Gradient index structures are gaining increased importance with the constant development of Transformation Optics and metamaterials. Our ability to fabricate such devices, while limited, has already demonstrated the extensive capabilities of those designs, in the forms of invisibility devices, as well as illusion optics and super-lensing. In this paper we present a low loss, high index contrast lens that is integrated with conventional nanophotonic waveguides to provide improved tolerance in fiber-to-chip optical links for future communication networks. This demonstration represents a positive step in making the extraordinary capabilities of gradient index devices available for integrated optics. (C) 2011 Optical Society of America
We measure optical absorption in color-producing enzymatic reactions for biochemical analysis with a microscale optofluidic device. Cavity-enhanced laser spectrophotometry is performed on analytes within a microfluidic channel at visible wavelengths with silicon nitride microring resonators of 100 mu m radius and quality factor of similar to 180,000. The resonator transmission spectrum is analyzed to determine optical absorption with a detection limit of 0.12 cm(-1). The device can be used to detect the activity of individual enzymes in a few minutes within a 100 fL sensing volume. The high sensitivity, small footprint, and low analyte consumption make absorption-based microring resonators attractive for lab-on-a-chip applications. (C) 2011 Optical Society of America
We experimentally show vertically stacked, multi-layer, low-temperature deposited photonics for integration on processed microelectronics. Waveguides, microrings, and crossings are fabricated out of 400 degrees C PECVD Si3N4 and SiO2 in a two layer configuration. Waveguide losses of similar to 1 dB/cm in the L-band are demonstrated using standard processing and without post-deposition annealing, along with vertically separated intersections showing -0.04 +/- 0.002 dB/cross. Finally 3D drop rings are shown with 25 GHz channels and 24 dB extinction ratio. (C) 2011 Optical Society of America
We demonstrate the generation of broad-bandwidth optical frequency combs from a CMOS-compatible integrated microresonator. We characterize the comb quality using a novel self-referencing method and verify that the comb line frequencies are equidistant over a bandwidth of 115 nm (14.5 THz), which is nearly an order of magnitude larger than previous measurements. (C) 2011 Optical Society of America
We experimentally demonstrate four-wave-mixing (FWM)-based continuous wavelength conversion of optical differential-phase-shift-keyed (DPSK) signals with large wavelength conversion ranges as well as simultaneous wavelength conversion of dual-wavelength channels with mixed modulation formats in 1.1-cm-long dispersion-engineered silicon waveguides. We first validate up to 100-nm wavelength conversion range for 10-Gb/s DPSK signals, showcasing the capability to perform phase-preserving operations at high bit rates in chip-scale devices over wide conversion ranges. We further validate the wavelength conversion of dual-wavelength channels modulated with 10-Gb/s packetized phase-shift-keyed (PSK) and amplitude-shift-keyed (ASK) signals; demonstrate simultaneous operation on multiple channels with mixed formats in chip-scale devices. For both configurations, we measure the spectral and temporal responses and evaluate the performances using bit-error-rate (BER) measurements. (C) 2011 Optical Society of America
We demonstrate photodiodes in deposited polycrystalline silicon at 1550 nm wavelength with 0.15 A/W responsivity, 40 nA dark current, and gigahertz time response. Subband absorption is mediated by defects that are naturally present in the polycrystalline material structure. The material exhibits a moderate absorption coefficient of 6 dB/cm, which allows the same microring resonator device to act as both a demultiplexing filter and a photodetector. We discuss the use of deposited silicon-based complementary metal-oxide semiconductor materials for nanophotonic interconnects. (C) 2010 Optical Society of America
We report the first demonstration of cw wavelength conversion from the telecommunications band to the mid-IR (MIR) region via four-wave mixing in silicon nanowaveguides. We measure a parametric bandwidth of 748nm by converting a 1636nm signal to produce a 2384nm idler and show continuously tunable wavelength conversion from 1792 to 2116nm. This report indicates that the advantages of silicon photonics may be leveraged to create devices for a large range of MIR applications that require cw operation. (C) 2011 Optical Society of America
Optical isolators are essential components in optical networks and are used to eliminate parasite reflections that are detrimental to the stability of the optical systems. The challenge in realizing optical isolators lies in the fact that in standard optoelelectronic materials, including most semiconductors and metals, Maxwell’s equations, which governs the propagation of light, are constraint by reciprocity or time-reversal symmetry. As a result, standard optical devices on chip, including some of the passive metallo-dielectric structures recently explored for isolation purposes, all have a symmetric scattering matrix and therefore fundamentally cannot function as an optical isolator. In order to break this symmetry, traditional optical isolators rely upon magneto-optical effects, which require materials that are difficult to integrate in current micro-electronic systems. The breaking of this symmetry without the need for magnetic materials has been a long-term goal in photonics. Nonlinear structures for optical isolation have been explored. However, these typically provide optical isolation only within a particular range of operating power. Here we create a non-magnetic CMOS-compatible optical isolator on a silicon chip. The isolator is based on indirect interband photonic transition, induced by electrically-driven dynamic refractive index modulation. We demonstrate an electrically-induced non-reciprocity: the transmission coefficients between two single-mode waveguides become dependent on the propagation directions only in the presence of the electrical drive. The contrast ratio between forward and backward directions exceeds 30dB in simulations. We experimentally observe a strong contrast (up to 3 dB) limited only by our electrical setup, for a continuous-wave (CW) optical signal. Importantly, the device is linear with respect to signal light. The observed contrast ratio is independent of the timing, the format, the amplitude and the phase of the input signal.
