JPH082039B2 - Radiation resistant optical transmission system - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a radiation resistant optical transmission system, and more particularly to a radiation resistant optical transmission system in which monitor light is incident to reduce optical power loss in a radiation environment.

[Technical background of the invention] In recent years, the use of optical fibers under a radiation environment is increasing. As a sensor for radiation exposure using an optical fiber, a "leakage radiation detector" (JP-A-60-15)
9670), "Leakage radiation detector" (JP-A-60-159671),
"Radiation exposure detector using optical fiber" (JP-A-60
-161577) and so on. The main component of optical fiber is glass, so when irradiated with radiation, the colored center,
That is, a light absorption band is formed, which causes deterioration of transmission loss. In the past, a method was taken to construct a system by taking a margin for the increase in transmission loss from this experimental value.

[Problems of background art] However, there are drawbacks such as being restricted by the laying environment when a margin is not enough, and being unable to accurately grasp in real time how much the cable being laid is degraded. there were.

[Object of the Invention] The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional ones, and a monitor light is made incident on an optical fiber at the same time as a signal light to detect an increase in transmission loss due to a coloring center. The purpose of the present invention is to provide a long-life radiation resistant optical transmission system that is capable of stable signal optical transmission by feedback and is not easily restricted by the installation environment.

[Summary of the Invention] In order to achieve the above object, a radiation resistant optical transmission system according to the present invention includes a multiplexer connected to a signal light source and a monitor light source, and an optical fiber connected to the multiplexer.
A demultiplexer connected to the other end of the optical fiber, a signal photodetector and a monitor photodetector connected to the demultiplexer, and a comparator for comparing the outputs of the monitor photodetector and the monitor light source, It comprises a control means for inputting the result of the comparator and controlling the output of the signal light source.

[Examples of the Invention] When an optical fiber is irradiated with radiation, colored centers (light absorption bands) are generated, and transmission loss increases. However, there is a phenomenon in which the colored center disappears due to external light or heat, and as a result, the transmission loss is recovered. The case of using light is called a photobleaching effect, and the case of using heat is called a thermal bleaching effect. The present invention utilizes this photobleaching effect. A graph showing the photobleaching effect is shown in FIG. Specifically, light that does not affect the signal transmission light is always incident, the degree of deterioration is grasped by comparing the incident power with the output power, and the decrease is compensated by the photobleaching effect. Feedback is performed to increase the incident power as much as possible.

First, in this embodiment, a step index type optical fiber is used, and signal light having a wavelength of 0.85 μm is made incident. The monitor light has a wavelength different from that of the signal light.

Next, the connection relationship of this embodiment will be described. As shown in FIG. 1, the signal light source 2 and the monitor light source 3 are simultaneously connected to the multiplexer 4, and the multiplexer 4 is connected to one end of the optical fiber 5. It The optical fiber 5 passes through the radiation environment 6 and enters the demultiplexer 7, and its output is connected to the monitor photodetector 8 and the signal photodetector 9. The outputs of the monitor light source 3 and the monitor light detector 8 are input to the comparator 10, and the results are sent to the controller 11 as a control means, and the controller 11 controls the output of the signal light source 2.

Next, the operation of the system according to the present embodiment will be described. First, the signal light source 2 and the monitor light source 3 emit light of different wavelengths and send them to the multiplexer 4. The multiplexer 4 is 2
The two lights are combined and guided into the optical fiber 5. The optical fiber 5 passes through the radiation environment 6 as shown. Therefore,
The transmission loss of signal light and monitor light transmitted through the optical fiber 5 increases. The signal light and the monitor light that have passed through the optical fiber 5 are separated again into the original signal light and the monitor light by the demultiplexer 7. The signal light is sent to the signal light detector and taken out as a system output. On the other hand, the monitor light is sent to the monitor light detector 8. Here, the monitor light source 3, that is, the intensity of the original light, and the output of the monitor photodetector 8, that is, the light after the transmission loss changes due to radiation, are compared.
Entered in 10 and compared. As a result, when the output of the monitor photodetector 8, that is, the level of the light passing through the radiation environment 6, is smaller, the control means 11 controls the signal light source to increase the output of the signal light source. At this time, due to the photobleaching effect, an equilibrium state is reached at a position where the transmission loss is recovered.

[Effects of the Invention] As can be seen from the above embodiments, in the radiation resistant optical transmission system according to the present invention, the monitor light is transmitted at the same time as the signal light in the optical fiber, and the transmission loss increase due to the coloring center is detected and fed back. As a result, it is possible to reduce the margin of the increase in transmission loss, which can be used for signal transmission, so that a longer distance system can be constructed with the same configuration and it is less likely to be constrained by the installation environment. It can be applied to the environment of the dose rate (or the life can be extended under the same environment), and the degree of deterioration of the system due to radiation can be grasped in real time.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing the photobleaching effect which is the principle of the present invention. 2 ... Signal light source 3 ... Monitor light source 4 ... Multiplexer 5 ... Optical fiber 6 ... Radiation environment 7 ... Splitter 8 ... Monitor photodetector 9 ... Signal photodetector 10 ... Comparator 11 …… Control means (controller)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04B 10/14

Claims (1)

[Claims] 1. A multiplexer connected to a signal light source and a monitor light source, an optical fiber connected to the multiplexer, a demultiplexer connected to the other end of the optical fiber, and connected to the demultiplexer. A signal photodetector and a monitor photodetector, a comparator for comparing the outputs of the monitor photodetector and the monitor light source, and control means for receiving the result of the comparator and controlling the output of the signal light source. A radiation resistant optical transmission system characterized by being configured.