1092 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 52, NO. 4, AUGUST 2003 Interrogation of Extrinsic Fabry–Pérot Interferometric Sensors Using Arrayed Waveguide Grating Devices Pawel Niewczas, Lukasz Dziuda, Grzegorz Fusiek, Andrew J. Willshire, James R. McDonald, Graham Thursby, Dave Harvey, and W. Craig Michie Abstract—In this paper, we present details of a solid state inter- rogation system based on a 16-channel arrayed waveguide grating (AWG) for interrogation of extrinsic Fabry–Pérot interferometric sensors. The sensing element is configured in a reflecting mode and is illuminated by a broad-band light source through an optical fiber. The spectrum of light reflected from the sensor is analyzed using an AWG device acting as a coarse spectrometer. Using mea- surement points from the AWG channels, the original spectrum of the sensing element is reconstructed by a means of curve fitting. This allows sufficient information for the position of the reflection peak (or inverted peak) to be uniquely determined and the value of a measurement quantity obtained. In addition to the theoretical simulations of the proposed measurement system, we provide de- tails of the laboratory evaluation. Index Terms—Arrayed waveguide gratings (AWGs), Fabry–Pérot sensors, strain sensors. I. INTRODUCTION A DVANCES in the fiber-optic telecommunications in- dustry have always attracted significant attention of researchers from the field of fiber-optic sensors. Many com- ponents developed specifically for the telecommunication industry found their use in fiber-optic sensor systems. These are the optical fibers themselves, semiconductor light sources and detectors, tuned laser diodes, scanning Fabry–Pérot filters, and so on. The devices that enable either emitting single wavelengths that are tuned across a desired bandwidth, or scanning filters operating with broadband sources, can be directly utilized in the interrogation of Fabry–Pérot or fiber Bragg grating (FBG) Sensors. This has been demonstrated by many researchers [1], [2] and commercial measurement systems are now available that make use of this technology. The fundamental problem associated with the present tuned or scanning components is the necessity of the physical shifting of the mechanical subassemblies through either piezo-electric actuation or techniques available through microelectromechan- Manuscript received June 15, 2002; revised December 24, 2002. This work was supported in part by the Department of Trade and Industry (DTI) and the En- gineering and Physical Sciences Research Council (EPSRC) through the “LINK Sensors and Sensor Systems for Industrial Application” Program and in part by Dr. J. Bonnar of Kymata Ltd. P. Niewczas, A. J. Willshire, and J. R. McDonald are with the Department of Electronic and Electrical Engineering, Institute for Energy and Environment, University of Strathclyde, Glasgow, U.K. (e-mail: p.niewczas@strath.ac.uk). L. Dziuda and G. Fusiek are with the Faculty of Electrical Engineering, Lublin Technical University, Lublin, Poland. G. Thursby is with the Institute for Sensors and Control, Department of Elec- tronic and Electrical Engineering, University of Strathclyde, Glasgow, U.K. D. Harvey is with the Rolls-Royce Strategic Research Center, Derby, U.K. W. C. Michie is with Kamelian Ltd., Glasgow, U.K. Digital Object Identifier 10.1109/TIM.2003.814828 ical Systems (MEMS) technology [3]. This imposes a practical limitation on the measurement system response time when the condition of the mechanical resonance is reached in the particular component. However, recently developed MEMS scanning Fabry–Pérot filters, potentially suitable for this application, have the impressive maximum scanning frequency in the order of 100 kHz [4]. This, however, imposes extremely harsh demands on the design of a monitoring photo-receiver that must usually represent both ac and dc signals. Another interrogation technique in which the problem of me- chanical resonance is nonexistent is based on charge coupled device (CCD) spectrometers [5], [6]. These devices make use of a dispersive element (prism or grating) which spreads the an- alyzed spectrum of light across an array of photodetectors on a CCD element. The system has the advantage of no moving parts; however, it involves precision alignment of constituent optical components and is limited to the operation of up to ap- proximately 900 nm due to the spectral response of the CCD element. The operating spectrum can be shifted up (to make use of the telecommunication components, e.g., super-fluores- cent light sources) by coating the CCD element with a phosphor layer. However, this approach has not yet been demonstrated in sensing applications. In this paper, we propose the use of an arrayed waveguide grating (AWG) device for analyzing the spectrum of light re- flected from extrinsic Fabry–Pérot interferometric (EFPI) sen- sors. AWGs were specifically developed for the fiber-optic telecommunication industry. AWG devices offer an attractive dense wavelength-division multiplexing (DWDM) solution for increased communication system capacity [7]. The component splits the input broad-band light into a number of narrow-band components, equivalent to the number of AWG channels. The operation is analogous to a transmission diffraction grating that splits light into its constituent colors. This can be used to recreate the original spectrum reflected from an EFPI or FBG sensor, provided that the number of channels is sufficient for the particular sensor arrangement. The proposed solid state approach has a number of potential ad- vantageswhencomparedwiththesensorinterrogationtechniques highlighted above. These advantages are outlined as follows: • high speed of operation due to the solid nature of the com- ponent (no moving parts); • each channel is monitored by its individual photo-receiver which relaxes demands on the photo-receiver design; • compact size and passive nature (fully athermal AWG modules have been demonstrated [8]); 0018-9456/03$17.00 © 2003 IEEE