G. Kakarantzas

Structural long-period gratings in photonic crystal fibers

We report what is believed to be the first example of structural long-period gratings written in pure silica photonic crystal fibers (PCFs). The gratings are realized by periodic collapse of the holes of the PCF by heat treatment with a CO(2) laser. The resulting periodic hole-size perturbation produces core-to-cladding-mode conversion. These results can lead to a new family of structural all-fiber devices that use the unique properties of PCFs.

Splice-free interfacing of photonic crystal fibers.

We report a new method for making low-loss interfaces between conventional single-mode fibers and photonic crystal fibers (PCFs). Adapted from the fabrication of PCF preforms from stacked tubes and rods, this method avoids the need for splicing and is versatile enough to interface to virtually any type of index-guiding silica PCF. We illustrate the method by forming interfaces to two problematic types of PCF, highly nonlinear and multicore. In particular, we believe this to be the first method capable of individually coupling light into and out of all the cores of a fiber with multiple closely spaced cores, without input or output cross talk.

Miniature all-fiber devices based on CO(2) laser microstructuring of tapered fibers.

A focused carbon dioxide laser beam is used to microstructure fibers that have already been narrowed by conventional fiber tapering. We describe three new miniature devices made with this technique: a fused fiber microcoupler with an interaction length of 200 mum, a long-period grating made from a periodic chain of microtapers, and a new type of prolate whispering-gallery mode microcavity.

Carbon dioxide laser fabrication of fused-fiber couplers and tapers

We report the development of a fiber taper and fused-fiber coupler fabrication rig that uses a scanning, focused, CO(2) laser beam as the heat source. As a result of the pointlike heat source and the versatility associated with scanning, tapers of any transition shape and uniform taper waist can be produced. Tapers with both a linear shape and an exponential transition shape were measured. The taper waist uniformity was measured and shown to be better than +/-1.2%. The rig was also used to make fused-fiber couplers. Couplers with excess loss below -0.1 dB were routinely produced.

Structural rocking filters in highly birefringent photonic crystal fiber

We report what we believe is the first example of efficient rocking filter formation in polarization-maintaining photonic crystal fiber. Very high coupling efficiencies (as much as -23.5-dB suppression of the input polarization) and loss of < 0.02 dB were achieved for fibers as short as 11 mm. The filters, which we prepared by periodic mechanical twisting and heating with a scanned CO2 laser beam, are highly compact, and they are expected to be temperature stable.

1.9-μm operation of a Tm:lead germanate glass waveguide laser

We report what we believe to be the first planar-technology waveguide laser in the 2-μm region. Laser operation of the 3H4 to 3H6 transition of Tm3+ ions in a lead germanate glass host has been observed in an ion-implanted planar waveguide.

Compact all-fiber acoustooptic tunable filters with small bandwidth-length product

All-fiber acoustooptic tunable filters (AOTFs) with bandwidth as small as 2.8 nm were fabricated from highly uniform, tapered optical fiber. These filters have typical excess loss of 0.02 dB, greater than 20 dB extinction, are polarization insensitive, and have the smallest bandwidth-length products reported to date.

Bending loss and thermo-optic effect of a hybrid PDMS/silica photonic crystal fiber

In this paper, we demonstrate and report a photonic crystal fiber (PCF) infiltrated with PDMS elastomer which is sensitive to external bending and temperature perturbations. Numerical simulations and experimental measurements were carried out to investigate the fundamental TIR-based guiding mechanism of the hybrid PDMS/silica PCF in terms of effective index, effective modal area and loss. Wavelength dependence of bending losses was also measured for different bend diameters as well as the temperature dependence of the fundamental guiding mode for a range of temperatures from 20°C to 75°C. Experimental measurements have shown a ~6% power recovery of the bend-induced loss for a 6-cm long PDMS-filled PCF at 4 cm bend diameter.

Numerical study of guided modes in arrays of metallic nanowires

We numerically investigate the band structure and guided modes within arrays of metallic nanowires. We show that bandgaps appear for a range of array geometries and that these can be used to guide light in these structures. Values of attenuation as low as 1.7 dB/cm are predicted for arrays of silver wires at communications wavelengths. This is more than 100 times smaller than the attenuation of the surface plasmon polariton modes on a single silver nanowire.

Direct measurement of optical phase in the near field

To fully characterize photonic crystal guided wave optical devices, one needs to measure the spatial variation of both the phase and amplitude of the electromagnetic field. In this work, we simultaneously measure the intensity and phase in the near field of both propagating and evanescent fields by incorporating a scanning near-field optical microscope into one arm of a Mach–Zehnder interferometer. We demonstrate the technique by imaging the phase fronts of an evanescent wave formed by total internal reflection and by measuring the phase variation in the LP11 mode in an overmoded optical fiber.