Takuya Inoue

The control of thermal emission spectra using optical resonances has been attracting increased attention both with respect to fundamental science and for various applications, including infrared sensing, thermal imaging, and thermophotovoltaics. In this mini-review, we describe the recent experimental demonstrations of narrowband thermal emission with optical nanostructures, including metallic cavities, metamaterials, and all-dielectric photonic crystals. The spectral features of the controlled

Thermal radiation transfer between two objects separated by a subwavelength gap (near-field thermal radiation transfer) can be orders of magnitude larger than that in free space, which is attracting increasing attention with respect to both fundamental nanoscience and its potential for high-power-density and high-efficiency conversion of heat to electricity in thermophotovoltaic (TPV) systems. However, the realization of near-field thermal radiation transfer in TPV systems involves significant c

Realization of one-chip, ultra-large-area, coherent semiconductor lasers has been one of the ultimate goals of laser physics and photonics for decades. Surface-emitting lasers with two-dimensional photonic crystal resonators, referred to as photonic-crystal surface-emitting lasers (PCSELs), are expected to show promise for this purpose. However, neither the general conditions nor the concrete photonic crystal structures to realize 100-W-to-1-kW-class single-mode operation in PCSELs have yet to b

We experimentally demonstrate single-peak narrow-bandwidth thermal emission with a quality factor (Q factor) of more than 100 at a wavelength of 9.1 μm. The emission is significantly suppressed at all other wavelengths. Our emitter is based on an intersubband transition in a multiple quantum well structure combined with a single high-Q resonant mode in a two-dimensional photonic crystal slab, which allows strong light-matter interaction only at a specific wavelength. Strong thermal emission is e

We develop a time-dependent three-dimensional coupled-wave theory (3D-CWT) for the transient analysis of photonic-crystal surface-emitting lasers (PCSELs). Our model takes into account the temporal evolution of both the photon and carrier distribution inside PCSELs, which enable the analysis of various above-threshold lasing characteristics including the relaxation oscillation, spatial hole burning, and multimode lasing. With the developed time-dependent 3D-CWT, we perform transient analysis of

Near-field thermal radiation transfer overcoming the blackbody limit has attracted significant attention in recent years owing to its potential for drastically increasing the output power and conversion efficiency of thermophotovoltaic (TPV) power generation systems. Here, we experimentally demonstrate a one-chip near-field TPV device overcoming the blackbody limit, which integrates a 20-μm-thick Si emitter and an InGaAs PV cell with a subwavelength gap (<140 nm). The device exhibits a photocurr

Photonic-crystal surface-emitting lasers (PCSELs) use the two-dimensional (2D) resonance at the band-edge of a photonic crystal for lasing, and they feature various outstanding functionalities such as high-brightness lasing, arbitrary shaping of beam patterns and on-chip 2D beam steering. In this paper, to investigate the applicability of PCSELs for high-speed operation, we design PCSELs with enhanced in-plane optical feedback, which enable single-mode lasing inside a circular region the diamete

Narrowband thermal emitters operating in the mid-wavelength infrared (MWIR, 3–8 μm) are important for spectroscopic sensing systems in various fields of research such as chemistry, healthcare, and environmental science. To increase the signal-to-noise ratio in these spectroscopic applications, it is required that only thermal emission in a narrow target wavelength range be modulated electrically while other wavelength components are unmodulated. In addition, an increase of the emitter’s temperat

We propose a scheme for near-field thermophotovoltaic (TPV) energy conversion, where thermal emission from an emitter is extracted by an intermediate transparent substrate attached to the top of a photovoltaic (PV) cell. The addition of an intermediate transparent substrate suppresses the unwanted heat transfer from the emitter to the PV cell due to the surface modes on the PV cell while maintaining the enhancement in the interband absorption. We confirm that our scheme is applicable for near-fi

Ultrafast dynamics in nanophotonic materials is attracting increasing attention from the perspective of exploring new physics in fundamental science and expanding functionalities in various photonic devices. In general, such dynamics is induced by external stimuli such as optical pumping or voltage application, which becomes more difficult as the optical power to be controlled becomes larger owing to the increase in the energy required for the external control. Here, we demonstrate a concept of

We design efficient thermal emitters based on intersubband transitions (ISB-Ts) in quantum wells and two-dimensional photonic crystal (PC) slabs that have single-mode, very narrowband emission with high emissivity. Our design strategy involves positioning a single isolated mode of the PC within the absorption range of the ISB-T, where the mode&#x2019;s radiation rate is precisely matched with the absorption rate of the ISB-T. The optimized design for this class of thermal emitters has a single-p

Photonic-crystal surface-emitting lasers (PCSELs), which utilize a two-dimensional (2D) optical resonance inside a photonic crystal for lasing, feature various outstanding functionalities such as single-mode high-power operation and arbitrary control of beam polarizations. Although most of the previous designs of PCSELs employ spatially uniform photonic crystals, it is expected that lasing performance can be further improved if it becomes possible to optimize the spatial distribution of photonic

We experimentally demonstrate filter-free nondispersive infrared (NDIR) sensing of organic solvents using single-peak narrow-bandwidth mid-infrared thermal emitters. Our emitters are based on multiple quantum wells (MQWs) and two-dimensional (2D) photonic crystal (PC) slabs, and show a single thermal emission peak with a quality factor of over 100 at the fingerprint wavelength (around 9 µm) of the target organic solvents. Using these narrow-bandwidth thermal emitters and commercial pyroelectric

We experimentally demonstrate the high-speed, on-chip wavelength switching of thermal emission in the mid-infrared region. Our device consists of multiple integrated thermal emitters of different colors, each of which is composed of quantum wells and a photonic crystal. On current injection, the device exhibits narrowband (Q &amp;gt; 70) thermal emission with low electric power consumption. By applying a reverse bias to each section of the device, we achieve high-speed (&amp;gt;kHz) switching of