JPS5814112A - Optical demultiplexer - Google Patents

Abstract

PURPOSE:To prevent the degradation in filter characteristics by using two sheets of filter elements which are disposed on both surfaces of a triangular prism and reflect light of different wavelengths, respectively. CONSTITUTION:An interference filter which reflects light of a wavelength lambda1 is formed on one surface of a thin triangular prism 5 of a vertical angle alpha and an interference filter which reflects the light of a wavelength lambda2 is formed on the other face opposite thereto in such a way that the light is reflected in the same direction and therefore if the multiplie light waves of the wavelengths lambda1 and lambda2 are projected from an input optical fiber 71, said waves are collimated by a projecting lens 8, and are made incident to the above-mentioned optical fiber, by which the light of the wavelength lambda1 is reflected as shown by chain lines and the light of the wavelength lambda2 is branched as shown by dotted lines, respectively, and these beams of the light are made incident to the lens 8 at desired angles. The wavelengths lambda1, lambda2 are condensed by the lens 8 and are made respectively incident to output fibers 72, 73, whereby said wavelengths are transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical demultiplexer used for optical multiplex communication.

In optical transmission systems, optical signals are often multiplexed and transmitted in order to utilize optical transmission paths more effectively. This involves superimposing independent optical signals sent from light emitters with different wavelengths in an optical multiplexer and transmitting them within an optical cable, and on the receiving side, the wavelength-multiplexed optical signals are optically demultiplexed. The wavelength is separated by a wave detector and sent to each receiver.

The first diagram shows the configuration diagram of an optical demultiplexer using a conventional interference filter.
As shown in the figure.

In Fig. 1, 3 is an interference filter in which several materials with different refractive indexes are alternately deposited on a glass substrate with a predetermined thickness determined by the relationship with the wavelength of the light to be separated, and the light of wavelength λ is reflected. , wavelength λ is transmitted. wavelength λ
8. On the optical axis of the input optical fiber 1, which projects multiple electric lights of λ, onto the interference filter 3 at an incident angle of 45°, an output optical fiber 22 is arranged on the opposite side of the interference filter 3. The output optical fiber 2I that receives the reflected light is arranged at a predetermined position perpendicular to the optical axis of the input optical fiber 1.

At a predetermined position on the optical axis of the input optical fiber 1 between it and the interference filter 3, there is a convex lens 4 for collimating the incident light. However, the output fiber 2. A convex lens 4 condensing the reflected light is placed in front of the output optical fiber 2. A convex lens 4° for condensing transmitted light is disposed on the front surface of each of the lenses.

In an optical demultiplexer having such a configuration, the input optical fiber 1
wavelength λ1. to the interference filter 3. When multiplexed light with a wavelength of λ is projected, the light with a wavelength of λ is reflected to the output optical fiber 21, and the light with a wavelength of λ is transmitted to the output optical fiber 2. The signals are separated and sent to each other.

A crosstalk prevention filter 3' having substantially the same structure as the interference filter 3 is disposed behind the interference filter and perpendicular to the optical axis to reduce crosstalk.

However, it is necessary to form an anti-reflection coating on the back surface of the glass substrate of such a conventional optical demultiplexer phase interference filter so as not to reflect light at wavelengths, and the angle of incidence must be relatively large. Therefore, there is a risk that the characteristics of the filter will deteriorate due to differences in the polarization characteristics of the light. That is, the polarization of light can be expressed by two independent polarization components S and P. Normally, an optical demultiplexer uses a mixture of S and P light, that is, randomly polarized light. Therefore, when 2 randomly polarized light is incident on the filter, the filter characteristics are 11
It can be expressed as By the way, the filter characteristics of S and P exhibit different characteristics when the incident angle is 10 degrees or more, and the characteristic of - is deteriorated compared to when the incident angle is 00 degrees. Furthermore, each of the input and output optical fibers requires a convex lens, resulting in a complex configuration and high cost.

In view of the above-mentioned problems of conventional optical demultiplexers, an object of the present invention is to
To provide an optical demultiplexer that has very little deterioration of filter characteristics and is simple in configuration and inexpensive by projecting multiplexed light with a small angle of incidence onto two filter elements that each reflect light of different wavelengths. There is a particular thing.

The purpose of this is to arrange a pair of optical lenses in front of an optical filter in which filter elements that reflect light of different desired wavelengths are formed on both sides of a triangular prism so that the respective reflected lights are in the same direction. This can be achieved by projecting wavelength-multiplexed light at a small angle of incidence through the optical lens from the input circuit elements arranged in parallel with the arrayed light receiving circuit elements.

The principle of the present invention will be explained with reference to FIG.

