Weisong Wang

Date of Award

Spring 2004

Document Type


Degree Name

Doctor of Philosophy (PhD)


Micro and Nanoscale Systems

First Advisor

Khodadad Varahramyan


The objective of this work is to develop a gradient refractive index structure based on polymer materials and different actuation mechanisms by microfabrication techniques, nanotechnology and electrochemical methods for optical lens applications.

The polymer lens is one of the most promising alternatives to traditional glass lenses due to its varieties of advantages, such as low-cost and desirable mechanical properties (flexible and not fragile). Lenses with gradient refractive index (GRIN) can largely reduce the aberration and simplify the focusing system. For practical applications, it is necessary to reduce the fabrication cost as well as to improve the lens' performance by developing a polymer based GRIN structure. An actuated GRIN lens system could largely simplify the optical structure and easily change the focal point for a multi-focal system. In this work a novel method has been developed to make GRIN structure. Two actuation mechanisms have been investigated and developed for polymer optical lens applications.

Firstly, a flexible Polydimethylsiloxane (PDMS) microlens with a microfluidic chip has been fabricated by combining conventional lithography technology and a novel three dimensional fabrication technique. A novel PDMS mold transfer has been developed to realize mass production of PDMS microlens. The size of PDMS microlens ranges from 300 μm to 1500 μm in diameter. The PDMS microlens is integrated with a microfluidic chip. A variable focal microlens system has been accomplished with the aid of microfluidic actuation. The back focal length of this system can vary from 16.4 mm to 3.815 mm.

Subsequently, a novel application of the electrophoresis method has been investigated to form gradient refractive index structure in hydrogel. This technique relies on charged nanoparticles and the matrix structure of hydrogel to obtain the distribution of nanoparticles in hydrogel materials. Various analysis methods are employed, including X-ray photoelectron spectroscopy (XPS) and fluorescent microscopy, to characterize the structure made. The analyzed results have shown that electrophoresis is a good and effective technique to form gradient refractive index structure. From the refractive index measurement results, a higher density of nanoparticles has resulted in a higher value of refractive index. This method will greatly help in developing a polymer based GRIN lens in the future with further research work.

In order to achieve dynamically wide-view angle for polymer lens system, a dielectric elastomer actuation mechanism has been investigated for optical applications. PDMS film shows good performance when subjected to high voltage. The response time is much faster than for a microfluidic powered lens system. The manner in which the voltage affects the deformation of PDMS films is also characterized and discussed in this work.