摘要:

The dispersion relations, stability to propagation, absorption effects and Gaussian beam excitation of nonlinear TE waves guided by graded-index planar waveguides with both Kerrlaw and saturable nonlinear cladding media are discussed numerically. The spatial soliton emission and the effects of linear absorption on spatial soliton emission in graded-index planar waveguides with Kerr-like nonlinear cover media are investigated by numerical techniques. The stationary field distribution and the guided wave power flow-effective mode index relationship are obtained using the finite element method. The propagation down the waveguide of nonlinear TE waves excited by a specific input beam is investigated numerically using the Crank-Nicolson finite-difference scheme combined with the Newton-Picard method for solving the corresponding system of nonlinear equations.

DOI:10.1049/ip-j.1991.0062

出版商:IEE    

年代:1991

数据来源: IET

摘要:

An interlaboratory comparison of mode field diameter measurements on six single mode fibres of both conventional and dispersion modified design has been performed within the framework of the COST 217 Project. Fourteen laboratories took part in the intercomparison using five different measurement techniques. The results showed clear systematic differences in the measured mode field diameter between the methods. These differences can be explained in terms of the theory of the methods. It is suggested that the most accurate values of mode field diameter are obtained using the far field scan technique and hence this is the most suitable technique to use as a reference test method.

DOI:10.1049/ip-j.1991.0063

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A frequency domain analytic study of laser nonlinear distortion is presented, based on the Volterra nonlinear functional series. This analysis is shown to predict all the intermodulation products up to third order, of particular relevance to the design of subcarrier multiplexed systems, when the laser is modulated by an arbitrary number of channels. Illustrative analytic and simulation results are presented for two and three input subcarriers and are shown to match very closely.

DOI:10.1049/ip-j.1991.0064

出版商:IEE    

年代:1991

数据来源: IET

摘要:

The propagation of electromagnetic waves in cylindrical waveguides with gyroelectric core and cladding is treated analytically. The electric field inside the core and the cladding regions is expressed as an appropriate superposition of cylindrical waves. The satisfaction of the boundary conditions leads to a characteristic equation for the propagation constants of the possible guided modes. The propagation properties of such structures are then investigated by studying this characteristic equation. Dispersion curves are given for various parameters of the guides considered.

DOI:10.1049/ip-j.1991.0065

出版商:IEE    

年代:1991

数据来源: IET

摘要:

Mode index measurements of planar waveguides fabricated by proton-exchange and annealed proton-exchange inz-cut LiNbO3have been made. A Fermi function was found to accurately model the index profile in a PE waveguide resulting in a better agreement between the measured mode indices and the computed dispersion curves compared to the conventional step-index profile. In addition, the effects of various fabrication parameters on the propagation characteristics of single-mode annealed proton-exchange waveguides have been investigated in detail. Such information will be useful in the analysis, design, and optimisation of devices to be fabricated with the proton-exchange and annealed proton-exchange technology.

DOI:10.1049/ip-j.1991.0066

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A heterodyne signal processing scheme is demonstrated as a ‘proof-of-principle’ of a technique to increase greatly the ‘carrier’ frequency available in low coherence interferometric sensor systems. An interferometer is formed containing a Bragg cell which acts as the local interferometer. The sensing interferometer is formed in a second remotely placed modulated Michelson interferometer which is optical-fibre-coupled to the local interferometer. The Doppler frequency shift generated in the sensing interferometer modulates the ‘carrier’ in a single sideband fashion. The scheme operates as a conventional heterodyne system over the coherence profile of the source. The system is fully fibre optic compatible and potentially has applications in wide modulation bandwidth sensor systems.

DOI:10.1049/ip-j.1991.0067

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A waveguide structure semiconductor Raman laser for which the pump beam is incident through a multilayer dielectric film transparent for the pump light but highly reflective for the Stokes light is reported. There is no need to open a window for pump beam introduction. Accord ingly, narrow waveguides with a width of 10μm have been fabricated and successful operation has been achieved using a pulse-modulated pump beam from a CW-YAG laser, instead of a Q-switched YAG laser used in the previous experiments. This structure is capable of further reducing the size of the waveguide cross-section to realise very low threshold operation necessary for use in wideband optical communications.

DOI:10.1049/ip-j.1991.0068

出版商:IEE    

年代:1991

数据来源: IET

摘要:

We have studied the performance of a heterodyne DPSK receiver operating with an intermediate frequency of only half the bit rate. The system degradation owing to laser phase noise and additive receiver noise has been analysed and is compared to experimentally obtained results. The theoretical shot noise limit of our system is 24.7 photoelectron/bit for a BER of 10−9which is only 0.9 dB from the shot noise limit of a conventional heterodyne DPSK system. The degradation of our system owing to laser phase noise is smaller than for a conventional heterodyne DPSK system because an IF linewidth of 0.8% of the bit rate introduces a 1 dB system penalty at 10−9BER compared to 0.5% for heterodyne DPSK systems. To achieve a system performance with less than 1 dB penalty from the optimum the IF may vary within a range of up to 7.5% of the bit rate. An experimental verification of the system has been carried out with a 1 Gbit/s system.

DOI:10.1049/ip-j.1991.0069

出版商:IEE    

年代:1991

数据来源: IET

摘要:

Optimisation of the bandwidth of semiconductor lasers subject to direct intensity modulation has been undertaken taking account of the effect of nonlinear gain suppression on the damping of relaxation oscillations. A novel relationship between the damping and the 3 dB intrinsic bandwidth of semiconductor lasers has been obtained and is used to examine the effect of the damping in limiting the intrinsic bandwidth of conventional and advanced (quantum well and strained layer) semiconductor lasers. It is shown that enhanced nonlinear gain in quantum well and strained layer lasers significantly limits bandwidth improvements anticipated for such advanced laser structures on the basis of their relatively high differential gain. The operating conditions appropriate to maximum intrinsic bandwidth have been identified in these cases.

DOI:10.1049/ip-j.1991.0070

出版商:IEE    

年代:1991

数据来源: IET