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Guided-wave devices demonstrated in lithium niobate have been seen for many years as highly functional components for applications in fields such as optical communications and sensor systems. The potential for their use has been recognized by the substantial research and development effort the technology has witnessed, and the subject matter of this article is born from these endeavours. The material reviewed includes a survey of devices built, including their design, functionality, and performance, as well as parallel activities that have been undertaken in materials processing, theory, and the development of lithium niobate itself, all of which are closely linked, and all of which have played an important part in the overall development of this major branch of contemporary optics research.

The temperature distributions of heated turbulent jets of air were determined using two dimensional (planar) laser induced phosphorescence. The jets were heated to specific temperature increments, ranging from 300 - 850 K and several Reynolds numbers were investigated at each temperature. The spectral ratio technique was used in conjunction with thermographic phosphors BAM and YAG:Dy, individually. Single shot and time averaged results are presented as two dimensional stacked images of turbulent jets. YAG:Dy did not produce a high enough signal for single shot measurements. The results allowed for a direct comparison between BAM and YAG:Dy, revealing that BAM is more suitable for relatively lower temperature, fast and turbulent regimes and that YAG:Dy is more suited to relatively higher temperature, steady flow situations.

This paper reports user requirements for frequency standards for optical communications and reviews physical possibilities for measurement standards to support those needs. A survey of the industrial and regulatory requirements for frequency standards for optical communications was made between October 1991 and January 1992. This was centred on the UK and Europe, but also took in responses from the USA and Japan. Over 70 representatives from 49 organisations were contacted, and a response exceeding 50% was achieved. The main requirement found was a need for two frequency standards per band in each of the 1.5 jim and 1.3 jim bands, with those in the 1.5 jim band needed first, and in the next 3-5 years. An curacy of order 1 part in 10' was desired for laboratory use, with an order of magnitude less for a transfer standard, and an order less again in the field.The physical possibilities for frequency standards in these bands are reviewed, addressing the use of atomic and molecular resonances. In these bands transitions in atoms are from excited states, and in molecules they are either overtone or combinationband transitions. This makes the transitions difficult to saturate, to obtain sub-Doppler feature suitable for 1 part in 1O frequency standards. A summary table is presented of the stronger relevant spectra from the literature and from recent high-resolution Fourier transform spectroscopy at the University of Strathclyde. A further table lists frequency standards already measured mainly by heterodyne techniques, and which are mainly in the 1.5 i.un band. The potential adequacy of the standards to meet the requirements, and a hierarchy for band sub-division in frequency are discussed. 106