JPS6050294B2 - Demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to splitting light containing at least two wavelength components transmitted through one optical fiber according to the wavelength components, and transmitting the light through two optical fibers. This invention relates to fiber demultiplexing equipment.

A conventional device of this type will be explained. To simplify the explanation, the wavelength λ1 transmitted through one optical fiber is
A case will be described in which the light of λ2 and λ2 are demultiplexed. FIG. 1 shows an example of a conventional demultiplexing device, and FIG. 2 shows a sectional view thereof.
1 and 2 are gradient index rod lenses with a distribution in which the refractive index decreases approximately in proportion to the square of the distance from the rod center, and the length is such that the focal plane of the rod lens is at the end surface of the rod. It has a length (114 period length) such that

3 transmits light of wavelength λ1, and wavelength λ. It is a multilayer filter that reflects the light of Usually, the filter 3 is coated on the end face of the rod lens 1 or 2. 4
, 5 and 6 are optical fibers for input and output, and their end faces 4s
, 5s, and 6s are respectively arranged on the focal plane of the rod lens.

The operation of this conventional demultiplexing device will be explained with reference to a cross-sectional view of the device (FIG. 2). The wavelengths λ, and λ transmitted into the optical fiber 4. The light 7 is converted into a parallel light beam by the rod lens 1 and enters the multilayer filter 3, as shown by the light ray J. Of these, the light having the wavelength λ passes through the multilayer filter 3 and is focused by the rod lens 2 as shown by the light ray 8, and enters the optical fiber 6. On the other hand, as shown by a branch line 9, the light having the wavelength 7 and the wavelength λ2 is reflected by the multilayer filter 3 and enters the optical fiber 5 which is condensed by the rod lens 1. The lights of wavelengths λ1 and λ2 thus transmitted through the optical fiber 4 are demultiplexed and sent to the optical fibers 5 and 6, respectively.
However, in general, the characteristics of a multilayer filter are not perfect, and have characteristics as shown in FIG. 3, for example. Third
The figure shows an example of the characteristics of a bandpass filter that is transparent to wavelength λ1. In this way, in the bandpass filter, the transmittance at the required wavelength λ1 is approximately S゛10
Although a transmittance close to 0% can be obtained, it usually has a slight transmittance in other wavelength regions as well. For this reason, the second
In the conventional demultiplexing device shown in the figure, when a band pass filter with the characteristics shown in FIG. The optical fiber 6 passes through the multilayer filter 3.
sent to. For this reason, it has been difficult to obtain a duplexer with good performance so that, in addition to the light of wavelength λ1, the light of wavelength λ2 that has leaked into the optical fiber 6 due to the imperfection of the filter 3 is inputted into the optical fiber 6. Note that the wavelength λ incident on the optical fiber 6
It is conceivable to insert multiple filters between rod lenses 1 and 2 in order to reduce the light of 2, but in this case,
By overlapping the filters, the amount of light reflected at wavelength λ1 increases and these lights enter the optical fiber 5, which is undesirable. As described above, using this conventional demultiplexing device alone is inconvenient because deterioration of the demultiplexing characteristics due to imperfections in the multilayer filter cannot be avoided. In order to eliminate this drawback of the conventional demultiplexing device and obtain a demultiplexing device with a simple configuration and high performance demultiplexing characteristics, this invention uses two gradient index rod lenses. It has a structure in which a prism is interposed between them, and a multilayer film filter is sandwiched between two gaps between the prism and the rod lens, and will be described in detail below with reference to the drawings. FIG. 4 shows an embodiment j of an optical demultiplexing device according to the present invention,
FIG. 5 is a sectional view thereof.

To simplify the explanation, a case will be described in which the present demultiplexer is used to demultiplex the lights of wavelengths λ1 and λ2 transmitted through the optical fibers, and the demultiplexers are sent into two optical fibers. Reference numerals 1 and 2 are 4-distribution index rod lenses with a period length of 114, and multilayer filters 4, 5, and 6, which transmit light with wavelength λ1 and reflect light with wavelength λ2, are optical fibers for input and output. The end surfaces 4s, 5s, and 6s are arranged at the focal planes of the rod lenses 1 and 2, respectively.

