In this paper in-line digital holography has been explored for dynamic micro metrological applications. In in-line digital holography, full CCD sensor area is utilized for real image reconstruction of the objects with less speckle noise. Numerical evaluation of the amplitude and phase information during reconstruction process finds promising applications in optical micro-metrology. Vibration analysis of the smaller object has been performed by combining the time average principle with in-line digital holographic methods. A double exposure method has been explored for measurements, which is simultaneously used to suppress the overlapping of zero-order and twin image wave with real image wave. The vibration amplitude and mean static state deformation of the harmonically excited object are analysed separately from time average in-line digital holograms. The experimental results are presented for a thin aluminium membrane of 5mm diameter.
This paper deals with comparative study of various types of optical fibers in non-destructive evaluation of different smart structures. Performance of single mode, high-birefringent, low-birefringent fibers, multifibers and plastic fibers embedded into concrete and composite structures are experimentally evaluated under different conditions. The results are discussed with respect to overall sensor performance and structural environment, which facilitates the selection of appropriate fiber sensor for a particular structure.
The paper describes a portable, remote controlled Michelson interferometer using a laser pointer. The mirror on one of the arms was mounted on an encoded stepper motor. A motor driver controller circuit has also been fabricated, which is interfaced with a personal computer and that can be controlled through Web.
An experimental study of the performance of a multi-fiber polarimetric sensor in real time structural health monitoring is carried out. The sensor is in the form of a two-fiber assembly composed of a polarization maintaining (PM) lead-in fiber spliced to a high-birefringent (Hi-Bi) fiber. Experiments are conducted on composite structure under static loading conditions. The results are compared with individual fiber performances. The polarization behavior of the assembly is analyzed theoretically using Stokes matrix method for the monochromatic case.
Real time structural health monitoring using fiber optic sensors is an interesting field of research in recent years. This paper presents the performance of fiber optic polarimetric sensor (FOPS) using plastic fiber. The experiments were conducted on concrete structures using plastic fiber sensor embedded in two different configurations. The dynamic responses of these sensors are experimentally evaluated under different conditions. Their performances are discussed for dynamic applications and the results are compared with that of glass fiber.
Fiber reinforced structures and machines are becoming increasingly popular in recent years, as they facilitate nondestructive damage detection in these systems. Fiber Optic Polarimetric Sensor (FOPS) is an interesting device in real time structural health monitoring. In this paper the authors present their experimental results on the health monitoring of aluminum, concrete and composite structures using FOPS. The sensor monitors the change in state of polarization of the light beam traversing in the fiber under dynamic loading. The dynamic response of high-birefringence fiber has been evaluated for the three types of structures by embedding the fiber into the specimen. The performances of FOPS is damage detection of the three smart structures under impact loading condition are compared.
Since fiber reinforced polymer composites are becoming increasingly popular, nondestructive damage detection in these materials has become an important issue. Real time structural health monitoring using Fiber Optic Polarimetric Sensors (FOPS) in an interesting field of research in recent years. This paper presents the performance of FOPS using three different optical sensing fibers: low birefringence (low-bi), high birefringence (high-bi) and an ordinary single mode polarization maintaining fiber. The static and dynamic response of these fibers are experimentally evaluated under different conditions. The experiments were conducted on composite structures by embedding the optical fibers into specimen. Composite materials are extensively used in aerospace applications. The sensitivity of all fibers under different conditions is discussed for static and dynamic loading.
The principal aim of the Photonics Centre at NgeeAnn Polytechnic, Singapore, is to provide a broad-based and practice-oriented education and training in photonics and laser technology. Students who choose to do their final-year project in this field, do not have any photonics background at all at the start of their project. However, the Centre's project-based learning programs have been successfully tried and tested. Through a series of specially selected lectures and experiments, the students are eventually led into the project proper. By the time the students complete their project, they would have gained immense knowledge and hands- on experience in photonics and laser technology. Some examples of completed projects include development of a fiber laser using erbium-doped fiber, polarimetric sensors for damage detection of aluminum materials and concrete structures, development of holographic optical elements and external cavity semiconductor laser sensor. The students have gone on to participate in R&D competitions and have been awarded either the second or top positions. The aim of this paper is to examine the methodology used that has made this form of training successful.
