JPH0647841U - BOTDA device for displaying far end points - Google Patents

Abstract

(57) [Summary] [Object] To provide a BOTDA device for preventing an error in far end position determination by displaying the far end position of an optical fiber 10 measured by the OTDR method together with a distortion measurement waveform of BOTDA. thing. In a BOTDA device adapted to convert an optical signal 13 into an electric signal and input the signal to a display 7 to display a distorted waveform of an optical fiber 10, an optical filter for controlling a transmission frequency of an optical filter 3. Timing control circuit 9B for switching the control circuit 9A and the optical filter control circuit 9A
And a bias circuit 8 for controlling the multiplication factor of the APD 4, and a recording circuit 9C for detecting the Rayleigh scattered light of the pulsed light and recording the far end position thereof, and the far end position of the optical fiber measured by the OTDR method. Is displayed simultaneously with the BOTDA distortion measurement waveform.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an apparatus for Brillouin optical time domain analysis (hereinafter referred to as BOTDA), and more particularly to an apparatus for BOTDA capable of displaying the far end point of an optical fiber to be measured.

[0002]

[Prior art]

 In BOTDA, in principle, it is displayed as if there is an optical fiber with a pulse width equivalent length beyond the far end of the optical fiber.

The configuration of a BOTDA device according to the related art will be described with reference to FIG. In FIG. 2, 1A and 1B are light sources, 2 is an optical coupler, 3 is an optical filter, 4 is an APD, 5A and 5B are amplifiers, 6 is an A / D converter, 7 is a display, 8 is a fixed bias circuit, 10 is an optical fiber to be measured. The light source 1A generates continuous light 11 and the light source 1B generates pulsed light 12. The BOTDA device is described in JP-A No. 2-6725.

In FIG. 2, continuous light 11 is incident on one end of the optical fiber 10, and pulsed light 12 is incident on the other end of the optical fiber 10 through the optical coupler 2. When the difference frequency between the continuous light 11 and the pulsed light 12 becomes equal to the Brillouin shift frequency, the Brillouin-amplified optical signal 13 passes through the optical filter 3 and an electric signal is taken out by the APD 4. The optical filter 3 is for removing Rayleigh scattered light of pulsed light. The electric signal is transmitted to the amplifiers 5A and 5B, converted by the A / D converter 6, and the loss waveform of the optical fiber 10 is measured. The bias circuit 8 is for controlling the multiplication factor of the APD 4, and the distorted waveform of the optical fiber 10 is displayed on the display unit 7.

[0005]

[Problems to be solved by the device]

 However, in the BOTDA device shown in FIG. 2, the area beyond the far end of the optical fiber is displayed as if there is an optical fiber having a considerable pulse width. Therefore, the quality judgment of the optical fiber may be erroneous.

The present invention solves such a drawback of the conventional technique and displays the far end position of the optical fiber measured by the OTDR method together with the distortion measurement waveform of the BOTDA, so that the error of the far end position determination is corrected. An object is to provide a device for BOTDA that prevents the same.

[0007]

[Means for Solving the Problems]

 In order to achieve this object, in the present invention, the continuous light 11 from the light source 1A is incident on one end of the optical fiber 10, and the pulsed light 12 from the light source 1B is incident on the other end of the optical fiber 10 through the optical coupler 2. And the Brillouin-amplified optical signal 13 by the pulsed light 12 are incident on the optical filter 3, the optical signal 13 is removed by Rayleigh scattered light by the optical filter 3 and is incident on the APD 4, and the APD 4 converts the optical signal 13 into an electric signal. Then, in a BO TDA device adapted to input a signal to the display 7 to display the distorted waveform of the optical fiber 10, an optical filter control circuit 9A for controlling the transmission frequency of the optical filter 3 and an optical filter control circuit 9A Timing control circuit 9B for switching between, the bias circuit 8 for controlling the multiplication factor of AP D4, the Rayleigh scattered light of the pulsed light is detected, and its far end position is determined. And a recording circuit 9C for recording, are displayed simultaneously with the strain measuring waveform of BOTDA the far end position of the fiber-optic measured by OTDR method.

[0008]

[Action]

 In the display of the far-end point in BOTDA, the far-end position of the optical fiber measured by the OTDR method is recorded in advance and displayed together with the strain measurement waveform of BOTDA to prevent erroneous judgment and to observe an accurate strain waveform. it can

[0009]

【Example】

 Next, the configuration of the BOTDA device for displaying the far end point according to the present invention will be described with reference to FIG. In FIG. 1, the same components as those shown in FIG. 2 are designated by the same reference numerals.

In FIG. 1, 9A is a control circuit for passing the continuous light 11 or the Rayleigh scattered light of pulsed light, 9B is a timing control circuit for controlling the control circuit 9A, 9C is a recording circuit, and other configurations. Are all the same as in FIG.

In FIG. 1, the pulsed light 12 passes through the optical coupler 2 and enters one end of the optical fiber 10, and the continuous light 11 enters from the other end. When the frequency difference between the pulsed light 12 and the continuous light 11 coincides with the frequency shift of Brillouin scattering, the continuous light 13 having the maximum intensity is incident on the optical filter 3 through the optical coupler 2.

