Drexel University's Research Experiences for Teachers (RET)
Switchable Holographic Polymer Dispersed Liquid Crystals (HPDLCs) and Their Applications
This research is being pursued, as it has specific applications to:
replacing diffraction grating/prisms in optical spectrometers, improving
visual display technology (cell phones, TVs, computer monitors), and
acting as 'light switches' for transmission lines in the fiber optics
In the laboratory, the writer was shown how to prepare an HPDLC mixture, from its basic components: two polymers,a liquid crystal (LC), a light-sensitive initiator, and a surfactant. Since the mixture was photosensitive, all sample preparation had to be performed under red lighting. After preparation, the 532 nm laser was properly aligned, and the samples were exposed at 5 watts of power (sufficient to burn the retina) for a minute duration. By varying the incident angle of the beam, a Bragg grating of a specified pitch could be produced.
The exposed samples were then placed in an optical spectrometer to measure the percent transmittance, allowing the notch wavelength of the transmitted light to be determined for each grating pitch.
Wire leads were attached to the samples and they were stacked together, as though one were making a sandwich. A specified voltage potential was placed across one interface of the stack to allow the HPDLC to 'switch'. That is, the refractive indicies of the polymer and the LC match and allow more light to be transmitted under this potential.
A waveform analysis was performed on the samples to verify the
amount of light transmitted thought the switched stack.
Next summer, the writer hopes to return to Dr. Adam Fontecchio's laboratory to continue other investigations into electo-optics.