Further, 11 is a right angle prism with an apex angle of 45. The lights of wavelengths λ1 and λ2 transmitted through the optical fiber 4 are converted by the rod lens 1 into a parallel beam of light as shown by the light ray 7, and then enter the multilayer filter 3. The light of different wavelengths is reflected by the multilayer film filter 3, focused by the rod lens 1, and enters the optical fiber 5. In this case, if a bandpass filter with the characteristics shown in FIG. 3 is used as the multilayer filter, the amount of light with wavelength λ1 reflected by this filter can be made extremely small, so that the amount of light with wavelength λ1 entering the optical fiber 5 can be reduced. Leakage can be made extremely small. On the other hand, the light transmitted through the multilayer filter 3 includes light with a wavelength λ1 (indicated by ray 8) and light with a wavelength λ2 (indicated by ray 10) due to imperfections in the filter 37. These lights are totally reflected by the slope of the prism and enter the multilayer filter 12 . Of these, the wavelength λ1
The light passes through the multilayer filter 12, is focused by the rod lens 13, and enters the optical J fiber 6. In this case, the wavelength λ2 transmitted through the filter due to the imperfection of the filter
The light can be made sufficiently small by keeping in mind that the light is filtered twice by the multilayer filter 3 and the multilayer filter 12. Alternatively, it is more effective to use a band-elimination filter that reflects almost 100% of the light with wavelength λ2 as the multilayer filter 12. As shown in FIG. 6, the characteristic of a band-elimination filter is that it usually has a reflectance of approximately S]00% at a desired wavelength, but also has a slight reflectance at other wavelengths. If such a band-elimination filter is used as the multilayer filter 12, almost 100% of the light with the wavelength λ2 will be reflected by the filter 12, so the light with the wavelength λ2 to the optical fiber 6 can be made smaller by a relatively small layer. Is possible. Now, the light of wavelength λ2 (ray 10) reflected by the multilayer filter 12 and the light of wavelength λ1 (ray 11) generated due to the imperfection of this filter are emitted from the side of the prism as shown by rays 10 and 14. Since the light is radiated to the optical fibers 5 and 6 and is lost, the light does not enter the optical fibers 5 and 6 and impair the characteristics of the demultiplexer. As described above, in the demultiplexing device according to the present invention, reflected or transmitted light of wavelengths other than the required wavelength due to imperfections in the multilayer filter can be removed without damaging the demultiplexing characteristics by interposing a prism between the rod lenses. be able to. In this embodiment, a case has been described in which a right-angle prism with an apex angle of 45 degrees is used as the prism, but the apex angle does not particularly need to be 45 degrees, nor does it need to be a right-angle prism.

In short, it is easy to understand from the above explanation that the effects of the present invention can be obtained as long as a prism is inserted to prevent the light reflected by the multilayer filter 12 from entering the optical fiber 5 or 6 again. I can do it. However, if a right-angle prism with an apex angle of 45° is used as the prism, the angles formed by the two rod lenses will be orthogonal, and the incident angles of the light rays to the multilayer filters 3 and 12 will be equal, so optical design and mechanical design will be difficult. It is advantageous. Furthermore, although we used gradient index rod lenses 1 and 2 with a period length of 114, the length of the head throat lens should also be limited to this length.
It is only necessary that the end surfaces 4s, 5s, and 6s of the rod lenses are arranged so that they are in the focal plane of the rod lens. However, when the rod lens has a period length of l, the focal plane and the end surface of the rod lens coincide, and therefore the end surfaces 4s, 5s, 6s of the optical fibers 4, 5, 6 can be brought into close contact with the end surfaces of the rod lens, which reduces Fresnel reflection. It is extremely advantageous. It is also obvious that an optical fiber bundle obtained by bundling a plurality of optical fibers can be used as the optical fibers 4, 5, and 6. Although the above description has been made for the case of splitting light of two wavelengths, this invention is not limited to this, and the same invention can be applied to the case of splitting light of three or more wavelengths into two depending on the wavelength. effect can be obtained.

As described above, the demultiplexing device according to the present invention has a structure in which a prism is interposed between two gradient index rod lenses, and a multilayer filter is sandwiched between the prism and the rod lens. This has the advantage that unnecessary transmitted light or reflected light due to imperfections can be removed, and a demultiplexer with good demultiplexing characteristics can be obtained.

Brief Description of the Drawings Figure 1 shows a conventional demultiplexer, Figure 2 is a sectional view of the conventional demultiplexer shown in Figure 1, and Figure 3 shows an example of the characteristics of a band-pass filter. FIG. 4 is a diagram showing an embodiment of the demultiplexing device according to the present invention, FIG. 5 is a sectional view of an embodiment of the demultiplexing device according to the present invention shown in FIG. 4, and FIG. FIG. 3 is a diagram showing an example of characteristics of a blocking filter.

In the figure, 1 and 2 are gradient index rod lenses, 3 is a multilayer filter, 4, 5, and 6 are input/output optical fibers, and 7 is a wavelength λ1 emitted from the input optical fiber into the rod lens.
and λ2, 8 is an example of a light beam of wavelength λ transmitted through the multilayer filter 3, and 9 is a wavelength λ reflected by the multilayer filter 3.

Claims (1)

[Scope of Claims] 1. A demultiplexing device that splits light of at least two wavelength components transmitted through one optical fiber or optical fiber bundle according to wavelength and sends it to two optical fibers or optical fiber bundles. A gradient index rod lens having a length of 1/4 period length or less is arranged with a prism interposed between its end faces, and a multilayer film filter is sandwiched between the prism and each rod lens. Two optical fibers or optical fiber bundles are arranged on the focal plane of the lens opposite to the prism, and one optical fiber or optical fiber bundle is arranged on the focal plane of the other rod lens opposite to the prism. A demultiplexing device characterized by: 2. The demultiplexing device according to claim 1, characterized in that a rod lens is disposed on each of two surfaces sandwiching a right angle of a right angle prism having an apex angle of 45 degrees. 3 A band transmission filter is sandwiched between a prism and a rod lens with two optical fibers arranged on its focal plane, and a band rejection filter is sandwiched between another rod lens and the prism. A demultiplexing device according to claim 1.