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Nanocavity devices based on silicon that can operate in the 1.2-µm band would be beneficial for several applications. We fabricate fifteen cavities with resonance wavelengths between 1.20 and 1.23 µm. Experimental quality (Q) factors larger than one million are obtained and the average Q values are lower for shorter wavelengths. Furthermore, we observe continuous-wave operation of a Raman silicon laser with an excitation wavelength of 1.20 µm and a Raman laser wavelength of 1.28 µm. The Q values of the nanocavity modes used to confine the excitation light and the Raman scattered light are about half of those for our Raman silicon laser operating in the 1.55-µm band. Nevertheless, this device exhibits an input–output characteristic with a clear laser threshold. Finally, we consider the effect of the higher scattering probability at shorter wavelengths on the Raman laser performance in the 1.2-µm band.

Raman silicon lasers based on photonic crystal nanocavities with a threshold of several hundred microwatts for continuous-wave lasing have been realized. In particular, the threshold depends on the degree of confinement of the excitation light and the Raman scattering light in the two nanocavity modes. Here, we report lower threshold values for Raman silicon nanocavity lasers achieved by increasing the quality (Q) factors of the two cavity modes. By using an optimization method based on machine learning, we first increase the product of the two theoretical Q values by a factor of 17.0 compared to the conventional cavity. The experimental evaluation demonstrates that, on average, the actually achieved product is more than 2.5 times larger than that of the conventional cavity. The input–output characteristic of a Raman laser with a threshold of 90 nW is presented and the lowest threshold obtained in our experiments is 40 nW.

Near-field thermophotovoltaic (TPV) power generation has been attracting increasing attention as a promising approach for efficient conversion of heat into electricity with high output power density. Here, we numerically investigate near-field TPV devices with surrounding reflectors for efficient recycling of low-energy photons, which do not contribute to the power generation. We reveal that the conversion efficiency of a near-field TPV system can be drastically increased by introducing a pair of reflectors above and below the system, especially when the two mirrors are not in contact with the emitter and absorber. In addition, we investigate the influence of non-perfect photon recycling on the TPV efficiency and reveal that near-field TPV systems are more robust against the decrease of the reflectivity of the reflectors than the far-field TPV systems.

The performance of a Raman silicon laser based on a high quality-factor nanocavity depends on the degree of free-carrier absorption, and this characteristic may be useful for certain applications. Here we demonstrate that laser oscillation in a Raman silicon nanocavity laser stops abruptly after an exposure to a weak flux of negatively ionized air for a few seconds. Spectral measurements reveal that the laser interruption is mainly caused by the transfer of extra electrons from the negatively ionized air molecules to the silicon nanocavity. These electrons affect the efficiency of the Raman laser by free carrier absorption. We find that the laser output gradually recovers as the extra electrons escape from the nanocavity and confirm that such a detection of ionized air is repeatable. These results show that a Raman silicon nanocavity laser can be used for the detection of ionized air with a high spatial resolution.

application/pdf, Article, Optics Express. 2017, 25 (1), p.367-376

The radiation pattern and out-coupling efficiency of light from the end surface of interlayer (oblique) waveguides in stacked-stripe 3-D photonic crystals are numerically investigated. It is shown that the coupling to the surface mode of the 3-D photonic crystal decreases the out-coupling efficiency to free-space modes down to 60%, whereas the reflection at the surface is negligibly small. The efficiency can be improved to 90% by introducing a 2-D grating-like structure to create a surface-mode gap, where surface modes are prohibited.

