A reconfigurable plasmofluidic lens

A1: A reconfigurable plasmofluidic lens

Figure: Schematic of the reconfigurable plasmofluidic lens, wherein a laser-induced surface bubble is used to control the propagation of SPPs at the metal surface. (c–e) Surface bubbles with different diameters (18, 14 and 6 microns, respectively) generated on the gold film. The white dashed circle represents the surface bubble boundary on gold film. Scale bar, 10 microns.

Plasmonics provides an unparalleled method for manipulating light beyond the diffraction limit, making it a promising technology for the development of ultra-small, ultra-fast and power-efficient optical devices. To date, the majority of plasmonic devices are in the solid state and have limited tunability or configurability. Moreover, individual solid-state plasmonic devices lack the ability to deliver multiple functionalities. Here we utilize laser-induced surface bubbles on a metal film to demonstrate, for the first time, a plasmonic lens in a microfluidic environment. Our ‘plasmofluidic lens’ is dynamically tunable and reconfigurable. We record divergence, collimation and focusing of surface plasmon polaritons using this device. The plasmofluidic lens requires no sophisticated nanofabrication and utilizes only a single low-cost diode laser. Our results show that the integration of plasmonics and micro- fluidics allows for new opportunities in developing complex plasmonic elements with multiple functionalities, high-sensitivity and high-throughput biomedical detection systems, as well as on-chip, all-optical information processing techniques.

Reference: Chenglong Zhao, Yongmin Liu, Yanhui Zhao, Nicholas Fang, and Tony Jun Huang, A Reconfigurable Plasmofluidic LensNature Communications, Vol. 4, pp. 2305, 2013.[PDF]

A2: Tunable optofluidic cylindrical microlens

Figure: The 3D architectures of water flow obtained with confocal microscopy at the flow rates of (a) 100 ml min21 , (b) 150 ml min21 , and (c) 250 ml min21 . Images in (d–f) show the corresponding CFDsimulated 3D fluidic interfaces (isosurface of CaCl2 concentration = 2.5 M).

We report the design, fabrication, and characterization of a tunable optofluidic microlens that focuses light within a microfluidic device. The microlens is generated by the interface of two co-injected miscible fluids of different refractive indices, a 5 M CaCl2 solution (nD = 1.445) and deionized (DI) water (nD = 1.335). When the liquids flow through a 90-degree curve in a microchannel, a centrifugal effect causes the fluidic interface to be distorted and the CaCl2 solution bows outwards into the DI water portion. The bowed fluidic interface, coupled with the refractive index contrast between the two fluids, yields a reliable cylindrical microlens. The optical characteristics of the microlens are governed by the shape of the fluidic interface, which can be altered by simply changing the flow rate. Higher flow rates generate a microlens with larger curvature and hence shorter focal length. The changing of microlens profile is studied using both computational fluid dynamics (CFD) and confocal microscopy. The focusing effect is experimentally characterized through intensity measurements and image analysis of the focused light beam, and the experimental data are further confirmed by the results from a ray-tracing optical simulation. Our investigation reveals a simple, robust, and effective mechanism for integrating optofluidic tunable microlenses in lab-on-a-chip systems.


Reference: Xiaole Mao, John Robert Waldeisen, Bala Krishna Juluri, Tony Jun Huang, Hydrodynamically Tunable Optofluidic Cylindrical MicrolensLab on a Chip, Vol. 7, pp. 1303-1308, 2007. [PDF