We report the results of a systematic study on planar optical waveguides fabricated in z-cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single-mode waveguide at a 633-nm wavelength was 2.4 dB/cm.

Objectives To compare the efficacy of diamorphine administered by a patient-controlled pump (patientcontrolled analgesia) with intramuscular administration for pain relief in labour. Design Randomised controlled trial.Setting The South Glasgow University Hospitals NHS Trust.Sample Primigravidae and multigravidae in labour at term (37 -42 weeks).Methods Women were randomised in labour to the study (patient-controlled analgesia) or control group (intramuscular). Randomisation was achieved through a random permuted block design stratified by parity. Study group women were given a loading dose of 1.2 mg diamorphine intravenously and then attached to the pump. Control group women received intramuscular diamorphine as per hospital protocol. Participants were also given 3 mg of buccal Stemetil. Data were collected throughout labour and at six postnatal weeks. Main outcome measures Analgesia requirements during labour and women's satisfaction with the method of pain relief. Results Women in the study group (patient-controlled analgesia) used significantly less diamorphine than women in the control group (intramuscular) but were significantly more likely to state that they were very dissatisfied with their use of diamorphine and were significantly more likely to opt out of the trial before the birth of the baby. The majority of women in both groups used other analgesia concurrent with diamorphine such as Entonox, aromatherapy or TENS. Conclusions Patient-controlled analgesia administration of diamorphine for the relief of pain in labour offers no significant advantages over intramuscular administration. The results also suggest that diamorphine is a poor analgesic for labour pain irrespective of the mode of administration.

Laboratory experiments were used to extend the application of the Shields entrainment function to both organic sediments and inorganic sediments overpassing a bed composed of particles of a different size. A total of 89 flume experiments were conducted to simulate organic sediment motion over sand and gravel stream beds. Although the study emphasis was on organic particles, some of the test included inorganic sediments. The bed particle diameters ranged from 0.7 x 10-3m to 22 x 10-3rn, while the organic particle diameters ranged from 0.56 x 10-3m to 7.45 x 10-3 m. A visual technique was used to determine the initiation of motion. The laboratory results were used to derive a modified Shields relationship which includes both the transported and bed particle characteristics. This modified Shields function predicts the initiation of motion of both organic and inorganic particles overpassing beds whose composition is significantly different than these particles. These results have direct application to the prediction of incipient motion of organic and inorganic detritus particles in streams and estuaries.

It is shown that use of the effective-index method for a rectangular-core waveguide is equivalent to analysis of a pseudorectangular-core waveguide, the dielectric constant of which is higher in some of the cladding regions than that of the actual waveguide. This explains why the effective-index method gives higher values for the propagation constants for the various guided modes than other methods and different results depending on whether one starts with the longer dimension or the shorter dimension to construct the effective-index waveguide.

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The presence of a chemical may be sensed by its effect on the evanescent field of an optical wave; the evanescent field may conveniently be established through use of an optical waveguide.We have applied three techniques to the problem of estimating the sensitivity of a variety of guide structures to the presence of a chemical species.The results for an asymmetric guide show that for a given mode, sensitivity is highly dependent on the guide thickness.Additionally, the effect of buffer layers (fouling) at the waveguide surface has been examined and results indicate the need for careful control of the surface conditions.

The paper reports on a systematic study of planar optical waveguides in X-cut LiNbO 3 fabricated by the proton-exchange technique. The extent of the exchange process was monitored by measuring the infrared absorption peak at 3510 cm" 1 . It was established that the waveguide profile could be accurately modelled by a step index change with An = 0.127 at X o -632.8 nm and An = 0.096 at X o = 1150 nm. From the mode effective refractive index measurements, the effective diffusion coefficients for the exchange process were calculated. A value for the activation energy for the proton-exchange process was established. The effect of off-Y-axis propagation on the mode effective indices of the waveguide was studied. A waveguide mode cutoff at 29° from the C-axis was established. The lowest optical losses measured in single-mode planar waveguides were 1.4 dB/cm at X o = 632.8 nm and 1.3 dB/cm at X o = 1150 nm for light propagating normal to the C-axis.

A simple modification to the Fabry-Perot technique for the measurement of semiconductor waveguide losses is described. The modification dispenses with the need for knowing implicitly the reflectivities of end faces of the waveguide, which are usually difficult to ascertain experimentally.