Yujian Huang

Integrated silicon optofluidic ring resonator

The feasibility of an integrated silicon optofluidic ring resonator is demonstrated. Liquid core antiresonant reflecting optical waveguides are used to realize a rectangular ring resonator with a multimode interference liquid core coupler between the ring and the bus waveguide. In this configuration the same waveguide used to confine the light is able to deliver the liquid sample without the need for any additional microfluidics, resulting in a very compact device with a required liquid volume of about 0.11 nl. Optical characterization shows that ring with a good quality factor (Q ? 800) can be achieved in good agreement with the numerical results.

Liquid Core ARROW Waveguides by Atomic Layer Deposition

We report on the use of the atomic layer deposition (ALD) process for fabricating liquid core antiresonant reflecting optical waveguides (ARROWs). The ALD permits the deposition of a very conformal sub-100-nm titanium dioxide antiresonant layer. This results in a low loss liquid core ARROW waveguide with a broadband output transmission spectrum. Optical transmitted spectrum from the fabricated structure has been reported, and the measured attenuation losses agree with the theoretical predictions.

Characterization of low temperature deposited atomic layer deposition TiO2 for MEMS applications

TiO2 is an interesting and promising material for micro-/nanoelectromechanical systems (MEMS/NEMS). For high performance and reliable MEMS/NEMS, optimization of the optical characteristics, mechanical stress, and especially surface smoothness of TiO2 is required. To overcome the roughness issue of the TiO2 films due to crystallization during deposition at high temperatures (above 250?°C), low temperature (80–120?°C) atomic layer deposition (ALD) is investigated. By lowering the deposition temperature, the surface roughness significantly decreases from 3.64?nm for the 300?°C deposited crystalline (anatase phase) TiO2 to 0.24?nm for the 120?°C amorphous TiO2. However, the layers deposited at low temperature present different physical behaviors comparing to the high temperature ones. The refractive index drops from 2.499 to 2.304 (at 633?nm) and the stress sharply decreases from 684 to 133?MPa. Superhydrophilic surface is obtained for the high temperature deposited TiO2 under ultraviolet illumination, while little changes are found for the low temperature TiO2. The authors demonstrate that by suitable postdeposition annealing, all the properties of the low temperature deposited films recover to that of the 300?°C deposited TiO2, while the smooth surface profile (less than 1?nm roughness) is maintained. Finally, micromachining of the low temperature ALD TiO2 by dry etching is also studied.

High-visibility optofluidic Mach–Zehnder interferometer

A high-visibility integrated optofluidic Mach-Zehnder interferometer based on liquid-core antiresonant reflecting optical waveguides is reported. The devices geometry has been optimized to minimize the intensity imbalance between the two arms for highly unbalanced Mach-Zehnder configurations. This results in a very compact device with a total length of only 2.5 mm and with required liquid volume of about 0.16 nl. High visibility is demonstrated for two interferometers corresponding to different sensing lengths. The devices have been optically characterized, and the measured interference fringes in the transmitted spectra show good agreement with the theoretical ones.

Hybrid Silicon-PDMS Optofluidic ARROW Waveguide

A hybrid silicon-poly (dimethysiloxane) (PDMS) liquid core antiresonant reflecting optical waveguide (ARROW) is proposed and analyzed. The waveguide hollow core is defined in the bottom silicon wafer sealed by a top PDMS layer. This configuration permits a strongly simplified fabrication process with respect to conventional full silicon-based ARROW waveguides. Furthermore, the transparent PDMS permits out-of-plane light detection and excitation improving the sensing capability. The numerical simulations and the experimental results show that a low loss liquid core ARROW waveguide with a broadband output transmission spectrum can be achieved.

Reflectance-based two-dimensional TiO2 photonic crystal liquid sensors

We propose and experimentally demonstrate a reflectance-based photonic crystal (PC) liquid sensor. The PC is made of two-dimensional TiO2 nanopillar arrays. Such a reflectance-based structure with large functional area not only simplifies the optical guiding but also enhances the sensor signal. A linear shift of reflectance peaks is found for liquids with refractive indices varying from 1.333 to 1.390 at wavelength near 1.5 μm. Excellent agreement between measured values and the generated reflectance model at a fixed wavelength is obtained, indicating the high potential of these PC-based liquid sensors for biological and environmental applications.

Reflectance-based TiO 2 photonic crystal sensors

Reflectance-based photonic crystal (PC) sensors with ALD TiO2 pillars for sensing materials with different refractive index (RI) are presented here. The relatively high RI, transparency in visible and IR region and chemical stability make TiO2 a promising material for PC sensors for applications in food or biomedical industry. An IC-compatible fabrication technique called Atomic layer deposition ARrays Defined by Etch-back technique (AARDE) is employed to form the high aspect ratios TiO2 nanopillar (240 nm radius and 800 nm pitch) arrays. The optical signals are characterized by means of reflectance other than transmittance, resulting in easier coupling and simpler process steps. High sensitivity of 739.7nm per RI unit is obtained in the 1.4 – 1.6 µm wavelength region.

All ALD TiO 2 -Al 2 O 3 -TiO 2 horizontal slot waveguides for optical sensing

We report for the first time on the use of Atomic Layer Deposition (ALD) to produce TiO2-AlO3-TiO2 horizontal slot waveguides optical sensors. The propagation losses of the waveguides are measured and found to be 18 dB/cm for the quasi-TM mode. These losses are better than the losses reported in slot waveguides made using PECVD techniques (for materials like SiC of similar refractive index as TiO2) with the advantage of a very accurate layer thickness control thanks to the ALD process and the possibility to decrease by a factor 3 the slot size. The field being so confined in the slot we investigated allows the implementation of these slots in a cantilever based sensor. A sensitivity of 0.5 dB/nm is reported.

Waveguide based optofluidics

Integrated liquid core AntiResonant Reflecting Optical Waveguide (ARROW) are used as basic component for the realization of complex optofluidic devices. Liquid core ARROW waveguides permit to confine the light in a low refractive index liquid core, by means of two high refractive index cladding layers designed to form a high reflectivity Fabry-Perot antiresonant cavity. This arrangement allows to realize liquid core waveguides that can be very useful in optofluidic applications. We report the fabrication and the characterization different optofluidic devices based on hollow core ARROW waveguide like tuneable couplers and Mach-Zehnder interferometers. The proposed devices have been realized by silicon technology. The channels have been realized by etching the silicon wafer, while the two claddings have been deposited on both wafers by LPCVD or ALD depositions.

Optofluidics: waveguides and devices

In this work we review recent results of our work on optofluidics. We show that single mode optofluidic waveguides with low loss can be realized using antiresonant reflecting optical confinement (ARROW). These waveguides can be fabricated using full standard silicon technology or hybrid silicon-polymer processes. ARROW waveguides have been used in order to realize complex optofluidic devices like Mach-Zehnder interferometers and ring resonators. The advantage of using optofluidic waveguide results in very compact devices with a total length of 2.5 mm and a required liquid volume less then 0.16nl.