JPH0754994B2 - Optical time division exchange method and device - Google Patents

Description

The present invention relates to an optical time division switching method and apparatus for performing time division switching using optical wavelength division multiplexing transmission.

[Conventional technology]

With the spread of optical fiber transmission, an optical communication network configuration including exchange has been studied. In particular, the application of optical technology to subscriber line exchanges and trunk line exchanges, which are the core nodes of subscriber services, is expected to have a great impact toward the digital integration era of networks, and as an ultimate form, It is desired to realize an optical switch that directly exchanges optical signals from fiber cables. Although research on this optical switch is in its infancy, some system ideas have been reported.

2 and 3 are schematic configuration diagrams of a conventional optical switching system, both of which are examples of a time division system. First, FIG. 2 will be described. A signal obtained by electrically time-division multiplexing the image signals from a plurality of subscribers by the multiplexer 201 is
It is converted into an optical signal by the electric-optical switch 202. This optical signal is sent to the optical fiber delay lines 205 having different lengths in the first optical switch 204 configuring the optical time switch 203 for each time slot, and after a predetermined delay time of each optical fiber, the second optical signal is transmitted. It is read by the optical switch 206.
The order of the optical signals read by the second optical switch 206 is the first order.
The optical switch 204 changes depending on which optical signal is sent to which optical fiber delay line 205, so that time-division exchange of optical signals is realized. That is, the optical fiber delay line 205 operates as an optical memory. Then, the optical signal is converted into an electric signal again by the optical-electrical converter 207, and separated into each electric signal by the separating device 208. Also, the third
In the case of the figure, bistable semiconductor lasers 304a to 304d are used instead of the optical fiber delay line, and this bistable semiconductor laser has a memory function of shifting to an oscillation state in which a large output is generated by a weak input light. And write optical switch 303
The presence / absence of an optical signal divided for each time slot is stored in the form of presence / absence of laser oscillation of the bistable semiconductor lasers 304a to 304d. When the stored states are read by the read optical switch 305 in a desired order, time division exchange is performed. However, these conventional examples include a multiplexer,
The separation device is an electrical system, and since the communication path system in the exchange is composed of a mixed optical and electrical type, ultra-high speed and broadband,
There remains a problem in realizing ultra-multi-channel transmission. In addition, although an optical switch is used for time-division switching, there are still problems with insertion loss, extinction ratio, and band characteristics, making long-distance transmission difficult, ultra-high speed and wide band,
There is a problem in performing super multi-channel transmission.

[Problems to be Solved by the Invention] The above-mentioned prior art does not consider the point of exchanging high-speed broadband information signals, and since the communication path system in the exchange is an optical / electric mixed type, it is possible to achieve ultra-high speed and broadband. However, there is a problem that it becomes an obstacle to the realization of super multi-channel transmission.

An object of the present invention is to provide a novel optical time division switching method and apparatus capable of performing time division multiplex switching with a simple configuration and realizing super high speed and wide band, super multi channel transmission and long distance transmission. To provide.

[Means for Solving the Problem] The above object is to provide an optical signal obtained by multiplexing an optical signal of wavelength λ ₁ containing an information signal and an optical signal of wavelength λ ₂ containing an exchange control signal from a plurality of terminals. Are transmitted to the optical switch through the respective optical fiber cables, and the wavelength λ ₂
Of the optical signal of, and the switching control signal is extracted from this to generate the time slot conversion control signal, while the wavelength λ
₁ time-division multiplexing, time-division switching, and demultiplexing of the information signal among the ₁ optical signals are performed by using the time slot conversion control signal, and the optical signal of the wavelength λ ₁ including the separated information signal is re-generated. This is achieved by parallel transmission to a plurality of terminals by another optical fiber cable.

[Action]

With the above configuration, an optical signal obtained by multiplexing an optical signal of wavelength λ ₁ containing information signals from a plurality of transmission side terminals and λ ₂ containing an exchange control signal is transmitted in the first optical fiber cable. Then, in the optical switch, the optical signal of the information signal is used in the optical switch to perform time division multiplexing and demultiplexing with the optical signal as it is, and then by the corresponding optical fiber cable of the second optical fiber cable. It is transmitted to a plurality of receiving terminals. Only two optical fiber cables are used for transmission, and the wavelength is only two wavelengths λ ₁ and λ ₂ . As a result, all the time division multiplexing and demultiplexing and switching can be performed with the optical signal in the optical switch, and the communication system can be all opticalized.

