Rajesh V. Nair

Three-dimensionally ordered photonic crystal heterostructures with a double photonic stop band

The recently reported inward growing self-assembling method is used to fabricate photonic crystal heterostructures in less than 6h using polymeric colloidal suspensions. Structural characterization shows good ordering of the two types of photonic crystals constituting the heterostructure. The reflection/transmission spectra measured from the (111) plane of the heterostructure clearly demonstrate the signature of the double photonic stop band. The reduction in the reflectance values obtained for the heterostructure is explained in terms of the interface roughness. The double photonic stop band of the heterostructures exactly matches the stop bands of the individual photonic crystals.

Emission studies on photonic crystals fabricated using dyed polystyrene colloids

Three dimensionally ordered photonic crystals are fabricated with rhodamine B dyed polystyrene colloidal spheres using the inward growing self-assembling method in less than 3 h. This avoids the difficulties due to infiltration of active materials into passive photonic crystals. The superior optical quality of the photonic crystals fabricated using this method results in high reflectance values even at large angles of incidence. The study of emission characteristics on these functionalized photonic crystals shows a clear trend dependent on the angle of emission, wavelength, and the angle-resolved transmittance. The dip observed in the emission spectrum clearly matches the photonic stop band position at different angles of observation. The emission spectrum measured at different angles was found to follow a simple functional form related to the intrinsic emission of the dye and the stop band effect due to the photonic crystal environment.

Infiltration of ZnO in polymeric photonic crystal by the sol-gel process

Three-dimensionally ordered photonic crystals were fabricated using the vertical self-assembly method from colloidal polystyrene spheres of sub-micrometre diameters. Structural and optical characterization results indicate the extent of good ordering present in these samples. The photonic stop band was tuned by infiltrating two important oxide materials, namely, SiO2 and ZnO. Infiltration was done using a low cost room-temperature sol?gel process which does not require any sophisticated instrumentation. The optical measurements clearly demonstrate that the infiltration is significant. The experimentally measured values of wavelength shift and peak reflectance were compared with theoretically estimated values and found to be in good agreement.

Optical properties of functionalized polymeric photonic crystals

We present a systematic analysis of three dimensionally ordered photonic crystals made of dyed-polystyrene spheres fabricated using the newly reported inward growing self assembling method. The SEM and AFM images show good ordering of the spheres with (111) plane parallel to the substrate. The photonic stop band is tuned by varying the angle of incidence of light and made to coincide with the emission wavelength of the dyes. The multiple Bragg diffraction effects observed at high angles of incidence are interpreted. The high reflectance values obtained along with the observation of the higher order bands, and the photonic stop band splitting at high angles of incidence show the superior quality of the photonic crystals fabricated using these dyed polystyrene spheres in less than three hours.

Multiple Bragg diffraction in polymeric photonic crystals

A systematic study of the angle-resolved photonic stop band of three-dimensionally (3D) ordered polymeric photonic crystals fabricated using a colloidal self-assembling method is presented. The first-order photonic stop band shows a single peak in reflection and shifts toward shorter wavelengths for larger angles of incidence. Beyond an angle of incidence of 45 degrees , a new peak arises in the reflection spectrum due to the coupling of the incident light into other directions of the fcc Brillouin zone. The predominant contribution is identified as being due to reflection from the (200) plane.