Oleg V. Butov

Gamma radiation-induced refractive index change in Ge- and N-doped silica

We measured the change of the refractive index over a wide wavelength range in Ge- and N-doped high purity (fiber optics grade) silica glasses subjected to gamma irradiation. The radiation-induced change of the refractive index tends to be greater in the infrared part of the spectrum compare to the values measured in the UV-visible part of the spectrum. By means of the Kramers–Kronig relations, we estimate that a weak broadening of the optical vibration band of the silica network adds to this effect. The paper also discusses the difference observed in the spectral behavior of the induced refractive index change for both types of doped glass.

Optical fiber with distributed Bragg-type reflector

Optical fiber (OF) with a relatively high level of the backward signal at a certain wavelength is developed and studied. An increase in the backward signal is reached due to the recording of multiple weak fiber Bragg gratings (FBGs) in the course of fiber pulling. A scheme that is simpler than the direct FBG recording through a phase mask is proposed and implemented. Fibers with FBG recorded with different ratios of the region with recorded gratings to the total length of OF are fabricated. An increase in the level of the backward signal relative to the level of the Rayleigh scattering by more than 30 dB is reached. Results of experimental study of the proposed OFs and examples of practical application are presented.

Radiation resistant optical fiber with a high birefringence

A radiation resistant optical fiber with a high birefringence is fabricated on the basis of nitrogen-doped silica glass using the PANDA technology and studied. The loss in this fiber for an absorbed @[gamma]-radiation dose of 2–10 kGy does not exceed 5–10 dB/km, which is an order of magnitude lower than that of standard telecommunication fibers with a germanium silicate core.

Fibers and sensors for monitoring nuclear power plants operation

The radiation resistant sensor system for measuring deformations of the fuel channels of the RBMK-1000 nuclear power reactor is by now developed and tested. Concept of the system is the application of metal-coated radiation resistant nitrogen-doped-silica-core fiber and Bragg gratings written in it. Performance of the fiber and sensor elements measured in conditions of the extreme radiation environment inside core of operating nuclear reactors is being reported.

Fiber Bragg gratings in the radiation environment: Change under the influence of radiolytic hydrogen

The change of the transmission spectra of fiber Bragg gratings written in the optical fibers, whose silica cores are doped with either germanium or nitrogen, is studied experimentally under the influence of gamma-radiation. The transmission spectra in the neighborhood of the resonance (Bragg) wavelengths were regularly recorded “in-situ” in the course of irradiation during 24 days. For this purpose, uncoated gratings were placed in a pool near the spent fuel rods of a nuclear reactor. The fibers with the gratings written in them were in immediate contact with water. The estimated total absorbed radiation dose of the fibers is approximately 5 MGy. Molecular hydrogen, which is produced by radiolysis of water and penetrates into the core of silica fiber, is found to interact with the defects of Ge-doped silica induced by gamma-radiation, thereby causing a strong impact on the parameters of the spectrum of the Bragg gratings. On the contrary, in the case of gratings inscribed in N-doped silica fibers, the hyd...

N-doped-silica-core polarization maintaining fibre for gyros and other sensors for application in space industry

PANDA-type optical fibre with nitrogen-doped silica as core and pure silica as cladding material is fabricated and tested. The fibre demonstrates birefringence as high as 5·10-4, polarization holding h-parameter 2·10-5 m-1, loss 1.5 dB/km at a wavelength of 1.56 microns and 250 dB/km at 0.4 microns. Gamma radiation induced loss is found not exceeding 5-10 dB/km at a dose of 2-10 kGy, which is by an order of magnitude lower as compared to similar fibre with Ge-doped silica in the core.

Polarization stable plasmonic sensor based on tilted fiber Bragg grating

This paper presents a solution to one of the major problems of plasmonic fiber Bragg grating sensors concerning their high sensitivity to changes in the polarization state of light propagating through optical fiber. For the first time these kind of sensors have been produced using polarization maintaining fibers, thereby stabilization has been achieved using mechanical action and bending the supplied fiber. Comparative experiments have demonstrated that the sensor readings stability is at least an order of magnitude higher relative to other sensors, which record in a standard fiber with an isotropic structure.