Thermal emitters generally exhibit a broad spectrum and are widely used for various light sources from far-infrared to the visible range. However, in many applications involving non-dispersive infrared sensing and thermo-photovoltaics, only a specific spectral component that is much narrower than the original broad spectrum of thermal emitters is utilized, which reduces efficiency. Therefore, it is important to develop a single-mode narrow-bandwidth thermal emitter that achieves high emissivity at a target wavelength while suppressing it as much as possible at other wavelengths. To achieve such an ideal spectrum, we demonstrated mid-infrared thermal emitters by combining multiple quantum wells (MQWs) and two-dimensional photonic crystal (PC) slabs [1]. In our emitters, intersubband transitions of MQWs allow a strong interaction between light and matter around a target wavelength, and a γ — point resonant effect of PCs further narrow down the thermal emission peak at a target wavelength and enable vertical emission. Ultrafast modulation (∼MHz) of thermal emission without changing the temperature of emitters has been also realized by changing the electron density of MQWs using applied electric field [2]. Near-infrared narrowband thermal emitters have been also recently demonstrated by using arrays of intrinsic Si nanorods [3].

We carry out the structural design of photonic crystals to enhance the optical absorption of thin-film microcrystalline silicon (μc-Si) solar cells using two methods. First, by exhaustive search, we choose a structure with the largest absorption within the investigated patterns. Then we employ a sensitivity analysis to finely modulate the structure for further increase of the optical absorption. The obtained μc-Si solar cell structure with a photonic crystal in this work has more than twice as much optical absorption as that without a photonic crystal.

A Si nanorod array enables the concentration of thermal emission in the near-infrared range while suppressing other components., Control of the thermal emission spectra of emitters will result in improved energy utilization efficiency in a broad range of fields, including lighting, energy harvesting, and sensing. In particular, it is challenging to realize a highly selective thermal emitter in the near-infrared–to–visible range, in which unwanted thermal emission spectral components at longer wavelengths are significantly suppressed, whereas strong emission in the near-infrared–to–visible range is retained. To achieve this, we propose an emitter based on interband transitions in a nanostructured intrinsic semiconductor. The electron thermal fluctuations are first limited to the higher-frequency side of the spectrum, above the semiconductor bandgap, and are then enhanced by the photonic resonance of the structure. Theoretical calculations indicate that optimized intrinsic Si rod-array emitters with a rod radius of 105 nm can convert 59% of the input power into emission of wavelengths shorter than 1100 nm at 1400 K. It is also theoretically indicated that emitters with a rod radius of 190 nm can convert 84% of the input power into emission of

Measurement of optical loss in nanophotonic waveguides is necessary for monitoring the properties of integrated photonic devices. We propose a simple method of measuring the optical loss using integrated nanocavities. It is shown theoretically that weak coupling between the waveguide and cavities leads to a direct estimation of the optical loss by measuring light radiated from the cavities. In addition, we experimentally demonstrate the optical loss in a fabricated photonic crystal waveguide. Our method gives not only a degree of freedom in real-time monitoring of the optical properties of nanophotonic structures, but it also can be used for various waveguide-based applications.

An oblique waveguide in a stripe-stacked three-dimensional photonic crystal is a useful structure for interlayer coupling, but has a problem that the out-coupling to free-space is inclined and spatially asymmetric. We propose a new end structure that provides vertical and less-frequency-dependent out-coupling characteristics.

We investigate the radiation angle of an oblique waveguide in a stripe-stacked three-dimensional photonic crystal. We show that the output-light is radiated in a different direction from the oblique waveguide direction. Moreover, the radiation polar angle varies from 30° to 50° depending on the frequency. To inhibit the frequency dependence and obtain vertical radiation, we introduced a symmetric structure at the end of the waveguide. As a result of cancellation of the in-plane asymmetric wavenumber, the radiation polar angle is less than 6° from the surface-normal direction and does not depend on frequency.

We experimentally demonstrate a photonic crystal (PC) thermal emitter that enables the electrical switching of dual emission peaks from a single light-emitting surface. The emitter consists of an n-GaAs/p-GaAs/n-GaAs stack that incorporates multiple quantum wells (MQWs) inside each pn junction. The MQWs induce narrowband thermal emission at two different wavelengths owing to the intersubband transition (ISB-T), which is enhanced by the second and third-order Γ-point resonant modes of the PC. By changing the electron density in one of the two MQWs with a reverse bias to each pn junction, we realize the separate control of the thermal emission intensity of the two peaks. Such two-wavelength switchable mid-infrared narrowband thermal emitters will benefit a number of practical applications including environmental monitoring and health diagnosis.

