A strongly anisotropic photonic crystal structure was designed using form birefringence. It has a low group velocity
close to a split band edge (SBE) and large field enhancements proportional to the fourth power of the number of periods
are predicted. Numerical results are presented illustrating the bandgap behavior as a function of anisotropy and an
effective negative index property is discussed.
A strongly anisotropic photonic crystal structure was made exploiting form birefringence. It was designed to have a low
group velocity close to a degenerate band edge (DBE) which is also associated with large field enhancements
proportional to the fourth power of the number of periods. Numerical results are presented illustrating the expected
properties and these are compared with experimental data. There are interesting discrepancies in behavior and possible
reasons are discussed which include the nature of the anisotropy and fabrication-related structural disorder. At
microwave frequencies, unexpected field enhancements at specific frequencies and locations outside the structure have
been observed which have potential applications
Much work has been reported on attempting to identify spores from their spectral signatures. Since
spores are also complex scattering objects, with a layered internal refractive index structure, it makes
sense to explore the possibility of making an identification simply from a scattering pattern or from
anticipated scattering characteristics combined with a spectral signature. Models for scattering from
simple geometrical coated shapes have been developed and recently Bragg spheres and onion-ring
resonator-like scatterers in the Mie regime have received considerable attention driven by other
applications. Also, our own group has recently advanced a method for inverting scattered field data
from strongly scattering penetrable targets. We present here some very early considerations of the
convergence of these possibilities and suggest some simple experiments that might advance our
understanding of spore detection and identification.
This work focuses on the effects of custom-designed, two-dimensional grating structures on the sensitivity of optical
waveguides biosensors in the input grating coupler configuration. Calculations suggest that suitably designed diffractive
structures with optimum pitch in two orthogonal directions can increase the sensitivity of devices when compared to a
conventional one-dimensional grating under the same conditions. A set of six diffractive structures designed for 1550 nm
wavelength were fabricated by thermal nano-imprint lithography on silicon oxynitride waveguides; the silicon master
stamp was patterned by deep UV stepper lithography. Preliminary experimental results indicate a sensitivity
enhancement of a factor two due to the 2D diffractive couplers.
We present designs of a diffractive polarizer having low zeroth-order reflectivity that is compact, potentially mass-producible and cost-effective, and compatible for high-power applications. It consists of subwavelength grating structures superimposed over a diffraction grating. Using rigorous coupled wave analysis, we optimized the parameters of multilevel grating structures to achieve antireflection for both incident TE and TM polarization states with one polarization passing in the zeroth order and the other into the first and higher orders. We focused on polarizer designs for the 1.31-µm wavelength range, and the theoretical values for zeroth-order reflection were calculated to be 0.01% for TE and 0.29% for TM modes. The zeroth-order transmission efficiencies were 97.2% for TE and 0.01% for TM modes. A prototype of one design was fabricated and tested to verify the functionality of the device, and the zeroth-order reflection was determined to be 1.2% and 3.5% for the two modes.
We have been studying a novel 1D anisotropic photonic crystal structure which can be designed to have a strong resonant effect, a very low group velocity over a specific bandwidth. The structure requires two anisotropic layers and one isotropic layer per period and was first introduced by Figotin and Vitebskiy. By the careful design of the parameters of the structure, we can find a special band edge point which has fourth order degeneracy, and is called degenerate band edge (D.B.E). It was predicted that in the case of a transmission resonance in the vicinity of the D.B.E, the resonant field intensity increases as N4, where N is the total number of periods, while in the case of a regular band edge, the field intensity is proportional to N2. By making a comparison among different anisotropic materials, we have found that the giant resonant effects in the vicinity of the D.B.E also need a large anisotropy of the materials. However, materials with the required anisotropy at optical wavelengths are difficult to find and so we use equivalent form-birefringence layer to replace the anisotropic layer in our photonic crystal structure design. In order to verify our design, we make a real device for use at microwave frequencies using a rapid-prototyping tool. Our measurement results show that using form-birefringence to design this novel device is feasible and can push this novel photonic crystal structure to a lot of potential applications.
Grating-based optical waveguide devices offer label-free biodetection capabilities relying on optical
response to adsorption of analytes and corresponding changes of refractive index. Various
configurations of this measurement approach were explored with the goal of obtaining a
miniaturized system. In particular, we evaluated the use of a two-dimensional grating coupler both
experimentally and theoretically. Design criteria for optimized sensing structures are presented.
