Ayoub Chakari

Angular displacement fiber-optic sensor: theoretical and experimental study

An optical-fiber sensor based on twist-induced optical activity has been developed for measuring angular displacements at low temperature. The sensing part is composed of a fiber coil rotated between two points, which induces a twist of two sections of fiber. A theoretical study of the evolution of a general input state of polarization in the sensor gave us its main characteristics. Then experimental investigations permitted the construction of a sensor to take angular measurements over a 100-deg range with an accuracy of 0.2 deg. The thermal sensitivity of this kind of sensor is also briefly reported.

Fiber optic sensor for angular position measurement: application for an electrical power-assisted steering system

To achieve a very effective automotive power steering system, we need two important data, the angular position of the wheel and the torque applied on the shaft by the driver of the car. We present a new accurate optical fiber angular position sensor connected to an automotive power steering column. In this new design, the sensor allows the measurement of the angular position of a car steering wheel over a large and adjustable range (± several turns of the wheel). The wheel rotation induces micro-bending in the transducer part of the optical fiber sensing system. This system operates as an amplitude modulation sensor based on mode coupling in the transducing fiber in the case when all the modes are equally excited. We study the sensor response both theoretically and experimentally with a multimode step index optical fiber [rf (fiber radius) = 300 μm; rc (core radius) = 50 μm; nc (core index) = 1,457; N.A. = 0, 22 and the wavelength is 632,8 nm at the ambient Temperature (20°C)]. We show that the sensitivity can be controlled as a function of the sensors length. We compare modeling and experimental validation and we conclude with a perspective on what could soon be an industrial sensor.

Design, study, and achievement of a fiber optic amplitude modulation sensor for angular position detection: application to an automotive steering sytem

The reliable, accurate and low cost measurement of angular position is an important challenge for numerous industries such as aerospace or automotive industries. We propose a new optical fiber angular position sensor connected to an automotive power steering column. This sensor allows the measurement of the angular position of a car steering wheel over a large range (± 3 turns of wheel). The wheel rotation induces micro-bending in the transducer part of the optical fiber sensing system. This system operates as an amplitude modulation sensor based on mode coupling in the transducing fiber in the case when all the modes are equally excited. We study the sensors response both theoretically and experimentally with a multimode step index optical fiber [Rf (fiber radius) = 300μm; rc (core radius) = 50μm; nc (core index) = 1,457; N.A. = 0, 22 and the wavelength is 632, 8 nm at the ambient Temperature (20°C)]. This sensor has been tested between (-3x360) and (+3x360) degrees with 0,147 sensitivity. We show that the sensitivity can be controlled as a function of the sensors length and the study of the sensors output power as a function of the angular position has been achieved. We compare modeling and experimental validation and we conclude by a perspective of what could be soon an industrial sensor.

Characterization of solid materials by a polarimetric fiber optic sensor

We present a solid material characterisation method using a very acccurate polarimetric fiber optic sensor. This very accurate and sensitive transductor permits us to measure the rigidity modulus G of several solid materials presenting several differents geometries. The G determination, in the first part, is achieved by measuring the torsion angle optically and by a non destructive method. The rigidity modulus of Aluminum, Plexiglas and Steel shaft presenting different geometries has been experimentally achieved: we obtained (2.013±0.008)×1010, (1.384±0.025)×109 and (1.040±0.012)×1011N.m-2 for the Aluminum, Plexiglas and Steel respectively. The second part of our study presents the dependance of the torsion angle as function of an applied torque for different shaft lengths (from 5 to 32 cm). The comparison between the theoritical and experimental results shows us a good validation criteria of this non destructive optical characterisation method.

Characterization of a conventional optic fiber (monomode and multimode) and its use for the elaboration of a new vibration and sonor pressure detection system

Accurate vibration measurement of mechanical structures is a relevant problem in aerospace or automotive industry and sismic detection. Used methods concern for instance non guided optics devices, contact resistive systems, contact mechanical systems. We introduce a modelling and an experimental validation of an intrinsic vibration sensor using polarization modulation of the light propagation in an optical fiber as a result of modulated constraints applied to this fiber. We demonstrate that this method allow measurements of vibration frequencies with a good accuracy and a large dynamic. We first analyze the intrinsic birefringence in telecom monomode fiber. Then, we analyze the extrinsic birefringence coming from twisting and bending the fiber. On this basis, we introduce a polarisation controller. We then apply a static force on the fiber through a spring. With vibration applied to the fiber, this force will become dynamic and will induce a dynamic modulation of the polarization at the output of the fiber that we will read. The optimal signal sensing of sound and vibration is obtained by integrating all the characteristics of the device mentioned above.

