report an experimental study which shows how time jitter in semiconductor lasers, which arises when such sources are switched from below to above threshold, is related to the actual operating conditions. The effect is observed both in distributed feedback and in Fabry–Perot lasers, even if in the latter case it becomes more and more negligible when the output power of the final state is increased.

Investigation of carrier heating and spectral hole burning in semiconductor amplifiers by highly nondegenerate four‐wave mixing

A highly nondegenerate (up to 1 THz) four‐wave mixing experiment is performed in a bulk semiconductor amplifier. The simultaneous presence of carrier heating and spectral hole burning shows up in a four‐wave mixing experiment. A simple physical picture is given that explains the relative weight of the two saturation mechanisms in active semiconductor devices.

Four‐wave mixing efficiency in traveling wave semiconductor optical amplifiers at high saturation

We report an experimental investigation of the conversion efficiency of a frequency converter based on four‐wave mixing in semiconductor optical amplifiers. We find that the maximum of conversion efficiency has a nonlinear dependence on the unsaturated gain of the device. The observed features are explained by the presence of the Auger and bimolecular recombination.

High saturation behavior of the four‐wave mixing signal in semiconductor amplifiers

We show by a simple model that, in semiconductor amplifiers, the functional dependence of the four‐wave mixing signal on the output power of pump and probe depends on the underlying optical nonlinearity. The observation, at different pump‐probe detunings, of a different dependence of the conjugate power on pump and probe output permits the identification of the dominant optical nonlinearity at a given detuning.

Polarization-insensitive four-wave mixing in a semiconductor optical amplifier

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.

Analysis of transients in pulse modulated semiconductor lasers biased near threshold

A theory of time jitter in semiconductor lasers initially biased just below threshold is developed. Simulations of the buildup of emitted optical pulses in lasers starting from below or above threshold are also presented which, for initial biasing up to threshold, are in good agreement with the theory. In particular, we show that time jitter does not vary for biasing currents up to about 0.95 of the threshold value, while it suffers a small increase at threshold and a steep decrease for higher biasing currents.

Time jitter in multimode Fabry--Perot laser diodes

Time jitter, which affects the switch‐on instant of pulse modulated semiconductor lasers, has recently been shown to be lower in Fabry–Perot than in distributed feedback lasers. In this letter starting from the rate equations for the field and the number of excited carriers in multimode lasers, and considering the stochastic nature of spontaneous emissions, we are able to find an expression for time jitter which explains the above‐mentioned experimental results.

Noise in wavelength conversion using four-wave mixing in semiconductor optical amplifiers

We measure the pump power dependence of efficiency and signal-to-background ratio in wavelength conversion using four-wave mixing in semiconductor optical amplifiers, for different lengths of the device. We show that the efficiency for a 1-mm-long amplifier is about 40 dB larger and the signal-to-noise ratio is about 23 dB larger than for a 0.25 mm amplifier. We also show that, unlike the efficiency, for constant ratio between pump- and signal-power, the signal-to-background ratio monotonically increases with the pump power. We show theoretically that this behavior holds for any range of pump-power values.