Using the transfer matrix method to analyze a 1D anisotropic photonic crystal usually involves a 4×4 matrix, which
means for any given ω and β (the Snell quantity nsinθ), four eigenvalues of K can be found. Based on the degeneracy of
K, the band edge in the dispersion curves can be divided into two types. One is the regular band edge (R.B.E) which has
degeneracy of the order 2 and another is the degenerate band edge (D.B.E) which has fourth order degeneracy. It was
predicted that in the case of a transmission resonance in the vicinity of the D.B.E, the resonant field intensity
enhancement is proportional to N4, where N is the total number of periods, while in the case of a regular band edge, the
field intensity enhancement is proportional to N2. Based on this prediction, we have calculated the band edge resonant
effect of a novel D.B.E photonic crystal structure with a unit cell having two misaligned in-plane anisotropic layers and
one isotropic layer. By making a comparison among different anisotropic materials, we have found that the giant
resonant effects in the vicinity of the D.B.E also need a large anisotropy of the materials. However, whether the
anisotropy is large or small, the field intensity enhancement is approximately proportional to N4 once the number of the
periods is large enough to cause the strong enough resonance effect inside the structure. We believe this DBE resonant
effect will have applications requiring slow-light and in nonlinear optics.
A comprehensive study of the oblique frozen modes in a finite 1-D anisotropic photonic crystal is presented. The most attractive property of these waves is near-zero axial group velocity in conjunction with small reflection from the lattice interface. We use a characteristic matrix analysis to describe both monochromatic wave and pulse propagation in a 1-D anisotropic photonic crystal of finite length. Using a layered structure consisting of air and an example of a suitable material, SbSI, we demonstrate the slow down factor, intensity enhancement, bandwidth, and transmission coefficient of axially frozen modes.
A comprehensive study of the oblique frozen modes in a finite one-dimensional anisotropic photonic crystal is presented. The most attractive property of these waves is near-zero axial group velocity in conjunction with small reflection from the lattice interface. We use a characteristic matrix analysis to describe both monochromatic wave and pulse propagation in one-dimensional anisotropic photonic crystal of finite length. Using a layered structure consisting of air and an example of a suitable material, SbSI, we demonstrate the slow down factor, intensity enhancement, bandwidth, and transmission coefficient of axially frozen modes.
Distributed Raman amplifiers (DRAs) are an enabling technology for long- haul and metropolitan- area broadband optical networks. These devices utilize the stimulated Raman scattering process in order to achieve gain over the bandwidth of ~ 40 THz from the transmission fiber itself. While DRAs’ offer various advantages by their ubiquitous presence in the transmission path, they also pose challenges such as gain flattening in the broadband spectral regime. Evidently, one cannot use fiber Bragg gratings (FBGs) and other filtering devices such as thin-films filters. However, gain flattening over wideband can be achieved using multi–wavelength (multi-λ) pumping , that is accomplished with spectral slicing based on Raman fiber lasers (RFLs). Novel test amplifiers have been designed and simulated with various pump parameters such as the number of RFLs pumps, their wavelengths, and relative powers. The results obtained using a 6-λ pump module in the range 1460-1510 nm, showed a better gain-flattened amplification . We have designed various network test topologies, which are simulated using commercially available software packages. A 6- λ pump module using 2 to 5 pairs of fiber Bragg gratings  seems optimal. The output FBGs are tunable in order to provide reconfigurable pump module. Details of the results and design optimization will be presented.
 Y. Cao, M. Y. A. Raja, “Gain-Flattened Ultra Wide Band Fiber Amplifiers,” J. Opt. Eng., Vol. 42,
No. 12, 3347-3451 (2003).
 Y. Cao, J. G. Naeini, K. Ahmad, and M. Y. A. Raja, “Gain-flattened Distributed Raman
Amplification using Multi-l Raman Fiber Laser Pumping”, presented in OISE’03, Orlando, FL.
This paper presents a novel design of a gain-flattened amplifier that covers an ultra-wide band including the S, C, and L bands. The amplifier has a split-band architecture, which amplifies the S-, C-, and L-band signals in separate paths and then recombines the amplified signals for the final output. Using a commercial software package VPI Component MakerTM, the design was simulated and tested for optimization. The gain and noise figure of the new amplifier were analyzed by computer simulation. A gain of 29 dB, a ripple factor of about 1.7 dB, a nominal low noise figure <5 dB, and gain-bandwidth products >120 nm can be achieved.