JPH0466835A - Testing device of optical waveguide - Google Patents

Abstract

PURPOSE:To shorten a dead zone and also to obtain a waveform being free from fluctuation by making a light pulse from a light pulse generator enter one end of an optical waveguide, an object of measurement, and by taking out a light signal through a directional coupler. CONSTITUTION:A pulse signal PS is supplied from a pulse generator 11 to a laser light source 12 and a light pulse PI of a prescribed period obtained therefrom is made to enter one end 1a of an optical fiber 1 being an optical waveguide, an object of measurement, through a directional coupler 14 and a photoconnector 15. A light signal PO obtained at one end 1a of the optical fiber 1 is supplied to an optical amplifier 16 through the photoconnector 15 and the directional coupler 14 and converted into an electric signal in a photoelectric converter 17, and it is subjected to amplification 18 and A/D conversion 21 and supplied to an adder 22. In the adder 22, digital signals in a plurality of times of periods of the pulse signal PS are added up, one period thereof being taken as one time, and subjected to logarithmic transformation 23, and thereafter a transformation output thus obtained is supplied to a display unit 24 and displayed as a waveform.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention is directed to "observing backscattered light obtained at one end of an optical waveguide by injecting a light pulse into one end of an optical waveguide such as an optical fiber." The present invention relates to an optical waveguide testing device that measures the characteristics of an optical waveguide.

"Prior Art" The optical waveguide testing apparatus as described above has conventionally been generally constructed as shown in the third part.

That is, a pulse signal PS with a constant period as shown in FIG. 4 from the pulse generator 31 is supplied to a laser light source 32 such as a laser diode 1, and the laser light source 32 generates light with a constant period as shown in FIG. A pulse PI is obtained, and the optical pulse PI is passed through an optical directional coupler 34 and connected to an optical connector 35.
The optical signal PO obtained at one end 1a of the optical fiber 1 passes through the optical collector 35, and the optical signal PO is input to the optical waveguide to be measured, in this case, one end 1a of the optical fiber 1. It is supplied to a photoelectric converter 37 such as a photodiode through a coupler 34 and converted into an electrical signal, and the electrical signal is amplified by an amplifier 38 and then supplied to an A/D converter 41 and converted to a digital signal. The digital signal is supplied to the adder 42, where the digital signals for a plurality of times are added, where one cycle of the pulse signal PS is counted as one time, and the output signal of the adder 42 is sent to the logarithmic converter 43. The signal is supplied and subjected to logarithmic transformation, and the converted output is supplied to the display 44 and displayed as a waveform. The pulse generator 31 and the laser light source 32 constitute an optical pulse generator 33, and the photoelectric converter 37 and the amplifier 38 constitute a light receiving system 39.

In this case, Fresnel reflection occurs at the optical connector 35, and the level of the optical signal PO increases during the pulse width period P1 of the optical pulse PI, as shown as reflected light P○a in FIG. The level of the scattered light POe is about 1/1000 to 1/10000 of the reflected light POa. Then, the sensitivity of the light receiving system 39 is set so that this backscattered light POe is observed. Therefore, if the reflected light POa is supplied as is to the light receiving system 39, the light receiving system 39 will be saturated and the backscattered light POe cannot be observed.

Therefore, an optical switch constituted by an acousto-optic element or the like is used as the optical directional coupler 34, and the optical pulse P
In the pulse width period Pi of I, the optical pulse generator 33
The optical pulse PI from is input to the optical fiber 1 as it is, and the level of the reflected light POa is greatly attenuated as shown in FIG. 4 as reflected light PQa.
During the subsequent period when backscattered light POe is obtained,
The backscattered light POe is supplied as is to the light receiving system 39 as shown in FIG. 4 as backscattered light PQe.
Optical switch 34 is switched.

"Problems to be Solved by the Invention" However, optical switches that are generally constructed from acousto-optic elements and the like have a long switching time of about 100 nanoseconds and are polarization dependent.

