We demonstrate simultaneous switching of wavelength-division-multiplexed (WDM) data consisting of four 44-Gb/s channels (176 Gb/s total) through an electro-optically active second-order microring switch with a 0.7-ns rise and a 3.4-ns fall time. The higher order microring device allows fast simultaneous switching of multiple high data rate WDM channels. We verify the correct active switching operation and low resultant power penalties on both switch output ports. The ability to switch multiple high data rate channels simultaneously at high speed with low power consumption makes higher order ring switches attractive components for silicon photonic switching fabrics.
We experimentally demonstrate switching of a 40-Gb/s differential-phase-shift-keyed (DPSK) signal through a coupled silicon photonic microring switch. By simultaneously electro-optically biasing both microring cavities, we achieve 14-dB extinction ratio for signals egressing from both output ports of the switch. Packetized transmission of the 40-Gb/s DPSK signal is achieved with power penalties of 0.6 and 2.4 dB for through port and drop port signals, respectively. The effects of a coupled silicon microring are investigated, showing a broad bandwidth and a linear phase response for the drop port are necessary characteristics for routing 40-Gb/s data through the switch for photonic interconnection networks.
We present a broadband packet-switching node that utilizes silicon photonic technology. The node design uses a silicon microring for switching functionality, leverages in-flight header processing for arbitration, and has a tunable driving circuit for thermal-effect mitigation. Moreover, these integrated microring switches are capable of scaling to tremendously high port counts in a compact area, which are attractive for data-center networks. We experimentally characterize the extinction ratio of the switch for varying packet durations, interarrival times, and driving voltages and demonstrate an error-free routing of 10-Gb/s wavelength-striped packets with lengths of up to 1536 ns. We further study the resonance thermal drifting for long-hold-time packet switching through carrier injection and show thermal-effect mitigation using a pre-emphasized gating signal.
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 an optical cavity 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 toward reconfigurable synchronized oscillator networks.
We propose and experimentally demonstrate ultrawideband monocycle pulse generation using nondegenerate two-photon absorption in a silicon waveguide. The free-carrier absorption induced pulse tail at the rising edge of inverted probe pulse is largely compensated by the overlapped pump pulse and results in a symmetric negative monocycle pulse. A 143 ps Gaussian monocycle pulse is successfully obtained with a 131.7% fractional 10 dB bandwidth using a 68 ps pulsed pump. The 10 dB bandwidth and center frequency of the RF spectrum for the generated monocycle pulse can be largely tuned using an optical delay line. An operational bandwidth of 30 nm is demonstrated experimentally with stable performance, and larger optical bandwidth is expected. (C) 2012 Optical Society of America
We demonstrate a frequency comb spanning an octave via the parametric process of cascaded four-wave mixing in a monolithic, high-Q silicon nitride microring resonator. The comb is generated from a single-frequency pump laser at 1562 nm and spans 128 THz with a spacing of 226 GHz, which can be tuned slightly with the pump power. In addition, we investigate the RF amplitude noise characteristics of the parametric comb and find that the comb can operate in a low-noise state with a 30 dB reduction in noise as the pump frequency is tuned into the cavity resonance. (C) 2011 Optical Society of America
Transformation optics allows the creation of innovative devices; however, its implementation in the optical domain remains challenging. We describe here our process to design and fabricate such devices using silicon as a platform for broad band operation in the optical domain. We discuss the approximations and methods employed to overcome the challenges of using dielectric materials as a platform for transformation optics, such as the anisotropy and gradient refractive index implementation. These encompass conformal and quasi-conformal mappings, and a dithering process to discretize and quantize the continuously inhomogeneous index function. We show examples of devices that we fabricated and tested, including the carpet invisibility cloak, a broad bandwidth light concentrator, and a perfect imaging device, known as Maxwell's fish eye lens. Finally, we touch on future directions under investigation to further develop transformation optics based on dielectric materials.
We propose and experimentally demonstrate for the first time a hybrid optical packet and wavelength selective switching platform for high-performance data center networks. This architecture based on cascaded silicon microrings and semiconductor optical amplifiers (SOAs) supports wavelength reconfigurable packet and circuit switching, and is highly scalable, energy efficient and potentially integratable. By combining the wavelength-selective behavior of the microring and the broadband behavior of the SOA switch, we are able to achieve fast switching transitions, high extinction ratios, and low driving voltages, which are all requirements for future optical high-performance data center networks. Routing correctness and error-free operation (<10(-12)) are verified for both 10-Gb/s and 40-Gb/s packets and streaming data with format transparency. (C) 2011 Optical Society of America
We demonstrate an optical access network architecture utilizing the wavelength-selective behavior of micro-ring modulators to achieve single-sideband (SSB) modulation, which generates a downstream signal and simultaneously provides a centrally distributed carrier for upstream phase-remodulation. Cascaded silicon micro-rings are capable for complementary metal-oxide-semiconductor (CMOS) integration and multichannel SSB modulations which can help to significantly reduce the cost of the wavelength-division-multiplexed (WDM) passive optical networks (PONs). We further study the power penalty induced by Rayleigh backscattering from the centrally distributed carrier and show a power penalty of less than 0.6 dB when propagating 43 km of a single feeder fiber.
