JPS6150036A - Light splitting circuit - Google Patents

Abstract

PURPOSE:To obtain a light splitting circuit, which can be used both for a single mode optical fiber to be measured and a multimode optical fiber to be measured, by utilizing the band width of the deflected 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 signal from a driving circuit 8 is applied to the light beam, the light beam is diffracted in the direction of theta obtained by the expression in the Figure. Namely, when f=f1, theta=theta1 is obtained. When f=f2, theta=theta2 is obtained. The light beam is guided to an optical fiber to be measured through a lens 5 or 5' and an optical fiber 2 or 2'. The light from the optical fiber to be measured is diffracted when the signal is applied to the light from the driving circuit 8. The light is guided to a light detector through a lens 6 and a light receiving optical fiber 3. Namely, with respect to the light passing the lens 5, theta=theta3 is obtained when f=f3, and theta=theta4 is obtained when f=f4. Thus the direction of the light agrees with the direction of the lens 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical branching circuit, and more particularly to a deflection type optical branching circuit used for measuring backscattered light of an optical fiber.

Conventional groove formation and its problems When a light pulse propagates through an optical fiber, backscattering occurs due to reflection and Rayleigh turbulence. Today, a method of detecting and processing this backscattered light has become an effective means for searching for fault points and measuring loss in optical fibers, and this device is generally called an optical pulse tester. .

The tester is equipped with enough optical branching circuits to separate the incident light pulse and backscattered light, but the performance of this optical branching circuit greatly influences the performance of the optical pulse tester. The optical branching circuit that has been reported so far includes: (1) splitting light using the birefringence of crystals such as calcite;
1. Polarization separation method.

(2) Beam splitting method using a half ffyj N"jl mirror.

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

There are methods such as It is well known that the most fraudulent method among these is the method using the acousto-optic optical deflector described in (3) above, which allows masking in the optical domain, and the conventional configuration of the optical branch circuit is A diagram is shown in FIG.

In the optical branching circuit shown in FIG.
, and enters the optical fiber to be measured via the optical fiber 2. The reflected light from the optical measurement optical fiber containing information regarding defects and losses in the optical fiber to be measured passes through the lens 5 and the acousto-optic optical deflector 7. At this time, the driving circuit 8
When an electric signal is applied from the deflection booklet, it is diffracted in the direction θ given by the following equation (1) due to the action of sound waves propagating through the deflection booklet.

θ−λ−f/v・・・・・・・・・
(1) Here, λ is the optical wavelength, f is the acousto-optic optical deflector,
1 is the carrier wave frequency that moves, and 2 is the sound speed of the sound wave propagating in the medium of the acousto-optic optical deflector. The diffracted scattered light passes through the lens 6 and the optical fiber 3 and enters the photodetector, where information regarding the failure point and loss of the optical fiber 2 is obtained. Therefore, in the above circuit, if the drive circuit 8 drives the acousto-optic optical deflector when the reflected light pulse from the fiber under test passes through the deflector 7, the scattered light containing the necessary information is connected to the optical fiber 3. In other words, we can ask the photodetector.

In the optical branching circuit with the above-mentioned conventional configuration, the light that passes from the light source through the optical fiber 1, the lens 4, and the acousto-optic optical deflector 7 is concentrated in only one place. Only one terminal was provided for connecting the optical fiber to be measured.

(In the figure, the right end 2a of the optical fiber 2 is the connection part with the optical fiber to be measured.) The connection terminal of this optical fiber to be measured, which is made up of the lens 5 and the optical fiber 2, is The type is determined by whether it is a mode fiber or a multimode fiber.

Therefore, it is necessary to separately manufacture two types of optical branch circuits, one for single mode fiber and one for multimode fiber, according to the mode type of the optical fiber to be measured. The drawbacks were that the first configuration was separate, increased costs, and lacked versatility.

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

In other words, when the constant optical fiber 11 is a single mode fiber, the optical fiber 2 is made into a single mode fiber, and the coupling portion between the lens 6 and the optical fiber 2 is also made to have dimensions specific to the single mode fiber. If the optical fiber to be measured is a multi-mode fiber, it must be a multi-mode fiber, and the junction between the lens 5 and the optical fiber 2 must also have dimensions specific to a multi-mode fiber. This is because there is.

OBJECTS OF THE INVENTION The present invention aims to eliminate such conventional drawbacks, and aims to provide an optical branching circuit that can use both a single mode fiber and a multimode fiber as the optical fiber to be measured.

