Topological photonics in strongly coupled light-matter systems offer the possibility for fabricating tunable optical devices that are robust against disorder and defects. Topological polaritons, ...i.e., hybrid exciton-photon quasiparticles, have been proposed to demonstrate scatter-free chiral propagation, but their experimental realization to date has been at deep cryogenic temperatures and under strong magnetic fields. We demonstrate helical topological polaritons up to 200 kelvin without external magnetic field in monolayer WS
excitons coupled to a nontrivial photonic crystal protected by pseudo time-reversal symmetry. The helical nature of the topological polaritons, where polaritons with opposite helicities are transported to opposite directions, is verified. Topological helical polaritons provide a platform for developing robust and tunable polaritonic spintronic devices for classical and quantum information-processing applications.
Electro-optic modulators perform a key function for data processing and communication. Rapid growth in data volume and increasing bits per second rates demand increased transmitter and thus modulator ...performance. Recent years have seen the introduction of new materials and modulator designs to include polaritonic optical modes aimed at achieving advanced performance in terms of speed, energy efficiency, and footprint. Such ad hoc modulator designs, however, leave a universal design for these novel material classes of devices missing. Here we execute a holistic performance analysis for waveguide-based electro-absorption modulators and use the performance metric switching energy per unit bandwidth (speed). We show that the performance is fundamentally determined by the ratio of the differential absorption cross-section of the switching material's broadening and the waveguide effective mode area. We find that the former shows highest performance for a broad class of materials relying on Pauli-blocking (absorption saturation), such as semiconductor quantum wells, quantum dots, graphene, and other 2D materials, but is quite similar amongst these classes. In this respect these materials are clearly superior to those relying on free carrier absorption, such as Si and ITO. The performance improvement on the material side is fundamentally limited by the oscillator sum rule and thermal broadening of the Fermi-Dirac distribution. We also find that performance scales with modal waveguide confinement. Thus, we find highest energy-bandwidth-ratio modulator designs to be graphene, QD, QW, or 2D material-based plasmonic slot waveguides where the electric field is in-plane with the switching material dimension. We show that this improvement always comes at the expense of increased insertion loss. Incorporating fundamental device physics, design trade-offs, and resulting performance, this analysis aims to guide future experimental modulator explorations.
As electronic device feature sizes scale‐down, the power consumed due to onchip communications as compared to computations will increase dramatically; likewise, the available bandwidth per ...computational operation will continue to decrease. Integrated photonics can offer savings in power and potential increase in bandwidth for onchip networks. Classical diffraction‐limited photonics currently utilized in photonic integrated circuits (PIC) is characterized by bulky and inefficient devices compared to their electronic counterparts due to weak light–matter interactions (LMI). Performance critical for the PIC is electro‐optic modulators (EOM), whose performances depend inherently on enhancing LMIs. Current EOMs based on diffraction‐limited optical modes often deploy ring resonators and are consequently bulky, photon‐lifetime modulation limited, and power inefficient due to large electrical capacitances and thermal tuning requirements. In contrast, wavelength‐scale EOMs are potentially able to surpass fundamental restrictions set by classical (i.e. diffraction‐limited) devices via (a) high‐index modulating materials, (b) nonresonant field and density‐of‐states enhancements such as found in metal optics, and (c) synergistic onchip integration schemes. This manuscript discusses challenges, opportunities, and early demonstrations of nanophotonic EOMs attempting to address this LMI challenge, and early benchmarks suggest that nanophotonic building blocks allow for densely integrated high‐performance photonic integrated circuits.
The performances of electro‐optic modulators (EOM) is determined by the interaction strength between light and matter. Here, EOMs based on sub‐diffraction‐limited optical modes are summarized and discussed. These devices show performance metrics that are able to surpass classical device limits through (a) optical field enhancements, (b) low‐Q resonators and (c) synergistic integration schemes including emerging materials for strong index modulation.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Plasmon lasers are a new class of coherent optical amplifiersthat generate and sustain light well below its diffraction limit. Their intense, coherent and confined optical fields can enhance ...significantly light-matter interactions and bring fundamentallynew capabilities to bio-sensing, data storage, photolithography and optical communications. However, metallic plasmon laser cavities generally exhibit both high metal and radiation losses, limiting the operation of plasmon lasers to cryogenic temperatures, where sufficient gain can be attained. Here, we present a room-temperature semiconductor sub-diffraction-limited laser by adopting total internal reflection of surface plasmons to mitigate the radiation loss, while using hybrid semiconductor-insulator-metal nanosquares for strong confinement with low metal loss. High cavity quality factors, approaching 100, along with strong λ/20 mode confinement, lead to enhancements of spontaneous emission rate by up to 18-fold. By controlling the structural geometry we reduce the number of cavity modes to achieve single-mode lasing.
