Xiaoqiang Zhu

Tunable focusing properties using optofluidic Fresnel zone plates.

A Fresnel zone plate (FZP) is a unique diffractive optical device and widely used in integrated optical systems such as interferometers and antennas. A traditional FZP utilizes solid materials and cannot be modulated in real time for desired focusing properties. This paper reports a tunable optofluidic FZP based on a solid-liquid hybrid structure. This FZP consists of two parts including a fast microfluidic mixer, which can adjust the refractive index of liquids from 1.332 to 1.432, and subsequently an optical FZP with a solid-liquid combination. Simulations and experiments successfully showed the real-time tunability of the focusing properties such as peak intensity, focal spot sizes and focal lengths. The focal spot size can be modulated from 16 μm to 80 μm at λ0 = 532 nm in experiments with focal length changes of approximately 700 μm. Moreover, it can be easily switched between focusing, defocusing and collimation. The dispersion with different wavelengths was also investigated, showing that these types of focusing properties are quite different from a traditional optofluidic lens by refraction or reflection. It is foreseeable that such a hybrid FZP may find wider applications in lab-on-a-chip systems and optical devices.

Light Manipulation in Inhomogeneous Liquid Flow and Its Application in Biochemical Sensing

Light manipulation has always been the fundamental subject in the field of optics since centuries ago. Traditional optical devices are usually designed using glasses and other materials, such as semiconductors and metals. Optofluidics is the combination of microfluidics and optics, which brings a host of new advantages to conventional solid systems. The capabilities of light manipulation and biochemical sensing are inherent alongside the emergence of optofluidics. This new research area promotes advancements in optics, biology, and chemistry. The development of fast, accurate, low-cost, and small-sized biochemical micro-sensors is an urgent demand for real-time monitoring. However, the fluid flow in the on-chip sensor is usually non-uniformed, which is a new and emerging challenge for the accuracy of optical detection. It is significant to reveal the principle of light propagation in an inhomogeneous liquid flow and the interaction between biochemical samples and light in flowing liquids. In this review, we summarize the current state of optofluidic lab-on-a-chip techniques from the perspective of light modulation by the unique dynamic properties of fluid in heterogeneous media, such as diffusion, heat transfer, and centrifugation etc. Furthermore, this review introduces several novel photonic phenomena in an inhomogeneous liquid flow and demonstrates their application in biochemical sensing.

Gold nanoparticle sorting based on optofluidics

Gold nanoparticles have very unique physical, chemical and biological characters, which makes them have widespread applications in many fields. Sorting gold nanoparticles with different size is of great importance because the unique properties of gold nanoparticles relate with their sizes extremely close. Optical sorting is an excellent way due to much better sorting precision compared with the traditional sorting methods. In this paper, a new chip design sorting gold nanoparticles is presented and results of sorting two different nanoparticles have been analyzed as well. Mie theory is used to calculate the optical force of nanoparticles in different diameter, and finite element analysis is used to analysis the variation of flow field and sorting process of gold nanoparticles.

Tunabe liquid transformation optical waveguide bends

Optical waveguide bend is indispensable to integrated optical systems, and thus many methods have been proposed for better bending effect. In an optical waveguide bends, transformation optics (TO) makes light travel along the curve bend just as if it were propagating in a straight waveguide, which can eliminate so-called bend loss. Many reported TO waveguide bends made use of solid materials, causing fundamental difficulties for real applications due to the hindrances of complex fabrication, lack of reconfiguration and so-called effective medium condition. Here, we develop a unique method by the convective diffusion of liquids to overcome the current problems. For the first time, it enables the real-time tunable transformation optical waveguide bends using the natural liquid diffusion, while it still inherits the major merits of the quasi-conformal mapping. We have experimentally demonstrated the bend of visible light by 90 and 180 degrees while preserving the intensity profile at a reasonably high level of fidelity. This work broadens the realm of fluid dynamic and optics, and has potential for the applications in on-chip biological, chemical and biomedical measurements and detections and tunable optical systems.