JPS6046682B2 - Optical multiplexing/demultiplexing circuit for optical beams - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical circuit for optical fiber communication, and particularly to a light beam multiplexing circuit for separating light containing a plurality of wavelength components according to the wavelength or combining a plurality of lights with different wavelengths. Regarding wave circuits.

As the performance of semiconductor light sources and optical fibers improves, optical fiber communication is expected to become a new communication system of the future.
Some practical applications are also beginning to be realized.

In optical fiber communication, as in conventional telecommunications, various communication systems are being considered. Among them is optical multiplex transmission, which transmits multiple light beams through a single optical fiber. Although there are various methods of optical multiplexing, so-called optical wavelength division multiplexing transmission, which makes use of differences in the wavelengths of light, is considered to be the most suitable for optical fiber communication because it can effectively utilize the broadband properties of optical fibers for optical wavelengths. It will be done. Optical wavelength multiplexing/demultiplexing circuits are one of the important optical circuits in realizing such optical wavelength division multiplexing communications, and are broadly divided into those using wavelength dispersion elements such as prisms and diffraction gratings, and those using wavelength dispersion elements such as interference filters. Some use wavelength-selective reflective films.
The former is constructed by combining a prism or a diffraction grating with a lens, so it has disadvantages such as a somewhat complicated structure, a larger shape, and lack of stability for long-term use. Since the diffraction grating is expensive, the demultiplexing circuit is also expensive, which is an unavoidable drawback. On the other hand, in the latter case, the wavelength-selective reflective film can be made at a relatively low cost, so the multiple demultiplexing circuit can be made at low cost, but the demultiplexing circuit that combines an independent reflective film and a lens is not as good as the former in terms of shape and stability. It has similar drawbacks. The end faces of two convergent optical transmitters whose refractive index gradually decreases from the center to the periphery in a cross section perpendicular to the central axis are used to create a small and stable demultiplexing circuit using a wavelength selective reflective film. There is one that utilizes the meandering of a light beam in a convergent light transmitter by sandwiching a wavelength-selective reflective film between them. Regarding this, for example, the invention by the applicant of the present invention, ``An optical wavelength demultiplexer using a focusing optical transmitter,
(Details can be found in Utility Model Application No. 51-176-145.) In this multiplex demultiplexing circuit, the converging light transmitting body, which is a lens, is extremely small, and a reflective film is sandwiched between its end faces, so the demultiplexing circuit as a whole However, in a demultiplexing circuit that uses a reflective film, for example, when demultiplexing two wavelengths, the reflective film transmits light of a certain wavelength and reflects light of other wavelengths. Since the waves are transmitted, the separated lights are emitted in different directions.For example, in the multiplexing and demultiplexing circuit using the above-mentioned focusing optical transmitter, the demultiplexed lights are emitted in almost opposite directions and are multiplexed. The light for this purpose must be input into the multiplex demultiplexer circuit from almost the opposite direction.However, since the output light from the multiplex demultiplexer circuit is detected by a photodetector coupled to the receiving electric circuit, the demultiplexer is When the number of signals to be output is large, that is, when the degree of multiplicity is high, it is desirable that the output lights of the multiplexing/demultiplexing circuit are emitted in approximately the same direction in order to integrate the receiving electric circuit into the receiving device with high density. Even in the case of multiplexing, it is desirable that the light for multiplexing be incident on the multiplexing/demultiplexing circuit from approximately the same direction in order to incorporate the transmitting electric circuits at a high density.

In conventional multiplexing/demultiplexing circuits using converging optical transmitters, the separated lights are emitted in opposite directions by connecting the multiplexing/demultiplexing circuit and a photodetector or light source with an optical fiber, etc. However, compared to the method of directly coupling a photodetector or light source to a multiplexing/demultiplexing circuit, this method eliminates the inconvenience caused by inputting the light to be multiplexed from the opposite direction. The disadvantage is that the insertion loss increases due to the additional coupling loss of the optical fiber. An object of the present invention is to provide a compact optical multiplexing/demultiplexing circuit for light beams that has low insertion loss and can have receiving or transmitting electric circuits mounted in high density. Ru.

