JPH03257414A - Variable optical attenuator - Google Patents

Abstract

PURPOSE:To provide a variable optical attenutor with which a stable attenuation quantity is obtainable regardless of propagation modes by providing lenses, which are misaligned from the optical axes of optical fibers, between the optical fibers to be coupled and disposing optical fibers approximately perpendicular to the optical axes of the lenses. CONSTITUTION:The lenses 2, 6, which are respectively misaligned in the axial center by alpha from the optical axes of the optical fibers 1, 5, are provided between the optical fibers 1 and 5 to be coupled and the optical fibers 3, 4 which vary the quantity of the light to be passed are disposed between the lenses 2 and 6 approximately perpendicularly to the optical axes of the lenses. The return of the exit light from the lens 2 to the optical fiber 1 is prevented by the misalignment of the axial centers of the lenses 2, 6, and the optical fibers 1, 5 in spite of the reflection of this light by the optical fibers 3, 4 and the light past the optical fibers 4 is emitted to the position misaligned by alpha from the optical axis and is coupled to the optical fiber 5. Thus, the distance between the lenses 2 and 6 is then shortened and the variable optical attenuator which is stable regardless of the propagation modes in the optical fibers is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a variable optical attenuator that is provided between optical fibers to vary the amount of light passing therethrough.

2. Description of the Related Art Conventional variable optical attenuators have been developed using two methods: inserting an optical filter into the optical path and narrowing down the beam on the optical path. The former method provides stable attenuation regardless of the propagation mode within the optical fiber, but is large in size. On the other hand, the latter is smaller, but since the beam amount is changed by changing the aperture, the amount of attenuation changes depending on the propagation mode within the optical fiber.

As a method using an optical filter, there is a method as shown in FIG. The light emitted from the optical fiber 1 on the input side is converted into parallel light by the first lens 2. This parallel light is then filtered through a disc-shaped optical filter 3 which is installed obliquely with respect to the optical axis of the first lens 2 and whose attenuation rate differs stepwise, and which is tilted with respect to the lens optical axis in the same way as the disc 3. The light passes through a disc-shaped optical filter 4 having a fan-shaped attenuation rate that differs slightly. The parallel light that has passed through the optical filter 3.4 is configured to enter the optical fiber 5 on the output side via the second lens 6.

The operation of this attenuator is to roughly adjust the amount of attenuation by switching optical filters 3 with different attenuation factors in a stepwise manner, and to finely adjust the amount of attenuation using the disc-shaped optical filter 4. . In such a lens system, the optical filters 3 and 4 are tilted with respect to the axis of the optical path so that the reflected light from the optical filters 3 and 4 does not return to the optical fiber 1 on the incident side.

Must be attached.

Problems to be Solved by the Invention However, in such a configuration, as described above, the optical filter 3.4 must be installed at an angle with respect to the lens 2.6, which increases the distance between the lenses 2.6. ,
There was a problem that the shape became large.

The present invention solves the above-mentioned conventional problems.

The present invention provides a small-sized variable optical attenuator that has a simple configuration and can provide a stable attenuation amount regardless of the propagation mode within the optical fiber.

Means for Solving the Problem In order to solve this problem, the present invention provides a method in which the optical axis of the lens is shifted from the axis of the optical fiber, and an optical filter is arranged approximately perpendicular to the optical axis of the lens. This is what I did.

Effect: By arranging the optical axis of the lens to be offset from the axis of the optical fiber in this manner, the beam emitted from the lens is inclined with respect to the optical axis of the lens. Therefore, the reflected light from the optical filter provided perpendicularly to the optical axis of the lens does not return on the incident optical path.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

In the figure, 1 is an optical fiber on the input side, and 2 is a first converging Ronde lens (hereinafter referred to as the first lens) that converts the light emitted from the optical fiber 1 into parallel light. The axis of the first lens 2 is offset from the axis of the optical fiber 1 by α. 3.4 is an optical filter in which the surface of one disk is shaped like a fan with different attenuation rates.
H changes stepwise, and 4 changes continuously.

Reference numeral 6 denotes an optical fiber on the output side, which, like the first lens 2, is attached with its axis shifted by α from the second converging Rondo lens (hereinafter referred to as the second lens), and is attached to the optical filter 3.
．． Parallel light that has passed through 4 is made incident.

The optical variable attenuator configured in this way is the first one.
-7 Since the axis of the lens 2 is offset by α from the axis of the optical fiber 1, the output angle φ from the lens end is tilted by the angle shown by the following formula with respect to the lens axis. Become.

φ=−n·γ·α Here, γ is the refractive index distribution constant of the lens, and n is the refractive index at the center of the lens.

Since the output beam from the end of the first lens 2 enters the first optical filter 3 at an angle of φ, the light reflected on the surface of the optical filter 3 travels in a direction inclined by 2φ from the incident direction. become. Similarly, the light enters the second optical filter 4 at an angle of φ, and the reflected light travels in a direction inclined by 2φ.

The light that has passed through the second optical filter 4 is passed through the second lens 6
The light enters the lens 6 at an angle of φ, exits to a position shifted by α from the optical axis of the lens 6, and is coupled to the optical fiber 6.

Although a circular optical filter is used here, a rectangular optical filter whose attenuation rate is changed in the elongated direction can also be used without increasing the size.

Effects of the Invention As described above, according to the present invention, since the lenses provided between the optical fibers to be coupled are offset from each other with respect to the optical axis of the optical fibers, it is possible to reduce the amount of light passing through the optical filter. reflected light does not return to the input fiber. Therefore, the optical filter can be arranged perpendicularly to the optical axis of the lens, and the distance between the lenses can be shortened and the size can be reduced. In addition, a stable optical variable attenuator can be realized regardless of the propagation mode within the optical fiber.

[Brief explanation of drawings]

FIG. 1 is a front view of a variable optical attenuator according to an embodiment of the present invention, FIG. 2 is a front view showing the state of reflected light on an optical filter of the variable optical attenuator, and FIG. 3 is a front view of the variable optical attenuator used in the present invention. FIG. 4 is a perspective view of an optical filter and a front view of a conventional variable optical attenuator. 1.6...Optical fiber, 2.6...1st. Second lens, 3.4... optical filter.

Claims (1)

[Claims] Optical variable attenuation is an optical variable attenuation system in which an optical filter that changes the amount of light passing through the optical path is installed approximately perpendicular to the lens optical axis between a pair of lenses whose optical axes are offset from the axis of the optical fiber. vessel.