Hau Ping Chan

High extinction ratio and low transmission loss thin-film terahertz polarizer with a tunable bilayer metal wire-grid structure.

A thin-film terahertz polarizer is proposed and realized via a tunable bilayer metal wire-grid structure to achieve high extinction ratios and good transmission. The polarizer is fabricated on top of a thin silica layer by standard micro-fabrication techniques to eliminate the multireflection effects. The tunable alignment of the bilayer aluminum-wire grid structure enables tailoring of the extinction ratio and transmission characteristics. Using terahertz time-domain spectroscopy (THz-TDS), a fabricated polarizer is characterized, with extinction ratios greater than 50 dB and transmission losses below 1 dB reported in the 0.2-1.1 THz frequency range. These characteristics can be improved by further tuning the polarizer parameters such as the pitch, metal film thickness, and lateral displacement.

Reconfigurable two-mode mux/demux device

A reconfigurable two-mode mux/demux device in planar waveguide was proposed. The simulated mux/demux extinction ratio was ≥ 35 dB with ≤ 0.4 dB excess loss. The device was realized in polymer materials using the thermo-optic effect. It was characterized via a tunable laser source at 1550 nm. Its mux/demux performance in both routes was demonstrated and compared with the theoretical prediction. The device is easy to implement and has applications in future multimode optical communication systems to further extend transmission capacity.

Low Loss, High Extinction Ration and Ultra-Compact Plasmonic Polarization Beam Splitter

In this letter, an ultra-compact plasmonic polarization beam splitter (PBS) is proposed and investigated by numerical simulations using the finite element method. The PBS is based on a three-core plasmonic directional coupler, which uses a long range surface plasmon polaritons waveguide as the middle waveguide to achieve polarization selective coupling. The calculations show that with proper structural parameters, the PBS with low insertion losses of 0.17 and 0.25 dB for TE and TM polarizations, respectively, and high extinction ratios of 20.17 and 19.83 dB for TE and TM polarizations, respectively, can be realized at a telecommunication wavelength of 1550 nm. Furthermore, an insertion loss and an extinction ratio > 14 dB can be realized across the entire C-band for both TE and TM polarizations.

Planar Optical Waveguide Platform for Gas Sensing Using Liquid Crystal

We propose a simple method for detecting chemical gases using liquid crystal on a planar optical waveguide. Through measuring waveguide output power, this method detects changes in the director of liquid crystal molecules as well as the refractive index, which attributed to gas exposure. We demonstrate this idea by constructing a compact and fast-response ethanol gas sensor.

UV exposure on a single-mode fiber within a multimode interference structure

We experimentally study the effects of UV exposure on a single-mode fiber (SMF) with a fiber multimode interferometer (MMI) based on the singlemode-multimode-singlemode-multimode-singlemode (SMSMS) fiber structure. We observe a wavelength shift of over 33 nm when irradiating the central SMF in the SMSMS fiber structure with a 3-mm-width UV beam (the UV laser has a wavelength of 193 nm and pulse energy of 3 mJ). According to our numerical simulation, the SMSMS fiber structure can achieve a very high refractive-index (RI) sensitivity of 67670 nm/RIU with a very good linearity of R2≈0.9999. The structure can find potential application for high-sensitivity RI sensing by replacing the central SMF with a hollow-core optical fiber filled with the sample under test. The UV exposure technique can be used for tuning the characteristics of fiber MMI devices.

Efficient design of polarization insensitive polymer optical waveguide devices considering stress-induced effects

We present an approach for the efficient design of polarization insensitive polymeric optical waveguide devices considering stress-induced effects. In this approach, the stresses induced in the waveguide during the fabrication process are estimated first using a more realistic model in the finite element analysis. Then we determine the perturbations in the material refractive indices caused by the stress-optic effect. It is observed that the stresses cause non-uniform optical anisotropy in the waveguide materials, which is then incorporated in the modal analysis considering a multilayer structure of waveguide. The approach is exploited in the design of a Bragg grating on strip waveguide. Excellent agreement between calculated and published experimental results confirms the feasibility of our approach in the accurate design of polarization insensitive polymer waveguide devices.

Broadband high-order mode pass filter based on mode conversion

We propose a unique concept to implement a higher-order mode pass filter using mode-converters. The proposed filter has a simulated extinction ratio greater than 20 dB with an excess loss less than 0.6 dB in the C-Band.

Robust and accurate terahertz time-domain spectroscopic ellipsometry

In this work, we show how fiber-based terahertz systems can be robustly configured for accurate terahertz ellipsometry. To this end, we explain how our algorithms can be successfully applied to achieve accurate spectroscopic ellipsometry with a high tolerance on the imperfect polarizer extinction ratio and pulse shift errors. Highly accurate characterization of transparent, absorptive, and conductive samples comprehensively demonstrates the versatility of our algorithms. The improved accuracy we achieve is a fundamental breakthrough for reflection-based measurements and overcomes the hurdle of phase uncertainty.

Broadband higher-order mode pass filter based on mode conversion

We propose a unique concept to implement a higher-order mode pass filter using mode-converters. The proposed filter has a simulated extinction ratio greater than 20 dB with an excess loss less than 0.6 dB in the C-Band.

Investigation on stress/strain sensing characteristics for magnetorheological smart composite material by a SMS fiber structure

A single-mode-multimode-single-mode (SMS) fiber structure based stress/strain sensor is applied to monitor internal stress variations in magnetorhelogical elastomers (MREs) matrix. The liquid silicone rubber mixture with embedded fibers, i.e. SMS fiber and Fiber-Bragg-Grating (FBG), are enclosed into an aluminum mould for curing within a permanent magnet field at room temperature for 5 days. Then the cured sample is utilized for internal stress/strain measurement by applying different magnetic field intensity, of the results show that SMS structure has higher stress/strain sensitivity than that of FBG when a variable magnetic flux density was applied the MRE. The present investigation shows capability of using SMS sensor for online feedback and operation of MREs materials and commercial potential in medical and healthcare applications.