High-Speed Modulation of Polarized Thermal Radiation from an On-Chip Aligned Carbon Nanotube Film

Spectroscopic analysis with polarized light has been widely used to investigate molecular structure and material behavior. A broadband polarized light source that can be switched on and off at a high speed is indispensable for reading faint signals, but such a source has not been developed. Here, using aligned carbon nanotube (CNT) films, we have developed broadband thermal emitters of polarized infrared radiation with switching speeds of ≲20 MHz. We found that the switching speed depends on whether the electrical current is parallel or perpendicular to the CNT alignment direction with a significantly higher speed achieved in the parallel case. Together with detailed theoretical simulations, our experimental results demonstrate that the contact thermal conductance to the substrate and the conductance to the electrodes are important factors that determine the switching speed. These emitters can lead to advanced spectroscopic analysis techniques with polarized radiation

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

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