Stimulated emission from sensitized erbium ions in silicon-rich silicon nitride is demonstrated by pump-probe measurements carried out in waveguides. A decrease in the photoinduced absorption of the probe at the wavelength of erbium emission is observed and is attributed to stimulated emission from erbium excited indirectly via localized states in the silicon nitride matrix. (C) 2010 Optical Society of America
We theoretically investigate a wavelength-selective all-optical switch using Raman-induced loss in a silicon resonator add-drop filter. We show that picojoule control pulses can selectively modulate and "erase" a single cavity resonance from full extinction to greater than 97% transmission while leaving adjacent resonances undisturbed. Full switching is achievable in less than 300 ps with only a few hundred femtojoule energy dissipation. This represents, to our knowledge, the first scheme for selective modulation of single resonances of an optical cavity. (C) 2011 Optical Society of America
We theoretically investigate a wavelength-selective all-optical switch using Raman-induced loss in a silicon resonator add-drop filter. We show that picojoule control pulses can selectively modulate and "erase" a single cavity resonance from full extinction to greater than 97% transmission while leaving adjacent resonances undisturbed. Full switching is achievable in less than 300 ps with only a few hundred femtojoule energy dissipation. This represents, to our knowledge, the first scheme for selective modulation of single resonances of an optical cavity.
We demonstrate broadband tuning of an optomechanical microcavity optical resonance by exploring the large optomechanical coupling of a double-wheel microcavity and its uniquely low mechanical stiffness. Using a pump laser with only 13 mW at telecom wavelengths we show tuning of the silicon nitride microcavity resonances over 32 nm. This corresponds to a tuning power efficiency of only 400 mu W/nm. By choosing a relatively low optical Q resonance (approximate to 18,000) we prevent the cavity from reaching the regime of regenerative optomechanical oscillations. The static mechanical displacement induced by optical gradient forces is estimated to be as large as 60 nm. (C) 2011 Optical Society of America
We design, fabricate and characterize a CMOS-compatible, Mach-Zehnder-coupled, second-order-microring-resonator filter with large Free Spectral Range and demonstrate non-blocking thermo-optical filter reconfiguration. The device consists of 10-mu m radius silicon microring resonators, with an FSR equivalent to that of a structure consisting of 5-mu m radii microrings. The structure is reconfigurable over an 8.5 nm range without blocking other channels in the network. (C) 2011 Optical Society of America
We demonstrate broadband continuous wavelength conversion based on four-wave mixing in silicon waveguides, operating with data rates up to 40 Gb/s, validating signal integrity using bit-error-rate measurements. The dispersion-engineered silicon waveguide provides broad phase-matching bandwidth, enabling complete wavelength-conversion coverage of the S-, C-, and L-bands of the International Telecommunication Union (ITU) grid. We experimentally show this with wavelength conversion of high-speed data exceeding 100 nm, and characterize the resulting power penalty induced by the wavelength conversion process. We then validate the bit-rate transparency of the all-optical process by scaling the data rate from 5 Gb/s up to 40 Gb/s at the 100-nm wavelength conversion configuration, showing consistent low power penalties, validating the robustness of the four-wave mixing process in the silicon platform for all-optical processing.
We show that in high-index-contrast nanoscale waveguides counter propagating waves can posses distinct spatial near-field profiles. Using transmission-based near-field scanning optical microscopy (TraNSOM), we identify and map the unique near-field intensity distributions of these counter-propagating modes in a single-mode silicon waveguide. Based on this phenomenon, we design and simulate an integrated device 45 mu m in length that selectively attenuates reflected light with an insertion loss of -3.6 dB and an extinction of greater than -20 dB. (C) 2011 Optical Society of America
We experimentally demonstrate for the first time switching of differential-phase-shift-keyed (DPSK) signals through a silicon photonic electrooptic microring switch. DPSK format has been shown to be robust to nonlinear effects, and has 3-dB improved receiver sensitivity with balanced detection compared to the on-off-keyed format. Moreover, an extension to multilevel phase-shift-keyed (PSK) format enables higher data bandwidth. Packetized transmissions of single-and multichannel 10-Gb/s DPSK signals are demonstrated. Error-free transmission and power penalties of less than 1.7 dB are achieved for all the examined wavelength channels, confirming format transparency of the microring switch for PSK format, and validating the use of DPSK signaling for photonic interconnection networks.
We present a fully reconfigurable optical filter built by cascading four identical unit cells. The devices are fabricated using two distinct methods: a complementary metal–oxide–semi-conductor (CMOS) compatible process utilizes deep ultraviolet (DUV) lithography with tuning elements defined by ion implantation to make lateral p-i-n diodes for current injection regions, while an electron beam (E-beam) lithography process uses nickel chrome (NiCr) heaters as tuning elements. The fabricated devices are characterized using swept optical vector network analyzer (OVNA) coherent measurements.
We demonstrate second-and third-harmonic generation in a centrosymmetric CMOS-compatible material using ring resonators and integrated optical waveguides. The chi((2)) response is induced by using the nanoscale structure of the waveguide to break the bulk symmetry of silicon nitride (Si3N4) with the silicon dioxide (SiO2) cladding. Using a high-Q ring resonator cavity to enhance the efficiency of the process, we detect the second-harmonic output in the visible wavelength range with milliwatt input powers at telecom wavelengths. We also observe third-harmonic generation from the intrinsic chi((3)) susceptibility of the silicon nitride. Phase matching of the harmonic processes occurs due to the near coincidence of indices of refraction of the fundamental mode at the pump frequency and the corresponding higher-order modes of the harmonic fields. (C) 2011 Optical Society of America
We demonstrate high quality factor etchless silicon photonic ring resonators fabricated by selective thermal oxidation of silicon without the silicon layer being exposed to any plasma etching throughout the fabrication process. We achieve a high intrinsic quality factor of 510,000 in 50 mu m-radius ring resonators, corresponding to a ring loss of 0.8 dB/cm. The device has a total chip insertion loss of 2.5 dB, achieved by designing etchless silicon inverse nanotapers at both the input and output of the chip. (C) 2011 Optical Society of America