Woo-Joong Kim

Low-loss strip-loaded slot waveguides in Silicon-on-Insulator

Electro-optic polymer-clad silicon slot waveguides have recently been used to build a new class of modulators, that exhibit very high bandwidths and extremely low drive voltages. A key step towards making these devices practical will be lowering optical insertion losses. We report on the first measurements of low-loss waveguides that are geometrically suitable for high bandwidth slot waveguide modulators: a strip-loaded slot waveguide. Waveguide loss for undoped waveguides of 6.5 ± 0.2 dB/cm was achieved with 40 nm thick strip-loading, with the full silicon thickness around 220 nm and a slot size of 200 nm, for wavelengths near 1550 nm.

Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry

Dipartimento di Fisica “Galileo Galilei”, Universit`a di Padova, Via Marzolo 8, Padova 35131, Italy(Dated: December 1, 2008)We have performed precision electrostatic calibrations in the sphere-plane geometry, and observedanomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was foundto be smaller than expected on the basis of the pure Coulombian contribution, and the residualpotential found to be distance dependent. We argue that these findings affect the accuracy of theelectrostatic calibrations and invite reanalysis of previous determinations of the Casimir force.

Low-loss asymmetric strip-loaded slot waveguides in silicon-on-insulator

We report on low-loss asymmetric strip-loaded slot waveguides in silicon-on-insulator fabricated with 248 nm photolithography. Waveguide losses were 2 dB/cm or less at wavelengths near 1550 nm. A 40 nm strip-loading allows low-resistance electrical contact to be made to the two slot arms. The asymmetric design suppresses the TE1 mode while increasing the wavelength range for which the TE0 mode guides. This type of waveguide is suitable for building low insertion-loss, high-bandwidth, low drive-voltage modulators, when coated with an electro-optic polymer cladding.

Sub-Volt Silicon-Organic Electro-optic Modulator With 500 MHz Bandwidth

Lowering the operating voltage of electro-optic modulators is desirable for a variety of applications, most notably in analog photonics and digital data communication. In particular for digital systems such as CPUs, it is desirable to develop modulators that are both temperature-insensitive and compatible with typically sub-2 V CMOS electronics; however, drive voltages in silicon-based Mach-Zehnder interferometers (MZIs) currently exceed 1.8 V. Here, we show an MZI modulator based on an electro-optic polymer-clad silicon slot waveguide, with a halfwave voltage of only 0.69 V (corresponding to a 0.62 V(·)cm modulation figure of merit), and a bandwidth of 500 MHz. We also show that there are paths to significantly improve both the bandwidth and drive voltage.Lowering the operating voltage of electrooptic modulators is desirable for a variety of applications, most notably in analog photonics , and digital data communications . In particular for digital systems such as CPUs, it is desirable to develop modulators that are both temperature-insensitive and compatible with typically sub-2V CMOS electronics ; however, drive voltages in silicon-based MZIs currently exceed 6.5V . Here we show an MZI modulator based on an electrooptic polymer-clad silicon slot waveguide, with a halfwave voltage of only 0.69V, and a bandwidth of 500 MHz. We also show that there are also paths to significantly improve both the bandwidth and drive voltage . Our silicon-organic modulator has an intrinsic power consumption less than 0.66 pJ/bit, nearly an order of magnitude improvement over the previous lowest energy silicon MZI .

Detectability of dissipative motion in quantum vacuum via superradiance

We propose an experiment for generating and detecting vacuum-induced dissipative motion. A high frequency mechanical resonator driven in resonance is expected to dissipate mechanical energy in quantum vacuum via photon emission. The photons are stored in a high quality electromagnetic cavity and detected through their interaction with ultracold alkali-metal atoms prepared in an inverted population of hyperfine states. Superradiant amplification of the generated photons results in a detectable radio-frequency signal temporally distinguishable from the expected background.

Reply to "Comment on 'Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry' "

In a recent Comment, Decca et al. [Phys. Rev. A 79, 026101 (2009)] discussed the origin of the anomalies recently reported by us in Phys. Rev. A 78, 036102(R) (2008). Here we restate our view corroborated by their considerations that quantitative geometrical and electrostatic characterizations of the conducting surfaces (a topic not discussed explicitly in the literature until very recently) are critical for the assessment of precision and accuracy of the demonstration of the Casimir force and for deriving meaningful limits on the existence of Yukawian components possibly superimposed to the Newtonian gravitational interaction.

Towards a precision measurement of the Casimir force in a cylinder-plane geometry

We report on a proposal aimed at measuring the Casimir force in the cylinder-plane configuration. The Casimir force is evaluated including corrections due to finite parallelism, conductivity, and temperature. The range of validity of the proximity force approximation is also discussed. An apparatus to test the feasibility of a precision measurement in this configuration has been developed, and we describe both a procedure to control the parallelism and the results of the electrostatic calibration. Finally we discuss the possibility of measuring the thermal contribution to the Casimir force and deviations from the proximity force approximation, both of which are expected at relatively large distances.

On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration

We report on measurements of forces acting between two conducting surfaces in a spherical-plane configuration in the 35 nm-1 μm separation range. The measurements are obtained by performing electrostatic calibrations followed by a residuals analysis after subtracting the electrostatic-dependent component. We find in all runs optimal fitting of the calibrations for exponents smaller than the one predicted by electrostatics for an ideal sphere-plane geometry. We also find that the external bias potential necessary to minimize the electrostatic contribution depends on the sphere-plane distance. In spite of these anomalies, by implementing a parametrization-dependent subtraction of the electrostatic contribution we have found evidence for short-distance attractive forces of magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss the relevance of our findings in the more general context of Casimir-Lifshitz force measurements, with particular regard to the critical issues of the electrical and geometrical characterization of the involved surfaces.

Direct contact buckling of electrochemically grown gold nanowires

We report the electrochemical growth and direct probing of near-vertical gold nanowires several micrometers long that are attached at one end to a substrate. Controllable contact is made to the wires using a straightforward tip-probe arrangement inside a scanning electron microscope. The contact allowed us to perform mechanical and electrical measurements. Through elastic nanowire buckling, we have observed dynamic low-frequency parametric pumping caused by small vibrations of the probe. A numerical simulation of the recorded motion is consistent with an estimated value of Young’s modulus of about 80GPa, which is close to that of bulk gold.

Modelling superradiant amplification of Casimir photons in very low dissipation cavities

Recent advances in nanotechnology and atomic physics may allow for a demonstration of the dynamical Casimir effect. An array of film bulk acoustic resonators (FBARs) coherently driven at twice the resonant frequency of a high-quality electromagnetic cavity can generate a stationary state of Casimir photons. These are detected using an alkali atom beam prepared in an inverted population of hyperfine states, with an induced superradiant burst producing a detectable radio-frequency signal. We describe here the results of the simulations of the dynamics of superradiance and superfluorescence, with the aim to optimize the parameters for the detectability of Casimir photons. When the superradiant lifetime is shorter than the dissipation time, we find superradiant evolution to be similar in character but dramatically slower than in the usual lossy case.