According to this invention, it has two end faces perpendicular to the central axis,
A reflective film with wavelength selectivity is provided between the end face of each of the two convergent light transmitting bodies whose refractive index gradually decreases from the center to the periphery in a cross section perpendicular to the central axis. A light beam multiplexing/demultiplexing circuit for a light beam including a plurality of sandwiched two-wavelength optical multiplexing/demultiplexing elements and an optical waveguide for optically coupling between one end face of the two-wavelength optical multiplexing/demultiplexing elements is obtained. .

This invention uses a plurality of two-wavelength optical multiplexing/demultiplexing elements in which a wavelength-selective reflective film is sandwiched between the end faces of a focusing optical transmission body.
By connecting one end face of these elements with an optical waveguide, the directions of the incident or output light beams of each two-wavelength optical multiplexing/demultiplexing element are made to be in substantially the same direction.

By doing this, there is no need to use an optical fiber to connect the two-wavelength optical multiplexing/demultiplexing element and the photodetector or light source, and the optical detector or light source can be directly brought close to the end face of the two-wavelength optical multiplexing/demultiplexing element. This makes it impossible to install the device in a similar manner, thereby reducing insertion and loss. Furthermore, if the photodetector and subsequent receiving electric circuit or the light source and the transmitting electric circuit are integrated, these multiple electric circuits can be used together to form a high-density receiving or transmitting device (if the multiplicity is large). It can be incorporated inside. The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows a plan view of a first embodiment of the invention. This embodiment consists of three two-wavelength optical multiplexing/demultiplexing elements 1 that emit light of different wavelengths λ1, λ2, and λ3 as output light.
, 2 and 3 are connected by the waveguide portions 41 and 42 of the optical waveguide 4, and the output side end surfaces 20 and 30
, 40, and are connected to receiving electric circuits 12, 22, 32. The two-wavelength optical multiplexing/demultiplexing elements 1, 2, and 3 are the same as those disclosed in the patent application. This is an application of Japanese Patent Application No. 51-122653 "Optical branching/coupling device" filed by Mr. Taking the two-wavelength optical multiplexing/demultiplexing element 1 as an example, this is a convergent optical transmission body whose refractive index gradually decreases from the center to the periphery in a cross section perpendicular to the central axis. An interference film made of a dielectric multilayer film by vacuum deposition is placed on one end face of the convergent light transmitter 13, which has both end faces cut and polished so that the length between the vertical end faces is about 114 times the meandering period of the different-axis incident light beam. A filter film 15 is attached, and another convergent light transmitter 14 having approximately the same length as the convergent light transmitter 13 is adhesively fixed thereto. Next, its operation will be explained. When the end of the optical fiber 8 is fixed at a position offset from the central axis of the incident side end face 19 opposite to the side on which the interference filter film 15 is attached to the convergent light transmitter 13, the output light beam meanders and the beam diameter changes. becomes an expanding light beam 16, travels through the convergent light transmission body 13, and enters the interference filter film 15. Wavelength dependent characteristic 10 of transmittance of interference filter film 15
1 is shown in FIG. 2 along with the coherence characteristics 102 and 103 of the interference filter films 25 and 35 of other two-wavelength optical multiplexing and demultiplexing elements 2 and 3. In other words, the interference filter film 15 has a property of transmitting almost all the light around the wavelength λ1 and reflecting almost all the light around the wavelength λ1, so that the light beam 16 has the property of transmitting almost all the light around the wavelength λ1.
The light is separated into a light beam 17 consisting of nearby light and a light beam 18 consisting of light of other wavelengths by transmission and reflection of the interference filter film 15, respectively.