Improvement of a polarisation optical fibre sensor for the detection of seismic vibration

Near acoustic frequencies from seismic activities can be observed by sensors with band pass higher than the 5-second period peak noise. By using a single mode fibre optic specially adjusted, a planar vibration travelling on surface can modify the optogeometrical properties of its material and enhanced a birefringence effect. This type of sensor already effective in acoustic frequencies is now adapted to seismic vibration. The high noise background at these frequencies disturbs greatly the measure and isolation by adjustment of spring and plates dimensions leads to interesting questions in regard of dynamic behaviour in this window. Currently, the sensor can detect small and local vibrations but cannot measure with good precision its velocity and acceleration value. In the first part of this paper, the basics of seismic vibration will be briefly exposes in coordination with the way the sensor works; a brief walkthrough of the fibre optic sensing behaviour will be exposed. The next part will display the different elements of the sensor and the choices that were made at this stage. Eventually, the behaviour of the sensor will be displayed along with the calibration method and the different errors that need to be corrected.

Ultrasensitive polarimetric torque sensor

We propose the study and the design of an ultra sensitive polarimetric torque sensor. The principle is based on the measurement of the torsion angle (theta) induced on the shaft when a torque T is applied on it. This optical torque sensor has been tested for aluminum, steel and Plexiglas shafts with different geometries. The torsion angle has been measured with 0,001 degree(s) accuracy. The torsion angle is then studied as a function of the applied torque. The comparison between the theoretical and the experimental results give us respectively 4,33%, 1,30% and 1,24% for the Plexiglas, the aluminum and the steel shafts. These results permit us good perspectives for our applications.

New nondestructive optical method for measuring the rigidity modulus of solid materials

We propose a new optical method for the determination of the rigidity modulus G of solid materials. With this method, the rigidity modulus is determined by measuring of the twisted angle (theta) of the material, depending on an applied force. The measuring of this twisted angle is obtained by using an ultra sensitive polarimetric sensor. The effective measurement of rigidity modulus G for Aluminum and Plexiglas are experimentally achieved, we obtained respectively 1,44464.1010N/m2 and 0,99417.109N/m2.

Control of thermal effects with a Poincare sphere model and experimental validation on a polarimetric angular displacement sensor using telecom optical fiber as transducer

The effects of a (Delta) T equals 300 K thermal perturbation is modelized theoretically in the case of a telecom singlemode optic fiber that we use as a transducer in an angular displacement polarimetric sensor. This model allows to optimize the fibers spatial path and to select the light input polarization and the wavelength (lambda) in order to minimize the thermal modulation of the sensor signal. Therefore, the angular calibration error with (Delta) T equals 300 K will stay below 0.1 degrees with a 90 degree measurement range. We present two series of experiments where the wavelength is respectively (lambda) 1 equals 1300 nm and (lambda) 2 equals 780 nm. In the first case, we apply a thermal perturbation (Delta) T equals (293 K; 453 K). We observe a sensor signal fitting the one of the simulation, showing that experimental conditions are similar to the model ones. In the second case, (Delta) T equals (293 K; 213 K), we measure a greater thermal modulation of the sensors signal than the simulation one. This linear birefringence is due to the fibers gluing on its substrate and to the fibers mechanical homogeneity in the bent parts. These stresses will be minimized by adapted gluing and substrate materials and optic fibers design selection.

Minimisation of thermal effects on the polarisation in a polarimetric sensor using a single-mode optical fibre

Optic fibre sensors and especially polarimetric ones provide high accuracy and sensitivity. They are insensitive to electromagnetic perturbations. The simulation of an angular position polarimetric sensor using telecom single-mode optic fibre as a transducer showed a thermal dependence [Mane 95], [Mane 96].