We introduce a thin-film spectrometer that is based on the superprism effect in photonic crystals. While the reliable fabrication of two and three dimensional photonic crystals is still a challenge, the realization of one-dimensional photonic crystals as thin-film stacks is a relatively easy and inexpensive approach. Additionally, dispersive thin-film stacks offer the possibility to custom-design the dispersion profile according to the application. The thin-film stack is designed such that light incident at an angle experiences a wavelength-dependent spatial beam shift at the output surface. We propose the monolithic integration of organic photo detectors to register the spatial beam position and thus determine the beam wavelength. This thin-film spectrometer has a size of approximately 5 mm2. We demonstrate that the output position of a laser beam is determined with a resolution of at least 20 μm by the fabricated organic photo detectors. Depending on the design of the thin-film filter the wavelength resolution of the proposed spectrometer is at least 1 nm. Possible applications for the proposed thin-film spectrometer are in the field of absorption spectroscopy, e.g., for gas analysis or biomedical applications.
Photonic crystal superprism structures exhibit a rapid change in the group propagation direction with wavelength. For a fixed wavelength, a small change of the refractive index in a superprism structure also results in a rapid change of the group propagation direction. We present a theoretical investigation of switching in active one-dimensional photonic nanostructures with coupled defects (cavities). This switch can be realized as a multilayer thin-film stack or alternatively in a planar waveguide geometry. The device will allow the switching of an incident laser beam to one of N output positions using either electro-optical or all-optical effects. We consider organic optically nonlinear layers, since organic materials show large nonlinear effects and fast switching times. The proper design of the layer structure is a key component for optimizing the performance of the device. We investigate the most effective position for the integrated nonlinear layers. The active layers can be placed inside the cavities or they can serve as coupling layers between cavities. Both approaches are evaluated with respect to performance parameters such as switching energy and necessary number of layers.
Thin-film stacks exhibiting a high spatial dispersion similar to the photonic crystal superprism effect can be employed to multiplex or demultiplex several wavelength channels using a single thin-film stack. The phase properties of these stacks are designed such that a small change in the wavelength results in a large change of the effective group propagation angle and therefore of the beam exit position for light beams of oblique incidence angle. Here we demonstrate that such a structure also exhibits a large change in the exit position for a fixed incident wavelength due to a small refractive index variation. We investigate theoretically the introduction of optically nonlinear polymer layers into multilayer thin-film structures for electro-optic switching of the refractive index. Polymers offer a number of advantages as nonlinear materials - they are simple to process, they show high, non-resonant nonlinear coefficients and they posses low refractive indices. A dispersive thin-film stack containing tunable polymer layers is therefore promising as a 1:N spatial beam switch with switching times in the nanosecond range. We developed and simulated different designs for dispersive thin-film stacks consisting of dielectric and polymer layers. The approaches range from Bragg stacks with two alternating materials, one of them the active polymer, over impedance matched Bragg stacks to coupled cavities that contain the active material. The achievable refractive index changes with guest-host polymer systems were evaluated and integrated into our calculations.