JPS6150035A - Light splitting circuit - Google Patents

Abstract

PURPOSE:To obtain a light splitting circuit, which can be used for measuring both a single mode fiber and a multimode fiber, by utilizing the band width of the deflecting frequency of an acoustooptic deflector. CONSTITUTION:Light from a light sending optical fiber 1 is made to be an approximately parallel light beam by a lens 4 and inputted to an acoustooptic deflector 7. When a driving circuit 8 does not send an electric signal, the light beam is guided to an optical fiber to be measured through a lens 5 and an optical fiber 2. When the electric signal is applied from the driving circuit 8, the light beam is guided to the optical fiber to be measured through a lens 5' and an optical fiber 2', which are arranged in the direction of theta=theta1 when f=f1 in the expression in the Figure. Then the light through the lens 5 from the optical fiber to be measured is discarded to the direction of a light source at the time of OFF. At the time of ON, the light is diffracted to the direction of theta3. The light is guided to a light detector through a lens 6 and a light receiving optical fiber 3. The light through the lens 5' is discarded to the direction of a broken line at the time of OFF. At the time of ON, the light is diffracted to the direction of theta2 and guided to the light detector through the lens 6 and the light receiving optical fiber 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical branch circuit. This invention relates to a deflection type optical branching circuit used for measuring backscattered light of an optical fiber.

Conventional Structure and Problems When a light pulse propagates through an optical fiber, backscattering occurs due to reflection and Rayleigh scattering. Today, a method of detecting and processing information by detecting this backscattered light has become an effective means for searching for failure points in optical fibers and measuring loss.
This device is commonly called an optical pulse tester. In this test, the test device is equipped with an optical branch circuit that separates the incident light pulse and backscattered light, and the performance of this optical branch circuit greatly influences the performance of the optical/Grus test device. /11 Optical branching circuits that have been reported in the past include: (1) A polarization branching method that separates light by making use of the birefringence of crystals such as crystals such as crystals.

(2) Beam splitter method using a semi-transparent mirror.

(3) A method of digitally separating light using an acousto-optic optical deflector.

There are methods such as It is well known that the most superior method among these is the method using an acousto-optic optical deflector described in (3) above, which allows masking in the optical region. is shown in Figure 1.

In the optical branch circuit shown in FIG. Lens 4. Acousto-optic light deflector 7/lens 5. The light reflected from the optical fiber 2, which contains information about defects and losses in the optical fiber 2, passes through the lens 5 and enters the acousto-optic optical deflector 7. At this time, when an electric signal is applied from the small vibration circuit 8, the direction θ given by the following equation (1) is caused by the action of the sound wave propagating through the deflector 7.
is diffracted into

θ=λ・f/'l) ・・・・・・(
1) Here, λ is the optical wavelength, f is the carrier wave frequency that drives the acousto-optic optical deflector, and V is the sound speed of the sound wave propagating in the sister body of the acousto-optic optical deflector. The diffracted scattered light is transmitted through the lens 6
, and enters the photodetector via the optical fiber 3, where information regarding fault points and lapses in the optical fiber to be measured can be obtained. In the above circuit, when the reflected light pulse from the fiber under test passes through the deflector 7, 1 This allows the light to be guided to the photodetector connected to the fiber 3.

In the optical branching circuit having the above-mentioned conventional configuration, an optical fiber 1. Lens 4. Since the light passing through the acousto-optic optical deflector 7 is focused only at one point, only one connection point for the optical fiber to be measured formed by the lens 5 and the optical fiber 2 is provided. There wasn't. (Optical phino in the figure)
The right end 2a of 2 is the connection part to the 1111 constant optical fiber. ) The connection terminal for this optical fiber to be measured consisting of the lens 5 and the optical fiber 2 has a type specified by whether the constant optical fiber to be measured I11 is a single mode fiber or a multimode fiber. One thing. Therefore, it is necessary to manufacture two separate optical branch circuits, one for single-mode fiber and one for multi-mode fiber, depending on the mode of the optical fiber to be measured. tl (1') as a vessel becomes separate, and the child's expenses are
It had the disadvantage of being thick and lacking in versatility.

Note that the connection terminal is specified depending on the mode type of the optical fiber to be measured for the following reason.

That is, when the optical fiber to be measured is a single mode fiber, it is necessary to make the optical fiber 2 a single mode fiber and to make the coupling between the lens 5 and the optical fiber 2 tJ4, which has dimensions specific to a single mode fiber. -F: If the optical fiber to be measured is a multimode fiber (in other words, the original fiber 2 is a multimode fiber), and the joint between the lens 5 and the optical fiber 2 also needs to have dimensions specific to a complex mode fiber. This is because there is.

OBJECTS OF THE INVENTION The present invention obviates these conventional drawbacks and aims to provide an optical branching circuit that can be used for measurements on both single mode and multimode fibers.

Structure of the Invention To achieve this object, the present invention provides an acousto-optic optical 1d1
Utilizing the deflection frequency bandwidth of the three-direction device, the light from the source fiber for light transmission has a high ji! within the deflection frequency band. A circle with l,
A single-mode fiber and a multi-mode fiber are placed as the optical fibers to be measured, and lenses for inputting light into these fibers are placed in two places, one in the direction in which the optical fibers are diffracted by reflection, and the other in the direction in which the light is transmitted as is. The light-receiving optical fiber and lens are arranged in a direction in which the light reflected or scattered from the optical fiber is diffracted by each of the lower frequencies within the deflection frequency band of the acousto-optic optical deflector.

