摘要:

The state of polarization in helically wound single-mode fibres is described in terms of coupled-mode equations and the Mueller matrix for an elliptically birefringent single-mode fibre in the quasi-monochromatic case. Possible depolarization has been accounted for by means of the mutual correlation function |γ| between eigenpolarization modes. The polarization state in closed-loop fibre-optic helices has been studied experimentally under single- and dual-mode operation. It has been shown that the closed-loop set-up can be used for the development of compact fibre-optic sensors.

ISSN:0950-0340    

DOI:10.1080/09500348914550331

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Prism coupling is employed to investigate the nonlinear properties of CdS0·9Se0·1semiconductor-doped glass slab waveguides. Experiments performed with a nanosecond laser source show distributed-coupling phenomena typical of thermally-driven processes, with compensating effects due to band-filling contributions.

ISSN:0950-0340    

DOI:10.1080/09500348914550341

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The performance of several optical logic gates implemented with liquid-crystal televisions (LCTVs) is discussed. A description is given of an optical OR gate constructed with three LCTVs which has potential for speckle metrology. Using this optical gate together with a standard optical processor, the fringes produced by an in-plane displacement of an object are displayed on an additional LCTV and the correlation spots which result may be observed directly. Examples are given of the application of the system to the real-time (video rate) display of object motion.

ISSN:0950-0340    

DOI:10.1080/09500348914550351

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Drift of the input power levels at which optically-bistable nonlinear interference filters switch between their transmission states has been studied experimentally. In addition to the small initial drift already observed by various groups, we have monitored, and characterised, a slower irreversible drift associated with the high internal operating irradiances. This pre-damage effect appears to be photo-structural in origin. The results show a small increase in refractive index (∼0·35%) and a decrease in the absorption coefficient (∼20%) over periods ranging from a few minutes to approximately one hour, depending on operating conditions. We have shown that the drift rate can be minimized by going to thicker spacer devices and by using molecular beam deposition techniques to grow the multilayer structures in place of conventional thermal evaporation.

ISSN:0950-0340    

DOI:10.1080/09500348914550361

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We describe a number of multiplexing techniques which may be used for fibre-optic sensors in which the sensing element is a ring resonator. The basic optical unit comprises a sensing ring resonator connected to a second interrogating ring resonator of nearly equal length, and illuminated by a source of short coherence length. A number of such units may be combined to form an array, using coherence multiplexing techniques. Using such an arrangement, the high finesse of the ring resonator may be exploited to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer. When a high-coherence source is used, then multiplexing may be accomplished using frequency-division techniques. However, in this case, the resonators must have low finesse, in order to avoid cross-talk. We also show that when a source of moderate coherence length is used, it is possible to use both frequency division and coherence multiplexing simultaneously, with the potential of realizing a large sensor array.

ISSN:0950-0340    

DOI:10.1080/09500348914550371

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We derive some statistical properties of photons emitted from bulk tissue that has been irradiated by a continuous beam of laser light. The properties include the distribution and moments of the depth reached by a photon, conditional on its having reached the surface at a (dimensionless) distance, ϱ, from the point of entry of the beam into the tissue. Theoretical predictions are made on the basis of a lattice random-walk model and are checked by simulations of the light penetration problem for a more realistic continuum model.

ISSN:0950-0340    

DOI:10.1080/09500348914550381

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The performances of different types of zone plate are analysed and compared. It is shown that, with a modified geometry, the resolution closely matches that of a diffraction-limited lens.

ISSN:0950-0340    

DOI:10.1080/09500348914550391

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A photorefractive deconvolution process for optical differentiation of images is suggested. The problems associated with the intrinsic resolution capabilities of this technique, resulting from the reading process, application of external fields and the spontaneous excitation rate of the carriers are discussed. The potential of this scheme is illustrated by using two well known test functions.

ISSN:0950-0340    

DOI:10.1080/09500348914550401

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This paper presents two concepts new to the design of anti-reflection coatings for grazing incidence angles. One is the use of the movement of the reflection band edges of a normal-incidence weak mirror with variation in angle of incidence. The second is the use of the change in equivalent index with wavelength of a symmetrical three-layer combination whose layers are quarter-wave thick at normal incidence.

ISSN:0950-0340    

DOI:10.1080/09500348914550411

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The distribution of electric-field amplitude inside multilayer thin-film polarizers is evaluated for various polarizer designs. The polarizers, based on (H/2, L, H/2) as the basic stack, show higher field amplitude than those based on all quarter-wave layers. Here H and L represent quarter-wave layers of high- and low-index materials respectively. It has been pointed out that, to avoid damage to the polarizers in high-power laser systems, it is necessary to know the field distribution inside the layers both for radiation incident from the air-multilayer interface as well as the glass-multilayer interface. Some implications of the positioning of thin-film polarizers in Faraday isolators used in high-power laser chains are discussed in relation to the susceptibility of these polarizers to optical damage. The results indicate that the liquid-prism MacNeille polarizer shows a higher damage threshold, which can possibly be further improved by increasing the angle of incidence at the multilayer.

ISSN:0950-0340    

DOI:10.1080/09500348914550421

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor