Optical Building Blocks Research Articles

Fundamental Asymmetries between Spatial and Temporal Boundaries in Electromagnetics

Time-varying materials bring an extra degree of design freedom compared to their conventional time-invariant counterparts. However, few discussions have focused on the underlying physical difference between spatial and temporal boundaries. In this letter, we thoroughly investigate those differences from the perspective of conservation laws. By doing so, the building blocks of optics and electromagnetics such as the reflection law, Snell’s law, and Fresnel’s equations can be analogously derived in a temporal context, but with completely different interpretations. Furthermore, we study the unique features of temporal boundaries, such as their nonconformance to energy conservation and causality.

On-chip coherent frequency-domain THz spectroscopy for electrical transport

We developed a coherent frequency-domain terahertz (THz) spectroscopic technique on a coplanar waveguide in the ultrabroad frequency range from 200 MHz to 1.6 THz based on continuous wave (CW) laser spectroscopy. Optical beating created by mixing two frequency-tunable CW lasers is focused on photoconductive switches to generate and detect high-frequency current in a THz circuit. In contrast to time-domain spectroscopy, our frequency-domain spectroscopy enables an unprecedented frequency resolution of 10 MHz without using the complex building blocks of femtosecond laser optics. Furthermore, due to the coherent nature of the photomixing technique, we are able to identify the origin of multiple reflections in the time domain using the Hilbert analysis and inverse Fourier transform. These results demonstrate that the advantages of on-chip coherent frequency-domain spectroscopy, such as its broadband, frequency resolution, usability, and time-domain accessibility, provide a unique capability for measuring ultrafast electron transport in integrated THz circuits.

O-band N-rich silicon nitride MZI based on GST

We have experimentally demonstrated an O-band Mach–Zehnder interferometer (MZI) based on an N-rich silicon nitride platform combined with Ge2Sb2Te5 for future optical communication applications. The device operation relies on controlling the waveguide's losses using a phase change material cell, which can be changed from amorphous (low-loss) to crystalline (high-loss). An extinction ratio as high as 11 dB was obtained between the amorphous (ON) and the crystalline (OFF) states of the MZI optical building block. The insertion loss of the MZI structure per cell unit length was measured to be as high as 0.87 dB/μm in the OFF state and as low as 0.064 dB/μm in the ON state for TM polarization.

Tunable Optical Properties in Self‐Assembled Oxide‐Metal Hybrid Thin Films via Au‐Phase Geometry Control: From Nanopillars to Nanodisks

AbstractPlasmonic oxide‐metal hybrid nanostructures exhibit unprecedented optical properties because of the nanoscale interactions between the oxide and metal components. Precise control of the geometry and arrangement of optical building blocks is key to tailoring system properties toward various nanophotonic applications. Herein, self‐assembled BaTiO3‐Au vertically aligned nanocomposite thin films with a series of thicknesses are fabricated using a one‐step pulsed laser deposition technique. By reducing the film thickness, the geometry of Au phase is effectively tailored from nanopillars to nanodisks, with the aspect ratio (height/width) varied from ≈4.0 to ≈1.0. The experimental optical spectra and numerical simulation results demonstrate that localized surface plasmon resonance and hyperbolic dispersion wavelength can be effectively tuned in the visible to near‐infrared regime by varying the film thickness due to the change of Au aspect ratio and free electron density. This study demonstrates a feasible approach in tuning the optical responses in hybrid oxide‐metal nanostructures, and opens up enormous possibilities in design and fabrication of novel optical components toward all optical integrated devices.

Discorrelated quantum states

The statistical properties of photons are fundamental to investigating quantum mechanical phenomena using light. In multiphoton, two-mode systems, correlations may exist between outcomes of measurements made on each mode which exhibit useful properties. Correlation in this sense can be thought of as increasing the probability of a particular outcome of a measurement on one subsystem given a measurement on a correlated subsystem. Here, we show a statistical property we call “discorrelation”, in which the probability of a particular outcome of one subsystem is reduced to zero, given a measurement on a discorrelated subsystem. We show how such a state can be constructed using readily available building blocks of quantum optics, namely coherent states, single photons, beam splitters and projective measurement. We present a variety of discorrelated states, show that they are entangled, and study their sensitivity to loss.

