JPS63290934A - Measuring instrument for optical fiber transmission characteristic - Google Patents

Abstract

PURPOSE:To improve measurement accuracy by adding an aligning mechanism to a connection terminal of an optical fiber to be measured and aligning the optical fiber to be measured and a fiber core on a measuring instrument side with each other before the start of measurement. CONSTITUTION:The optical fiber 25 to be measured is connected to the connection connector 24 of the measuring instrument. A switch 30 is switched to a side (b) prior to the level measurement of reflected light. Laser beam from a laser beam source 21 is guided to the optical fiber 25 to be measured through the connection connector 24 and backward scattered light from this optical fiber is light-received by a light receiving device 26 through a directional coupler 23. Then aligning mechanisms 31-33 are so driven that the level of the backward scattered light detected by the light receiving device 26 is maximum, thereby aligning the connection terminal of the optical fiber 25 to be measured. In this state, the switch 30 is switched to a side (a) and the measurement is started. Consequently, the maximum incident light is guided to the optical fiber 25 to be measured at the time of the measurement and the dynamic range of the backward scattered light to be measured becomes wide, so the accuracy of the measurement is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber transmission characteristic measuring device useful for measuring the transmission characteristics of an optical fiber using backscattered light.

[Summary of the invention]

The optical fiber transmission characteristic measuring device of the present invention is a device that supplies pulsed laser light to an optical fiber to be measured via an optical directional coupler and measures the transmission characteristics of the optical fiber from the backscattered light. In this method, an alignment mechanism driven by a two-axis alignment motor is added to the connection terminal of the optical fiber to be measured, and this alignment mechanism is controlled by the level of backscattered light after removing the reflected light from the connection terminal before starting the measurement. Since the optical fiber is controlled to have a constant level of incidence on the optical fiber to be measured, the dynamic range of the measured value can be increased.

[Conventional technology]

One of the important measurement items for optical fibers is the measurement of transmission characteristics, which determines optical loss, transmission band, etc.

Generally speaking, methods for measuring transmission characteristics include measuring optical loss using the transmission method and measuring optical loss using backscattered light. By detecting the resulting Fresnel reflection and Rayleigh backscattered light, local optical loss, connection loss, etc. can be determined with a relatively simple operation.

FIG. 4 shows a schematic diagram of an apparatus lO that measures the transmission characteristics of an optical fiber using such backscattered light.
1 is a laser emission source; 12 is a drive circuit for the laser emission source; 1
3 indicates an optical directional coupler, and this optical directional coupler 13 converts the laser beam incident from the input end 13A to the first output end 1.
3B and reflected light incident from the first output end 13B is configured by an optical system that allows the reflected light to pass through the second output end 13C.

14 is a connector for connecting the optical fiber 15 to be measured; 16 is a light receiver; 17 is an amplifier for amplifying the reflected light signal detected by the light receiver; 18 is an arithmetic circuit; It samples the light level, converts it into a signal of a predetermined level, measures it, and supplies it to the display device 19.

Conventional transmission characteristic measurements of optical fibers are formed by a double-stranded structure, so the laser light source 11 is driven by the drive circuit 12, and the optical pulse signals from the laser light source 11 are optically directionally coupled. The light enters the optical fiber 15 to be measured, which is connected to the connector 14 via the device 13.

Then, a part of the Rayleigh scattered light is generated by Fresnel reflection caused by the local refractive index step existing in the longitudinal direction of the core inside the optical fiber, and by the weak refractive index fluctuation below the wavelength that exists inside the core. is reflected to the input end side of the optical fiber, and these reflected lights are input from the connection connector 14 to the optical receiver 16 via the optical directional coupler 13.

Therefore, the transmission characteristics of the optical fiber 15 to be measured are measured by analyzing the intensity of the received reflected light using an arithmetic circuit.

[Problem that the invention attempts to solve]

In the conventional measurement method using backscattered light, the measurement target is the reflected light that returns from the measured light frame 15 to the incident end side in a double series, but some of this reflected light is due to the missing connector. Since the light reflected by the matching is included, there is a problem in that the measured value is larger than the actual transmission loss of the optical fiber to be measured.

