We report an optical link on silicon using micrometer-scale ring-resonator enhanced silicon modulators and waveguide-integrated germanium photodetectors. We show 3 Gbps operation of the link with 0.5 V modulator voltage swing and 1.0 V detector bias. The total energy consumption for such a link is estimated to be similar to 120 fJ/bit. Such a compact and low power monolithic link is an essential step towards large-scale on-chip optical interconnects for future microprocessors. (C) 2009 Optical Society of America
We demonstrate low loss silicon waveguides fabricated without any silicon etching. We define the waveguides by selective oxidation which produces ultra-smooth sidewalls with width variations of 0.3 nm. The waveguides have a propagation loss of 0.3 dB/cm at 1.55 mu m. The waveguide geometry enables low bending loss of approximately 0.007 dB/bend for a 90 degrees bend with a 50 mu m bending radius.(C) 2009 Optical Society of America
We experimentally demonstrate generation of high-intensity short optical pulses obtained by the controlled ultrafast release of the stored energy confined in silicon microcavities. This is achieved using ultrafast tuning of the coupling from a coupled-ring cavity to an external waveguide on time scales shorter than cavity photon lifetime. (C) 2009 Optical Society of America
We demonstrate that optomechanical devices can exhibit nonreciprocal behavior when the dominant light-matter interaction takes place via a linear momentum exchange between light and the mechanical structure. As an example, we propose a microscale optomechanical device that can exhibit a nonreciprocal behavior in a microphotonic platform operating at room temperature. We show that, depending on the direction of the incident light, the device switches between a high and low transparency state with more than a 20 dB extinction ratio.
The ability to render objects invisible using a cloak (such that they are not detectable by an external observer) has long been a tantalizing goal(1-6). Here, we demonstrate a cloak operating in the near infrared at a wavelength of 1,550 nm. The cloak conceals a deformation on a flat reflecting surface, under which an object can be hidden. The device has an area of 225 mu m(2) and hides a region of 1.6 mu m(2). It is composed of nanometre-size silicon structures with spatially varying densities across the cloak. The density variation is defined using transformation optics to define the effective index distribution of the cloak.
We demonstrate horizontal slot waveguides using high-index layers of polycrystalline and single crystalline silicon separated by a 10 nm layer of silicon dioxide. We measure waveguide propagation loss of 7 dB/cm and a ring resonator intrinsic quality factor of 83,000. The electric field of the optical mode is strongly enhanced in the low-index oxide layer, which can be used to induce a strong modal gain when an active material is embedded in the slot. Both high-index layers are made of electrically conductive silicon which can efficiently transport charge to the slot region. The incorporation of conductive silicon materials with high-Q slot waveguide cavities is a key step for realizing electrical tunneling devices such as electrically pumped silicon-based light sources. (C) 2009 Optical Society of America
We experimentally demonstrate wavelength-preserving spectral phase conjugation for compensating chromatic dispersion and self-phase modulation in optical fibers. Our implementation is based on a temporal imaging scheme that uses time lenses realized by broadband four-wave mixing in silicon waveguides. By constructing a temporal analog of a 4-f imaging system, we compensate for pulse distortions arising from second-and third-order dispersion and self-phase modulation in optical fibers. (C) 2009 Optical Society of America
We have measured magnetic fields up to 17.7 T with a rise time of 75 ns using temporally resolved Faraday rotation of a single longitudinal mode laser beam through a magneto-optically active bulk waveguide. We believe this to be the first time that such large, rapidly varying magnetic fields have been measured with this class of materials (multicomponent terbium berate glass). As there was no measurable lag between the magnetic field inferred from the angle of rotation of the laser beam and the electromagnetically measured field, our sample of terbium berate glass has a spin-lattice relaxation time of a few tens of nanoseconds at most at approximately room temperature (300 K). The highest peak magnetic fields were measured in wire-array Z-pinch experiments on a 0.5 MA pulsed power machine. (C) 2009 Optical Society of America
Photonic systems provide access to extremely large bandwidths, which can approach a petahertz(1). Unfortunately, full utilization of this bandwidth is not achievable using standard electro-optical technologies, and higher (>100 GHz) performance requires all-optical processing with nonlinear-optical elements. A solution to the implementation of these elements in robust, compact and efficient systems is emerging in photonic integrated circuits, as evidenced by their recent application in various ultrahigh-bandwidth instruments(2-4). These devices enable the characterization of extremely complex signals by linking the high-speed optical domain with slower speed electronics. Here, we extend the application of these devices beyond characterization and demonstrate an instrument that generates complex and rapidly updateable ultrafast optical waveforms. We generate waveforms with 1.5-ps minimum features by compressing lower-bandwidth replicas created with a 10 GHz electro-optic modulator. In effect, our device allows for ultrahigh-speed direct 270 GHz modulation using relatively low speed devices and represents a new class of ultrafast waveform generators.