Further, the time-slot conversion control signal required for the time division multiplexing and demultiplexing is generated by demultiplexing the optical signal of the exchange control signal of the optical signals entering the optical switch, which simplifies the apparatus. be able to.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The present embodiment is an example of the configuration of an optical switching system between a subscriber and a local station switch, assuming a videophone system, and is the case where the number of subscribers is 16.

In FIG. 1, 1-1 to 1-16 are camera devices of respective subscribers. 3-1 to 3-16 are devices provided for each subscriber, each of which includes an electro-optical converter and an optical multiplexer. That is, this device has a function of converting image information from a camera device into an optical signal of wavelength λ ₁ , a function of converting an exchange control signal into an optical signal of wavelength λ ₂ , and the wavelength λ ₁ ,
The two optical signals of λ ₂ are combined by the multiplexer, and the optical signals are indicated by arrows 17-1 to 17-16 in the optical fiber cable 5-1.
It has the function of propagating in 5-16 and transmitting to the optical switch 7 . The optical switch 7 includes an optical device section 8 having an optical time division multiplexing function and a time division switching function, an optical time division demultiplexing section.
9 , an exchange control signal light receiving optical device section 10, and a time slot conversion control electronic circuit section 11. The optical signal from each subscriber is input to the optical device section 8. Among the optical signals, each optical signal of wavelength λ ₂ including the exchange control signal is demultiplexed to the exchange control signal receiving optical device section 10. Then, the light-to-electricity is converted respectively, and the converted signals are input to the time slot conversion control electronic circuit section 11. Then, the output signals 14 and 15 of the time slot conversion control electronic circuit section 11 are fed back to the optical device section 8 and the optical time division demultiplexing section 9 , respectively. It is possible to obtain an optical signal subjected to division demultiplexing. The output signals 14 and 15 of the time slot conversion control electronic circuit section 11 control the emission time sequence of the laser array for generating the sampling optical pulse signal of the optical device section 8 and the optical time division demultiplexing section 9 . The optical signal 19 time-division exchanged by the optical device unit 8 is input to the optical time-division demultiplexing unit 9 , where optical demultiplexing is performed, and the desired subscribers are sent by the optical fiber cables 6-1 to 6-16. Respectively transmitted to. As described above, this embodiment is suitable for ultra-high speed, wide band, and ultra-multi-channel transmission because the time division multiplexing, exchange, and demultiplexing processing can all be performed by light.

FIG. 4 is a diagram for explaining the principle of the optical device unit 8 used in the present invention. In FIG. 4, 17-1 to 17-16 are the respective optical fiber cables 5 as shown in FIG.
These are optical signals propagating in -1 to 5-16. These optical signals enter the distributed index flat plate microlens array 20 and are converted into parallel light by the respective lenses 20-1 to 20-16. The output optical signal of the microlens array 20 is
The light enters the matrix type optical multiplexer / demultiplexer 27. The matrix type optical multiplexer / demultiplexer 27 is composed of, for example, elements 27-1 to 27-16 each having an interference film filter on the incident side and a half mirror immediately behind it. The interference film filters transmit the optical signals of wavelength λ ₁ and
_The half mirror transmits approximately half of the optical signal of wavelength λ ₁ and reflects the remaining approximately half of the optical signal. Therefore, among the optical signals incident on the elements 27-1 to 27-16, the optical signals containing the exchange control signal of the wavelength λ ₂ are reflected by the elements 27-1 to 27-16, respectively, and the wavelength λ 2 is reflected. The light enters the interference film filter 25 that passes only the _two optical signals. The optical signal that has passed through the interference film filter 25 is incident on each of the light receiving elements 26-1 to 26-16 of the light receiving element array 26, is optoelectrically converted, and is an electronic circuit section for time slot conversion control.
Entered in 11. On the other hand, the optical signal of wavelength λ ₁ incident on the elements 27-1 to 27-16 (video information signal from each subscriber)
Passes through the elements 27-1 to 27-16 after being attenuated by about 3 dB and enters the optical AND gate array 28. Further, the elements 27-1 to 27-16 include laser arrays from the lower side in the figure.
The sampling optical pulse signals (wavelength λ ₁ ) from the respective 22 lasers 22-1 to 22-16 are supplied to the respective lenses 21-1 to 21- of the distributed index flat plate microlens array 21.
The light enters through the element 16, is reflected by the elements 27-1 to 27-16 after being attenuated by about 3 dB, and enters the optical AND gate array 28.

