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.

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SynopsisProbes in which the usual connecting leads to the detector have been eliminated have been constructed for measuring the intensity of an electromagnetic field. The new devices are modulated reradiating or scattering antennas that consist of either a small dipole (for measuring the electric field) or a small shielded loop (for measuring the magnetic field) centre-loaded with a photocell illuminated by a chopped beam of light. The modulated scattered signal from the probe is proportional either to the component of the E-field which is parallel to the axis of the dipole, or to the component of the H-field which is perpendicular to the plane of the shielded loop. The scattered signal is received by an additional antenna or by the same antenna as is used for transmission. The received signal is amplified by a lock-in amplifier.The same principle has also been applied to the measurement of the distribution of current along an antenna of arbitrary shape. This was accomplished by sliding a small shielded-loop probe, centre-loaded with a photocell, along the antenna. A very small and constant gap was maintained between the probe and the antenna. The modulation factor of the scattered signal was determined from the measured instantaneous impedance of the photocell.Both the near-field pattern of a A/2 dipole antenna and the distribution of current along the antenna as measured with these optical probes are in general agreement with theory. The properties of several other types of probes based on the same principle were also explored. List of symbolsa = radius of the shielded-loop probe B{f) = time-dependent magnetic flux intensity E\(x, y, z) = electric field intensity at (x, y, z), set by I el E D = electric field intensity associated with dipolemode potential H x (x, y, z) -magnetic field intensity at (JC, y, z) set by I eX •20",(x, y, z) = amplitude and space variation of H x (x, y, z) H [av = average of the H x (x, y, z) over the area of the loop y£\ ao = average of the 2^x{x, y, z) over the area of the loop H D {x, y, z) = space variation component of H x (x, y, z) HQ = ^-component of magnetic field with respect to the co-ordinate axis along the antenna Heao = average of H e h e = complex effective height of the probe of length h I eX -impressed current on the antenna I 2 = current through the load Z L2 I e2 = impressed current on the probeI c -conduction current on the antenna . I r = current of the reflected signal due to V 2 J dr = back-scattered signal received by the antenna from the photocell when it is not illuminated I lr = back-scattered signal received by the antenna from the photocell when it is illuminated J r -back-scattered signal from the shielded-loop probe used as an H probe A / r = difference in the back-scattered signal between when the shielded-loop probe is illuminated and when it is not K r = back-scattered signal from the shielded-loop probe used as a current probe / = closed contour encircling the antenna in questionPaper 4285 E, first received 4th Januarv and in revised form 8th April 19...

A new method for the recording of a microwave field using a moiré interference pattern is presented. The moiré interference pattern was used to map the thermal expansion of a microwave absorbing slab when irradiated by a microwave field. The technique was evaluated by applying it to the recording of a number of different microwave holograms. The moiré recording method is found to be relatively sensitive and usable to produce holographic images of good quality.