Since the emergence of optical fiber communications, lithium niobate (LN) has been the material of choice for electro-optic modulators, featuring high data bandwidth and excellent signal fidelity. ...Conventional LN modulators however are bulky, expensive and power hungry, and cannot meet the growing demand in modern optical data links. Chip-scale, highly integrated, LN modulators could offer solutions to this problem, yet the fabrication of low-loss devices in LN thin films has been challenging. Here we overcome this hurdle and demonstrate monolithically integrated LN electro-optic modulators that are significantly smaller and more efficient than traditional bulk LN devices, while preserving LN's excellent material properties. Our compact LN electro-optic platform consists of low-loss nanoscale LN waveguides, micro-ring resonators and miniaturized Mach-Zehnder interferometers, fabricated by directly shaping LN thin films into sub-wavelength structures. The efficient confinement of both optical and microwave fields at the nanoscale dramatically improves the device performances featuring a half-wave electro-optic modulation efficiency of 1.8 V∙cm while operating at data rates up to 40 Gbps. Our monolithic LN nanophotonic platform enables dense integration of high-performance active components, opening new avenues for future high-speed, low power and cost-effective communication networks.
Optical phased arrays are a promising beam-steering technology for ultra-small solid-state lidar and free-space communication systems. Long-range, high-performance arrays require a large beam ...emission area densely packed with thousands of actively phase-controlled, power-hungry light emitting elements. To date, such large-scale phased arrays have been impossible to realize since current demonstrated technologies would operate at untenable electrical power levels. Here we show a multi-pass photonic platform integrated into a large-scale phased array that lowers phase shifter power consumption by nearly 9 times. The multi-pass structure decreases the power consumption of a thermo-optic phase shifter to a P π of 1.7 m W / π without sacrificing speed or optical bandwidth. Using this platform, we demonstrate a silicon photonic phased array containing 512 actively controlled elements, consuming only 1.9 W of power while performing 2D beam steering over a 70 ∘ × 6 ∘ field of view. Our results demonstrate a path forward to building scalable phased arrays containing thousands of active elements.
We propose and demonstrate an integrated wavemeter capable of accurate and broadband measurements without control or knowledge of the temperature. In our design, interferometers composed of silicon ...and silicon nitride waveguides enable accurate measurements of an input optical wavelength despite large and rapid temperature fluctuations of 20°C by leveraging the disparity in thermo-optic properties of the waveguides. We derive formulas which resolve the wavelength and temperature ambiguity of the interferometers. The fabricated wavemeter chip is found to have a mean accuracy of 11 pm over an 80 nm range near 1550 nm. To our knowledge, this is the first demonstration of an athermal silicon wavemeter and the lowest measurement error across such a broad wavelength range using silicon photonics. This result may reduce the cost and size of wavemeters used in combination with integrated lasers for optical communications, sensing, and other applications.
We report on the self-biasing effect of carrier depletion based silicon microring modulators (MRM) by demonstrating that a silicon MRM can generate open eye diagrams for non-return-to-zero (NRZ) ...on-off keying (OOK) modulation without an external reverse bias supplied to it. Two modulator configurations are investigated namely single-ended drive in a ground-signal-ground and differential drive in a ground-signal-signal-ground pad configurations. The single-ended modulator is designed with an on photonic integrated circuit (PIC) 50 Ω termination. Open eye diagrams are obtained at 25 Gbit/s and 36 Gbit/s NRZ OOK modulations. We carry-out thorough experimental characterization of the self-biasing of single-ended MRM under various operating conditions of input optical power, carrier wavelength, ring quality factor and extinction ratio as well as modulation speeds, driving voltage swing and pattern length. We demonstrate that the self-biasing is robust and works well in almost all tested conditions. The differential drive MRM is designed with a high impedance without an on-PIC 50 Ω termination. Open eye diagrams are obtained at 30 Gbit/s and 60 Gbit/s NRZ OOK modulations for modulating voltage swing of ∼2.5 V pp . As demonstrated, the self-biasing works well in both single-ended and differential drive configurations as well as for on-PIC 50 Ω terminated and non-terminated MRMs. The electrical passive parts are all co-designed and fabricated on the same silicon chip as the PIC. The reported self-biasing eliminates the need of having bipolar DC biases supplied to the anode and cathode of the differential drive modulator and allows for simpler driver / modulator interfaces without inductive bias tees.
