Optical microcavity experiments using high dielectric contrast mirrors

Abstract

An ideal laser has near-zero threshold, unity quantum efficiency, narrow spectral linewidth, high modulation rate, and controllable photon statistics. It can be realized with use of microresonators whose optical cavity lengths are on the order of a wavelength. Laser optical microresonators are now made with more than 10 alternating layers of two materials, which have an optical reflective index ratio of 3.5/3.0. Because of the many layers required, these resonators have long effective cavity lengths. To obtain shorter cavity lengths, high index contrast materials must be used. This is currently achieved by deposition of nonepitaxial layered materials (e.g., ZnS and SiO2). Such techniques can be used for the top mirror of an optical cavity enclosing an active layer grown by molecular beam epitaxy (MBE) but not for the bottom mirror. Here, we report new fabrication techniques that are compatible with the MBE method. The techniques involve selectively etching layered AlxGa1−xAs materials grown by MBE and then replacing the etched regions with acrylic polymers or air. The replacement techniques involve the use of a low-viscosity acrylic and carbon-dioxide critical-point drying apparatus that is commonly used in histological studies. The resulting mirror structures have index contrast ratios of 3.5/1.5 and 3.5/1.0, respectively. Related experiments on controlled spontaneous emission and low laser thresholds will also be reported.