Mehmet Naci Inci

Two-axis bend measurement using multicore optical fibre

Abstract We describe the first use of a four-core optical fibre to measure bending about two orthogonal axes simultaneously. Individual cores in the fibre act as independent strain gauges where local curvature determines the difference in strain between cores. The multicore sensing element, interrogated in reflection, generates a two-dimensional far-field interferogram. The component of fibre curvature in the plane of the two cores shifts the corresponding fringes in the interferogram. Bend angle is then calculated using phase values derived from Fourier analysis of the far-field interferogram. This technique achieved a bend angle resolution better than 120 μrad.

Measurement of bending in two dimensions using multicore optical fibre

We describe the use of a four-core optical fibre as the basis of a sensor capable of measuring the angle through which the fibre is bent in two dimensions. The intended application of the sensor is in measuring the shape of flexible structures.

In situ measurement of humidity induced changes in the refractive index and thickness of polyethylene glycol thin films

Humidity induced changes in the refractive index and thickness of polyethylene glycol (PEG) thin films are in situ determined by optical waveguide spectroscopy. PEG brushes are covalently attached to the surface of a thin gold film on a borosilicate crown glass using a grafting-from chemical synthesis technique. The measurements are carried out in an attenuated total internal reflection setup. At low humidity levels, both the refractive index and the thickness change gradually due to swelling of the PEG thin films upon water intake. At around 80% relative humidity, a steep decrease in the refractive index and a steep increase in the thickness are observed as a result of a phase change from a semicrystalline state to a physical gel state. The hydrogenation of PEG films causes a less pronounced phase change from a semicrystalline state to a gel state. Due to fewer ether oxygen atoms available for the water molecules to make hydrogen bonding, the polymer has a more stable structure than before and the phase ...

Simultaneous measurements of thermal optical and linear thermal expansion coefficients of Ta 2 O 5 films

An experimental determination technique for simultaneous measurements of the thermal optical and the linear thermal expansion coefficients of tantalum pentoxide thin films at infrared wavelength region is described. A tantalum pentoxide thin film deposited directly onto the end face of a single mode optical fiber was illuminated with a SLD source and its spectrum on reflection was monitored at various temperatures using an optical spectrum analyzer. Temperature induced change in the index of refraction and the film thickness were determined from the spectrum to calculate the thermal optical and the linear thermal expansion coefficients simultaneously.

Experimental determination of the thermo-optic properties of zirconium dioxide coatings

An experimental determination of optical constants and thermal optical properties of thin solid films is described in which the test element is a zirconium dioxide film coated onto the end face of a multimode fused silica optical fibre. Refractive index and thermal optic coefficient of the thin films for wavelengths between 700 nm and 900 nm were experimentally measured from the reflectance spectrum. The change in reflectance for the test element was measured as a function of temperature. The use of the results in the design of a thin-film fibre optic temperature sensor is discussed.

Fourier transform optical profilometry using fiber optic Lloyd’s mirrors

A fiber optic Lloyds mirror assembly is used to obtain various optical interference patterns for the detection of 3D rigid body shapes. Two types of fiber optic Lloyds systems are used in this work. The first consists of a single-mode optical fiber and a highly reflecting flat mirror to produce bright and dark strips. The second is constructed by locating a single-mode optical fiber in a v-groove, which is formed by two orthogonal flat mirrors to allow the generation of square-type interference patterns for the desired applications. The structured light patterns formed by these two fiber Lloyds techniques are projected onto 3D objects. Fringe patterns are deformed due to the objects surface topography, which are captured by a digital CCD camera and processed with a Fourier transform technique to accomplish 3D surface topography of the object. It is demonstrated that the fiber-optic Lloyds technique proposed in this work is more compact, more stable, and easier to configure than other existing surface profilometry systems, since it does not include any high-cost optical tools such as aligners, couplers, or 3D stages. The fringe patterns are observed to be more robust against environmental disturbances such as ambient temperature and vibrations.

Monitoring excimer formation of perylene dye molecules within PMMA-based nanofiber via FLIM method

Confocal fluorescence lifetime imaging microscopy method is used to obtain individual fluorescence intensity and lifetime values of aromatic Perylene dye molecules encapsulated into PMMA based nanofibers. Fluorescence spectrum of aromatic hydrocarbon dye molecules, like perylene, depends on the concentration of dye molecules and these dye molecules display an excimeric emission band besides monomeric emission bands. Due to the dimension of a nanofiber is comparable to the monomer emission wavelength, the presence of nanofibers does not become effective on the decay rates of a single perylene molecule and its lifetime remains unchanged. When the concentration of perylene increases, molecular motion of the perylene molecule is restricted within nanofibers so that excimer emission arises from the partially overlapped conformation. As compared to free excimer emission of perylene, time-resolved experiments show that the fluorescence lifetime of excimer emission of perylene, which is encapsulated into NFs, gets shortened dramatically. Such a decrease in the lifetime is measured to be almost 50 percent, which indicates that the excimer emission of perylene molecules is more sensitive to change in the surrounding environment due to its longer wavelength. Fluorescence lifetime measurements are typically used to confirm the presence of excimers and to construct an excimer formation map of these dye molecules.

Two Dimensional Force And Longitudinal Twisting Measurements With A Four-Core Optical Fiber Sensor

Shifts in 2-D interferograms of a four-core optical fiber are used to measure 2-D bending. Repeatable linear phase shifts versus 2-D force-induced deflection and the first simultaneous measurement of twisting and bending were demonstrated.

Scanning Acoustic Microscopy and Time-Resolved Fluorescence Spectroscopy for Characterization of Atherosclerotic Plaques

Atherosclerotic plaques constitute the primary cause of heart attack and stroke. However, we still lack a clear identification of the plaques. Here, we evaluate the feasibility of scanning acoustic microscopy (SAM) and time-resolved fluorescence spectroscopy (TRFS) in atherosclerotic plaque characterization. We perform dual-modality microscopic imaging of the human carotid atherosclerotic plaques. We first show that the acoustic impedance values are statistically higher in calcified regions compared with the collagen-rich areas. We then use CdTe/CdS quantum dots for imaging the atherosclerotic plaques by TRFS and show that fluorescence lifetime values of the quantum dots in collagen-rich areas are notably different from the ones in calcified areas. In summary, both modalities are successful in differentiating the calcified regions from the collagen-rich areas within the plaques indicating that these techniques are confirmatory and may be combined to characterize atherosclerotic plaques in the future.

Heat transfer measurements with a four-core optical fiber

A four-core optical fiber is used to investigate one-dimensional heat transfer measurements. Heat pulses from a Nd:YAG laser of 600 ms duration with a repetition rate of the order of 10 s are delivered onto one of the fiber cores. This results in an optical path length difference between the guiding cores due to the change in the refractive index and physical length of the targeted fiber core. As a result of this process, a phase shift of 1.30 rad is measured with a digital camera for 140 mW pulses in reflection scheme. The heat diffusion length in the selected fiber core is determined to be 2.8 mm, which contains 33.2 kJ/m2s heat, causing a temperature rise of 4.30 K.