JPH061319B2 - WDM optical switching circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a wavelength division multiplexing optical switching circuit in wavelength division multiplexing optical communication in which optical signals of a plurality of wavelengths are multiplexed.

(Prior Art) In recent years, along with the complexity of office processing, transmission of moving images, still images and various high-speed data is desired in addition to the conventional telephone service, and a large capacity of communication network is required. There is. Although optical fiber communication has advantages such as large capacity and non-induction noise, it is becoming widespread, but it is possible to further increase the capacity by wavelength division multiplexing transmission.

In wavelength division multiplex transmission, it is not necessary to increase the transmission speed of the highway like time division multiplex transmission to increase the line capacity, and it is not necessary to increase the number of optical fibers like space division multiplex transmission. It has excellent features and is considered to be one of the important technologies in the future.

When using an optical fiber for the transmission line,
It is desirable that the exchanging operation itself, which is one of the constituent elements, is performed while keeping the light as it is, in order to utilize the high speed of the light. Switching in wavelength division multiplexing optical communication is an operation of converting an optical signal of a desired wavelength into an optical signal of an arbitrary wavelength, and a wavelength division multiplexing switching circuit as shown in FIG. 6 has been conventionally proposed.

FIG. 6 shows a case in which four different wavelengths λ ₁ , λ ₂ , λ ₃ and λ ₄ are multiplexed. When a wavelength division multiplexed optical signal enters from the input side optical fiber 20, it is separated into signal lights having wavelength components of λ ₁ , λ ₂ , λ ₃ and λ _{4 by} the optical splitting circuit 21. The optical signals of the respective wavelengths are transmitted by the wavelength conversion circuit 22 ...
The information held by the optical signal is converted by 25 into an arbitrary wavelength alone, and then wavelength-multiplexed again by the optical multiplexing circuit 26 and guided to the output side optical fiber 27. In FIG. 6, the wavelengths λ _a , λ _b , λ _c , and λ _{d of the} light emitted from the wavelength conversion circuits 22, 23, 24, and 25 are λ _a = λ _b and λ, respectively.
_{If b} = λ ₁ , λ _c = λ ₃ , and λ _d = λ ₄ , it means that the information carried on the wavelength λ ₁ and the wavelength λ ₂ in the incoming fiber 20 are exchanged with each other.

(Problems to be Solved by the Invention) In the wavelength division multiplexing optical switching circuit shown in FIG. 6, in the wavelength conversion circuits 22 to 25, an optical signal of a specific wavelength is converted into an optical signal of an arbitrary wavelength by control information. Need to be converted. It is extremely difficult to form such a circuit with an all-optical circuit, and no one that can withstand practical use has yet been revealed. Therefore, one wavelength conversion circuit in FIG.
As shown in the figure, a method is being studied in which a semiconductor laser is oscillated at a fixed wavelength and a plurality of semiconductor lasers each having a different oscillation wavelength, a semiconductor laser drive circuit, and a gate are used.
However, in the above method, one wavelength conversion circuit requires a semiconductor laser corresponding to the number of channels, and an extra optical demultiplexing circuit is also required. Therefore, there are problems in cost, power consumption, reliability, etc. It is probably an obstacle to channelization.

In the configuration of FIG. 6, the signal light of the wavelength components λ ₁ , λ ₂ , λ ₃ , and λ ₄ is first separated by the optical demultiplexing circuit, so that the signal light of the wavelength λ ₁ is used. Only the information has wavelengths λ _a , λ _b , λ _c , λ _d (where λ _a , λ _b , λ
It is not possible to wait for a function such as so-called broadcast communication in which all the signal lights of _c and λ _d are different). As described above, it is difficult for the wavelength multiplex switching circuit having the configuration shown in FIG. 6 to provide a wide variety of flexible services.

An object of the present invention is to provide a wavelength division multiplexing optical switching circuit capable of realizing a highly functional switching service with a simple structure by eliminating the above-mentioned drawbacks.

