Signal averaging for optical time domain relectometers

Claim 2

In an optical time domain reflectometer which includes (a) a laser for firing signals into a fiber strand, (b) means for receiving and measuring continuously varying returning signals representing reflection values during a waveform sweep along the fiber strand, and (c) a computer controller, means for extracting useful waveform-determining values from the noise in which they are embedded, comprising: a comparator which receives two analog signals as first and second inputs, and outputs a 1 or 0 signal indicating which of the received signals is higher; means for directing the varying analog voltage values from the receiving/measuring means into the comparator as its first input signal; means for providing a large number of comparison voltage values, which are varied so as to be substantially evenly distributed in the range of possible values; each such comparison signal providing the second input signal to the comparator during a waveform sweep representing the length of the fiber strand; means for providing a series of time-bins, each of which represents a certain time, and thus a certain distance along the length of the fiber strand; clocking means for determining the frequency of output signals from the comparator; and means for causing each time-bin to accumulate the comparator output signals from a given segment of the waveform during successive waveform sweeps caused by successive laser firings.

Claim 3

The apparatus of claim 1 in which each time-bin comprises: multiple registers for temporarily storing successive output signals from the comparator; multiple binary counters, each connected to one of the registers; and clocking means for simultaneously transferring the stored information from each register into its counter after each waveform sweep.

Claim 4

The apparatus of claim 2 which also comprises: means controlled by the computer controller for interrogating each counter after a desired number of successive laser firings/waveform sweeps have been accomplished; and means responsive to the interrogating means for transferring to the computer controller, from each counter in succession, the word accumulated therein representing a binary number obtained by co-adding the values transferred to the counter from its connected register during the desired number of laser firings/waveform sweeps.

Claim 5

The apparatus of claim 1 in which: a random number generator is used to supply the comparison voltage values to the second input of the comparator.

Claim 6

The apparatus of claim 1 in which: an automatically varying ordered series of values is used to supply comparison voltage values to the second input of the comparator.

Claim 7

The apparatus of claim 2 which also comprises: one or more integrated circuit chips, each of which contains a large number of counters, and an equal number of shift register stages.

Claim 8

The apparatus of claim 2 in which: the clocking means which times each output signal from the comparator also times the change from one temporary storage register to the next.

Claim 9

The apparatus of claim 7 which also comprises: means for changing the frequency of the comparator/register clock, in order to change the resolution, in time and distance, of the waveform digital signal intervals.

Claim 10

In an optical time domain reflectometer which includes (a) a laser for firing signals into a fiber strand, (b) means for receiving and measuring continuously varying returning signals representing reflection values during a waveform sweep along the fiber strand, and (c) a computer controller, a method for extracting useful waveform-determining values from the noise in which they are embedded, comprising: directing to the first input of a comparator an analog voltage signal representing the values returning from the fiber strand during a given waveform sweep; directing to the second input of the comparator an analog voltage signal selected from a large number of signal values which are substantially evenly distributed in the range of possible values; maintaining the same signal at the second input of the comparator during one complete waveform sweep; outputting from the comparator at clocked intervals a digital signal indicating which of its input signals is instantaneously higher; storing each digital signal from the comparator in a different storage register stage; clocking the comparator output signals and the storage register stage inputs at a frequency which provides the desired waveform resolution; transferring the signal stored in each register stage to a separate counter at the end of a waveform sweep; changing the signal at the second input of the comparator; repeating during the next waveform sweep the steps taken during the previous waveform sweep; adding the values from successive sweeps into the respective counters; and repeating the foregoing process the number of times needed to obtain a desired signal-to-noise ratio in the recorded waveform.

Claim 11

In an optical time domain reflectometer which includes (a) a laser for firing signals into a fiber strand, (b) means for receiving and measuring continuously varying returning signals representing reflection values during a waveform sweep along the fiber strand, and (c) a computer controller, a method for extracting useful waveform-determining values from the noise in which they are embedded, comprising: directing to the first input of a comparator an analog voltage signal representing the values returning from the fiber strand during a given waveform sweep; directing to the second input of the comparator an analog voltage signal selected from a large number of signal values which are substantially evenly distributed in the range of possible values; maintaining the same signal at the second input of the comparator during one complete waveform sweep; outputting from the comparator at clocked intervals a digital signal indicating which of its input signals is instantaneously higher; storing each digital signal from the comparator in a different storage register stage; clocking the comparator output signals and the storage register stage inputs at a frequency which provides the desired waveform resolution; transferring the signal stored in each register stage to a separate counter at the end of a waveform sweep; changing the signal at the second input of the comparator; repeating during the next waveform sweep the steps taken during the previous waveform sweep; adding the values from successive sweeps into the respective counters; and repeating the foregoing process the number of times needed to obtain a desired signal-to-noise ratio in the recorded waveform.