1,721,055 research outputs found
Single and multiple phase shifts tilted fiber Bragg gratings
Full text linkThe 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 device
Multifunction fiber optic sensing system for smart applications
No full textThe end of the twentieth century was witness to the merger of several technological disciplines that could eventually revolutionize engineering design philosophy and lead to the creation of intelligence within otherwise inanimate structures. This new technology will endow a structure with senses and the ability to react to its environment and change its state, shape and geometry. The key point for the practical realization of the so-called smart materials is the availability of robust and reliable structurally integrated sensors able to monitor the state of the structure. To this aim, a fiber optic multiparameter sensing system for process and structural health monitoring in concrete structures is presented. The reflectometric technique has been implemented for refractive-index measurements by using as transducer the fiber end /host interface. Results on the capability of the developed sensor to monitor the curing process of thermoset-based composites are presented. The integration with fiber Bragg gratings (FBGs) with the aim to perform temperature and strain measurements has been discussed. Two low-cost intensity-based demodulation techniques for FBGs interrogation have been developed and tested
Fiber optic sensor arrays: a new method to improve multiplexing capability with a low complexity approach
No full textIn this paper, we show some preliminary numerical results in order to increase the multiplexing capability of a multipoint fiber Bragg grating (FBG) sensor network without increase the system complexity. We base the new approach on the possibility of exploiting the chirped-pulsed frequency modulation technique (C-PFM). This technique, extensively used in radar applications, is based on the amplitude modulation of the emitted signal (pulsed) by a chirped frequency signal and on the demodulation of the reflected signal by means of adaptive filter. FBG sensors are instrumental to obtain cheap and easy handling multipoint sensing arrays
SYSTEM FOR REAL-TIME MONITORING OF THE STATE OF OCCUPATION OF RAILWAY LINES
No full textAxle-count automatic-block system for monitoring the state of occupation of a section of railway line by means of sensors designed to count the number of axles of railway vehicles that enter the section of line, the system comprising two optical-fibre Bragg-grating sensors, which are mounted at a distance from one another in positions corresponding to end portions of a section of railway line to be monitored and identify a block section, connected by means of an optical fibre to a querying system, which is able to send a light radiation to the sensors and process the radiation back-reflected by each of the sensors in order to acquire the information on the direction of travel of the railway vehicles and on the state of occupation of the block section
Low-cost all-fiber Bragg grating sensing system for temperature and strain measurements
No full textA low-cost all-fiber Bragg grating sensing system for temperature and strain measurements is presented. Broadband interrogation and grating-based optical filtering are used to detect a strain- or temperature-induced Bragg wavelength shift with a resolution of 1 us and 0.1 degrees C. The passive nature of the grating demodulation enables dynamic measurements, limited only by the electronic circuitry involved in the system read out. The same system is also used for dynamic strain detection. A fiber grating is bonded to a piezoceramic actuator in different configurations. A laser-triangulation-based system is used as a reference measurements up to 10 kHz, while dynamic strain measurements by a Fiber Bragg grating (FBG) are carried out up to 50 kHz, demonstrating a dynamic resolution of approximate to 40 n epsilon/(Hz)(1/2)
Miniaturized lenses integrated on optical fibers: Towards a new milestone along the lab-on-fiber technology roadmap
No full textLong-Period Gratings in Hollow Core Fibers by Pressure-Assisted Arc Discharge Technique
No full textWe report on the fabrication of long-period gratings (LPGs) in hollow-core air-silica photonic bandgap fibers by using the pressure-assisted electrode arc discharge (EAD) technique. The EAD procedure combined with pressure actuation inside fiber holes enables the modification of hole size and shape in both core and cladding region avoiding holes collapsing and thus acts as a useful tool to impress effective refractive index modulation leading to low loss gratings. Periodically repeated EAD treatments permit the fabrication of LPG-based devices in hollow core optical fibers enabling new functionalities hitherto not possible. Here, the experimental demonstration of LPG prototyping with different characteristics exhibiting attenuation bands with depth up to 12 dB are reported
Use of the time windowing on the chirped-pulsed frequency modulation (C-PFM) technique to improve the multiplexing performance of a fiber optic Bragg sensor array
No full textIn this paper, we present a novel approach to increase the multiplexing capability of a multipoint fiber Bragg grating (FBG) sensor network. Our approach is based on the possibility of exploiting the chirped-pulsed frequency modulation technique (C-PFM) to the optical pulses used to read a FBG sensor network. This technique, extensively used in radar applications, in the case of optical sensors is based on the amplitude modulation of the emitted signal (pulsed) by a chirped frequency signal and on the demodulation of the reflected signal by means of adaptive filter. The main parameters for a multiplexing systems are the minimum distance between two adjacent sensors and the cross-talk achievable. We show that the use of a well designed time shaping windowing of the transmitted pulse can improve both such parameters
- …
