Sanzhar Korganbayev

Linearly chirped fiber Bragg grating response to thermal gradient: from bench tests to the real-time assessment during in vivo laser ablations of biological tissue

Abstract. The response of a fiber optic sensor [linearly chirped fiber Bragg grating (LCFBG)] to a linear thermal gradient applied on its sensing length (i.e., 1.5 cm) has been investigated. After these bench tests, we assessed their feasibility for temperature monitoring during thermal tumor treatment. In particular, we performed experiments during ex vivo laser ablation (LA) in pig liver and in vivo thermal ablation in animal models (pigs). We investigated the following: (i) the relationship between the full width at half maximum of the LCFBG spectrum and the temperature difference among the extremities of the LCFBG and (ii) the relationship between the mean spectrum wavelength and the mean temperature acting on the LCFBG sensing area. These relationships showed a linear trend during both bench tests and LA in animal models. Thermal sensitivity was significant although different values were found with regards to bench tests and animal experiments. The linear trend and significant sensitivity allow hypothesizing a future use of this kind of sensor to monitor both temperature gradient and mean temperature within a tissue undergoing thermal treatment.

Towards inline spatially resolved temperature sensing in thermal ablation with chirped fiber Bragg grating

We investigate the theory and feasibility of an inline spatially resolved temperature sensor, suitable for thermal ablation monitoring. The sensor is based o a chirped fiber Bragg grating (CFBG). The CFBG is modelled as a chain of Bragg gratings, each sensitive to local temperature variations. By using a combination of iterative and statistical optimization techniques, it is possible to use demodulate the CFBG, in case of a Gaussian-like spatial temperature profile. A feasibility test based on CFBG simulation shows that the CFBG returns error <;1 mm on cellular damage threshold spatial estimation and good noise resilience.

Linearly chirped fiber-optic Bragg grating as distributed temperature sensor for laser ablation

We report a novel technique for estimating spatially distributed temperature profile, with a linearly chirped fiber Bragg grating (LCFBG) fiber-optic sensor, and its application in laser ablation of tissue. Our algorithm determines the temperature profile from LCFBG optical spectrum with sub-0.1mm resolution; a spectral flattening filter compensates for LCFBG spectral ripples, allowing operation with commercial gratings. A preliminary experimental analysis on LCFBG monitoring laser ablation of porcine liver has been carried out.

Detection of various Thrombin concentrations using etched fiber Bragg gratings functionalized with DNA aptamer

The response of etched fiber Bragg grating (EFBG) functionalized with 29-mer DNA aptamer to the different concentrations of Thrombin protein has been investigated. Etched FBGs are an efficient technology for detection of refractive index, and have been demonstrated also for biosensors applications. EFBGs have a simpler manufacturing approach comparing to other methodologies and are based on a low-cost device; their fabrication can be achieved by simple chemical etching, without requiring fusion splicing. During the test we assessed its feasibility for small variations of thrombin concentrations (10μg/ml, 20μg/ml, 40μg/ml and 80μg/ml). In particular, we performed experiments of chemical etching with hydrofluoric acid, which progressively depletes the fiber cladding exposing the core to the outer medium. Additionally, unstriped not etched FBGs were also used as a control for temperature pattern compensation. Before functionalization, EFBG was calibrated with different sucrose and ethanol solutions that validated the sensitivity to refractive index change. EFBG was further silanized with 3-Aminopropyl-triethoxysilane (APTES) in order to immobilize Thrombin binding aptamer on the silica surface of the fiber. The change of Bragg wavelength when functionalized EFBG is exposed to different concentrations of Thrombin using Micron Optics Hyperion si255-x55 sensing system was demonstrated. A small yet detectable sensitivity (several tens of nanomolars) even between small protein variations allows hypothesizing a future use of this kind of functionalized fiber for biosensor development.

An etched chirped fiber Bragg grating for measurement of refractive index and temperature pattern

In this work, partially etched chirped fiber Bragg grating (pECFBG) for the real-time multi-parameter measurement of temperature and refractive index is proposed. The sensor is fabricated by wet-etching a portion of a linearly chirped FBG with linear chirp profile. Obtained CFBG has two active areas: the unetched part of the grating that can be used either as a uniform temperature sensor, or to detect thermal gradients experienced through the grating length; the etched part, besides having a similar thermal sensitivity, is exposed to refractive index sensing through the variations of external refractive index. Overall, the pECFBG structure behaves as a compact sensor with multi-parameter capability, that can both measure temperature and refractive index on the same grating, but also spatially resolve temperature detection through the grating section. The results have been validated through both a model and experimental setup, showing that the mutual correlation algorithm applied to different spectral parts of the grating is able to discriminate between uniform and gradient-shaped temperature profiles, and refractive index changes. The reflected spectra showed a clear correlation between the RI change of the surrounding media and spectral shift with temperature variations.

Partially etched chirped fiber Bragg grating (pECFBG) for joint temperature, thermal profile, and refractive index detection

In this work, a partially etched chirped fiber Bragg grating (pECFBG) is introduced, as a compact sensor for multi-parametric measurement of temperature, thermal gradients over the active length, and refractive index. The sensor is fabricated by wet-etching a portion of a 14-mm linearly chirped FBG with linear chirp profile. The resulting device has two active areas: the unetched part of the grating (2 mm) can be used either as a uniform temperature sensor, or to detect thermal gradients experienced through the grating length by means of a spectral reconstruction technique; the etched part (12 mm), besides having a similar thermal sensitivity, is exposed to refractive index sensing through the introduction of a sensitivity to external refractive index. Overall, the pECFBG structure behaves as a compact sensor with multi-parameter capability, that can both measure temperature and refractive index on the same grating, but also spatially resolve temperature detection through the grating section. The results have been validated through both a model and experimental setup, showing that the mutual correlation algorithm applied to different spectral parts of the grating is able to discriminate between uniform and gradient-shaped temperature profiles, and refractive index changes.

Characterization of a nanoparticles-doped optical fiber by the use of optical backscatter reflectometry

The use of nanoparticles is gaining large interest in modern photonic technology, mainly because nanoparticles can drastically change the properties of optical media. Here, a custom special fiber has been considered for investigation. The fiber presents a co-doped erbium and magnesium oxide nanoparticles core, and standard telecommunication size. Modified Chemical Vapor Deposition technique, together with the spontaneous phase separation, permits to grow inside the core a random distributed pattern of nanoparticles, whose size varies between 20 to 100 nm, considering the transversal section. The nanoparticle increases the scattering, which is, in general, an unwanted occurrence. Nevertheless, interesting applications can emerge in sensor field. In this work the focus has been concentrated on the distributed sensing applications offered by the enhanced backscattering. The fiber has been characterized by the use of an Optical Backscatter Reflectometer (OBR) Luna 4600. Results show that the intensity of backscattering, induced by the nanoparticles, is 50 dB larger than the one shown by standard single mode fiber. This results in an exponential decay of the reflected optical power, which vanish after 1.7 meter of propagation. Moreover, using the OBR, it has been possible to characterize the polarization properties of this special fiber. Because the nanoparticles are stretched during the drawing process, the fiber presents a well-defined polarization signature pattern, with a random alternation of polarization state every, roughly, 10 cm. These properties are promising for creating a distributed, high reflectivity, sensors, in application like OBR spatial multiplexing.