Full text
Available for:
IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The ability to modulate light using 2-dimensional (2D) materials is fundamentally challenged by their small optical cross-section leading to miniscule modal confinements in diffraction-limited ...photonics despite intrinsically high electro-optic absorption modulation (EAM) potential given by their strong exciton binding energies. However the inherent polarization anisotropy in 2D materials and device tradeoffs lead to additional requirements with respect to electric field directions and modal confinement. A detailed relationship between modal confinement factor and obtainable modulation strength including definitions on bounding limits are outstanding. Here, we show that the modal confinement factor is a key parameter determining both the modulation strength and the modulator extinction ratio-to-insertion loss metric. We show that the modal confinement and hence the modulation strength of a single-layer modulated 2D material in a plasmonically confined mode is able to improve by more than 10× compared to diffraction-limited modes. Combined with the strong-index modulation of graphene, the modulation strength can be more than 2-orders of magnitude higher compared to Silicon-based EAMs. Furthermore, modal confinement was found to be synergistic with performance optimization via enhanced light-matter-interactions. These results show that there is room for scaling 2D-material EAMs with respect to modal engineering toward realizing synergistic designs leading to high-performance modulators.
Advances in opto-electronics are often led by discovery and development of
materials featuring unique properties. Recently, the material class of
transparent conductive oxides (TCO) has attracted ...attention for active photonic
devices on-chip. In particular, indium tin oxide (ITO) is found to have
refractive index changes on the order of unity. This property makes it possible
to achieve electrooptic modulation of sub-wavelength device scales, when thin
ITO films are interfaced with optical light confinement techniques such as found
in plasmonics; optical modes are compressed to nanometer scale to create strong
light-matter interactions. Here we review efforts towards utilizing this novel
material for high performance and ultra-compact modulation. While high
performance metrics are achieved experimentally, there are open questions
pertaining to the permittivity modulation mechanism of ITO. Finally, we review a
variety of optical and electrical properties of ITO for different processing
conditions, and show that ITO-based plasmonic electro-optic modulators have the
potential to significantly outperform diffractionlimited devices.
Spotlight on Plasmon Lasers Sorger, Volker J.; Zhang, Xiang
Science (American Association for the Advancement of Science),
08/2011, Volume:
333, Issue:
6043
Journal Article
Peer reviewed
A plasmonics-based design approach is enabling coherent light sources to be built at the nanometer scale.
Lasers are the workhorse of the information age, sending massive amounts of light packets ...through vast networks of optic fibers. Demands for ever-increasing speed and functionalities call for scaling down of photonic devices, similar to the trend in electronics. However, photonic devices face the fundamental challenge of the diffraction limit of light—a limitation that prevents squeezing light into spaces smaller than half of its wavelength. This barrier limits traditional optical components to sizes that are hundreds of times larger than that of their electronic counterparts. Surface plasmons are collective electronic oscillations on a metal-dielectric interface with a much smaller wavelength than the excitation or emitted photons, and have emerged as a promising solution to overcome such a barrier (
1
). In 2003, the surface plasmon laser or “spaser” was theoretically proposed. The idea was to tightly confine light in the form of localized plasmons into deep subwavelength dimensions overlapping with a gain medium to achieve stimulated emission and light amplification or lasing, creating a coherent light source at the nanometer scale (
2
). That proposal is now being realized with several plasmonics-based design approaches being used to fabricate nanometer-scale coherent light sources.
The success of information technology has clearly demonstrated that miniaturization often leads to unprecedented performance, and unanticipated applications. This hypothesis of "smaller-is-better" ...has motivated optical engineers to build various nanophotonic devices, although an understanding leading to fundamental scaling behavior for this new class of devices is missing. Here we analyze scaling laws for optoelectronic devices operating at micro and nanometer length-scale. We show that optoelectronic device performance scales non-monotonically with device length due to the various device tradeoffs, and analyze how both optical and electrical constrains influence device power consumption and operating speed. Specifically, we investigate the direct influence of scaling on the performance of four classes of photonic devices, namely laser sources, electro-optic modulators, photodetectors, and all-optical switches based on three types of optical resonators; microring, Fabry-Perot cavity, and plasmonic metal nanoparticle. Results show that while microrings and Fabry-Perot cavities can outperform plasmonic cavities at larger length-scales, they stop working when the device length drops below 100 nanometers, due to insufficient functionality such as feedback (laser), index-modulation (modulator), absorption (detector) or field density (optical switch). Our results provide a detailed understanding of the limits of nanophotonics, towards establishing an opto-electronics roadmap, akin to the International Technology Roadmap for Semiconductors.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
PDF
