Waveguide measurement method

The reduction of dimensions also reduces volumes that are accessible for the detector. Thus, detection principles that are related to the volume of the detector cell, as absorbance measurements, are not ideally suited for coupling to microsystems, whereas surface sensitive principles, such as electrochemical methods or optical methods utilizing the evanescent field of a waveguide, or methods that can be focused on a small amount of liquid, such as fluorescence, are better suited. That is why fluorescence detectors are most often combined with microsystems, with an increasing number of reports appearing on the integration of electrochemical detectors. 

Another class of loss-measurement methods is based on the detection of the hght which is scattered out of the waveguide a fundamental advantage shared by ah the scattering-detection methods is that of being non-destructive and also non-contact. 

A new one-dimensional mierowave imaging approaeh based on suecessive reeonstruetion of dielectrie interfaees is described. The reconstruction is obtained using the complex reflection coefficient data collected over some standard waveguide band. The problem is considered in terms of the optical path length to ensure better convergence of the iterative procedure. Then, the reverse coordinate transformation to the final profile is applied. The method is valid for highly contrasted discontinuous profiles and shows low sensitivity to the practical measurement error. Some numerical examples are presented. 

Optical losses in the liquid-filled ARROWs are typically measured using the cutback method. This measurement technique assumes optical transmission in the waveguide can be described according to... 

As initial distribution corresponds to the linear mode (2.11) of the given waveguide, the deviation of T z) with respeet to unity may he eonsidered as a measure of the error in this method. The results presented in Fig.2 allow one to analyze the accuracy of the method depending on the type of finite-difference scheme (Crank-Nicholson" or Douglas" schemes have been applied) and on the method of simulation of conditions at the interface between the core and the cladding for both (2D-FT) and 2D problems. 

This paper summarizes the results of our study of PE and APE waveguides in LiNb03 and EiTa03. We foeused on the optical and structural characterization of PE layers formed on Z-eut substrates. The reffaetive index ehange was measured and the propagation losses were estimated. Raman speetroseopy was used as a method providing direct information about the phonon spectrum. The latter was related to the structure and ehemieal bonds of a given erystalline phase. Sueh information may be useful for eorreet identification of both phase eomposition and the microscopic mechanisms responsible for the observed variation of the properties from phase to phase. 

Fiber-optic fluorometry. Fiber-optic waveguides provide excellent means for delivering excitation energy to fluorescing media in remote, hostile, or inaccessible environments (8) such as reactors and plant streams, and for guiding the emitted fluorescence to a detector or a spectrometer, thus facilitating in-situ monitoring of the resin fluorescence (5,6). In our case, the autoclave represents a hostile environment (350°F and 100 psl) which is inaccessible for optical measurements by conventional methods. 

Distributed circuit methods use coaxial lines, waveguides and resonant cavities at microwave frequencies. The circuits are designed for measuring an attenuation factor and a phase factor, from which sample dielectric properties can be calculated. The sample may form the dielectric medium between the two conductors of a coaxial line (Scaife et al, 1971), or an open coaxial line is brought into contact with the sample surface (Roussy and Pearce, 1995). Fagan et al, (2004) used an open coaxial line method to demonstrate that the moisture and salt contents of processed cheese could be predicted by measuring dielectric properties over a range of frequencies. 

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