Abstract: An optical time domain reflectometer suitable for determining its front panel insertion loss comprises a four-port coupler having first and second ports connected to a light source and an optical detector, respectively, and third and fourth ports connected to a front panel connector and a reference reflector, respectively. In use, a fiber-under-test is connected to the front panel connector. The coupler splits light from the light source between the front panel connector and the reference reflector and couples light returning from the front panel connector and reflector to the detector. The optical path between the front panel connector and the coupler is longer than the optical path between the reference reflector and the coupler by such a distance that a Fresnel reflection pulse from the reference reflector, produced by a pulse emitted by the light source, will be received by the detector before a corresponding reflection pulse returned from the front panel connector.

Abstract: Attenuation of an optical fiber is measured by transmitting an optical signal having a predetermined wavelength to the fiber, and FSK modulating the optical signal with information identifying the wavelength and transmitted power of the optical signal. At a receiver, the optical signal is detected and the information is recovered by demodulation. Wavelength-dependent sensitivity information for the detector is read from a store in dependence upon the wavelength information and used to control the gain of an amplifier for amplifying a subsequently transmitted continuous wave optical signal used for attenuation measurement. The received power level of this optical signal is converted into a digital value and used with the transmitted power information to determine the fiber attenuation at the predetermined wavelength.