JPH01259317A - Optical multiplexer and demultiplexer and optical module - Google Patents

Abstract

PURPOSE:To make an isolation large, and also, to reduce the manufacturing cost by bringing five pieces of directional couplers having input two- and output two-ports to prescribed connection, and also, setting the structural dimensions of each coupler of a second, a third, and a fourth, a fifth to the same. CONSTITUTION:To output ports of the first coupler 4a of five pieces of directional couplers 4a-4e having input two- and output two-ports, input ports of the second and the third couplers 4b, 4c are connected, and to output ports of the second and the third couplers 4b, 4c, input ports of the fourth and the fifth couplers 4d, 4e are connected. Also, structural dimensions of the second and the third couplers 4b, 4c and the fourth and the fifth couplers 4d, 4e are set to the same. An optical signal of wavelength lambda1 and that of wavelength lambda2 are demultiplexed to an output port 1e-0 and an output port 2d-0, respectively. As a result, the optical signal passes through three couplers, therefore, an isolation becomes large, and since the structural dimensions are the same, the manufacturing cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide type optical multiplexer/demultiplexer and an optical module using the same.

[Conventional technology]

Optical wavelength division multiplexing transmission technology in optical fiber communications is important for economicalization of communication systems. In the optical wavelength division multiplexing transmission described above, an optical multiplexer/demultiplexer is an essential device.

Recently, the cost has been reduced as a method of configuring optical multiplexer/demultiplexer.

There has been a movement to research waveguide-type structures with the aim of creating a single-chip monolithic structure. As an example, [Directional coupler type optical demultiplexer J (N, Takato et al.: Low loss directional coupler using high silica buried channel waveguide,
OEC'86. Technical Digest, A3-3.2
2-23, July 1986), this is a method of arranging two optical waveguides in parallel and obtaining optical demultiplexing characteristics by utilizing the wavelength dependence of the coupling of the leading waveguide of the nif. In addition, as a construction method that maintains high isolation characteristics, for example, ``Directional coupler type optical demultiplexer'' by Sasaki and Daikoku, 1973 National Conference of the Institute of Electronics and Communication Engineers, 56-2゜4-
There are pages 2G3 to 264.

[Problem to be solved by the invention]

As shown in the wavelength characteristics in Figure 12, the optical demultiplexer with the former configuration maintains high isolation (passage attenuation of 25dF3 or more) when considering optical demultiplexing at wavelengths of 1.3μm and 1.55μm. The bandwidth for transmission is only about 30 nm.

Therefore, if the values of the wavelengths 183 μm and 1.55 μm change due to temperature fluctuations in the semiconductor light emitting device, optical signals of undesired wavelengths will leak into the system that demultiplexes the desired wavelength, causing interference and deteriorating signal quality. There's a problem.

An optical demultiplexer with the latter configuration can maintain high isolation, but because it requires the use of three directional couplers and two demultiplexers with different structural dimensions, the overall size increases. The loss increases due to waveguide loss. Also, for directional couplers with different structural dimensions.

Masks must be prepared for each type, which increases costs. Moreover, the complicated structure increases the mask manufacturing cost. In particular, since the size is large, two or more exposure masks are required for patterning, which causes problems such as high cost and deterioration of fM production accuracy. Furthermore, since the structure is asymmetrical, the output port end faces are aligned, cut, and polished to create the semiconductor laser and photodetector.

When connecting optical devices such as a pre-receiver 31, the length of the transmission path from the input port to each output port differs. When the transmission path lengths differ in this way, in systems that perform phase control such as coherent optical communication, the difference in transmission path lengths becomes a serious problem in optical device design. This leads to deterioration of optical transmission characteristics.

Therefore, one object of the present invention is to solve the above-mentioned conventional problems.

[Means to solve the problem]

The above purpose is to input 2. Five directional couplers each consisting of two output ports are used, and the second directional coupler is connected to the output port of the first directional coupler.
and the input ports of the third directional coupler, and
and the input ports of the fourth and fifth directional couplers are connected to the output port of the third directional coupler, and at least the second and third directional couplers and the fourth and fifth directional couplers are connected to each other.
This is achieved by making the structural dimensions of the directional couplers the same.