Furthermore, if the level of light incident on the optical fiber to be measured decreases due to mismatching of the connectors, the dynamic range of the measuring instrument decreases, causing a problem of increased measurement errors.

Furthermore, in order to completely eliminate axis misalignment with the connecting connector, a high-precision connector is required, and there is also the problem that measurement work takes time due to careful alignment of the connector. .

[Means for solving problems]

The present invention has been made in view of these problems.
The optical fiber connection terminal that connects the measuring device and the optical fiber under test is equipped with an alignment mechanism that can perform alignment using a two-axis alignment motor, and this alignment mechanism allows the optical fiber to be measured to be aligned with the optical fiber under measurement before starting measurement. This allows alignment of the optical fibers on the device side.

[Effect]

Before connecting the optical fiber to be measured to the fiber connector of the measurement device and starting measurement, activate the optical directional coupler or time gate device to ensure that the reflected light from the connection terminal of the measurement device reaches the receiver. Prevent it from entering. Then, the level of backscattered light from the optical fiber to be measured obtained at this time is detected, and the alignment mechanism of the connecting device is controlled so that this detected level becomes the maximum. With this alignment control,
Alignment is performed so that the core center of the optical fiber under test and the fiber core center on the measurement device side match, so after this alignment is completed, the maximum amount of incident light will be supplied to the optical fiber under test. , it is possible to widen the dynamic range of backscattered light to be measured.

〔Example〕

FIG. 1 is a schematic diagram for measuring the transmission characteristics of an optical fiber showing an embodiment of the present invention, in which 21 and 22 indicate a laser emission source and its driving circuit, and 23 indicates an optical directional coupler. , for example, an ultrasonic light deflection element, a light beam separation prism, etc. The optical pulse input from the first input end 23A is transmitted to the first output end 23B,
The reflected light incident from the first output end 23B is transmitted to the second output end 23B.
The signal is configured to be transmitted to the output terminal 23C of.

Furthermore, by operating the ultrasonic optical deflection element using a control signal supplied from the electrical input terminal 23D, it is possible to transmit the reflected light from the first output terminal 23B to the second output terminal 23C for an arbitrary period of time. It has a time gate function that can be used.

Reference numeral 24 indicates a connector attached to the side of the aligner which is adopted in the optical fiber transmission characteristic measuring device of the present invention, and as described later, the optical fiber to be measured 25 and the optical fiber of the measuring device (P2 ).

26 is a light receiver (Ge-APD) that detects the level of reflected light.
), 27 is an amplifier, 28 is an arithmetic circuit, and 29 is a display device, which are used in the device described above.

Reference numeral 30 indicates a switch that is normally switched before starting measurement, and when this switch 30 is in the b contact, an electrical signal indicating the level of reflected light is input to the alignment circuit 31. Then, the output of the alignment circuit 31 is input to the motor drive circuit 32, and the laser beam is aligned in the X-Y axis direction so that the amount of laser light reflected at the connection connector 24 is minimized, that is, the incident light is maximized. The two-axis motors 33A and 34A that drive the mm are controlled.

Note that 34 represents a directional coupler drive circuit for supplying a signal for adding a time gate function to the optical directional coupler 23.

FIG. 2 shows an outline of the alignment mechanism, in which a connecting connector 24B movable in the X-Y direction is in contact with a connecting connector 24A of the optical fiber to be measured.

The connecting connector 24B is fixed to a Y-axis base 24G, and the Y-axis base 24C is slidably coupled to an X-axis base 24E mounted on a guide 24D in the X-axis direction.

And a two-axis motor 33A (not shown).

33B, the YilI base 24C, the X vehicle base 24
E is movable in the Y-axis direction and the X-axis direction, which are orthogonal to each other.

Hereinafter, a method for measuring transmission characteristics of an optical fiber according to the present invention will be explained.

