摘要:

The marked depression of the refractive index by injected carriers in the InGaAsP-lnP material system essentially influences the performances of laterally inhomogeneously pumped laser diodes such as the usual ridge-waveguide structures. This is because, together with the built-in index guiding, anM-shaped waveguide is formed that may become leaky even for the fundamental waveguide mode. The characteristics of these waveguides are calculated and compared with previous results. Hence, the waveguide structure is studied for a wide range of device parameters showing that optical losses can be kept within acceptable limits by applying effective index steps in excess of 0.02. Furthermore, the mode gain is calculated for the corresponding carrier profiles and the threshold current is estimated. According to experiment, the results show that threshold currents around 20 mA can be achieved with appropriate waveguide structures at wavelengths of 1.3 μm and 1.55 μm

DOI:10.1049/ip-j.1986.0059

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Results are presented for analytical computer modelling and experimental studies of optically induced frequency tuning of W-Band (75–110 GHz) impatt oscillators. Predictions from an analytical theory are compared with those from a large-signal time-domain computer model, and the effect of unequal electron and hole ionisation coefficients on the tuning performance is illustrated. Experimental measurements are presented showing an optical tuning range of about 10 MHz for an optically generated current of 20 μA, and comparisons are made with the theoretical predictions.

DOI:10.1049/ip-j.1986.0060

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper describes the use of an avalanche diode to provide the combined functions of optical detection and harmonic electrical mixing. A simple analytic theory of avalanche optoelectronic mixer operation is presented and used to evaluate the conversion loss and noise performance of the mixer. The theoretical predictions are compared with experimental measurements of harmonic optoelectronic mixing up to the fifth harmonic. Measured conversion losses relative to direct optical detection ranged from 3 dB for fundamental mixing to IS dB for fifth-harmonic mixing. Frequency response limitations are briefly discussed.

DOI:10.1049/ip-j.1986.0061

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A method has been developed, based on the transformation of a noncommensurate system to a pseudocommensurate system, to enable the optical lowpass multilayer to be designed and analysed along similar lines as the classical commensurate networks. Using this transformation, the insertion loss of an optical multilayer can be expressed in the polynomial form with frequency-varying coefficients. In other words, the poles of an optical multilayer filter migrate in the complex plane as the frequency changes. By equating the insertion loss of the multilayer at the cutoff frequency to that of the Cheby̅chev insertion-loss function, optimised (though not optimum) multilayers having Cheby̅chev-like performance in the passband, have been designed.

DOI:10.1049/ip-j.1986.0064

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Pseudo-error monitoring is becoming a popular technique for on-line error monitoring in digital communication systems. However, optical communication systems are significantly different from other digital communication systems in that they exhibit signal-dependent noise. In this paper we examine in detail the theory of pseudo-error monitoring in optical communication systems and prove that minimising the pseudoerror rate can, under certain circumstances, result in a minimum in the bit error rate of an optical communication system.

DOI:10.1049/ip-j.1986.0065

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Fundamental core-mode ‘cutoff is a useful concept for tapered ‘single-mode’ lightguides with either a finite cladding surrounded by a lower-index external medium (= ‘second cladding’) or, equivalently, a raised inner cladding. This cutoff is not acutely sensitive to the external index for reasonable cladding/core diameter ratios. The dependence on core grading is given via universal step core curves and simple moment formulas for both planar guides and fibres. Arbitrary core profiles can be treated; generalisation to higher-order modes is given, and polarisation effects may be included.

DOI:10.1049/ip-j.1986.0067

出版商:IEE    

年代:1986

数据来源: IET

摘要:

In the paper, the local-mode evolution in a single-mode optical fibre is examined during tapering. Observed mode coupling effects are explained using the mode coupling theory between the fibre core and cladding. Alternatively, the taper is viewed as a multimode waveguide and local-mode interference of relevant modes explains the power transfer between the core and cladding. Practical applications of such tapers as all-fibre devices are highlighted.

DOI:10.1049/ip-j.1986.0068

出版商:IEE    

年代:1986

数据来源: IET