Technology of silicon-based liquid crystal wavefront correctors (DOE.5490)

The project aims to development of novel low-cost wavefront correctors for science, industry, medicine and astronomy. Everyone has seen LC intensity modulators in wristwatches, displays of laptop computers etc. Phase modulators are different from just mentioned LC displays: they do not change the intensity of the light; instead they change the phase of transmitted light. Selective control of the spatial distribution of the phase of transmitted (reflected) light is the basis of all imaging optical systems - any lens changes the phase of light according to the quadratic law. Liquid crystal devices allow for dynamic control of the phase distribution and having quite fast response time, they are very attractive for adaptive optics. An adaptive optics system uses a wavefront phase corrector with electronic feedback control, which corrects the distorting effects of the atmospheric and other phase aberrations, and therefore produces compensated high-quality real-time images. Recently only a few major astronomical observatories used adaptive optics, but the technology is rapidly developing and currently includes non-astronomical applications, such as laser technology, metrology, confocal microscopy and ophthalmology [1].

Using technology similar to LC display technology, large array of phase modulators can be designed to precisely control the shape of optical wavefront in real time. Reflective LC wavefront correctors with silicon active matrices consisting of 512x512 pixels are produced already. However, the large number of pixels requires very expensive and bulky control electronics, narrowing the field of potential application.

Optical wavefronts are traditionally represented by continuous smooth functions such as astigmatism, defocus, coma etc. Pixelated devices are badly suited for compensation of optical aberrations. For instance to produce a high quality lens with a variable focal distance, thousands of individually controlled pixels will be required, while in principle variable control of only one parameter in a wavefront corrector with MODAL response will be sufficient to produce a high-quality adaptive lens.
Modal approach described in [2,3] makes it possible to form smooth and continuous wavefront using rather limited number of control channels. The design of such a LC corrector of the wavefront will be quite different from the traditional pixelated LC device. We propose to use a combination of

1. Special configuration of the electrode structure integrated in the silicon chip;
2. Special shape of the AC meander driving voltage applied to the control electrode.

Since the local phase delay produced by the LC modulator depends only on the rms value of the applied AC voltage, a very smooth distribution of rms control voltage, producing precisely the required aberration, can be created by simple combination of two mentioned factors. This method of control can be realised by purely digital electronics integrated together with optical LC part of the device in a single silicon chip.

To get a low-cost and compact integrated optoelectronic device for fine-scale wavefront correction we propose to develop the technology of low-cost modal LC corrector with active silicon backplane.
(See also the parallel project DOE.5375)

More information can be found at the website of the optical microsystems group.

Er zijn vijf bedrijven bij dit project betrokken.