Abstract: Various embodiments of an apparatus for measuring a length of an optical fiber are provided. In one embodiment, a method of testing an optical fiber comprises measuring a length of the optical fiber based on a time of flight of an optical pulse launched through the optical fiber from a first optical time domain reflectometer (OTDR) system and received by a second OTDR system; and controlling the first and the second OTDR systems to characterize the optical fiber based on the measured length of the optical fiber. In this way, defects and other physical characteristics of an optical fiber may be accurately determined.

Abstract: A passive optical element defining an optical propagation path is tested by coupling a buffer fiber between an input of the propagation path and an optical time domain reflectometer. The OTDR launches optical radiation into the buffer fiber via one end thereof, measures power level of return light received at the OTDR via the buffer fiber, and creates an OTDR signature representing power level of return light as a function of distance from the end of the buffer fiber. The OTDR selects a first marker point by applying data reduction to a portion of a segment of the OTDR signature corresponding to the buffer fiber, selects a second marker point downstream of the input of the optical propagation path, and calculates a first power difference value as difference between a power level at the first marker point and a power level at the second marker point.

Abstract: A passive optical element defining an optical propagation path is tested by coupling a first end of a first buffer fiber to an input of the optical propagation path and coupling a second end of the buffer fiber to an optical time domain reflectometer (OTDR). The OTDR launches optical radiation into the first buffer fiber via the second end thereof, measures power level of return light received at the OTDR via the second end of the first buffer fiber, and creates a first OTDR signature representing power level of return light as a function of distance from the second end of the first buffer fiber. The OTDR selects a first marker point by applying data reduction to at least a portion of a segment of the first OTDR signature corresponding to the first buffer fiber, selects a second marker point downstream of the input of the optical propagation path, and calculates a first power difference value as difference between a power level at the first marker point and a power level at the second marker point.

Abstract: A precision aircraft landing system comprising at least four receivers which are located at different predetermined positions. Each receiver includes a precision timer for measuring the timer interval between the receiver's detection of an interrogation signal and a reply signal from a transponder onboard the aircraft. The system also includes a central processing unit (computer) at a base station which collects the time measurements from the receivers, and calculates the location of the aircraft. Because more than three independent measurements are used, the base station can compute not only the three-dimensional coordinates of the aircraft, but also the transponder reply time. Preferably estimation filtering calculations, such as Kalman filtering, are used to improve the accuracy. The aircraft's position is compared with a mathematical description of a desired approach path, and the position error is then communicated to the aircraft.