A method for identifying optical features along the length of a fiber optic cable in response to injecting a pulse of light into the fiber optic cable and collecting data corresponding to signals which are reflected, the method comprising the steps of: identifying potential optical features in the data according to a first set of parameters; constructing a pattern for selecting optical features from said potential optical features; fitting said pattern to said optical features; determining a position along the cable for each of said optical features; and computing a reflectance/loss level for each of said optical features.

A method for characterizing an event in acquired digital data is described where the event has a known shape and a pattern having amplitude and location coefficients is applied to the data for determining a best fit between the data and the pattern as a function of a peak RMS value. The derived RMS value is compared to a threshold value for verifying the existence of the event. The event is characterized as to amplitude and location using the amplitude and location coefficients of the pattern. Such a method is useful in characterizing non-reflective events in acquired optical time domain reflectometry data.

An optical time domain reflectometer (OTDR) is treated as a linear shift-invariant system modeled as a ideal resistive-capacitive network. A step pulse is applied to a fiber under test and the return optical energy from the fiber under test is converted to signal samples representative of the return optical energy. The signal samples are processed in a controller for producing step impulse stimulus signal samples corrected for the bandwidth limited system response of the optical time domain reflectometer by modeling the OTDR as an exponential linear shift-invariant system that includes the optical transmitter, optical receiver and the fiber under test. The controller takes the time derivative of the step impulse stimulus signal samples for generating signal samples representative of the impulse response for the fiber under test. Standard OTDR interrogating pulses may be used to produce signal samples representing the ideal impulse response with bandwidth correction over the region of the pulsewidth for improved event dead zone accuracy.

An optical time domain reflectometer acquires and displays waveform data as a waveform trace on a display device having a viewport defined by a start distance and an end distance using waveform data segments having data points where each waveform segment is acquired using different pulsewidth and sample spacing and different starting distance. A processor sets a horizontal pixel skip value and a horizontal distance skip value for each waveform segment and calculates a horizontal distance per pixel value for the display area as a function of dividing the distance between the viewport start distance and the viewport end distance by the number of horizontal pixels in the display area. Each horizontal pixel is mapped to a distance by setting an initial pixel count to zero and sequentially adding the horizontal pixel skip value to the pervious pixel count and setting an initial horizontal distance value to the start distance of the viewport and sequentially adding the horizontal distance skip value to the previous horizontal distance value. The distance values for the horizontal pixels are correlated to amplitude values of the data points of the waveform segment using an index into the array of waveform data points related to distance. The amplitude values of the acquired data are mapped to appropriate vertical pixels associated with the horizontal pixels to produce a bit representation of the waveform trace, which is displayed on the display device.

A multimode optical time domain reflectometer has first and second wavelength optical transmitters for launching optical pulses into a fiber under test and optical receivers responsive to the respective wavelengths for converting the optical return signals from the test filer into electrical signals for acquiring waveform data representative of the optical return signals at the respective wavelengths. A processor receives the waveform data and determines a difference in fiber slopes between the optical return signal at the respective wavelengths and adds the fiber slope difference to the waveform data of the second optical return signal for producing composite waveform data having a uniform fiber slope for the waveform data acquired at the first and second wavelengths. A multimode optical time domain reflectometer of this design provides improved two point resolution for 1310 nm testing of multimode optical fiber.