Armindo L. V. S. Lage

Mach-Zehnder and Michelson topologies for self-referencing fiber optic intensity sensors

A theoretical and experimental study of self-referencing fiber optic intensity sensors based on Michelson and on Mach-Zehnder configurations is conducted. Via the definition of the measurement parameter R, sensor linearity and sensitivity are analyzed. Theoretical and experimental results are compared, considering the problem of sensor design and optimization. The choice between the two configurations is addressed; the Michelson one is recommended for practical reasons.

Wavelength multiplexing of frequency-based self-referenced fiber optic intensity sensors

A new wavelength multiplexing configuration for self-referenced fiber optic intensity sensors using fiber Bragg gratings and wavelength division multiplexing (WDM) couplers is investigated. First, the network multiplexing concept is characterized, and then the self-referenced intensity sensor is presented, which is the basis of each individual sensor in the network. The implemented experimental setup of the multiplexing network is described, and results are presented considering the crosstalk, resolution, and power budget of the sensing multiplexing network. The characteristics and features of the configuration proposed are addressed.

Self-referenced fibre optic intensity sensor based on a multiple beam Sagnac topology

A theoretical and experimental characterisation of a self-referenced fibre optic intensity sensor based on a multiple beam Sagnac configuration is conducted. Via the definition of the measurement parameter (R parameter) sensor linearity and sensitivity are analysed. Theoretical and experimental results are compared, being considered the problem of sensor design and optimisation.

Fiber Bragg sensor interrogation system based on a CCD spectrometer

The demand for a low cost, portable and accurate instrumentation system for structural monitoring is increasing as civil structures appear to be monitored for their lifetime. Face to conventional solutions, the issue can be handled as to develop an interrogation system based on a CCD spectrometer. A method pointing out to improve the instrumentation characteristics of the whole system was developed. The initial low wavelength resolution of the spectrometer (0.2 nm) is enhanced through a sub-pixel resolution algorithm. This algorithm, capable of a /spl ap/ 200 times improvement in the resolution, is presented in this work. Final characteristics are validated within the calibration process. It is made a comparison between the results obtained with the designed system and others reported, using similar models. As the measurement quality depends on the interrogation method and associated wavelength resolution, future developments are planned. They are described and analyzed in the final part of the paper.

Fiber optic intensity sensors based on a Michelson head configuration with self-referentiation

We have described two self-referenced intensity based optical fiber sensors supported on a Michelson sensing head configuration with and without optical feedback. Theoretical and experimental studies were carried out. The model developed proved to be effective in describing the sensor properties, which validates its utilization for sensor design and optimization.

Measurement of refractive index in oils using a self-referenced fiber optic intensity sensor

We have described a self-referenced fiber optic intensity sensor for measurement of refractive index in oils. Theoretical and experimental studies were carried out. The model developed proved to be effective in describing the sensor properties, validating its use for sensor design and optimization.

Evaluation of an interrogation system of fiber Bragg sensors conditioned with a PZT based tunable filter

Application of fiber Bragg sensors has grown in different engineering domains due to high performance of such measurement method. Usually the all measurement chain is completely performed in the optical domain. However, to adapt the output of the interrogation system to a signal measurable with low cost optoelectronic devices would become a good approach in order to improve the usage of this technique. The paper describes a new solution based on the introduction of a tunable filter in the conventional interrogation system. Electric transducers and micro-actuators are used to precisely tune the filter FBG and measure the imposed displacement in order to calculate the applied strain passing to the electric domain most of the processing. Since the filter FBG and the sensor itself are matched, knowing the measured strain with the filter it allows at measuring the balanced strain on the sensing FBG

Load cell for structural monitoring based on a microbend self-referenced fiber optic intensity sensor

This study develops microbend fiber optical sensor embedded in a composite laminate and demonstrates its capability of measuring applied pressure up to 750 kPa. The sensing configuration described in this work is a versatile structure for monitoring of static and dynamic physical parameters, requiring a small number of optical components and simple signal processing. Of significant importance is the concept of self-referencing which solves the problem of the referentiation of the optical power fluctuations along the optical system. The load cell shows interesting properties, namely the low cost of the microbend sensing head and the fiber optic based interrogation system. On top of that, the use of optical fibers overcomes some of the problems of conventional load cells, which are sensitive to a number of factors such as environment, durability of materials and presence of electromagnetic fields. Moreover, this sensing technology has also the potential to be integrated in multiplexed sensor networks.

Multiplexing of self-referenced fibre optic intensity sensors using fibre Bragg gratings and wavelength division couplers

In this work a wavelength multiplexing concept was demonstrated for frequency based self-referenced fibre optic intensity sensors relying on the utilisation of Bragg gratings and WDM couplers. The experimental results obtained showed a fairly good agreement with those predicted from the theory. It turned out that the system had negligible crosstalk between the two sensors. The resolution obtained for the sensors was found to be /spl ap/0.05 dB/spl radic/Hz. It should be emphasised, that the sensing concept described in this work is particularly favourable in terms of the minimisation of system noise. This happens because what is monitored is the amplitude of two sinewaves, i.e., the detection bandwidth can be made as narrow as practically feasible, with the consequent decrease of the system noise level. The power budget of the sensing network can be improved if shorter lengths of delay fibre are used, with the penalty, however, of working with higher frequencies. On the other hand, if the reflectivity of the FBGs is optimised, the power received by the detectors will increase correspondingly. Finally, a proper choice of the coupling coefficient of the couplers in the reflective ladder topology will have a strong impact on the optical power levels reaching the detector unit.

Fiber optic intensity sensors based on Michelson topologies

An investigation is performed on the characteristics of two self-referencing resonant fiber optic intensity sensors supported by a Michelson topology. The sensors are based on transmissive and reflective configurations respectively. Via the definition of the measurement parameter (R parameter), the sensitivity and linearity of the sensors are analyzed. The problem of sensor design and optimization is considered and the features of the two configurations are addressed.