Researchers experimentally demonstrate on-demand transfer of trapped photons on a photonic crystal chip for the first time., Photonic crystal nanocavities, which have modal volumes of the order of a cubic wavelength in the material, are of great interest as flexible platforms for manipulating photons. Recent developments in ultra-high quality factor nanocavities with long photon lifetimes have encouraged us to develop an ultra-compact and flexible photon manipulation technology where photons are trapped in networks of such nanocavities. The most fundamental requirement is the on-demand transfer of photons to and from the trapped states of arbitrary nanocavities. We experimentally demonstrate photon transfer between two nearly resonant nanocavities at arbitrary positions on a chip, triggered by the irradiation of a third nonresonant nanocavity using an optical control pulse. We obtain a high transfer efficiency of ~90% with a photon lifetime of ~200 ps.

We experimentally demonstrate a narrowband (Q>90) thermal emitter with a peak wavelength of ∼ 4 μm operating at 600°C by employing a photonic crystal structure containing n-doped GaN/AlGaN quantum wells.

We demonstrate electrical high-speed wavelength switching of narrowband thermal emission on a single chip by using intersubband transitions in multiple quantum wells and optical resonances of photonic crystals.

Converting from a broadband to a narrowband thermal emission spectrum with minimal loss of energy is important in the creation of efficient environmental sensors and biosensors1,2 as well as thermo-photovoltaic power generation systems3,4. Here, we demonstrate such thermal emission control by manipulating photonic modes with photonic crystals as well as material absorption with quantum-well intersubband transitions. We show that the emission peak intensity for our device can be more than four times greater than that of a blackbody sample under the same input power and thermal management conditions due to an increase in the temperature compared to the blackbody reference, and the emission bandwidth and angular spread are narrowed by a factor of 30 and 8, respectively. These results indicate that the energy saved by thermal emission control can be recycled and concentrated to enhance the narrow peak emission intensity. By constructing a thermal emission control device based on a multiple-quantum-well layer embedded in a two-dimensional photonic crystal, researchers demonstrate that they can convert a broadband thermal emission spectrum into a narrowband spectrum with minimal loss of energy.

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-field TPV systems using a silicon (Si) or tungsten (W) emitter. As a specific example, we designed a near-field TPV system composed of a one-dimensional Si photonic crystal thermal emitter, an InGaAs PV cell, and an intermediate Si substrate, and displayed that our scheme could realize both high power density (>5 × 104 W/m2) and high power conversion efficiency (>40%) at a 50-nm gap between the emitter and the intermediate substrate.

Photonic crystal nanocavities are expected to make great contributions in areas of physics and engineering such as the slowing and stopping of light and optical quantum information processing. We first review approaches to the goal of increasing the quality factor of two-dimensional photonic crystal nanocavities. Losses from a cavity can be suppressed, with a consequent increase of the quality factor, by containing the electromagnetic field in the form of a Gaussian envelope function. We then propose a new method of analytical cavity design, based on the detailed investigation of waveguide modes, in order to realize Gaussian cavity mode fields. This has enabled us to achieve a quality factor of while maintaining a cavity volume of one cubic wavelength.

High-quality (Q) factor photonic-crystal nanocavities are currently the focus of much interest because they can strongly confine photons in a tiny space. Nanocavities with ultrahigh Q factors of up to 2,000,000 and modal volumes of a cubic wavelength have been realized. If the Q factor could be dynamically controlled within the lifetime of a photon, significant advances would be expected in areas of physics and engineering such as the slowing and/or stopping of light and quantum-information processing. For these applications, the transfer, storage and exchange of photons in nanocavity systems on such a timescale are highly desirable. Here, we present the first demonstration of dynamic control of the Q factor, by constructing a system composed of a nanocavity, a waveguide with nonlinear optical response and a photonic-crystal hetero-interface mirror. The Q factor of the nanocavity was successfully changed from approximately 3,000 to approximately 12,000 within picoseconds.

