Adaptive Correction to the Speckle Correlation Fringes using twisted nematic LCD

Conclusion

Theory, simulation and experimental investigation has shown the feasibility of improving speckle fringe patterns by modulating the I_M values pixelwise with an amplitude-only LCD SLM. From Fig. 9c we can see that without adaptive modulation the intensity in the central region of the fringe pattern is saturated and the fringes at the rim area are rather weak. In contrast, from Fig. 9d we note that the fringe pattern after adaptive modulation is much more homogeneous, and fringes are also discernible along the rim area. This can be understood from the histograms in Figs. 9e and 9f of the marked bright fringes in figs. 9a and 9b respectively. Most of the pixels are clustered close to zero grey value in Fig. 9e resulting in a weak appearance of the fringe whereas the pixels in Fig. 9f have a broad spectrum of values leading to a better quality fringe pattern. The SNR has been improved significantly. Complete reduction of the spectrum to a single value was not possible with our LCD SLM because of the limitation of its dynamic range.