Optical devices that introduce and compensate for dispersion serve an important role in communication networks, photonic signal processing, and nonlinear optics. In this article, we demonstrate a ...silicon photonic Bragg grating which simultaneously achieves a large dispersion and wide bandwidth. We measure the grating to have a dispersion of −146 ps/nm over a 171 GHz bandwidth, representing the highest demonstrated grating dispersion over this wide bandwidth in a standard thickness silicon photonics process. Additionally, we show a significant reduction of group delay ripple by tuning the grating using an integrated phase shifter array to address fabrication variations. We further use the silicon grating as a dispersive element in a direct-detection phase retrieval receiver for 40 GBd quadrature phase shift keying (QPSK) signals and achieve a bit error rate (BER) below the 20% forward error correction (FEC) threshold. These results establish the potential for scalable silicon photonic circuits leveraging large dispersion for optical communication and other applications.
The unc-6 gene is required for the guidance of pioneer axons and migrating cells along the body wall in C. elegans. In mutants, dorsal and ventral migrations are disrupted, but longitudinal movements ...are largely unaffected. The gene was tagged for molecular cloning by two independent transposon insertions. Based on genomic and cDNA sequencing, the gene encodes a novel laminin-related protein, UNC-6 (591 amino acids). The N-terminus is homologous to the N-termini (i.e., domains V1, V-1, V-2, and V-3) of laminin subunits, while the C-terminus is a unique domain. We propose that UNC-6 is a component of an extracellular matrix cue that guides dorsoventral migrations on the epidermis.
California community college transfer students face issues of increased time to degree due to courses not being accepted for credit at the receiving four-year institution. The purpose of this study ...was to investigate if the California Student Transfer Achievement Reform Act decreased units completed and shortened time to graduation for transfer students at a California State University campus. Graduation rates for students admitted to the data collection site with an associate degree for transfer were compared with other community college students admitted on three-year graduation rates, the student’s time to degree, and the units earned to receive a bachelor’s degree. Using an ex post facto design, the groups were compared on admission with receipt of an associate degree for transfer or other community college student admits. To isolate the effect of the type of transfer associate degree, a propensity score matching technique was used to minimize the influence of the confounding variables. Results of the study were statistically significant for all questions tested. Based on a regression analysis, students showed an 84% increased chance of graduation in three years for students who transfer with a transfer associate degree compared to other community college transfer students.
In the last decade, coherent optical transmission technology has dominated the provision of high-capacity communications in metro and long-haul networks and is expected to expand to short-reach ...networks such as data center and passive optical networks. Capacities of more than 1.5 Tb/s have been demonstrated for a single wavelength. In-phase/quadrature (IQ) modulation allows information to be encoded in both the phase and amplitude of light (or in-phase and quadrature components) and is typically achieved by nested multiple Mach–Zehnder modulators (MZMs). MZMs have advantages including low chirp, broadband operation, and easy to achieve high-order quadrature amplitude modulation (QAM), but they are typically large and have high RF power consumption and excess losses. A small IQ transmitter with low RF power consumption is therefore in demand for low-cost and highly integrated coherent modules. In this paper, we experimentally demonstrate a directly reflectivity-modulated laser that can potentially achieve this goal. We demonstrate the device on a hybrid silicon/III-V platform, where silicon photonics offers compact components for filters, modulators, and reflectors, and the III-V material provides gain. In principle, the device could inherit the benefits of conventional directly modulated lasers while overcoming their speed limits. We demonstrate 32/50 Gbaud quadrature phase-shifted keying with low bit error ratios and experimentally prove the feasibility of 30 Gbaud 16-QAM.
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