The optical AND gate array 28 includes optical AND gate elements 28-1 to 28-2.
28-16 are arranged in an array.
Room by SDSmith and others
Temperer Visible Wavelengths Optical Bistability in ZnSe Interference Filters (Room Temperature, Visible Wave
−length Optical Bistability In ZnSe Inter−ferenc
e Filters) ", Optics Communications, Vol.51, No.5, p357
, 362, 1984, it can be realized by using the semiconductor differential gain device. That is, FIG. 5 shows the input / output characteristics of the optical element. In the optical input / output characteristics shown in FIG. 31, the optical AND gate input terminal of the sampling optical pulse signal generating laser (for example, 22-1) is used. The optical pulse amplitude at is set to a value slightly lower than the optical input level at which a non-linear change of input and output occurs, and the optical level 32- that merges with the optical signal from the subscriber (for example, 17-1)
If 1 is set so as to exceed the optical input level at which the above-mentioned non-linear change occurs, the output optical pulse is generated only during the time when the sampling optical pulse exists, and the optical sampling can be performed.

The time-series optical signal obtained as described above is used for each lens 29-1 of the distributed index flat plate microlens array 29.
It is input to the fiber coupler 30 through .about.29-16. This fiber coupler 30 has 16 input ports and 1 output port.
Is a so-called 16 to 1 type fiber coupler. Therefore, the respective optical signals collected by the lenses 29-1 to 29-16 are incident on the respective input ports of the fiber coupler 30, and 16 multiplexed time-series optical signals are output to the output port. It is taken out, propagated as shown by arrow 19 in FIG. 1, and input to the optical time division demultiplexer 9 in the next stage.

Further, in FIG. 4, the output signal 14 of the electronic circuit section 11 for controlling the time slot conversion is the driving circuits 23-1 to 23-16 of the driving circuit array 23 for generating the sampling light pulse signal of the laser array 22. Ordering circuit for driving
Has been fed back to 24. That is, the light emission time sequence is controlled so that the sampling optical pulse signal is output by shifting the time by τ / 16 period with respect to the pulse width τ of the optical signals 17-1 to 17-16 sent from the subscriber. In the time division multiplexing method, as is well known in the electrical system, bit interleaving that multiplexes the signals of each channel one bit at a time in one frame, and how many bits are combined in one channel are collected. There is word interleaving for multiplexing, but here, for simplicity, the case of bit interleaving is shown. Further, a signal for synchronization and the like are also required in the frame, but since they are not essential in signal exchange, description thereof will be omitted here.

FIG. 6 shows a specific example of the optical device section 8 described above.
In the figure, those denoted by the same reference numerals as those in FIGS. 1 and 4 have the same functions. In the figure, the optical fiber cables 5-1 to 5-16 are arranged in 4 rows and 4 columns. The distributed index flat plate microlens array denoted by reference numerals 20, 21, and 29 is composed of lenses arranged in 4 rows and 4 columns, as shown in FIG. This lens array is already well known. In the matrix type optical multiplexer / demultiplexer denoted by reference numeral 27, for example, as shown in FIG. 8, an interference film filter 34 and a half mirror 35 are inserted between two triangular glass blocks 33-1 to 33-2. It will be done. Reference numeral 22 is a laser array that oscillates an optical pulse signal for sampling, and "GaInAsP / InP" by Uchiyama and Iga.
By applying the one described in the document "Surface emitting two-dimensional laser array (1985 National Electrotechnical Society General Conference, No.932)", a structure as shown in FIG. 9 can be considered. This is because the surface emitting lasers 22-1 to 22-16 are 4
16 are formed in 4 rows. In FIG. 6, reference numeral 25 is an interference film filter, which is specifically a well-known one in which a dielectric multilayer film is formed on a glass plate. Reference numeral 26 is a light-receiving element array composed of light-receiving elements arranged in 4 rows and 4 columns, which also has a structure as shown in FIG. 9 and can be similarly realized. A distributed index flat plate microlens array for collecting optical signals may be inserted between the interference film filter 25 and the light receiving element array 26.
The optical AND gate array indicated by reference numeral 28 is an array of 16 optical AND gate elements arranged in 4 rows and 4 columns. Code 30 is 16 to 1
Fig. 10 shows a schematic view of a type fiber coupler. The input side fibers are arranged in 4 rows and 4 columns, and the output side has a shape portion 36 which is twisted, fused, and stretched in a taper shape, and the respective lights are multiplexed on the output side. And is emitted in the direction of arrow 19.

