JPS6298306A - Wavelength selective coupler - Google Patents

Abstract

PURPOSE:To reduce the size of an optical waveguide circuit and to facilitate the handling of an interference film filter forming an interference filter on the surface of a base which faces an end surface of an optical waveguide and also forming a reflection part inside it. CONSTITUTION:The base 14 is a transparent cube and has a surface 14a facing the end surface of the optical waveguide 2 and a surface (b) facing a photodetector 13. The reflecting surface 11 is formed in the base at about 45 deg. to the top surface of a substrate 1, and an optical path is formed between the surfaces 14a and 14b. Further, the interference film filter 12 is formed on the surface 14a and positioned at about 90 deg. to the top surface of the substrate 1. Then, luminous wave flux which is propagated in the optical waveguide 2 as shown by a solid line is selected by its wavelength through the filter 12 of a wavelength selective coupler 10 which contacts the end surface of the waveguide 2 and only a light wave having specific wavelength shown by a dotted line is projected on the reflecting surface 11 and photodetected efficiently by the photodetector 13. Consequently, the need for an optical waveguide extending from the interference film filter to the photodetector is eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a wavelength selection function that enables the realization of a small, low-loss waveguide optical multiplexing/demultiplexing module, which is essential in the field of wavelength division multiplexing optical communications. This invention relates to a coupler between an optical waveguide and a light receiving/emitting element.

[Conventional technology]

In a wavelength division multiplexing transmission system in which optical signals with different wavelengths are transmitted through a single optical fiber, an optical multiplexing/demultiplexing module is required to separate and combine optical signals with different wavelengths. FIG. 7 shows a perspective view of a waveguide optical multiplexing/demultiplexing module developed to meet this requirement. The waveguide optical multiplexing/demultiplexing module is 81
Optical waveguide 2 pre-formed on substrate 1. Optical fiber guide 3. The interference film filter insertion groove 4 connects the optical waveguide 2 and the optical fiber 5, which is a mounting element. The mutual positional relationship with the glass block 6 with an interference film filter, the minute reflecting mirror 7, etc. is ensured. This waveguide type optical multiplexing/demultiplexing module has the advantage that it does not require sophisticated optical axis adjustment compared to conventional bulk type optical multiplexing/demultiplexing devices in which highly accurate individual elements are assembled on a substrate. The optical multiplexer/demultiplexer module is an interference film filter formed on a thin film substrate, which has a higher optical loss from the light receiving element or the light emitting element 8 to the optical fiber 5 than a bulk type optical multiplexer/demultiplexer, and requires careful handling. There was a problem when assembling that it had to be installed in a predetermined position.

FIG. 8 is a perspective view of the glass block 6 with an interference film filter, where 9 is an interference film filter and 10 is a glass block. The interference film filter 9 is a basic component of an optical multiplexer/demultiplexer, and the interference film filter 9 splits light wave bundles with different wavelengths into individual optical paths (or splits the light waves on the optical path on the side into one
It has the function of merging into two light wave packets. At present, the thickness t of the interference film filter mainly used is about 30 μm, and the interference film filter is installed and fixed in the optical waveguide with a width of about 50 μm.

The role of the glass block 10 in FIG. 8 is to facilitate the handling of the minute interference film filter 9 and to stably fix it on the substrate 1. Also, the role of the glass block 10 in FIG. The reason for having a target of 50 μm is to take into account the difficulty in inserting an interference film filter into an optical waveguide groove and the possibility of damage to the interference film filter.

[Problem that the invention seeks to solve]

Light waves propagating in an optical waveguide have a spread angle determined by Fresnel's law of reflection, so the light waves spread in the groove for inserting an interference film filter that does not have a waveguide structure, and the light waves propagate through the groove into the opposite guide. Loss occurs between wave paths. , Figure 9 shows the relationship between the normalized gap and the loss, in which the optical waveguide groove width is normalized by the optical waveguide width.As is clear from Figure 5, as the normalized gap increases, the optical waveguide Is the loss big? For example, in a commonly used optical multiplexing/demultiplexing module, the optical waveguide groove width is 50 μm while the optical waveguide width is 50 μm.
μm, the normalized gap is 1, and the loss at that time is about 0.6 aB.The 5-waveguide optical multiplexing/demultiplexing module is designed for the ease of insertion of the interference film filter into the groove in the design of the waveguide groove, and for the interference Considering the possibility of damage when inserting the membrane filter into the groove, it is necessary that the groove width be sufficiently larger than that of the interference membrane filter.On the other hand, considering the optical waveguide loss mentioned above, 1. As I recall, there was a contradictory problem in that the groove width needed to be as small as possible.

