In this paper, we experimentally demonstrated the fabrication and hydrostatic pressure characteristics of a twin-core photonic crystal fiber (TC-PCF). Mode couplings in the TC-PCF for x- and y-polarizations were analyzed simultaneously using group effective index of guiding modes. The output spectrum of the TC-PCF was modulated due to the combined couplings of the two polarizations. To the best of our knowledge, it is the first time to measure hydrostatic pressure through the dual-polarization mode coupling in a TC-PCF. The measured sensitivity of the pressure sensor was -21 pm/MPa. The length of the TC-PCF used for pressure measurement was 20 cm, which is much shorter than pressure sensor based on PM-PCF, and does not require any external polarizing components, meaning that it is a good candidate for compact pressure sensor.

We demonstrate a polarization-maintaining (PM) photonic crystal fiber (PCF) based Sagnac interferometer for downhole high pressure sensing application. The PM PCF serves as a direct pressure sensing probe. The sensor is transducer free and thus fundamentally enhances its long-term sensing stability. In addition, the PM PCF can be coiled into a small diameter to fulfill the compact size requirement of downhole application. A theoretical study of its loss and birefringence changes with different coiling diameters has been carried out. This bend-insensitive property of the fiber provides ease for sensor design and benefits practical application. The pressure sensitivities of the proposed sensor are 4.21 and 3:24 nm= MPa at ∼1320 and ∼1550 nm, respectively. High pressure measurement up to 20 MPa was achieved with our experiment. It shows both good linearity in response to applied pressure and good repeatability within the entire measurement range. The proposed pressure sensor exhibits low temperature cross sensitivity and high temperature sustainability. It functions well without any measurable degradation effects on sensitivity or linearity at a temperature as high as 293°C. These characteristics make it a potentially ideal candidate for downhole pressure sensing.

We propose and demonstrate a highly sensitive in-line photonic crystal fiber (PCF) microfluidic refractometer. Ultrathin C-shaped fibers are spliced in-between the PCF and standard single-mode fibers. The C-shaped fibers provide openings for liquid to flow in and out of the PCF. Based on a Sagnac interferometer, the refractive index (RI) response of the device is investigated theoretically and experimentally. A high sensitivity of 6621 nm/RIU for liquid RI from 1.330 to 1.333 is achieved in the experiment, which agrees well with the theoretical analysis.

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We report compression of low-power femtosecond pulses at 1.06 microm in a dispersion-decreasing holey fiber. Near-adiabatic compression of 130 fs pulses down to 60 fs has been observed. Measured spectra and pulse shapes agree well with numerical simulations. Compression factors of ten are possible in optimized fibers.