JPH05119220A - Optical coupler - Google Patents

Abstract

PURPOSE:To constitute the this optical coupler in such a manner that the function to multiplex and demultiplex lights of two different wavelengths and the function to output the inputted light from a prescribed output end by each wavelength can be attained with one coupler and that the need for an optical multiplexer/demultiplexer and directional coupler is eliminated and the connection losses by the connection of optical parts are decreased and the coupler is miniaturized when the coupler is applied to an optical transmission system of large capacity one-way and small capacity bidirection. CONSTITUTION:A 2nd optical waveguide 24 and a 3rd optical waveguide 25 are formed on a substrate 30 so as to be line symmetrical with a 1st optical waveguide 23 as a symmetrical axis. The length of the optical coupling region where three pieces of such optical waveguides distribute and couple is so set that the light of lambda1 is outputted to the 1st optical waveguide 23 and the light of lambda2 is distributed from the 2nd and 3rd optical waveguides 24, 25 when the two light rays of the wavelengths lambda1, lambda2 are made incident on the 1st optical waveguide 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler which can be used, for example, in an optical communication system of a subscriber system for performing one-way large capacity and bidirectional small capacity optical transmission by time axis compression.

[0002]

2. Description of the Related Art In recent years, optical fibers have been installed not only in the conventional backbone network connecting exchanges but also in subscriber networks between exchanges and general buildings to simultaneously transmit voice, computer data, and video at high speed. A subscriber optical communication system capable of communication has been actively developed. As one form thereof, an optical transmission system as shown in FIG. 5 has been proposed.

In FIG. 5, A is an exchange station and B is a subscriber station. First, in the exchange A, 1a is a large-capacity (for example, several hundred megabits / second) optical transmitter, from which light of wavelength λ ₁ is output, and A and B are transmitted through the optical multiplexer / demultiplexer 5.
It is sent to the transmission line optical fiber 6 which is a transmission line between them. 2a
Is an optical transmitter with a small capacity (for example, tens of megabits / second),
Transmit light of wavelength λ ₂ . Reference numeral 3a is a small-capacity optical receiver that receives light of wavelength .lambda.2. The optical receiver 3a and the optical transmitter 2a are connected to the transmission line optical fiber 6 via a directional coupler 4 and an optical multiplexer / demultiplexer 5. In the opposite station (subscriber side) B, a large capacity optical receiver 1b,
A small capacity optical receiver 2b and a small capacity optical transmitter 3b are provided.

The lights of wavelengths λ ₁ and λ ₂ that have passed through the transmission path optical fiber 6 are demultiplexed by the optical multiplexer / demultiplexer 7. Wavelength λ
The light of ₁ is received by the optical receiver 1b. The light of wavelength λ ₂ is received by the optical receiver 2b via the directional coupler 8. Small-capacity transmission of wavelength λ ₂ is bidirectional in time division.
This is so-called ping-pong transmission for receiving. Therefore, in this system, the directional couplers 4 and 8 are used.

In the above-described optical transmission system, for example, for transmitting a large amount of information such as a video distribution service, the wavelength λ ₁
The wavelength λ is used for small capacity information transmission such as telephone service.
Assign ₂ each. As a result, two types of services can be independently transmitted using one transmission path optical fiber. However, the above optical transmission system has the following drawbacks because each station uses the optical multiplexer / demultiplexer and the directional coupler. (1) The optical multiplexer / demultiplexer and the directional coupler must be connected, which requires a lot of time and effort. (2) Connection loss occurs at the connection between each optical component and the optical fiber. (3) Since the number of optical components is large, the device becomes large. In particular, assuming that it will be installed in a general building or home, the installation location will be greatly restricted.

[0006]

As described above, one light is used for one-direction large-capacity optical transmission, and the other light is used for so-called ping-pong transmission, which is bidirectional small-capacity optical transmission by time axis compression. When performing, an optical multiplexer / demultiplexer and a directional coupler are used.