We describe the recent experimental progress in the control of spontaneous emission by manipulating optical modes with photonic crystals. It has been clearly demonstrated that the spontaneous emission from light emitters embedded in photonic crystals can be suppressed by the so-called photonic bandgap, whereas the emission efficiency in the direction where optical modes exist can be enhanced. Also, when an artificial defect is introduced into the photonic crystal, a photonic nanocavity is produced that can interact with light emitters. Cavity quality factors, or Q factors, of up to 2 million have been realized while maintaining very small mode volumes, and both spontaneous-emission modification (the Purcell effect) and strong-coupling phenomena have been demonstrated. The use of photonic crystals and nanocavities to manipulate spontaneous emission will contribute to the evolution of a variety of applications, including illumination, display, optical communication, solar energy and even quantum-information systems.

In this paper, we review the fundamentals of heterostructures in two-dimensional photonic-crystal (PC) slabs and demonstrate ultra-high-Q nanocavities, which are key components for the realization of PC devices. Heterostructure PCs (hetero-PCs) consist of multiple PC waveguides with different lattice constants. Here we theoretically demonstrate the selective transmission and reflection characteristics of various hetero-PCs, including photonic-tunnelling structures. On the basis of these traits, we construct photonic double-heterostructure nanocavities and detail their optical properties, including the transmission characteristics of the input waveguides and the Q factors of the cavities. We show that ultra-high-Q factors (~1 200 000) can be realized in the nanocavities and are limited by imperfections in the fabrication process. Ultra-high-Q photonic double-heterostructure nanocavities are important not only in the development of various photonic applications but also for advancing our knowledge of photonic heterostructures.

We have succeeded in fabricating a photonic crystal nanocavity with a photon lifetime of 2.1 ns, which corresponds to a quality factor of 2.5 x 10(6). This lifetime is the longest recorded thus far in photonic crystal cavities, and was brought about by improvements in the fabrication process. Comparing our experimental quality factor with the results of calculations shows that we have suppressed variations in the radii and positions of the air holes composing a nanocavity such that their standard deviations are less than 1 nm.

We develop a nanocavity Raman Si laser with a sub-microwatt threshold of 0.52 μW by accurately matching a frequency spacing of the two nanocavity modes to the Raman shift of Si nanocavity.

We have precisely measured the Raman shift of photonic crystal silicon heterostructure nanocavities for Raman laser applications. We utilized a near-infrared excitation laser of wavelength 1.42 μm in order to avoid local sample heating and exploited two high-Q nanocavity modes to calibrate the Raman frequency. The measured Raman shift was 15.606 THz (520.71 cm(-1)) with a small uncertainty of 1.0 × 10(-3) THz. In addition, we investigated the compressive stress generated in a photonic crystal slab in which a ~5.1 × 10(-3) THz blue shift of the Raman peak and a slight warpage of the slab were observed. We also demonstrated that the stress could be eliminated by using a cantilever structure.

In-plane channel-drop filters consisting of point and line defects in a two-dimensional photonic-crystal slab are investigated. A clear channel-drop operation was successfully demonstrated by employing an ultrahigh quality factor nanocavity and a suitably designed waveguide bend. Moreover, improvements in the channel-drop efficiency of the device were made using a feature of heterostructure photonic crystals, as proposed previously. It is shown theoretically that drop efficiencies much higher than the maximum of 25% for a conventional configuration are achievable using reflection at the heterostructure interface. Drop operations with efficiencies of almost 100% were experimentally demonstrated by the fabricated devices. Moreover, a four-channel drop operation with a high drop efficiency and a constant quality factor was demonstrated by in-plane channel-drop filters in a two-dimensional photonic-crystal slab, with a simple configuration based on heterostructure photonic crystals.

