JP2528640B2 - Radiation resistant optical fiber transmission device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an optical fiber transmission device using a silica glass optical fiber as a transmission path, and more particularly to a radiation resistant optical fiber transmission device having low loss even in a radiation environment.

[Prior art]

Conventionally, in a transmission path using a silica glass optical fiber, if the optical fiber is placed in an environment where X-rays, γ-rays, electron beams, etc. are irradiated, transmission loss increases, and the increase in loss is
It is known to depend on the type, intensity, and amount of radiation, the composition of the optical fiber, the impurity concentration, the defect concentration in glass, and the like. As an example, for a step-type optical fiber having pure silica glass made of SiCl ₄ as a raw material in the core and doped with B and F in the clad, the loss increase under radiation is measured. The results shown in Fig. 5 are obtained. In this measurement, cobalt-60 was used as a radiation source.
Γ rays are used, and three stages of 5000R / H (roentgen / hour), 10000R / H, and 50000R / H are selected as irradiation conditions. The length of the optical fiber irradiated with radiation was 100 m, and the measurement was performed with light having a wavelength of 0.85 μm. The measured optical fiber has a core diameter of 50 μm, a cladding diameter of 125 μm, and a relative refractive index difference between the core and the cladding of about 0.7%. From FIG. 5, it can be clearly seen that the transmission loss increases as the dose rate increases and as the total dose increases. Therefore, conventionally, since the optical fiber transmission device is used under the irradiation of such radiation, it has been practiced to use a material made of a material that shields the optical fiber from the radiation.

[Problems to be Solved by the Invention]

However, such a radiation-shielding coating is not convenient because a special optical fiber dedicated to radiation must be manufactured. By the way, it is known that absorption due to colored centers (glass defects) caused by irradiation of radiation is reduced by passing light through an optical fiber. This is commonly called photo bleaching. This photo
Due to the bleaching, when the transmission loss of the optical fiber under radiation is evaluated, the measured value may change depending on the intensity of the measuring light incident on the optical fiber. As an example, the same optical fiber as that used in the measurement of FIG. 5 above was used, and the measurement result of irradiating γ-rays for 30 minutes while keeping the dose rate constant at 10,000 R / H is shown in FIG. Show. In this measurement, after irradiating with γ-ray for 30 minutes, this is stopped and the recovery characteristic is measured. It can be seen from FIG. 6 that when the intensity of the measuring light incident on the optical fiber is changed by two digits, the increase in loss due to radiation is reduced by about one digit, and the loss recovery after the irradiation is stopped is quicker. I understand. Conventionally, as a method of positively utilizing such photo bleaching, there is merely a method of injecting light into an optical fiber whose loss is increased by irradiation of radiation to recover the loss. The present invention uses the active use of the photo bleaching not only in such a stage but more actively, so that the increase in loss due to radiation irradiation can be suppressed without using a special optical fiber. An object is to provide a radiation optical fiber transmission device.

[Means for solving problems]

To achieve the above object, in the radiation resistant optical fiber transmission device according to the present invention, a silica glass optical fiber transmission line, an optical signal source for generating an optical signal for transmission, and a wavelength of the optical signal for transmission are different. A light source for generating light for photo-bleaching of a wavelength, an optical coupler for making both the transmission optical signal and the photo-bleaching light incident on one end of the silica glass optical fiber transmission line, and An optical wavelength selector that extracts only the transmission optical signal based on the difference in wavelength between the transmission optical signal and the photo-bleaching light from the light emitted from the other end of the silica glass optical fiber transmission line. Is a feature.

