We report on the optical activities of left-and right-handed micro-spirals fabricated in dichromate gelatin emulsions using a holographic interference technique involving six linearly polarized side beams and one circularly polarized central beam. Photonic bandgaps in the visible range are observed. More importantly, opposite optical activities - a polarization rotation of a few degrees and a circular dichroism (CD) of about 20% at the photonic band edges - are observed for the left-and right-handed spirals. Furthermore, the transmittance of circularly polarized light obeys the Lorentz reciprocity lemma for forward and backward incidence. However neither polarization rotation nor CD is observed for achiral split rings and hollow rods fabricated using all linearly polarized beams and six side beams without the central beam, respectively; this indicates that the chiral nature of the spirals is essential for the observed optical activities.
- chiral photonic band-gap materials
- microstructure fabrication
- optical activity
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics