JP2593647Y2 - BOTDA device for displaying far-end point - Google Patents

Description

[Detailed description of the invention]

[0001]

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

[0002]

2. Description of the Related Art In BOTDA, in principle, it is displayed as if an optical fiber having a length equivalent to the pulse width exists beyond the far end of the optical fiber.

The configuration of a conventional BOTDA device will be described with reference to FIG. 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 the 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
No. 2-6725.

In FIG. 2, continuous light 11 is incident on one end of an optical fiber 10, and pulsed light 12 is incident on the other end of the optical fiber 10 through an 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 extracted by the APD 4. The optical filter 3 is for removing the Rayleigh scattered light of the pulse 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 controls the multiplication factor of the APD 4, and the display 7 displays the distortion waveform of the optical fiber 10.

[0005]

[Problems to be solved by the invention] However, FIG.
In the OTDA device, the far end of the optical fiber is displayed as if there is an optical fiber having a considerably long pulse width. Therefore, the quality judgment of the optical fiber may be erroneously made.

The present invention solves such disadvantages of the prior art and sets the far end position of the optical fiber measured by the OTDR method to BO.
It is an object of the present invention to provide a BOTDA device that prevents an error in the determination of the far-end position by displaying it together with a TDA distortion measurement waveform.

[0007]

According to the present invention, a continuous light 11 from a light source 1A is incident on one end of an optical fiber 10 and a light source 1B is incident on the other end of the optical fiber 10 according to the present invention.
Is input through the optical coupler 2, and the optical signal 13, which has been Brillouin-amplified by the continuous light 11 and the pulse light 12, is input to the optical filter 3. Incident on APD4, A
The PD 4 converts the optical signal 13 into an electric signal and inputs the signal to the display 7 to display the distortion waveform of the optical fiber 10. In the BOTDA device, the optical filter control for controlling the transmission frequency of the optical filter 3 is performed. A circuit 9A, a timing control circuit 9B for switching the optical filter control circuit 9A,
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 pulse light and recording the far end position thereof are provided. Is displayed simultaneously with the distortion measurement waveform.

[0008]

In the display of the far end point in BOTDA, the far end position of the optical fiber measured in advance by the OTDR method is recorded and displayed together with the BOTDA distortion measurement waveform, thereby preventing erroneous judgment and preventing accurate distortion. Waveform can be observed

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a BOTDA device for displaying a far end point according to the present invention will be described with reference to FIG. FIG.
2, the same components as those shown in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, reference numeral 9A denotes a control circuit for passing the continuous light 11 or a pulsed Rayleigh scattered light, 9B a timing control circuit for controlling the control circuit 9A, 9C a recording circuit, and all other components. It is the same as FIG.

In FIG. 1, a pulsed light 12 enters one end of an optical fiber 10 through an optical coupler 2 and a continuous light 11
Is incident. 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 enters the optical filter 3 through the optical coupler 2.

In principle, in the BOTDA device, the far end of the optical fiber 10 is observed as if there is an optical fiber having a length equivalent to the pulse width. To prevent this,
First, to remove the Rayleigh scattered light of the pulse 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 pulse 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 pulse light 12 is converted into an electric signal 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 position of the far end of the optical fiber 10 is recorded by the recording circuit 9C. Thus, 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 pulse light is removed by the optical filter 3, and the continuous light component passes through the APD 4. And converted into an electrical signal. 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 distortion waveform. This can prevent the optical fiber 10 from being observed as if the optical fiber had a length equivalent to the pulse width beyond the far end.

As the pulse light source 1B and the continuous light source 1A,
For example, 1.55 μm obtained by ATC (automatic temperature control) and AFC (automatic frequency control) of a semiconductor laser diode
Use the DFB LD of the band. Then, the laser injection current is changed within the range of ± 5 mA by the current control to the AFC circuit, and the pulse light 12 and the continuous light 11 are supplied to the optical fiber 10 at the same frequency as the Brillouin shift frequency.

As the optical filter 3, for example, FSR = 2
A 1.8 GHz, finesse = 25 solid etalon is used. The optical filter control circuit 9A uses an ATC (automatic temperature control circuit) circuit to control the temperature of the solitary etalon and to select the passing optical frequency.

FIG. 3 shows a display waveform of a conventional distortion waveform, in which an optical fiber length equivalent to a pulse width beyond the far end is displayed as if it exists. In contrast, in the device of the present invention,
The far end of the optical fiber is measured by the OTDR method by the timing control circuit 9B, the position of the far end of the optical fiber is recorded by the recording circuit 9C, and the distortion waveform of the optical fiber is measured by the BOTDA method by the timing control circuit 9B. The display 7 displays the distorted waveform and the far-end position together to obtain the waveform shown in FIG. That is, with the above configuration, the far end point display in BOTDA is characterized in that the far end position of the measurement optical fiber is displayed together with the BOTDA distortion measurement waveform without being affected by the measurement conditions (particularly the pulse width). It becomes possible.

[0019]

According to the present invention, it is possible to accurately and quickly observe the far end of an optical fiber based on the position of the far end of the optical fiber measured by the OTDR method. Strain measurement provides higher reliability and higher accuracy than conventional devices.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a conventional BOTDA.

FIG. 3 is a display waveform diagram of a conventional distortion waveform displayed on a display 7;

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

[Explanation of symbols]

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

Continuation of the front page (56) References JP-A-6-167422 (JP, A) JP-A-6-167421 (JP, A) JP-A-6-94570 (JP, A) JP-A-4-132931 (JP) , A) JP-A-1-141331 (JP, A) JP-A-2-107054 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01M 11/00

Claims (1)

(57) [Scope of request for utility model registration] A first light source (1A) is connected to one end of an optical fiber (10).
And a pulse light (12) from a second light source (1B) is incident on the other end of the optical fiber (10) through an optical coupler (2), and the continuous light (11) and the The optical signal (13) Brillouin-amplified by the pulsed light (12) is incident on the optical filter (3) via the optical coupler (2), whereby the Rayleigh scattered light is removed from the optical signal (13). Incident on the APD (4)
A DOT (4) converts the optical signal (13) into an electric signal, and then inputs the signal to a display (7) to display a distortion waveform of the optical fiber (10). , An optical filter control circuit (9A) for controlling the transmission frequency of the optical filter (3), a timing control circuit (9B) for switching the optical filter control circuit (9A), and a 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. The far end position of the optical fiber (10) measured by the OTDR method is a A BOTDA device for displaying a far end point, which is displayed simultaneously with a measured waveform.