In this case, due to the difference in the angle of incidence with respect to the sound j and f planes of the acousto-optic light deflector, the light from each optical fiber to be measured produces diffracted light in the opposite direction to the direction of the respective transmitted light. By selecting an appropriate frequency, the light can be diffracted in the same direction, and the only receiving optical fiber is placed in that direction.

With this arrangement, light from the light source is introduced into one of the optical fibers to be measured when the acousto-optic optical deflector is driven, and light from the optical fiber to be measured is also guided to the source fiber for light reception during one drive. The carrier wave frequencies during each drive are different. For the other optical fiber under test,
Light from the light source is focused during non-vibration, and light from the optical fiber to be measured is guided to the light-receiving optical fiber during driving. d((1) As a connection terminal of a constant optical fiber, a single mode fiber.

If you prepare terminals for multi-mode fibers, you can connect them to either terminal depending on the type of fiber, and close the other one so that they can be used together.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 2. In Fig. 2, the same parts as in Fig. 1 are given the same numbers. (5) When the optical signal is incident on the optical deflector 7 and there is no electrical signal from the drive circuit 8 (hereinafter referred to as OFF time), the optical fiber 5 and the original fiber 2 (f
All of them are guided to a 1111I fixed optical fiber via a multimode fiber. , (, When the electrical signal from the U-motion circuit 8 is applied (hereinafter referred to as ON time), f = f in equation (1), the direction of 0-01 when closed ((the arranged lens 5 ' and an optical fiber 2' (for example, a single mode fiber) to the optical fiber to be measured.

Next, regarding the light from the optical fiber to be measured, the light passing through the lens 5 is thrown away in the direction of the light source when it is OFF, and ○N
At times, the light is diffracted in the direction of θ-03 when f215 is used in equation (1), and is guided to the photodetector via the lens 6 and the light-receiving optical fiber 3. The light passing through the lens 5' is thrown away in the direction of the broken line when it is OFF, and when it is ON, f-
The light is diffracted in the direction of θ-02 when 12, and is guided to a photodetector via a lens 6 and a light-receiving optical fiber 3.

If you use the optical branch circuit configured in this way, you can connect it to either optical fiber 2 or 2' depending on the type of optical fiber under test and keep the other closed, and use it as a single source pulse tester. It will be shared for one mode and multiple modes.

Furthermore, since the acousto-optic optical deflector can change the diffraction efficiency depending on the amplitude of the electrical signal being moved,
A. The attenuator function can also be used at the same time. In other words, 1
By shifting the fibers, it is possible to eliminate the negative effects caused by Raman scattering and Prillouin scattering, which tend to occur when measuring single mode fibers, and also to increase the light intensity when measuring multimode fibers. It is possible to use a common light source with a high light intensity, and stable measurements with a height of 41" can be achieved.

1/ This is another advantage of the present invention: Which of the 9V constant optical fibers for Senebisu d has the 4th best S/N?
There are also things that can be obtained from C. In other words, since diffracted light is always used when guiding light to the source fiber for light reception, it is possible to easily receive light only at the necessary times using electrical signals, and unnecessary reflected light can be removed. be.

The positional accuracy in manufacturing will also be improved by the relaxation. That is,
When the light is transmitted to the optical fiber 2' to be measured and the receiving optical fiber 3, there is a noise.
,,f2. Since the direction is determined by f5, it is possible to improve the light efficiency by adjusting this frequency.

Effects of the Invention As described above, the optical branching circuit according to the present invention makes it possible to configure an optical pulse tester that can be used for both single-mode fiber and multi-mode fiber measurements, resulting in a significant reduction in cost (t41), increased versatility, and improved performance. is obtained.

[Brief explanation of drawings]

FIG. 1 is a (1'4) diagram of an optical branching circuit using a conventional acousto-optic optical deflector, and FIG. 2 is a Bz diagram showing an embodiment of the present invention.
s) It is a block diagram of an optical branching circuit using a Φ optical light deflector. 1... Optical fiber for light transmission, 2, 2'...
・Optical fiber, 3...Optical fiber for light reception, 4,
5.5', 6...Cylindrical lens, 7...Acousto-optic light deflector, 8...For acousto-optic deflector,
drive circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] an optical fiber for transmitting light, a first lens that controls the spread of the emitted light from this optical fiber, an acousto-optic optical deflector that can change the traveling direction and intensity of this emitted light by an electric signal, and this acoustic a second lens for making the light that has passed through the optical light deflector enter a single mode optical fiber to be measured; and a second lens that makes the light that has passed through the acousto-optic light deflector enter a multimode fiber to be measured. a third lens for reflecting or scattering from the optical fiber to be measured;
and the second or third lens, a light-receiving optical fiber that receives the light that has passed through the acousto-optic optical deflector, and a fourth lens that causes the light to enter the light-receiving optical fiber, Either a second or third lens is disposed in a direction in which the light from the light transmission optical fiber is diffracted by a signal having the first frequency as a carrier wave applied to the optical deflector, and the light transmission The rest of the second or third lens is arranged in a direction in which the light from the optical fiber to be measured passes through the acousto-optic light deflector as it is, and the light is reflected or scattered from the optical fiber to be measured and the second or third lens is the fourth lens in a direction in which the light passing through the lens is diffracted by a signal having a carrier wave having a second or third frequency different from the first frequency applied to the acousto-optic light deflector; An optical branch circuit characterized by the following arrangement.