摘要:

In many practical applications of time-integrating acousto-optic correlators, constraints are placed both on the signal and on the devices used in the correlator. These constraints limit control of the spatial carrier frequency on which the output cross-correlation is formed. We examine the theory and present practical results of spatial heterodyning using a diffraction grating applied to a ‘joint collinear’ interferometric correlator which overcomes this limitation.

DOI:10.1049/ip-j.1985.0020

出版商:IEE    

年代:1985

数据来源: IET

摘要:

This paper presents the generalisation of the complex-source-point method for all the ‘series A’ and ‘series B’ Laguerre-Gaussian beams. When complex values are assigned to the source co-ordinates in the field expressions of point multipoles, the resulting fields have paraxially the form of a Laguerre-Gaussian beam. An application of this technique is found in deducing a generalised resonant formula for the spherical open resonator with a ‘large aperture’. The result is more accurate than the conventional one in order of magnitudes. Moreover, the small difference in resonant frequencies between the ‘series A’ and the ‘series B’ modes of the same order when l > 0 confirms the nonexistence of the commonly accepted linearly polarised modes with angular dependence. The theoretical pedictions are substantiated by experimental work.

DOI:10.1049/ip-j.1985.0021

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The induced absorption losses for ZrF4-based fluoride glass and fibre after being subjected to gamma-ray irradiation are measured in the 0.2–5 μm wavelength range. The induced loss in the 2.55–3.65 μm wavelength range is 1050–2300 dB/km/106roentgens, which is comparable with that for doped silica fibre at 1.5 μn. The formation of colouration in ZrF4-based fluoride fibre material can be suppressed by iron or titanium doping.

DOI:10.1049/ip-j.1985.0022

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The paper describes an integrated electro-optical frequency shifter operating at λ = 1.3 μ m. This is a wavelength of great interest in fibre-optical systems such as heterodyne and sensor systems.

DOI:10.1049/ip-j.1985.0023

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The problem of nonlinear pulse propagation in optical fibres is investigated. The nonlinear Schrodinger equation, which governs the evolution of the pulse envelope, is reformulated as a variational problem. Using a Ritz optimisation procedure, approximate solutions are obtained for the evolution of the main pulse parameters: pulsewidth, pulse amplitude and nonlinear frequency chirp.

DOI:10.1049/ip-j.1985.0024

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The basic physics and the various methods of optoelectronic microwave switching are reviewed. To achieve a clearly arranged presentation, the diverse techniques known to date are reported in the light of a trisection classification scheme according to three basic principles: the optical control of a photosensitive transmission path in CW-fed two-port devices, the optical control of charged-line pulsers or normally CW-operated solid-state oscillators, and the electrical control of photosensitivity in optically coupled microwave switching devices.

DOI:10.1049/ip-j.1985.0025

出版商:IEE    

年代:1985

数据来源: IET

摘要:

For the realisation of a distributed feedback (DFB) laser, the properties of a waveguide with a grating adjacent to the laser stripe are investigated. The results are applied to the metal-clad ridge-waveguide (MCRW) structure with DFB grating. It is found that, for small stripe widths, and if the optical field is mainly concentrated within the active region of the waveguide, enough optical feedback may be expected to realise laser operation with efficient longitudinal mode filtering.

DOI:10.1049/ip-j.1985.0026

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A first-principles calculation of the linewidth of a distributed-feedback (DFB) semiconductor laser is presented. The treatment involves a detailed account of the longitudinal power distribution in the laser cavity, including the effects of spontaneous emission. The result is expressed in terms of output power, cavity length, and a normalised function of the product of coupling coefficient and length. For large values of this latter product (greater tharf about five), the linewidth varies approximately as the inverse square of the coupling coefficient and as the inverse cube of the cavity length.

DOI:10.1049/ip-j.1985.0027

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The volume current method is used to obtain the curvature radiation loss from an integrated-optics dielectric rib waveguide in contact with the air. Following earlier workers, a single component of the electric field is assumed to satisfy a scalar Helmholtz equation. The electric field component is assumed to vanish on the air/dielectric interface; the introduction of this large discontinuity in the refractive index reduces the curvature loss considerably. The time and spatial decay constants appear as the product of two factors: a curvature factorCFand a shape discriminating factorDF. The factorCFis of lower order of magnitude than the curvature factor for an optical fibre, but contains similar features which may be compared. The discriminating factorDFmay be calculated by the numerical solution of Helmholtz equations, but is discussed qualitatively here. Comparative shape studies are in agreement with physical intuition.

DOI:10.1049/ip-j.1985.0028

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The fluctuations of the lasing mode intensity due to weakly excited satellite modes are discussed, in terms of the probability distribution, for a semiconductor laser with homogeneous gain saturation. The dependence of the intensity distribution on the injection rate and on the gain spectrum shift is investigated.

DOI:10.1049/ip-j.1985.0029

出版商:IEE    

年代:1985

数据来源: IET