JPS58113831A - Measuring device for loss distribution - Google Patents

Abstract

PURPOSE:To measure a loss distribution including a near end of an optical fiber to be measured, by eliminating the influence exercised by a reflecting light from a photo connector. CONSTITUTION:A laser device 23 generates a laser pulse light by means of a pulse from a pulse generator 22, and the light is caused to enter an optical fiber 30 via a guide optical fiber 24, a photo coupler 27, a guide optical fiber 25, and a photo connector 28. A switch control signal, outputted at the same timing as that of a pulse from the pulse generator 22, is delayed by a delay circuit 33, it is applied to a photo switch 32 to turn ON the switch 32, and a back scattering light of an optical fiber 30 to be measured, except a reflecting light from the photo connector 28, is caused to enter a photo detector 29. The output of the photodetector 29 is amplified by an amplifier 31 and is applied to a signal processing part 21 which finds a loss distribution of the optical fiber 30 to be measured based on the detecting signal of the back scattering light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a loss distribution measuring device for measuring loss distribution of an optical fiber.

Laser pulse light is input from one end of the original fiber, and the loss of the original fiber can be measured based on the level of reflected light due to Rayleigh scattering. Such conventional measuring devices are
Conventionally, the structure was as shown in FIG. In the figure, 1 is a signal processing section, 2 is a pulse generator, 3 is a laser device, 4 to 6 are guide optical fibers, 7 is an optical coupler, 8 is an optical connector, 9 is a photodetector, and 10 is a receiver. measurement optical fiber,
11 is an amplifier.

The pulse generator 2 generates pulses based on the timing signal from the signal processing section 1, and the pulses are added to the laser device 3, and the laser device is installed! 5 generates laser pulse light.

This laser pulse light is transmitted through the guide light fiber 4. Optical coupler 7
, is input to the optical fiber to be measured 10 via the guide optical fiber 5 and the optical connector 8. The source coupler 7 is used to input the laser pulse light into the optical fiber 10 to be measured, and to input the backscattering light of the optical fiber 10 to be measured into the photodetector 9 via the guide optical fiber 6.

The output of the photodetector 9 is amplified by an amplifier 11 and applied to the signal processing section 1. The signal processing unit 1 determines the loss distribution of the optical fiber 10 to be measured based on the detection signal of the backscattering light.

However, the reflected light from the optical power grapher 7 and the original connector 8 is also included, and this reflected light is expressed as to
-15-a·Pj%. Note that α is the total loss until the pulsed light enters the optical fiber to be measured. Further, the maximum backscattering optical power of the optical fiber 10 to be measured is 0.6414 x 1O-5Pi%.

If the aforementioned total loss αf is 5 dB, the ratio of the reflected light from the original connector 8 to the backscattering light of the optical fiber 10 to be measured is 2.5×10′. Therefore amplifier 11
When the gain was selected to amplify the detection signal of the backscattering light, the amplifier 11 rarely became saturated due to the detection signal of the reflected light from the original connector 8.

An object of the present invention is to make it possible to measure the loss distribution including the near end of an optical fiber to be measured, excluding the influence of reflected light from the original connector. Examples will be described in detail below.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 21 is a signal processing section, 22 is a pulse generator, 23 is a laser device,
24 to 26 are guide optical fibers, 27 is an optical coupler, 28
29 is an optical detector consisting of an avalanche photodiode or the like, 60 is an optical fiber to be measured, 61 is an amplifier, 62 is an original switch, and 56 is a delay circuit. The laser device 26 generates a laser pulse light by the pulse from the pulse generator 22, and the guide optical fiber 241 is connected to the original coupler 27. The point that the pulse is input to the optical fiber to be measured 60 via the guide optical fiber 25 and the optical receiver 28 is similar to the conventional example, but the pulse is applied to the laser device 25 from the pulse generator 22 at the same timing as the original switch 62. This outputs a switch control signal. This switch control signal is delayed by a delay circuit 66 and applied to the optical switch 52.

The delay time Td of the delay circuit 35 is given by: However, C-speed of light (3x 108m),
L-length of guide optical fibers 24-26 (m), #=
This is the group refractive index of the optical fiber (41,4585). Each length fJlf1 of the guide optical fibers 24 to 26
When A/3 is assumed, L=n/1+n/24-λf6. Also, Tw = 6, which is the pulse width of the incident pulsed light.

For example, It/1 = Itf2 = Itf5 = 0.5
If m, Tw = 20 nS, then the delay circuit 65 will delay 27 seconds from the emission of the laser pulse light.
．． The main switch 32 is turned on with a delay of 5 ns, and all of the backscattering light from the optical fiber to be measured 30 can be made incident on the photodetector 29, excluding the reflected light from the main coictor 28.

FIG. 3 is an explanatory diagram of the operation, in which (,) shows the pulse from the pulse generator 22, (b) shows the laser pulse light from the laser device w, 23, and (6) shows the light switch from the optical power grapher 27. 5
2, (d) is a switch control signal that is applied to the optical switch 32 with a delay of time Td from the generation of the laser pulse light, and (#) indicates the source that is input to the photodetector 29. That is, only the backscattering light of the optical fiber 60 to be measured is applied to the photodetector 29. Therefore, a detection signal of a large level due to the light reflected from the optical connector 28 that would saturate the amplifier 31 is not output from the photodetector 29, so that the backscattering light at the near end of the optical fiber 50 to be measured is also reliably amplified and signalled. It can be added to the processing section 21.

FIG. 4 shows an example of a backscattering detection signal, where the loss on the curved line is lower than that on the curved line G. The loss measurement point of the fiber to be measured p1 can be determined by the time t, The loss Lf is 1 Lf = 101. og-・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・(2) It can be found by 2. Therefore, the p1 loss distribution can be obtained by calculating the loss for each time t in the signal processing section 21.

As explained above, the present invention provides an optical fiber to be measured 60
0 backscattering light is applied from the source coupler 27 to the photodetector 29 via the source switch 32, and then the light switch 52
By delaying the control signal from the laser pulse source generation of the laser device, the reflected light from the optical connector 28 is not incident on the photodetector 29, thereby preventing the detection of the photodetector 29. The amplifier 61 that amplifies the output and applies it to the signal processing section 21 does not become saturated, and therefore the detection amplification of the source of backscattering at the near end of the optical fiber 60 to be measured becomes accurate, making it possible to measure the near end loss distribution. becomes.

\,4.Brief explanation of the drawings>1 Figure 1 is a block diagram of a conventional loss distribution measuring device, Figure 2 is a block diagram of an embodiment of the present invention, Figure 3 is an operation explanatory diagram, FIG. 4 is a curve diagram showing an example of a bank scattering detection signal.

21 is a signal processing unit, 22 is a pulse generator, 26 is a laser device, 24 to 26 are guide fibers, 27 is an optical coupler, 28 is a source connector, 29 is a photodetector, 30 is an optical fiber to be measured, 61 is a An amplifier, 32 is a source switch, and 33 is a delay circuit.

Figure 1 Figure 2 167- Figure 3 Figure 4 Human A1 time

Claims (1)

[Claims] Laser pulse light from a laser device is input to the optical fiber to be measured via an optical coupler and an optical connector, and the measured light 7
In an optical fiber loss distribution measuring device that applies fiber backscattering light from the optical power grapher to a photodetector, a source switch provided between the optical coupler and the photodetector, and a control of the optical switch. A loss distribution measuring device that measures t% by providing a delay circuit that delays the entire signal from the generation of the laser pulse light and applies the signal to the source switch.