Abstract: A composite quantum dot structure (4) comprises a charge carrier confinement region, such as a quantum dot (2), a barrier (5) and an electrically conductive layer (3). This structure allows the dimensions of the conductive layer (3) to be substantially independent of the size of the region (2), so that the dimensions of the region (2) can thus be selected in order to achieve desired optical properties, while the electrically conductive layer (3) can be of sufficient thickness to ensure that it can be reliably deposited. The structure may also include a cladding layer (7) (FIG. 4) to compensate for any lack of chemical affinity between the barrier (5) and conductive layer (3). An ensemble of such structures be provided in which the quantum dots (1) have various radii but the dimensions of the conductive layers (3) and the overall dimensions of the structures are substantially uniform, e.g. for use in an amplifier configured to amplify light of various wavelengths.

Abstract: An optical diffraction grating is formed from a region of photonic crystalline material Light is coupled into the photonic crystalline material, and the grazingly emergent output beam is collected. The photonic crystalline material may include an array of holes formed in a substrate of dielectric material, e.g., InP, and integrated with planar waveguide structures.

Abstract: By forming quantum well (QW) structures with two different heterojunctions having different band offsets it is possible to form QWs having, when subjected to optical excitation, dipoles. The presence of a dipole in a narrow enough well results in QWs having absorption edges which, unlike those of conventional QWs can be shifted to the blue by application of an electric field of appropriate polarity.

Abstract: An optical device having controllable absorption for an optical signal having a wavelength corresponding to a photon energy not exceeding 1.2 ev comprises (i) a semiconductor structure including one or more quantum well layers and (ii) means adapted for applying to the quantum well layers(s) an electric field such that the component of the field normal to the layer(s) may be controlled so as to determine the absorption edge of the quantum well layer(s) to be on either side of the optical signal wavelength. The device may be used as an optical modulator or switch and in optical demultiplexing.