Abstract: In terminating an optical element, such as an optical fiber, a housing includes an entry aperture for the fiber and terminating apparatus defining mutually discontinuous surfaces in abutting relation to the fiber end face, the surfaces being spaced from one another in a circular locus having a diameter not greater than the diameter of the fiber.

Abstract: An optical modulator has two closely spaced optical fibre end surfaces, the optical path length between which can be altered in response to an applied modulating signal. Light is partially reflected from the two surfaces, the two beams interfering according to their phase difference. Alternatively the modulator may be operated in a transmissive mode. To obtain modulation either the refractive index of material between the fibre end surfaces is altered or one of the fibres is longitudinally vibrated. A method of operating a modulator in a wavelength selective mode is also described.

Abstract: The invention uses the phenomenon of self-coupling by which light emitted from, and reflected back into, a laser produces self-coupling with consequent change in lasing activity. The invention proposes using the laser as a detector by inducing the self-coupling and monitoring the change in lasing activity. The invention enables fibre length, and the position of a reflective discontinuity in a fibre to be determined without the sophisticated and costly equipment required by current optical time domain reflectometry techniques.