Brent L. Bachim

Polarization-dependent loss and birefringence in long-period fiber gratings

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.

Microinterferometric optical phase tomography for measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices

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 techniques 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.

Prototype CO~2 laser-induced long-period fiber grating variable optical attenuators and optical tunable filters

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.

Refractive-index profiling of azimuthally asymmetric optical fibers by microinterferometric optical phase tomography

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.

Chip-level waveguide-mirror-pillar optical interconnect structure

Waveguides, mirrors, and polymer pillars can be integrated together to provide optical interconnects to the chip level. Total internal reflection in the polymer pillar provides a high level of spatial confinement of the light. The metallized mirror terminating the waveguide may be at 45deg or at a nearby angle such as 54.74deg (anisotropically etched silicon) and produce nearly equal coupling efficiencies. For a polymer waveguide, a gold mirror, and a polymer pillar of the dimensions fabricated, the simulated coupling efficiencies are 80.7% or 0.93 dB (45deg mirror) and 82.5% or 0.84 dB (54.74deg mirror), respectively. These simulations together with the fabrication and testing of a 54.74deg mirror configuration demonstrates the viability of the waveguide-mirror-pillar structure, its insensitivity to mirror angle, and its compatibility with current substrate fabrication technologies

Two-wave-plate compensator method for full-field retardation measurements

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.

Optical-fiber-to-waveguide coupling using carbon-dioxide-laser-induced long-period fiber gratings

Optical fibers are expected to play a role in chip-level and board-level optical interconnects because of limitations on the bandwidth and level of integration of electrical interconnects. Therefore, methods are needed to couple optical fibers directly to waveguides on chips and on boards. We demonstrate optical-fiber-to-waveguide coupling using carbon-dioxide laser-induced long-period fiber gratings (LPFGs). Such gratings can be written in standard fiber and offer wavelength multiplexing-demultiplexing performance. The coupler fabrication process and the characterization apparatus are presented. The operation and the wavelength response of a LPFG-based optical-fiber-to-waveguide directional coupler are demonstrated.

Automated flexure testing of axially rotated optical fiber gratings

The design and performance of an automated system for flexure testing of optical fiber gratings is described. In addition to flexing (bending) a fiber grating through a specified curvature range, the system can change the axial rotational orientation of the grating relative to the plane of curvature. Flexure is accomplished by holding the grating against a smooth plastic platform. A linear stage deflects the center of the pinned platform to create a curved surface. Two small weights, hanging on the optical fiber, hold the fiber grating against the curved platform and provide constant tension on the optical fiber over the entire range of curvatures. The fiber grating is axially rotated to a different orientation by returning the platform to zero curvature, removing the weights from the optical fiber, and rotating the optical fiber about its axis using a pair of rotation stages. After replacing the weights on the optical fiber, flexure testing resumes at the new axial rotational orientation. The grating tra...

Refractive-Index Profiling of Optical Fibers by Microinterferometric Optical Phase Tomography

Transverse cross-sectional refractive-index profiling is demonstrated using a new technique, microinterferometric optical phase tomography (MIOPT). MIOPT allows measurement of fiber profiles containing small and azimuthally asymmetric index variations. Several measured fiber profiles are presented.

Micro-interferometric optical phase tomography for refractive index profiling of optical fibers

A new technique, micro-interferometric optical phase tomography, has been developed for measuring small, asymmetric refractive index differences in the profiles of optical fibers. The technique combines interferometry with computed tomography to conduct accurate profiling. The theory governing the technique is discussed and results presented for several types of optical fibers.