H. Geiger

Modeling and performance analysis of a fiber Bragg grating interrogation system using an acousto-optic tunable filter

The performance of a fiber grating interrogation system using an acousto-optic tunable filter (AOTF) is analyzed. An equivalent linear circuit is presented to describe the system, which tracks the wavelength of a fiber Bragg grating (FBG) sensor in a FBG sensor array. From the model, the tracking resolution of a shot-noise-limited system has been determined for both transmissive and reflective interrogation of FBGs. An optimum ratio between the bandwidths of the FBG and the AOTF has been derived. Experimental results of a tracking system are presented to validate the theoretical predictions. The theory should also be suitable for interrogation systems using other forms of tunable bandpass filters for tracking the FBG wavelength.

Distributed grating sensors using low-coherence reflectometry

Distributed grating sensors have recently been interrogated with low-coherence reflectometry. Initial results have been enhanced using two new and versatile configurations. The first system tracks the wavelength using a closed-loop scheme, while the second system scans the distance using an open-loop approach. Arbitrary strain and temperature profiles along gratings have been examined with 300 /spl mu/m spatial resolution and 5.4 /spl mu//spl epsiv///spl radic/Hz accuracy. A theoretical model of the interrogation technique is derived and the predicted performance limits are examined experimentally.

Demonstration of a simple CDMA transmitter and receiver using sampled fibre gratings

A short pulse reflected off a single sampled fibre grating is used as a transmitter and a second sampled fibre grating with a photodiode is used as a receiver. This provides a simple encoding/decoding solution, applicable to optical CDMA networks.

Multiplexed point and stepwise-continuous fiber grating based sensors: practical sensor for structural monitoring?

The paper describes recent progress on developing a complimentary pair of fiber grating-based sensor methods for structural monitoring. Particular emphasis is placed, firstly, on interrogating arrays of point-sensors based on fiber gratings using an acousto-optic tunable filter and, secondly, on determining the optical path length between these point sensors using optical time domain reflectometry. The combined system is capable of measuring both local and spatially-averaged strain. A new approach which permits the simultaneous measurement of strain and temperature, using superimposed fiber gratings, is presented. Potential applications in aerospace composites are also discussed.

Comparison of DSF- and SOA-based phase conjugators employing noise-suppressing fiber

In this paper, semiconductor optical amplifier (SOA)- and dispersion shifted fibre (DSF)-based conjugators are compared using identical fiber-grating-based filter networks and l0-Gbit/s nonreturn-to-zero (NRZ) intensity-modulated data. We believe we report for the first time the use of fiber gratings for efficient ASE filtering and signal extraction. We identify ASE from the amplifiers, rather than the conjugation efficiency, as the limitation to phase conjugation in both approaches.

Novel frequency-agile interrogating system for fiber Bragg grating sensors

We have demonstrated a new frequency-agile system for the interrogation of in-fiber Bragg grating sensors. The scheme involves frequency shift keying (FSK) of the rf drive to an acousto-optic tunable filter (AOTF) to track the wavelength shifts of a Bragg grating. Theoretical studies to derive the optimum frequency deviation for achieving maximum sensitivity are given, and experimental results are presented for temperature measurement. This technique is capable of rapid, random access and very wide tuning range, showing the potential for interrogating multiplexed arrays of Bragg-grating-based sensors.

Optimization of DSF- and SOA-based phase conjugators by incorporating noise-suppressing fiber gratings

We compare the performance of dispersion-shifted-fiber (DSF) and semiconductor-optical-amplifier (SOA) based laser phase conjugators for a 10-Gb/s nonreturn-to-zero system with respect to conversion efficiency, noise figure, and distortion. Fiber gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF-based conjugator has the advantage of distortion tolerance at higher input power.

Optimum receivers with fiber gratings

Summary form only given. We demonstrate such a matched fibre grating filter experimentally by generating an optical pulse from the cw output (O dBm) of a tunable laser diode by using a LiNbO/sub 3/ Mach-Zehnder modulator together with a pulse generator (HP 8131A, risetime 110 ps).

Low-cost high-resolution time-domain reflectometry for monitoring the range of reflective points

A new OTDR technique to interrogate the range of reflective markers in an optical fiber (or an electrical cable) is presented. The technique has been developed to monitor strain in sections of a fiber over gauge lengths of several meters. Signal-to-noise analysis shows that current OTDR systems do not fully exploit the spatial resolution theoretically available. The available resolution is explored with a new OTDR technique. >

Fibre DFB lasers in a 4/spl times/10 Gbit/s WDM link with a single sinc-sampled fibre grating dispersion compensator

WDM transmission and dispersion compensation at 40 Gbit/s over 200 km standard fibre is demonstrated on a 100 GHz grid using four high power single-polarisation single-sided output DFB fibre lasers and one chirped 4 channel WDM fibre Bragg grating.