Next, a specific example of the optical time division demultiplexing unit 9 described above will be described. Figure 11 shows the schematic diagram. In the figure, the sixth
Those given the same reference numerals as those in the figure have the same functions. In the figure, reference numeral 37 is a laser array similar to reference numeral 22, but it is adapted to generate hold pulse light as shown in the time chart (d) of FIG. This laser array 37 is the other laser array 22.
Is synchronized with. Reference numeral 38 is a bistable semiconductor device array, which can be obtained by changing the usage conditions of the differential gain device described in the above-mentioned S. Smith et al. The optical input / output characteristics are shown in FIG. 12, and the optical output has a hysteresis characteristic with respect to the optical input signal.

Next, the operation of the optical time division demultiplexer 9 shown in FIG.
This will be described with reference to the time chart of FIG. In FIG. 11, the output optical signal 19 from the optical device section 8 is incident on the inside of the 16: 1 type fiber coupler 30. 4 of the fiber coupler 30
The optical signals are divided into 16 and output to the emission ends of the 16 optical fibers arranged in 4 rows, and are incident on the distributed refractive index flat plate microlens array 20. The respective optical signals incident on the microlens array 20 are converted into parallel light and reach the matrix type optical multiplexer / demultiplexer 27, where the optical signals of the laser array 22 that oscillates the sampling optical pulse are merged, and the optical AND It is incident on the gate array 28. In the above optical signal system, the time-series signals from the respective output fibers of the fiber coupler 30 are as shown in FIG. 13 (a),
A 16-channel signal is multiplexed one bit at a time within one frame of time width τ. Further, FIG. 13 (b) shows a waveform of a sampling light pulse from one laser of the laser array 22, and as in the case of the optical device section 8 described above, the operation of the optical AND gate is performed. A waveform obtained by extracting a signal for one channel from the time division multiplexed signal is obtained as shown in FIG. Such an operation is performed on the output light of each output fiber of the 16: 1 type fiber coupler 30, and the time division multiplexed signal is converted into 16 spatially divided channel signals. The optical output signal of the optical AND gate array 28 enters the second matrix type optical multiplexer / demultiplexer 27, merges with the hold pulse light (FIG. 13 (d)) from the laser array 37 described above, and outputs a dual signal. It is incident on the stable semiconductor device array 38. Since each element of the bistable semiconductor device array 38 has the optical input / output characteristics as shown in FIG. 12 described above, the amplitude of the hold pulse is changed to the input of each bistable element of the bistable semiconductor device array 38. If the input pulse does not exist, the sum of the signal pulse width of each channel exceeds the level at the output side of each bistable element. The output from the optical bistable element follows the locus of →→ even if there is a hold pulse, but if there is an input pulse, it follows the locus of →→→→ and there is a hold pulse even if the input pulse disappears. As long as the light output is obtained. Therefore, if a reset portion as shown in FIG. 13 (d) is provided at the end of the hold pulse, the output of each bistable element of the bistable semiconductor device array 38 will be as shown in FIG. 13 (e). An optical signal having a pulse width before time division multiplexing as shown is obtained, and optical demultiplexing is performed. Then, the optical signal is condensed by the distributed index flat plate microlens array 29, is incident on one optical fiber in the optical fiber cables 6-1 to 6-16, and is sent to the subscriber side.

