Low-pressure MOCVD has been used to grow layers of inP, InGaAs, GalnAsP and quantum weii material on planar substrates patterned with silica masks. The thicknesses and, where relevant, the compositions of these selectively grown layers were investigated by optical and scanning electron microscopy, surface profiling, energy dispersive x-ray analysis, secondary-ion mass spectroscopy and spatially resolved photoluminescence. The epitaxial layers were found to be both thicker and richer in indium in the vicinity of a mask. The perturbations in the thickness and composition of material grown around a given mask pattern were independent of the orientation of the pattern with respect to the gas flow and the crystallographic axes of the substrate. Lateral movement of material from the masked regions to the surrounding areas was found to take place in the gas above the wafer surface. A gas-phase diffusion model based on Laplace's equation was used to analyse the thickness and compositional variations caused by selective growth. The emission wavelength of selectively grown InGaAsl GalnAsP MOW material was shifted by over 100 nm without degradation in emission efficiency. The lasing wavelength of Fabry-Pbrot lasers fabricated on such material was increased by a similar amount without degradation of threshold current.

An iris-type variable aperture fabricated using microelectromechanical systems (MEMS) technology is described. The device contains a number of shutter blades, which are each driven by a separate microactuator, and translated synchronously to create a variable polygonal aperture. The optical performance of devices with different numbers of blades is compared using simple analytic models and diffraction theory. The mechanism is simulated by finite element analysis. Four-blade devices driven by buckling mode electrothermal actuators are formed by double-sided patterning and deep reactive ion etching of bonded silicon-on-insulator and characterized experimentally. Symmetric deflections are obtained, and used to create a square pupil. Variable attenuation is demonstrated using optical fibres with thermally expanded cores.

A new geometry of high-force electrothermal actuator is demonstrated using microelectromechanical systems technology. The actuator consists of two sets of inclined, parallel, suspended beams, which are tethered at one end and linked together at the other. The first set is divided into two halves, which are connected in series and heated electrically. The second set acts as a tether for the first, so that differential thermal expansion gives rise to a lateral deflection. The design can be scaled easily to increase the actuation force, which is sufficient to deflect a cantilevered optical fibre. A bi-directional fibre alignment device is formed from two opposed actuators, which are designed to grip the fibre, and a set of fixed mounting features. Prototype devices are demonstrated by deep reactive ion etching of bonded silicon-on-insulator, and in-plane alignment of single-mode fibre is demonstrated.

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A tuning element has been constructed using micro-opto-electro-mechanical systems (MOEMS) technology for Littman configuration external cavity tunable lasers. The device is fabricated by deep reactive ion etching of bonded silicon-on-insulator, using a single layer of patterning to integrate a fixed grating and a mirror that is rotated about a virtual pivot by an electrostatic comb drive. The mirror is mounted on a compound flexure. To ensure mode-hop free tuning, the pivot point should lie at the intersection of the mirror and grating planes. Candidate elastic suspensions are compared, and a combination of a cantilever and a portal spring, is selected. Interferometric measurements of electromechanical performance show that the mirror is rotating about a suitable remote point. Preliminary data are given for a Littman external cavity laser operating with a fixed MOEMS structure.