Pure and Efficient Single-Photon Sources by Shortening and Functionalizing Air-Suspended Carbon Nanotubes

A single-photon source (SPS) based on a single-walled carbon nanotube (SWCNT) is a promising candidate for uncooled on-chip quantum information optoelectronics because a single photon can be generated at both room temperature and telecommunication wavelengths on silicon chips. However, for the applications of quantum information, such as quantum computing and quantum cryptography, higher performance SPSs that exhibit both high purity and high efficiency of single-photon generation are required. Here, we theoretically propose high-performance SPSs that simultaneously achieve high-purity and high-efficiency single-photon generation by using short and functionalized air-suspended SWCNTs. The simulated exciton dynamics, time-resolved photoluminescence, and photon correlation properties indicate that exciton–exciton annihilation, end quenching, and trapping in the defect introduced by functionalization such as oxygen or aryl doping play important roles in determining the emission and single-photon properties, which strongly depend on SWCNT length and excitation intensity. We found that high performance SPSs that exhibit simultaneously high single-photon purity of 99.87% and high single-photon generation efficiency of 99.84% can be realized by using air-suspended functionalized SWCNTs with a length of approximately 100 nm under high excitation conditions. This ideal SPS can enable high rate and long-distance quantum key distributions at room temperature

Microemitter-Based IR Spectroscopy and Imaging with Multilayer Graphene Thermal Emission

IR analyses such as Fourier transform infrared spectroscopy (FTIR) are widely used in many fields; however, the performance of FTIR is limited by the slow speed (∼10 Hz), large footprint (∼ millimeter), and glass bulb structure of IR light sources. Herein, we present IR spectroscopy and imaging based on multilayer-graphene microemitters, which have distinct features: a planar structure, bright intensity, a small footprint (sub-μm2), and high modulation speed of >50 kHz. We developed an IR analysis system based on the multilayer-graphene microemitter and performed IR absorption spectroscopy. We show two-dimensional IR chemical imaging that visualizes the distribution of the chemical information. In addition, we present high-spatial-resolution IR imaging with a spatial resolution of ∼1 μm, far higher than the diffraction limit. The graphene-based IR spectroscopy and imaging can open new routes for IR applications in chemistry, material science, medicine, biology, electronics, and physics

Electrical Generation of Polarized Broadband Radiation from an On-Chip Aligned Carbon Nanotube Film

Microsized light sources with polarized or broadband emission can be used for a variety of applications. However, the system directly generating polarized and broad-spectrum light without using polarizers has not been established. Here, we found that a nano-device of densely packed and highly aligned carbon nanotube (CNT) films on silicon chips can emit polarized light with a broad spectrum. We observed spatial emission patterns that are dependent on the angle between the electrical bias and the CNT alignment direction, which are caused not only by the large thermal conductivity anisotropy of the film but also by finite thermal conductance in the CNT-electrode contact. Utilizing the thermal and electrical anisotropy, strongly localized emission was achieved from a narrow (∼1 μm) strip of aligned CNTs connecting edges of two displaced electrodes. This device’s unique ability to directly generate polarized ultrabroadband radiation may greatly expand the range of applications of microsized light sources

Metastable Liquid Crystal as Time-Responsive Reaction Medium: Aging-Induced Dual Enantioselective Control

A metastable liquid crystal (LC) was found to serve as a time-responsive reaction medium, in which the enantioselectivity of a photoreaction was perfectly switched through isothermal annealing of the reaction system. When the LC salt of an enantiopure amine with a photoreactive acid was irradiated with UV/vis light, <i>in situ</i> photodimerization of the acid moiety proceeded smoothly to afford the (+)-isomer of the photodimer with high enantioselectivity (+86% ee). In contrast, photoirradiation of an aged sample, isothermally annealed for 20 h, gave predominantly the (−)-isomer (−94% ee). Systematic studies revealed that the reversal in selectivity originated from metastability of the LC system, which gradually transformed into a crystalline phase during annealing. This finding demonstrates the potential use of metastable aggregates as dynamic time-responsive media, reminiscent of biological systems

High-Speed and On-Chip Optical Switch Based on a Graphene Microheater

Graphene is a promising material for producing optical devices because of its optical, electronic, thermal, and mechanical properties. Here, we demonstrated on-chip optical switches equipped with a graphene heater, which exhibited high modulation speed and efficiency. We designed the optimal structure of the optical switch with an add/drop-type racetrack resonator and two output waveguides (the through and drop ports) by the electromagnetic field calculation. We fabricated the optical switch in which the graphene microheater was directly placed on the resonator and directly observed its operation utilizing a near-infrared camera. As observed from the transmission spectra, this device exhibited high wavelength tuning efficiency of 0.24 nm/mW and high heating efficiency of 7.66 K·μm3/mW. Further, we measured the real-time high-speed operation at 100 kHz and verified that the graphene-based optical switch achieved high-speed modulation with 10%–90% rise and fall response times, 1.2 and 3.6 μs, respectively, thus confirming that they are significantly faster than typical optical switches that are based on racetrack resonators and metal heaters with response times of ∼100 μs. These graphene-based optical switches on silicon chips with high efficiency and speed are expected to enable high-performance silicon photonics and integrated optoelectronic applications

