The growth of integrated photonics has driven the need for efficient, high-bandwidth electrical-to-optical (EO) signal conversion over a broad range of frequencies (MHz–THz), together with efficient, high bandwidth photodetection. Efficient signal conversion is needed for applications including fiber/wireless telecom, data centers, sensing/imaging, metrology/spectroscopy, autonomous vehicle platforms, etc., as well as cryogenic supercomputing/quantum computing. Diverse applications require the ability to function over a wide range of environmental conditions (e.g., temperatures from <4 to >400 K). Active photonic device footprints are being scaled toward nanoscopic dimensions for size compatibility with electronic elements. Nanophotonic devices increase optical and RF field confinement via small feature sizes, increasing field intensities by many orders of magnitude, enabling high-performance Pockels effect materials to be ultimately utilized to their maximum potential (e.g., in-device voltage-length performance ≤0.005 V mm). Organic materials have recently exhibited significant improvements in performance driven by theory-guided design, with realized macroscopic electro-optic activity (r33) exceeding 1000 pm/V at telecom wavelengths. Hybrid organic/semiconductor nanophotonic integration has propelled the development of new organic synthesis, processing, and design methodologies to capture this high performance and has improved understanding of the spatial distribution of the order of poled materials under confinement and the effects of metal/semiconductor-organic interfaces on device performance. Covalent coupling, whether from in situ crosslinking or sequential synthesis, also provides a thermally and photochemically stable alternative to thermoplastic EO polymers. The alternative processing techniques will reduce the attenuation of r33 values observed in silicon organic hybrid and plasmonic organic hybrid devices arising from chromophore-electrode electrostatic interactions and material conductance at poling temperatures. The focus of this perspective is on materials, with an emphasis on the need to consider the interrelationship between hybrid device architectures and materials.

Novel approaches towards new generations of graphene plasmonic modulators and detectors with responses of 500 GHz and beyond are introduced. Important performance parameters such as losses, efficiency or responsivity are addressed by combining the technologies.

We demonstrate a new concept in an electro-optical memristor where a global light stimulus induces non-volatile conductance changes. The optical signal acts as a third, independent stimulation channel, similar to neuromodulators in three-factor learning rules.

We integrate memristors in a silicon photonic/plasmonic platform and demonstrate modulators, photodetectors and electronic devices complemented with memory effect. The demonstrated memristors could be the key photonic building blocks in hybrid photonic-electronic neuromorphic chips.

Ultra-short, low-loss graphene-organic hybrid phase modulators are introduced. 20 Gbit/s PAM-2 and PAM-4 data modulation are demonstrated with devices of 25 μm length and on-chip losses of 0.86 dB.

A plasmonically enhanced graphene organic hybrid electro-optic phase modulator of 10 μm length with low plasmonic losses of 2.5 dB and a bandwidth of 270 GHz and beyond is demonstrated. The device is verified for high-speed on-off-keying data modulation at a line rate of 140 Gbit/s.

Plasmonics has emerged as a promising technological solution for realizing high-performance nanoscale communication photonic devices. This paper reports our recent advances on high-performance plasmonic modulators and photodetectors.

An electrically tunable graphene-organic hybrid ring resonator using graphene electrodes and organic nonlinear electric-optic materials is proposed and realized. The presented ring resonator demonstrates a high loaded quality factor of 960 and an extracted effective Pockels effect coefficient of 24 pm/V.

We present a plasmonic platform featuring efficient, broadband metallic fiber-to-chip couplers that directly interface plasmonic slot waveguides, such as compact and high-speed electro-optic modulators. The metallic gratings exhibit an experimental fiber-to-slot coupling efficiency of -2.7 dB with -1.4 dB in simulations with the same coupling principle. Further, they offer a huge spectral window with a 3 dB passband of 350 nm. The technology relies on a vertically arranged layer stack, metal-insulator-metal waveguides, and fiber-to-slot couplers and is formed in only one lithography step with a minimum feature size of 250 nm. As an application example, we fabricate new modulator devices with an electro-optic organic material in the slot waveguide and reach 50 and 100 Gbit/s data modulation in the O- and C-bands within the same device. The devices' broad spectral bandwidth and their relaxed fabrication may render them suitable for experiments and applications in the scope of sensing, nonlinear optics, or telecommunications.

