Radiation-induced Optical Attenuation Research Articles

Радиационная стойкость оптических компонентов волоконно-оптического гироскопа

The paper presents the results of an experimental study of specialized fiber-optic components of a fiber-optic gyroscope (FOG) developed and manufactured by PJSC PNPPK. The study aimed to test their resistance to continuous and pulse ionizing radiation (IR). When exposed to continuous IR, the FOG performance is determined by radiation-induced optical attenuation (RIA) of both the Panda-type polarization maintaining optical fiber (OF) of the gyroscope fiber circuit and the active OF, which is part of the superluminescent fiber radiation source (SFS), as well as by the average wave-length stability of the SFS. It is advisable to compensate a change in the average wavelength as a systematic error. In the case of pulse IR, the recovery time of the FOG is determined primarily by the relaxation time of the RIA of the Panda OF.

Effect of Temperature and Gamma-Ray Irradiation on Optical Characteristics of Fiber Bragg Grating Inscribed Radiation-Resistant Optical Fiber

A new radiation-hard germano-silicate glass optical fiber with a pure silica glass buffer and a boron-doped silica glass inner cladding was fabricated for temperature sensor application based on the fiber Bragg grating (FBG) under γ-ray irradiation environment. The temperature dependences of optical attenuation at 1550.5 nm and Bragg reflection wavelength shift from 18 °C to 40 °C before the γ-ray irradiation were about 4.57×10−4 dB/ °C and 5.48 pm/ °C, respectively. The radiation-induced optical attenuation at 1550.5 nm and the radiation-induced Bragg reflection wavelength shift under the γ-ray irradiation with the total dose of 22.85kGy at 35 °C were about 0.03dB/m and 0.12nm, respectively, with the γ-ray irradiation sensitivity of 5.25×10−3 pm/Gy. The temperature and the γ-ray irradiation dependence of optical attenuation at 1550.5nm in the FBG written fiber with boron-doped silica glass inner cladding were about 6 times and 4 times lower than that in the FBG written fiber without boron-doped silica glass inner cladding under a temperature change from 18 °C to 40 °C and the γ-ray irradiation with the total dose of 22.85 kGy at 35 °C, respectively. Furthermore, the effect of temperature increase on the Bragg reflection wavelength of the FBG written fiber with boron-doped silica inner cladding was much larger about 1000 times than that of the γ-ray irradiation. However, no influence on the reflection power of the Bragg wavelengths and the full width at half maximum (FWHM) bandwidth under temperature and the γ-ray irradiation change was found. Also, after the γ-ray irradiation with the dose of 22.85kGy, no significant change in the refractive index was found but the residual stresses developed in the fiber were slightly relaxed or retained.

Gamma-Ray Irradiation-Induced Optical Attenuation in Co/Fe Co-Doped Alumino-Silicate Optical Fiber for Dosimeter Application

Dose dependence of radiation-induced optical attenuation (RIA) at 1310 nm of the Co/Fe co-doped alumino-silicate optical fiber was investigated under gamma-ray irradiation at dose rates from 6.7 to 78.3 Gy/min. From the measured RIA, radiation dose sensitivity (ΔRIA/ΔDose) and rate of RIA change with irradiation time (ΔRIA/ΔTime) at the different dose rates were estimated. RIAs at various wavelengths (800 to 1600 nm) of the optical fiber were also measured and the RIA characteristics at 800 and 1310 nm under discrete gamma-ray irradiation were investigated. The measured RIA of the Co/Fe co-doped fiber showed very high dose sensitivity regardless of the dose rates and the ΔRIA/ΔTime was found to show linear response with respect to the dose rate. The significantly large RIA was attributed to Co, Fe, and Al-related defects in the fiber core which were formed by the irradiation, and it became larger at shorter wavelength. The high radiation dose sensitivity, linear response of the ΔRIA/ΔTime with respect to dose rate, and the high reproducibility of the dose dependence of RIA under the discrete irradiation clearly indicate that the Co/Fe co-doped fiber is able to provide highly accurate information of not only total accumulated dose but also dose rate of the radiation with irradiation time.

