Electrically Tuned Research Articles

Free spectral range electrical tuning of a high quality on-chip microcavity.

Reconfigurable photonic circuits have applications ranging from next-generation computer architectures to quantum networks, coherent radar and optical metamaterials. Here, we demonstrate an on-chip high quality microcavity with resonances that can be electrically tuned across a full free spectral range (FSR). FSR tuning allows resonance with any source or emitter, or between any number of networked microcavities. We achieve it by integrating nanoelectronic actuation with strong optomechanical interactions that create a highly geometry-dependent effective refractive index. This allows low voltages and sub-nanowatt power consumption. We demonstrate a basic reconfigurable photonic network, bringing the microcavity into resonance with an arbitrary mode of a microtoroidal optical cavity across a telecommunications fibre link. Our results have applications beyond photonic circuits, including widely tuneable integrated lasers, reconfigurable optical filters for telecommunications and astronomy, and on-chip sensor networks.

Reversible modification of electrical properties at the nanoscale level in bilayer oxide systems

We report the results of experimental study of resistive switching effects in heterogeneous oxide systems based on bilayers with different sequences of two oxide layers (TiO2 and Al2O3) by means of tunnelling atomic-force microscopy (AFM). These systems demonstrate a bipolar resistive switching. Moreover, the resistance state of metal-insulator-metal capacitors with TiO2/Al2O3 bilayers can be electrically tuned over seven orders of magnitude. To elucidate a possible influence of nanoscale characteristics of these bilayers on the parameters of both bipolar resistive switching and electrical tuning of the resistance state, electrical properties of TiO2/Al2O3 bilayers with different thicknesses of the top Al2O3 layer and Al2O3/TiO2 bilayers were investigated. The presence of more conductive anatase crystallites in the amorphous phase of TiO2 layer was experimentally observed only for TiO2/Al2O3 bilayers. Measurements of the current distribution justify the reversible formation of conductive areas in the top Al2O3 layer located directly above the anatase crystallites, under the voltage application between the AFM tip and the bottom electrode of the structure. These conductive areas could be switched back into the high resistive state by application of bias voltage of reverse polarity.

Switching time of electrical tuning of permeability in strain-mediated multiferroic heterostructures

The switching time of the electrically tunable permeability of the NiFeTa/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 multiferroic material was characterized by using a Vector Network Analyzer and a pulse generator. The measured switching time for the permeability to be electrically tuned from the initial value to the final value upon the change of the applied electrical field is 0.15 s, which is independent of the magnitude of the electrical field and the measured frequency. The result is verified by the measurement of the time response permeability under a series of pulses with different pulse widths. It was found that for the cases of the pulse width smaller than the switching time, the rise time of the permeability response pulse is the same as the pulse width and the pulse height of the response permeability is linearly dependent on the pulse width. It is suggested that the temporal relaxation process of the interface arising from the strain transfer delay time between the film and the substrate plays a dominant role in the contribution of the total switching time of the material.

BK Channels in the Vertebrate Inner Ear.

The perception of complex acoustic stimuli begins with the deconstruction of sound into its frequency components. This spectral processing occurs first and foremost in the inner ear. In vertebrates, two very different strategies of frequency analysis have evolved. In nonmammalian vertebrates, the sensory hair cells of the inner ear are intrinsically electrically tuned to a narrow band of acoustic frequencies. This electrical tuning relies on the interplay between BK channels and voltage-gated calcium channels. Systematic variations in BK channel density and kinetics establish a gradient in electrical resonance that enables the coding of a broad range of acoustic frequencies. In contrast, mammalian hair cells are extrinsically tuned by mechanical properties of the cochlear duct. Even so, mammalian hair cells also express BK channels. These BK channels play critical roles in various aspects of mammalian auditory signaling, from developmental maturation to protection against acoustic trauma. This review summarizes the anatomical localization, biophysical properties, and functional contributions of BK channels in vertebrate inner ears. Areas of future research, based on an updated understanding of the biology of both BK channels and the inner ear, are also highlighted. Investigation of BK channels in the inner ear continues to provide fertile research grounds for examining both BK channel biophysics and the molecular mechanisms underlying signal processing in the auditory periphery.

Electric tuning of direct-indirect optical transitions in silicon

Electronic band structures in semiconductors are uniquely determined by the constituent elements of the lattice. For example, bulk silicon has an indirect bandgap and it prohibits efficient light emission. Here we report the electrical tuning of the direct/indirect band optical transition in an ultrathin silicon-on-insulator (SOI) gated metal-oxide-semiconductor (MOS) light-emitting diode. A special Si/SiO2 interface formed by high-temperature annealing that shows stronger valley coupling enables us to observe phononless direct optical transition. Furthermore, by controlling the gate field, its strength can be electrically tuned to 16 times that of the indirect transition, which is nearly 800 times larger than the weak direct transition in bulk silicon. These results will therefore assist the development of both complementary MOS (CMOS)-compatible silicon photonics and the emerging “valleytronics” based on the control of the valley degree of freedom.

P‐136: Electrical Color and Intensity Tuning in Cholesteric Reflective Display

AbstractWe developed reflective cholesteric displays whose color and reflectance can be electrically tuned. The displays were made from polymer stabilized cholesteric liquid crystals. Monomers and cholesteric liquid crystals were mixed and then polymerized under UV light. When the monomer was achiral, the resulted display exhibited a narrow reflection band, and the reflectance and color can be tuned by applying AC voltages. When the monomer is chiral, the resulted display exhibited a broad reflection band, and the reflectance can be tuned by applying DC voltages.