Metallic grating couplers can be extremely broadband and efficient. In this work, we investigate an all-plasmonic fiber-to-chip coupler with a coupling efficiency of -2.7 dB and an optical 3-dB passband of 300 nm.

A ferroelectric, metal-oxide-semiconductor (MOS) based, hybrid-plasmonic modulator is shown to feature bandwidths of >150 GHz and is tested with 32 Gbit/s NRZ. The device is relying on BaTiO3-on-SOI and potentially offers CMOS compatibility.

The typically nonlinear and asymmetric response of synaptic memristors to positive and negative electrical pulses makes the realization of accurate deep neural networks very challenging. Here, we integrate a two-terminal valence change memory (VCM) into a photonic/plasmonic circuit and show that the switching properties of this memristor become more gradual and symmetric under light irradiation. The added optical input acts on the VCM as a third, independent modulation channel. It locally heats the active area of the device, which enhances the generation of oxygen vacancies and broadens the resulting nanoscale conductive filaments. The measured conductance modulation of the VCM is then inserted into a neural network simulator. Using the MNIST data set of handwritten digits as an application, a light-enhanced recognition accuracy of 93.53% is demonstrated, similar to ideally performing memristors (94.86%) and much higher than those without light (67.37%). Notably, the optical signal does not increase the overall energy consumption by more than 3.2%. Finally, an approach to scale up our electro-optical technology is proposed, which could allow high-density, energy-efficient neuromorphic computing chips.

A novel plasmonic graphene-organic hybrid phase modulator featuring the short length and fast speed of plasmonics (10µm length, bandwidths in excess of 70GHz) but benefitting from the lower losses of graphene (on-chip insertion losses of 4.5dB) is introduced. Successful operation at 100 Gbit/s is shown.

A plasmonic modulator spanning both C- and O-band for dual-band data modulation up to 100 Gbit/s in one single device is presented. Fiber-to-fiber insertion loss can be as low as 11 dB.

An ultra-compact plasmonic resonator is experimentally demonstrated. The presented sub-gm long inline waveguide-coupled plasmonic resonator features a resonance around 1550 nm with a measured loaded quality factor of 20.

Memristive-based electro-optical neuromorphic hardware takes advantage of both the high-density of electronic circuits and the high bandwidth of their photonic counterparts, thus showing potential for low-power artificial intelligence applications. In this Perspective paper, we introduce a class of electro-optical memristors that can emulate the key properties of synapses and neurons, which are essential features for the realization of electro-optical neuromorphic functionalities. We then describe the challenges associated with existing technologies and finally give our viewpoint on possible developments toward an energy-efficient neuromorphic platform.

Intensive efforts have been devoted to the exploration of new optoelectronic devices based on two-dimensional transition-metal dichalcogenides (TMDCs) owing to their strong light-matter interaction and distinctive material properties. In particular, photodetectors featuring both high-speed and high-responsivity performance are of great interest for a vast number of applications such as high-data-rate interconnects operated at standardized telecom wavelengths. Yet, the intrinsically small carrier mobilities of TMDCs become a bottleneck for high-speed application use. Here, we present high-performance vertical van der Waals heterostructure-based photodetectors integrated on a silicon photonics platform. Our vertical MoTe2-graphene heterostructure design minimizes the carrier transit path length in TMDCs and enables a record-high measured bandwidth of at least 24 GHz under a moderate bias voltage of -3 V. Applying a higher bias or employing thinner MoTe2 flakes boosts the bandwidth even to 50 GHz. Simultaneously, our device reaches a high external responsivity of 0.2 A W-1 for incident light at 1,300 nm, benefiting from the integrated waveguide design. Our studies shed light on performance trade-offs and present design guidelines for fast and efficient devices. The combination of two-diemensional heterostructures and integrated guided-wave nano photonics defines an attractive platform to realize high-performance optoelectronic devices, such as photodetectors, light-emitting devices and electro-optic modulators. The low carrier mobilities of TMDCs pose a challenge for applications in high-speed photodetection. Integrating vertical two-dimensional heterostructures with photonic waveguides allows the intrinsic speed limitations to be overcome and record-high photodetection bandwidths to be achieved.

