Widely used descriptions and relationships for birefringence and polarization-dependent loss (PDL), developed primarily for ultraviolet-induced long-period fiber gratings (LPFGs) written in optical fiber, can be invalid for other types of LPFG. The understanding of PDL is expanded to include LPFGs with birefringence in the core only, in the cladding only, and in both the core and the cladding. Equations that link resonant wavelength separation, one factor that determines PDL, and birefringence for the three categories are presented, along with relevant approximations. Measurement results for two LPFGs fabricated by different techniques are presented that illustrate the effect of birefringence on PDL.

Prototype devices capable of variable attenuation at a fixed wavelength, wavelength tuning at a constant attenuation, and combinations of these spectral characteristics are demonstrated in CO2 laser-induced long-period fiber gratings (LPFGs). These devices are based on controlled flexure by means of a piezoceramic platform. CO2 laser-induced LPFG characteristics along with the fabrication and testing processes of these gratings are discussed. Devices with a optical attenuation of 13 dB and a wavelength tuning of 7 nm are reported.

A new technique, microinterferometric optical phase tomography, is introduced for use in measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices. The method combines microscopy-based fringe-field interferometry with parallel projection-based computed tomography to characterize fiber index profiles. The theory relating interference measurements to the projection set required for tomographic reconstruction is given, and discrete numerical simulations are presented for three test index profiles that establish the technique's ability to characterize fiber with small, asymmetric index differences. An experimental measurement configuration and specific interferometry and tomography practices employed in the technique are discussed.

The two-wave-plate compensator (TWC) method is expanded for full-field retardation measurements by use of a polarization microscope. The sample image is projected onto a CCD camera connected to a computer, allowing the retardation to be measured at all pixels. The retardation accuracy of this implementation of the TWC is evaluated to be 0.06 nm. The method is applied to polarization-maintaining fibers and long-period fiber gratings. The measured retardation is in good agreement with the crossed-polarizer images of the fibers. The method achieves a spatial resolution of 0.45 microm and a retardation resolution of 0.07 nm. The full-field TWC method can thus be a useful tool for characterizing and monitoring the fabrication of optical devices.

Accurate nondestructive refractive-index profiling is needed in the modeling, design, and manufacturing of optical fibers and fiber devices. Most profile measurement techniques cannot correctly characterize fibers with small or irregular refractive-index variations over their cross sections. Microinterferometric optical phase tomography (MIOPT) is a technique that allows measurement of fiber refractive-index profiles exhibiting such variations. We present the first demonstration, to our knowledge, of MIOPT. The profile of a polarization-maintaining fiber is measured by MIOPT and shown to be in agreement with (destructive) fiber end-face measurements. MIOPT is also applied to the limiting case of a symmetric single-mode fiber.