Electrical tuning and transduction in short hair cells of the chicken auditory papilla

The avian auditory papilla contains two classes of sensory receptor, tall hair cells (THCs) and short hair cells (SHCs), the latter analogous to mammalian outer hair cells with large efferent but sparse afferent innervation. Little is known about the tuning, transduction, or electrical properties of SHCs. To address this problem, we made patch-clamp recordings from hair cells in an isolated chicken basilar papilla preparation at 33°C. We found that SHCs are electrically tuned by a Ca(2+)-activated K(+) current, their resonant frequency varying along the papilla in tandem with that of the THCs, which also exhibit electrical tuning. The tonotopic map for THCs was similar to maps previously described from auditory nerve fiber measurements. SHCs also possess an A-type K(+) current, but electrical tuning was observed only at resting potentials positive to -45 mV, where the A current is inactivated. We predict that the resting potential in vivo is approximately -40 mV, depolarized by a standing inward current through mechanotransducer (MT) channels having a resting open probability of ∼0.26. The resting open probability stems from a low endolymphatic Ca(2+) concentration (0.24 mM) and a high intracellular mobile Ca(2+) buffer concentration, estimated from perforated-patch recordings as equivalent to 0.5 mM BAPTA. The high buffer concentration was confirmed by quantifying parvalbumin-3 and calbindin D-28K with calibrated postembedding immunogold labeling, demonstrating >1 mM calcium-binding sites. Both proteins displayed an apex-to-base gradient matching that in the MT current amplitude, which increased exponentially along the papilla. Stereociliary bundles also labeled heavily with antibodies against the Ca(2+) pump isoform PMCA2a.

Tonotopic variations of calcium signalling in turtle auditory hair cells

Turtle cochlear hair cells are electrically tuned by a voltage-dependent Ca2+ current and a Ca2+-dependent K+ current (IBK(Ca)). The effects of intracellular calcium buffering on electrical tuning were studied in hair cells at apical and basal cochlear locations tuned to 100 and 300 Hz, respectively. Increasing the intracellular BAPTA concentration changed the hair cell's resonant frequency little, but optimized tuning at more depolarized membrane potentials due to a positive shift in the half-activation voltage (V ) of the IBK(Ca). The shift in V depended similarly on BAPTA concentration in basal and apical hair cells despite a 2. 4-fold difference in the size of the Ca2+ current at the two positions. The Ca2+ current amplitude increased exponentially with distance along the cochlea. Comparison of V values and tuning properties using different BAPTA concentrations with values measured in perforated-patch recordings gave the endogenous calcium buffer as equivalent to 0.21 mM BAPTA in low-frequency cells, and 0.46 mM BAPTA in high-frequency cells. High conductance Ca2+-activated K+ (BKCa) channels recorded in inside-out membrane patches were 2-fold less Ca2+ sensitive in high-frequency than in low-frequency cells. Confocal Ca2+ imaging using the fluorescent indicator Calcium Green-1 revealed about twice as many hotspots of Ca2+ entry during depolarization in high-frequency compared to low-frequency hair cells. We suggest that each BKCa channel is gated by Ca2+ entry through a few nearby Ca2+ channels, and that Ca2+ and BKCa channels occupy, at constant channel density, a greater fraction of the membrane area in high-frequency cells than in low-frequency cells.

The Electrical Properties of Auditory Hair Cells in the Frog Amphibian Papilla

The amphibian papilla (AP) is the principal auditory organ of the frog. Anatomical and neurophysiological evidence suggests that this hearing organ utilizes both mechanical and electrical (hair cell-based) frequency tuning mechanisms, yet relatively little is known about the electrophysiology of AP hair cells. Using the whole-cell patch-clamp technique, we have investigated the electrical properties and ionic currents of isolated hair cells along the rostrocaudal axis of the AP. Electrical resonances were observed in the voltage response of hair cells harvested from the rostral and medial, but not caudal, regions of the AP. Two ionic currents, ICa and IK(Ca), were observed in every hair cell; however, their amplitudes varied substantially along the epithelium. Only rostral hair cells exhibited an inactivating potassium current (IA), whereas an inwardly rectifying potassium current (IK1) was identified only in caudal AP hair cells. Electrically tuned hair cells exhibited resonant frequencies from 50 to 375 Hz, which correlated well with hair cell position and the tonotopic organization of the papilla. Variations in the kinetics of the outward current contribute substantially to the determination of resonant frequency. ICa and IK(Ca) amplitudes increased with resonant frequency, reducing the membrane time constant with increasing resonant frequency. We conclude that a tonotopically organized hair cell substrate exists to support electrical tuning in the rostromedial region of the frog amphibian papilla and that the cellular mechanisms for frequency determination are very similar to those reported for another electrically tuned auditory organ, the turtle basilar papilla.

Electrical tuning of semiconductor interferometric laser

A semiconductor laser with a Michelson interferometer type cavity was electrically tuned by pumping each of its two branches separately. Two tuning modes were observed, small continuous tuning over 2.5 to 3 A and step tuning with a total shift of 34 A.