We have developed a new pulsed laser ablation–deposition (PLAD) apparatus and techniques for fabricating films of high-temperature or functional materials, including two short-wavelength lasers: (a) a YAG 5th harmonic (213 nm) and (b) Raman-shifted lasers containing vacuum ultraviolet light; also involved are (c) a high-temperature heater with a maximum temperature of 1350 °C, (d) dual-target simultaneous ablation mechanics, and (e) hybrid PLAD using a pico-second YAG laser combined with (c) and/or (d). Using the high-T heater, hetero-epitaxial films of 3C–, 2H– and 4H–SiC have been prepared on sapphire-c. In situ p-doping for GaN epitaxial films is achieved by simultaneous ablation of GaN and Mg targets by (d) during film growth. Junctions such as pGaN (Mg-doped)-film/n-SiC(0 0 0 1) substrate and pGaN/n-Si(1 1 1) show good diode characteristics. Epitaxial films with a diamond lattice can be grown on the sapphire-c plane by hybrid PLAD (e) with a high-T heater using a 6H-SiC target. High quality epitaxial films of ZnO are grown by PLAD by introducing a low-temperature self-buffer layer; magnetization of ferromagnetic materials is enforced by overlaying on a ferromagnetic lattice plane of an anti-ferromagnetic material, showing the value of the layer-overlaying method in improving quality. The short-wavelength lasers are useful in reducing surface particles on functional films, including superconductors.

We discuss spontaneous-emission phenomena in semiconductor slabs with a two-dimensional photonic bandgap. Calculations predict that the spontaneous emission coupled to the slab modes, which is strongly confined within the slab plane, is inhibited. Simultaneously, the saved energy is redistributed to the spontaneous emission that is coupled to the vertical emission modes. Control of the spontaneous emission is experimentally demonstrated by measuring time-resolved photoluminescence spectra from GaInAsP quantum-well samples. The suppression of non-radiative processes is achieved by the introduction of InAs quantum dots, which can confine carriers in three dimensions. This method allows control of the spontaneous emission to a degree close to the theoretical limit calculated by the finite-difference time-domain method. Our results demonstrate the realization of an ideal two-dimensional photonic-bandgap environment, and open up possibilities for various applications of photonic crystals using spontaneous-emission phenomena.

The two-dimensional photonic crystal cavities employing local three-dimensional structures are investigated. Donor-type cavities with small and shallow holes are examined as examples of cavities with a local three-dimensional structure. It is shown that both the far-field and near-field patterns of the cavities can be controlled by the addition of small and shallow holes. The fabrication of such structures using a focused ion beam is proposed and investigated. Residual gallium ions, used in fabrication with a focused ion beam, lead to optical absorption; these gallium ions can be removed by heat treatment at 800 °C. The near-field pattern of a fabricated three-dimensional cavity is measured, and is shown to be consistent with a theoretical analysis.

An in-plane, multi-channel drop filter with high efficiency, in a two-dimensional photonic crystal (PC) slab, is experimentally demonstrated. Based on the concept of heterostructure photonic crystals proposed previously, the device consists of multiple simply connected, PC-based filter units, in which each unit has a structure proportional to an optimized basic unit and operates at a different wavelength. Four-channel drop operation was successfully obtained, with high efficiencies of almost 100%, and equal quality factors, across all channels.

We investigated the characteristics of an ultra-high-Q photonic nanocavity (Q = ~230,000 and modal volume = ~1.2 cubic wavelengths) at various input light powers. The cavity characteristics were red-shifted as the input power increased. This nonlinearity could be explained by coupled-mode theory, taking into account two-photon absorption, the associated free-carrier absorption, consequent free-carrier absorption, plasma effect, thermo-optic effect, and a Kerr effect. Nonlinear cavity characteristics were observed at an extremely low input light power of 10 muW. We confirmed that these low-power nonlinear optical effects could be attributed to the ultra-high Q factor of the nanocavity.