[Effect]

The waveguide type optical multiplexer/demultiplexer of the present invention is shown in FIG.
Five directional couplers shown in FIG. 1 are used, or five directional couplers are used in combination. First, FIG. 10 shows a directional coupler that demultiplexes optical signals with wavelengths λ1 and λ1, which are incident on port 1-i. The coupling length of the coupling part 3 when the optical signal of wavelength λl is completely transferred to port 2-0 among the optical signals of λ2 is called the complete coupling length,
If the coupler length Q is chosen to be an even number L(λ2), the optical signal of wavelength λ goes to the port 2-o side.

The optical signal of wavelength λ2 propagates through the port 1-o side. Similarly, in the case of FIG. 11, if Q is chosen such that L (λ2) is an odd number, it becomes a directional coupler that demultiplexes the optical signal of wavelength λ2, and the optical signal of wavelength λl is sent to port 1-o. On the side, the optical signal of wavelength λ2 is sent to port 2-.

It propagates down the side.

The waveguide type optical multiplexer/demultiplexer of the present invention is shown in FIG.
It uses the directional coupler shown in Fig. 1, the basic configuration of which is shown in Fig. 1.The directional coupler 4a to 4e that separates the optical signal of wavelength λL is used. Wavelength λ1. incident on input port 1a-i. Regarding the optical signal of λ2, the optical signal of wavelength λl is demultiplexed to output port 1s-o, and the optical signal of wavelength λ2 is demultiplexed to output port 2d-o.

Since the light passes through three directional couplers and is output, it is possible to achieve extremely high isolation between the wavelengths λl and λ2. The features of this optical multiplexer/demultiplexer are as follows.

(1) Directional connectivity Since the same structure is used for 4b and 4c, and the same structure is used for 4d and 40, the wavelength λ1. The positions of the output ports of λ2 in the X direction can be aligned, making it easier to connect other optical devices to the output ports (for example, when mounting semiconductor lasers, photodetectors, optical fibers, etc., cutting the end face, (polishing can be done the same). Furthermore, the photomask can be easily drawn and manufactured at low cost.

(2) Since it is vertically symmetrical with respect to o-o', the photomask can be similarly easily drawn and manufactured at low cost.

(3) Due to the reason in (1), the transmission path lengths from the input port to each output port can be made equal. Therefore, when used for coherent optical communication, it is possible to ignore phase shifts due to differences in the transmission path lengths of the respective demultiplexed optical signals, facilitating optical device design.

〔Example〕

FIG. 2 shows another embodiment of the waveguide type optical multiplexer/demultiplexer of the present invention. This is a case in which directional couplers 78 to 7e are used to demultiplex an optical signal of wavelength λ2.

Figure 3 shows directional couplers 4a, 4b, 4e that separate optical signals with a wavelength of λ2 and directional couplers 4a, 4b, 4e, which have the same characteristics as those in Figure 1.
This is an embodiment of an optical multiplexer/demultiplexer configured using directional couplers 7d and 7e that demultiplex optical signals. By using the same directional couplers 4b and 4c of block 5 and the same structure of directional couplers 7d and 78 of block 6,
Output boats 1d-o, 2d-o.

The X-direction positions of 1e-o and 2e-o can be aligned, making it very easy to draw a photomask, and cutting and polishing the output port end face can be done at the same time, so it can be realized at low cost. Furthermore, connection of other optical elements and optical components is also easy.

Similarly to FIG. 3, FIG. 4 is also configured using a directional coupler 4a that demultiplexes an optical signal of wavelength λ1, and directional couplers 7b, 7c, 7d, and 7e that demultiplexes an optical signal of wavelength λ2. This is what I did. The optical signal of wavelength λ1 is demultiplexed to a boat of 1e-o, and the optical signal of wavelength λ2 is demultiplexed to a boat of 2d-0 and output.

The case shown in FIG. 5 is an embodiment of an optical multiplexer/demultiplexer which outputs an optical signal of 7 wavelengths λl to a port 1d-0 and an optical signal of wavelength λ2 to a port 1- of 2e-o.

In the case of Fig. 6, as in Fig. 5, the wavelength λ1 is set to 1d-o,
This is an example of a configuration in which an optical signal having a wavelength λ2 is demultiplexed into 2e-o.

