摘要:

We propose a novel scheme using non-linear effects to obtain time division multiplexed optical packet switching in real time. Signals can be both switched and amplified through the routing processes by nonlinear optical four-wave-mixing devices.

DOI:10.1049/ip-j.1990.0025

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The locking range of an optically injected semiconductor laser is discussed, including the spectral hole burning and lateral carrier diffusion effects. These effects are modelled with a gain suppression coefficient. In addition, an expression for the mean square phase jitter of an injection-locked semiconductor laser is derived when these effects are insignificant. The power spectrum of a locked laser is obtained and compared with experimental results.

DOI:10.1049/ip-j.1990.0026

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The influence of temperature on the absorption, fluorescence and small-signal gain characteristics of a silica-based erbium-doped fibre is investigated. The observed changes in the fluorescence and absorption spectra are found to be consistent with a Boltzmann-type redistribution of ion populations within the manifolds of the4I13/2:4I15/2transition. The influence of this behaviour on the gain characteristics of a cooled fibre amplifier is studied at two particular wavelengths: 1536 and 1553 nm. Significant improvements in amplifier performance are measured at both wavelengths when pumping into the4I9/2absorption band at liquid-nitrogen temperatures. The gain results are related to the absorption and fluorescence changes observed on cooling the fibre, and predictions of the importance of these results to device performance are made. The effect of cooling on the pump threshold performance of an erbium-doped fibre laser is also measured.

DOI:10.1049/ip-j.1990.0027

出版商:IEE    

年代:1990

数据来源: IET

摘要:

To calculate the propagation characteristics of a graded-index optical fibre with a parabolic core, such as a dual-shape core optical fibre having a parabolic-index centre core, one needs to solve a vector wave equation in the inhomogeneous core region. The paper derives a coupled second-order differential equation with respect to the radial functions linking to the transverse electric fields through the refractive-index distribution, and solve it by the perturbation method. Analytical results show that the first-order perturbed solution plays a dominant role in the vector wave solution, especially for the fundamental mode. In fact, normalised frequencies and waveguide dispersions calculated using the first-order solution hold at least seven significant figures in the single-mode region. Comparison between cutoff frequencies of the conventional square-law optical fibre calculated here and those obtained by the numerical methods also guarantees the accuracy of the first-order solution. Using the first-order solution, the paper examines the waveguide dispersion and the mode field distribution of the dual-shape core optical fibre. Results show that the fibre with a parabolic-index centre core is one of the best dispersion-shifted optical fibres. The waveguide dispersion can be flattened over a relatively wide range of the waveguide parameters, and the confinement of modal power is good.

DOI:10.1049/ip-j.1990.0028

出版商:IEE    

年代:1990

数据来源: IET

摘要:

With the aim of seeking the optimal design for photodiode, we investigate thep+-π-n−-n+structure of photodetectors. For this structure, the π type layer is the boron diffused region, and thep+type active region with a near exponent impurity distribution is formed by diffusing boron through thin silicon dioxide. This is a high quantum efficiency photodiode. Its internal quantum efficiency is near 100% within the wavelength of light from 900 nm to 350 nm, and as high as 1.13 and 1.41 at the wavelength of 300 nm and 250 nm, respectively.

DOI:10.1049/ip-j.1990.0029

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Measurements are made of the thermal response of coated single-mode optical fibres to microwave power at 2.45 GHz using an all-fibre Mach-Zehnder interferometer. A carbon based secondary coating has been used as the energy absorbing medium. Computer based analysis of the thermal transient includes consideration of thermal conduction within the fibre together with both radiative and convective heat losses at the outer surface. A simplified treatment of the convection loss has been employed, in which the convective heat transfer coefficient is assumed to be constant during the thermal transient. The predictions of the adopted model are compared with measurements, the degree of agreement justifying the model. A convective process is identified as the dominant heat loss mechanism.

DOI:10.1049/ip-j.1990.0030

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A method is described for the design and realisation of optimised receiver filters based on the numerical optimisation of preselected low order structures using a modified Chernoff bound on error probability as the objective function. The filters are readily realised by doubly terminated L-C ladder networks and have a performance that is very close indeed to the strict optimum. They have low complexity and low sensitivity, in addition to improved robustness and performance compared with conventional designs.

DOI:10.1049/ip-j.1990.0031

出版商:IEE    

年代:1990

数据来源: IET

摘要:

It has been shown that the gain spectrum obtained by cascading two or more semiconductor laser amplifiers (SLAs) can have a ripple amplitude that is significantly smaller than that currently attainable with a single stage of optical amplification. The paper examines the performance of optically preamplified receivers employing cascaded SLAs, emphasis being placed on the influence of signal frequency fluctuations. The analyses make use of a lightwave simulation package designed to accommodate laser chirp, fibre dispersion, laser preamplifiers and receiver characteristics. Our results suggest that cascaded SLAs offer improved receiver sensitivity in the presence of laser chirp compared with a single-stage amplifier of the same net gain and facet reflectivity. The best performance may be achieved when the cascaded preamplifiers are synchronously tuned rather than stagger-tuned, despite the smaller gain ripple associated with the latter case. We have used these techniques to investigate a new approach for cascading SLAs to realise optically preamplified receivers, which are less sensitive to optical signal polarisation. The approach uses a single optical receiver and no additional receiver electronics. The difference in receiver sensitivity for orthogonal polarisations is reduced to 0.7 dB, compared with 4.5 dB for a single preamplifier receiver and at the cost of 1.6–2.3 dB power penalty compared with perfectly matched polarisation for the latter case.

DOI:10.1049/ip-j.1990.0032

出版商:IEE    

年代:1990

数据来源: IET