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.
We demonstrate tunable superluminal propagation in a silicon microphotonic device in a solid-state room-temperature device of tens of micrometers in dimension allowing easy integration with high-bandwidth room-temperature systems. We achieve tunable negative delays up to 85 ps and effective group indices tunable between -1158 and -312. (C) 2008 Optical Society of America
We demonstrate high bit rate electro-optic In modulation in a resonant micrometer-scale silicon modulator over an ambient temperature range of 15 K. We show that low bit error rates can be achieved by varying the bias current through the device to thermally counteract the ambient temperature changes. Robustness in the presence of thermal variations can enable a wide variety of applications for dense on chip electronic photonic integration. (C) 2008 Optical Society of America
We demonstrate a 1x2 all-optical comb switch using a 200 mu m diameter silicon ring resonator with a switching time of less than 1 ns. The switch overcomes the small bandwidth of the traditional ring resonator, and works for wavelength division multiplexing applications. The device has a footprint of similar to 0.04 mm(2) and enables switching of a large number (similar to 40) of wavelength channels spaced by similar to 0.85 nm. (c) 2007 Optical Society of America.
We demonstrate highly broad-band frequency conversion via four-wave mixing in silicon nanowaveguides. Through appropriate engineering of the waveguide dimensions, conversion bandwidths greater than 150 nm are achieved and peak conversion efficiencies of -9.6 dB are demonstrated. Furthermore, utilizing fourth-order dispersion, wavelength conversion across four telecommunication bands from 1477 nm (S-band) to 1672 nm (U-band) is demonstrated with an efficiency of -12 dB. (c) 2007 Optical Society of America.
Using interferometric couplers and thermal tuning, we demonstrate a novel design of compact microring resonators on silicon-on-insulator platform with tunable bandwidth from 0.1 to 0.7 nm. The structures present an extinction ratio higher than 23 dB and a footprint of less than 0.001 mm(2), which are suitable for integrated optical signal processing such as reconfigurable filtering and routing. (c) 2007 Optical Society of America.
We show a scheme for achieving high-speed operation for carrier-injection based silicon electro-optical modulator, which is optimized for small size and high modulation depth. The performance of the device is analyzed theoretically and a 12.5-Gbit/s modulation with high extinction ratio > 9dB is demonstrated experimentally using a silicon micro-ring modulator. (c) 2007 Optical Society of America.
We demonstrate all-optical logic in a micron-size silicon ring resonator based on the free-carrier dispersion effect in silicon. We show AND and NAND operation at 310 Mbit/s with similar to 10-dB extinction ratio. The free-carrier-lifetime-limited bit-rate can be significantly improved by active carrier extraction. (c) 2007 Optical Society of America.
We demonstrate optical 2R regeneration in an integrated silicon device consisting of an 8-mm-long nanowaveguide followed by a ring-resonator bandpass filter. The regeneration process is based on nonlinear spectral broadening in the waveguide and subsequent spectral filtering through the ring resonator. We measure the nonlinear power transfer function for the device and find an operating peak power of 6 W. Measurements indicate that the output pulse width is determined only by the bandwidth of the bandpass filter. Numerical modeling of the nonlinear process including free-carrier effects shows that this device can be used for all-optical regeneration at telecommunication data rates. (c) 2007 Optical Society of America.
Storing light on-chip, which requires that the speed of light be significantly slowed down, is crucial for enabling photonic circuits on-chip. Ultraslow propagation(1-3) and even stopping(4,5) of light have been demonstrated using the electromagnetically induced transparency effect in atomic systems(1,3-5) and the coherent population oscillation effect in solid-state systems(2). The wavelengths and bandwidths of light in such devices are tightly constrained by the property of the material absorption lines, which limits their application in information technologies. Various slow-light devices based on photonic structures have also been demonstrated(6-10); however, these devices suffer a fundamental trade-off between the transmission bandwidth and the optical delay. It has been shown theoretically(11-13) that stopping light on-chip and thereby breaking the fundamental link between the delay and the bandwidth can be achieved by ultrafast tuning of photonic structures. Using this mechanism, here we report the first demonstration of storing light using photonic structures on-chip, with storage times longer than the bandwidth-determined photon lifetime of the static device. The release time of the pulse is externally controlled.
As the demand for high bandwidths in microelectronic systems increases, optical interconnect architectures are now being considered that involve schemes commonly used in telecommunications, such as wavelength-division multiplexing (WDM) and wavelength conversion(1). In such on-chip architectures, the ability to perform wavelength conversion is required. So far wavelength conversion on a silicon chip has only been demonstrated using schemes that are fundamentally all-optical(2-6), making their integration on a microelectronic chip challenging. In contrast, we show wavelength conversion obtained by inducing ultrafast electro-optic tuning of a microcavity. It is well known that tuning the parameters of an optical cavity induces filtering of different colours of light(7). Here we demonstrate that it can also change the colour of light. This is an effect often observed in other disciplines, for example, in acoustics, where the sound generated by a resonating guitar string can be modified by changing the length of the strings (that is, the resonators)(8). Here we show this same tuning effect in optics, enabling compact on-chip electrical wavelength conversion. We demonstrate a change in wavelength of up to 2.5 nm with up to 34% on-off conversion efficiency.
A 4 x 4 Gb/s microring modulator cascade, which can directly convert data from a parallel electrical bus to a multiple-wavelength optical signal in a single silicon-on-insulator waveguide, is demonstrated and characterized. The integrity of the modulated optical signal is verified using Q-factor extrapolations. In addition, the frequency characteristics and crosstalk, in terms of total harmonic distortion, are quantified. A transparent translator from electronics to optics such as this is crucial for the development of large-scale high-bandwidth interconnects based on photonic integrated circuits.
We experimentally demonstrate a micron-size electro-optic modulator using a high-index-contrast silicon Fabry-Perot resonator cavity. This compact device consists of a 1-D cavity formed within a single mode silicon channel waveguide and an embedded p-i-n junction on a silicon-on-insulator platform. The entire device is 6.0 microns in length. We demonstrate modulation depths as large as 5.87 dB at speeds of 250 Mbps limited only by fabrication imperfections, with optimized theoretical speeds of several Gbps. (c) 2007 Optical Society of America.
We experimentally demonstrate the optical transmission at 1550 nm of the fundamental slot modes (quasi-TM modes) in horizontal single and multiple slot waveguides and ring resonators consisting of deposited amorphous silicon and silicon dioxide. We demonstrate that the horizontal multiple slot configuration provides enhanced optical confinement in low index slot regions compared to a horizontal single slot structure with the same total SiO2 layer thickness by comparing their thermo-optic coefficients for the horizontal slot ring resonators. We show in these early structures that horizontal slot waveguides have low propagation loss of 6 similar to 7 dB/cm. The waveguide loss is mainly due to a-Si material absorption. The addition of a Si/SiO2 interfaces does not introduce significant scattering loss in a horizontal multiple slot waveguide compared to a horizontal single slot waveguide. (c) 2007 Optical Society of America.