Therefore, it takes a lot of time and labor to connect both optical components, and there are problems of connection loss and enlargement of the device. These have been problems to be solved in the development of the subscriber type optical communication system.

The present invention has been made to solve the above problems, and an object thereof is to provide an optical coupler having both a function as an optical multiplexer / demultiplexer and a function as a directional coupler.

[0009]

In order to solve the above-mentioned problems, the present invention provides a second light which is formed on a substrate and whose one end is different from the first light of the first wavelength band and the first wavelength band. A first optical waveguide which is an input end for inputting second light in the wavelength band of
The second and third optical waveguides formed in parallel on the substrate with the first optical waveguide interposed therebetween and the second and third optical waveguides centering on the first optical waveguide are line-symmetrical to each other. And an optical coupling section in which the lengths of the regions are set so that the ends of the second and third optical waveguides are the output ends of the second and third lights. It is characterized by doing.

[0010]

In the optical coupler of the present invention, distributed coupling occurs in the portion where the first to third optical waveguides are close to each other, and the second and third optical waveguides among the three optical waveguides are the first optical waveguide. Are formed symmetrically with respect to the first optical waveguide, the optical waveguide length of this portion is set to the first optical waveguide length when the first and second lights having different wavelengths are input from the input end of the first optical waveguide. If the setting is made such that the first light is output from the output end of the optical waveguide and the light of the second wavelength is output from the second and third optical waveguides, the two input lights are combined. It has both a demultiplexing function and a function to output the light of each wavelength from a predetermined output end.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the optical coupler of the present invention.

In FIG. 1, reference numerals 22, 23 and 24 denote optical waveguides formed on the substrate 30. The substrate 30 is made of glass, for example, and the optical waveguides 22, 23, 24 are formed on the substrate 30 by so-called ion exchange.

As shown in the figure, the optical waveguide 23 is linearly formed with an input end 21 and an output end 26. The optical waveguides 22 and 24 are formed in line symmetry with the longitudinal direction of the optical waveguide 23 as the axis of symmetry. The optical waveguides 22 and 24 are formed so as to gradually approach the optical waveguide 21 when viewed from the output end 26 toward the input end 21. Then, in the region closest to each other, the distance between the optical waveguide 22 and the optical waveguide 23 is much shorter than the distance between the one end 27 and the output end 26.

The dotted line AA'-B in the figure in which the interval is narrowed
A region 31 surrounded by B ′ is an optical coupling region, and is a region where distributed coupling occurs between the optical waveguides 21 and 22 and the optical waveguides 22 and 23 which are adjacent to each other.

At the input end 21 of this optical coupler, the wavelength λ ₁
When the light having the wavelength λ ₂ and the light having the wavelength λ ₂ are incident, the two lights are demultiplexed in the optical coupling region 31 because the perfect coupling lengths are different between λ ₁ and λ ₂ .

In the optical coupler shown in FIG.
If 2 (0) light is incident, the output ends 25, 26,
The light intensity of the light output from 27 is expressed by the following equations (1), (2), and (3) by applying the coupling mode theory in consideration of the arrangement of the optical waveguides.

[0017]

[Equation 1]

Here, A1 (z), A2 (z), A3
(Z) indicates the amplitude of the output light at the output ends 25, 26, and 27, and z indicates the coupling length of the optical coupling region 31. Further, k is a coupling coefficient, which is proportional to the wavelength λ. As can be seen from the above equation, the equations (1) and (3) have the same shape, and the light output from the output ends 25 and 27 have the same intensity.

Therefore, at the input end 21, λ ₁ = 1.5 μm, λ
_{When 2} = 1.3 μm light is incident, the output of the output end 26 (optical waveguide 27) and the output ends 25 and 27 (optical waveguide 2
2, 24) output is as shown in FIG.

As shown in FIG. 2, the light intensity of each light of λ ₁ and λ ₂ periodically changes with the coupling length z as the horizontal axis. Therefore, the coupling length z is set to z _p at which both the light intensities of λ ₁ and λ ₂ reach their peaks. By doing so, this optical coupler can realize a function of multiplexing and demultiplexing two input lights and outputting light of each wavelength from a predetermined output end,
It can be applied to the optical subscriber system described above.

