Optical time domain reflectometry is a powerful tool for analyzing and characterizing passive optical circuits containing optical fibers, connectors, splicers, etc. Optical time domain reflectometry determines the loss and reflection properties of each element in the optical circuit by attaching an instrument to either end of the circuit (replacing either the transmitter or receiver) without disturbing the passive optical circuit. Optical time domain reflectometry sends a short pulse of light down an optical circuit and displays the amplitude of the reflected and scattered light as a function of time and distance. Fortunately, optical fiber is easily identified by optical time domain reflectometry because of Rayleigh scattering that results from small non-uniformity in the refractive index of glass or other media. Large, abrupt discontinuities in an optical path can be determined due to Fresnel reflections. Thus, it is possible to characterize each element as reflective or lossy or both, and to remotely measure the reflectance and loss of each element. In addition, optical time domain reflectometry is utilized to detect breaks in optical circuits.
Unfortunately, it is well known that optical time domain reflectometry cannot be utilized in optical circuits which contain an optical splitter. Utilizing techniques of the prior art, optical time domain reflectometry instrument (OTDR) 101 of FIG. 1 is incapable of measuring the optical circuit consisting of optical elements 102 through 111. The reason is that when the pulse of light is transmitted through splitter 103, splitter 103 splits the light into two halves. One-half the light goes through optical element 104 through 107 and the the other half of the light goes through optical elements 108 through 111. When the two light pulses reflect back from receiver 107 and receiver 111, OTDR 101 cannot distinguish which optical subcircuit is producing which portions of the returning light. Furthermore, if there are unknown numbers of optical splitters, it is not possible to determine how many optical subcircuits exist through use of the prior art optical time domain reflectometry techniques.