JPH01232844A - Optical communication unit and optical communication system - Google Patents

Abstract

PURPOSE:To enable bidirectional communication between a master station and some slave stations without optical branching by detecting an incident light to a liquid crystal cell capable of being controlled to the transparent state and the scattering state with the utilization of the scattering state of the liquid crystal. CONSTITUTION:Bidirectional communication is applied between one master station 5 and some slave stations 6-8 connected in series. The master station 5 is provided with a light emitting element 51 and a light receiving element 52, and the slave stations 6, 7 are respectively provided with liquid crystal cells 61, 71 and a light receiving elements 62, 72, and the slave station 8 is provided with a liquid crystal cell 81, a light receiving element 82 and a reflecting mirror 83. The liquid crystal cells 61, 71 and 81 can be controlled at the transparent state and the scattering state and the light receiving elements 62, 72 and 82 detect the light in the scattering state. The master station 5 and the slave stations 6-8 are connected in series by an optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical communication unit and an optical communication system capable of bidirectional communication.

[Conventional technology]

In conventional optical communication systems, in order to enable bidirectional communication, each serially connected slave station usually
In order to receive the optical signal from the master station, a part of the light from the master station must be branched and received using an optical splitter or the like.

[Problem to be solved by the invention]

However, in such optical communication systems,
For example, if the optical branching is 1:1, the amount of light received by the downstream slave station will be 1/2 of that of the preceding slave station, so there is a drawback that the number of slave stations that can be serially connected is extremely limited. Ta.

The present invention has been made in view of these points, and its purpose is to provide communication between a master station having optical transmission and reception functions and several slave stations serially connected by a single optical fiber. An object of the present invention is to obtain an optical communication unit and an optical communication system devised to enable bidirectional communication without performing optical branching.

[Means to solve the problem]

In order to achieve such an object, the optical communication unit according to the present invention includes a liquid crystal cell that can control two states, a transparent state and a scattering state, and uses the scattering state of the liquid crystal to control the incident light to this liquid crystal cell. A light-receiving element for detecting and identifying whether the incident light is on or off is provided.

Further, an optical communication system according to the present invention includes a slave station comprising the communication unit described above, and a master station having a light emitting element and a light receiving element, and connects one master station and a plurality of slave stations serially through an optical fiber. This is what I did.

[Effect]

In the optical communication system according to the present invention, many slave stations can be connected serially.

〔Example〕

An embodiment of the optical communication unit according to the present invention is shown in FIG.
), shown in (b). Same figure (al is front view, same figure (bl is front view)
is a side view, ■ is a liquid crystal cell, 2 is a reflective film made of aluminum vapor deposition, etc., 3 is a liquid crystal cell control tap, 4 is a light receiving element, H
l is the incident light.

The liquid crystal cell 1 has a cylindrical shape, and light emitted from a light source of a master station is incident parallel to the central axis of the cylinder. The side surfaces of the liquid crystal cell 1 are covered with a reflective film 2 made of vapor-deposited aluminum or the like, and only a portion is removed.

The light receiving element 4 is directed toward this removed portion. This set of liquid crystal cell 1 and light receiving element 4 is called an optical communication unit.

The operation of this optical communication unit will be explained using FIGS. 2 to 4. In these figures, H1 is incident light, H2 is transmitted light, and H3 is scattered light, and the same or equivalent parts as in FIG. 1 are given the same reference numerals.

The optical communication unit has three operating modes: bypass mode, scattering mode and transmitting mode. In the bypass mode, the liquid crystal cell 1 is maintained in a transparent state, and most of the incident light passes through the liquid crystal cell 1.

Almost no incident light is sensed by the light receiving element 4. In the scattering mode (also called reception mode), the liquid crystal cell 1 becomes cloudy, and the light receiving element 4 can sense whether the incident light is on or off (brightness or darkness). In the transmission mode, the liquid crystal cell 1 performs light chopping that repeats a transmission state and a scattering state depending on the digital signal to be transmitted.

FIG. 5 is a block diagram showing an embodiment of an optical communication system according to the present invention, in which the optical communication unit shown in FIGS. 1 to 4 is incorporated. In FIG. 5, 5 is a master station, 6 to 8 are slave stations, 51 is a light emitting element, 52.
6'2. 72. 82 is a light receiving element; 61. '71.
81 is a liquid crystal cell, and 83 is a reflecting mirror. This system attempts to establish bidirectional communication between one master station 5 and several serially connected slave stations 6 to 8.

