Nadhum K. Zayer

Heat transfer modelling in CO2 laser processing of optical fibres

The diameter self-regulation of optical fibre tapers produced using a CO2 laser has been examined theoretically and modelled numerically. Results of the simulation show that for small diameters, where the geometric model of absorption cannot be used, the Mie theory of absorption derived from the Maxwell equations exhibits structure due to resonances of the CO2 laser radiation in the tapered fibre. At small diameters, the polarisation state of the CO2 laser is important, and resonance effects cause the equilibrium temperature/diameter graph to exhibit oscillations.

In situ monitoring of sputtered zinc oxide films for piezoelectric transducers

Abstract We report the application of in situ ellipsometry to monitor the growth by RF reactive sputtering of zinc oxide thin film piezoelectric transducers on silicon substrates. To establish the effect of substrate temperature on film quality and piezoelectric activity, films were grown at substrate temperatures of 100–300°C. Films of refractive index as high as 1.940 are achieved compared with refractive index of 1.99 for bulk zinc oxide crystals. Under optimum deposition conditions, transparent homogenous films of high piezoelectric activity are formed from the initial stage of growth. A simple single layer model is used to predict the in situ ellipsometry measurement data for films deposited under optimum conditions, while a two layer model (duplex model) is needed to model the ellipsometry measurement data for rough films formed under conditions away from the optimum. Films grown at the optimum substrate temperature of 200°C were smooth and of reproducibly good quality, having high piezoelectric activity. Although the refractive index remained constant during growth, the rate of growth was not quite linear, and was found to increase slowly with time according to a weakly quadratic law. X-ray diffraction and pulse echo techniques were used to establish that films deposited close to 200°C have good oriented structure and high piezoelectric activity. We have thus shown that a strong correlation exists between the optical properties measurable with a simple in situ ellipsometer, and the appearance of highly oriented films of zinc oxide having excellent piezoelectric activity.

Broadband monolithic acousto-optic tunable filter.

Broadband monolithic acousto-optic tunable filters that combine a piezoelectric transducer array and an acousto-optic interaction medium in a single crystal have been investigated. A linearly chirped acoustic superlattice with an optical tuning range of lambda = 1.3-1.6 mum was formed by domain inversion in LiNbO(3) . X-propagating longitudinal acoustic waves are excited in a crossed-field scheme by a rf E(y) field applied to the superlattice and couple collinearly propagating e- and o-polarized optical modes. At mu = 1.319 mum and mu = 1.55 mum the spectral bandwidths (FWHM) were 1.54 and 2.3 nm, respectively. A relative conversion efficiency of 43%/W and a maximum conversion efficiency of 51% were measured at 1.319 mum.

Crossed-field excitation of an acoustic superlattice with matched boundaries: theory and experiment

Electrical characteristics of a new type of acoustic transducer have been investigated theoretically and experimentally. The agreement between calculated and measured results is excellent. The transducer consists of an acoustic superlattice, made of periodically poled LiNbO/sub 3/ (PPLN), with acoustically matched boundaries, facilitating the construction of acousto-optic (AO) devices through monolithic integration.

In situ substrate temperature measurements during radio frequency sputtering of ZnO thin film using fiber Bragg grating

Several research groups throughout the world are currently working on fiber acousto-optic components, principally phase modulators, made by depositing a film of piezoelectric materials such as zinc oxide (ZnO) directly onto the optical fiber. It is well known that the quality of the resulting film is highly dependent on the temperature of the substrate (i.e., the fiber), but this has not been directly measured in situ. We present for the first time in situ measurements of the fiber temperature during the deposition process using a fiber Bragg grating temperature sensor. We show that the fiber temperature may rise substantially above that of its immediate surroundings. We also present a simple model for the heat flow for the fiber and the holder based on the heat gain from the plasma and the radiation loss between the various components in the sputtering chamber.

A monolithic acousto-optic tunable filter using domain-inverted lithium niobate

Summary form only given.Acousto-optic tunable filters (AOTFs) find many applications. The prototype AOTF was designed for a tuning range between 1300 and 1600 nm. Phase matching between polarization modes within this interval is accomplished by collinearly propagating bulk longitudinal acoustic waves. A linearly chirped acoustic grating of length 10 mm with transducer periods covering that interval provides the matched acoustic sources.