The above embodiments have been described with respect to the case of the optical switching system between the subscriber and the slave station switch, but the present invention is not limited to the above embodiments, and for example, one slave station to another slave station may be used. It can also be applied when connecting to a station or from a child station to a parent station. Further, the number of subscribers is not limited to 16, and may be larger or smaller. Further, as the transmission information from the subscriber side, the conventionally considered information can be used. The information transmission service may be a telephone, data, a facsimile, or a combination of these, in addition to the above video information. The code used is a unipolar NRZ code, but other codes such as a unipolar RZ code may be used. A light emitting diode may be used instead of the laser array 22.

〔The invention's effect〕

According to the present invention, high-speed wideband information signals can be handled because time division multiplexing and optical demultiplexing are all performed by light without conversion to electrical signals, and a call system for circuit switching can also be performed entirely by light. Also, since signal processing is performed with light having two wavelengths using two optical fiber cables,
It is possible to significantly improve noise resistance, and further miniaturization and improved economic efficiency can be expected.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an apparatus of an embodiment of the present invention, FIGS. 2 and 3 are schematic configuration diagrams showing a conventional optical switching system, and FIG.
FIG. 5 is a diagram for explaining the principle of the optical device unit used in the present invention, FIG. 5 is a characteristic diagram for explaining the principle of the optical AND gate element used in the optical device unit, and FIG. 6 is the optical device unit. FIG. 7 to FIG. 10 are diagrams for explaining specific examples of the optical device used in the optical device section, and FIG. 11 is a specific example of the time division demultiplexing section used in the present invention. Configuration diagram shown, No.
FIG. 12 is a diagram for explaining a specific example of the optical device used in the separating section, and FIG. 13 is a time chart for explaining the operation of the separating section. Explanation of reference numerals 1-1 to 1-16 ... Camera device 2-1 to 2-16 ... Monitor device 3-1 to 3-16 ... Device composed of electric-optical conversion unit and optical multiplexing device 5-1 to 5-1 5-16, 6-1 to 6-16 ...... Optical fiber cable 7 ...... Optical switch 8 ...... Optical device section 9 ...... Optical time division demultiplexing section 10 ...... Optical device section for receiving exchange control signal 11 ...... Electronic circuit for time slot conversion control

Claims (2)

[Claims] _1. An optical signal obtained by multiplexing an optical signal having a wavelength λ ₁ containing an information signal and an optical signal having a wavelength λ ₂ containing an exchange control signal from a plurality of terminals, respectively. The signals are transmitted in parallel to the optical switch by a cable, and in the optical switch, the exchange control signal is extracted from the optical signal of wavelength λ ₂ among the transmitted optical signals to generate the time slot conversion control signal, and the time slot conversion control is performed. Signals are used to perform time-division multiplexing of information signals among optical signals of wavelength λ ₁ , time-division switching of optical signals for each line based on the time-division multiplexed optical signal sequence, and time-division switching. The information signal based on the optical signal train is demultiplexed for each line, and the optical signal having the wavelength λ ₁ including the separated information signal is transmitted again in parallel to the plurality of terminals by the second optical fiber cable. Characterized by Optical time division switching how. 2. An optical signal of wavelength λ ₁ containing an information signal and an optical signal of wavelength λ ₂ containing an exchange control signal, which have been transmitted in parallel by a first optical fiber cable from a plurality of terminals, respectively. The multiplexed optical signal is input, the optical signal of wavelength λ ₂ is demultiplexed, the information signal in the optical signal of wavelength λ ₁ is time-division multiplexed, and based on the time-division multiplexed optical signal sequence. And an optical device section for time-division-switching optical signals for each line, and an information signal for each line based on the time-division-switched optical signal train, and a wavelength λ ₁ containing the separated information signals. And an optical time division demultiplexing unit for transmitting the optical signal of 1 to the terminal side again in parallel by the second optical fiber cable,
An exchange control signal receiving optical device unit that receives an optical signal having a wavelength λ ₂ demultiplexed by the optical device unit, and a signal from the exchange control signal receiving optical device unit are input to input the optical device unit and the optical device unit. An optical time division switching apparatus comprising: a time slot conversion control electronic circuit section for outputting a switching control signal to each of the optical time division demultiplexing sections.