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The authors demonstrate a hollow core photonic crystal fiber (HCPCF) surface-enhanced Raman probe consisting of a HCPCF with Au nanoparticles coated on the inner surface of the air holes serving as the substrate of surface-enhanced Raman scattering (SERS). The experimental results indicate that the confinement of light inside the HCPCF and the coating of nanoparticles/analyte inside the air holes of the HCPCF offer a large area for the light to interact with the SERS particles. An optimized design of the HCPCF is provided to further improve the probe sensitivity.

The dispersion and mode characteristics in a dual-concentric-core photonic crystal fiber, based on pure silica, are simulated by the multipole method. The fiber exhibits very large negative dispersion due to anticrossing of two individual inner core and outer core modes. Near the wavelength of 1.55 microm, we could obtain narrowband dispersion-compensating fiber with dispersion values of -23,000 ps/km/nm, broadband dispersion-compensating fiber with dispersion values from -1000 ps/km/nm to -2500 ps/km/nm over a 200 nm range, and kappa values near 300 nm, which matched well with standard single mode fiber. It shows that even if there are some changes in the structure parameters during fabrication, these fibers can still maintain a fine dispersion-compensating property.

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We demonstrate a novel index-guided (IG) photonic crystal fiber (PCF) surface-enhanced Raman probe. Different from a regular PCF, the IGPCF has four big air holes inserted between the solid silica core and the photonic crystal cladding holes. The gold nanoparticles, serving as the surface enhanced Raman scattering (SERS) substrate, are either coated on the inner surface of the holes or mixed in the analyte solution in two separate experiments, respectively. The analyte solution enters the holes via the capillary effect. The excitation light propagating in the silica core interacts with the gold nanoparticles and the analyte through the evanescent wave which extends significantly into the four big holes when they are filled with liquid leading to a large interaction volume between the excitation light and the nanoparticles/analyte.

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We demonstrate a novel method for the fabrication of glass photonic crystal fibers (PCFs) with a die-cast process. SF6 glass is used as the material for PCFs, and the die is made of heat-resisting alloy steel, whose inner structure matches the PCF's structure. The die is put vertically in the vessel with SF6 glass, and the vacuum hose is attached to the top of the die. The die and glass are put in the furnace to heat at 870 K. The die is slowly filled with the softening glass under vacuum conduction until it is full. It is kept in the furnace to anneal at a rate of 20 K/h to remove the thermal stress that could lead to cracks. The outer tube of the die is taken apart when its temperature is close to room temperature, and the fused glass bundle is etched in an acidic solution to remove the heat-resisting alloy steel rods. Thus, the etched bundle is ready to use as a PCF preform. The PCF is observed in the generation of a supercontinuum, with the flat plateau in the spectrum of the output emission stretching from 400 to 1400 nm by experimental measurement. The transmission loss is 0.2-0.3 dB/m at wavelengths of 420-900 nm.