Coupled-mode theory for stimulated Raman scattering in high-Q/Vm silicon photonic band gap defect cavity lasers

We demonstrate the dynamics of stimulated Raman scattering in designed high-Q/Vm silicon photonic band gap nanocavities through the coupled-mode theory framework towards optically-pumped silicon lasing. The interplay of other chi(3) effects such as two-photon absorption and optical Kerr, related free-carrier dynamics, thermal effects, as well as linear losses such as cavity radiation and linear material absorption are included and investigated numerically. Our results clarify the relative contributions and evolution of the mechanisms, and demonstrate the lasing and shutdown thresholds. Our studies illustrate the conditions for continuous-wave and pulsed highly-efficient Raman frequency conversion to be practically realized in monolithic silicon high-Q/Vm photonic band gap defect cavities.Comment: 40 pages, 11 figures, submitted to Physics Review

Panoramic-reconstruction temporal imaging for seamless measurements of slowly-evolved femtosecond pulse dynamics

Single-shot real-time characterization of optical waveforms with sub-picosecond resolution is essential for investigating various ultrafast optical dynamics. However, the finite temporal recording length of current techniques hinders comprehensive understanding of many intriguing ultrafast optical phenomena that evolve over a time scale much longer than their fine temporal details. Inspired by the space-time duality and by stitching of multiple microscopic images to achieve a larger field of view in the spatial domain, here a panoramic-reconstruction temporal imaging (PARTI) system is devised to scale up the temporal recording length without sacrificing the resolution. As a proof-of-concept demonstration, the PARTI system is applied to study the dynamic waveforms of slowly-evolved dissipative Kerr solitons in an ultrahigh-Q microresonator. Two 1.5-ns-long comprehensive evolution portraits are reconstructed with 740-fs resolution and dissipative Kerr soliton transition dynamics, in which a multiplet soliton state evolves into stable singlet soliton state, are depicted

Cascaded uncoupled dual-ring modulator

We demonstrate that by coherent driving two uncoupled rings in same direction, the effective photon circulating time in the dual ring modulator is reduced, with increased modulation quality. The inter-ring detuning dependent photon dynamics, Q-factor, extinction ratio and optical modulation amplitude of two cascaded silicon ring resonators are studied and compared with that of a single ring modulator. Experimentally measured eye diagrams, together with coupled mode theory simulations, demonstrate the enhancement of dual ring configuration at 20 Gbps with a Q ~ 20,000

Realizing quantum controlled phase-flip gate through quantum dot in silicon slow-light photonic crystal waveguide

We propose a scheme to realize controlled phase gate between two single photons through a single quantum dot in slow-light silicon photonic crystal waveguide. Enhanced Purcell factor and beta factor lead to high gate fidelity over broadband frequencies compared to cavity-assisted system. The excellent physical integration of this silicon photonic crystal waveguide system provides tremendous potential for large-scale quantum information processing.Comment: 9 pages, 3 figure

Dynamic dissipative cooling of a mechanical oscillator in strong-coupling optomechanics

Cooling of mesoscopic mechanical resonators represents a primary concern in cavity optomechanics. Here in the strong optomechanical coupling regime, we propose to dynamically control the cavity dissipation, which is able to significantly accelerate the cooling process while strongly suppressing the heating noise. Furthermore, the dynamic control is capable of overcoming quantum backaction and reducing the cooling limit by several orders of magnitude. The dynamic dissipation control provides new insights for tailoring the optomechanical interaction and offers the prospect of exploring macroscopic quantum physics.Comment: accepetd in Physical Review Letter

EuclidNet: Deep Visual Reasoning for Constructible Problems in Geometry

In this paper, we present a deep learning-based framework for solving geometric construction problems through visual reasoning, which is useful for automated geometry theorem proving. Constructible problems in geometry often ask for the sequence of straightedge-and-compass constructions to construct a given goal given some initial setup. Our EuclidNet framework leverages the neural network architecture Mask R-CNN to extract the visual features from the initial setup and goal configuration with extra points of intersection, and then generate possible construction steps as intermediary data models that are used as feedback in the training process for further refinement of the construction step sequence. This process is repeated recursively until either a solution is found, in which case we backtrack the path for a step-by-step construction guide, or the problem is identified as unsolvable. Our EuclidNet framework is validated on complex Japanese Sangaku geometry problems, demonstrating its capacity to leverage backtracking for deep visual reasoning of challenging problems.Comment: Accepted by 2nd MATH-AI Workshop at NeurIPS'2

Design, fabrication, experimentation and analysis of high-speed microscale gas bearings

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. [183]-190).Microengine Program. The all-silicon device consist of a free-rotating microturbine, with 4.2 mm rotor diameter, enclosed within a five wafer fusion-bonded stack. Of note are the low aspect ratio journal bearing and large journal bearing clearances, primarily limited by microfabrication, from which stable bearing operation must first be demonstrated as viable. Theoretical modeling of the gas-lubricated hydrostatic journal bearing presents design charts, a comparative study of existing predictions and investigation into rotational effects to consider the bearing stiffness during operation. Continued experimental refinements and exploration with our microfabricated rotor achieved rotational speeds up to 1.4 million rpm and peripheral speeds in excess of 300 m/s. Extensive experimental data is presented with analysis, focusing on whirl motion and its harmonic resonances as candidates for instability. Causes of ultimate failure is suggested with recommendations for further improvements. Moreover, in an effort to accomplish self-sustained microbearings, the axial thrust bearing is redesigned for a self-acting spiral groove bearing. The chosen constraint is to incorporate the hydrodynamic thrust bearing with minimal changes to the current device, whilst providing the required load and stiffness. Stability analysis and rarefaction considerations on the optimized design suggests an operating range for the bearing, leading to a hybrid design for ample stiffness during initial operation. The design is then developed into a microfabrication process flow and implemented successfully into the MicroBearing test devices. Experiments on a hybrid bearing were performed to gage the spiral grooves characteristics. A purely hydrodynamic aft thrust bearing device is then tested for operation through low speeds, although the effects of the spiral grooves could not be accurately determined. Finally, transition to a hydrodynamic operating mode for a hybrid bearing is demonstrated.by Chee Wei Wong.S.M