(Means for Solving the Problems) A wavelength division multiplexing switching circuit of the present invention is an optical branching circuit for distributing optical signals of one or a plurality of different wavelengths propagating in an input optical waveguide to N optical waveguides. N wavelength-tunable optical wavelength filters that pass only signal light of an arbitrary wavelength among the optical signals distributed in the optical waveguides that are respectively connected to the optical waveguides, and the optical wavelengths that each corresponds to An N optical wavelength converter that converts the light passing through the filter into an optical signal of a specific wavelength, and an optical multiplexing circuit that multiplexes the outgoing signal light of the optical wavelength converter and guides it to one output optical waveguide. It is configured to include.

(Operation) FIG. 1 is a block diagram showing an example of a wavelength division multiplexing circuit for illustrating the principle of the present invention. First, the wavelength division multiplexing signal propagated through the input side optical waveguide 101 is branched into N by the optical branching circuit 102. Since the branching is performed here instead of demultiplexing, the branched optical signals are still wavelength-multiplexed signals. The branched wavelength-multiplexed signals pass through the variable optical wavelength filters 103 to 106 each having a variable passing wavelength, and only the optical signal having the wavelength determined by the control signal passes through this optical wavelength filter. By the operation up to this point, it becomes possible to spatially separate the wavelength-multiplexed optical signal in the optical waveguide 101 on the input side. The wavelength signals spatially separated are converted by the wavelength conversion circuits 107 to 110 into optical signals of specific wavelengths. Light emitted from the wavelength conversion circuits 107 to 110 is wavelength-multiplexed again by the optical multiplexing circuit 111, and output side optical waveguide 112 is output.
Be led to.

The light passing through the tunable optical wavelength filters 103 to 106 is converted into optical signals of specific wavelengths by the wavelength converting circuits 107 to 110, respectively.
If the wavelength of the transmitted light is controlled, the wavelength conversion circuits 107 to 1
Since the emitted light of 10 has a specific wavelength, optical signal conversion is possible.

Further, in the configuration of the present invention, the tunable optical wavelength filter 103 is not subjected to demultiplexing upon incidence, but is simply branched.
The spatially separated optical signals multiplexed by ˜106. At this time, it is also possible to make all the wavelengths of the passing lights of the N (four in FIG. 1) variable optical wavelength filters 103 to 106 the same. At this time, the wavelength conversion circuits 107 to 11
If the wavelengths of the emitted light of 0 are all different, broadcast communication is also possible.

That is, in FIG. 1, the wavelength conversion circuits 107 and 10
The wavelengths λ _a , λ _b , λ _c of the emitted light of 8, 109 and 110,
λ _d is λ _a = λ _b , λ ₁ = λ ₂ , λ _c = λ ₃ , λ _d = λ
It is assumed to be ₄ . At this time, the tunable optical wavelength filter 103,
When the wavelengths of the transmitted lights of 104, 105 and 106 are λ ₄ , λ ₂ , λ ₃ and λ ₁ , respectively, the wavelength conversion circuit 107,
108, 109 and 110 respectively have λ ₄ → λ ₁ and λ ₂ →
The wavelength conversion of λ ₂ , λ ₃ → λ ₃ , λ ₄ → λ ₁ is performed, and the signals of λ ₄ and λ ₄ are converted. Further, if all the wavelengths of the transmitted light of the variable light wavelength filters 103, 104, 105, 106 are λ ₂ , the wavelength conversion circuits 107, 1
08, 109 and 110 respectively, λ ₂ → λ ₁ , λ ₂ → λ
The wavelength conversion of ₂ , λ ₂ → λ ₃ and λ ₂ → λ ₄ is performed, and the signal of λ _{2 on} the incoming side is carried on all wavelengths on the outgoing side to enable broadcast communication.

