Ground based near-infrared observations have long been plagued by poor sensitivity when compared to visible
observations as a result of the bright narrow line emission from atmospheric OH molecules. The GNOSIS instrument
recently commissioned at the Australian Astronomical Observatory uses Photonic Lanterns in combination with
individually printed single mode fibre Bragg gratings to filter out the brightest OH-emission lines between 1.47 and
1.70μm. GNOSIS, reported in a separate paper in this conference, demonstrates excellent OH-suppression, providing
very “clean” filtering of the lines. It represents a major step forward in the goal to improve the sensitivity of ground
based near-infrared observation to that possible at visible wavelengths, however, the filter units are relatively bulky and
costly to produce.
The 2nd generation fibre OH-Suppression filters based on multicore fibres are currently under development. The
development aims to produce high quality, cost effective, compact and robust OH-Suppression units in a single optical
fibre with numerous isolated single mode cores that replicate the function and performance of the current generation of
“conventional” photonic lantern based devices. In this paper we present the early results from the multicore fibre
development and multicore fibre Bragg grating imprinting process.
The ability to measure the concentration of hydrogen peroxide (H2O2) in solution is critical for quality assessment and
control in many disparate applications, including wine, aviation fuels and IVF. The objective of this research is to
develop a rapid test for the hydrogen peroxide content that can be performed on very low volume samples (i.e. sub-μL)
that is relatively independent of other products within the sample.
For H2O2 detection we use suspended core optical fibers to achieve a high evanescent field interaction with the fluid of
interest, without the constraint of limited interaction length that is generally inherent with nanowire structures. By filling
the holes of the fiber with an analyte/fluorophore solution we seek to create a quick and effective sensor that should
enable detection of desired species within liquid media. By choosing a fluorophore that reacts with our target species to
produce an increase in fluorescence, we can correlate observed fluorescence intensity with the concentration of the target
A photonic microcell (PMC) is a length of gas-filled hollow core-photonic crystal fiber (HC-PCF) which is hermetically
sealed at both ends by splicing to standard single mode fiber. We describe advances in the fabrication technique of PMCs
which enable large core Kagome-lattice HC-PCFs to be integrated into PMC form. The modified fabrication technique
uses fiber-tapering to accommodate the large dimensions of the fiber and enables low loss splices with single mode fiber
by reducing mode field mismatch. Splice losses as low as 0.6 dB are achieved between 1-cell defect Kagome HC-PCF
and single mode fiber. Relative to the previously reported PMCs, which were based on photonic bandgap HC-PCF, the
present Kagome HC-PCF based PMC provides broad optical transmission, surface mode-free guidance and larger core at
the cost of slightly increased fiber attenuation (~0.2 dB/m). Therefore, the integration of this fiber into PMC form opens
up new applications for PMC-based devices. The advantage of the large core dimensions and surface mode free guidance
for quantum optics in gas-filled HC-PCF are demonstrated by generation of narrow sub-Doppler features in an acetylenefilled
large core PMC.
A static tandem Michelson interferometer configuration is reported for remote measurements of group delay change in a
thermally modulated, optically dispersive BK7 glass sample. Using a superluminescent diode (SLD) to illuminate the
interferometer, low-coherence measurement interferograms with signal-to-noise ratios as low as 16 dB were captured
and subsequently processed using dispersive Fourier transform spectrometry (DFTS). Measurements of thermallyinduced
delay change were made with < 2 fs root mean square error for optical path delay scans lengths of only 260 μm.
Photonic crystal fibers (PCFs) have been receiving increasing attention over the past few years. They are single material fibers that use an array of air holes in the cladding to confine light to a core, instead of the more usual refractive index step within the solid material of a conventional fiber. As PCFs become more well-understood mainstream structures, the need arises to develop techniques to process them post-fabrication to form all-fiber devices. We have chosen to study heat-treatment processes analogous to the tapering of conventional fibers, except that in PCFs there is a second degree of freedom to exploit. Not only can the fiber be stretched to locally reduce its cross-sectional area, the air holes can be changed in size by heating alone under the effect of surface tension.
A low-coherence optical fiber interferometric technique for simultaneous measurement of geometric thickness and group refractive index of highly dispersive materials is described. The technique, immune to the dispersion-induced asymmetry of the low-coherence interferograms obtained, overcomes some of the drawbacks associated with recently reported low-coherence approaches to this simultaneous measurement. The technique uses the experimental configuration of a tandem interferometer with the samples to be characterized placed in an air-gap in one arm of the measurement interferometer. Dispersion- insensitive measurements of the group delay imbalances in the measurement interferometer are made using dispersive Fourier transform spectrometry (DFTS). Sample thickness and group refractive index are calculated from these group delays which are unambiguously determined from the optical frequency dependence of the measured phases of the interferograms. Thickness measurements accurate to within 1 micrometer and group index measurements accurate to within one part per thousand have been achieved for BK7 and fused-silica glass samples in the thickness range 2000 to 6000 micrometers.