Self-assembly approaches to photonic structures

Self-assembly of spherical colloids has been demonstrated as a simple and effective strategy for fabricating a variety of photonic structures that include photonic crystals, arrayed microlenses, and waveguides. Unlike the top-down fabrication techniques, self-assembly approaches can produce functional structures under ambient conditions of pressure and temperature without the need for costly instruments.; A confined self-assembly approach was developed to organize spherical colloids into highly ordered three-dimensional photonic crystals. Such colloidal photonic crystals can block the propagation of photons for a range of wavelengths along specific directions. The capability of this method has been demonstrated with monodispersed spherical colloids of various materials and a range of dimensions. The orientation of the crystals can be controlled by assembling the colloids against two-dimensional arrays of templates patterned in the surfaces of substrates. The colloidal crystals were further explored to fabricate inverse opals with complementary structures. Photonic bandgap properties of these crystals have been characterized by measuring their transmission and reflectance spectra.; Self-assembly of nonspherical building blocks may lead to the formation of photonic crystals that can prohibit a band of optical frequencies in all directions of propagation. As the first step along this direction, a general approach based on physical confinement and attractive capillary force has been developed to produce nonspherical building blocks with well-defined structures and dimensions. Complex aggregates such as polygonal and polyhedral clusters, zigzag or helical chains have been fabricated using monodispersed polymer or silica colloids.; Arrayed microlenses were fabricated by self-assembling monodispersed polymer colloids in two-dimensional arrays of cylindrical holes patterned on substrates. The spherical colloids were subsequently transformed into mushroom-shaped and then hemispherical microlenses by annealing the samples at elevated temperatures. The optical parameters of these microlenses could be precisely controlled by changing the annealing time.; The minimization of waveguiding structures would allow the fabrication of highly integrated lightwave circuits. A number of methods have been developed based on the self-assembly approaches, including coupled resonator optical waveguide constructed from arrays of plain colloids, plasmon waveguide built from arrays of gold@silica core-shell colloids, and photonic crystal waveguide generated by introducing line defects into a photonic crystal.