The present invention deals with the problem of how to realize a coupler that solves the above-mentioned problems. It is characterized by the fact that i.e. 1
In the present invention, a surface facing an end surface of an optical waveguide and a surface facing a light receiving/emitting element are provided. an interference film filter formed on a surface of the support that faces the end surface of the optical waveguide at an angle of approximately 90° with respect to the substrate surface of the waveguide optical multiplexing/demultiplexing module; , a reflecting portion formed inside the support at an angle of approximately 45° with respect to the substrate surface and forming an optical path between a surface facing the end surface of the optical waveguide and a surface facing the light receiving/emitting element; The support is characterized in that at least a portion of the support where the optical path is formed is transparent. Conventionally, an interference film filter with a wavelength selection function is installed and fixed in an interference film filter groove located in the middle of an optical waveguide, and is connected to the optical waveguide via a minute reflection pin located at one end of the optical waveguide. They were bonding light-emitting devices. According to the wavelength selective coupler of the present invention, there is no need for an optical waveguide from the interference film filter insertion groove and the nuclear interference film filter insertion groove to the light receiving and emitting elements in the conventional waveguide type optical multiplexing/demultiplexing module, and optical loss in the groove portion is eliminated. This makes it possible to prevent an increase in the amount of noise and to design a small waveguide multiplexing/demultiplexing circuit. Furthermore, handling of the interference film filter, which has been a problem in the prior art, becomes easier.

〔Example〕

FIG. 1 is a cross-sectional view of a waveguide type optical multiplexing/demultiplexing module for explaining the basic principle of the present invention, in which 1 is a substrate, 2 is an optical waveguide,
0 is a wavelength selective coupler according to the present invention, 11 is a reflecting surface (reflection part), 12 is an interference film filter, 13 is a light receiving element, and 14 is a support body.

The support body 14 is a transparent cube, and has a surface 14a facing the end face of the optical waveguide 2 and a surface 14 facing the light receiving element 13.
The reflective surface 11 having a surface b is formed inside the support body, is formed at an angle of approximately 45° with respect to the upper surface of the substrate 1, and forms an optical path between the surface 14a and the surface 14b. It is something.

The interference film filter 12 is formed on the surface 145L, and is positioned at an angle of approximately 90° with respect to the upper surface of the substrate 1.

The light wave bundle shown by the solid line in the figure propagating through the optical waveguide 2 is subjected to wavelength selection in the interference film filter 12 of the wavelength selective coupler 10 which is in contact with the end face of the converging waveguide, and the wavelength is selected by the interference film filter 12 shown by the dotted line in the figure. Only the light wave having the wavelength is emitted to the reflecting surface 11 and is received by the light receiving element 13 with efficiency. Reflective surface 11
Effective materials include metal materials such as gold and aluminum, or dielectric multilayer films. Furthermore, if an interference film filter having a wavelength Yuzawa function is used on the reflecting surface 11, only specific wavelengths will be selectively reflected toward the receiver. Since crosstalk is possible, it is also possible to further improve the crosstalk characteristics.

The above is an embodiment in which a light-receiving element is mounted on the wavelength selective coupler according to the present invention, but it is also possible to mount a light-emitting element as 13 in place of the light-receiving element. Fig. 2 shows details of the present invention. 5 2 is an optical waveguide, 10 is a wavelength selective coupler according to the present invention, 12 is an interference film filter, and 11 is a reflective surface. In this embodiment, the end face of the optical waveguide is an interference film filter. In this example, the size of the interference film filter is not limited to the size of the end face of the optical waveguide. Covering with a high reflectance layer will improve efficiency (coupling with the receiver and emitter will be possible). Figure 5 shows an embodiment of the present invention in which the upper surface of the lower cladding layer 15 is in contact with the end of the reflective surface. .

According to this embodiment, the distance between the end of the optical waveguide and the reflecting surface is shorter than that in the embodiment shown in FIG. 2, so that the coupling efficiency between the optical waveguide and the light receiving/emitting element increases.

