Optical microtube cavities monolithically integrated on photonic chips for optofluidic sensing.

Microtubular optical resonators are monolithically integrated on photonic chips to demonstrate optofluidic functionality. Due to the compact subwavelength-thin tube wall and a well-defined nanogap between polymer photonic waveguides and the microtube, excellent optical coupling with extinction ratios up to 32 dB are observed in the telecommunication relevant wavelength range. For the first time, optofluidic applications of fully on-chip integrated microtubular systems are investigated both by filling the core of the microtube and by the microtube being covered by a liquid droplet. Total shifts over the full free spectral range are observed in response to the presence of the liquid medium in the vicinity of the microtube resonators. This work provides a vertical coupling scheme for optofluidic applications in monolithically integrated so-called "lab-in-a-tube" systems.

Enhanced optical axial confinement in asymmetric microtube cavities rolled up from circular-shaped nanomembranes.

Asymmetric cone-like microtube cavities have been fabricated by unevenly rolling-up prestrained SiO/SiO(2) circular-shaped nanomembranes. Spatially localized axial resonant modes are obtained due to an axial confinement mechanism that is defined by the variation of the tube radius and windings along the tube axis. A theoretical model is applied to quantitatively explain and confirm our experimental results.

Lab-in-a-tube: on-chip integration of glass optofluidic ring resonators for label-free sensing applications.

The fabrication of tubular rolled-up optofluidic ring resonators (RU-OFRRs) based on glass (SiO(2)) material with high quality factors is reported. A novel methodology combining lab-on-a-chip fabrication methods and rolled-up nanotech is presented for the fabrication of fully integrated tubular optofluidic sensors. The microfluidic integration of several RU-OFRRs on one chip is solved by enclosing the microtubes with a patterned robust SU-8 polymeric matrix. A viewport on each microtube enables exact excitation and monitoring of whispering gallery modes with a photoluminescence spectroscopy system under constant ambient conditions, while exchanging the content of the RU-OFRR with liquids of different refractive indices. The refractrometric sensor capabilities are investigated regarding signal stability, sensitivity and reliability. The sensitivity of the integrated RU-OFRR, which is the response of the modes to the change in refractive index of the liquid, is up to 880 nm/refractive index units (RIU).

Lab-in-a-tube: ultracompact components for on-chip capture and detection of individual micro-/nanoorganisms.

A review of present and future on-chip rolled-up devices, which can be used to develop lab-in-a-tube total analysis systems, is presented. Lab-in-a-tube is the integration of numerous rolled-up components into a single device constituting a microsystem of hundreds/thousands of independent units on a chip, each individually capable of sorting, detecting and analyzing singular organisms. Such a system allows for a scale-down of biosensing systems, while at the same time increasing the data collection through a large, smart array of individual biosensors. A close look at these ultracompact components which have been developed over the past decade is given. Methods for the capture of biomaterial are laid out and progress of cell culturing in three-dimensional scaffolding is detailed. Rolled-up optical sensors based on photoluminescence, optomechanics, optofluidics and metamaterials are presented. Magnetic sensors are introduced as well as electrical components including heating, energy storage and resistor devices.

Rolled-up optical microcavities with subwavelength wall thicknesses for enhanced liquid sensing applications.

Microtubular optical microcavities from rolled-up ring resonators with subwavelength wall thicknesses have been fabricated by releasing prestressed SiO/SiO(2) bilayer nanomembranes from photoresist sacrificial layers. Whispering gallery modes are observed in the photoluminescence spectra from the rolled-up nanomembranes, and their spectral peak positions shift significantly when measurements are carried out in different surrounding liquids, thus indicating excellent sensing functionality of these optofluidic microcavities. Analytical calculations as well as finite-difference time-domain simulations are performed to investigate the light confinement in the optical microcavities numerically and to describe the experimental mode shifts very well. A maximum sensitivity of 425 nm/refractive index unit is achieved for the microtube ring resonators, which is caused by the pronounced propagation of the evanescent field in the surrounding media due to the subwavelength wall thickness design of the microcavity. Our optofluidic sensors show high potential for lab-on-a-chip applications, such as real-time bioanalytic systems.

Optical resonance tuning and polarization of thin-walled tubular microcavities.

We present experimental and finite-difference time-domain simulation results on the tunability of optical resonant modes of spiral microtube cavities, rolled-up from square patterned SiO/SiO(2) thin nanomembranes on glass substrates. The peak positions of resonant TM modes shift to lower energies by coating the microtube wall with Al(2)O(3) monolayers, which is well described by simulations. Moreover, a second group of tunable resonant modes appears beyond a certain critical thickness of the coated Al(2)O(3). The polarization of this group of modes is TE, as we find out by a detailed analysis of the polarization-dependent photoluminescence spectra.