Therefore, since the light emitted from the output side end face 20 of the convergent optical transmitter 14 consists of light with a wavelength of around λ1, if it is detected by the photodetector 11 and processed by the receiving electric circuit, it will become light with a wavelength of around λ1. The transmitted signal can be reproduced without interference from optical signals of other wavelengths. On the other hand, the light beam 18 consisting of light having a wavelength other than the wavelength λ1 is reflected by the interference filter film 15 and then travels in the direction opposite to the light beam 16 while meandering through the convergent light transmission body 13 and reaches the end surface 19 on the incident side. The light is emitted from a location different from where the end of the optical fiber 8 is installed. Therefore, this part and the input side end face 29 of the next two-wavelength optical multiplexing/demultiplexing element 2 are connected by the waveguide section 41 of the optical waveguide 4, and the light other than the wavelength λ1 is transferred to the next two-wavelength optical multiplexing/demultiplexing element. 2, only light around the wavelength λ2 is emitted from the output side end face 30, as described above.
Thereafter, in the same manner, the output side end face 4 of the two-wavelength optical multiplexing/demultiplexing element 3
Only light with wavelength λ3 near 0 is emitted, and wavelength demultiplexing is realized. Focusing light transmission body 13, 14, 23, 24, 33
, 34 is a glass round rod made using the well-known ion exchange method and has a diameter of about 2? , approximately 5 in length.
The optical waveguide section 4 used was one in which U-shaped waveguide sections 41 and 42 were formed by covering a glass flat plate with a mask and also performing ion exchange. As you can easily see from Figure 1,
The emitted light from each of the two-wavelength optical multiplexing/demultiplexing elements 1, 2, and 3 is emitted in the same direction, and the interval between each emitted light is determined by appropriately selecting the shape and dimensions of the waveguide portions 41, 42 of the optical waveguide 4. Therefore, the photodetectors 11 and 2 can be determined almost arbitrarily.
1, 31 and receiving electric circuits 12, 22, 32 can be installed in parallel and densely in the receiving device.

Furthermore, since the photodetectors 11, 21, and 31 can be installed directly adjacent to the output side end faces 20, 30, and 40 of the two-wavelength optical multiplexing and demultiplexing elements 1, 2, and 3, the optical fibers or the like can be used to couple these together. The insertion loss can be reduced compared to the case where
Low loss has also been achieved in the entire optical multiplexing and demultiplexing circuit. FIG. 3 shows a plan view of a second embodiment of the invention. In this embodiment, the waveguide section 41 of the optical waveguide 4 of the first embodiment is
Instead, the two-wavelength optical multiplexing and demultiplexing elements 1 and 2 are coupled using an optical waveguide 5 consisting of a convergent optical transmission body 51 and 61 and a transparent body 52 and 62 having oblique reflective surfaces. The light beam 18 reflected by the interference filter film 15 of the two-wavelength optical multiplexing and demultiplexing element 1 is converted into a substantially parallel light beam 54 with a large diameter by the converging light transmission body 51, and then the light beam 18 is converted into a substantially parallel light beam 54 with a large diameter. It is totally reflected by the reflecting surface, enters another convergent optical transmission body 61, is focused, and enters the next two-wavelength optical multiplexing/demultiplexing element 2. Although not shown in the figure, multiple wavelengths can be demultiplexed in a similar manner. In this embodiment as well, since the light demultiplexed by each two-wavelength optical multiplexing/demultiplexing element is emitted in substantially the same direction, it is possible to incorporate the photodetector and the receiving electric circuit into the receiving device with high density. Furthermore, since the photodetector can be installed directly close to the output side end face of each two-wavelength optical multiplexing/demultiplexing element, insertion loss can also be reduced. In this embodiment, transparent bodies 52, 6
Since the light beams 54 and 55 in 2 have large diameters, the transparent body 5
2 and the transparent body 62 does not require great precision. In other words, the transparent body 52 and the transparent body 62
may be in close contact with each other or may be a little apart. Also,
The optical axes of both may be slightly shifted. Therefore, for example, the two-wavelength demultiplexing element 2, the focusing optical transmission bodies 61, 63, the transparent bodies 62, 64, the photodetector 21, and the receiving electric circuit 22 are assembled in advance as one unit, and these can be assembled as needed. Multiple pieces can be connected one after another. With such a configuration, it becomes possible to increase the multiplicity relatively easily when it is desired to increase the transmission capacity later. FIG. 4 is a plan view for explaining the waveguide 7 of the third embodiment of the present invention.

