Chaolong Song

Biconcave micro-optofluidic lens with low-refractive-index liquids

One of the current problems of micro-optofluidics is the choice of a suitable liquid with a high refractive index (RI). We report the use of a low-RI liquid in a biconcave liquid-core liquid-cladding lens for focusing light. For the characterization of the lens, a telescope system was constructed from polydimethylsiloxane lenses to collimate and expand a light beam emitted from an optical fiber. The tunable optofluidic biconcave lens focuses the parallel beam. Fluorescent dye diluted in an index-matching liquid was used for the visualization of the light rays in a beam-tracing chamber. The focused beam is tuned by adjusting the flow rate ratio between core and cladding streams.

Disposable flow cytometer with high efficiency in particle counting and sizing using an optofluidic lens

Flow cytometers are widely applied to environmental monitoring, industrial testing, and biochemical studies. Integrating a flow cytometer into microfluidic networks helps to miniaturize the system and make it portable for field use. The integration of optical components, such as lenses, further improves the compactness and thus has been intensively studied recently. However, the current designs suffer from severe light scattering due to the roughness of the solid-based lens interface. In this Letter, we propose a flow cytometer using an optofluidic lens to focus the light beam. Benefiting from the smooth liquid-liquid lens interface and the refractive-index matching liquid as cladding streams, a light beam can be well focused without scattering. The variations of the signal peak values are reduced, owing to the small beam width at the beam waist. The device presents an efficient and accurate performance on both the counting and sizing of particles.

Tunable micro-optofluidic prism based on liquid-core liquid-cladding configuration.

The integration of optical components into microfluidic systems has the potential to reduce the amount of bulky external devices and thus reduce the cost. However, one of the challenges of this concept is the accurate alignment of the optical path among multiple optical components inside a chip. We propose a tunable micro-optofluidic prism based on the liquid-core liquid-cladding structure formed in a sector-shape chamber. The optical interface of the prism is maintained in a straight line shape by distributing a row of pressure barriers in the chamber. By adjusting the flow rate ratio between core and cladding streams, the apex angle of the prism can be tuned accordingly. As a consequence, the deviation angle of the light beam refracted by the prism can be changed continuously. This tunability of our optofluidic prism can be utilized for the alignment of the optical path inside a chip or for the development of optical switches.

An electrokinetically tunable optofluidic bi-concave lens

This paper numerically and experimentally investigates and demonstrates the design of an optofluidic in-plane bi-concave lens to perform both light focusing and diverging using the combined effect of pressure driven flow and electro-osmosis. The concave lens is formed in a rectangular chamber with a liquid core-liquid cladding (L(2)) configuration. Under constant flow rates, the performance of the lens can be controlled by an external electric field. The lens consists of a core stream (conducting fluid), cladding streams (non-conducing fluids), and auxiliary cladding streams (conducting fluids). In the focusing mode, the auxiliary cladding stream is introduced to sandwich the biconcave lens to prevent light rays from scattering at the rough chamber wall. In the diverging mode, the auxiliary cladding liquid has a new role as the low refractive-index cladding of the lens. In the experiments, the test devices were fabricated in polydimethylsiloxane (PDMS) using the standard soft lithography technique. Ethanol, cinnamaldehyde, and a mixture of 73.5% ethylene glycol and 26.5% ethanol work as the core stream, cladding streams and auxiliary cladding streams. In the numerical simulation, the electric force acts as a body force. The governing equations are solved by a finite volume method on a Cartesian fixed staggered grid. The evolution of the interface was captured by the level set method. The results show that the focal length in the focusing mode and the divergent angle of the light beam in the diverging mode can be tuned by adjusting the external electric field at fixed flow rates. The numerical results have a reasonable agreement with the experimental results.

Tunable optofluidic aperture configured by a liquid-core/liquid-cladding structure

Miniaturized and tunable optical components, such as the waveguide, lens, and prism, have been of great interest for lab-on-chip systems. This Letter reports an optofluidic aperture stop formed by the liquid-core/liquid-cladding flow. The aperture size can be tuned accordingly by adjusting the flow rates. Manipulation of the aperture size allows control of the amount of light passing through the corresponding optical system as well as the angular aperture on the image side. This optofluidic aperture enables lab-on-chip optical systems to have a greater flexibility and more functionalities.