Therefore, in a conventional optical waveguide testing apparatus in which an optical switch constituted by an acousto-optic element or the like is used as the optical directional coupler 34 and the optical switch 34 is switched as described above, the light obtained through the optical switch 34 is As shown in FIG. 4 in signal PQ, backscattered light PQ
It takes a long time, about 100 nanoseconds, for the rise of e, and during that time several tens of nanoseconds are emitted from one end 1a of the optical fiber 1.
Backscattered light from areas up to about a meter cannot be observed, and the polarization dependence of the optical switch 34 causes waveform fluctuations.

Therefore, the present invention provides an optical waveguide testing device that measures the characteristics of an optical waveguide by injecting a light pulse into one end of an optical waveguide such as an optical fiber and observing the backscattered light obtained at one end of a leading waveguide. This makes it possible to significantly shorten the so-called Punt zone, which is the part at one end of the optical waveguide where backscattered light cannot be observed, and to obtain a waveform without fluctuation.

"Means for Solving the Problem" The present invention includes an optical pulse generator, and an optical pulse from the optical pulse generator that is incident on one end of an optical waveguide to be measured. an optical directional coupler for taking out the obtained optical signal; a light receiving system for converting the optical signal obtained through the optical directional coupler into an electrical signal and taking it out; and a combination of the optical directional coupler and the light receiving system. The optical amplifier placed between and the gain of this optical amplifier,
A gain control circuit is provided for controlling the pulse width period of the optical pulse from the optical pulse generator so that it is sufficiently smaller than the period during which backscattered light is obtained.

"Function" In the optical waveguide testing apparatus of the present invention configured as described above, the optical amplifier The gain of is made sufficiently small,
Since the reflected light is sufficiently attenuated, the light receiving system is not saturated by the reflected light. The gain of the optical amplifier is made sufficiently large during the period in which backscattered light is obtained, but since the switching time of the optical amplifier is short, ranging from several nanoseconds to tens of nanoseconds, the so-called dead zone is several meters long. It becomes extremely short, ranging from about 10 meters to more than 10 meters. Furthermore, since the optical amplifier has no polarization dependence or can significantly reduce polarization dependence, a waveform without fluctuation can be obtained.

"Example" FIG. 1 shows an example of an optical waveguide testing apparatus of the present invention.

A pulse signal PS having a constant period as shown in FIG. 2 from the pulse generator 11 is supplied to a laser light source 12 such as a laser diode, and the laser light source 12 generates a light pulse PI having a constant period as shown in FIG. obtained, and its optical pulse PI
is made to pass through the optical directional coupler 14 and enter the optical waveguide to be measured, in this case, one end 1a of the optical fiber I, through the optical connector 15, whereby the optical signal PO obtained at the one end 1a of the optical fiber I is supplied to the optical amplifier I6 through the optical connector 15 and the optical directional coupler 14, and the optical signal PC from the optical amplifier 16 is supplied to a photoelectric converter 17 such as a photodiode to be converted into an electrical signal. After the electrical signal is amplified by the amplifier 18, it is supplied to the A/D converter 21 and converted into a digital signal, and the digital signal is supplied to the adder 22, which divides one period of the pulse signal PS into one. The digital signals for a plurality of times are added, and the output signal of the adder 22 is supplied to a logarithmic converter 23 for logarithmic conversion, and the converted output is supplied to a display 24 and displayed as a waveform.

The pulse generator 11 and the laser light source 12 are the optical pulse generator 1
A photoelectric converter 17 and an amplifier 18 constitute a light receiving system 19.
Configure.

As the optical directional coupler 14, for example, an optical fiber coupler is used instead of an optical switch. As the optical amplifier 16, an optical fiber amplifier or a semiconductor optical amplifier is used.

In FIG. 2, in addition to the reflected light POa due to Fresnel reflection generated at the optical connector 15, in the optical signal P○ supplied to the optical amplifier 16 through the optical directional coupler 14,
A case is shown in which reflected lights POb and POc due to freble reflection generated at a connection point (not shown) of the optical fiber 1 are included.

