Juraj Topolancik

Experimental Observation of Strong Photon Localization in Disordered Photonic Crystal Waveguides

We demonstrate experimentally that structural perturbations imposed on highly dispersive photonic crystal-based waveguides give rise to spectral features that bear signatures of Anderson localization. Sharp resonances with effective Qs of over 30 000 are found in scattering spectra of disordered waveguides. The resonances are observed in a approximately 20-nm bandwidth centered at the cutoff of slowly guided Bloch modes. The origin of the spectral features can be explained by the interference of coherently scattered electromagnetic waves which results in the formation of a narrow impurity (or localization) band populated with spectrally distinct quasistates. Standard photon localization criteria are fulfilled in the localization band.

All-optical switching with bacteriorhodopsin protein coated microcavities and its application to low power computing circuits

We show all-optical switching of an input infrared laser beam at 1310 nm by controlling the photoinduced retinal isomerization to tune the resonances in a silica microsphere coated with three bacteriorhodopsin (BR) protein monolayers. The all-optical tunable resonant coupler re-routes the infrared beam between two tapered fibers in 50u2002μs using a low power (<200u2002μW) green (532 nm) and blue (405 nm) pump beams. The basic switching configuration has been used to design all-optical computing circuits, namely, half and full adder/subtractor, de-multiplexer, multiplexer, and an arithmetic unit. The design requires 2n−1 switches to realize n bit computation. The designs combine the exceptional sensitivities of BR and high-Q microcavities and the versatile tree architecture for realizing low power circuits and networks (approximately mW power budget). The combined advantages of high Q-factor, tunability, compactness, and low power control signals, with the flexibility of cascading switches to form circuits, and r...

Random high-Q cavities in disordered photonic crystal waveguides

We present direct observations of electromagnetic fields localized in disordered photonic crystal waveguides and report the modal volumes and quality factors of the confined modes. Geometrical perturbations distributed uniformly throughout the crystal lattice were introduced by changing orientations of the polygonal lattice elements. Cavities in the disordered waveguides were excited by resonant coupling through a chain of random open resonators. Localized optical resonances with sub-(λ∕n)3 modal volumes and quality factors of up to ∼150000 were observed.

All-optical switching in the near infrared with bacteriorhodopsin-coated microcavities

Photoinduced molecular transitions in bacteriorhodpsin are used to reversibly configure a micron-scale photonic component in which the optical response is resonantly enhanced. The chromophore retinal undergoes photoinduced all-trans to 13-cis conformational change, which tunes resonances in a silica microsphere coated with three bacteriorhodopsin monolayers. The tunable, all-optical resonant coupler reroutes a near-infrared beam (λprobe≅1311nm) between two tapered optical fibers using a low-power (<200μW) green pump (λpump=532nm). The approach represents a bottom-up paradigm for fabrication of hybrid molecular-photonic architectures that employ self-assembled biomolecules for optical manipulation at small scales.

All-Optical Reversible Logic Gates with Optically Controlled Bacteriorhodopsin Protein-Coated Microresonators

We present designs of all-optical reversible gates, namely, Feynman, Toffoli, Peres, and Feynman double gates, with optically controlled microresonators. To demonstrate the applicability, a bacteriorhodopsin protein-coated silica microcavity in contact between two tapered single-mode fibers has been used as an all-optical switch. Low-power control signals (<200u2009μW) at 532u2009nm and at 405u2009nm control the conformational states of the protein to switch a near infrared signal laser beam at 1310 or 1550u2009nm. This configuration has been used as a template to design four-port tunable resonant coupler logic gates. The proposed designs are general and can be implemented in both fiber-optic and integrated-optic formats and with any other coated photosensitive material. Advantages of directed logic, high Q-factor, tunability, compactness, low-power control signals, high fan-out, and flexibility of cascading switches in 2D/3D architectures to form circuits make the designs promising for practical applications.

Enhanced photoluminescence from embedded PbSe colloidal quantum dots in silicon-based random photonic crystal microcavities

The experimental observation of enhanced photoluminescence from high-Q silicon-based random photonic crystal microcavities embedded with PbSe colloidal quantum dots is being reported. The emission is optically excited at room temperature by a continuous-wave Ti-sapphire laser and exhibits randomly distributed localized modes with a minimum spectral linewidth of 4nm at 1.5μm wavelength.

Out-of-plane scattering from vertically asymmetric photonic crystal slab waveguides with in-plane disorder

We characterize optical wave propagation along line defects in two-dimensional arrays of air-holes in free-standing silicon slabs. The fabricated waveguides contain random variations in orientation of the photonic lattice elements which perturb the in-plane translational symmetry. The vertical slab symmetry is also broken by a tilt of the etched sidewalls. We discuss how these lattice imperfections affect out-of-plane scattering losses and introduce a mechanism for high-Q cavity excitation related to polarization mixing.

Disorder-induced high-Q cavities in photonic crystal waveguides

We demonstrate experimentally that random departure from high-index-contrast periodicity in photonic crystal waveguides gives rise to spectral features that bear signatures of Anderson localization. Disorder-induced high-Q cavities are observed in a narrow frequency band close to the guided modes cut-off where the light propagates with slow group velocity. Spectrally distinct quasi-states with Qs as high as ~250,000 are distributed at random locations along the waveguide and can find applications for example in optical sensing systems.

All-optical reversible logic gates with microresonators

We present designs of all-optical reversible logic gates, namely, Feynman, Toffoli, Peres and Feynman Double gates, based on switching of a near-IR (1310/1550 nm) signal by low-power control signals at 532 nm and 405 nm, in optically controlled bacteriorhodopsin protein-coated silica microcavities coupled between two tapered single-mode fibers.

All-optical computing circuits based on bacteriorhodopsin protein coated microcavity switches

We present designs of all-optical MUX/DEMUX and half-adder/subtractor circuits based on switching of an infrared laser beam at 1310 nm in bacteriorhodopsin protein coated silica microsphere using low power (<;200 μW) pump beams.