Artificial Neuron Based on Integrated Semiconductor Quantum Dot Mode-Locked Lasers.

Neuro-inspired implementations have attracted strong interest as a power efficient and robust alternative to the digital model of computation with a broad range of applications. Especially, neuro-mimetic systems able to produce and process spike-encoding schemes can offer merits like high noise-resiliency and increased computational efficiency. Towards this direction, integrated photonics can be an auspicious platform due to its multi-GHz bandwidth, its high wall-plug efficiency and the strong similarity of its dynamics under excitation with biological spiking neurons. Here, we propose an integrated all-optical neuron based on an InAs/InGaAs semiconductor quantum-dot passively mode-locked laser. The multi-band emission capabilities of these lasers allows, through waveband switching, the emulation of the excitation and inhibition modes of operation. Frequency-response effects, similar to biological neural circuits, are observed just as in a typical two-section excitable laser. The demonstrated optical building block can pave the way for high-speed photonic integrated systems able to address tasks ranging from pattern recognition to cognitive spectrum management and multi-sensory data processing.

Magnetoplasmonic Faraday Rotators: Enabling Gigahertz Active Polarization Control for Integrated Plasmonics

We present the design and theoretical characterization of a magnetoplasmonic Faraday rotator for active polarization control in integrated plasmonics. By incorporating bismuth-substituted yttrium iron garnet (Bi:YIG) into a unique hybrid ridge–plasmonic waveguide structure, we effectively overcome the phase-matching limitations between photonic TE and plasmonic TM modes, and hence attain efficient Faraday rotation within a plasmonic device. The device provides 99.4% polarization conversion within a length of 830 μm, while the two modes exhibit propagation lengths in excess of 1 mm. This versatile optical building block can be operated with either a TE or TM input, making it ideal for polarization switching and polarization division multiplexing. Additionally, a buried Ag transmission line under the waveguide facilitates high-speed active polarization modulation by generating transient magnetic fields and modulating the Bi:YIG magnetization. We show that with these transient fields and an external static b...

Focus on sensors and detectors

Focus on sensors and detectors

Optical Buffering for Chip Multiprocessors: A 16GHz Optical Cache Memory Architecture

We demonstrate a 16GHz physical layer optical cache memory architecture for direct mapping associativity, organized in four cache lines with every line being capable of storing two bytes of optical data. WDM formatting of both the memory address and the optical data words is exploited, while the proposed design relies on the interconnection of subsystems that comprise experimentally proven optical building blocks. The performance of the optical cache is evaluated via physical layer simulations showing successful functionality both during Read and Write operation. Going a step further and considering a higher capacity optical cache module, we present its impact when performing with true processor workload benchmarks in Chip Multiprocessor configurations, employed as a L1 cache shared among multiple cores. Its performance is compared with the conventional electronic CMP topology, where dedicated L1 electronic caches and a shared L2 cache are used, showing that the use of optical 16GHz cache can lead to performance speed-up up to 40% while reducing the cache total capacity requirements by 84%. With optical interconnects having already resulted to high-bandwidth CPU-memory bus solutions, our optical cache architecture forms a fully compatible system solution for bridging the gap between optically connected CPU-cache schemes and high-speed optical RAM cell solutions.

Development of electro‐optical PCBs with polymer waveguides for high‐speed intra‐system interconnects

