Liquid-infiltrated photonic crystals: enhanced light-matter interactions for lab-on-a-chip applications

Abstract

Optical techniques are finding widespread use in analytical chemistry for chemical and bio-chemical analysis. During the past decade, there has been an increasing emphasis on miniaturization of chemical analysis systems and naturally this has stimulated a large effort in integrating microfluidics and optics in lab-on-a-chip microsystems. This development is partly defining the emerging field of optofluidics. Scaling analysis and experiments have demonstrated the advantage of microscale devices over their macroscopic counterparts for a number of chemical applications. However, from an optical point of view, miniaturized devices suffer dramatically from the reduced optical path compared to macroscale experiments, e.g. in a cuvette. Obviously, the reduced optical path complicates the application of optical techniques in lab-on-a-chip systems. In this paper we theoretically discuss how a strongly dispersive photonic crystal environment may be used to enhance the lightmatter interactions, thus potentially compensating for the reduced optical path in lab-on-a-chip systems. Combining electromagnetic perturbation theory with full-wave electromagnetic simulations we address the prospects for achieving slow-light enhancement of Beer-Lambert-Bouguer absorption, photonic band-gap based refractometry, and high-Q cavity sensing.

Analysis of ultra-high sensitivity configuration in chip-integrated photonic crystal microcavity bio-sensors

“…The response can be understood by first order perturbation theory, 14 in which the change in eigenfrequency Dx m of the mth mode can be described as…”

“…Consequently, at the resonance frequency, group index n g of the mode can be considered the same as in an open ended PC microcavity (or equivalently a PCW). Taking into account the effect of slow light and f B enhancement on absorbance by a factor c, 14,17 Eq. (4) can now be written as…”

Silicon photonic crystal nanostructures for refractive index sensing

“…[3][4][5] Nanoscale optical cavities formed by introducing point defects into two dimensional PhCs are particularly interesting since they typically support highly localized cavity modes. The wavelength ͑ m ͒ and quality factor ͑Q = m / ⌬ ͒ of these modes are sensitive to the local refractive index ͑RI͒ of the environment, providing a transducer signal for constructing nanoscale optical sensors.…”

Temperature stabilization of optofluidic photonic crystal cavities

“…20 At the wavelength Stab the mode profile is such that the negative thermo-optic coefficient of the infiltrated liquid ͑‫ץ‬n L / ‫ץ‬T =−3ϫ 10 −4 K −1 for Cargille immersion oil type B͒ compensates the intrinsic positive thermo-optic coefficient of the PhC ͑‫ץ‬n Si / ‫ץ‬T =+2ϫ 10 −4 K −1 for silicon͒. From Eq.…”

“…We now express this concept mathematically by considering the field distribution in a resonant fluid-infiltrated PhC cavity. To calculate the change in resonance frequency with temperature, we use standard electromagnetic perturbation theory, 20 linearizing the refractive index around a reference temperature T 0 . For a two-component structure, such as a silicon membrane PhC with an infiltrated liquid, we find for the change of resonant wavelength,…”