JPH03285129A - Processing method for receiving signal of optical fiber back-scattered light - Google Patents

Abstract

PURPOSE:To improve the resolving power in a length direction to a large extent by adding the differential signal obtained by applying time differential processing to the temp. distribution signal calculated from the intensity of scattered light to the delay signal obtained by delaying the differential signal by the time equal to the pulse width of incident light. CONSTITUTION:A light receiving circuit is constituted of a differentiation circuit 8, an adder 9 and a delay circuit 10. Back scattering light is converted to an electric signal which is, in turn, subjected to averaging processing to obtain a noise removed input signal and this signal is differentiated timewise by the differentiation circuit to be deformed. Next, the differential signal is added to the signal delayed by the delay circuit 10 generating the delay corresponding to the width (t) of a sent-out light pulse. By adding the differential signal to the delay signal by the adder 9, the distortion of a waveform generated by the width of the sent-out light pulse is removed and the output signal 11 equal to temp. distribution to be calculated is obtained. Therefore, temp. distribution shorter than the width of the sent-out light pulse can be calculated and the resolving power in a length direction can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to temperature measurement using Raman scattered light generated in an optical fiber, and particularly to a method for processing received signals of optical fiber backscattered light.

[Prior Art] FIG. 3 is a block diagram when temperature measurement is performed using backscattered light of a light pulse.

The optical pulse 5 output from the pulse light source 1 is passed through the optical demultiplexer 3
is guided to the optical fiber 4 via.

On the other hand, the backscattered light generated in the optical fiber 4 is received and processed at the optical receiving port B2 via the optical demultiplexer 3.

Figure 4(a) shows the temperature distribution in the length direction of the optical fiber.
Figure (b) shows the light pulse output from the pulsed light source, and Figure 4 (fc) shows the backscattered light pulse obtained.The width t of the light pulse output from the pulsed light source is the resolution of the backscattered light pulse. Conventionally, the obtained backscattered light was directly converted into temperature.

[Problems to be Solved by the Invention] However, in order to increase the resolution in the longitudinal direction, it is necessary to reduce the width t of the optical pulse as much as possible. Since the output is as high as several 100 mW to several W, there is a limit to reducing the pulse width.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for processing received signals of optical fiber backscattered light, which eliminates the drawbacks of the prior art described above and can significantly improve the resolution in the longitudinal direction.

[Means for Solving the Problems] The signal processing method of the present invention is a device that measures temperature using Raman scattered light generated by a light pulse incident on an optical fiber. A differential signal obtained by subjecting the signal to time differential processing and a delayed signal obtained by delaying the differential signal by a time equal to the incident light V<the pulse width are added.

Effect: After being converted into an electrical signal, the input signal from which noise has been removed by averaging processing, etc. is differentiated with respect to time, and this differentiated signal is added to a delayed signal delayed by a time equal to the width of the incident light pulse. Waveform distortion caused by the width of the optical pulse is removed, thereby improving longitudinal resolution.

"Example code" Hereinafter, the present invention will be explained based on illustrated embodiments.

Similar to the conventional example shown in FIG. 3, the optical pulse 5 output from the pulsed light source 1 is guided to the optical fiber 4 via the optical demultiplexer 3. The backscattered light generated in the optical fiber 4 then passes through the optical demultiplexer 3 to the optical receiving circuit F! Received and processed by @2.

FIG. 1 shows a specific example of the improved signal processing circuit section in the optical receiving circuit 2, which is composed of a differentiating circuit 8, an adder 9, and a delay circuit 10. Reference numeral 7 indicates an input signal that has been converted into backscattered light or an electrical signal and has noise removed by averaging processing or the like, and 11 indicates an output signal with improved resolution in the length direction.

In the waveform diagram in Figure 2, (a) is the temperature distribution in the length direction, (b) is the transmitted optical pulse waveform, and (C) is the intensity of the backscattered light obtained from these directly converted into temperature distribution. That is, the input signal 7 in FIG.

The input signal 7 (FIG. 2(C)) is differentiated with respect to time by a differentiating circuit 8 and transformed as shown in FIG. 2(d).

Next, a signal delayed by a delay circuit 10 that generates a delay corresponding to the width t of the transmitted optical pulse (see FIG. 2(e)
) is added. In this way, the differential signal is sent to the adder 9
By adding the delayed signal <Figure 2 (e)> at
Waveform distortion caused by the width of the transmitted optical pulse is removed, and an output signal 11 equal to the desired temperature distribution (Fig. 2 (f)
)) can be obtained.

Therefore, it is possible to obtain a temperature distribution that is shorter than the width of the optical pulse to be sent out, and it is possible to improve the resolution in the longitudinal direction.

[Effects of the Invention] As described above, according to the present invention, waveform distortion caused by the width of the transmitted optical pulse can be removed, and a temperature distribution shorter than the width of the transmitted optical pulse can be obtained. The resolution in the length direction can be improved.

[Brief explanation of drawings]

FIG. 1 is a signal processing circuit diagram showing one embodiment of the present invention, and FIG.
The figure shows a waveform example showing the processing process in the embodiment of Figure 1, Figure 3 is a block diagram of a conventional temperature measurement using Raman scattered light generated in an optical fiber, and Figure 4 is a diagram of a conventional temperature measurement. It is a figure which shows the temperature distribution in the length direction in temperature measurement, and the temperature distribution calculated from the sending pulse waveform and the backscattered light intensity. In the figure, 1 is a pulsed light source, 2 is a receiving/processing circuit, 3 is an optical demultiplexer, 4 is an optical fiber, 5 is a transmitted optical pulse, 6 is a received backscattered light, and 7 is a backscattered light intensity 8 is a differential circuit, 9 is an adder, 10 is a delay circuit, and 11 is a signal whose resolution has been improved in the length direction.

Claims (1)

[Claims] 1. In a device that measures temperature using Raman scattered light generated by a light pulse incident on an optical fiber,
Receiving optical fiber backscattered light, characterized by adding a differential signal obtained by time differential processing to a temperature distribution signal obtained from scattered light intensity, and a delayed signal obtained by delaying the differential signal by a time equal to the incident light pulse width. Signal processing method.