High-Speed and On-Chip Optical Switch Based on a Graphene Microheater

Graphene is a promising material for producing optical devices because of its optical, electronic, thermal, and mechanical properties. Here, we demonstrated on-chip optical switches equipped with a graphene heater, which exhibited high modulation speed and efficiency. We designed the optimal structure of the optical switch with an add/drop-type racetrack resonator and two output waveguides (the through and drop ports) by the electromagnetic field calculation. We fabricated the optical switch in which the graphene microheater was directly placed on the resonator and directly observed its operation utilizing a near-infrared camera. As observed from the transmission spectra, this device exhibited high wavelength tuning efficiency of 0.24 nm/mW and high heating efficiency of 7.66 K·μm3/mW. Further, we measured the real-time high-speed operation at 100 kHz and verified that the graphene-based optical switch achieved high-speed modulation with 10%–90% rise and fall response times, 1.2 and 3.6 μs, respectively, thus confirming that they are significantly faster than typical optical switches that are based on racetrack resonators and metal heaters with response times of ∼100 μs. These graphene-based optical switches on silicon chips with high efficiency and speed are expected to enable high-performance silicon photonics and integrated optoelectronic applications

Carbon Nanotubes Coupled with Silica Toroid Microcavities as Emitters for Silicon-Integrated Photonics

A light source based on single-walled carbon nanotubes (SWNTs) is one of the promising candidates for a microsized light source on a silicon chip at telecommunication wavelengths in optical communications and optical interconnects. However, SWNT-based light emitters possess the disadvantage of having a very broad emission spectrum. Here, we present an ultranarrow-linewidth photoluminescence (PL) emitter based on a silica toroid resonator, along with SWNTs, on a silicon chip. We simultaneously managed both excitation and emission lights at telecommunication wavelengths on a silicon chip by employing a very simple in-line configuration consisting of a toroid resonator and a tapered fiber for light input and output. Owing to the extremely high Q factor of our silica toroid resonator, we obtained an ultrahigh Q factor (∼2.1 × 104) of C-band PL emission. We also demonstrated strong PL emission under laterally polarized excitation conditions owing to the strong coupling to the toroid resonator, and laterally polarized PL emission can be selectively generated independently of the excitation polarization direction. This SWNT-based PL emitter based on a simple system with a silica toroid resonator can open routes to highly integrated photonics and optoelectronics on silicon-based platforms

Carbon Nanotubes Coupled with Silica Toroid Microcavities as Emitters for Silicon-Integrated Photonics

A light source based on single-walled carbon nanotubes (SWNTs) is one of the promising candidates for a microsized light source on a silicon chip at telecommunication wavelengths in optical communications and optical interconnects. However, SWNT-based light emitters possess the disadvantage of having a very broad emission spectrum. Here, we present an ultranarrow-linewidth photoluminescence (PL) emitter based on a silica toroid resonator, along with SWNTs, on a silicon chip. We simultaneously managed both excitation and emission lights at telecommunication wavelengths on a silicon chip by employing a very simple in-line configuration consisting of a toroid resonator and a tapered fiber for light input and output. Owing to the extremely high Q factor of our silica toroid resonator, we obtained an ultrahigh Q factor (∼2.1 × 104) of C-band PL emission. We also demonstrated strong PL emission under laterally polarized excitation conditions owing to the strong coupling to the toroid resonator, and laterally polarized PL emission can be selectively generated independently of the excitation polarization direction. This SWNT-based PL emitter based on a simple system with a silica toroid resonator can open routes to highly integrated photonics and optoelectronics on silicon-based platforms

Chiral Inversion of Thalidomide During Crystal Growth by Sublimation

3′-(N-Phthalimido)glutarimide, commonly known as thalidomide (TD), is one of the most famous chiral drugs, because of its tragic history. Although the R-enantiomers of TD have positive medical effects, the S-enantiomers have dangerous side effects, and consequently, the enantiomeric purity of TD in a solid state and the chiral inversion of TD in physiological conditions have attracted considerable attention and prompted discussion on the “TD paradox”. Subsequently, the physicochemical properties of TD in the solid state have been indicated to be as essential as those in the solution state for understanding the pharmacodynamics and pharmacokinetics of TD. Herein, we demonstrate that the sublimation method is beneficial in the crystal growth of TD compared with solvent–evaporation methods. Structural and optical analyses demonstrated that sublimination produced very thin, transparent, and defect-free single crystals with high crystal-surface parallelism; chromatographic analysis suggested that a chiral inversion of TD molecules occurs during the sublimation even beneath the melting point under ambient humidity. The potential occurrence of chiral inversion of TD in the gas phase with atmospheric water vapor is a crucial finding in the use of sublimation in purifying chiral drugs to avoid adverse drug-induced outcomes. The crystal growth and potential chiral inversion of TD by sublimation should contribute to providing important information for pharmaceutical sciences and industry