There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Singular perturbations and order reduction in control theory - An overview

Singular perturbations and time-scale methods in control theory: Survey 1976-1983

A marriage of optical fibre fabrication technology and LSI microfabrication technology gave birth to fibre-matched silica waveguides on silicon: thick glass layers of high-silica-content glass are deposited on silicon by flame hydrolysis, a method originally developed for fibre preform fabrication. Silica channel waveguides are then formed by photolithographic pattern definition processes followed by reactive ion etching. This ‘high silica (HiS) technology’ offers the possibility of integrating a number of passive functions on a single silicon chip, as well as the possibility of the hybrid integration of both active and passive devices on silicon. This paper reviews the NTT HiS technology and its application to integrated-optic components such as optical beam splitters, optical switches, wavelength-division multi/demultiplexers and optical frequency-division multi/demultiplexers. The clear and simple waveguide structures produced by the HiS technology make it possible to design and fabricate these components with high precision and excellent reproducibility.

Silica waveguides on silicon and their application to integrated-optic components

The transmission characteristics of analogue video signals are investigated by using semiconductor laser diodes. It is shown that the linearity degradation due to speckle noise depends on the optical-fibre types adopted. Based on this investigation, transmission over 32 km is carried out by using a 1·3 μm laser diode and single-mode fibres, with 46 dB unweighted s.n.r.

Analogue baseband TV transmission experiments using semiconductor laser diodes

PURPOSE:To obtain a wave coupling and branching filter which does not increase in scale much even if the number of channels increases, by composing the device of a concave or cylindrical diffraction grating. CONSTITUTION:This sevice has an optical filter, the 1st and 2nd concave diffraction gratings 30 and 31 provided corresponding to two wavelength bands separated by the optical filter, optical filter 10 for transmission and optical fibers 34 for composite wave input coupling optically with the optical filter and the 1st concave diffraction grating 30, and optical fibers 1 and 2 for branched wave output coupling optically with the 2nd concave diffraction grating 31. Then, the branching of lights lambda1 and lambda2 from fiber 10 to fibers 1 and 2 and the coupling of lights lambda3 and lambda4 from fibers 3 and 4 with the optical fiber for transmission are performed simultaneously.

Optical wave coupling and branching filter

The letter describes the experimental performance of a 1×2 optical switch using a new type of pentagonal prism. The proposed pentagonal prism is a glass block consisting of a pentagonal pole with two roof prisms on each side. The insertion loss and repeatability were estimated to be less than 0.76 dB and 0.15 dB without reflection losses, respectively.

1×2 optical switch using new type of pentagonal prism

Differential phase distortion of the light-emitting diode is measured and analysed. An effective technique is proposed to compensate the d.p. distortion. An experimental result shows that 2.8° d.p. distortion has been reduced to within 1°.

Nonlinear phase distortion and its compensation in l.e.d. direct modulation

PURPOSE:To retrieve a failed point in a short time even if the number of terminal stations is increased and to complete the loop back, by performing simultaneous folding without checking the sequential loop back and releasing the folding. CONSTITUTION:In taking a terminal station 113 as an example, a reception section receives a signal from a terminal station 114, and the reception signal is given to the next terminal station 112 via a transmission line 210 from a transmission section. Sumultaneously, the receoption signal of the reception section is folded from the transmission section through a transmission line 220. After a prescribed time, a centralized monitor station 110 instructs the release of folding to each terminal station. Terminal stations 111-115 receive a control signal from the line 210 and terminal stations 117, 116 receive a control signal from the line 220. The terminal stations 111-114 and 117 receiving the signals from both the lines 210, 220 release the folding and the terminal stations 115, 116 receiving the signal from one of the lines only keep the folding.

Koichi Asatani

Papers

Analogue baseband TV transmission experiments using semiconductor laser diodes

Optical wave coupling and branching filter

1×2 optical switch using new type of pentagonal prism

Nonlinear phase distortion and its compensation in l.e.d. direct modulation

Folding control method of loop transmission system