Photonics has emerged as multidisciplinary technology of the future. Hence photonics has become an important course to be reckoned with in all disciplines of technology. We have developed a new basic and advanced lecture and laboratory course on optics, lasers, interferometry and fiber optics for mechanical engineers. This course is the primary senior level experimental physics course with emphasis on practical experience with necessary theoretical knowledge. The course is structured to cover the relevant topics in photonics, from wave nature of light to ultra short pulse generation, types of lasers and various applications.
As a premier school, Raffles Institution (RI) seeks relevant and forward-looking educational initiatives. Bringing emerging technologies into the school encourages the students to cultivate skills and attitudes that will empower them to ride the present and future waves of information and technology most meaningfully and innovatively. Photonics has diverse applications in the modern technological world, and Singapore aims to become a center of excellence for optics and photonics in the region. However, a serious study of photonics begins only at the college level (K - 11/12). Entrusted with Singapore's brightest young minds, RI pioneered the development of a Photonics Exploratory Laboratory (X-LAB), being the first among secondary (K-7 to K- 10) schools in Singapore and possibly in the region. Young RI students are learning photonics fundamentals and recognizing photonics as a potentially rewarding field of study. With the expertise of lecturers from tertiary institutions, selected RI students are instructed in basic theory and trained in fundamental experiments. These students progress to embark on projects and in-depth studies under the wing of tertiary institutions and universities. Studies on Haidinger Fringes, Laser Doppler Anemometry and Optical Gratings have thus been successfully completed. Furthermore, the X-LAB acts as a focal point for students to experiment with Holography and Laser Animation.
We have fabricated and tested an external cavity laser with a micromachined flat polysilicon micro-mirror. The device works using a very short external cavity laser configuration (approximately equals 10micrometers ) allowing to remove all optical element in the cavity while providing enough feedback to modulate the intensity of the laser. We have shown that we could obtain feedback coefficient larger than 0.5, providing an increased sensitivity for sensor application. The device shows interesting characteristics for developing a compact and simple displacement/acceleration sensor with large dynamical range and a resolution estimated below 0.01 nm.
Integrated optical components formed by sol-gel process and MEMS devices created on silicon substrate can be used to realize different types of sensing elements for smart structure applications. In this paper we report the fabrication of Ce, Ge and (Ce + Er) doped sol-gel based waveguides on silicon substrates and their optical characterization in terms of light amplification and photosensitivity. We also report results of fabrication and characterization of Bragg gratings in sol-gel based waveguides. The number of layers required for waveguidance and single mode operation has been calculated using the dispersion equations for asymmetric planar waveguides.
The spectral characteristics of a diode laser are significantly affected due to interference caused between the laser diode output and the optical feedback in the external-cavity. This optical feedback effect is of practical use for linewidth reduction, tuning or for sensing applications. A sensor based on this effect is attractive due to its simplicity, low cost and compactness. This optical sensor has been used so far, in different configuration such as for sensing displacement induced by different parameters. In this paper we report a compact optical sensor consisting of a semiconductor laser coupled to an external cavity. Theoretical analysis of the self- mixing interference for optical sensing applications is given for moderate optical feedback case. A comparison is made with our experimental observations. Experimental results are in good agreement with the simulated power modulation based on self-mixing interference theory. Displacements as small as 10<SUP>-4</SUP> nm have been measured using this sensor. The developed sensor showed a fringe sensitivity of one fringe per 400nm displacement for reflector distance of around 10cms. The sensor has also been tested for magnetic field and temperature induced displacement measurements.