PurposeThe purpose of this paper is to study fabrication of optical‐PCBs on panel scale boards in a conventional modern PCB process environment. It evaluates impacts on board design and manufacturing with the developed optical board verifiers outlining challenges and requirements for manufacturing low‐loss waveguide structures and optical building blocks. The study aims to expand the current knowledge in the field by adding results obtained by utilizing industrial production infrastructure and developed scalable manufacturing processes to fabricate optical‐PCBs and board assemblies in high‐volumes and low‐cost manner.Design/methodology/approachImpacts on board design and manufacturing were studied with the developed optical technology verifiers. One verifier is optical‐PCB with embedded waveguides, integrated i/o couplers and optical vias. Another verifier is large size PCB with optical layer. A system‐level optical board assembly with 12.5 Gb/s Tx/Rx devices on surface mounted ball grid array (BGA) modules is designed for optical link analysis. Fabricated optical structures on verifiers are evaluated of their physical characteristics utilizing optical, SEM, LSCM analysis methods. Performance testing is conducted using standard optical transmission measurement methods and equipment.FindingsThe paper provides empirical results about fabrication of multimode optical waveguides with conventional PCB process equipment. Results suggest that current coating and imaging equipments are capable of producing optical waveguide patterns with high resolution and size accuracy. However, fabricators would require larger process window and defect tolerance for processing optical materials to obtain low‐loss waveguides with sufficient yields.Research limitations/implicationsBecause of the limited amount of design variants in production verifiers evaluated in this paper, some impacts like effect of base material, board construction, optical layer location and beam coupling solution were not evaluated. Likewise, impacts on long‐term stability and cost were not addressed. These factors however require further investigation to address technical feasibility of optical PCBs technology prior commercial high volume production.Practical implicationsThe paper includes implications for the development of a fabrication methods and testing procedures for optical polymer waveguide layers on PCBs.Originality/valueThis paper fulfils need to provide results on design, fabrication and characterization of optical PCBs and backplanes from industrial fabricator's perspective. The paper provides input for end‐user and developers to evaluate technical performance, robustness, and maturity of building blocks and supply chain to support polymer waveguide based technology for intra‐system optical links.

Wavelength-Agile Silicon Photonic Integrated Circuit forLow-Cost Optical Receiver

We report our recent work on wavelength-agile silicon photonic integrated circuit for low-cost optical receiver, which includes a monolithic integrated germanium p-i-n photodetector and a tunable filter. The circuit is fabricated using standard CMOS technology on SOI platform, paving the way for further integration with more optical building blocks and CMOS transistor circuits. The wavelength tuning range of the integrated circuit is ~11.5 nm along with the tuning speed of less than 400 μs. The tuning efficiency is ~0.16 nm/mW. The measured fiber-to-PD responsivity of the photonic integrated circuit is ~0.10 A/W. A photonics packaging structure for the silicon PIC is also proposed.

AWG-based metro WDM networking

A plethora of metropolitan area wavelength-division multiplexing networks have been proposed and examined in recent years with the aim to alleviate the bandwidth bottleneck between increasingly higher-speed local/access networks and high-speed backbone networks. Many of the considered metropolitan area networks use the arrayed waveguide grating as an optical building block. As we review in this article, in ring, interconnected ring, and meshed metro WDM networks, the AWG is typically used to realize wavelength multiplexers, demultiplexers, or optical add-drop multiplexers without capitalizing on spatial wavelength reuse. By using the AWG as a wavelength router, highly efficient star metro WDM networks can be realized due to extensive spatial wavelength reuse. We give an overview of star metro WDM networks that are able to meet modular upgradability, transparency, flexibility, efficiency, reliability, and protection requirements of future metro networks. AWG-based star networks also enable an evolution path of ring networks toward highly efficient and fault-tolerant hybrid star-ring metro network solutions.

Optics modules for circular accelerator design

This paper is intended as a comparison paper to “Circular Machine Design Techniques and Tools” presented at this conference by Roger Servranckx. The intent here is to provide a tutorial discussion on the basic optics of circular particle accelerators for the benefit of those readers who have a fundamental knowledge of charged particle optics but do not make it their profession to design particle accelerators. We begin the tutorial by presenting the solutions of the first-order differential equations of motion for a single particle in a closed circular machine introducing the concepts of phase shift, beta functions, and the Courant-Snyder invariant. From these solutions we derive the transfer matrix between two points in the machine as a function of the phase shift and the parameters contained in the Courant-Snyder invariant. We then introduce typical optical building blocks (modules) used in circular machine designs and relate them to their characteristic transfer matrix elements, the phase shift through them, and the Courant-Snyder-Twiss parameters, β, α, and γ. Next we discuss the systematics of some elementary phase ellipse matching problems between optical modules. The report ends with a discussion of second-order optical modules and how they are used to provide the momentum bandwidth needed for the design of a typical circular machine.

Chirped-grating output couplers in dielectric waveguides

This paper reports on the method of fabrication and first experiments of chirped (variable period) gratings in a dielectric waveguide. Such gratings, which are proposed as a new optical building block, are used in this work as focusing output couplers.