Here, a description will be given taking as an example the waveguide section 7 that connects the two-wavelength optical multiplexing/demultiplexing elements 2 and 3. This waveguide 7 is made up of convergent light transmitters 71, 72, a transparent body 80, and a reflective film 81, which are installed close to the incident side end faces of the two-wavelength optical multiplexing/demultiplexing elements 2, 3. The length of the convergent optical transmitters 71 and 72 is selected to be approximately 114 times the meandering period of the optical beam.The optical beam 28 in the two-wavelength optical multiplexing/demultiplexing element 2 enters the convergent optical transmitter 71 on different axes, and the diameter A large, almost parallel light beam 74 is obliquely emitted from the convergent light transmission body 71.

This light beam 74 is reflected by a reflective film 81 attached to one surface of a transparent body 80 to become a light beam 75, which is again focused by another convergent light transmission member 72 to become a light beam 76, which is then converted into a light beam 76, which becomes the next two-wavelength light beam. The light is incident on the multiplexing and demultiplexing element 3. In the waveguide 7 of this embodiment, similarly to the waveguides 5 and 6 of the second embodiment, the output light beam of the two-wavelength optical multiplexing/demultiplexing element is converted into a substantially parallel light beam with a large diameter by a focusing optical transmission body. The transparent body 80 and the convergent light transmitting body 7 are used to convert the beam into a beam and then reflect it.
The relative positional accuracy of 1 and 72 is not so strict, and the assembly of the optical multiplexing/demultiplexing circuit is relatively easy.

Although the present invention has been described above based on the embodiments, the two-wavelength optical multiplexing and demultiplexing element, which is the main component of the optical multiplexing and demultiplexing circuit, is small with a diameter of about 2wn and a length of about 10TIn, so any embodiment is extremely A compact optical multiplexing/demultiplexing circuit has been realized.

Here, a case has been described in which the multi-wavelength optical multiplexing/demultiplexing circuit according to the present invention is used as a demultiplexing circuit. If a light source and a transmitting electric circuit are used instead of the photodetector and receiving electric circuit of the embodiment, the light source and the transmitting electric circuit can be incorporated in a transmitting device with high density.It can also be used as an optical multiplexing circuit for multiple wavelengths. be able to. The optical waveguide that optically connects one end face of the two-wavelength optical multiplexing/demultiplexing element is not limited to the one shown in the embodiment, but may also be a semi-waveguide using a semiconductor multilayer structure or using ion implantation. It's okay if it's hot.

The interference filter film of the two-wavelength optical multiplexing/demultiplexing element does not have to have the characteristics shown in FIG. 2, and may also have the characteristics of transmitting (or reflecting) only light of a certain wavelength or more.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the first embodiment of the present invention, Fig. 2 is a diagram showing the transmittance characteristics of the interference filter film used therein, and Fig. 3 is a plan view of the second embodiment of the invention. Floor plan, 4th
The figures each show a partial plan view of a third embodiment of the invention. In the figure, 1, 2, 3... two-wavelength optical multiplexing/demultiplexing element, 4, 5, 6, 7... optical waveguide, 8...
...Optical fiber, 11,21,31...Photodetector, 12,22,32...Reception electric circuit, 13,
14, 23, 24, 33, 34, 51, 61, 63, 7
1,72...Focusing optical transmission body, 15,25,3
5...Interference filter membrane, 16, 17, 18, 2
6, 27, 28, 36, 37, 54, 55, 56, 57
, 58, 59, 73, 74, 75, 76... light beam, 19, 29, 39... incident side end surface, 20, 3
0, 40... Output side end surface, 41, 42...
Optical waveguide section, 52, 62, 64, 80...transparent body, 8
1... Reflective film, 101, 102, 103...
The transmittance characteristics are shown separately.

Claims (1)

[Claims] 1. One end surface of each of two convergent optical transmission bodies having two end surfaces perpendicular to the central axis, the refractive index of which gradually decreases from the center to the periphery within a cross section perpendicular to the central axis. Optical wave multiplexing for light beams, comprising a plurality of two-wavelength demultiplexing elements with a film having wavelength selectivity sandwiched therebetween, and an optical waveguide optically coupling between one end face of the two-wavelength demultiplexing elements. Branching circuit.