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.

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.

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.

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.

We report what we believe to be the first planar-technology waveguide laser in the 2-,um region. Laser operation of the 'H4 to 3 H 6 transition of Tm 3 + ions in a lead germanate glass host has been observed in an ion-implanted planar waveguide.The development of coherent light sources in the wavelength region around 2 ,um is of interest because of the presence of absorption bands of several important molecules. Lead germanate was shown to be a particularly suitable glass host for operation of the 2-Am Tm 3 , 3 H 4 to 3 H 6 transition in fiber samples" 2 (see Fig. 1). The maximum phonon energy is greater than in fluoride glasses, leading to efficient population of the upper laser level through nonradiative decay out of the 3 F 4 pump level. The maximum phonon energy is, however, less than in silicate glasses, leading to an increase in the lifetime of the upper laser level 3 H 4 . This favorable combination of decay rates has permitted us to demonstrate, using a fiber made of modified lead germanate (55GeO 2 -2OPbO-lOBaO-lOZnO-5K 2 0), thresholds for 790-nm pumping that are easily within reach of single-stripe diode lasers. ' Waveguides based on planar technology offer a number of potential advantages over fibers. For example, there is the possibility of diode-bar side pumping for high-power operation. 3 In addition, the active region is readily accessible for fabrication of feedback gratings, possibly through the photorefractive effect. Because high doping levels are possible with this glass, compact single-longitudinal-mode devices may be possible.Recently it was shown that waveguides could be fabricated in this modified lead germanate glass by use of He' ion implantation 4 and that, in addition, the losses of these guides were significantly lower than the -1-dB cm-' value that has been typical for ion implantation. 5 In fact, losses of 0.15 dB cm-' were obtained 4 (compared with 0.02 dB cm'I for the fiber), with index profiles suitable for guiding 2-/ttm radiation. The effect of the propagation loss can be reduced further by the use of shorter cavity lengths and correspondingly higher doping levels. The use of Tm 3 + is also attractive because there exists a cross-relaxation process that offers the possibility of 200% pumping quantum efficiency for highly doped samples. To assess the prospects for active waveguide devices in lead germanate glass, we have made an initial investigation of the 2-Am Tm 3 + laser in a planar waveguide.The waveguide used in these experiments was a planar guide (i.e., with guiding in one transverse dimension) created by implantation of the polished surface of the Tm-doped glass with 2.9-MeV 3 He' ions at liquid-nitrogen temperature at a dose of 4 X 1016 ions/cm 2 . This was followed by annealing at 200'C, which was found to be the annealing temperature at which propagation losses were minimized while the index increase in the guide region remained relatively large. 4 The dark mode pattern of the resultant waveguide was investigated, and from this the refractive-index profile shown ...

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.

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.

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