The photosensitivity of ytterbium-doped optical fibers with aluminophosphosilicate glass cores

The phenomenon of photoinduced refractive index change in active optical fibers with Al2O3/P2O5/Yb2O3/SiO2 core composition has been observed under the action of UV laser radiation with 193-nm wavelength. It is established that hydrogen treatment of active fibers plays a key role in ensuring a radical (about two orders of magnitude) increase in their photosensitivity. It is shown that intrafiber Bragg gratings with reflection coefficients above 99% can be formed, which are promising mirror reflectors for fiber laser cavities.

Sensitivity of high Rayleigh scattering fiber in acoustic/vibration sensing using phase-OTDR

Distributed acoustic/vibration sensing schemes based on phase-OTDR are naturally sensitive to environmental perturbation. Nevertheless, further sensitivity enhancement is possible by using specialty fibers. In this paper, a nitrogen doped single-mode fiber with increased Rayleigh scattering properties is tested alongside a standard telecommunications single-mode fiber (SMF) for comparative phase-OTDR measurements. The high Rayleigh scattering fiber (HRF) does not only benefit from a higher numerical aperture, but also from a higher non-homogeneity of material density resulting in an enhanced scattering coefficient. For perturbations caused by shaker-induced vibration applied on a fiber section or by an acoustic signal emitted from a loudspeaker, the ability of localizing the perturbation and determining the frequency is studied simultaneously for the HRF and the SMF, using a direct detection phase-OTDR setup. Vibration frequencies in the range 100-7000 Hz with accelerations of up to 0.1g and acoustic signals in the frequency range 100-10000 Hz at sound pressure levels up to 115 dBC are tested. The signal-to-noise ratios (SNRs) for the differential phase-OTDR traces are calculated as the maximum difference signal level in the perturbation zone and a noise reference level outside the zone. Moving average methods are also employed for further enhancement. As expected, the HRF has superior performance for the localization and the frequency characterization, and it allows detection of signal levels that are undetectable with an SMF without using of denoising methods. On average, a 7 dB and a 3 dB improvement can be achieved for vibration detection and acoustic detection, respectively.

High-resolution fiber optic surface plasmon resonance sensor for biomedical applications

This paper presents a modified design of a high-resolution fiber optic sensor that operates on the surface plasmon resonance effect. The sensor is based on the well-known method of generating surface plasmons with the help of an inscribed tilted fiber Bragg grating that excites the cladding modes. Because the original design solution used a polarizing fiber, it was possible to significantly improve the stability of the sensor readings. The specialized mathematical apparatus was used to determine the surface plasmon resonance spectral position. It was experimentally shown that the limit of detection to the refractive index of such a sensor is 2 × 10−6 refractive index units. The sensors response to the investigated medium temperature change is presented and analyzed. The high resolution of the sensor in detecting protein molecules was demonstrated. Such sensors open wide perspectives for their application in real high-sensitivity sensor systems as biosensors for immune analysis in medical diagnostics.This paper presents a modified design of a high-resolution fiber optic sensor that operates on the surface plasmon resonance effect. The sensor is based on the well-known method of generating surface plasmons with the help of an inscribed tilted fiber Bragg grating that excites the cladding modes. Because the original design solution used a polarizing fiber, it was possible to significantly improve the stability of the sensor readings. The specialized mathematical apparatus was used to determine the surface plasmon resonance spectral position. It was experimentally shown that the limit of detection to the refractive index of such a sensor is 2 × 10−6 refractive index units. The sensors response to the investigated medium temperature change is presented and analyzed. The high resolution of the sensor in detecting protein molecules was demonstrated. Such sensors open wide perspectives for their application in real high-sensitivity sensor systems as biosensors for immune analysis in medical diagnostics.