<p>We proposed and developed an integrated fluorescent oxygen gas-sensor probe module based on asymmetric 1 × 2 optical waveguides that can transmit power from an optical source and the fluorescence signal with high efficiency simultaneously. The fluorescent oxygen gas-sensor comprises an optical source part, optical detector part, and optical sensing probe part. The optical sensing probe comprises asymmetric 1 × 2 optical waveguides coated with an oxygen-sensitive fluorescent film on the end face of the optical waveguide. This optical probe module can transmit the optical power and fluorescence signal with high efficiency because of the same optical path for transmission of the optical source and the fluorescence signal. In addition, this structure facilitates an integrated miniature oxygen-sensor module. We optimally designed the asymmetric 1 × 2 optical waveguides with an asymmetric structure and different two core size. Then, we fabricated the polymeric asymmetric optical waveguides using the UV imprint lithography process suitable for cost-effective mass production. The optical oxygen-sensor probe transmitted the optical source power and the fluorescence signal with 80% and 82% efficiency, respectively. An oxygen-sensitive fluorescent film was coated on the end face of the optical waveguide by using the spray coating method. The oxygen-gas detection sensor constructed using this optical probe module with 1 × 2 asymmetric optical waveguides could measure the concentration with 0.3% resolution for a gas concentration range of 0% to 25%. This optical oxygen-sensor probe module facilitates a compact, simple, and cheap measurement system.</p>
Photonic crystals (PCs) are recently fabricated by the Nano Imprint Lithography (NIL) on the polymers with low indexes
because of the simple and short process time and ease of precise manufacturing. But, PCs require high dimensional
accuracy due to their optical characteristics. The dimensional accuracy of PCs using NIL depends on the stamp. NIL
stamps are usually fabricated by EBL, lift off and etching process. The damage of PC structures happens during the lift
off process due to the tearing and ripping problem. So, we report on novel fabrication of NIL stamp using PMGI/PMMA
bi-layer lift off technique. We can control the extent of the undercut in the support layer through independent
development of PMGI and PMMA. We simulate the band structure of a triangle lattice with a polymer refractive index
of 1.495. From the simulation results, we derive that dimensional accuracy of PCs should be maintained below ±30 nm.
We make the original pattern by EBL. An optimal dose for achieving this dimension on the PMMA is determined by
experiment and has 110 μC/cm<sup>2</sup> at the aperture 10 μm and EHT 20 kV. To establish optimal process condition,
development for PMMA and PMGI is performed according to development time. Then, we deposit the Ni layer using e-beam
evaporator and perform the lift off process. We can obtain the PCs structure of Ni metal layer with 70 nm undercut
at the optimal development condition. The fabricated PCs structure has dimensional accuracy below 5 nm. These values
are sufficient for meeting with optical characteristics of PCs.