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Protein Bacteriorhodopsin (bR) is one of the most promising and widely studied biomaterials for photonic applications
like optical storage, modulation devices and photosynthetic light energy transduction. In this paper, we present the
corresponding experimental results when pH-controlled modifications of bR doped polymeric films are realized in order
to apply these systems to all-optical switching processes and technologies.
In this work, the performance of wild type bR processed in polymeric films with different pH was tested in several series
of experiments by varying the pump beam (532 nm) period of ON and OFF and analyzing the amplitude contrast and
switching time of the probe beam (633 nm). The influence of pH values on contrast ratio and switching time were also
discussed and the optimal value was found by defining a new parameter called "switching speed". As a result, the
variation of pH can be used to obtain different time of response and speed of modulation. Concretely, we find that, in
function of pH, variations of a magnitude order in contrast ratio and time response can be obtained. So, at the red region
of the probe beam, high pH values produce high transmission with flat response in the contrast ratio and a magnitude
order variation in switching time. On the other hand, at medium pH values and when high intensities are used, the
switching time and contrast ratio are better. Moreover, it is demonstrated that as a function of the wavelength of the
probe beam the transmission response curve changes. Absorption response is very important and depends on relaxation
time processes of intermediate species which are function of pH values. Therefore, these results bring the possibility for
controlling the contrast ratio and the switching time in a specific way which could be useful for different applications.
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