Vertical hybrid microcavity based on a polymer layer sandwiched between porous silicon photonic crystals

Abstract

A vertical hybrid microcavity is fabricated by sandwiching a polymer layer between distributed Bragg reflectors ͑DBRs͒ composed of porous silicon photonic crystals. The DBRs are made by electrochemical etching of Si and consist of alternating porous Si layers of high and low porosity, the top DBR being a freestanding film. The hybrid microcavity demonstrates a deep microcavity mode placed within a 200 nm wide photonic band gap, and reveals a many-fold enhancement of the third-order nonlinearity of the microcavity layer. The fabrication technique employed is rather simple, enabling the use of a variety of functional materials as the microcavity spacer. © 2009 American Institute of Physics. ͓doi:10.1063/1.3245319͔One of the most attractive features of microcavity ͑MC͒ photonic band gap ͑PBG͒ structures is the localization of optical field in the MC layer at the wavelength resonant to the MC mode. At such wavelength, the local optical field strength is Q times enhanced with respect to that of the incident wave, Q being the MC quality factor. If the MC layer is made out of a functional material, this phenomenon enables to enhance drastically all optical field-dependent effects that this material presents, such as linear and nonlinear absorption, 1,2 optical harmonics generation, 3 nonlinear magneto-optical effects, 4 and luminescence. 5 Hence composite MCs with a functional MC layer are very attractive photonic structures for potential applications in optoelectronic devices.Up to now, two main technological approaches are considered for the fabrication of functional vertical MCs. The first one is the deposition of the multilayered distributed Bragg reflectors ͑DBRs͒ and of the MC layer in a single technological process, 4,6 while the second one is the infiltration of a porous MC template by functional materials. [7][8][9][10] These approaches have a common disadvantage which relates to the restriction of the set of functional materials which can be employed for infiltration in nanoporous templates or for the deposition of conjugated layers. One more possibility is the fabrication of one-dimensional hybrid MC based on the separate fabrication of the bottom DBR and of the MC layer. So far, using this approach, only thick metal layer such as aluminum or silver can be used as the top mirror in these structures, 11,12 which leads to a low MC quality factor. In this paper, the successful fabrication of a compact functional MC is shown, based on the separate composition of porous silicon DBRs, the top one being a freestanding film, and a spin-coated polymer MC layer. Such a technique results in the fabrication of a viable structure exhibiting a wide PBG, containing a narrow MC mode, which leads to a many-fold enhancement of the third-order nonlinearity of the polymer MC layer. This Si-compatible technology is rather simple, inexpensive and enables the use of a variety of functional materials such as dyes, chromophores or nanoparticles, which can be immobilized in a polymer-based MC.Porous silicon DBRs are fabricated by ele...