摘要:

We report the observation of a self-switching effect from an opaque to a transparent state occurring at a critical incident intensity in a polymer dispersed liquid crystal. This self-transparency effect is analysed taking into account the beam profile variations of the light propagating inside such a medium. A clear self-confinement of the laser beam travelling in this composite material is also presented.

ISSN:0950-0340    

DOI:10.1080/09500340008233378

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The unusually fast response of the two-wave mixing process in fibre-like Bi12TiO20crystals on transient change of the external electric field was experimentally observed. Pulses of the amplification of the signal wave with a rise time of 0.2 ms and a width of 0.5 ms at a total input intensity of 6 mW mm−2are obtained when applying a rising or decreasing front of an external electric field to the crystal. The two-wave coupling without external field has a response time of 200 ms. A simple calculation based on the bandtransport model qualitatively explains the fast transient amplification but fails to explain the slow response without the electric field.

ISSN:0950-0340    

DOI:10.1080/09500340008233379

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A physical random number generator based on the intrinsic randomness of quantum mechanics is described. The random events are realized by the choice of single photons between the two outputs of a beam splitter. We present a simple device, which minimizes the impact of the photon counters' noise, dead-time and after pulses.

ISSN:0950-0340    

DOI:10.1080/09500340008233380

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A type of monomode step-index channel guide is presented, such that modal propagation can be solved by the effective index method, in a quasi-exact form. With these results both the designing and fabrication of integrated optical devices based on channel guides, such as directional couplers, can be greatly simplified and improved.

ISSN:0950-0340    

DOI:10.1080/09500340008233381

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The focusing of partially coherent light by a lens with spherical aberration (SA) is studied. The numerical calculation results are given, showing that the axial intensity distribution not only depends on the SA, but also on the coherence of partially coherent light and the Fresnel number of the lens. As the coherence decreases, the influence of the SA on the axial intensity distribution decreases, and the positions of maximum axial intensity shift towards the lens.

ISSN:0950-0340    

DOI:10.1080/09500340008233382

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A theoretical analysis of oscillation characteristics is developed for Ti-diffused Nd:MgO:LiNbO3waveguide lasers by using the formalism of mode overlap. Simple and explicit expressions in terms of mode sizes are derived for effective mode volume and coupling efficiency between pump mode and laser mode, which are directly proportional to the threshold pump power and slope efficiency, respectively, both for transverse and coaxial pumping considering the spatial distribution of the pump beam and the laser beam. A comparison for the two pumping configuration has shown that the transverse pumping requires much higher input pump power and has much lower slope efficiency than the coaxial pumping. The fundamental transverse mode (TM0) oscillation conditions relative to the cavity loss are also discussed for the two pumping configurations.

ISSN:0950-0340    

DOI:10.1080/09500340008233383

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A novel approach for analysing an optical fibre electric field sensor by using the finite element method is presented. A singlemode optical fibre carrying a transversely poled piezoelectric poly(vinylidene fluoride) polymer coating was successfully modelled by using three-dimensional analysis. The response of the optical fibre electric field sensor was determined over a wide frequency range from 100 Hz to 50MHz. The modelling predicts a phase shift of 0.019 rad V−1m−1in the low frequency (axially unconstrained) region and 0.000 82 rad V−1m−1in the high frequency (axially constrained) region. At frequencies higher than 7 MHz the optical response is dominated by radial resonances of the fibre—jacket composite. Good agreement exists between the resonance peaks predicted by the simulation and those theoretically calculated using composite theory.

ISSN:0950-0340    

DOI:10.1080/09500340008233384

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Hilbert—Schmidt distance between two arbitrary normalizable states is discussed as a measure of the similarity of the states. Unitary transformations of both states with the same unitary operator (e.g. the displacement of both states in the phase plane by the same displacement vector and squeezing of both states) do not change this distance. The nearest distance of a given state to the whole set of coherent states is proposed as a quantitative measure of non-classicality of the state which is identical when considering the coherent states as the most classical ones among pure states and the deviations from them as non-classicality. The connection to other definitions of the non-classicality of states is discussed. The notion of distance can also be used for the definition of a neighbourhood of considered states. Inequalities for the distance of states to Fock states are derived. For given neighbourhoods, they restrict common characteristics of the state as the dispersion of the number operator and the squared deviation of the mean values of the number operator for the considered state and the Fock state. Possible modifications in the definition of non-classicality for mixed states with dependence on the impurity parameter and by including the displaced thermal states as the most classical reference states are discussed.

ISSN:0950-0340    

DOI:10.1080/09500340008233385

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We propose and demonstrate a unidirectional photorefractive ring oscillator that couples with an external angular multiplexing volume hologram for pattern recognition. By configuring the hologram externally, a computer-generated hologram (CGH) and a spatial light modulator are utilized to generate reference beams for the hologram. Two-dimensional images are stored in the form of resonating beams in the system, whereby the nonlinear interaction between the beams allows the image that most resembles an input object to be recognized. Five images were used to illustrate the pattern recognition ability of the oscillator. It was found that the input object was successfully recognized within 10s. The fact that CGHs can generate a large number of beamlets enhances significantly the storage capacity in this system.

ISSN:0950-0340    

DOI:10.1080/09500340008233386

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The optical band gap and optical constants have been studied as a function of photon energy for a-GaxSe100–xthin films (wherex× 0, 2.5, 5.0, 7.5 and 10.0) in the wavelength region 450–1000 nm. The optical band gap decreases with the increase of Ga concentration in the a-GaxSe100–xsystem. The refractive index (n) decreases while the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states.

ISSN:0950-0340    

DOI:10.1080/09500340008233387

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor