An optical time domain reflectometer that injects at least two complementary code sequences into an optical fiber and detects the return signal produced by each of these code sequences. These return signals are processed to extract the function h.sub.k that is equal to the response function for the fiber when a single pulse is injected into the fiber. This processing utilizes a correlation scheme that has no sidelobe distortion. Various combinations of Golay codes are suitable for use as the complementary codes.
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of application Ser. No. 07,139, filed 02/06/89, now abandoned, which is a continuation of application Ser. No. 935,661, filed 11/26/86, now abandoned.
An optical time domain reflectometry method and apparatus that employs Hadamard transforms to increase the signal-to-noise ratio. A sequence of N pulses of light corresponding to a Hadamard derived code are launched down a fiber optic cable for each of N such codes. Selected combinations of pulses of reflected light are transformed by a Hadamard derived matrix to a set of equations that are solved simultaneously to determine the power reflected from each of N points. Where a Hadamard code is used the average mean square error is reduced by a factor of 1/N. Where a simplex code is employed the average mean square error is reduced by a factor of 4N/(1+N).sup.2. In addition, N measurements of the power reflected at each point are computed and averaged.
A method for examining a propagative medium, such as a signal transmission cable, that requires the acquisition and examination of a minimum number of data points to determine the presence of an anomaly in the medium. When an anomaly is detected, its characteristics, such as loation, type and amount of loss are determined. The characteristics are then displayed. If the anomaly is a reflectionless loss, the region containing the anomaly is examined repetitively to determine its location and to improve the accuracy of its location measurement. With each successive level of examination, additional samples are collected within the region. The new samples are combined with the existing samples to reduce random noise in the data. Through this method the location of the anomaly is re-determined with greater accuracy.
The present invention relates to a single ended line testing method for qualifying an electrically conducting line. This method includes the steps of sending a plurality of excitation signals from a first end of the line towards a second end of the line and before the sending of this plurality of excitation signals, randomizing each excitation signal of the plurality of excitation signals. Subsequently, measurements are performed, at the first end of the line, of each reflection of the plurality of excitation signals sent towards the second end of the line. Then an inverse randomization on each of the measurements of reflections is performed which is succeeded by determining an average of all the measurements of reflections of the excitation signals. Finally, from the average a qualification of the electrically conducting line is determined.
A time domain reflectometer transmission line interface includes a pulse driver for generating a transmitted pulse signal. A coupling transformer coupled to the pulse driver couples the transmitted pulse signal to a transmission line and receives a reflected pulse signal from the transmission line. A differential amplifier is coupled to the pulse driver and to the coupling transformer through a network configured such that said transmitted pulse is balanced at the inverting and non-inverting inputs of the differential amplifier.
Incident signal beam pulses are transmitted by an on-state region, and an optical path for the signal beam pulses is spatially switched in an optical switch. Signal beam pulses transmitted by the on-state region of the optical switch are detected at a pixel corresponding to a transmitting region of a photo-detector equipped with a plurality of pixels. A timing computation unit acquires position information of a pixel at which a predetermined signal beam pulse has been detected, on the basis of a result of the detection conducted by the photo-detector, and computes timing of arrival of a predetermined signal beam pulse at the optical switch on the basis of the position information of the pixel and time when a region corresponding to the pixel is brought to an on-state.
