Application and Design Developments in Diffractive Optics

Doctoral thesis, 2001

There has been strong development in the field of diffractive optics (DO) in research laboratories over the past two decades. Much progress has been made, both in design and analysis, as well as in manufacturing techniques. However, so far DO have only reached the market in small numbers. This thesis reports on new applications and design methods, which may hopefully contribute to the spread of DO in society. A multichannel diffractive optic rotary joint was designed, manufactured and evaluated regarding cross talk, uniformity and wavelength sensitivity. An experimental cross-talk margin of 25 dB was reached. A new ultra-fast analog-to-digital conversion scheme, based on diffractive optics, was proposed. The optical part of the converter was tested experimentally with satisfactory results. To give a DO device anti-reflection properties, a subwavelength relief grating was superimposed on it. The manufactured device displayed significantly reduced reflectivity. High-fidelity replication of such a DO will result in low-cost, high performance components. An existing 1 x 8 reconfigurable free-space optical switch, based on a ferro-electric liquid-crystal-on-silicon spatial light modulator, was modified to operate adaptively under PC control. Using feedback, optical connections were established and maintained, the system automatically adapting to changes in the environment. An iterative algorithm for design of speckle-free diffraction patterns was developed. Experiment confirmed the speckle-free behavior. The algorithm uses repeated Fourier transformations and gentle modifications of the field amplitudes. An existing design algorithm for fan-outs was modified so that the uniformity of the diffraction spot patterns becomes less susceptible to a manufacturing relief-depth error. The uniformity is valuable for instance in laser machining, multiple line laser lithography and biomedical fluorescent sensing applications.