JPH04132931A - Optical fiber failure point position inspector - Google Patents

Abstract

PURPOSE:To enable a device to be compact and inexpensive with a simple circuit configuration and at the same time distance resolution to be improved by feeding a signal to a time interval measuring equipment only when the signal exceeding a certain level is detected by a comparator. CONSTITUTION:A pulse signal from a pulse light source 1 is introduced to an optical fiber to be measured 2 through an optical coupler 3 and an optical connector 4. Then, reflection light from the optical fiber 2 is converted to electrical signal 5. Then the converted output is input to an analog signal processing circuit 20 and is corrected to a waveform signal on a straight line base without any change with time. Then, the output waveform is compared with a reference voltage from a controller 22 by a comparator 21. The comparator 21 feeds the signal to a time interval measuring equipment 23 only when a signal exceeding the reference voltage is detected. A trigger for generating pulse waveforms from the controller 22 is input to the measuring equipment 23 for generating a reference clock and a count value when signal from the comparator 21 is entered is stored 7. Then, the stored data 7 is displayed 9 through the controller 22.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an optical fiber fault position inspection machine (OTDR) that detects the position of a fault point occurring in an optical fiber, and in particular, an OTDR with improved distance resolution. Regarding.

(Prior Art) OTDR is an inspection machine used for locating break points, discontinuity points, etc. of optical fibers. Conventionally, even in coaxial cables, failure points have been searched for using the pulse method. When a pulse wave is propagated from one end of a coaxial cable, if there is a discontinuity point, reflection occurs due to impedance mismatch, and the reflected pulse wave returns to the input end. In the case of complete rupture, approximately 100% reflection occurs, and the position of the rupture point can be measured from the time difference between the incident pulse and the reflected pulse. In the case of optical fibers, the pulse method is similarly used to detect the break point, but the reflectance at the break point is based on the ideal break shape tv! Even in the case of (mirror-like fracture perpendicular to the fiber axis), it is only about 4%. Depending on the state of the break, there are cases where almost no reflected waves are generated, and in this case, the point of failure in the optical fiber can be located by observing the backscattered light.

(Problems to be Solved by the Invention) Incidentally, in order to efficiently perform maintenance for optical fiber failures, it is necessary to improve the distance resolution. 0T
The distance resolution of DR corresponds to the time resolution in the measurement system. Therefore, in order to increase the distance resolution, a measuring instrument with high time resolution is required.
There is an example of using a digital sampling oscilloscope having two bands, but the digital sampling oscilloscope is very expensive and large, which is an obstacle to miniaturization and cost reduction of the device.

The basic circuit configuration of a conventional 0TDR is shown in FIG. In the figure, reference numeral 1 denotes a pulse light source that generates optical pulses to be sent to the optical fiber under test 2. The generated optical pulses are introduced into the optical fiber under test 2 by an optical coupler 3 via an optical connector 4, and are then transmitted from the failure point. The reflected light enters the optical coupler 3 via the optical connector 4 and is introduced into the photoelectric converter 5. Photoelectric converter 5
converts the reflected light into an electrical signal, and this electrical signal is converted into a digital signal by the AD converter 6 and stored in the memory 7. The controller 8 controls the timing of light generation from the pulsed light source 1, supplies a clock for sampling to the AD converter 6, processes data stored in the memory 7, and causes the display 9 to display the data. ing. The output waveform of the photoelectric converter 5 is as shown in FIG. This waveform is composed of backscattered light 11 and reflected light 12 that attenuate in proportion to time, that is, in proportion to propagation distance. The AD converter 6 samples at sampling intervals Δt and obtains n pieces of data (n-T/Δt) corresponding to the measurement range. The data stored in the memory 7 is all the amplitude data and time data of this waveform, and requires a huge amount of memory. The distance resolution in this 0TDR is determined by the sampling period of the AD converter,
The sampling frequency of the AD converter is about 300MH2 or a limit, and the speed of light in the optical fiber is 200.000k.
If it is m/s, the distance resolution will be about 33 cm, making it impossible to obtain a good distance resolution.

The present invention has been made in view of the above points, and its purpose is to realize an 0TDR that has highly accurate distance resolution, has a simplified circuit configuration, and can be made smaller and lower in price. It is in.

(Means for Solving the Problems) The present invention solves the above-mentioned problems by injecting pulsed light into an optical fiber to be measured, reflecting the pulsed light at a fault point of the optical fiber to be measured, and returning to the input end. An optical fiber fault position inspection machine that detects the position of a fault point in the optical fiber under test includes a photoelectric converter that converts reflected light from the fault point into an electrical signal, and an exponentially decreasing number of fault points on the optical fiber to be measured. an analog signal processing circuit that converts signal light from an optical fiber into a signal on a linear base; a comparator that compares the reflected light signal with an arbitrarily settable reference voltage and outputs a signal that exceeds the reference voltage; The present invention is characterized by comprising a time interval measuring device that measures the time interval from the time when an optical signal is generated to the time when a signal exceeding the reference voltage is inputted in order to detect the position of a fault point.