Then, the pulse signal PS from the pulse generator 11 is supplied to the mask pulse forming circuit 25, and first the display 24
By manually operating the mask pulse forming circuit 25 while looking at the waveform displayed in FIG. MP
At the same time, the pulse signal PS is supplied to the period segment signal forming circuit 26, and the pulse width period Pi of the optical pulse PI is obtained from the period segment signal forming circuit 26 as shown in FIG.
A signal PX indicating a period Px during which backscattered light POx having a relatively large level is obtained in the optical signal PO immediately after the signal PO, and a signal PY indicating a period py during which backscattered light POy having a small level is obtained in the subsequent optical signal PO. is obtained, and the pulse signal P
S, mask pulse MP and signals PX, PY are supplied to the gain control circuit 27, and as shown in FIG. Also in the optical amplifier 16
For example, the gain of the optical amplifier 16 is set to zero during the period Pχ except for the period pb, and the gain of the optical amplifier 16 is made sufficiently large during the period Py except for the period Pc. Double the period py
During the period Pz between and period P1, a gain control signal GC is obtained that makes the gain of the optical amplifier 16 zero, and the gain control signal GC is supplied to the optical amplifier 16 and the optical amplifier W16 is
gain is controlled.

Therefore, the reflected lights POa, POb and P Oc' in the optical signal Pc supplied to the optical amplifier 16 =:, the reflected lights PCa, P in the optical signal PC from the optical amplifier 16, respectively.
The levels are greatly attenuated as shown as Cb and PCc, and the backscattered lights POx and PO in the optical signal Pc
The level of y is set to be sufficiently large as shown by the backscattered lights PCx and PCy in the optical signal PC, respectively, and the sensitivity of the light receiving system 19 is set so that the amplified backscattered lights PCx and PCy can be observed. By doing so, saturation of the light receiving system 19 does not occur.

The switching time of the optical amplifier 16 is as short as about several nanoseconds when a semiconductor optical amplifier is used as the optical amplifier 16, and about 10-odd nanoseconds even when an optical fiber amplifier is used as the optical amplifier 16. ,
[One end of the optical fiber 1] The part on the a side where backscattered light cannot be observed, the so-called put zone, is extremely short, ranging from several meters to more than 10 meters.

Furthermore, when an optical fiber amplifier is used as the optical amplifier 16, the optical amplifier 16 has no polarization dependence, and even when a semiconductor optical amplifier is used as the optical amplifier 16, the polarization dependence of the optical amplifier 16 can be significantly reduced. As a result, a waveform without fluctuation can be obtained. Furthermore, especially when an optical fiber amplifier is used as the optical amplifier 16,
When the gain of the optical amplifier 16 is made zero during periods PPb and Pc, the reflected light POaPOb is
The level of POc is greatly attenuated to about 60 dB, and as shown in Part 3, the isometry is about 15 to 20 dB compared to the conventional optical waveguide test equipment that uses an optical switch as the optical directional coupler 34. ration is improved.

In addition, as shown in the example shown in the figure, backscattered light P
When the gain of the optical amplifier 16 is particularly increased for Oy, even the minute backscattered light POy is A/D converted with high sensitivity in the A/D converter 21.
A logarithmic converter 234 performs logarithmic conversion with high resolution.

"Effects of the Invention" As described above, according to the present invention, it is possible to significantly shorten the so-called Punt zone, which is the part at one end of the optical waveguide where backscattered light cannot be observed, and
A waveform without fluctuation can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a time chart showing an example of the optical waveguide testing device of the present invention, and FIG. 2 is a time chart for explaining its operation.
The third panel shows an example of a conventional optical waveguide testing device, and FIG. 4 is a time chart for explaining its operation. Ya 2 circles

Claims (1)

[Claims] (1) An optical pulse generator, and an optical directional coupling that makes the optical pulse from the optical pulse generator enter one end of the optical waveguide to be measured, and extracts the optical signal obtained at one end of the optical waveguide. a light-receiving system that converts the optical signal obtained through the optical directional coupler into an electrical signal and extracts it; an optical amplifier provided between the optical directional coupler and the light-receiving system; an optical waveguide test comprising: a gain control circuit that controls the gain of the amplifier so that it is sufficiently smaller during the pulse width period of the optical pulse from the optical pulse generator than during the subsequent period during which backscattered light is obtained; Device.