As shown in FIG. 5, the configuration of this system includes a master station 5 equipped with a light emitting element 51 and a light receiving element 52, and slave stations as a plurality of optical communication units (the final stage is equipped with a reflecting mirror 83).
and an optical fiber that serially connects them.

Next, an overview of the operation of the optical communication system configured as described above will be described. Generally, when a slave station transmits to a master station, chopping is performed on continuous light emitted from the master station according to a transmission signal. The light emitted from the master station passes through each slave station, its direction is reversed by the reflecting mirror of the final stage liquid crystal cell (liquid crystal cell 81 in Figure 5), and returns to the light receiving element of the master station. The chopped optical signal is received by one of the following.

Next, when the master station transmits to a slave station, only the slave stations designated by the master station are maintained in reception mode (scattered state) and receive the signal from the master station.

Next, the operation of the optical communication system shown in FIG. 5 will be explained in more detail. First, system initialization will be explained.

At the start of communication, the master station 5 generates a continuous optical signal of a certain predetermined length.

Initially, the slave station is maintained in a receiving state, and when it detects continuous light from the master station 5 as an initial signal, it changes to bypass mode, and the lower station similarly detects the initial signal. When all of the slave stations are initialized in the same way, all of them go into bypass mode, and the light emitted from the master station 5 is reflected by the reflecting mirror 83 and returns to the light receiving element 52 of the master station 5, and the initialization is completed. El 7JR will be made.

Next, transmission from a slave station will be explained. The slave station is /)
After mutually different waiting times (set together with the sequence order), optical chopping of the transmission begins, and all other slave stations are kept in bypass mode. Thereafter, similar transmissions are repeated one after another. The master station 5 checks whether or not there has been a signal collision between the slave stations, and if it is determined that there has been a collision, it initializes again.

Next, transmission from the master station to the slave station will be explained.

Normally, after initialization, unidirectional transmission from the slave station to the master station 5 continues, but when the master station 5 wants to transmit to the slave station, the continuous Turn off the light for a period of time. The slave station continues its chopping operation while still in the transmitting state, but the light scattered by the chopping is monitored by the light receiving element of the slave station.
If no scattered light is detected even though chopping is being performed, it is recognized that the higher-order slave station has entered reception mode or that the light source of the master station 5 has been turned off.

When such a state is recognized, the slave station assumes initialization or transmission from the master station 5, and shifts to a continuous scattering state, that is, a reception mode. In order to select a specific slave station, the master station 5 continuously transmits a rectangular wave of a predetermined frequency to the slave station, and then determines whether or not it has been designated in order from the higher-ranking station, and determines whether it has been designated or not. If it determines that it is not, it changes to bypass mode, and only the slave stations that are recognized as designated maintain scattering mode (receiving mode). When the transmission from the master station 5 is completed, it is initialized again, and normal transmission from the slave station to the master station 5 is repeated.

〔Effect of the invention〕

As explained above, the optical communication system according to the present invention includes a slave station consisting of an optical communication unit and a master station having a light emitting element and a light receiving element, and one master station and a plurality of slave stations are serially connected via an optical fiber. Since it is possible to chop the light by controlling the liquid crystal cell, there is less attenuation of light compared to the case of using an optical switching element such as PLZT that has an optical splitter or polarizer inside. Therefore, it is possible to realize a communication system in which more slave stations are serially connected.

Furthermore, the use of liquid crystal cells has the effect of realizing an optical communication system with less extinction force.

Furthermore, even if one of the slave stations connected serially is in a failure state, the transparent state is maintained, which has the effect of ensuring communication throughout the system.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a configuration diagram showing an embodiment of an optical communication unit according to the present invention, FIGS. 2 to 4 are explanatory diagrams for explaining its operation, and FIG. 1 is a configuration diagram showing an embodiment of an optical communication system according to the invention. 1.61, 71.81... Liquid crystal cell, 2... Aluminum vapor deposition, 3... Liquid crystal cell control tap, 4... Light receiving element, 5... Master station, 6-8... Child Station, 51... Light emitting element, 52.62, 72.82... Light receiving element, 83...
·Reflector.

Claims (2)

[Claims] (1) A liquid crystal cell that can control two states, a transparent state and a scattering state, and a system that detects incident light to this liquid crystal cell using the scattering state of the liquid crystal and distinguishes whether the incident light is on or off. An optical communication unit equipped with a light receiving element. (2) a slave station comprising the optical communication unit according to claim 1;
An optical communication system that includes a master station that has a light emitting element and a light receiving element, and serially connects one master station and a plurality of slave stations through optical fibers.