Arturo Hale

Microstructured optical fiber devices

We present several applications of microstructured optical fibers and study their modal characteristics by using Bragg gratings inscribed into photosensitive core regions designed into the air-silica microstructure. The unique characteristics revealed in these studies enable a number of functionalities including tunability and enhanced nonlinearity that provide a platform for fiber device applications. We discuss experimental and numerical tools that allow characterization of the modes of the fibers.

Fabrication and study of bent and coiled free silica nanowires: Self-coupling microloop optical interferometer

We fabricated nanometer- and micrometer-order diameter optical fibers (NMOFs) by drawing them in a microfurnace comprising a sapphire tube heated with a CO(2) laser. Using very short - a few mm long - fiber biconical tapers having a submicron waist, which can be bent locally in a free space by translation of the taper ends, we studied the effect of bending and looping on the transmission characteristics of a free NMOF. In particular, we have demonstrated an optical interferometer built of a coiled self-coupling NMOF.

Recording media that exhibit high dynamic range for digital holographic data storage

A general strategy for fabricating thick, optically flat photopolymer recording media with high dynamic range (M/#) that exhibit low levels of recording-induced Bragg detuning for holographic data storage is presented. In particular, media with M/# values as high as 42 in 1-mm-thick formats are obtained. We believe that these results are the first demonstration of a holographic storage medium with a dynamic range of this magnitude. In addition, we report the holographic recording and recovery of high-capacity (480-kbit) digital data pages in these media, further illustrating their data-storage capabilities.

Optical microfiber loop resonator

We demonstrate a microloop resonator created from the subwavelength-diameter microfiber in free space. The resonator was tuned to exhibit Q-factor 15000 and to the critical coupling regime with the magnitude of transmission oscillations 34 dB

Integrated all-fiber variable attenuator based on hybrid microstructure fiber

We present a design for modulating light in a single-mode optical fiber by achieving efficient field interaction between the fundamental mode of an air–silica microstructure optical fiber and tunable materials incorporated in the air holes of the fiber. This method involves tapering microstructure optical fiber where light is guided by the air holes and modulated by a polymer incorporated in these capillary voids. Using this fiber design, we experimentally demonstrate a variable attenuator (loss filter) with 30 dB dynamic range, insertion loss of less than 0.8 dB, and minimal polarization dependence.

Cladding-mode resonances in hybrid polymer-silica microstructured optical fiber gratings

We examine the cladding-mode resonances of fiber gratings UV written into the core of a novel microstructured fiber whose air regions are subsequently infused with polymer. The cladding spectrum changes with temperature because of the strong temperature dependence of the polymer refractive index and we show that these changes can be understood qualitatively using a simple model of the polymer-silica waveguide. Our results imply wavelength and amplitude tuning regimes for long period gratings written into this fiber with tunability enhanced over conventional long period gratings because of the small effective inner cladding diameter of our fiber.

Highly tunable birefringent microstructured optical fiber.

We demonstrate a method for introducing and dynamically tuning birefringence in a microstructured optical fiber. Waveguide asymmetry in the fiber is obtained by selective filling of air holes with polymer, and tunability is achieved by temperature tuning of the polymers index. The fiber is tapered such that the mode field expands into the cladding and efficiently overlaps the polymer that has been infused into the air holes, ensuring enhanced tunability and low splice loss. Experimental results are compared with numerical simulations made with the beam propagation method and confirm birefringence tuning that corresponds to a phase change of 6pi for a 1-cm length of fiber.

High density, high performance optical data storage via volume holography: Viability at last?

The long held promise of using volume holography to deliver high performance optical storage is reviewed. The problems, which limited the development for many years, are accessed. Finally, we describe a series of innovations, which may make the technology viable at last.

Probing optical microfiber nonuniformities at nanoscale

We demonstrate a novel, simple, and comprehensive method for probing optical microfiber surface and bulk distortions with subnanometer accuracy. The method employs a regular optical fiber as a probe that slides along a microfiber transmitting the fundamental mode. The fraction of radiation power absorbed in the probe depends on the local distribution of the mode propagating in the microfiber. From the measured variation of the absorbed power, we determine the variation of the effective microfiber radius, which takes into account both the microfiber radius and refractive index variations. Furthermore, we verify the cylindrical symmetry of the microfiber nonuniformities by probing the microfiber from different sides. These results explain observed transmission losses in silica microfibers and open broad opportunities for microfiber investigation.

Cooperative relaxation processes in polymers

The basic mode of relaxation in polymer molecules involves the rotation of a conformer, with a time scale of the order of picoseconds. This fast relaxation process, however, cannot take place easily in the condensed state crowded by densely packed conformers, necessitating the intermolecular cooperativity among them. The domain of cooperativity grows at lower temperatures, towards the infinite size at the Kauzman zero entropy temperature, though the system deviates from the equilibrium as the glass transition intervenes at about 50°C above that temperature. From the temperature dependence of the domain size, the well-known Vogel equation is derived, which we consider is the basic origin of the empirical WLF and free volume equations. The molar volume is a crucial factor in determining molar free volume. The molecular weight of a conformer with a density correction, therefore, can be used as a parameter in determining the T g of liquids and amorphous polymers. A larger size conformer means a higher glass transition temperature. A conformer at the chain end, on the other hand, has a higher enthalpy, i.e., a smaller effective size for that conformer. If a conformer is reacted trifunctionally, the resulting conformer is a combination of the two conformers and T g increases, but a further addition of another conformer to that branch point reduces the average size of the conformers, so T g decreases. The model for cooperative relaxation can be directly applied to predicting T g S from the chemical structure of polymers, the kinetics and T g S of thermosets during the crosslinking reaction, the distribution of relaxation times from the domain size distribution at a given temperature, the dynamics of the physical aging process, and other complex behaviors of polymers and liquids near the glass transition temperature.