A micro optofluidic lens with short focal length

A micro optofluidic lens is formed by laminar streams of immiscible liquids with different refractive indices. This paper reports modelling and characterization for a new design of a micro optofluidic lens. The lens has a circular chamber allowing the formation of interfaces with a perfect arc shape. The inlet and the outlet of the lens chamber are placed with an offset to the chamber axis to achieve a radius of curvature smaller than the limiting chamber radius. A model mathematically predicts the relationship between the flow rate ratio and the curvature of the interface and the resulting focal length. The device was fabricated and tested with laser light guided by optical fibres. Experiments were carried out to verify the analytical model. Benzyl alcohol and ethylene glycol were used as optical media to form the lens. Due to the small radius of curvature, better focusing ability than the previous symmetric design was achieved. On-chip focusing with fibre-to-fibre transmission was demonstrated with this micro optofluidic lens.

A Perspective on the Rise of Optofluidics and the Future

In the recent past, the field of optofluidics has thrived from the immense efforts of researchers from diverse communities. The concept of optofluidics combines optics and microfluidics to exploit novel properties and functionalities. In the very beginning, the unique properties of liquid, such as mobility, fungibility and deformability, initiated the motivation to develop optical elements or functions using fluid interfaces. Later on, the advancements of microelectromechanical system (MEMS) and microfluidic technologies enabled the realization of optofluidic components through the precise manipulation of fluids at microscale thus making it possible to streamline complex fabrication processes. The optofluidic system aims to fully integrate optical functions on a single chip instead of using external bulky optics, which can consequently lower the cost of system, downsize the system and make it promising for point-of-care diagnosis. This perspective gives an overview of the recent developments in the field of optofluidics. Firstly, the fundamental optofluidic components will be discussed and are categorized according to their basic working mechanisms, followed by the discussions on the functional instrumentations of the optofluidic components, as well as the current commercialization aspects of optofluidics. The paper concludes with the critical challenges that might hamper the transformation of optofluidic technologies from lab-based procedures to practical usages and commercialization.

Optical alignment of a cylindrical object

This paper reports the use of theory of geometrical optics to analyze how an optical field interacts with a cylindrical object. Of great interest is the mechanism with which a laser beam with a special profile manipulates a particle which has a similar shape as the beam profile. The present paper investigates the interaction between a cylinder-shape fiber and a laser beam with a line-shape profile. Based on the Fresnel equation, a numerical model was formulated to describe the optical torque generated by a projected line-shape optical image. The drag force was also considered in the model to accurately describe the fibers movement in a liquid. A differential equation is established to describe this damped movement of the cylinder. Parametric analysis was carried out to investigate the influence of the beam power and the liquid viscosity as well as the density, the length, and the diameter of the cylindrical object. The movement of a carbon fiber was measured with a CCD camera. The observed experimental results agree well with the theoretical results.

Tunable multi-functional optofluidic biconcave lens

Recently using the integrated micro-lens to improve the fluorescence detection in microfluidic systems has been intensively studied. This paper describes the design and demonstration of an optofluidic in-plane bi-concave lens to perform both light focusing and diverging. In both focusing and diverging mode, the optical properties of the lens can be tuned by adjusting the flow rate. Numerical simulation and experiment are conducted and the results are compared. Our device shows a good tunability.

A Micro Optofluidic System for Counting and Size Measurement of Particles

This paper reports the integration of a biconvex micro optofluidic lens into a flow cytometer. The complex optofluidic and microfluidic channel networks are integrated on a single chip. Flow cytometers are widely applied to environmental monitoring, industrial testing and biochemical studies. Integrating a fow cytometer into microfluidic networks helps to miniaturize the system and make it portable for field use. The integration of optical components, such as lenses, further improves the compactness and thus has been intensively studied recently. However, the current designs suffer from severe light scattering due to the roughness of the solid-based lens interface. In this paper, we propose a micro optofluidic system using an optofuidic liquid lens to focus the light beam. Benefting from the smooth liquid-liquid lens interface and the refractive index matching liquid as cladding streams, a light beam can be well focused without scattering. The variations of the signal peak values are reduced owing to the small beam width at the beam waist. Compared to the macroscale systems and microscale systems with solid lenses, the device presents a more efficient and accurate performance on both counting and sizing of particles. The paper reports an analytical parametric study of the lens, followed by the experimental performance of the cytometer. The cytometer was able to detect and discriminate particles with different sizes.Copyright