As described above, by using the configuration of the present invention, by controlling the wavelengths of the light passing through the variable optical wavelength filters 103 to 106, not only the broadcast communication but also various exchange services are possible.

In the structure according to the present invention, since the wavelength of the emitted light of each wavelength conversion circuit may be a specific wavelength, it is not necessary for one wavelength conversion circuit to have a plurality of semiconductor lasers like the wavelength conversion circuit shown in FIG. One wavelength conversion circuit may be provided with one semiconductor laser that oscillates at one certain wavelength.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a first embodiment of the wavelength division multiplexing switching circuit according to the present invention.

In FIG. 2, an incident optical fiber 201 is connected to a lithium niobate substrate 200 in which an optical branch circuit and a variable optical wavelength filter are integrated on one substrate. The wavelength division multiplexed optical signal branched by the optical branching circuit 202 by the Ti diffusion waveguide in the lithium niobate substrate 200 is converted into parallel light by the geodesic lens 203, and then the variable light using the plug cell 220 by the acousto-optic effect. Only the optical signal of the desired wavelength is diffracted by the wavelength filter and guided to the wavelength conversion circuit 208. Wavelength conversion circuit 2
Reference numeral 08 denotes a light receiving element such as a photodiode, avalanche photodiode, or photo conductor, an electric amplification circuit, and a light emitting element such as a semiconductor laser integrated on a single substrate. Only the wavelength is converted into specific wavelengths λ _a to λ _d while maintaining the information of the diffracted light, and the wavelength is guided to the lithium niobate substrate 211 in which the optical multiplexing circuit 209 is formed by the Ti diffusion waveguide. The emitted light from the lithium niobate substrate 211 on which the optical multiplexing circuit 209 is formed is guided to the outgoing optical fiber 21. The wavelength multiplexing optical switching circuit according to the present invention is configured as described above.

In the incident optical fiber 201, four different wavelengths λ ₁ ,
When the signal lights of λ ₂ , λ ₃ and λ ₄ are multiplexed and propagated, the wavelength division multiplexed signal light is branched into four by the optical branching circuit 202. Here, the four branched lights include all four wavelength components λ _{1 to} λ ₄ . As the optical branch circuit 202, a waveguide type optical branch circuit is used in which titanium is formed in a waveguide pattern on a lithium niobate substrate and is thermally diffused. In the variable optical wavelength filter, only the signal of a desired wavelength is selectively passed from the signal light of wavelengths λ _{1 to} λ ₄ . That is, at one time, the wavelengths passed by the four tunable optical wavelength filters are λ ₃ , λ ₄ , λ ₂ , and λ ₁ , respectively, and in some figures, all are λ ₃ , and the signal light of the desired wavelength is arbitrarily passed by the control information. .

In this embodiment, a Braxel utilizing the acousto-optic effect as shown in FIG. 3 is used as such a variable light wavelength filter. The principle of its operation is to utilize the phenomenon that periodic density of fine particles generated in a medium by sound waves plays a role of grating and diffracts light. In this case, the diffraction angle θ is a function of the ratio of the wavelength λ of the incident light and the wavelength Λ of the sound wave. Therefore, by appropriately selecting the wavelength of the sound wave and thus the frequency of the sound wave, It is possible to diffract only light and transmit light of other wavelengths. In FIG. 3, the LiNbO ₃ substrate 3 is shown.
01, an optical waveguide layer 302 in which Ti is thermally diffused is provided, and a comb-shaped electrode 303 is formed thereon. Comb electrode 30
By controlling the frequency of the electric signal applied to 3, it is possible to diffract only the optical signal of an arbitrary wavelength. Third
The guided light 305 shown in the figure corresponds to the signal light that has passed through the Geodeck lens 203 shown in FIG. 2, and the diffracted light 306 shown in FIG.
Corresponds to the diffracted light 206 in FIG. 2 and the transmitted light 30 in FIG.
7 corresponds to the transmitted light 207 in FIG.

