JPH04317009A - Optical attenuator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical attenuator for attenuating optical power transmitted through an optical fiber in a transmission line.

0002

2. Description of the Related Art In recent years, various optical attenuators have been considered for adjusting the power of received light in optical fiber communication systems and for evaluating optical fiber transmission.

There are two types of optical attenuators: fixed optical attenuators that attenuate a certain amount of optical power, and variable optical attenuators that can arbitrarily vary the amount of attenuation. The latter is used for adjustment and evaluation of optical fiber transmission.

Although the fixed optical attenuator described above can be easily manufactured in a small size and at low cost, there is a problem in that many types of fixed optical attenuators must be prepared depending on the transmission loss.

On the other hand, a variable optical attenuator has the advantage that a wide range of permissible received optical power can be obtained because the amount of attenuation can be varied according to transmission loss, but it has the problem that it has a complicated structure and is expensive.

The conventional variable optical attenuator described above will be explained below with reference to FIG. FIG. 3 is a block diagram showing the configuration of a conventional variable optical attenuator. First, 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 passes through disk-shaped optical filters 3 and 4, which are installed obliquely with respect to the optical axis of the first lens 2 and whose attenuation coefficient changes stepwise. The parallel light passing through the optical filters 3 and 4 was configured to enter the optical fiber 5 on the output side via the second lens 6.

The optical attenuator configured as described above performs coarse adjustment of the amount of attenuation by rotating and switching the optical filter 3 having stepwise different attenuation factors as shown by the arrows in the figure. 4, the attenuation amount was similarly finely adjusted.

[0008]

However, in the above-mentioned conventional configuration, an optical filter whose attenuation rate changes stepwise must be fabricated radially, resulting in an increase in cost. Furthermore, since the optical attenuator was configured to rotate as a circular filter to change the attenuation rate, there were also problems such as the overall structure of the optical attenuator becoming large.

The present invention solves the above-mentioned conventional problems, and aims to provide a small, low-cost optical attenuator.

0010

[Means for Solving the Problem] In order to solve this problem, the optical attenuator of the present invention includes an optical collimating system that converts light from an optical fiber into parallel light, and a focusing lens that focuses the parallel light onto the optical fiber. An isosceles triangular prism that changes the direction of the optical path is placed between the system and the prism so that its base is parallel to the optical axis of the light emitted from the light collimating system and the emitted light is incident on the hypotenuse. A striped optical filter formed to have gradually different reflectances is arranged below the base of the isosceles triangular prism and parallel to the base.

[0011]

[Operation] With this configuration, the light emitted from the optical fiber is collimated by the optical system and enters the isosceles triangular prism, then changes its optical path and is reflected by the striped optical filter, and then returns to the isosceles triangular prism. Through,
The optical fiber is now coupled to the optical fiber by a focusing lens system, and if the amount of attenuation is to be changed, the optical path is moved to a position where the reflectance of the optical filter is different by moving the isosceles triangular prism parallel to the optical axis direction of the optical fiber. moves, and the amount of attenuation can be changed.

0012

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an optical attenuator in a first embodiment of the present invention. In FIG. 1, 11 is a lens that converts light from an optical fiber 10 on the incident side into parallel light. . 12 is an isosceles triangular prism for changing the optical path, and the base portion 13 of this isosceles triangular prism 12
is arranged parallel to the optical axis of light emitted from the lens 11, and the light incident from the hypotenuse portion 14 enters the isosceles triangular prism 12 by 2.
The angle is set so that the light is refracted and emitted from the bottom portion 13. Reference numeral 15 denotes a filter, which is manufactured so that the light transmittance gradually varies on its surface in the longitudinal direction (in the direction of the arrow in the figure). A triangular prism glass block 16 is bonded to the back surface of the filter 15 to prevent light reflected from the back surface of the filter 15 from passing through substantially the same optical path as light reflected from the front surface.

Reference numeral 17 denotes the oblique side of the isosceles triangular prism 12 on the output light side, so that the light reflected from the surface of the filter 15 is output at a position symmetrical to the input side. 18 is a lens for focusing the light emitted from the isosceles triangular prism 12 onto the output optical fiber 19.

