Brian T. Mayers

Integrated fluorescent light source for optofluidic applications

This letter describes a simple fluidic light source for use “on-chip” in integrated microsystems. It demonstrates the feasibility of light sources based on liquid-core, liquid-cladding (L2) microchannel waveguides, with liquid cores containing fluorescent dyes. These fluorescent light sources, using both miscible and two-phase systems, are tunable in terms of the beam size, intensity and spectral content. The observed output intensity from fluorescent L2 light sources is comparable to standard fiber optic spectrophotometer light sources. Integration of fluorescent light sources during device fabrication removes both the need for insertion and alignment of conventional, optical-fiber light sources and the constraints on channel size imposed by fiber optics, albeit at the cost of establishing a microfluidic infrastructure.This letter describes a simple fluidic light source for use “on-chip” in integrated microsystems. It demonstrates the feasibility of light sources based on liquid-core, liquid-cladding (L2) microchannel waveguides, with liquid cores containing fluorescent dyes. These fluorescent light sources, using both miscible and two-phase systems, are tunable in terms of the beam size, intensity and spectral content. The observed output intensity from fluorescent L2 light sources is comparable to standard fiber optic spectrophotometer light sources. Integration of fluorescent light sources during device fabrication removes both the need for insertion and alignment of conventional, optical-fiber light sources and the constraints on channel size imposed by fiber optics, albeit at the cost of establishing a microfluidic infrastructure.

Optical waveguiding using thermal gradients across homogeneous liquids in microfluidic channels

This letter describes the design and operation of a liquid-core liquid-cladding (L2) optical waveguide composed of a thermal gradient across a compositionally homogeneous liquid flowing in a microfluidic channel at low Reynolds number. Two streams of liquid at a higher temperature (the cladding) sandwich a stream of liquid at a lower temperature (the core). This temperature difference results in a contrast in refractive index across the width of the channel that is sufficient to guide light. The use of a single homogeneous liquid in this L2 system simplifies recycling, and facilitates closed-loop operation. Furthermore, with radiative and inline heating of the liquids, it should be possible to reconfigure this optical system with considerable flexibility.

Diffusion-controlled optical elements for optofluidics

Diffusion at the interface between two streams of liquids with different refractive indices, flowing laminarly, creates a controllable concentration gradient and a corresponding refractive index gradient. Using flow rate to change the time over which diffusion occurs in a liquid-liquid (L2) optical waveguide, we demonstrate an optical splitter and a wavelength filter. The optical splitter comprises two parallel L2 waveguides which smoothly merge into a single L2 waveguide by diffusion. The wavelength filter comprises an optical splitter in which the two L2 waveguides contain an absorbing dye.

Self-Assembly and Nanostructured Materials

Nanostructured materials are those having properties defined by features smaller than 100 nm. This class of materials is interesting for the reasons: i) They include most materials, since a broad range of properties-from fracture strength to electrical conductivitydepend on nanometer-scale features. ii) They may offer new properties: The conductivity and stiffness of buckytubes, and the broad range of fluorescent emission of CdSe quantum dots are examples. iii) They can mix classical and quantum behaviors. iv) They offer a bridge between classical and biological branches of materials science. v) They suggest approaches to materials-by-design. Nanomaterials can, in principle, be made using both top-down and bottom-up techniques. Self-assembly bridges these two techniques and allows materials to be designed with hierarchical order and complexity that mimics those seen in biological systems. Self-assembly of nanostructured materials holds promise as a low-cost, high-yield technique with a wide range of scientific and technological applications.

Optical waveguiding in suspensions of dielectric particles.

An optical waveguide formed by a suspension of dielectric nanoparticles in a microchannel is described. The suspensions, chosen for their guiding and scattering properties, are silica and polystyrene particles that have diameters of 30–900 nm and are dispersed in water with volume fractions up to 10%. Changing the diameter and concentration of the particles causes the suspensions to transition from Rayleigh to Mie scattering and from single to multiple scattering. The threshold for optical guiding in a waveguide core composed of these suspensions is set by the numerical aperture of the effective refractive-index difference introduced by the suspension and not by the average interparticle distance.

Optical waveguiding in suspensions of dielectric particles

Waveguiding is observed in a liquid core/liquid cladding waveguide containing a suspension of dielectric particles in the core. The threshold for guiding is determined by the numerical aperture of the effective refractive index.