Integrated photonics has been slated as a revolutionary technology with the potential to mitigate the many challenges associated with on- and off-chip electrical interconnection networks. To date, all proposed chipscale photonic interconnects have been based on the crystalline silicon platform for CMOS-compatible fabrication. However, maintaining CMOS compatibility does not preclude the use of other CMOS-compatible silicon materials such as silicon nitride and polycrystalline silicon. In this work, we investigate utilizing devices based on these deposited materials to design photonic networks with multiple layers of photonic devices. We apply rigorous device optimization and insertion loss analysis on various network architectures, demonstrating that multilayer photonic networks can exhibit dramatically lower total insertion loss, enabling unprecedented bandwidth scalability. We show that significant improvements in waveguide propagation and waveguide crossing insertion losses resulting from using these materials enables the realization of topologies that were previously not feasible using only the single-layer crystalline silicon approaches.
Synchronization, the emergence of spontaneous order in coupled systems, is of fundamental importance in both physical and biological systems. We demonstrate the synchronization of two dissimilar silicon nitride micromechanical oscillators, that are spaced apart by a few hundred nanometers and are coupled through optical radiation field. The tunability of the optical coupling between the oscillators enables one to externally control the dynamics and switch between coupled and individual oscillation states. These results pave a path towards reconfigurable massive synchronized oscillator networks.
A nonblocking four-port bidirectional multiwave-length message router for use in photonic network-on-chip (NoC) architectures implementing two-dimensional mesh or torus topologies is fully characterized with bit-error-rate measurements and eye diagrams using three wavelength-parallel 10-Gb/s channels. The experiments demonstrate the feasibility of using this advanced switching subsystem within dynamically routed multiwave-length photonic NoCs.
We propose a new class of resonant silicon optical devices, consisting of a ring resonator coupled to a Mach-Zehnder interferometer, which is passively temperature compensated by tailoring the optical mode confinement in the waveguides. We demonstrate operation of the device over a wide temperature range of 80 degrees. The fundamental principle behind this work can be extended to other photonic devices based on resonators such as modulators, routers, switches and filters.
Silicon photonics enables the fabrication of on-chip, ultrahigh-bandwidth optical networks that are critical for the future of microelectronics(1-3). Several optical components necessary for implementing a wavelength division multiplexing network have been demonstrated in silicon. However, a fully integrated multiple-wavelength source capable of driving such a network has not yet been realized. Optical amplification, a necessary component for lasing, has been achieved on-chip through stimulated Raman scattering(4,5), parametric mixing(6) and by silicon nanocrystals(7) or nanopatterned silicon(8). Losses in most of these structures have prevented oscillation. Raman oscillators have been demonstrated(9-11), but with a narrow gain bandwidth that is insufficient for wavelength division multiplexing. Here, we demonstrate the first monolithically integrated CMOS-compatible source by creating an optical parametric oscillator formed by a silicon nitride ring resonator on silicon. The device can generate more than 100 new wavelengths with operating powers below 50 mW. This source can form the backbone of a high-bandwidth optical network on a microelectronic chip.
We report error-free long-haul transmission of optical data modulated using a silicon microring resonator electro-optic modulator with modulation rates up to 12.5 Gb/s. Using bit-error-rate and power penalty characterizations, we evaluate the performance of this device with varying modulation rates, and perform a comparative analysis using a commercial electro-optic modulator. We then experimentally measure the signal integrity degradation of the high-speed optical data with increasing propagation distances, induced chromatic dispersions, and bandwidth-distance products, showing error-free transmission for propagation distances up to 80 km. These results confirm the functional ubiquity of this silicon modulator, establishing the potential role of silicon photonic interconnects for chip-scale high-performance computing systems and memory access networks, optically-interconnected data centers, as well as high-performance telecommunication networks spanning large distances.
We use transformation optics to demonstrate 2D silicon nanolenses, with wavelength-independent focal point. The lenses are designed and fabricated with dimensions ranging from 5.0 um x 5.0 um to 20 um x 20 um. According to numerical simulations the lenses are expected to focus light over a broad wavelength range, from 1.30 um to 1.60 um. Experimental results are presented from 1.52 um to 1.61 um.
We demonstrate ultrabroad-bandwidth low-power frequency conversion of continuous-wave light in a dispersion engineered silicon nanowaveguide via four-wave mixing. Our process produces continuously tunable four-wave mixing wavelength conversion over two-thirds of an octave from 1241-nm to 2078-nm wavelength light with a pump wavelength in the telecommunications C-band.
We demonstrate a 120 GHz 3-dB bandwidth on-chip silicon photonic interleaver with a flat passband over a broad spectral range of 70 nm. The structure of the interleaver is based on an asymmetric Mach-Zehnder interferometer (MZI) with 3 ring resonators coupled to the arms of the MZI. The transmission spectra of this device depict a rapid roll-off on the band edges, where the 20-dB bandwidth is measured to be 142 GHz. This device is optimized for operation in the C-band with a channel crosstalk as low as -20 dB. The device also has full reconfiguration capability to compensate for fabrication imperfections.
We present a novel design approach for integrated Mach-Zehnder interferometers to minimize their temperature sensitivity and demonstrate, for the first time, near zero spectral shifts with temperature (similar to 0.005 nm/K) in these devices. This could lead to fully CMOS-compatible passively compensated athermal optical filters and modulators.
We demonstrate the simultaneous optical manipulation and analysis of microscale particles in a microfluidic channel. Whispering gallery modes (WGMs) in dielectric microspheres are excited using the evanescent field from a silicon nitride waveguide. A supercontinuum source is used to both trap the microspheres to the surface of the waveguide and excite their resonant modes. All measurements are in plane, thus providing an integrated optofluidic platform for lab-on-a-chip biosensing applications.