FIG. 2 shows an example in which four such Bragg cell variable wavelength filters and an optical branching circuit 202 are integrated on one lithium niobate substrate 200 or more. At this time, a surface acoustic wave stopper 204 is added to each plug cell so that the sound wave emitted by one Bragg cell 220 does not affect the other Bragg cells.

In FIG. 2, the transmitted light, that is, the diffracted light of the variable optical wavelength filter using the above-mentioned Bragg cell 220 is guided to the wavelength conversion circuit 208, and the specific wavelengths λ _a , λ _b , λ _c ,
It is converted into an optical signal of λ _d . In such a wavelength conversion circuit, an input optical signal is received by a single-receiver and converted into an electric signal, which is then amplified, and a light emitting element is driven by this amplified signal to convert the electric signal into an optical signal again. Circuit is used.

This embodiment embodies the configuration diagram of the present invention shown in FIG. 1, and the wavelength division multiplex optical switching including the above-mentioned broadcast communication is possible by the optical circuit shown in FIG. Needless to say.

The wavelength division multiplexing optical switching circuit shown in the present embodiment is a lithium niobate substrate 20 having one optical branching circuit and one variable optical wavelength filter.
It is highly integrated, and the wavelength conversion circuit is also a light receiver,
Since the amplifier and the light emitting element are integrated on one substrate, it can be configured with a very small optical circuit.

A second embodiment of the wavelength division multiplexing optical switching circuit according to the present invention is a fourth embodiment.
Shown in the figure.

In FIG. 4, an optical fiber coupler 401 which is an optical branching circuit, a lens array 402 which converts emitted light from the optical fiber into parallel light, an etalon array 403 which is a variable light wavelength filter, and a lens array 404 which collects parallel light. ,
Bistable laser diode array 40 which is a wavelength conversion circuit
5. The wavelength division multiplexing optical switching circuit shown in FIG. 1 is constituted by the optical fiber coupler 406 which is an optical multiplexing circuit.

When the signal lights of _four different wavelengths λ ₁ , λ ₂ , λ ₃ and λ ₄ are multiplexed and propagated, the optical fiber coupler 401
As a result, this wavelength division multiplexed signal light is branched into four. 4 here
The two branched lights still contain any of the four wavelength components λ _{1 to} λ ₄ . The optical fiber coupler 401 can be easily constructed by heat-sealing optical fibers. The light emitted from each of the optical fiber couplers 401 is transmitted through the lens array 40.
The light is converted into parallel light by 2 and enters the etalon array 403. Here, the etalon array 403 is an array of etalons each having a structure in which a substance whose refractive index such as a free carrier plasma effect or an electro-optical effect can be controlled by a current or an electric field is sandwiched by a thin film having a high reflectance. For example, when a compound semiconductor such as GaAs or InP is injected, the refractive index of the compound semiconductor changes greatly due to the free carrier plasma effect. Therefore, if metal electrodes are formed on both sides of these compound semiconductors, the metal electrode can be used as an electrode for current injection. The variable wavelength filter can be used as a reflection film and the transmission wavelength can be controlled by an electric current. Only the signal light of a desired wavelength is selectively transmitted by the etalon array 403 which is a variable optical wavelength filter, and the respective signal light is condensed by the lens array 404 onto the end face of the bistable laser diode array 405 which is a wavelength conversion circuit. To be done.