The operation of the optical attenuator constructed as above will be explained. First, light incident from the optical fiber 10 is collimated by the lens 11, refracted at the oblique side 14 of the isosceles triangular prism 12, and incident on the base 13 of the isosceles triangular prism 12. The light incident on the bottom part 13 is refracted at the boundary surface,
The light is incident on the surface of the filter 15. The surface of the filter 15 reflects only the amount of light according to the reflectance of the surface, and the rest is refracted and reflected on the slope of the triangular prism glass block 16.
It escapes in a direction outside the optical path.

The light reflected on the surface of the filter 15 is
The light enters the bottom side 13 of the isosceles triangular prism 12 again and is refracted toward the exit side slope 17. At the exit side slope 17, the light is refracted at the same angle as the incident side and exits. The emitted light is coupled to an optical fiber 19 by a focusing lens 18.

As described above, according to this embodiment, since the filter 15 whose attenuation is variable can be constructed in a straight line, the mass production of the filter 15 is good, and moreover, the light incident on the filter 15 is It does not return to the optical fiber 10 on the input side and can be made smaller.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a partial sectional view showing the configuration of an optical attenuator according to a second embodiment of the present invention. In FIG. 2, reference numeral 20 denotes a converging lens, which couples the light that has passed through the filter 15 to the optical fiber 21, and is arranged and coupled so as to coincide with the optical axis of the light that has passed through the filter 15. The focusing lens 20 and the isosceles triangular prism 12 are integrally coupled by a member 22, and are configured to move in conjunction with the movement of the isosceles triangular prism 12. The other configurations are similar to those shown in FIG. 1 described in the first embodiment. The difference from the configuration in FIG. 1 is that the transmitted light from the filter 15 is focused by a focusing lens 20 and coupled to an optical fiber 21.

The operation of the optical attenuator constructed as described above will be explained below. The light reflected on the surface of the filter 15 is the same as that in the first embodiment, and its explanation will be omitted. The light transmitted through the filter 15 is passed through the converging lens 2
0 and coupled to an optical fiber 21.

When the isosceles triangular prism 12 is moved,
Since the focusing lens 20 that is integrally attached to the member 22 moves together with the isosceles triangular prism 12, even if the optical path of the transmitted light changes, it always matches the optical axis of the focusing lens 20. Become.

As described above, by attaching the isosceles triangular prism 12 and the focusing lens 20 so as to be integrated with the member 22, even if the amount of attenuation is changed, the light transmitted through the filter 15 can be focused by the focusing lens 20. can be coupled to the optical fiber 21.

In other words, the first embodiment merely has the function of an optical attenuator, but the second embodiment has the function of a variable splitter that can use the attenuated light as a branch for monitors, etc. It has the following.

[0023]

[Effects of the Invention] As described above, the optical attenuator according to the present invention has
By providing an isosceles triangular prism and a linear variable filter between the optical paths of the optical collimating system and the focusing lens system, a small and low-cost optical attenuator can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the configuration of an optical attenuator in a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing the configuration of an optical attenuator in a second embodiment of the present invention.

[Figure 3] Configuration diagram showing the configuration of a conventional optical attenuator

[Explanation of symbols]

10, 19 Optical fibers 11, 18 Lens 12 Isosceles triangular prism 13 Base portion of the isosceles triangular prism 14 Incident side oblique portion of the isosceles prism 15 Optical filter 16 Glass block

Claims (2)

[Claims] 1. An isosceles triangular prism that changes the optical path is installed between an optical collimating system that converts light from an optical fiber into parallel light and a focusing lens system that focuses the parallel light onto the optical fiber. parallel to the output optical axis from the collimating system,
The output light is arranged so that it enters the oblique side, and an optical filter formed so that the light transmittance gradually changes in a straight line is placed below the base of the isosceles triangular prism and parallel to the base. Optical attenuator placed. 2. The optical attenuator according to claim 1, wherein an optical filter and a second focusing lens system are arranged and coupled to the member to which the isosceles triangular prism is coupled, arranged on the transmission side of the optical filter.