In this optical coupler, the reciprocity theorem of light is established. Therefore, when light of λ ₂ enters from one end 25, 28 of the optical waveguides 22, 24, this light is emitted from the input end 21 of the optical waveguide 23. To do. Similarly, the output end 2 of the optical waveguide 23
If incident lambda ₁ light than 6, the light of the lambda ₁ is emitted from the input end 21. When the above optical coupler is applied to the above-mentioned optical transmission system, it is performed as follows. FIG. 3 shows a schematic configuration diagram thereof.

As shown in FIG. 3, on the side of the switching center A, the input end 21 of the optical coupler 50 of the same type as in FIG. 1 is connected to the transmission line optical fiber 6 of FIG. 5, and the output end 26 is connected to the large capacity optical transmitter. 1a,
One end 25 of the optical waveguide 22 is connected to the small capacity optical transmitter 2a, and one end 27 of the optical waveguide 24 is connected to the small capacity optical receiver 3a.

Similarly, at the subscriber station B side, the input end 21 of the other optical coupler 51 is connected to the transmission line optical fiber 6, and the output end 26 is connected to the large capacity optical receiver 1b at the subscriber station B side by 25. Is connected to the small capacity optical receiver 2b, and 27 is connected to the small capacity optical transmitter 3b.

The lights of wavelengths λ ₁ and λ ₂ emitted from the optical transmitters 1a and 2a on the side of the switching center A are combined by passing through the optical coupler 50 and sent to the transmission line fiber 6. The lights having the wavelengths λ ₁ and λ ₂ are demultiplexed in the optical coupler 51. The wave of wavelength λ ₁ is output from the output end 26 and received by the optical receiver 1b. The light of wavelength λ ₂ is output from the output end 25 and received by the optical receiver 2b.

On the other hand, the light of λ ₂ output from the optical receiver 3b on the subscriber station B side is input from one end 27 which is an input port of the optical waveguide 24 and reaches the optical coupler 50 through the transmission line optical fiber 6. The light of the wavelength λ ₂ is output from the one end 27 which is the output port of the optical waveguide 24, and the optical receiver 3a
Is received by.

The light of λ ₂ sent from the exchange A side is also output from the one end 27 of the optical waveguide 23 of the optical coupler 51, but this does not cause noise. Similarly, the light of λ ₂ sent from the optical coupler 51 on the subscriber station B side is also output from the one end 27 of the optical waveguide 24 of the optical coupler 50, but this also does not become noise.

By connecting the optical coupler to each of the optical transmitter and the optical receiver in this manner, the optical multiplexer / demultiplexer and the directional coupler which have been used conventionally are not required. As a result, it is possible to save the trouble of connecting the optical multiplexer / demultiplexer and the directional coupler, eliminate the loss at the connection portion, and obtain good characteristics.

Furthermore, since the number of parts is reduced and the optical fiber connecting the optical multiplexer / demultiplexer and the directional coupler is not necessary, the device is downsized and the restrictions on the installation place are greatly eased.

The wavelengths of λ ₁ and λ ₂ can be easily manufactured by using 1.5 μm band and 1.3 μm band which are often used as a light source, and both wavelength bands are appropriately spaced. Good characteristics can be obtained.

FIG. 4 is a diagram showing an embodiment in which a semiconductor element or an optical element is integrated in the optical coupler of FIG. The embodiment of FIG. 4 is assumed to be applied to the subscriber station B side in the optical transmission system of FIG.

In FIG. 4, reference numeral 40 denotes a light receiving element such as a photodiode, which is installed on the optical waveguide 23.
Reference numeral 41 is also a light receiving element and is installed on the optical waveguide 24. The power monitor light receiving element 43 of the light emitting element 42 is installed at the tip of the optical waveguide 22.

