摘要:

The asymmetric rib waveguide directional coupler has previously been considered a complex structure to analyse, because the symmetry relied on by large-scale numerical techniques has been destroyed. Asymmetric couplers, however, have many applications in optoelectronics and are thus important structures to model. Here, the recently developed spectral index method is successfully applied to the asymmetric coupler. The propagation constants corresponding to the two polarised lowest-order supermodes of the entire structure are determined numerically from a transcendental equation.

DOI:10.1049/ip-j.1990.0048

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A new technique for modelling the dynamic spectral characteristics of DFB semiconductor lasers above threshold, which is based on the transmission-line laser model, is described. This includes the effects of index carrier dependence and longitudinal index variations. The time-domain responses and spectra of quarter-wave shifted grating devices are compared with unshifted devices under transient conditions.

DOI:10.1049/ip-j.1990.0049

出版商:IEE    

年代:1990

数据来源: IET

摘要:

An analytical solution of the field in a fibre up-taper with a parabolic index profile is obtained by solving the scalar wave equation. The field is expressed in generalised Laguerre-Gaussian polynomials. With this description, the evolution of the spot size and the wavefront curvature are easily seen. The presence of spot size oscillations along a taper is predicted in the case of a mismatch between the exciting beam at the taper entrance and the fundamental mode.

DOI:10.1049/ip-j.1990.0050

出版商:IEE    

年代:1990

数据来源: IET

摘要:

It is shown that any combinational function can be implemented by a multiplexer of appropriate width. Since these logic elements can also perform sequential operations, entire digital systems can be implemented with multiplexers. Such systems are of particular relevance to optical implementations as multiplexers using liquid crystal electro-optic elements can be realised. The large number of pixels available on a single display leads to the concept of significant optical systems implemented using two-dimensional arrays of uncommitted multiplexers. Since the multiplexer width is critical in determining the system efficiency, the implementation of commonly occurring logic functions is presented to determine the optimum width.

DOI:10.1049/ip-j.1990.0051

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The effect of profile imperfections, like axial index dip and layered structure in the inner cladding, on the leakage loss of LP01mode in MCVD made single-mode DIC fibres is investigated quantitatively through a Matrix approach. The study reveals that these apparent profile imperfections may greatly affect leakage loss coefficients especially at longer wavelengths. A typical example of the presence of a linear axial dip along with ripples in the inner cladding is seen to increase the leakage loss coefficient of the LP01mode to 43.44 dB/km from a value of 0.25 dB/km at 1.3 μm in the absence of profile perturbation; the corresponding figures at 1.6 μm being 2.76 × 103dB/km from 67.85 dB/km. However, if the shape of the dip is such that the dip width parameterq> 2, the leakage loss would not get affected by these profile imperfections in practical DIC fibres.

DOI:10.1049/ip-j.1990.0052

出版商:IEE    

年代:1990

数据来源: IET

摘要:

High-speed lasers are required for the implementation of high data rate digital and analogue fibre optic systems. Conventional laser structures are often limited in their operation speed by the high capacitance of their metallisation. Here we report a self-aligned high-speed laser with a −3 dB bandwidth of >10 GHz incorporating a 2-level metal interconnect system suitable for integration. A value for the quantity (resonance frequency/output power½) of 3.5 GHz mW−½has been measured, in agreement with theory for basic materials' parameters indicating that the device is not parasitic RC limited.

DOI:10.1049/ip-j.1990.0053

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The fluorescence spectra of trivalent samarium doped glass fibres are described. In silica glass Sm3+has a narrow fluorescence of 2.2 nm f.w.h.m. at a wavelength of 650 nm. The influence of fluorescence line narrowing and large external electric fields on this line is reported. Visible laser emission is obtained at this wavelength when the fibre is pumped in a Fabry Perot cavity. The performance of the laser in continuous,Q-switched and self mode-locked operation is described. The basic theory of self-mode-locking is presented.

DOI:10.1049/ip-j.1990.0054

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A new iteratively equivalent index method for the analysis of rectangular dielectric waveguide problems is presented. This analysis is found to be more accurate than the effective index method and the modified effective index method. The results obtained by this method compare very favourably with those produced by the variational analysis, weighted index analysis and numerical computation over a large range, but without the complexity of the latter. A simple analytical expression is also derived to describe the field distribution of such a waveguide from two equivalent coupled slab waveguides at right angles.

DOI:10.1049/ip-j.1990.0055

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The effect of inhomogeneous stress and temperature distribution in GaAlAs/GaAs stripe laser diodes at the pulsation properties was investigated. Under operation, the laser diode is heated. A stronger heating is found in the mirror region causing a shift of the absorption edge of GaAs. The absorption rise up to 1000–2000 cm−1. The parameters of the mechanical stress are also changed. The gain changes as a result of the change of the state of deformation and temperature rise. These effects influence the pulsation properties. The larger the heating in the active region, the lower is the onset current for self-sustained pulsations (SSP).

DOI:10.1049/ip-j.1990.0056

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The performance of an optical ASK receiver is analysed with the consideration of optical channel noise. Three noises are considered: the LO-channel noise, the signal-channel noise, and the shot noise. Their statistical properties and spectral distributions are investigated. Using correlation functions and a conditional probability scheme, we prove that the noises are independent Gaussian distributions. Through spectral analysis, the effect of optical filter bandwidth on the receiver performance is examined. The study reveals that the receiver performance degrades if a wide bandwidth optical filter is employed. In addition, there may exist an optimum amplifier gain to obtain a maximum signal-to-noise ratio when a high gain receiver preamplifier and a wide bandwidth optical filter are employed. The bit error probability is also evaluated. The results show that systems with little laser phase noise are subject to degradation by optical channel noise than those with larger phase noise.

DOI:10.1049/ip-j.1990.0057

出版商:IEE    

年代:1990

数据来源: IET