We report a theoretical analysis on light-extraction efficiency of the organic light-emitting diodes. We utilize both a numerical method such as the finite-difference time-domain method and an analytic method such as the mode-expansion method. The results of both methods are compared to confirm the accuracy of the results. It is found that even though the refractive index contrast between the Indium-tin-oxide (ITO) anode and the glass substrate is as small as 0.5, more than 40% of emitted light power is trapped in the ITO layer.

A photonic nanocavity with a high Q factor of 100,000 and a modal volume V of 0.71 cubic wavelengths, is demonstrated. According to the cavity design rule that we discovered recently, we further improve a point-defect cavity in a two-dimensional (2D) photonic crystal (PC) slab, where the arrangement of six air holes near the cavity edges is fine-tuned. We demonstrate that the measured Q factor for the designed cavity increases by a factor of 20 relative to that for a cavity without displaced air holes, while the calculated modal volume remains almost constant.

We have investigated ultra-short pulse propagation through 3D GaAs photonic crystals with a complete photonic band gap in the optical wavelength region. The pulse propagation was calculated by using the finite-differential time-domain (FDTD) method. This is the first time pulse shape measurements have been made using femtosecond pulses. From the experimental results, the shapes of the ultra-short pulses were found to change when the frequency was above the photonic band-gap after the propagation through the photonic crystal, corresponding to the simulation results.

application/pdf, Article, Optics Express. 2017, 25 (15), p.18165-18174

In this paper we investigate the optical forces induced by localized optical modes propagating along three parallel waveguides, of which only the central one is free to move. In this configuration, when all three waveguides are identical, the components of the optical-force acting on the free beam are decoupled along the axis of symmetry. As a result, two dimensional optomechanical control of the central waveguide, like single-mode optical trapping, can be achieved. We also study non symmetric configurations, that can be used, for example, to tailor the position of the optical trap. Unlike other techniques that rely on buckling, multi-mode excitation or radiation-pressure, single-mode optomechanical-operation should help the realization of faster and simpler on-chip positioning of a single nanobeam since most of the parameters involved can be controlled with great precision.

We demonstrate multiple-channel wavelength conversions in a photonic-crystal nanocavity by employing nonlinearity optical effects of SiC and multiple resonances of the cavity. Also, we investigate the polarization of the wavelength-converted light.

When a heterostructure is created at the center of a photonic crystal line-defect cavity to form a nanocavity, the photonic band gap contains several high-quality ($Q$) factor resonant modes. We have studied the optical properties of these modes to examine their applicability to Raman silicon lasers, which require two high-$Q$ resonant modes with a frequency spacing of 15.6 THz. Our experimental and numerical analyses reveal four types of resonant modes. We demonstrate that pairing the resonant mode originating from the first-order propagation mode with that arising from the second-order propagation mode is the most promising approach toward the realization of Raman silicon lasers.

In this letter, we experimentally demonstrate resonant-wavelength control of a series of 16 nanocavities in a two-dimensional photonic crystal slab structure by nanometer-order variation of the lattice constants and air-holes sizes. The cavities show a linear dependence on these parameters, a 1-nm increase of lattice constant or air-hole size leading to 4.2-nm increase or 1.56-nm decrease of the resonant wavelength, respectively. These experimental results are in good agreement with the finite-difference time-domain calculations and have a small standard deviation of wavelength (~1 nm) between samples on a single chip. These results will stimulate development in areas such as ultrasmall and multichannel filters, sensors, and switches.

Inhibiting spontaneous light emission and redistributing the energy into useful forms are desirable objectives for advances in various fields, including photonics, illuminations, displays, solar cells, and even quantum-information systems. We demonstrate both the “inhibition” and “redistribution” of spontaneous light emission by using two-dimensional (2D) photonic crystals, in which the refractive index is changed two-dimensionally. The overall spontaneous emission rate is found to be reduced by a factor of 5 as a result of the 2D photonic bandgap effect. Simultaneously, the light energy is redistributed from the 2D plane to the direction normal to the photonic crystal.

We demonstrate thermal emitters based on quantum wells and photonic crystals that have a single emission peak with a quality factor over 100. Our results will have potential applications to environmental sensors and thermo-photovoltaic systems.