In the BOTDA device, in principle, it is observed that there is an optical fiber having a pulse width corresponding to the length beyond the far end of the optical fiber 10. In order to prevent this, first, in order to remove the Rayleigh scattered light of the pulsed light, a control signal is output from the timing control circuit 9B and a control signal is sent from the optical filter control circuit 9A to the optical filter 3.

The Rayleigh scattered light of the pulsed light 12 passes through the optical filter 3, and the continuous light component is removed by the optical filter 3. The Rayleigh scattered light of the pulsed light 12 is converted into an electric signal by using the APD 4. The electric signal is amplified by the amplifier 5A and reaches the A / D converter 6 through the amplifier 5B. The far end position of the optical fiber 10 is recorded by the recording circuit 9C. As described above, the far-end measurement by the OTDR method is performed.

A control signal is output from the timing control circuit 9B, a control signal is sent from the optical filter control circuit 9A to the optical filter 3, the Rayleigh scattered light of the pulsed light is removed by the optical filter 3, and the continuous light component is It is converted into an electric signal using the APD4. The electric signal is amplified by the amplifier 5A and reaches the A / D converter 6 through the amplifier 5B.

The far-end position recorded in the recording circuit 9C is displayed on the display 7 together with the distorted waveform. As a result, it is possible to prevent the optical fiber 10 from being observed as if the optical fiber exists beyond the far end of the optical fiber 10.

As the pulse light source 1B and the continuous light source 1A, for example, a 1.55 μm band D FB LD obtained by subjecting a semiconductor laser diode to ATC (automatic temperature control) and AFC (automatic frequency control) is used. Then, the current injected into the AFC circuit is changed within a range of ± 5 mA by current control, and pulsed light 12 and continuous light 11 are supplied to the optical fiber 10 at a frequency equal to the Brillouin shift frequency.

As the optical filter 3, for example, a solit etalon with FSR = 21.8 GHz and finesse = 25 is used. The optical filter control circuit 9A uses an ATC (automatic temperature control circuit) circuit to control the temperature of the solit etalon and to select an optical frequency to pass.

FIG. 3 is a display waveform of a conventional distortion waveform, which is displayed as if an optical fiber length corresponding to the pulse width beyond the far end exists. On the other hand, in the device of the present invention, the timing control circuit 9B measures the far end of the optical fiber by the OTDR method, the recording circuit 9C records the position of the far end of the optical fiber, and the timing control circuit 9B measures. Then, the distortion waveform of the optical fiber is measured by the BOTDA method, the distortion waveform and the far end position are displayed together on the display 7, and the waveform shown in FIG. 4 is obtained. That is, with the above configuration, the far-end position in BOTDA is characterized in that the far-end position of the measurement optical fiber is displayed together with the distortion measurement waveform of BOTDA without being affected by the measurement conditions (particularly the pulse width). It becomes possible to display.

[0019]

[Effect of device]

 According to the present invention, it is possible to accurately and rapidly observe the far end of the optical fiber by the far end position of the optical fiber measured by the OTDR method. Highly reliable and highly accurate measurement can be obtained when compared with the device of.

[Brief description of drawings]

FIG. 1 is a block diagram of a BOTDA according to the present invention.

FIG. 2 is a block diagram of a BOTDA according to the related art.

FIG. 3 is a display waveform diagram of a conventional distorted waveform displayed on a display unit 7.

FIG. 4 is a waveform diagram in which a distorted waveform according to the present invention displayed on a display 7 and a far end position are displayed together.

[Explanation of symbols]

 1A light source 1B light source 2 optical coupler 3 optical filter 4 APD 5A amplifier 5B amplifier 6 A / D converter 7 indicator 8 bias circuit 9A optical filter control circuit 9B timing control circuit 9C recording circuit 10 optical fiber 11 continuous light 12 pulsed light 13 Optical signal

Claims (1)

[Scope of utility model registration request] 1. A first light source (1A) at one end of an optical fiber (10)
The continuous light (11) from the optical fiber (10) and the pulsed light (12) from the second light source (1B) to the other end of the optical fiber (10) through the optical coupler (2). The optical signal (13), which is Brillouin amplified by the pulsed light (12), is incident on the optical filter (3) through the optical coupler (2), and the Rayleigh scattered light is removed from the optical signal (13). Incident on the APD (4), the AP
BOTDA device for converting the optical signal (13) into an electric signal at D (4) and then inputting the signal to the display (7) to display the distorted waveform of the optical fiber (10) The optical filter control circuit (9A) for controlling the transmission frequency of the optical filter (3), the timing control circuit (9B) for switching the optical filter control circuit (9A), and the multiplication factor of the APD (4) Bias Circuit to Control (8)
And a recording circuit (9C) for detecting the Rayleigh scattered light of the pulsed light (12) and recording the far end position thereof, and the far end position of the optical fiber (10) measured by the OTDR method is distorted by BOTDA. A device for BOTDA that displays the far end point, which is displayed simultaneously with the measurement waveform.