Single and Multiple Phase Shifts Tilted Fiber Bragg Gratings

The spectral behavior of single and multiple phase shifts tilted fiber Bragg gratings has been experimentally investigated. To this aim, a simple and cost-effective postprocessing technique based on local thermal treatment was used to create arbitrary phase shifts along the tilted grating structure. In particular, UV written tilted fiber Bragg gratings were treated by the electric arc discharge to erase the refractive index modulation in well-defined regions. We demonstrate that these defects give rise to interference pattern for all modes, and thus defect states can be achieved within all the attenuation bands, enabling a simple wavelength independent spectral tailoring of this class of devices

Arc-Induced Long Period Gratings in Erbium-Doped Fiber

In this paper, we report about the fabrication of long period gratings (LPGs) directly into an Erbium-doped fiber, by using the electric arc discharge technique. The attention is focused on the writing process and the resulting properties, by considering gratings with different periods and measuring their spectra over a wide wavelength range. The LPGs show high order attenuation bands with tunable resonance wavelengths and depths up to 30 dB, while the lengths of the final devices are in range 20-45 mm. The polarization-dependent loss of these LPGs is also measured, for the first time in this kind of fiber. As further novelty, the influence of surrounding refractive index, applied strain, and temperature is investigated and discussed in comparative manner. Based on the achieved results, this fabrication procedure can be adapted to a specific application, for example in optical communications, signal processing, and sensing fields

Temperature profile of ex-vivo organs during radio frequency thermal ablation by fiber Bragg gratings.

We report on the integration of fiber optic sensors with commercial medical instrumentation for temperature monitoring during radio frequency ablation for tumor treatment. A suitable configuration with five fiber Bragg grating sensors bonded to a bipolar radio frequency (RF) probe has been developed to monitor the area under treatment. A series of experiments were conducted on ex-vivo animal kidney and liver and the results confirm that we were able to make a multipoint measurement and to develop a real-time temperature profile of the area, with a temperature resolution of 0.1°C and a spatial resolution of 5 mm during a series of different and consecutive RF discharges

Deflection Monitoring Method Using Fiber Bragg Gratings Applied to Tracking Particle Detectors

This paper proposes the use of fiber Bragg gratings (FBGs) for the deflection monitoring of a micromegas (MM) tracking particle detector to be installed at the European Organization for Nuclear Research during a major upgrade of the experiment ATLAS within 2018. MM detectors are designed to reach high spatial and time resolution, even if the design is not yet finalized. One mandatory issue for the MM detector is a precise monitoring of the deflection of the drift and read-out electrodes and/or of the panel hosting the electrodes. To this aim, FBG strain sensors are proposed and experimentally investigated as a sensing solution to monitor the strain state of the detector support panel hosting the drift and read-out electrodes. Finally, simple postprocessing analysis based on classical beam theory considering a rigid body permits calculating the panel deflection. Preliminary experimental results on first prototypes of small and large detector panels are presented and discussed

A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation

In this paper, we present several study cases focused on marine, oceanographic, and atmospheric environments, which would greatly benefit from the use of a deployable system for small satellite observations. As opposed to the large standard ones, small satellites have become an effective and affordable alternative access to space, owing to their lower costs, innovative design and technology, and higher revisiting times, when launched in a constellation configuration. One of the biggest challenges is created by the small satellite instrumentation working in the visible (VIS), infrared (IR), and microwave (MW) spectral ranges, for which the resolution of the acquired data depends on the physical dimension of the telescope and the antenna collecting the signal. In this respect, a deployable payload, fitting the limited size and mass imposed by the small satellite architecture, once unfolded in space, can reach performances similar to those of larger satellites. In this study, we show how ecology and Earth Observations can benefit from data acquired by small satellites, and how they can be further improved thanks to deployable payloads. We focus on DORA—Deployable Optics for Remote sensing Applications—in the VIS to TIR spectral range, and on a planned application in the MW spectral range, and we carry out a radiometric analysis to verify its performances for Earth Observation studies

Role of air pressure inside fiber holes during fabrication of long period gratings in bandgap fibers Via Electrode Arc Discharge

It has been recently demonstrated the fabrication of Long Period Gratings (LPGs) in hollow-core air-silica photonic bandgap fibers by means of pressure assisted Electrode Arc Discharge (EAD). The EAD procedure properly combined with air pressure inside fiber holes enables the localized modification of hole size and shape in both core and cladding region avoiding holes collapsing. LPGs are fabricated with a step-by-step approach by periodically repeated EAD treatment. In this paper, the role of pressure inside the fiber holes has been experimentally investigated in order to achieve design criteria of novel hollow core devices

Sensing features of long period gratings in hollow core fibers

We report the investigation of the sensing features of the Long-Period fiber Gratings (LPGs) fabricated in hollow core photonic crystal fibers (HC-PCFs) by pressure assisted Electric Arc Discharge (EAD) technique. In particular, the characterization of the LPG in terms of shift in resonant wavelengths and changes in attenuation band depth to the environmental parameters: strain, temperature, curvature, refractive index and pressure is presented. The achieved results show that LPGs in HC-PCFs represent a novel high performance sensing platform for measurement of different physical parameters including strain, temperature and, especially, for measurements of environmental pressure. The pressure sensitivity enhancement is about four times greater if we compare LPGs in HC and standard fibers. Moreover, differently from LPGs in standard fibers, these LPGs realized in innovative fibers, i.e. the HC-PCFs, are not sensitive to surrounding refractive inde

Microstructured Fiber Bragg Gratings

The first fiber Bragg gratings were accidentally written in a Ge-doped silica fiber using a high power argon-ion laser [Hill 1978]. Following this first evidence of photosensitivity in optical fibers, a huge effort was put into fiber gratings: improving their fabrication (they are now all externally inscribed), obtaining complex profiles, optimizing their performance, and incorporating them into devices and systems. On this line, the last decade was characterized by the birth of an emerging class of fiber gratings which can be defined as ldquomicrostructured fiber Bragg gratings.rdquo They refer to two main categories: one relies on short period gratings writing in microstructured optical fibers, whereas the second deals with standard short period gratings where structural defects at microscale are properly created within the hosting fiber by postprocessing techniques. This paper reviews the fabrication processes at the basis of this new technology as well as its properties and applications. Emphasis will be placed on principles of operation, technological developments and applications discussing perspectives, and challenges that lie ahea