Chris Fietz

Nonlinear polarization conversion using microring resonators.

We present a design of a polarization converter between linear, circular, and elliptic accomplished with an on-chip high-Q dielectric microring resonator. Nonlinear polarization switching can be accomplished at modest input intensities because of the high-intensity compression in the ring. We predict an optical bistability effect making the polarization of the transmitted light dependent on its spectral or intensity history.

Complex k band diagrams of 3D metamaterial/photonic crystals.

A finite element method (FEM) for solving a complex valued k(ω) vs. ω dispersion curve of a 3D metamaterial/photonic crystal system is presented. This 3D method is a generalization of a previously reported 2D eigenvalue method [Opt. Express 15, 9681 (2007)]. This method is particularly convenient for analyzing periodic systems containing dispersive (e.g., plasmonic) materials, for computing isofrequency surfaces in the k-space, and for calculating the decay length of the evanescent waves. Two specific examples are considered: a photonic crystal comprised of dielectric spheres and a plasmonic fishnet structure. Hybridization and avoided crossings between Mie resonances and propagating modes are numerically demonstrated. Negative index propagation of four electromagnetic modes distinguished by their symmetry is predicted for the plasmonic fishnets. By calculating the isofrequency contours, we also demonstrate that the fishnet structure is a hyperbolic medium.

Critically coupled surface phonon-polariton excitation in silicon carbide.

We observe critical coupling to surface phonon-polaritons in silicon carbide by attenuated total reflection of mid-IR radiation. Reflectance measurements demonstrate critical coupling by a double scan of wavelength and incidence angle. Critical coupling occurs when prism coupling loss is equal to losses in silicon carbide and the substrate, resulting in maximal electric field enhancement.

Measurements of the negative refractive index of sub-diffraction waves propagating in an indefinite permittivity medium.

An indefinite permittivity medium (IPM) has been fabricated and optically characterized in mid-infrared spectral range (10.7 µm-11.3 µm). Phase and amplitude transmission measurements reveal two remarkable properties of IPMs: (i) transmission of sub-diffraction waves (as short as λ/4) can exceed those of diffraction-limited ones, and (ii) sub-diffraction waves can propagate with negative refractive index. We describe a novel double-detector optical technique relying on the interference between sub-diffraction and diffraction-limited waves for accurate measurement of the transmission amplitude and phase of the former.

Polarization conversion in a silica microsphere

We experimentally demonstrate controlled polarization-selective phenomena in a whispering gallery mode resonator. We observed efficient ( approximately 75%) polarization conversion of light in a silica microsphere coupled to a tapered optical fiber with proper optimization of the polarization of the propagating light. A simple model treating the microsphere as a ring resonator provides a good fit to the observed behavior.

Simultaneous fast and slow light in microring resonators.

Two orthogonal light polarizations in a waveguide overcoupled to microring resonators can propagate as fast and slow light. Which polarization is fast (slow) is determined by input polarization and the number of resonators.

Finite element simulation of microphotonic lasing system

We present a method for performing time domain simulations of a microphotonic system containing a four level gain medium based on the finite element method. This method includes an approximation that involves expanding the pump and probe electromagnetic fields around their respective carrier frequencies, providing a dramatic speedup of the time evolution. Finally, we present a two dimensional example of this model, simulating a cylindrical spaser array consisting of a four level gain medium inside of a metal shell.

Observation of simultaneous fast and slow light

We present a microresonator-based system capable of simultaneously producing time-advanced and timedelayed pulses. The effect is based on the combination of a sharp spectral feature with two orthogonallypolarized propagating waveguide modes. We include an experimental proof-of-concept implementation using a silica microsphere coupled to a tapered optical fiber and use a time-domain picture to interpret the observed delays. We also discuss potential applications for future all-optical networks. Increasing bandwidth demands are pushing for the development of all-optical circuitry that will be able to quickly and reliably transmit and process vast amounts of data. Precise control of light propagation, such as the ability to advance, delay, or store a pulse transmitted through a waveguide, is a requisite ingredient for optical data processing in photonic circuits 1. Remarkably, exotic optical phenomena occurring in the presence of strong spectral dispersion such as slow 2 and fast 3 light have been found very useful for achieving these goals, generating a surge of experimental activities aimed at realizing fast or slow light in different media: atomic vapors 2‐4, crystals 5, semiconductors 6,7, and microresonators 8‐11. These demonstrations have shown either fast or slow light for a given configuration. Here we introduce a microresonator-based system that is capable of simultaneously producing time-advanced and time-delayed pulses, including an experimental proof-ofconcept implementation. The ability to simultaneously slow and advance pulses of light brings about a new perspective on photonics: one can easily envision applications involving all-optical processing of data headers and data packets where both fast and slow light may be desirable. Time-advanced signals can be used to compensate time delays inevitable in any complex opticalprocessing network 12. The appeal of strong spectral dispersion is not limited to the linear properties of light: the resulting high optical energy compression may lead to extraordinary enhancement of nonlinear effects and, one day, to

Whispering gallery mode microresonators as polarization converters.

A ring resonator coupled to a waveguide can be used as a highly efficient polarization converter when the input is properly polarized. We model this phenomenon and verify the predictions with a demonstration of very efficient polarization conversion (>90%) on a silica microsphere coupled to a tapered optical fiber.

Interferometric characterization of a sub-wavelength near-infrared negative index metamaterial.

Negative phase advance through a single layer of near-IR negative index metamaterial (NIM) is identified through interferometric measurements. The NIM unit cell, sub-wavelength in both the lateral and light propagation directions, is comprised of a pair of Au strips separated by two dielectric and one Au film. Numerical simulations show that the negative phase advance through the single-layer sample is consistent with the negative index exhibited by a bulk material comprised of multiple layers of the same structure. We also numerically demonstrate that the negative index band persists in the lossless limit.