[Action]

Since the light for photo bleaching is incident on one end of the silica glass optical fiber transmission line by the optical coupler together with the optical signal for transmission, so to speak, photo bleaching for silica glass is performed in real time. Therefore, instead of recovering the increase in loss due to radiation exposure after the fact, the increase in loss can be prevented in advance so as not to occur due to radiation exposure. Moreover, since the wavelength of this photo-bleaching light is different from the wavelength of the transmission optical signal, it can be easily separated by an optical wavelength selector such as a filter, and does not adversely affect the transmission optical signal. . Therefore, since it is possible to simultaneously transmit the optical signal while preventing the loss increase due to the radiation exposure, it is not necessary to temporarily suspend the transmission of the optical signal to recover the loss increase due to the radiation exposure. The optical signal can be transmitted with high reliability.
In other words, if the light for photo bleaching is passed instead of the optical signal for transmission when the loss increases due to radiation exposure, the transmission of the optical signal must be temporarily stopped. As described above, since the light for photo bleaching is transmitted together with the optical signal for transmission, it is possible to avoid such a situation of interruption of transmission, and it is impossible to stop the transmission of the optical signal even temporarily. It can be said that it is suitable for transmission lines. Furthermore, if the loss increase is monitored, and the photo bleaching is performed when the loss increase is recognized, the reliability of the monitoring becomes a problem, and when the loss increase is recognized, it is already actual. Although there is a possibility that the transmission of the optical signal of the above may interfere with the actual damage, it is possible to cause the actual damage due to such a transmission failure by passing the light for photo bleaching together with the optical signal for transmission as described above. It is possible to prevent the occurrence of.

【Example】

In FIG. 1, an image of a subject 1 is made incident on a multi-core image fiber 3 via a lens system 2, the multi-core image fiber 3 is arranged so as to pass through a radiation management area 4, and the lens system 5 is arranged at an emission end thereof. TV camera 6 is placed. In this way, the image of the subject 1 is transmitted by the multi-core image fiber 3 and displayed on the monitor 7 connected to the TV camera 6. In such an optical transmission device, the half mirror 8 and the filter 9 are arranged at the entrance end and the exit end of the multi-core image fiber 3, and the light flux 12 given from the light source 10 through the lens 11 passes through the multi-core 8 through the half mirror 8. It is incident on the image fiber 3. The light source 10 is a light source that generates light for photo bleaching, and has a wavelength different from that of the light that represents the image of the subject 1. The lens 11 is for adjusting the diameter of the light flux 12 to the diameter of the multi-core image fiber 3. The filter 9 provided at the emission end of the multi-core image fiber 3 is for cutting the light for photo bleaching by utilizing the difference in wavelength. In FIG. 2, a light source for signal transmission connected to the transmitter 21
The light from 22 is incident on one end of an optical fiber 25 passing through the radiation management area 24 via the lens 23, and the optical signal transmitted by this optical fiber 25 passes through the lens 26 provided at the emitting end. It is incident on the light receiver 27 via the light receiver 27, and the signal of the light receiver 27 is sent to the receiver 28. In this case, the first
Instead of using the half mirror 8 as shown in the figure, the fiber type optical coupler (isolator) 13 causes the light from the light source 10 for photo bleaching to have a wavelength different from that of the light source 22 for signal transmission through the lens 11. It is incident on the fiber 25. Further, a filter 9 for cutting the photo-bleaching light is placed at the emission end of the optical fiber 25. When the optical fiber 25 is long, as shown in FIG. 3, a light source 30 for photo bleaching is also provided on the exit side of the optical fiber 25.
Is provided, the light is made incident on the fiber type coupler (isolator) 33 via the lens 31, and the light for photo bleaching is made incident on the optical fiber 25 from the emission side. In this way, by injecting the light for photo bleaching from both ends of the optical fiber 25, if the optical fiber 25 is long, the light for photo bleaching is attenuated on the way only from one end. It is possible to solve the problem that the sufficient photo bleaching effect cannot be achieved. In this way, when the light for photo bleaching is entered from both ends,
A filter 39 for cutting the light for photo bleaching is also used on the incident side. Next, the effect of this photo bleaching in real time was confirmed by an experiment, which will be described. In the configuration of FIG. 2 using the fiber type isolator 13, a light having a wavelength of 0.85 μm is made incident as an optical signal for transmission, and a semiconductor laser having an oscillation wavelength of 0.78 μm is used as a light source 10 for photo bleaching. When the incident power of the light for photo bleaching was changed and the measurement was performed, the measurement results as shown in FIG. 4 were obtained. From this, it can be seen that when the incident power of the light for photo bleaching is set to 1 mW, a substantial increase in loss is no longer observed. This real-time photo bleaching is not limited to the above-mentioned multi-core fiber or single-core optical fiber, but a large number of optical fibers are bundled, or at least a plurality of optical fibers are bundled at a terminal portion. It is possible to obtain a great effect by applying the present invention to those that are fused or fused.