We demonstrate an on-chip coherent mode scrambling demultiplexer for polarization multiplexed few mode signals. The device has been fabricated in the standard silicon-on-insulator platform. The mode demultiplexer consists of an array of 2D grating couplers for dual polarization few mode fiber-to-chip coupling and optical hybrids realized by 4×4 MMIs. The array of perfect vertical 2D grating couplers allows us an efficient fiber-to-chip coupling with experimental peak coupling efficiencies of -5.2 dB and -9.0 dB at 1570 nm for LP01 and LP11 modes, respectively, while simulated coupling efficiencies at 1550 nm are -3.6 dB and -3.3 dB for LP01 and LP11, respectively. We successfully performed a back-to-back three LP modes division multiplexing transmission experiment with single polarization 32 Gbaud QPSK signals using the fabricated mode demultiplexer relying on offline MIMO DSP techniques.

We realize an all-plasmonic optical communication link operating at 100 Gbit/s NRZ, in which the optical transmitter and receiver rely on a plasmonic-organic modulator and a plasmonic-graphene photodetcctor. respectively. © 2019 The Author(s)

The atom marks the ultimate scaling limit of Moore’s law, which is why atomic scale devices have attracted significant research interests from the electronics industry. To allow efficient co-integration of electronics and photonics, key components such as photodetectors [1] and modulators [2] should match the footprint of electronic devices. Here we demonstrate the first atomic-scale plasmonic photodetector where atoms rather than electrons are responsible for the device operation. The concept is based on a so-called electro-chemical metallization (ECM) cell where an atomic-scale conductive filament is partially dissolved through a plasmonic-thermal effect. To realize this new type of photodetectors, three different disruptive technologies have been combined into one single fabrication process. First, a 3-D photonic technology based on a modified self-aligned approach of local-oxidation of silicon (LOCOS) has been developed for silicon-on-insulator (SOI) substrates. This is an important step as it enables the integration of tip-based atomic-scale plasmonics within a low-loss bus photonic waveguide. Second, vertical 3-D adiabatic plasmonic couplers have been fabricated using two e-beam lithography steps and a lift off process. The resulting metal-insulator-metal (MIM) waveguide that houses the ECM cell consists of a silver and a platinum contact separated by a gap of 20 nanometers. Finally, the atomic scale junction has been realized by electroforming a silver filament inside the ECM cell. To investigate the operation principle of this photodetector, a 3-D axis-symmetrical finite element method (FEM) model has been implemented that is able to self-consistently simulate the device resistance as a function of the applied voltage and temperature. The electrochemical growth and dissolution of a conductive filament between two electrodes is modeled analogously to the work of Refs. [3] and [4]. The current through the device is approximated as a tunneling current whose dependence on the filament state can be derived from ab initio quantum transport calculations. The microscopic nature of the device is also taken into account by considering an electrical double layer at the metal-insulator interfaces that accurately describes the electrostatic potential distribution within the ECM device. The incorporation of first-principles results [5] allowed us to significantly reduce the number of free parameters. Two light-matter interaction mechanisms have been identified and investigated, namely the optical force acting on individual filament atoms and the heating through electromagnetic dissipation in the metal. An atomistic study based on real-time time-dependent density-functional theory revealed that the optical forces are not strong enough to move single atoms, which leaves the optically-induced temperature as the main driving force behind the filament dissolution. In this paper we will show through accurate device simulations that this is indeed what is happening: the variation of the temperature at the metal-insulator interfaces strongly affect the electron transfer rates between these two regions, which explains the observed device behavior. Quantitative agreement between simulation and experiments will be demonstrated, thus opening up the possibility of future computer-aided designs of atomic-scale photodetectors. References [1] Emboras et al. doi:10.1021/acsnano.8b01811 [2] Emboras et al. doi:10.1021/acs.nanolett.5b04537 [3] Menzel. doi:10.1007/s10825-017-1051-2 [4] Lin et al. doi:10.1109/IEDM.2012.6479107 [5] Ducry et al. doi:10.1109/IEDM.2017.8268324