Abstract: A microbend-sensitive optical fiber is embedded in a thin pliable padding and laid under an area to be protected. An amplitude-modulated optical light beam is launched into one end of the fiber. The light beam is recovered from the other end of the optical fiber. The angular phase shift between the launched light beam and the recovered light beam is continuously measured and sampled at desired sample intervals. A change in the measured phase shift between any two sequential sample intervals is indicative of the presence of an intruding entity. The magnitude of the phase shift is a function of the mass of the entity. The pattern of repetitive phase shift differences as a function of time provides an estimate of the dynamic characteristics of the intruding entity.

Abstract: A data signal and a reference signal are multiplexed into a fiber optic communications link for transmission from a first secure location to a seond location. A replica of the reference signal is transmitted from the first location to the second location over a separate communication channel. At the second location, the angular phase difference between the reference signal and the replica thereof is continuously monitored. If the angular phase difference departs significantly from a specified value, an alarm is set as a warning that the fiber optic communications link has been compromised.

Abstract: A connector assembly comprises a female connector having a protruding portion extending from one end and with one or more sockets therein and a male connector having one or more pins for being received in a different one of the sockets and a retractable pin shield member in which the pins are recessed when the shield member is in a forward position. The pin shield member includes a cavity for receiving the protruding portion of the female connector and as the connectors are progressively engaged the protruding portion is urged against the shield member causing it to become gradually retracted and exposing the pins which are then progressively received in the sockets of the female connector.