(Function) The reflected light from the optical fiber to be measured is converted into an electrical signal by a photoelectric converter, and corrected into a linear-based signal in an analog signal processing circuit. These signals are compared in a comparator and a signal exceeding the reference voltage is output, and a time interval measuring device measures the time from generation of the pulsed light to measure the distance to the reflection point position.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In the figure, parts equivalent to those in FIG. 3 are given the same reference numerals. In the figure, 20 removes low frequency components of the input signal, and since the amplitude of reflected light decreases exponentially with distance as shown in Figure 4, it is corrected to remove the low frequency component of the input signal. An analog signal processing circuit 21 converts the waveform into a waveform on a linear base shown in FIG. 2, which compares the output of the analog signal processing circuit 20 with a reference voltage given from the controller 22, and outputs only signals exceeding the reference voltage. It is a comparator that The controller 22 controls the pulse light generation timing of the pulsed light source 1 and the timing of starting time measurement of the time interval measuring device 23, processes the data stored in the memory 7, and sends data to the comparator 21 for comparison. Supply reference voltage. The time interval measuring device 23 is composed of a reference clock generator and a counter.The reference clock generator generates a clock according to a control signal from the controller 22, and the counter counts the number of clocks and outputs a clock from the comparator 21. Outputs the count value up to the point when the signal is input.
Next, the operation of the embodiment configured as described above will be explained.

Pulsed light emitted from the pulsed light source 1 is introduced into the optical fiber 2 to be measured via the optical connector 4 by the optical coupler 3 . The reflected light corresponding to the fault point from the optical fiber 2 to be measured passes through the optical connector 4, is guided through the optical coupler 3 to the photoelectric converter 5, and is converted into an electrical signal.

The output of the photoelectric converter 5 is input to an analog signal processing circuit 20, where low frequency components are removed, and a signal waveform that decreases exponentially in proportion to the distance changes over time as shown in FIG. Corrected to a waveform signal on a straight line base without any

The output waveform shown in FIG. 2 is input to a comparator 21 and compared with a reference voltage from a controller 22. Comparator 2
1 inputs the signal to the time interval measuring device 23 only when a signal exceeding the reference voltage is detected. The time interval measuring device 23 receives a trigger for pulse wave generation from the controller 22 and generates a reference clock, and the counter starts counting this clock from the moment the trigger is input. The count value at the time when the signal from is input is stored in the memory 7. The data stored in the memory 7 is processed by the controller 22 and displayed on the display 9.

In the manner described above, it is possible to sample the distance of reflected light exceeding the reference value. Furthermore, by changing the base voltage, the detection level of the magnitude of the fault can be determined.

As explained above, according to this embodiment, the comparator 21 extracts only the signal of a certain level or higher, and the time of the signal from the time of pulsed light incidence is determined by counting the clock, so the time is measured. Accuracy is determined by the period of the clock that the counter can count. The clock frequency that this counter can process is several tens of GH
It can reach 2 to several hundred GHz2, and compared to the frequency of about 300 MHz of the previously mentioned AD converter, it is 100 to 10 GHz.
Since the frequency is multiplied by about 00 times, the time accuracy, that is, the distance accuracy is also multiplied by about 100 to 1000 times.

In addition, the data stored in the memory is not only the time data but also the amplitude data of all signals in the circuit shown in FIG. Since only time data is required, the memory may be small and simple.

Note that the present invention is not limited to the above embodiments. In combination with the conventional circuit shown in FIG. 3, the conventional 0TDR detects the backscattered light 11 with the waveform shown in FIG. 4, and measures the propagation loss of the optical fiber 2 to be measured.
It is also possible to use DR to perform a fault point location inspection that requires high resolution.

In the above, this embodiment has been explained with respect to failures that clearly appear due to reflected light, but within the dynamic range of the photoelectric converter, backscattered light can also be used for failure points that do not involve reflected light. It is possible to determine the location of a fault point by detecting consecutive points.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to realize an 0TDR with a highly accurate distance resolution that enables miniaturization and low cost with a simplified circuit configuration. It can be done, and the practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a block diagram of a conventional 0TDR, and FIG. 4 is a diagram of a signal waveform of the circuit shown in FIG. 3 after photoelectric conversion. 1... Pulse light source 2... Optical fiber to be measured 3.
...Optical coupler 5...Photoelectric converter 11...Backscattered light 12...Reflected light 20...Analog signal processing circuit 21...Comparator 22...Controller 23.
・・Time interval measuring device

Claims (1)

[Scope of Claims] Pulsed light is input into the optical fiber to be measured (2), and the pulsed light reflected at the fault point of the optical fiber to be measured (2) and returned to the input end is detected to detect the pulsed light to be measured. Optical fiber fault location inspection equipment that measures the location of fault points in optical fibers uses a photoelectric converter (which converts the reflected light from the fault point into an electrical signal).
5), an analog signal processing circuit (20) that converts the signal light from the optical fiber under test (2) that decreases exponentially into a signal on a linear basis, a reference voltage that can be set arbitrarily, and the reflected light. A comparator (21) that compares the signal with the reference voltage and outputs a signal that exceeds the reference voltage; and a comparator (21) that measures the time interval from the time when the optical signal is generated to the time when the signal exceeding the reference voltage is input in order to detect the location of the fault point. 1. An optical fiber fault position inspection device comprising: a time interval measuring device (23).