【The invention's effect】

According to the radiation-resistant optical fiber transmission device of the present invention, not only the passive one of photobleaching and recovering the silica glass optical fiber transmission line whose loss is increased by the irradiation of radiation, but also the positive loss The increase can be prevented. Moreover, it is possible to suppress such an increase in loss without causing any trouble while transmitting an optical signal. Therefore, it is not necessary to temporarily stop the transmission of the optical signal for photo bleaching. Further, since the increase in loss does not occur, it is possible to prevent the actual damage that the increase in loss causes a trouble in the transmission of the optical signal.

[Brief description of drawings]

1 is a schematic diagram of a first embodiment of the present invention, FIG. 2 is a schematic diagram of a second embodiment, FIG. 3 is a schematic diagram of a third embodiment,
FIG. 4 is a graph showing the experimental results in the second embodiment,
FIG. 6 is a graph showing the dose rate dependence of the loss increase, and FIG. 6 is a graph showing the optical power dependence of the photo bleaching. 1 ... Subject, 2, 5 ... Lens system, 3 ... Multi-core image fiber, 4, 24 ... Radiation control area, 6 ...
TV camera, 7 ... monitor, 8 ... half mirror, 9, 39
...... Photo bleaching light cut filter, 10, 30 ...
… Light source for photo bleaching, 11, 23, 26, 31 …… Lens, 21 …… Transmitting device, 22 …… Light source for signal transmission, 13, 33
...... Fiber type coupler, 25 …… Optical fiber, 27 ……
Receiver, 28 ... Reception device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Cho Fukuda 1440 Rokuzaki, Sakura City Fujikura Electric Cable Co., Ltd. Sakura Factory (56) References JP-A-60-204640 (JP, A) JP-A-59-102 (JP) , A) JP-A-59-126505 (JP, A)

Claims (6)

(57) [Claims] 1. A silica glass optical fiber transmission line, an optical signal source for generating a transmission optical signal, and a light source for generating photo-bleaching light having a wavelength different from the wavelength of the transmission optical signal. An optical coupler that makes both the transmission optical signal and the photo-bleaching light enter one end of the silica glass optical fiber transmission line, and the light that exits from the other end of the silica glass optical fiber transmission line. A radiation resistant optical fiber transmission device further comprising: an optical wavelength selector that extracts only the transmission optical signal based on a difference in wavelength between the transmission optical signal and the photo-bleaching light. 2. The radiation resistant optical fiber transmission device according to claim 1, wherein the silica glass optical fiber transmission line is a single-core silica glass optical fiber. 3. The radiation resistant optical fiber transmission device according to claim 1, wherein the silica glass optical fiber transmission line is a bundle of a large number of silica glass optical fibers. . 4. The radiation resistant optical fiber transmission device according to claim 1, wherein the silica glass optical fiber transmission line is a silica glass optical fiber having a plurality of cores. 5. The radiation resistant optical fiber according to claim 1, wherein the silica glass optical fiber transmission line is a plurality of silica glass optical fibers assembled at a terminal portion. Transmission equipment. 6. The light source for photo bleaching is provided not only on one end side but also on the other end side of a silica glass optical fiber transmission line, and the photo bleaching light is supplied from the other end to the silica glass light. The radiation resistant optical fiber transmission device according to any one of claims 1 to 5, wherein the radiation resistant optical fiber transmission device is incident on a fiber transmission line.