Long period gratings in hollow-core photonic-bandgap fibers were fabricated by use of a pulsed CO2 laser. The resonant
wavelengths of these gratings are sensitive to strain but insensitive to temperature, bend and external refractive index.
We have explored the use of index-guiding liquid-core (LC) photonic crystal fiber (PCF) as a robust platform for measurements of solutions of trace volume using normal and surface-enhanced Raman scattering (SERS). The LC PCF was fabricated by selectively sealing the cladding air channels at the distal ends of a hollow-core PCF while leaving the center core open, using a fusion splicer. Utilizing a 30-cm-long LC PCF with the entire center core filled with the ~0.1-µL solution of interest, we have obtained normal Raman spectra of water, ethanol, and 1 vol% ethanol in water. Sensitive and reproducible SERS detection of 1.7×10−7 M thiocyanate anions (14 ppb of NaSCN) in water has also been achieved.
We have explored the use of index-guiding liquid-core photonic crystal fiber (LC-PCF) as a platform for sensing and
measurements of analyte solutions of minute volume by normal and surface-enhanced Raman scattering (SERS). The
index-guiding LC-PCF was fabricated by selectively sealing via fusion splicing the cladding air channels of a hollow-core
PCF (HC-PCF) while leaving the center core open at both ends of the fiber. The center core of the resultant fiber
was subsequently filled with water-ethanol solution mixtures at various ethanol concentrations for normal Raman
scattering measurements and with water-thiocynate solutions containing Ag nanoparticle aggregates for SERS detection
of thiocynate at trace concentrations. The light-guiding nature in the solution phase inside the LC-PCF allows direct and
strong light-field overlap with the solution phase over the entire length of the PCF (~30 cm). This detection scheme also
dramatically reduces the contribution of silica to Raman spectral background, compared with the solid-core counterpart,
thus its potential interference in spectral analysis. These features attribute to ready normal Raman measurements of
water, ethanol, and water (99 vol.%)-ethanol (1 vol.%) solutions as well as sensitive and reproducible SERS detection of
~10 ppb thiocynate in water, all at a volume of ~0.1 μL.
A novel method for light coupling between single mode fibers and small-core photonic crystal fibers is demonstrated. The method is based on growing photopolymer micro-tips directly on the end face of single mode fibers. The advantages of this micro-tip fabrication method are its simplicity, controllability, reproducibility and being inexpensive. The shape and the size of the tips can be controlled, by adjusting the laser power, the exposure time and the oxygen diffusion concentration for polymerization, to match its mode field to the small-core photonic crystal fibers. A photopolymer micro-tip integrated on the end face of a single mode fiber is used to reduce the mode field diameter and increase the numerical aperture of the light beam coming out from the single mode fiber, so that there is a better match to the small mode field diameter and the large numerical aperture of small-core photonic crystal fibers. A 5 dB improvement in coupling efficiency between a single mode fiber and a commercial small-core, highly nonlinear photonic crystal fiber is experimentally demonstrated. This compact and efficient butt-coupling method is particularly suitable for photonic crystal fiber gas sensor applications where holes in the photonic crystal fiber need to be kept open at the joint for easier access to the evanescent field, This method also may be suitable for the connecting a single mode fiber to a hollow-core photonic crystal fiber with the central hole filled with a liquid sample for liquid sensor applications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.