As shown in FIG. 5, the bistable laser diode that constitutes the bistable laser diode array 405 includes a substrate and each layer on the substrate, for example, n-InP, PInP, InGaA.
A plurality of electrodes 50 made of sP, PInGaAsP, etc.
Supersaturated absorption region 5 which is a region where there is no electrode between 2 and 504
By providing 03, the incident light Pi to the active layer 501
n is a semiconductor laser having bistability in the light input-light output characteristics and the current-light output characteristics at the currents of the emitted light _Po and the electrodes 502 and 504, and is usually used as an optical memory. It can also be used as an optical amplifier having a relatively small dependency. Moreover, since the acid generation wavelength is always constant regardless of the wavelength of the incident light which is the injection light, it can be used as a wavelength conversion circuit having an amplification function. When a bistable laser diode is used as the wavelength conversion circuit, it is desirable to use a bistable laser diode having a so-called differential gain, which has a hysteresis width as small as possible from the viewpoint of eliminating the optical memory property.
The respective signal lights wavelength-converted by the bistable laser diode array 405 are multiplexed by the optical fiber coupler 406 and wavelength-multiplexed again.

It goes without saying that in this embodiment as well, various wavelength division multiplexing optical switching services including broadcast communication similar to that described in the first embodiment can be performed.

In the wavelength division multiplexing optical switching circuit shown in the present embodiment, any component can be formed into a surface configuration by using an etalon array or the like suitable for surface integration, and a configuration suitable for large-scale integration can be obtained. Has become.

(Advantages of the Invention) As described above, according to the present invention, a high-performance wavelength division multiplexing optical switching circuit capable of broadcast communication and the like with a simple configuration including an optical branch circuit, a variable optical wavelength filter, and a wavelength conversion circuit is provided. It can be realized.

In addition, the structure is adaptable to large-scale integration.

The present invention is not limited to the above embodiment. In FIG. 1, the number of wavelengths is 4 and the number of branches is 4 for convenience of explanation of the embodiment, but the number of wavelengths to be multiplexed is not limited to this. Further, the number of multiplexed wavelengths and the number of branches do not necessarily have to be equal. The optical branch circuit is not limited to the one obtained by diffusing titanium on the lithium niobate substrate or the optical fiber coupler, but as another example, it may be used by forming a quartz optical waveguide on the silicon substrate. it can.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of a wavelength division multiplexing optical switching circuit for illustrating the principle of the present invention, and FIGS. 2 and 4 show first and second embodiments of the wavelength division multiplexing optical switching circuit of the present invention, respectively. A schematic diagram and FIG. 3 are geodesic lenses 203 shown in FIG.
Showing an example of the configuration of a tunable wavelength filter that splits the light from light into diffracted light 206 and transmitted light 207, and FIG. 5 shows an example of the bistable laser diode that constitutes the bistable laser diode array 405 shown in FIG. 6 and 6 are block diagrams showing a conventional wavelength division multiplexing optical switching circuit, and FIG. 7 is a block diagram of the wavelength converting circuits 22 to 25 shown in FIG. 102, 202 ... Optical branch circuit, 103 ... Variable optical wavelength filter, 107, 22, 208 ... Wavelength conversion circuit, 1
11, 26, 42, 209 ... Optical multiplexing circuit, 21 ... Optical demultiplexing circuit, 200, 211, 301 ... Lithium niobate substrate, 302 ... Titanium diffusion waveguide, 205, 303
...... Comb type electrode, 203 ...... Geodesic lens, 22
0 ... Bragg cell, 401, 406 ... Optical fiber coupler, 402, 404 ... Lens array, 403 ... Etalon array, 405 ... Bistable laser diode array, 31 ... Photoreceiver, 32 ... Semiconductor laser drive circuit ,
38, 39, 40, 41 ... Semiconductor laser.

Claims (1)

[Claims] 1. An optical branching circuit for distributing one or a plurality of optical signals of different wavelengths propagating in an input optical waveguide to N optical waveguides, and distribution in the optical waveguides respectively corresponding to each other. Of N wavelength-variable optical wavelength filters that pass only the signal light of an arbitrary wavelength among the optical signals that have been transmitted, and the respective passing light of the corresponding optical wavelength filters are converted into optical signals of a specific wavelength. N optical wavelength converters,
An optical multiplexing circuit that multiplexes the signal light emitted from the optical wavelength converter and guides it to one output optical waveguide.