Distributed temperature sensing using a chirped fibre Bragg grating

A fully distributed temperature sensor consisting of a chirped fibre Bragg grating has been demonstrated. By fitting a numerical model of the grating response including temperature change, position and width of localized heating applied to the grating, we achieve measurements of these parameters to within 2.2 K, 149 µm and 306 µm of applied values, respectively. Assuming that deviation from linearity is accounted for in making measurement, much higher precision is achievable and the standard deviations for these measurements are 0.6 K, 28.5 µm and 56.0 µm, respectively.

Optically tunable fiber grating transmission filters

We propose and demonstrate single- and multiple-passband fiber grating transmission filters that are remotely tunable by exploitation of the optical pump-induced thermal effects in Er Yb-codoped fiber sections. A repeatable, wavelength-independent induced phase shift of 0.1p mW is obtained without hysteresis and anisotropic effects. A transmission extinction ratio of .23 dB with a 3-mW change in pump power is achieved.

Simultaneous refractive index and temperature measurement using a cascaded long-period grating device

We present a compact scheme for simultaneous temperature and surrounding refractive index (SRI) measurement using two long period gratings (LPGs) of different periods inscribed side-by-side in a single piece of a double-cladding fibre. One of the LPGs is sensitive to both SRI and temperature changes whilst the second is SRI-insensitive but shows spectral shift with temperature changes. In addition, we show that a resonance peak of the SRI-insensitive LPG can be designed to appear in the EDFA wavelength region with potential use for gain flattening applications.

A novel sensor interrogation technique using chirped fiber grating based sagnac loop

We demonstrate a novel and simple sensor interrogation scheme for fiber Bragg grating (FBG) based sensing systems. In this scheme, a chirped FBG based Sagnac loop is used as a wavelength-dependent receiver, and a stable and linear readout response is realised. It is a signijkant advantage of this scheme that the sensitivity and the measurement wavelength range can be easily adjhsted by controlling the chirp of the FBG or using an optical delay line in the Sagnac loop.

Effectively simultaneous temperature and strain measurement utilising a dual-grating sensor formed by type IA and type IIA FBGs

In this paper, we report a systematic investigation of the dependence of both temperature and strain sensitivities on the jiber Bragg grating (FBG) type, including the wellknown Type I, Type IIA, and a new type which we have designated Type 1.4, using both hydrogen-Ji-ee and hydrogenated B/Ge codoped jibers. We have identijed distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, duul-parameter sensor device. Three dual-grating sensing schemes with different combinations of gruting types have been constructed and compared. The Type IA-Type IIA combination exhibits the best pe$ormance and is superior to that of previously reported gruting-based structures. The characteristics of the measurement errors in such dualgrating sensor systems is also presented in detail.

First in-vivo trials of a fibre Bragg grating based temperature profiling system

We describe the results of in-vivo trials of a portable fiber Bragg grating based temperature profile monitoring system. The probe incorporates five Bragg gratings along a single fiber and prevents the gratings from being strained. Illumination is provided by a superluminescent diode, and a miniature CCD based spectrometer is used for demultiplexing. The CCD signal is read into a portable computer through a small A/D interface; the computer then calculates the positions of the center wavelengths of the Bragg gratings, providing a resolution of 0.2 °C. Tests were carried out on rabbits undergoing hyperthermia treatment of the kidney and liver via inductive heating of metallic implants and comparison was made with a commercial Fluoroptic thermometry system.

Bragg Grating fast Tunable Filter For Wavelength Division Multiplexing

A Bragg grating fast tunable filter prototype working over a linear tuning range of 45 nm with a maximum tuning speed of 21 nm/ms has been realized. The tunable filter system is based on two piezoelectric stack actuators moving a mechanical device thus compressing an apodized fiber Bragg grating. The filter allows both traction and compression and can work in transmission and in reflection. It is designed to work with a channel spacing of 100 GHz according to the ITU specifications for wavelength division multiplexing systems

High frequency sensing interrogation system using fiber Bragg grating based microwave photonic filtering

A high frequency sensing interrogation system by using fiber Bragg grating based microwave photonic filtering is proposed, in which the wavelength measurement sensitivity is proportional to the RF modulation frequency applied to the optical signal.

Recent advances in fibre grating devices and their sensing applications

Over the last twenty years, we have been continuously seeing R&D efforts and activities in developing optical fibre grating devices and technologies and exploring their applications for telecommunications, optical signal processing and smart sensing, and recently for medical care and biophotonics. In addition, we have also witnessed successful commercialisation of these R&Ds, especially in the area of fibre Bragg grating (FBG) based distributed sensor network systems and technologies for engineering structure monitoring in industrial sectors such as oil, energy and civil engineering. Despite countless published reports and papers and commercial realisation, we are still seeing significant and novel research activities in this area. This invited paper will give an overview on recent advances in fibre grating devices and their sensing applications with a focus on novel fibre gratings and their functions and grating structures in speciality fibres. The most recent developments in (i) femtosecond inscription for microfluidic/grating devices, (2) tilted grating based novel polarisation devices and (3) dual-peak long-period grating based DNA hybridisation sensors will be discussed.

High-frequency fiber Bragg grating sensing interrogation system using Sagnac-loop-based microwave photonic filtering

A novel high-frequency fiber Bragg grating (FBG) sensing interrogation system by using fiber Sagnac-loop-based microwave photonic filtering is proposed and experimentally demonstrated. By adopting the microwave photonic filtering, the wavelength shift of sensing FBG can be converted into amplitude variation of the modulated electronic radio-frequency (RF) signal. In the experiment, the strain applied onto the sensing FBG has been demodulated by measuring the intensity of the recovered RF signal, and by modulating the RF signal with different frequencies, different interrogation sensitivities can be achieved.

Simultaneous temperature and strain measurement with enhanced resolution up to 20 times by using a compact hybrid optical waveguide Bragg grating

A hybrid waveguide Bragg grating in optical fiber was fabricated and characterized, showing thermal responsivity of 211pm/°C. Proposed being used in fiber sensor, it demonstrates enhanced resolution by 20x and 2x for temperature and strain.

Microchannelled chirped fibre Bragg grating based refractive index sensor formed by femto-second laser processing and HF-etching

The microchannelled chirped fibre Bragg grating (MCFBG) was fabricated using femtosecond laser processing and HF-etching. Intrinsical refractive-index sensitivity induced by the microchannel makes MCFBGs ideal for biochemical sensing.

Thermal insensitive optical liquid level sensor based on excessively tilted fibre Bragg grating

We demonstrate a liquid level sensor based on the surrounding medium refractive index (SRI) sensing using of an excessively tilted fibre Bragg grating (ETFBG). The sensor has low thermal cross sensitivity and high SRI responsivity.