These optical elements correspond to the optical receiver and optical transmitter on the subscriber side in FIG. That is, the light receiving element 4
0 is the optical receiver 1b, the light receiving element 41 is the optical receiver 2b,
The light emitting elements 42 correspond to the optical transmitters 3b, respectively.

By configuring the optical coupler as shown in FIG. 4, only the connection between the optical waveguide 21 and the transmission line optical fiber 6 is required for the axis alignment which requires high accuracy. Therefore, the assembly is greatly simplified, the number of parts is reduced, and the device on the subscriber station side can be downsized. Of course, the same can be said on the exchange side.

Further, since the optical multiplexer / demultiplexer and the optical directional coupler are formed in one place by the distributed coupling of the three optical waveguides, the substrate size can be greatly reduced, and the number of wafers that can be obtained from one wafer is significantly increased. However, mass productivity is improved.

Reference numeral 44 in FIG. 4 denotes an optical filter. The optical filter 44 is a diffraction grating in which the pitch of the grating is determined so that only light of wavelength λ ₁ can be transmitted. By installing this optical filter 44 in front of the light receiving element 40, it is possible to prevent light of the wavelength λ _{2 from} entering the light receiving element 40. Similarly, it is of course possible to provide a filter in front of the light receiving element 41.

[0036]

As described above in detail, according to the present invention, the first optical waveguide and the second and second optical waveguides formed on the substrate in line symmetry with the first optical waveguide as the axis of symmetry. An optical waveguide No. 3 is formed on a substrate, a region where these optical waveguides are distributed and coupled is provided by making a part of these three optical waveguides close to each other, and the optical waveguide length of this region is set to a predetermined length. As a result, a single coupler can realize the function of multiplexing / demultiplexing two different wavelengths and the function of a directional coupler that outputs the input light from a predetermined output terminal for each wavelength.

Therefore, when the present invention is applied to an optical transmission system that performs unidirectional large-capacity optical transmission with the first light and bidirectional small-capacity optical transmission with the second light by time axis compression, Since the optical multiplexer / demultiplexer and directional coupling used in the past are not required, the connection loss due to the connection of optical components is reduced,
The system can be downsized.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an optical coupler of the present invention.

FIG. 2 is a diagram for explaining a multiplexing / demultiplexing characteristic of the optical coupler of the present invention.

3 is a diagram showing a schematic configuration when the optical coupler of FIG. 1 is applied to a subscriber type optical transmission system.

FIG. 4 is a perspective view showing the configuration of another embodiment of the optical coupler of the present invention.

FIG. 5 shows a schematic configuration diagram of a subscriber type optical transmission system.

[Explanation of symbols]

1a ... Large-capacity optical transmitter, 2a ... Small-capacity optical transmitter, 3a ...
Small capacity optical receiver, 1b ... Large capacity optical receiver, 2b ... Small capacity optical receiver, 3b ... Small capacity optical receiver, 22, 23, 24 ...
Optical waveguide, 30 ... Substrate, 31 ... Optical coupling region 40, 41 ... Light receiving element, 42 ... Light emitting element, power monitor light receiving element, 44 ... Optical filter

Claims (4)

[Claims] 1. An input end formed on a substrate, one end of which receives first light of a first wavelength band and second light of a second wavelength band different from the first wavelength band. A first optical waveguide, second and third optical waveguides formed in parallel on the substrate with the first optical waveguide interposed therebetween, and second and third optical waveguides centering around the first optical waveguide The optical waveguides are regions arranged in line symmetry with each other, and the other end different from the one end of the first optical waveguide serves as an output end of the first light, and each of the second and third optical waveguides. An optical coupler comprising: an optical coupling part in which the length of the region is set so that the end of the region becomes the output end of the second and third lights. 2. Of the first, second, and third optical waveguides,
The optical coupler according to claim 1, further comprising a light emitting element on at least one optical waveguide. 3. Among the first, second and third optical waveguides,
The optical coupler according to claim 1, further comprising a light receiving element on at least one optical waveguide. 4. Of the first, second and third optical waveguides,
The optical coupler according to claim 1, wherein an optical filter is provided on at least one optical waveguide.