JPS6210073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical switching system that connects a plurality of subscriber terminals on a 1:1 basis using optical signals.

With the development of LSI, the emergence of inexpensive intelligent code terminals with various information processing functions, the emergence of broadband optical relay transmission lines, and the emergence of digital,
Due to the development of transmission technology, it is becoming possible to provide not only telephone services but also video telephone and various data services at low cost. In order to transmit this information with high quality, it is essential to develop switching equipment that can connect and exchange these broadband spectra without distortion.

Considering these backgrounds, the present invention was made with the aim of realizing an optical switching system suitable for high-quality information exchange between subscribers in a relatively small and limited area, and its configuration is as follows. , in a switching system having an exchange that connects a plurality of subscriber terminals and the subscriber terminal on a 1:1 basis, the subscriber terminal transmits a control signal and a main signal of the first frequency component as an optical signal, and After the signals are separated by a duplexer, they are input to a control device that controls the exchange, and the control device spatially connects predetermined subscriber terminals to each other by controlling the space switch of the exchange, and the control device controls the space switch of the exchange. The main signal having the first frequency component is frequency-converted into the main signal having the second frequency component between the input end and the output end of the switch.

A conceptual diagram of one embodiment of the present invention is shown in FIG. The principle and operation of this system will be explained below using this figure.
As shown in FIG. 1, the configuration of this system is broadly divided into a subscriber terminal line 1, a transmission line 2, and an optical switch 3.

The subscriber terminal system consists of input/output devices such as TV, telephone, and fax, a device 4 for processing input signals from these devices and signals from the transmission line side, and a transmitting/receiving device 5 to the transmission line fiber. On the other hand, the transmission line 2 consists of an optical fiber cable. In addition, the optical switch 3 is
demultiplexing circuits 7-1, 7-2 that demultiplex signal light for controlling the spatial switch 6 from the transmission line fiber;
Optical electrical conversion circuits 8-1 and 8-2 that convert the control signal light from the branching circuit into electrical signals, and a control device 9 that processes the output signals and controls the spatial switch.
and a space switch 6.

The operation will be explained below using this system configuration diagram.

As shown in the figure, subscribers are numbered from 〓〓〓 to 〓〓〓. If a subscriber is a subscriber〓〓〓
and information shall be communicated. At this time, before information can be transmitted between the subscribers, it is necessary to establish a line between these subscribers. Therefore, it is necessary for the subscriber to send a signal to the optical exchange 3 to connect the line. If these signals and information signals are to be transmitted between each subscriber and an optical exchange using only one optical fiber cable from an economical point of view, it is necessary to distinguish these signals by some method. Furthermore, assuming bidirectional transmission between subscribers, it is considered desirable to distinguish these signals by optical wavelength division in terms of balance with the optical exchange. As a result, it is conceivable to use at least three different wavelengths. That is, one wave is allocated for an optical signal for requesting connection to the optical exchange 3 in order to establish a line, and two waves are allocated for bidirectional transmission between subscribers.

Optical demultiplexing and multiplexing circuits for coupling or separating these signals into optical fibers are described by Ishio et al.
"Characteristics of optical fiber image transmission equipment using the m to 1.2 μm band" (IEICE technical study group report CS78-
31pp81-88 1978, 5), it can be easily realized. On the other hand, in the embodiment shown in FIG. 1, a 1:n optical switch is required for connecting lines between subscribers. In addition, such switches have already been proposed in various places, such as the one reported by Tanaka and Tsujimoto ``1 x 6 optical switch'' (IEICE, 1978, National Conference of Optical Radio Division, 295). This can be easily realized.

Here, the general concept of bidirectional communication in optical transmission will be given as an example.

As shown in Figure 2, when performing bidirectional transmission using a single optical fiber cable, if the optical fiber cable is a multimode fiber, it is difficult to preserve the plane of polarization of the light, so an isolator cannot be used. If the wavelengths are the same, the D/u ratio cannot be maintained, so it is advantageous to use different wavelengths for transmission and reception. However, if such a method is adopted in this system, even if the number of subscribers is 3, three types of wavelengths will be required to arbitrarily perform bidirectional transmission between them, and the number of subscribers will increase. As the number increases, the wavelength used also increases. In addition, the optical demultiplexer/multiplexer used also demultiplexes the increasing number of wavelengths.
It is necessary to perform wave combining.

This is not a practical method as it significantly increases the economic cost of each terminal.

In the present invention, from these viewpoints, it is only necessary to prepare a maximum of three types of wavelengths for each terminal, and the spatial switch of the optical exchange is devised so that each terminal can use the same three types of wavelengths.

