A custom-developed ultrahigh resolution optical coherence tomography with an axial resolution of 1.1 μm in corneal tissue was used to characterize thickness and light scatter of the epithelium and Bowman's layer in keratoconic (KC) cornea noninvasively. A 4-mm wide vertical corneal section around the apex in nine KC and eight normal eyes was imaged in vivo. The epithelium and Bowman's layer were visualized and their thickness profiles were quantified. Scatter was quantified based on the sensitivity normalized mean signal intensity distribution. Average mean thickness of the epithelium and Bowman's layer in KC eyes was significantly smaller (p<0.05) than the normal eyes. The epithelium thickness variation across a central 3-mm cornea was significantly larger in KC eyes than in normal eyes. The scatter in KC eyes was significantly increased only for Bowman's layer. The changes observed in this study could improve our understanding of the underlying disease mechanism of KC and can provide new indications for early disease diagnosis.
We report an intracavity ring laser constructed using two parallel directional fiber couplers that generates up to sixth-order cascaded Stokes. Pumping with 1117 nm results in a Raman fiber laser operating at 1572 nm. Using 4.2-W pump power and a fiber Bragg grating at 1117 nm to reflect the residual pump, we obtain an output power of 0.65 W, and hence near 15% conversion efficiency. The linewidths of the dual-coupler laser are significantly narrower than those of the single-coupler laser. This enhanced wavelength selectivity is attributed to the significant increase in the contrast or the finesse of compound ring resonators constructed with two parallel couplers.
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.