A Silicon-Based Monolithic Optical Frequency Comb Source

Recently developed techniques for generating precisely equidistant optical frequencies over broad wavelength ranges are revolutionizing precision physical measurement [1-3]. These frequency "combs" are produced primarily using relatively large, ultrafast laser systems. However, recent research has shown that broad-bandwidth combs can be produced using highly-nonlinear interactions in microresonator optical parametric oscillators [4-11]. Such devices not only offer the potential for developing extremely compact optical atomic clocks but are also promising for astronomical spectroscopy [12-14], ultrashort pulse shaping [15], and ultrahigh-speed communications systems. Here we demonstrate the generation of broad-bandwidth optical frequency combs from a CMOS-compatible integrated microresonator [16,17], which is a fully-monolithic and sealed chip-scale device making it insensitive to the surrounding environment. We characterize the comb quality using a novel self-referencing method and verify that the comb line frequencies are equidistant over a bandwidth that is nearly an order of magnitude larger than previous measurements. In addition, we investigate the ultrafast temporal properties of the comb and demonstrate its potential to serve as a chip-scale source of ultrafast (sub-ps) pulses

An Integrated-Photonics Optical-Frequency Synthesizer

Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify that the fractional-frequency instability of the integrated photonics synthesizer matches the $7.0*10^{-13}$ reference-clock instability for a 1 second acquisition, and constrain any synthesis error to $7.7*10^{-15}$ while stepping the synthesizer across the telecommunication C band. Any application of an optical frequency source would be enabled by the precision optical synthesis presented here. Building on the ubiquitous capability in the microwave domain, our results demonstrate a first path to synthesis with integrated photonics, leveraging low-cost, low-power, and compact features that will be critical for its widespread use.Comment: 10 pages, 6 figure

Neuromorphic computing using wavelength-division multiplexing

Optical neural networks (ONNs), or optical neuromorphic hardware accelerators, have the potential to dramatically enhance the computing power and energy efficiency of mainstream electronic processors, due to their ultralarge bandwidths of up to 10s of terahertz together with their analog architecture that avoids the need for reading and writing data back and forth. Different multiplexing techniques have been employed to demonstrate ONNs, amongst which wavelength division multiplexing (WDM) techniques make sufficient use of the unique advantages of optics in terms of broad bandwidths. Here, we review recent advances in WDM based ONNs, focusing on methods that use integrated microcombs to implement ONNs. We present results for human image processing using an optical convolution accelerator operating at 11 Tera operations per second. The open challenges and limitations of ONNs that need to be addressed for future applications are also discussed.Comment: 13 pages, 8 figures, 160 reference

Plasmonic Terahertz Detector Based on Asymmetric Silicon Field-Effect Transistor for Real-Time Terahertz Imaging System

Department of Electrical EngineeringTerahertz (THz) technology has a great potential application owing to the unique properties of THz wave that has both permeability and feature of straight. Among the various technology in THz frequency range, THz imaging technology is very promising and attractive owing to harmlessness in human body by very low energy. In particular, for real-time THz imaging detectors, field-effect transistor (FET)-based THz detectors are now being intensively developed in multi-pixel array configuration by exploiting the silicon (Si) technology advantages of low-cost and high density integration. FET-based plasmonic wave detection mechanism, which is not limited by cut-off frequency as in transit-mode, has attractive features such as enhanced responsivity (Rv) according to frequency increase in THz range and robustness to high THz input power. To analyze the operation principle of plasmonic THz detector, an analytical device model has been implemented in terms of device physics. The non-resonant and ???overdamped??? plasma-wave behaviors have been modeled by introducing a quasi-plasma electron charge box as a two-dimensional electron gas (2DEG) in the channel region only around the source side of Si FETs. Based on the coupled non-resonant plasma-wave physics and continuity equation on the technology computer-aided design (TCAD) platform, the alternate-current (ac) signal as an incoming THz wave radiation successfully induced a direct-current (dc) drain-to-source output voltage as a detection signal in a sub-THz frequency regime under the asymmetric boundary conditions between source and drain. The significant effects of asymmetric source and drain structure, channel shape on the charge asymmetry and performance enhancement have been analytically investigated based on non-resonant plasmonic THz detection theory. By designing and fabricating an asymmetric transistor integrated with antenna, more enhanced channel charge asymmetry has been obtained for enhanced detection response. Through verification of the advanced non-quasi-static (NQS) compact model, the intrinsic FET delay and total detector delay in THz plasmonic detection are successfully characterized and are small enough to guarantee a real-time operating detector. These results can provide that the real-time THz imaging of moving objects has been experimentally demonstrated based on plasmonic 1x200 array scanner by using the high/fast detecting performance asymmetric FET and multiplexer/amplifier circuits. The highly-enhanced Rv and reduced noise equivalent power (NEP) have been demonstrated by exploiting monolithic transistor-antenna device considering impedance matching between transistor and antenna. This record-high enhancement is due to antenna mismatching and feeding line loss reduction as well as the enhanced charge asymmetry in the proposed monolithic transistor-antenna device. Therefore, high-performance plasmonic THz detector based on asymmetric Si FET can compete as commercial THz detector by taking advantages of monolithic device technology for real-time THz imaging system.ope

The physics of optical computing

There has been a resurgence of interest in optical computing over the past decade, both in academia and in industry, with much of the excitement centered around special-purpose optical computers for neural-network processing. Optical computing has been a topic of periodic study for over 50 years, including for neural networks three decades ago, and a wide variety of optical-computing schemes and architectures have been proposed. In this paper we provide a systematic explanation of why and how optics might be able to give speed or energy-efficiency benefits over electronics for computing, enumerating 11 features of optics that can be harnessed when designing an optical computer. One often-mentioned motivation for optical computing -- that the speed of light $c$ is fast -- is not a key differentiating physical property of optics for computing; understanding where an advantage could come from is more subtle. We discuss how gaining an advantage over state-of-the-art electronic processors will likely only be achievable by careful design that harnesses more than one of the 11 features, while avoiding a number of pitfalls that we describe.Comment: 31 pages; 11 figure