Micromirror array phase modulator for ultrashort optical pulse shaping

The methods developed during the last decade to generate and shape ultrashort optical pulses have formed several useful applications. A very critical component of the ultrashort optical pulse shaper is the programmable spatial light phase modulator (SLPM). The objective of this research is to explore a new programmable SLPM using a micromirror array.; We present a new micromirror array SLPM in which both the tilt and vertical displacements is controlled on each mirror. Vertical displacement of the mirror introduces the desired phase shift for each pixel while mirror tilt allows a piecewise linear approximation to the local phase variation. Our phased array effectively combines the capability for producing phase discontinuities while significantly reducing undesired sidebands associated with perfectly smooth phase filters.; A numerical simulation was developed to visualize the shaping of ultrashort pulse by the micromirror array. It also provides a helpful tool when we compare our new piecewise linear phase modulation approach with the existing stepwise phase modulation. We also demonstrated several dual-mode micromirror structure designs for the SLPM array. An on-chip reference mirror was designed for interferometric measurement of the arbitrary phase of the moving mirror, it reduces the sensitivity to the mircromirror array vibration when doing real-time monitoring. We give an analytical derivation of the phase retrieval algorithm. Based on that algorithm, a data analysis program was developed to retrieve the movable mirror motion, both tilt and vertical displacement from one measurement. We also experimentally demonstrated the coherent behavior of the micromirror array by turning a coarse brazed grating (when all the mirrors tilted the same angle) into a single tilting mirror. This is possible only when the mirrors have both tilt and vertical displacement control. Limitations of this MEMS SLPM are also given together with the possible solutions and future work.