E.A. De Souza

Low-loss intracavity AlAs/AlGaAs saturable Bragg reflector for femtosecond mode locking in solid-state lasers

We introduce a new low-loss semiconductor structure for femtosecond intracavity mode locking in low-gain solidstate lasers. This monolithic device can be engineered to exhibit specif ic saturation characteristics desirable for mode locking solid-state lasers. Self-starting 90-fs pulses are obtained with Ti:sapphire and diode-pumped Cr:LiSAF lasers. We discuss mode-locking mechanisms in quantum-well passively mode-locked solid-state lasers.

Wavelength-division multiplexing with femtosecond pulses

We demonstrate wavelength-division multiplexing with a single broadband femtosecond source by slicing the 3.7-THz spectral bandwidth of 85-fs laser pulses into 16 channels that are modulated individually.

Wavelength‐selective detector based on a quantum well in a standing wave

We present an example of a new class of optoelectronic devices realized by placing thin absorbers in a standing wave. Using quantum wells as absorbers and measuring the photocurrent from each of them separately it is possible to realize devices which accomplish complex tasks like separately detecting more than one wavelength at the same time or measuring the wavelength of a quasimonochromatic beam. In this letter we demonstrate a wavelength‐selective detector based on a single quantum well. It detects at 850 nm with a bandwidth <10 nm, while rejecting at the shorter wavelength of 835 nm by a factor of 120.

Analog differential self-linearized quantum-well self-electro-optic-effect modulator

We describe an analog self-electro-optic-effect device that gives a difference between two optical output powers that is linearly proportional to electrical or optical drive, permitting bipolar processing in novel image-processing arrays. The device is able to operate over a range of more than four orders of magnitude optical power, from 50 nW to 2.5 mW, corresponding to uniform incident intensities as low as 3.3 mW/cm(2).

LINEAR IMAGE DIFFERENTIATION BY USE OF ANALOG DIFFERENTIAL SELF-ELECTRO-OPTIC EFFECT DEVICES

We demonstrate one-dimensional linear image differentiation, using an array of symmetric self-electro-optic effect devices with 64 × 32 elements. The device operates with pairs of power-supply beams. The spatial derivative, which may be of either sign, is given as the difference in the reflected output powers.

Detecting edges using an analog electrooptic device

We characterized an analog self electrooptic effect device with five photodiode as an edge detector evaluating its performance using a step edge as input image. The device measured the second order derivative of the step and found the zero crossing point. The result agreed with the theory of edge detection.

An optical image-filtering based on spatial arrangement of multiple quantum well diodes

Linear operation and optimization of a cross-differentiator is presented. It is an analog/optical image filter operating in real time/space based on spatial arrangement of multiple quantum well diodes.

A new directional intensity variation detector based on self electro-optic effect device

We characterized a self electro-optic effect device (SEED) as a new directional intensity variation detector (CROSS-SEED). The photodetectors spatial layout enables the calculus of local cross derivative of an incident image. The results show that the device is simultaneously sensitive and selective to contrast orientation for any input image.We characterized a self electro-optic effect device (SEED) as a new directional intensity variation detector (CROSS-SEED). The photodetectors spatial layout enables the calculus of local cross derivative of an incident image. The results show that the device is simultaneously sensitive and selective to contrast orientation for any input image.

Diode-pumped femtosecond lasers modelocked with saturable Bragg reflectors

We discuss a new low loss semiconductor structure for femtosecond intracavity mode-locking in low-gain solid state lasers. This monolithic device can be engineered to exhibit specific saturation characteristics desirable for modelocking solid state lasers. Self-starting 100 fs pulses are obtained in a diode-pumped Cr:LiSAF laser. We discuss modelocking mechanisms in quantum well passively modelocked solid state lasers, and extensions to other wavelengths.

THz study of field screening: 10 fs-100 fs regime

Here, we present the first THz study of field screening on such a time scale by using a 10 fs laser, and a correlation technique. We prove for the first time that both the polarisation and the acceleration ofthe electron-hole pairs by the dc electric field contribute to THz emission. We show that the polarization contribution has a speed comparable to the optical pulse duration, while the transport contribution at early times is determined by the ballistic acceleration of the electron hole pairs.