In-situ gamma radiation induced attenuation in silica optical fibers heated up to 600 °C

In this work, the performance of silica fibers was experimentally studied under continuous gamma irradiation and periodic heating in steps to temperatures up to 600°C. The broadband optical attenuation in 10-meter lengths of three different types (one high-OH, two low-OH types) of multimode silica fibers was continuously monitored in-situ throughout the experiment. All three fiber types survived the experiment both optically and mechanically. Results showed that for the gamma dose rate tested in this experiment (476Gy per hour), gamma radiation primarily affects wavelengths below ~1000nm. For the low-OH silica optical fibers, gamma radiation has little effect on transmission in the infrared, particularly at 1300nm and 1550nm. These two wavelengths are commonly used in existing commercial optical sensing equipment. Thermal effects primarily contributed to the increase in absorption in the infrared region for low-OH silica optical fibers. The large OH concentration in the high-OH fiber results in large intrinsic absorption in the near-infrared, making the high-OH fiber unsuitable for transmission at 1300nm and 1550nm. However, the high-OH fiber had lower radiation-induced attenuation in the UV and visible ranges including 850nm, which is another wavelength that is commonly used for sensing applications. The steady state value for the gamma radiation-induced attenuation in the high-OH fiber at 600nm (the peak wavelength for the absorption due to non-bridging oxygen hole centers) and the time constant for reaching this steady state value both decreased as temperature was increased in the range of 100–400°C, with almost full annihilation of the radiation-induced defects achieved at 400°C. Time constants were on the order of minutes to hours for the gamma dose rate in this experiment and the high-OH fiber that was tested. In general, radiation-induced attenuation was observed to decrease significantly with increasing temperature, particularly at lower wavelengths where most of the defect centers are located. The conditions under which the measurements were made (in-situ as the temperature was varied) also gives insight into the dynamics of the optical attenuation, which may help provide a better understanding of the fundamental physics of radiation-induced optical attenuation. All of the results generated in this work were processed into movies that are available for download.

Fast-neutron radiation effects in a silica-core optical fiber studied by a CCD-camera spectrometer

A simple CCD-camera spectrometer was deployed at the Los Alamos Spallation Radiation Effects Facility to characterize fast-neutron irradiation effects in several silica-based optical fibers over the wavelength range ~ 450-1100 nm. The experimental arrangement allowed optical loss spectra to be developed from remotely recovered frame grabs at various times during irradiation without it being necessary to resort to cutback methods. Data recorded for a pure-silica-core/F-doped-silica-clad fiber displayed a peculiar artifact, which is described and mathematically modeled in terms of leaky modes propagating in an optical cladding that is substantially less susceptible to radiation-induced optical attenuation than is the core. Evidence from optical time-domain reflectometry supports the postulate that mode leakage into the cladding may be a result of light scattering from the tracks of ions displaced by the 14-MeV neutrons. These results suggest that fibers with fluorine doping in the core, as well as in the cladding, would be relatively resistant to radiation-induced attenuation in the UV-visible spectral region.

The role of hydrogen as a radiation protection agent at low temperature in a low-OH, pure silica optical fiber

It is demonstrated in a low-OH, pure-silica-core fiber waveguide that hydrogen plays a significant role in both suppressing the in situ steady-state radiation-induced optical attenuation near 850 nm reducing the subsequent recovery time at low temperature (-55 degrees C). The natural beneficial effects of radiolytic hydrogen formed from hydroxyl groups in silicas containing OH are here provided by externally impregnated molecular hydrogen. SiH was observed to form during both low-temperature irradiation and the subsequent recovery up to 10/sup 4/ s; radiolytic SiOH was not observed to form. Spectroscopic analysis of the radiation-induced loss in the visible and near-infrared demonstrates that there is more than one simple absorption band involved. However, these bands are not all equally suppressed by hydrogen impregnation. >

Radiation damage of optical fiber waveguides at long wavelengths

Measurements of the radiation-induced optical attenuation at 1.3 microm and the induced absorption spectra (0.4-1.7 microm) of state-of-the-art pure synthetic silica and doped silica core optical fiber waveguides have been undertaken to characterize their radiation response at long wavelengths. It has been observed that radiation-induced absorption bands at long wavelengths can give rise to substantial induced losses at both 1.3 and 1.55 microm in some fibers, especially those doped with P or B; the ratio of the damage at 1.3 and 1.55 microm to that at 0.82 microm in these fibers has been found to be only ~0.29 and 0.71, respectively. In contrast, pure fused silica and binary Ge-doped silica core fibers have shown the greatest hardness at long wavelengths. Suggestions have been made for the optimum wavelengths and preferred fiber compositions to minimize the effects of nuclear radiation in fiber-optic communications systems operating at long wavelengths.