Optical time-domain reflectometry (OTDR) is a widespread and commercially successful technique for performing several types of measurements on fiber-optic networks and components. An alternative method, also in widespread use, is optical frequency-domain reflectometry (OFDR). This technique uses cw light, which is either stepped or swept continuously in frequency. The reflected or backscattered light, as a function of the frequency, can yield information about the system under test that is equivalent to that obtained by OTDR. In OFDR, signal detection can occur in a much smaller bandwidth than in the time-domain case, for an equivalent resolution. Thus, frequency-domain techniques hold out the possibility of reduced noise and superior dynamic range.