We present a technology for miniaturized, chip-based liquid dye lasers, which may be integrated with microfluidic networks and planar waveguides without addition of further process steps. The microfluidic dye lasers consist of a microfluidic channel with an embedded optical resonator. The lasers are operated with Rhodamine 6G laser dye dissolved in a suitable solvent, such as ethanol or ethylene glycol, and optically pumped at 532 nm with a pulsed, frequency doubled Nd:YAG laser. Both vertically and laterally emitting devices are realized. A vertically emitting Fabry-Perot microcavity laser is integrated with a microfluidic mixer, to demonstrate realtime wavelength tunability. Two major challenges of this technology are addressed: lasing threshold and fluidic handling. Low threshold, in-plane emission and integration with polymer waveguides and microfluidic networks is demonstrated with distributed feed-back lasers. The challenge of fluidic handling is addressed by hybridization with mini-dispensers, and by applying capillary filling of the laser devices.

We demonstrated a continuously tunable optofluidic distributed feedback (DFB) dye laser on a monolithic poly(dimethylsiloxane) (PDMS) elastomer chip. The optical feedback was provided by a phase-shifted higher order Bragg grating embedded in the liquid core of a single mode buried channel waveguide. We achieved nearly 60nm continuously tunable output by mechanically varying the grating period with two dye molecules Rhodamine 6G (Rh6G) and Rhodamine 101 (Rh101). Single-mode operation was obtained with <0.1nm linewidth. Because of the higher order grating, a single laser, when operated with different dye solutions, can provide tunable output covering from near UV to near IR spectral region. The low pump threshold (< 1uJ) makes it possible to use a single high energy pulsed laser to pump hundreds of such lasers on a chip. An integrated array of five DFB dye lasers with different lasing wavelengths was also demonstrated. Such laser arrays make it possible to build highly parallel optical sensors on a chip. The laser chip is fully compatible with PDMS based soft microfluidics.

Optofluidics offers new functionalities that can be useful for a large range of applications. What microfluidics can bring to microphotonics is the ability to tune and reconfigure ultra-compact optical devices. This flexibility is essentially provided by three characteristics of fluids that are scalable at the micron-scale: fluid mobility, large ranges of index modulation, and adaptable interfaces. Several examples of optofluidic devices are presented to illustrate the achievement of new functionalities onto (semi)planar and compact platforms. First, we report an ultra-compact and tunable interferometer that exploits a sharp and mobile air/water interface. We describe then a novel class of optically controlled switches and routers that rely on the actuation of optically trapped lens microspheres within fluid environment. A tunable optical switch device can alternatively be built from a transversely probed photonic crystal fiber infused with mobile fluids. The last reported optofluidic device relies on strong fluid/ light interaction to produce either a sensitive index sensor or a tunable optical filter. The common feature of these various devices is their significant flexibility. Higher degrees of functionality could be achieved in the future with fully integrated optofluidic platforms that associate complex microfluidic delivery and mixing schemes with microphotonic devices.

We present a technique for manipulating the dispersive properties of low index periodic structures using microfluidic materials that fill the lattice with various fluids of different refractive indices. In order to quantify the modulation of the optical properties of the periodic structure we use Equi-frequency contours (EFC) data to calculate the frequency dependant refractive index and the refractive angle. We further introduce various types of defects by selectively filling specific lattice sites and measuring the relative change in the index of refraction. Finally we design and optically characterize an adaptive low index photonic crystal based lens with tunable optical properties using various microfluidics. We also present experimental results for a silicon based PhC lens used an optical coupling element.

We demonstrate a novel optical imaging device that can be directly integrated into a microfluidic network, and therefore enables on-chip imaging in a microfluidic system. This micro imaging device, termed optofluidic microscope (OFM) is free of bulk optics and is based on a nanohole array defined in a non-transmissive metallic layer that is patterned onto the floor of the microfluidic channel. The operation of the optofluidic microscope will be explained in details and its performance is examined by using a popular animal model, Caenorhabditis elegans (C. elegans). Images from a large population of nematode worms are efficiently acquired within a short time frame. The quality of the OFM images of C. elegans and the morphological characteristics revealed therein are evaluated. Two groups of early-stage C. elegans larvae, wild-type and dpy-24 are successfully separated even though their morphological difference at the larval stage is subtle. The experimental results support our claim that the methodology described therein can be effectively used to develop a powerful tool for fulfilling high-resolution, high-throughput imaging task in microfluidics-based systems.