FIG. 4 shows an embodiment of a wavelength selective coupler for further improving the coupling efficiency between the optical waveguide and the light receiving/emitting element. When the branching angle of two optical waveguides connected by an interference film filter is 2θ, the rectangular parallelepiped shown in Figure 4 is cut at an angle θ with respect to one vertical plane, and the angle θ portion is removed. According to the fifth embodiment, which is characterized in that the interference film filter 12 is formed on a new vertical surface, the longitudinal direction of one of the two optical waveguides coupled at the interference film filter surface is Since it is possible to oppose the reflective surface at an angle of 45° to the plane perpendicular to FIG. 4 is a diagram for explaining the effect of the wavelength selective coupler according to the present invention shown in FIG. 1, and shows the relationship between branching angle and loss by comparing the conventional branching section configuration and the branching section configuration according to the present invention. The branching angle is usually set around 30 degrees in consideration of the characteristics of the filter, and in the case of a branching angle of 30 degrees, the conventional branch loss (the loss at the filter insertion groove in Figure 7 and the slight loss from the filter insertion groove) The sum of the waveguide losses (1,400 and 4 losses) before reaching the reflecting mirror is about jclB, whereas the branch loss according to the present invention is about 0.3 dB, which makes it possible to reduce the loss by about 0.7 aB. FIG. 6 shows an embodiment in which the wavelength selective coupler according to the present invention is used as a two-wave multiplexer/demultiplexer. 10 is the wavelength selective coupler according to the present invention. According to the conventional multiplexing/demultiplexing circuit, there is no need for a waveguide from the interference film filter section to the minute reflector, so it can be significantly smaller than the conventional waveguide type multiplexing/demultiplexing module shown in Figure 7. becomes.

The relative positional relationship between the wavelength selective coupler and the optical waveguide according to the present invention can be easily determined by simply aligning the end face of the optical waveguide and the interference film filter.

It is also effective to form a guide portion similar to the optical fiber guide 1 in FIG. 7 on the substrate in advance.

〔Effect of the invention〕

As explained above, according to the present invention, which integrates the interference film filter section and the reflection section, which were conventionally located at separate locations on the substrate, the interference film filter insertion groove in the optical waveguide can be In addition to being able to eliminate loss, since there is no need for an optical waveguide from the interference film filter to the light receiving and emitting elements, it is possible to downsize the optical waveguide circuit, and the mounted elements are easier to handle than conventional ones. This will contribute to the economicalization of optical multiplexing/demultiplexing modules.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a waveguide optical multiplexing/demultiplexing module for explaining the present invention in detail, FIG. 2 is a perspective view showing one embodiment of the present invention, and FIG. 3 is a diagram showing another embodiment of the present invention. FIG. 4 is a perspective view showing an embodiment in which the upper surface of the lower cladding layer and the end of the reflective surface are in contact with each other; FIG. 4 is a perspective view showing another embodiment of the present invention; A perspective view showing an example in which the coupling efficiency between one of two optical waveguides coupled in a plane and a light receiving/emitting element is improved, and FIG. 5 shows a branch loss diagram to show the effect of the present invention. A diagram showing an example of calculation of characteristics, FIG. 6 is a perspective view showing an example of use of the wavelength selective coupler according to the present invention, FIG. 7 is a perspective view of a conventional waveguide type multiplexing/demultiplexing module,
FIG. 8 is a perspective view of a glass block with an interference film filter, and FIG. 9 is a diagram showing the relationship between the optical waveguide groove width and the optical waveguide loss. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Optical waveguide, 10... Wavelength selective coupler, 11... Reflection part (reflection surface), 12... Interference film filter, 13... Receiving/emitting element (light receiving element), 14
...Support. Applicant Nippon Telegraph Co., Ltd. Agent Patent Attorney Masa Shiga Take- m-' Figure 1 Figure 2 Figure 3 Figure 4 Factor 5 Negativeness (11!L) Figure 6 Figure 9 Rules Mending gap q9

Claims (1)

[Claims] A wavelength selective coupler for coupling an optical waveguide and a light receiving/emitting element of a waveguide type optical multiplexing/demultiplexing module whose basic components are an optical waveguide formed on a substrate and a light receiving/emitting element,
a support body having a surface facing the end surface of the optical waveguide and a surface facing the light emitting/receiving element;
an interference film filter formed at an angle of 0°; and an interference film filter formed inside the support at an angle of approximately 45° with respect to the substrate surface, and a surface facing the end surface of the optical waveguide and the receiver. A wavelength selective coupler comprising a reflective part that forms an optical path between a surface facing a light emitting element, and at least a portion of the support where the optical path is formed is transparent. .