We demonstrate waveguide integrated germanium detectors with capacitance as small as 2.4 fF and directly recorded impulse response as fast as 8.8 ps. Based on such detectors and cascaded silicon microring resonators we also demonstrate a highly scalable wavelength division demultiplexing system that can potentially provide tera-bit/s (Tbps) bandwidth over a small area. (C) 2009 Optical Society of America
The ability to manipulate nanoscopic matter precisely is critical for the development of active nanosystems. Optical tweezers(1-4) are excellent tools for transporting particles ranging in size fromseveral micrometres to a few hundred nanometres. Manipulation of dielectric objects with much smaller diameters, however, requires stronger optical confinement and higher intensities than can be provided by these diffraction- limited(5) systems. Here we present an approach to optofluidic transport that overcomes these limitations, using sub-wavelength liquid- core slot waveguides(6). The technique simultaneously makes use of near- field optical forces to confine matter inside the waveguide and scattering/ adsorption forces to transport it. The ability of the slot waveguide to condense the accessible electromagnetic energy to scales as small as 60 nm allows us also to overcome the fundamental diffraction problem. We apply the approach here to the trapping and transport of 75- nm dielectric nanoparticles and lambda-DNA molecules. Because trapping occurs along a line, rather than at a point as with traditional point traps(7,8), the method provides the ability to handle extended biomolecules directly. We also carry out a detailed numerical analysis that relates the near- field optical forces to release kinetics. We believe that the architecture demonstrated here will help to bridge the gap between optical manipulation and nanofluidics.
We demonstrate on-chip laser absorption spectroscopy using silicon microring resonators integrated with PDMS microfluidic channels. A 100 mu m radius microring resonator with Q > 100,000 is used to enhance the interaction length between evanescent light and a cladding liquid. We measure absorption spectra of less than 2 nL of N-methylaniline from 1460 nm to 1610 nm with 1 nm resolution and effective free space path lengths up to 5 mm. This work can help realize a completely on-chip spectroscopy device for lab-on-a-chip applications. (C) 2008 Optical Society of America.
We demonstrate long-range control of the radiative lifetime of a silicon optical nanocavity using a metallic atomic force microscope probe. We extract changes in the radiative lifetime from changes in the cavity's transmittivity resulting from probe-cavity interaction over distances of several optical wavelengths. Analogous to atomic systems, the cavity acts as an individual radiating dipole with a radiative rate that is modified by a metallic interface.
From first principles we develop figures of merit to determine the gain experienced by the guided mode and the lasing threshold for devices based on high-index-contrast waveguides. We show that as opposed to low-index-contrast systems, this quantity is not equivalent to the power confinement since in high-index-contrast structures the electric and magnetic field distributions cannot be related by proportionality constant. We show that with a slot waveguide configuration it is possible to achieve more gain than one would expect based on the power confinement in the gain media. Using the figures of merit presented here we optimize a slot waveguide geometry to achieve low-threshold lasing and discuss the fabrication tolerances of such a design. (C) 2008 Optical Society of America
We demonstrate germanium photodetectors integrated on submicron silicon waveguides fabricated with a low temperature (<= 400 degrees C) wafer bonding and ion-cut process. The devices shows a low dark current of similar to 100 nA, a fiber accessed responsivity of > 0.4 A/W and an estimated quantum efficiency of above 90%. (C) 2008 Optical Society of America.
We experimentally demonstrate on-chip active photonic devices fabricated from deposited polycrystalline silicon, which can be used for monolithic three-dimensional integration of optical networks. The demonstrated modulator is based on all-optical carrier injection in a micrometer-size resonator and has a modulation depth of 10 dB and a temporal response of 135 ps. Grain boundaries in the polycrystalline silicon (polysilicon) material result in faster electron-hole recombination, enabling a shortened carrier lifetime and a faster optical switching time compared to similar devices based on crystalline silicon. (C) 2008 American Institute of Physics.
We demonstrate electro-optic ultrafast control of the optical quality factor of an on-chip silicon microcavity. The micrometer-sized cavity is formed by light confinement between two microring resonators acting as frequency selective mirrors. The ring resonators are integrated into p-i-n junctions enabling ultrafast injection and extraction of carriers. We show tuning of the cavity quality factor from 20,000 to 6,000 in under 100 ps. We demonstrate both high-Q to low-Q and low-Q to high-Q transitions. (c) 2008 Optical Society of America.
We show the existence of direct photonic transitions between modes of a silicon optical microcavity spaced apart in wavelength by over 8 nm. This is achieved by using ultrafast tuning of the refractive index of the cavity over a time interval that is comparable to the inverse of the frequency separation of modes. The demonstrated frequency mixing effect, i.e., the transitions between the modes, would enable on-chip silicon comb sources which can find wide applications in optical sensing, precise spectroscopy, and wavelength-division multiplexing for optical communications and interconnects.
We demonstrate a technique for generating large, all-optical delays while simultaneously minimizing pulse distortion by using temporal phase conjugation via four-wave mixing in Si nanowaveguides. Using this scheme, we achieve continuously tunable delays over a range of 243 ns for 10 Gb/s NRZ data. (c) 2008 Optical Society of America.
We propose a novel geometry in a silicon planar resonator with an ultra-small modal volume of 0.01(lambda/2n)(3). The geometry induces strong electric field discontinuities to decrease the modal volume of the cavity below 1(lambda/2n)(3) The proposed structure and other common resonators such as 1D and 2D photonic crystal resonators are compared for tradeoffs in confinement and quality factors. (C) 2008 Optical Society of America