We develop a silicon photonic crystal nanocavity device capable of performing targeted optical pulse capture and release via distinct ports on demand, based on dynamic Q factor control. The capture of 4 ps pulses and their release up to 332 ps later is directly observed by time-resolved measurements of the energy behaviour in both the nanocavity and emitted from the release port. We also discuss how the behaviour of excited free carriers dictates the performance of such dynamic devices.

We report a unique design of a Raman silicon laser using a photonic crystal high-Q nanocavity without the reverse-biased p-i-n diode, which leads to the continuous-wave lasing operation with ultralow threshold power of ∼1 μW.

A reduction of the operating voltage is achieved for an organic light-emitting diode containing a corrugated photonic crystal structure fabricated by the etching of an indium-tin-oxide anode layer. This is due to a partial reduction in the thickness of the organic layer. The light extraction efficiency can be also improved due to the diffraction of confined light by the photonic crystal effect. The voltage reduction is demonstrated in combination with an improvement in the luminance efficiency at constant current for the fabricated device.

We report transmission and reflection characteristics of in-plane hetero-photonic crystals (IP-HPCs) consisting of two serially connected photonic crystal waveguides with differing lattice constants. We show experimentally and theoretically that the transmission spectrum of the structure corresponds to the transmission frequency range common to both waveguides. Also, there exists a frequency gap where the structure has a guiding mode for one waveguide but not for the neighboring one. Our calculated results reveal that light within the common frequency range is transmitted with approximately 100% efficiency through the waveguides while light within the gap is almost perfectly reflected.

An in-plane-type channel-drop filtering device with input/output waveguides and a point defect cavity in a two-dimensional photonic crystal slab is investigated. The in-plane operation becomes possible by employing a point defect cavity with an extremely high Q factor to suppress the radiation loss for the out-of-plane direction. 60° bends are also introduced in the output waveguide to avoid interference between the input/output waveguides. The transmission frequency range of the output waveguide with bends is tuned by changing the size of the air holes at the apex of the corner so that the resonant frequency of the point defect cavity is within the transmission band. A channel drop operation with a very high resolution of 0.12 nm is successfully observed at 1.55 μm wavelengths.

Here we investigate a line-defect-waveguide laser in a two-dimensional photonic-crystal slab. The change δλ in lasing wavelength for a change δW in waveguide width is found to be extremely large: δλ∕δW=2. It is two orders of magnitude greater than that for a conventional distributed-feedback laser. An investigation of the electromagnetic-field distribution at the waveguide-mode edge is made, giving an indication of the cavity-mode structure for lasing oscillation. Fourier transform analysis reveals that the extremely large tunability originates from the “zigzag” mode behavior of the line-defect waveguide in the photonic crystal, due to two-dimensional distributed feedback and reflection.

The optical properties of line-defect waveguides in two-dimensional photonic crystal slabs are investigated using picosecond light pulses. Time-domain waveforms of the light pulse propagating through the waveguide are successfully observed using an autocorrelation method. The group velocity of the waveguide is directly determined from the group delay time for light pulses reflected back and forth along the waveguide. A small group velocity of one-twentieth the speed of light in vacuum is observed at a frequency near the edge of the waveguide mode. The frequency dependence of the group velocity is also measured, and the group-velocity dispersion is found to be larger than that of normal single-mode optical fibers by a factor of 104–105.

We demonstrate a single-mode high-Q (Q>100) mid-infrared thermal emitter operating with high power-utilization efficiency. The emitter consists of a rod-type photonic crystal (PC) slab interacting with GaAs/AlGaAs multiple quantum wells (MQWs), a GaAs substrate frame supporting the PC slab, and electric wires for Joule heating of the device. We carefully design the structure of the PC slab and the supporting frame/wires to minimize unwanted thermal losses and realize narrowband thermal emission having a peak intensity, under a given electrical input power, that is an order of magnitude higher than that of a reference blackbody emitter due to the efficient increase of the device temperature.