Reference numeral 5 in FIG. 2 is an optical filter used in the present invention, in which a thin triangular prism 6° with an apex angle α has an interference filter 61 that reflects light of wavelength λ on the negative face, and an interference filter 61 that reflects light of wavelength λ on the other face. Interference filters 6 that reflect light are arranged to face each other so that the reflected light is directed in the same direction. When multiplexed waves with wavelength C and wavelength λ are projected onto the interference filter 61 of such an optical filter 5 from point A to point Oo at an incident angle θ0, the wavelength λ1 is projected.
The light is reflected at a reflection angle θ6 (θ'.=00) at point 0° and travels toward point B. Wavelength λ! The light passes through the interference filter 6, is refracted within the triangular prism 6°, travels, is reflected at the point O1 by the interference filter 6g, and is refracted at the point O1 on the incident side of the triangular prism 6o. The refractive index of the triangular prism 6°, which travels in the same direction as wavelength doubling, is n
The angles AO and B are 01, and the angle formed by the reflected lights O and C is θ!
Then, 0, -20°tom-? "・2α 4- If the incident angle θ0 is selected, it can be set to 01-02. In other words, at the angle θ1 where the incident light of the multiplexed light wave and the reflected light of wavelength λ1 are mixed, the reflected light of wavelength λ1 and the reflected light of wavelength λ are The angle θ formed by the light can be made equal, and the arrangement of the input optical fiber and the light-receiving element can be facilitated.

FIG. 3 shows a configuration diagram of an optical demultiplexer according to an embodiment of the present invention.

In the same figure, reference numeral 71 denotes an input optical fiber that transmits multiplexed light waves with wavelengths λ-fold and λ-rich, and output optical fibers 7 that receive light with wavelength λ1 are arranged in parallel with a spacing l, and output optical fibers 7 and a spacing l are arranged in parallel. Output optical fibers 7m that receive light of wavelength λ3 are arranged in parallel, and the end faces of the respective optical fibers are substantially on the same plane. Input optical fiber 71
A convex lens 8 whose focal point is at the end face of the input optical fiber 7 is disposed in front of the convex lens 8, and further in front of the convex lens 8 is disposed the optical filter 5 described with reference to FIG.

The optical demultiplexer in Figure 3 has an incident angle θ. -'0.50, the angle between the optical axis of the triangular output optical fiber 71 and the reflected light of wavelength λ is 10. Further, the angle between the light reflected to the wavelength and the light reflected by the snow with the wavelength λ is also 1°. 7 eyebar array spacing 1=
At 125 μm, the focal length of the convex lens 8 is 7.16 mm.

When multiplexed light waves with wavelengths C and λ are projected from the input optical fiber 71 of the optical demultiplexer having such a configuration, they are collimated by the convex lens 8 and enter the optical filter 5 . The light of the wavelength is reflected as shown by the chain line, and the light of the wavelength λ is split as shown by the dotted line, and is reflected and incident on the convex lens 8 at a desired angle. This wavelength λ1. The light of λ is focused by a convex lens 8, and each output fiber is buffed by *=1.
m and is transmitted.

FIG. 4 shows another embodiment in which output optical fibers 91 and 9s are connected to both sides of an input optical fiber 91, and the optical filter 5 is connected to the output optical fiber 9. It is arranged to be inclined at a desired angle with respect to the optical axis of the light beam, so that the light is reflected at the same angle.

By doing this, it was possible to significantly reduce crosstalk due to the aberration of the convex lens 8 compared to the optical demultiplexer shown in FIG.

It should be noted that the present invention is not limited to the illustrated embodiment, and may be modified as appropriate within the scope of the claims, such as using a photoelectric converter such as a photodiode at the position of the output optical fiber.

As described above, according to the present invention, it is possible to provide an optical demultiplexer that has a simple structure and is inexpensive, with little deterioration of filter characteristics, and the effects thereof are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional optical demultiplexer, FIG. 2 is an explanatory diagram showing the principle of the present invention, and FIGS. 3 and 4 are block diagrams of one embodiment of the present invention. In the figure, 1 is an output optical fiber, 21+21 is an input optical fiber, 3 is an interference filter, 4 is a convex lens, 5 is a 7- optical filter, 6o is a triangular prism, 6□, 6. is interference filter, 71+91 is input optical fiber, 7M+78
+9,. 9. 8 indicates an output optical fiber, and 8 indicates a convex lens. 8- 1st figure spirit j

Claims (1)

[Claims] an optical filter 6 in which filter elements that reflect light of different desired wavelengths are formed on both sides of a triangular prism so that the reflected light is directed in the same direction; an optical lens that collimates light and focuses reflected light; an input circuit element that is disposed in front of the optical lens and projects a wavelength-multiplexed light wave; and an optical filter parallel to the input circuit element that An optical demultiplexer comprising a pair of light receiving circuit elements that receive light.