Y.L. Hoo

Design and modeling of a photonic crystal fiber gas sensor

We report the modeling results of an all-fiber gas detector that uses photonic crystal fiber (PCF). The relative sensitivity of the PCF as a function of the fiber parameters is calculated. Gas-diffusion dynamics that affect the sensor response time is investigated theoretically and experimentally. A practical PCF sensor aiming for high sensitivity gas detection is proposed.

Fabrication of selective injection microstructured optical fibers with a conventional fusion splicer

A simple method for fabricating selective injection microstructured optical fibers (MOFs) using a conventional fusion splicer is described. The effects of fusion current, fusion duration and offset position on the hole collapse property of the MOFs are investigated. With this method, the central hollow-core and the holes in the cladding region can be selectively infiltrated, which allows for the fabrication of novel hybrid polymer-silica and liquid-silica MOFs for various applications.

Evanescent-wave gas sensing using microstructure fiber

We report the experimental demonstration of evanescent-wave gas detection with a silica-air microstructure fiber. Detection sensitivity of ~6% of that of direction absorption spectroscopy per equal length has been achieved. 0]

Temperature-controlled transformation in fiber types of fluid-filled photonic crystal fibers and applications

We investigated experimentally and theoretically an invertible fiber-type transformation from a photonic bandgap fiber into a nonideal waveguide and then into an index-guiding photonic crystal fiber via the thermo-optic effect of the fluid filled in the air holes. Such a transformation could be used to develop an in-fiber optical switch/attenuator with a high-extinction ratio of more than 35 dB over an extremely broad wavelength range from 600 to 1700 nm via a small temperature adjustment.

Fast Response Microstructured Optical Fiber Methane Sensor With Multiple Side-Openings

We have demonstrated a fast response optical fiber methane sensor by use of a hollow-core photonic bandgap fiber with periodic microchannels fabricated by a femtosecond Ti:sapphire laser. A diffusion limited response time of ~3 s and a sensitivity of ~647 ppm have been achieved for a 7-cm sensing fiber with seven side-holes separated by 1 cm along the fiber. The side holes introduce very little loss and hence it would be practically possible to construct fiber gas sensors with long sensing length (up to a few tens of meters) to achieve highly sensitive distributed sensing without compromising the response time.

Improved bending property of half-filled photonic crystal fiber.

A half-filling technique was demonstrated to improve the bending properties of a fluid-filled photonic crystal fiber. Such a technique can realize to fill selectively a fluid into half of air holes in a PCF. The bending properties of the half-filled PCF are quite different from those of the fully-filled PCF. Distinct bending properties were observed when the half-filled PCF was bent toward different fiber orientations. Especially, the transmission spectrum of the half-filled PCF was hardly affected while the fiber was bent toward the filled-hole orientation.

In-line devices and sensors based on air-silica microstructure optical fibers

This paper reports some of our recent work on in-line devices based on air-silica microstructrue optical fibers. These devices are fabricated by use of a CO2 laser/a femtosecond infrared laser and include strong long period gratings in index-guiding fibers and air-core photonic bandgap fibers, in-fiber polarizers, polarimeters, and modal interferometers. Applications of such devices for strain, temperature, directional bend, twist, and gas sensing are discussed.

Design of single-polarization PCF at 1300- and 1550-nm bands

The cut-off wavelengths of the two linearly polarized states in PCF can be designed by varying the diameters and pitch of the holes. Simulations show that single polarization operation over a range of up to 100 nm can be realized around 1.3 μm and 1.55 μm bands.