The optical fiber 25 to be measured is connected to the connector 24 of the measuring device, and the optical pulse from the laser emission source 21 is connected to the optical path PI.
, optical directional coupler 23. When incident through the optical path P2, the backscattered light from the optical fiber 25 to be measured is transmitted to the connector 24, the optical path P2, the optical directional coupler 23 . It is detected by the light receiver 26 via the optical path P3.

This backscattered light is detected, for example, at a level where the power (dB) of the reflected light gradually attenuates with respect to the propagation time (distance) on the horizontal axis, as shown in FIG.

The first peak point Q1 indicates the reflection level at the input end, and the next peak point Q2 indicates the level of reflected light when the optical fiber 25 to be measured has a connection point.

Further, the last peak point Q3 indicates the level of the reflected light at the output end of the optical fiber 25 to be measured.

In the present invention, before measuring the level of the reflected light, the switch 30 is switched to the b contact side, and only the reflected light after the propagation time is transmitted to the second output terminal 23C of the optical directional coupler 23. Directional coupler drive circuit 3 to output
Drive 4 to add a quit gate.

At this time, two-axis motors 33A and 33 are operated so that the level of backscattered light detected by the light receiver 26 is maximized.
By driving B, the alignment mechanism is driven, and the 1a connection terminal of the optical fiber 25 to be measured is aligned.

Then, by this alignment, the amount of incident light pulses from the laser emission source 21 is controlled to be maximum, and
Since the reflected light at the input end of the connector is controlled to be minimized, in this state, switch 30 is switched to the a contact side, the time gate function is canceled, and measurement is started.

In the measuring device of the present invention, as described above, the connecting connector 2
This can be easily done by aligning in step 4 or by applying a time gate to the reflected light before measurement.
During measurement, the incident level of the optical fiber to be measured is always constant, making the measuring device stable. Furthermore, since noise components are reduced, the original dynamic range of the measuring instrument can be maintained large, and measurement errors can be reduced.

Note that the time gate function of inputting only the backscattered light after a certain distance of the optical fiber to be measured does not necessarily have to be performed only by the optical directional coupler 23; for example, the light receiver 26, amplifier 27, etc. can be electrically controlled. It is also possible to do this by

〔Effect of the invention〕

As described above, the optical fiber transmission characteristic measuring device of the present invention adds an alignment mechanism to the connecting connector, and automatically operates the alignment mechanism using backscattered light from the connected optical fiber to be measured. Since it can be controlled, the optical pulse reflected at the input end of the optical fiber to be measured can be suppressed to be the first, and the dynamic range can be used effectively. Furthermore, even if the accuracy of the connector that connects the optical fiber to be measured is somewhat poor, it is corrected each time measurement is performed by the alignment mechanism, which has the effect of simplifying the connection work and shortening the measurement time.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the optical fiber transmission characteristic measuring device of the present invention, FIG. 2 is a perspective view showing an embodiment of the alignment mechanism of the connector, and FIG. 3 is a graph showing an example of backscattered light. FIG. 4 is a schematic diagram showing a conventional measuring device for optical fiber transmission characteristics. In the figure, 21 is a laser emission source, 23 is a light directional metal lid, 2
4 is a connector with alignment configuration, 26 is a light receiver, 27 is an amplifier, 28 is an arithmetic circuit, 29 is a display device, 31 is an alignment circuit, 32 is a motor drive circuit, 33A and 33B are two-axis alignment units. Shows the motor for. (Japanese pto tXJ/I"$J-

Claims (1)

[Claims] A pulsed laser beam is supplied to an optical fiber connection terminal through an optical directional coupler, and backscattered light from an optical fiber to be measured connected to the optical fiber connection terminal is transmitted through the optical directional coupler. In an optical fiber transmission characteristic measuring device that measures the transmission characteristics of the optical fiber to be measured by receiving light and analyzing the received backscattered light,
The optical fiber connection terminal is provided with an alignment mechanism capable of performing alignment using at least two axis alignment motors, and the alignment mechanism is adjusted by the level of reflected light from which reflected light from the optical fiber connection terminal is removed. 1. An optical fiber transmission characteristic measuring device, characterized in that it is configured to be centrally controlled.