Dr. James J. Burke and Guided-Wave Technology
By Leonardo Montilla
Associated with the Optical
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This paper focuses on the physical optics characteristic of Dr. James Burke's research in guided-wave technology. More specifically, the research focused herein is multilayer planar waveguides, attenuated total reflection spectrometry, and applications in organic thin film spectroscopy.
Dr. James J.
Burke is a Professor Emeritus at the
To understand James Burke’s research with guided-wave technology, one needs to understand what a waveguide is. An optical waveguide is a particular case of a fiber optic. The physics behind fiber optics is in light’s intrinsic nature to reflect at a boundary surface. The following equations, derived from Maxwell’s equations, calculates the reflectance coefficients given the relative index of refraction, n, and the angle of incident, θ, where n is the ratio of the index of refraction of the second medium to the index of refraction of the first medium:
The reflectance is found by squaring the respective coefficient Rs= |rs|2 and Rp= |rp|2. When θ > sin-1n the coefficients above result in a complex number which when taking the modulus squared just equal one as shown in the following example:
A reflection, R, of 1 means that 100% of the light is reflected for both cases of polarization. This condition is called Total Internal Reflection or TIR. A graph of internal reflection per angle clearly shows that total internal reflection occurs anywhere after the critical angle, the minimum angle for TIR, as in Figure 1.
Figure 1: A graph of the percentage of light reflected vs. incident angle when the second medium has a greater index of refraction
The subscripts 's' and 'p' refer to the electromagnetic wave nature of light where ‘s’ differentiates an electromagnetic wave linearly polarized so that the electric field is oscillating in the direction perpendicular to the plane of incidence. The subscript ‘p’ defines the other possibility where the electric field is oscillating in the plane of incidence.
Figure 2: A schematic showing the orientation of 's' polarized light and 'p' polarized light incident at a boundary surface at an incoming angle θ1
Figure 2  illustrates an electromagnetic wave incident on a boundary surface with both polarization cases shown. Note however that the electric field may only be propagating in one direction at any given instant in time. Fiber optics works by propagating light through fibers surrounded by a dielectric material of a lower index of refraction. Light that enters the fiber within the acceptance angle will continuously TIR through the length of the fiber as shown if Figure 3.
Figure 3: A cross-section of a possible fiber optic; will TIR as long as α = sin-1√( n12 - n22)
In other words, the light will bounce back and forth inside the fiber going from one end to the other which may be kilometers long. An optical waveguide exists when the fiber is very narrow, on the order of a few microns, and monochromatic light passing through it creates a definite wave pattern or mode  .
James Burke’s research lies in the are of optical waveguides. He found that the fields of radiation modes in the regions above and below a dielectric multilayer can be completely specified once the reflection and transmission coefficients of the stack are known . A stack consists of various thin layers of different indices of refraction. Burke also helped improve on the existing limitation of planar integrated optical waveguide’s use in attenuated total reflection spectroscopy of interfacial samples. Spectroscopy is the study of spectra or the analysis of a signal versus wavelength and attenuated total reflection spectroscopy is used to study the chemistry of membranes and various polymers. Traditional techniques of using this technology were efficient over a range of less than 5nm, a narrow bandwidth . However, Dr. James J. Burke and some colleagues developed a technique to use this technology for spectroscopy of a bandwidth greater than 150nm. This expands the capability of this technology for future work and “makes it possible to measure spectra of very weakly absorbing molecular films” .
It is clear that the work of Dr. James J. Burke focuses heavily on physical optics and the wave nature of light. Optical waveguides and total internal reflection are derived and made possible using physical optics. His research and work with spectroscopy and wave-guided technology is sure to have an impact in the future advancement of our knowledge and application of physical optics.
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techniques for organic thin film spectroscopy and chemical sensing.” Proc. SPIE Int. Soc. Opt. Eng. 3602,
 Fowles, Grant R. Introduction to Modern Optics.