We report a simple and highly versatile photonic crystal fiber (PCF) interferometer that operates in reflection mode. The
device consists of a short section of PCF fusion spliced at the distal end of a standard single mode fiber. The air-holes of
the PCF are intentionally collapsed over a microscopic region around the splice. The collapsed region broadens the
propagating mode because of diffraction. This allows the coupling and recombination of two PCF modes. Depending on
the PCF structure two core modes or a core and a cladding mode can be excited. In either case the devices exhibit
sinusoidal interference patterns with fringe spacing depending on the PCF length. The interferometers are highly stable
over time and can operate at high temperatures with minimal degradation. The interferometers are suitable for highresolution
sensing of strain, refractive index (biosensing), gases, volatile organic compounds, etc.
We report on compact and simple refractive index sensors suitable for measuring indexes in the 1.320-1.432 range with
high resolution. The devices are based on modal interference and consist of a stub of large-mode area photonic crystal
fiber spliced to standard single mode fiber. In the splice regions the voids of the holey fiber are fully collapsed which
allows the coupling and recombination of core and cladding modes. The devices are robust and highly stable over time.
The interference patterns are observed in a broad wavelengths range. The devices operate in both reflection or in
We report an in-reflection photonic crystal fiber (PCF) interferometer which exhibits high sensitivity to different volatile
organic compounds (VOCs), without the need of any permeable material. The interferometer is compact, robust, and
consists of a stub of PCF spliced to standard optical fiber. In the splice the voids of the PCF are fully collapsed, thus
allowing the excitation and recombination of two core modes. The device reflection spectrum exhibits very regular
interference pattern which shifts differently when the voids of the PCF are infiltrated with VOC molecules. The volume
of voids responsible for the shift is around 500 picoliters whereas the detectable levels are in the nanomole range.