Reflection occurs at an air-material interface. The development of antireflection schemes, which aims to cancel such reflection, is important for a wide variety of applications including solar cells and photodetectors. Recently, it has been demonstrated that a periodic array of resonant subwavelength objects placed at an air-material interface can significantly reduce reflection that otherwise would have occurred at such an interface. Here, we introduce the theoretical condition for complete reflection cancellation in this resonant antireflection scheme. Using both general theoretical arguments and analytical temporal coupled-mode theory formalisms, we show that in order to achieve perfect resonant antireflection, the periodicity of the array needs to be smaller than the free-space wavelength of the incident light for normal incidence, and also the resonances in the subwavelength objects need to radiate into air and the dielectric material in a balanced fashion. Our theory is validated using first-principles full-field electromagnetic simulations of structures operating in the infrared wavelength ranges. For solar cell or photodetector applications, resonant antireflection has the potential of providing a low-cost technique for antireflection that does not require nanofabrication into the absorber materials, which may introduce detrimental effects such as additional surface recombination. Our work here provides theoretical guidance for the practical design of such resonant antireflection schemes.
We introduce a light-stopping process that uses dynamic loss tuning in coupled-resonator delay lines. We demonstrate via numerical simulations that increasing the loss of selected resonators traps light in a zero group velocity mode concentrated in the low-loss portions of the delay line. The large dynamic range achievable for loss modulation should increase the light-stopping bandwidth relative to previous approaches based on refractive-index tuning.
Dynamic tuning of systems of microresonators coupled to waveguides allows a rich range of physical effects. Periodic
resonator arrays can be tuned to stop and store light pulses, theoretically allowing for tunable delay devices
in which the delay is limited neither by bandwidth nor by dispersion. For two-resonator systems, adjustable delays can be obtained from tuning a narrow transparency resonance. Similar behavior is also predicted in a quite different physical system, that of a single photon interacting with dynamically-tuned quantum bits.
We investigate dispersion effects in dynamically-tuned, coupled-resonator delay lines. Provided that the system is tuned to a zero-bandwidth state, a signal can be delayed indefinitely without dispersion. We present a theoretical analysis of such a light-stopping system and verify the results using numerical simulations of
an example system.