Structure of the Invention To achieve this objective, the present invention utilizes the deflection frequency bandwidth of an acousto-optic optical deflector to determine the direction in which light from a light transmitting optical fiber is diffracted by two frequencies within the deflection frequency band. Single-mode fibers and multi-mode fibers are placed as optical traveling fibers, and lenses are arranged to input light into these fibers, and the reflected or scattered light from each optical fiber to be measured is deflected again into the frequency band. The light is diffracted at a frequency within the range, and is made incident on a light-receiving optical fiber arranged in a direction different from the direction in which the light-transmitting optical fiber is arranged. With this arrangement, when the light from the light transmitting optical fiber passes through the acousto-optic optical deflector, the direction and intensity are controlled by electrical signals and the light is directed to one of the optical fibers to be measured. The light from the fiber under test enters the acousto-optic optical deflector from different angles, but at this time, if it is within the deflection frequency band, it can satisfy the incident condition called the Bragg angle with respect to the sound -1' wavefront. ,
By selecting appropriate frequencies, the lights incident from different angles travel in the same direction and are guided to the receiving optical fiber. Therefore, depending on the type of fiber, it can be connected to one of the optical fibers to be measured, the other being closed and used, and the carrier frequency and amplitude of the acousto-optic optical deflector can be set so that they can be used in common.

DESCRIPTION OF EMBODIMENTS A practical example of the present invention will be described below with reference to FIG. 2. In FIG. 2, parts that are the same as those in FIG. 1 are given the same numbers.

In FIG. 2, the light from the light transmitting optical fiber 1 enters the acousto-optic optical deflector 7 as a nearly parallel light beam through the lens 4, and when a signal from the 1 drive circuit 8 is applied (1)
It is diffracted in the direction according to Eq. That is, when f-f+ is set, θ=θ1, and when f-12 is set, θ-θ2. single mode fiber) to the optical fiber to be measured.

Next, for the light from the optical fiber to be measured, the drive circuit 8
When a signal is applied, it is diffracted and guided to a photodetector via a lens 6 and a light-receiving optical fiber 3. That is,
For light passing through lens 6, when f = fs, θ
-θ5, and for the light passing through lens 5', f
= f, then θ=θ4, which coincides with the direction of the lens 6. In this example, θ is within the frequency band of the acousto-optic light deflector.
3 is the minimum frequency, and θ2 is the maximum frequency. Since the optical signal is transmitted and received in a time-division manner, the signal from the drive circuit can be time-divisionally configured using each carrier wave frequency.

For example, four types of carrier waves can be constantly oscillated by an oscillator and the switching circuit can be switched as appropriate. If the optical branch circuit configured in this way is used, depending on the type of optical fiber to be measured, the optical fiber 2, By simply connecting one of the terminals 2' and closing the other, the optical pulse tester can be used both for single mode and multimode.

Furthermore, since the acousto-optic optical deflector can control the diffraction efficiency by 1 lilJ according to the amplitude of the driven electric signal, it can also function as an optical attenuator at the same time. In other words, by using an electrical signal with an appropriate amplitude depending on the light intensity of the light source,
By moving the ji: The intensity can be increased, and a shared light source with high light intensity can be used, making it possible to achieve highly accurate and stable measurements.

Another major effect of the present invention is that an extremely high S/N ratio can be obtained no matter which optical fiber to be measured (f) is used. This is because, since diffracted light is always used, it is possible to easily receive light only at the necessary times using electrical signals, and unnecessary reflected light can be removed.

Positional accuracy in manufacturing can also be relaxed. That is,
All light is introduced into the optical fiber to be measured and the receiving optical fiber at the carrier wave frequency f1+ when the acousto-optic optical deflector is in motion.
Since the direction is determined by f2r f5 + 8, the light coupling efficiency can be improved by adjusting this frequency. It becomes possible to construct an optical pulse tester that can share the ijl constant of single mode fiber and multimode fiber, resulting in significant cost savings, increased versatility, and improved performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical branching circuit using a conventional acousto-optic optical deflector, and FIG. 2 is a block diagram of an optical branching circuit using an acousto-optic optical deflector showing an example of the present invention. 1... Optical fiber for light transmission:, 2, 2'... Source fiber, 3... Optical fiber for light reception, 4 +
5 + 5 + 6...Cylindrical lens, 7...
Written by Acousto-Optic Light Deflector 3.8... Drive circuit for acousto-optic light deflector. Name of agent: Patent attorney Nakao ;・Hara Oka (・1 person) Figure 1 Figure 2

Claims (1)

[Claims] an optical fiber for transmitting light, a first lens for controlling the spread of the emitted light from this optical fiber, an acousto-optic optical deflector that can change the traveling direction and intensity of the emitted light by an electrical signal, and second and third lenses for making the light that has passed through the optical deflector enter the optical fiber to be measured; After that, a light-receiving optical fiber that receives the light that has passed through the acousto-optic optical deflector, and a fourth light-receiving optical fiber that makes the light enter the light-receiving optical fiber.
the second lens in the direction in which the light from the light transmission optical fiber is respectively diffracted by a signal having a first or second frequency as a carrier wave applied to the acousto-optic optical deflector. , a third lens is arranged, one of the optical fibers to be measured is a single mode fiber and the other is a multimode fiber, and the second or third optical fiber is reflected or scattered from the optical fiber to be measured. The light passing through the lens is diffracted in the same direction by a signal having a third or fourth frequency as a carrier wave applied to the acousto-optic optical deflector, and the fourth lens is disposed in this direction. optical branch circuit.