Nonimaging Optical Gain in Luminescent Concentration through Photonic Control of Emission Étendue

Luminescent and nonimaging optical concentration constitute two fundamentally different ways of collecting and intensifying light. Whereas nonimaging concentrators based on reflective, refractive, or diffractive optics operate most effectively for collimated light, luminescent concentrators (LCs) rely on absorption, re-emission, and waveguiding to concentrate diffuse light incident from any direction. LCs have been explored in many different shapes and sizes but have so far been unable to exploit the power of nonimaging optics to further increase their concentration ratio because their emission is angularly isotropic. Here, we use a luminescent thin film bilayer to create sharply directed conical emission in an LC and derive a nonimaging optical solution to leverage this directionality for secondary geometric gain ranging up to an order of magnitude or higher. We demonstrate this concept experimentally using a custom compound parabolic optical element index-matched to the LC surface and show that it delivers three times more luminescent power to an opposing GaAs photovoltaic cell when the emission profile is conically directed than when it is isotropic or the nonimaging optic is absent. These results open up a significant and general opportunity to improve LC performance for a variety of applications including photovoltaics, photobioreactors, and scintillator-based radiation detection

Passive Parity-Time Symmetry in Organic Thin Film Waveguides

Periodic media are fundamentally important for controlling the flow of light in photonics. Recently, the emerging field of non-Hermitian optics has generalized the notion of periodic media to include a new class of materials that obey parity-time (PT) symmetry, with real and imaginary refractive index variations that transform into one another upon spatial inversion, leading to a variety of unusual optical phenomena. Here, we introduce a simple approach based on interference lithography and oblique angle deposition to achieve PT-symmetric modulation in the effective index of large area organic thin film waveguides with the functional form Δ<i>ñ</i>_eff(<i>z</i>) ∼ <i>e</i>^<i>iqz</i>. Passive PT symmetry breaking is observed through asymmetry in the forward and backward diffraction of waveguided light that maximizes at the exceptional point, resulting in unidirectional reflectionless behavior that is visualized directly via leakage radiation microscopy. These results establish the basis for organic PT waveguide media that can be tuned for operation throughout the visible to near-infrared spectrum and provide a direct pathway to incorporate gain sufficient to achieve active PT symmetric lattices and gratings