JPS6029930B2 - optical attenuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical attenuator used for various experiments, investigations, etc. of optical communication systems.

Conventionally, the purpose of optical attenuators is to attenuate light, so various methods have been considered, such as making the coupling between optical transmission lines coarser or denser, or inserting an attenuation plate into the optical transmission line, etc., but the transmission characteristics Therefore, it is desirable to have an attenuator that does not affect the

Considering these conditions, the latter is more advantageous and is generally adopted. The attenuation plate of this type of optical attenuator is generally ND (Neutral Density).
There are two types of ND filters: a light-absorbing type and a light-reflecting type, and the latter is used because it has better wavelength flatness.

This reflective ND filter is a glass plate vacuum coated with metal such as chrome, and absorbs relatively little light. Therefore, when used in an optical attenuator, the following problems arise. FIG. 1 is an explanatory diagram thereof, in which 1 is a glass plate, 2 is a metal vapor-deposited plate, P is incident light, and P2 is transmitted light.

The reflected light of P3 then enters the incident light P, and becomes an obstacle. Therefore, if the glass plate is set at an angle of 8 with respect to the optical path as shown in Figure 2, the reflected light P3 becomes the incident light P,
There is no reverse incidence to the side. In this figure, the same parts as in FIG. 1 are given the same numbers. However, in this case, a difference in the refractive index of the glass plates causes a deviation Δd between the optical axes of P and P2, which is very inconvenient when designing an optical attenuator. The present invention has been developed in view of this point, and is intended to prevent reflected light from entering the incident light side in the opposite direction, and also to prevent light misalignment between incident light and transmitted light.

FIG. 3 is a schematic explanatory diagram of the present invention, in which a is a plan view and b is a side view. In this figure, 1 and 2 are the same as in FIGS. 1 and 2. 3 is a right angle prism for turning the optical path. After the incident light P, passes through the glass plate 1, its optical axis is shifted, but the optical path is turned back at 3 and enters the glass plate 1 again.
At this time, the optical axis is returned to the same position as P. Furthermore, since the light passes through the attenuation plate twice, an attenuation amount twice that of the attenuation plate can be obtained. The greater the amount of attenuation the damping plate has, the longer it takes to wear and the more expensive it becomes, so being able to obtain twice the amount of attenuation is a major advantage. It is also possible to insert separate attenuation plates set at the same angle, or by stacking two or more attenuation plates, or by using glass plates with different thicknesses and refractive indexes to align the optical axis. It is also possible to adjust. As described above, the present invention returns the light transmitted through the attenuation plate having a certain angle with respect to the incident light, transmits it through the attenuation plate having the same angle, and connects the incident light to the final attenuation plate. This is an optical attenuator characterized in that the optical axes of the transmitted light are aligned in one direction.

Note that the present invention can also be applied to optical circuits such as branching circuits, dividing circuits, and switching circuits.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional optical attenuator, FIG. 2 is a diagram for explaining the present invention, and FIGS. 3 a and 3 b are an embodiment of the present invention. Millet Figure 2 Figure 3

Claims (1)

[Claims] 1. An attenuating plate having an angle θ with respect to the incident light, and a means for folding the transmitted light of the attenuating plate to the incident light side parallel to the incident light, and the folded light is directed toward the incident light. An optical attenuator characterized in that light transmitted through an attenuation plate is output light. 2. The optical attenuator according to claim 1, wherein the folding means is a right angle prism.