Returning to the description of the embodiment of the present invention, the configuration of the spatial switch 6 shown in FIG. 1 will be described. FIG. 3 shows one embodiment of the spatial switch.

This spatial switch is an optical transmission line consisting of (n+1) 1×n optical switches 31-1 to 31-3 and corresponding optical fibers of these optical switches, which are connected to the transmission line from each terminal mentioned above. 32 and an optical wavelength converter 33.

This optical wavelength converter 33 has two
It is composed of one optical demultiplexing circuit 34-1, 34-2 and two optical wavelength conversion devices 35-1, 35-2.

Suppose that the subscriber terminal, 〓〓〓, is now connected. This is controlled by the 1×n switch 31-
1 and 1×n switch 31-3 are controlled in conjunction with each other and connected by a space switch.

If this configuration is adopted, for example, signals from subscribers to 〓〓〓 will be connected by a spatial switch,
Since wavelength input 2 is converted to wavelength input 3 by the optical conversion device 35-2, the optical receiver used for O/E conversion at the subscriber of 〓〓〓 may be sensitive to wavelength input 3, and vice versa. A similar conversion is performed when transmitting a signal from 〓〓 to 〓〓, so the emission wavelength in E/O conversion in 〓〓 can be the same as that in 〓〓, and the same optical receiver can be used as well.

Next, the optical wavelength conversion device 35- shown in FIG.
The configuration of 1,35-2 is JACopelandetal “p-n-p-n Optcal
Detectors and Light−Emitting Diodes”IEEE.
Journal of QE vol QE−14, No.11.
It is shown in detail in Nov1978pp810-813, but the general structure is shown in the fourth section.
As shown in the figure.

This device has a pnpn structure and exhibits S-type negative resistance in the air. This negative resistance makes the device bistable, and the current required to switch from low to high current is on the order of 1 μA. This current is obtained by the optical input power incident on the junction of this diode, and this optical input power is about 3 μW. On the other hand, when a high current flows, a light wavelength corresponding to the band gap is transmitted.

In order to realize an optical wavelength conversion device using such a device, the incident light must have an energy equal to or greater than the bandgap of the device. Therefore, in this method, since bidirectional transmission is performed, the wavelength of the optical wavelength conversion device, in other words, the optical wavelength used for bidirectional transmission at each terminal, is compared with the output of the optical wavelength conversion device, that is, the wavelength received at each terminal. You need to choose the shortest option.

Next, connections between subscribers will be specifically explained.

Consider a case where a call is made from subscriber to subscriber.

A control signal transmitted from a subscriber at wavelength λ1 is demultiplexed by a demultiplexing circuit 7-1 in FIG. 1, and converted into an electrical signal by an opto-electric conversion circuit 8-2. Here, the control signal consists of a preamble, a frame header, an identification number of the sending subscriber, an identification number of the destination subscriber, and a stop signal.

The control device 9 selects the optical switch 31-1 on the input side in FIG. 3 based on the identification number of the sending subscriber, and selects the optical switch 31-1 based on the identification number of the destination subscriber.
Select the output terminal.

On the other hand, as for the optical switch on the receiving side, the optical switch 31-2 is first selected based on the identification signal of the destination subscriber, and the terminal is selected based on the identification signal of the sending subscriber.

In the manner described above, optical switches are selected to establish connections between subscribers.

Incidentally, among the control signals, the preamble is a signal necessary for the operation of the optoelectric conversion circuits 8-1, 8-2, etc. to reach a steady value, and the frame header is a signal necessary to clearly indicate the start point of the control signal. .

As explained above, it is possible to exchange and transmit various data with high quality, and since each terminal can use the same light-emitting element and light-receiving element, an inexpensive system can be constructed.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of the present invention, Figure 2 is a conceptual diagram of general optical two-way communication, Figure 3 is an embodiment of the main part of the present invention, and Figure 4 is the optical wavelength shown in Figure 3. FIG. 2 is a diagram for explaining a conversion device. In the figure, 31-1 to 31-3 are 1×n optical switches, 32 is an optical fiber transmission line, 33 is an optical wavelength converter, 34-1 and 34-2 are optical demultiplexing circuits, and 35
-1 and 35-2 are optical wavelength conversion devices.

Claims (1)

[Claims] 1. In a switching system having an exchange that connects a plurality of subscriber terminals and the subscriber terminal on a 1:1 basis, the subscriber terminal transmits a control signal and a main signal of the first frequency component as an optical signal, and After the signals are separated by a splitter, they are input to a control device that controls the exchange, and the control device spatially connects predetermined subscriber terminals to each other by controlling the spatial switch of the exchange. An optical switching system characterized in that a main signal having the first frequency component is frequency-converted into a main signal having a second frequency component between an input end and an output end.