Fluidic optics is a new class of optical system with real-time tunability and reconfigurability enabled by the introduction of fluidic components into the optical path. We describe the design, fabrication, operation of a number of fluidic optical systems, and focus on three devices, liquid-core/liquid-cladding (L²) waveguides, microfluidic dye lasers, and diffraction gratings based on flowing, crystalline lattices of bubbles, to demonstrate the integration of microfluidics and optics. We fabricate these devices in poly(dimethylsiloxane) (PDMS) with soft-lithographic techniques. They are simple to construct, and readily integrable with microanalytical or lab-on-a-chip systems.

We explore the possibility of using optical tweezers to enable all optical control of optofluidic circuits. Optically trapped microspheres can be used as microlenses for optical signal switching and steering. By using cantilevers instead of microspheres we provide a method for robust and stable placement of switching elements in the optofluidic circuits. Cantilevers made of tapered optical fiber and polydimethyl siloxane are demonstrated. We also show that it is possible to use transverse optical tweezer beams to load silica beads into the hollow core photonic crystal fibers for tuning their transmission properties.

In this work we explore the possibility of developing micro-/nano-fluidic devices which exploits the intense electromagnetic fields present in nanophotonic structures as the primary transport mechanism. This transport mechanism is based on exploiting the near-field optical gradients (which serve to confine particles through a Lorenz force) and concentrated optical energy (resulting in intense scattering and absorption forces for propulsion through photon momentum transfer) present in these devices to perform a series of particle handling operations including transport, concentration and separation. Nanophotonic transport offers unique properties which give it several advantages over traditional techniques including: favorable transport scaling laws, extremely strong velocity dependence on particle size, insensitivity to surface/solution conditions and indefinitely long interaction lengths. In this work we detail the theory behind photonic transport and outline in detail the major advantages. Some of our initial experimental results on transport in liquid core photonic crystal devices and developing numerical simulation techniques describing photonic transport in such devices.

In this paper, we report a fast and facile method for fabricating colloidal photonic crystals inside microchannels of radially symmetric microfluidic chips. As the suspension of monodisperse silica or polystyrene latex spheres was driven to flow through the channels under the centrifugal force, the colloidal spheres were quickly assembled into face centered cubic arrangement which had photonic stop bands. The optical reflectance spectrum was modulated by the refractiveindex mismatch between the colloidal particles and the solvent filled in the interstices between the particles. Therefore, the present microfluidic chips with built-in colloidal photonic crystals can be used as in-situ optofluidic microsensors for high throughput screening, light filters and biosensors in integrated adaptive optical devices.

This paper describes the development of methods for the determination of the characteristics and the behavior of living neural cells. A technology which is used is the deep ultraviolet (DUV) modification of methylmethacrylate polymers which leads to a new surface chemistry affecting the selective absorption of proteins and the adhesion of living cells in vitro. The bi-functionality of the modified polymer chips supporting waveguides and cell anchorage capabilities at the same time provides the opportunity to monitor protein adsorption, cell attachment and spreading processes by evanescent-field techniques. This allows the defined spatial control of a cell/surface interaction and leads to a combination of desired biological and optical properties of the polymer. Among them are the high sensitivity of cultured mammalian cells to, for example, environmental changes and special features of integrated optical waveguides like their online compatibility, minuteness and robustness. The scientific fields, biology and optics, meet at the polymer surface becoming a cell culture substrate together with an optical waveguide by the application of special patterning and fabrication technologies. In addition to the already mentioned fabrication and immobilization technology, the technique proposed also offers the possibility of being able to couple to microstamping processes and to also incorporate electrical measurements on individual cells. Thus, by extending this method and coupling it to the DUV technique described above the possibility is given of being able to simultaneously optically and electrically interrogate individual cellular processes with spatial resolution.

We propose a bacterial detection scheme which uses no biochemical markers and can be applied in a Point-of-Care setting. The detection scheme aligns asymmetric bacteria with an electric field and detects the optical scattering.

We have invented a novel all-optical-logic microfluidic system which is automatically controlled only by visible or near infrared light with down to submilliwatt power. No electric power supply, no external or MEMS pump, no tubings or connectors, no microfluidic valves, nor surface patterning are required in our system. Our device only consists of a single-layer PDMS microfluidic chip and newly invented photoactive nanoparticles. Our photoactive nanoparticles are capable of converting optical energy to hydrodynamic energy in fluids. The nanoparticle themselves are biocompatible and can be biofunctionalized. Via these photoactive nanoparticles, we used only light to drive, guide, switch and mix liquid in optofluidic logic circuits with desired speeds and directions. We demonstrated the optofluidic controls in transportation of biomolecules and cells.

In this manuscript we describe the manipulation of surface plasmon polariton (SPP) modes excited in a two dimensional periodic nanohole array scattering structure by tuning the fluid over the metal surface. We describe the fabrication processes for making large area periodic nanohole arrays, and a soft lithography process for the addition of microfluidic channels. We then show the tuning of various modes and the application for such structures as multichannel, imaging SPP sensors.