The concept of differential phase is proposed for accurate target location by a step frequency CW sonar. By use of the differential phase, the locations can be determined with distance accuracy much shorter than the wavelength of the sound wave. The basic idea and experimental result are described.

A step frequency method (SFM) is proposed as a new scheme for an optical fiber fault locator. The principle of operation and significant features of the method are described. The feasibility was demonstrated by detecting the discontinuities in a 10-km long multimode fiber using the 830-nm wavelength. The results demonstrate the feasibility of using the SFM in practical fiber optical networks.

No abstract

No abstract

This paper deals with a new formulation for the diffraction of a plane wave by a periodic grating. As a simple example, the diffraction of a transverse magnetic wave by a perfectly conductive periodic array of rectangular grooves is discussed. On the basis of a shadow hypothesis such that no diffraction takes place and only the reflection occurs with the reflection coefficient −1 at a low grazing limit of incident angle, this paper proposes the scattering factor as a new concept. In terms of the scattering factor, several new formulas on the diffraction amplitude, the diffraction efficiency and the optical theorem are obtained. It is newly found that the scattering factor is an even function due to the reciprocity. The diffraction efficiency is defined for a propagating incident wave as well as an evanescent incident wave. Then, it is theoretically found that the 0th order diffraction efficiency becomes unity and any other order diffraction efficiencies vanish when a real angle of incidence becomes low grazing. Numerical examples of the scattering factor and diffraction efficiency are illustrated in figures.