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
We review recent research on nonlinear optical interactions in waveguides with sub-micron transverse dimensions, which are termed photonic nanowires. Such nanowaveguides, fabricated from glasses or semiconductors, provide the maximal confinement of light for index guiding structures enabling large enhancement of nonlinear interactions and group-velocity dispersion engineering. The combination of these two properties make photonic nanowires ideally suited for many nonlinear optical applications including the generation of single-cycle pulses and optical processing with sub-mW powers. (C) 2008 Optical Society of America.
We demonstrate a chip-scale photonic system for the room-temperature detection of gas composition and pressure using a slotted silicon microring resonator. We measure shifts in the resonance wavelength due to the presence and pressure of acetylene gas and resolve differences in the refractive index as small as 10(-4) in the near-IR. The observed sensitivity of this device ( enhanced due to the slot-waveguide geometry) agrees with the expected value of 490 nm/refractive index unit. (c) 2008 Optical Society of America.
We propose a new technique to realize an optical time lens for ultrafast temporal processing that is based on four-wave mixing in a silicon nanowaveguide. The demonstrated time lens produces more than 100 pi of phase shift, which is not readily achievable using electro-optic phase modulators. Using this method we demonstrate 20x magnification of a signal consisting of two 3 ps pulses, which allows for temporal measurements using a detector with a 20 GHz bandwidth. Our technique offers the capability of ultrafast temporal characterization and processing in a chip-scale device. (C) 2008 Optical Society of America.
With the realization of faster telecommunication data rates and an expanding interest in ultrafast chemical and physical phenomena, it has become important to develop techniques that enable simple measurements of optical waveforms with subpicosecond resolution(1). State- of- the- art oscilloscopes with high- speed photodetectors provide single- shot waveform measurement with 30- ps resolution. Although multiple- shot sampling techniques can achieve few- picosecond resolution, single- shot measurements are necessary to analyse events that are rapidly varying in time, asynchronous, or may occur only once. Further improvements in single- shot resolution are challenging, owing to microelectronic bandwidth limitations. To overcome these limitations, researchers have looked towards all- optical techniques because of the large processing bandwidths that photonics allow. This has generated an explosion of interest in the integration of photonics on standard electronics platforms, which has spawned the field of silicon photonics(2) and promises to enable the next generation of computer processing units and advances in high- bandwidth communications. For the success of silicon photonics in these areas, on- chip optical signal- processing for optical performance monitoring will prove critical. Beyond next- generation communications, siliconcompatible ultrafast metrology would be of great utility to many fundamental research fields, as evident from the scientific impact that ultrafast measurement techniques continue to make(3-5). Here, using time- to- frequency conversion(6) via the nonlinear process of four- wave mixing on a silicon chip, we demonstrate a waveform measurement technology within a silicon- photonic platform. We measure optical waveforms with 220- fs resolution over lengths greater than 100 ps, which represent the largest record- length- to-resolution ratio (> 450) of any single- shot- capable picosecond waveform measurement technique(6-16). Our implementation allows for single- shot measurements and uses only highly developed electronic and optical materials of complementary metal- oxide-semiconductor (CMOS)- compatible silicon- on- insulator technology and single- mode optical fibre. The mature silicon- on- insulator platform and the ability to integrate electronics with these CMOS-compatible photonics offer great promise to extend this technology into commonplace bench- top and chip- scale instruments.