FIG. 7 shows an embodiment in which the positions of the input and output ports are the same.

FIG. 8 shows an embodiment of an optical module for a wavelength multiplexing optical repeater to which the optical multiplexer/demultiplexer of the present invention is applied. This means that the optical signal of wavelength λ1 incident on the boat 1a-i is
-o boat, receives the light with the light receiving element 9b, converts it into an electrical signal, and reproduces the signal in the reproducing circuit 1. After amplification and waveform shaping at Lb, the signal is input to the single light emitting element drive circuit 10b. The optical signal of wavelength λ1 emitted by the light-emitting cable 8b is transmitted to the directional coupler 4e.
, 4c and output to the 2c −i boat 1
Sent to the next optical repeater. On the other hand, the optical signal of wavelength λ2 incident on the bow I- of 1a-i is transmitted to the directional coupler 411゜4b.
, 4d and output to the 2d -o boat.

After converting into an electric signal by the light receiving cable 9a, the reproducing circuit 11a.

Driving Circuit] Oa causes the light emitting element 8a to emit an optical signal of wavelength λ2. The optical signal is transmitted through directional couplers 4d, 4
b and is output to the boat 1 b -i.

Sent to the next optical repeater. By using five directional couplers in this manner, it is possible to realize an optical module for a wavelength multiplexing optical repeater with high isolation and at low cost.

FIG. 9 shows an optical multiplexer/demultiplexer and a light emitting element 8. This figure shows an example of an optical module for bidirectional transmission in which a light receiving element 9 is integrated. In addition to light emitting elements and light receiving elements.

It may include optical functional elements such as an optical modulator, an optical switch, an optical branch, and an optical amplifier. Light receiving cord 9c.

9d is for monitoring an optical signal of undesired light. A light receiving element for detecting monitor light may also be provided in the boats 2a-i, 1a-j, .

Input ports such as 2a-i, 1d-o, 2d-o.

At least one optical fiber is connected to output ports I- such as 1e-o and 2e-o. Also,
Although the wavelength of the optical signal propagating in the optical multiplexer/demultiplexer or the optical module has been described as two wavelengths, the present invention is not limited to this, and may be three or more wavelengths. For example, wavelength λ1
Using two or more wavelengths near λ2, output capo-hi
d-o.

For example, a narrowband filter is provided at 2d o, 1e-o, 2e-o, etc. to selectively separate the signals.

〔Effect of the invention〕

According to the present invention, very large isolation between wavelengths can be achieved, so low crosstalk characteristics can be achieved. Moreover, since the upper and lower structural dimension patterns are symmetrical with respect to the center, the photomask production cost can be extremely reduced, and deviations in characteristics due to structural dimension deviations from design values at the time of manufacturing can be corrected with good symmetry. is easy.

Furthermore, since the transmission path lengths from the input port to each output port are exactly the same, there is no phase shift in the optical multiplexer/demultiplexer, making it possible to provide an extremely good optical device for coherent optical communication.

[Brief explanation of the drawing]

1 to 7 are diagrams showing an embodiment of the four-wave path type optical multiplexer/demultiplexer of the present invention, FIGS. 8 and 9 are diagrams showing an embodiment of the optical module of the present invention, and FIGS. ] Figure 1 is a structural schematic diagram and original operating diagram of the directional coupler used in the present invention, Figure 12
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Claims (1)

[Claims] Five directional couplers each having one port, two input ports, and two output ports are used, and the input ports of the second and third directional couplers are connected to the output port of the first directional coupler. and the input ports of the fourth and fifth directional couplers are connected to the output ports of the second and third directional couplers, and at least the second and third directional couplers and the third directional coupler are connected to each other. An optical multiplexer/demultiplexer characterized in that the structural dimensions of the fourth and fifth directional couplers are the same. 2. An optical module having an optical functional element connected to at least one of the input port and the output port of the optical multiplexer/demultiplexer according to claim 1. 3. An optical multiplexer/demultiplexer according to claim 1, wherein an optical fiber is connected to at least one of the input port and the output port of the optical multiplexer/demultiplexer. 4. An optical module having an optical fiber connected to at least one of the input port and the output port of the optical multiplexer/demultiplexer according to claim 2.