Kidger Optics Associates: Michael Kidger Memorial Scholarship: Awardees: Winner 2009

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Update 2010 At the time of this update, May 2010, Dewen continues as a visiting student at the College of Optical Sciences, University of Arizona, but anticipates returning to Beijing Institute of Technology sometime soon to work as a research scientist. "At present, I am working on a tiling, free-form prism eyepiece that helps to extend the field of view of a head-mounted display system while maintaining an acceptable resolution. Using the theory of canonical coordinates by H. H. Hopkins, I have proposed a method for the rapid and accurate fitting of wave aberration polynomials to optical systems without symmetry. I am also exploring control methods for local surface deformations to optimize free-form surfaces in imaging systems. In my current designs, I am using these control methods to further improve the performance of free-form imaging systems."
Award Year 2009 Dewen Cheng, a PhD candidate at the College of Optoelectronics, Beijing Institute of Technology was selected as the 2009 Michael Kidger Memorial Scholarship awardee. Dewen’s thesis supervisor, a Fellow of SPIE, is Professor Yongtian Wang of the Beijing Institute of Technology. Dewen is currently conducting his research work at the College of Optical Sciences, University of Arizona under a joint education program. Dr. Hong Hua of the University of Arizona is his co-supervisor. The award was presented at SPIE’s Optics+Photonics conference, 2 – 6 August 2009, San Diego Convention Center, San Diego, California by Andy Wood, Kidger Scholarship Committee Chairman. Dewen's first project concerned the development of a comprehensive program using CODE V’s COM interface, which facilitates the design and analysis of optical systems with complex aperture settings (such as large telescopes with segmented mirrors). With the help of this program, one can easily and efficiently set up a mirror or lens with various segmentation. The segments can be circular, polygonal or fan-shaped, and they can be described in great detail including chamfers and gaps among them. A built-in graphic window shows instantly a plot of the current aperture setup. The segments are depicted as non-sequential surfaces in CODE V, so that shape, decenter, tilt errors and tolerances can be specified individually for each segment. The program has been used successfully to design telescopes with segmented mirrors, to calculate fabrication tolerances and to study alignment strategy. Use of the program has greatly reduced the workload of setting up and verifying system models.

Further research work has focused on the design, analysis, fabrication and testing of imaging systems with free-form surfaces (FFS). Dewen successfully designed and prototyped an extremely compact and light-weight optical see-through, head-mounted display (HMD) with a wide field-of-view and a large numerical aperture using a FFS prism composed of three XY-Polynomial surfaces. He also designed a series of off-axis HMDs with a tilted free-form combiner and a miniature projector system with its light path folded by free-form mirrors to be used in a volumetric display system. Recently, Dewen has proposed a new optical tiling method for the design of a wide field of view, high resolution optical see-through HMD system. Although it is a difficult task to fabricate and test the free-form elements, progress has been made in building the first prototype.

During the design process of these systems, Dewen has developed several useful algorithms that greatly facilitate the design of free-form optical systems. These include a differential equation method to obtain the starting point of a FFS prism HMD design (which is one of the most challenging steps in achieving a viable FFS design), an automatic performance balance algorithm for different fields of view, a way to determine the best location for a special element (such as asphere, DOE, decentered and tilted element), a flexible scheme for FFS fitting, and a fast ray tracing algorithm for FFS. He is currently working on a method to design a free-form lens with predetermined input and output wavefronts.

Dewen Cheng receives
2009 Kidger Scholarship Award
from Committee Chairman Andy Wood
at SPIE’s Optics+Photonics Conference,
2–6 August 2009, San Diego, California.

Besides his main work on free-form optical systems, Dewen also designed several conventional optical systems with rotational symmetry, including an all plastic endoscope objective lens and a compact eyepiece with a large field of view and a large numerical aperture. The latter has been successfully manufactured.