We demonstrate a low-cost colorless optical network unit (ONU) utilizing silicon photonic components for wavelength division multiplexed passive-optical-networks. At the ONU, a waveguide-coupled microring works as a demultiplexer for separating the downstream signal from the centrally distributed continuous-wave (CW) light. The 10-Gb/s downstream signal is received using a waveguide-integrated germanium photodetector while the CW light is further modulated at 5 Gb/s using a silicon microring modulator for upstream signal generation. Error-free transmission over 25-km single mode fiber is achieved with 0.2- and 0.4-dB power penalties for the downstream and upstream signals, respectively. Complementary metal-oxide semiconductor-compatible silicon photonic technology offers the potential for monolithic integration and mass production.
We demonstrate electrically driven nonreciprocity on a silicon chip. By achieving an indirect interband photonic transition, we show that the transmission coefficients between two single-mode waveguides become dependent on the propagation directions only in the presence of the electrical drive. Our structure is characterized by a nonsymmetric scattering matrix identical to a linear magneto-optical device.
A vital element in integrated optofluidics is dynamic tuning and precise control of photonic devices, especially when employing electronic techniques which are challenging to utilize in an aqueous environment. We overcome this challenge by introducing a new platform in which the photonic device is controlled using electro-optical phase tuning. The phase tuning is generated by the thermo-optic effect using an on-chip electric microheater located outside the fluidic channel, and is transmitted to the optofluidic device through optical waveguides. The microheater is compact, high-speed (> 18 kHz), and consumes low power (similar to mW). We demonstrate dynamic optical trapping control of nanoparticles by an optofluidic resonator. This novel electro-optofluidic platform allows the realization of high throughput optofluidic devices with switching, tuning, and reconfiguration capability, and promises new directions in optofluidics. (C) 2012 Optical Society of America
We demonstrate the generation of error-free binary-phase-shift-keyed (BPSK) data at 5 Gb/s using a silicon microring modulator. The microring-modulated BPSK signal is propagated at fiber lengths up to 80 km, maintaining error-free performance, while demonstrating resilience to chromatic dispersion. Bit-error-rate measurements and eye diagrams show near equivalent performance of a microring-based BPSK modulator as compared to commercial LiNbO3 phase modulators. (C) 2012 Optical Society of America
We present results for a broad bandwidth continuously tunable optical delay line based on the balanced side-coupled integrated space sequence of resonators scheme. A tunable delay of up to 345 ps is obtained without distortion of the optical signal. Fast thermal switching speed under 10 mu s is achieved without any measurable long-term transient by utilizing a novel balanced thermal tuning scheme.
We demonstrate a double-stage four-wave mixing (FWM) scheme in silicon nanowaveguides which allows effective optical time-division-multiplexed data generation and reception in the 2-mu m region. The scheme is based on a first mixing stage which unicasts a high-speed return-to-zero stream from the C-band to 1884-nm, followed by a second mixing stage which wavelength converts the data from 1884-nm down to the O-band for detection. The 10-Gb/s data traverses an aggregate record distance of 909 nm in the cascaded wavelength-conversion and unicast stages, with a power penalty of 2.5 dB. This scheme effectively overcomes the lack of commercially-available high-performance sources and receivers at 2 mu m by relying on telecommunication band components along with ultrabroad FWM silicon devices.
We demonstrate high quality factor and high confinement in a silicon ring resonator fabricated by a thermal oxidation process. We fabricated a 50 mu m bending radius racetrack resonator, with a 5 mu m coupling region. We achieved an intrinsic quality factor of 760,000 for the fundamental TM mode, which corresponds to a propagation loss of 0.9 dB/cm. Both the fundamental TE and TM modes are highly confined in the waveguide, with effective indices of 3.0 for the TE mode and 2.9 for the TM mode. (C) 2012 Optical Society of America
We demonstrate a stable complementary metal-oxide-semiconductor-compatible on-chip multiple-wavelength source by filtering and modulating individual comb lines from a parametric optical frequency comb generated in a silicon nitride microring resonator. We show comb operation in a stable lownoise state. Bit-error rate measurements demonstrate negligible power penalty from six independent frequency comb lines when compared with a tunable diode laser baseline. Open eye diagrams confirm the fidelity of the 10 Gb/s data transmitted at the comb frequencies and the suitability of this device for use as a fully integrated silicon-based wavelength-division-multiplexing source.
We measure near field radiative cooling of a thermally isolated nanostructure up to a few degrees and show that in principle this process can efficiently cool down localized hotspots by tens of degrees at submicrometer gaps. This process of cooling is achieved without any physical contact, in contrast to heat transfer through conduction, thus enabling novel cooling capabilities. We show that the measured trend of radiative cooling agrees well theoretical predictions and is limited mainly by the geometry of the probe used here as well as the minimum separation that could be achieved in our setup. These results also pave the way for realizing other new effects based on resonant heat transfer, like thermal rectification and negative thermal conductance.
Current optical communication systems rely almost exclusively on multimode fibres for short- and medium-haul transmissions, and are now expanding into the long-haul arena. Ultra-high bandwidth applications are the main drive for this expansion, based on the ability to spatially multiplex data channels in multimode systems. Integrated photonics, on the other hand, although largely responsible for today's telecommunications, continues to operate almost strictly in the single-mode regime. This is because multimode waveguides cannot be compactly routed on-chip without significant inter-mode coupling, which impairs their data rate and prevents the use of modal multiplexing. Here we propose a platform for on-chip multimode devices with minimal inter-mode coupling, opening up the possibilities for integrated multimode optics. Our work combines a novel theoretical approach-large-scale inverse design of transformation optics to maximize performance within fabrication constraints-with unique grayscale-lithography fabrication of an exemplary device: a low-crosstalk multimode waveguide bend.
We demonstrate power insensitive silicon microring resonators without the need for active feedback control. The passive control of the resonance is achieved by utilizing the compensation of two counteracting processes, free carrier dispersion blueshift and thermo-optic redshift. In the fabricated devices, the resonant wavelength shifts less than one resonance linewidth for dropped power up to 335 mu W, more than fivefold improvement in cavity energy handling capability compared to regular microrings. (C) 2012 Optical Society of America
We describe and demonstrate the use of a feedback control system to thermally stabilize a silicon microring modulator subjected to a thermally volatile environment. Furthermore, we establish power monitoring as an effective and appropriate mechanism to infer the temperature drift of a microring modulator. Our demonstration shows that a high-performance silicon microring-based device, normally inoperable in thermally volatile environments, can maintain error-free performance when a feedback control system is implemented. (C) 2012 Optical Society of America
We report extremely large probe-idler separation wavelength conversion (545 nm) and unicast (700 nm) of 10-Gb/s data signals using a dispersion-engineered silicon nanowaveguide. Dispersion-engineered phase matching in the device provides a continuous four-wave-mixing efficiency 3-dB bandwidth exceeding 800 nm. We report the first data validation of wavelength conversion (data modulated probe) and unicast (data modulated pump) of 10-Gb/s data with probe-idler separations spanning 60 nm up to 700 nm accompanied with sensitivity gain in a single device. These demonstrations further validate the silicon platform as a highly broadband flexible platform for nonlinear all-optical data manipulation. (C) 2012 Optical Society of America
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.