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Fluorescence color imaging at an extremely low excitation intensity was performed using an optical transition edge sensor (TES) embedded in a confocal microscope for the first time. Optical TES has the ability to resolve incident single photon energy; therefore, the wavelength of each photon can be measured without spectroscopic elements such as diffraction gratings. As target objects, animal cells labeled with two fluorescent dyes were irradiated with an excitation laser at an intensity below $$1\,\upmu \hbox {W}$$ . In our confocal system, an optical fiber-coupled TES device is used to detect photons instead of the pinhole and photomultiplier tube used in typical confocal microscopes. Photons emitted from the dyes were collected by the objective lens, and sent to the optical TES via the fiber. The TES measures the wavelength of each photon arriving in an exposure time of 70 ms, and a fluorescent photon spectrum is constructed. This measurement is repeated by scanning the target sample, and finally a two-dimensional RGB-color image is obtained. The obtained image showed that the photons emitted from the dyes of mitochondria and cytoskeletons were clearly resolved at a detection intensity level of tens of photons. TES exhibits ideal performance as a photon detector with a low dark count rate ( $$

Optical transition edge sensors (TESs) are characterized by a very fast response, of the order of $$\upmu $$ s, which is $$10^3$$ times faster than TESs for X-ray and gamma-ray. To extract important parameters associated with the optical TES, complex impedances at high frequencies (> 1 MHz) need to be measured, where the parasitic impedance in the circuit and reflections of electrical signals due to discontinuities in the characteristic impedance of the readout circuits become significant. This prevents the measurements of the current sensitivity $$\beta $$ , which can be extracted from the complex impedance. In usual setups, it is hard to build a circuit model taking into account the parasitic impedances and reflections. In this study, we present an alternative method to estimate a transfer function without investigating the details of the entire circuit. Based on this method, the complex impedance up to 30 MHz was measured. The parameters were extracted from the impedance and were compared with other measurements. Using these parameters, we calculated the theoretical limit on an energy resolution and compared it with the measured energy resolution. In this paper, the reasons for the deviation of the measured value from theoretically predicted values will be discussed.

Optical transition edge sensors (TESs) which can resolve an energy of a single photon have proven desirable in quantum information and biology. TESs can provide spectra ranging from near-infrared to visible regions, and have the potential to reveal new phenomena in biology. To obtain reliable spectra, wavelength dependence of the system detection efficiency should be calibrated. The dependence is due to a cavity structure of the detector, consisting of an anti-reflection coating and a mirror. We will present a calibration using a supercontinuum laser and acousto-optic tunable filters (AOTF).

Broadband low reflectance materials have various applications in the field of optical energy management; however, materials with ultra-low reflectance (below 0.1%) have been considered as mechanically delicate. We have developed a novel hard-surface optical absorber with microstructured, diamond-like carbon coated ion tracks on CR-39 plastic substrate. The spectral reflectance of the first prototype was below 2% for wavelengths ranging from 400 nm to 1400 nm; moreover, the optical absorber had mechanically hard surface and exhibited temporal durability. Choosing the appropriate design of the surface structure and coating layer is likely to reduce the reflectance to the order of 0.1%. This technique yields easy-to-handle broadband ultra-low reflectance absorbers.

Classical correlation can be locked via quantum means--quantum data locking. With a short secret key, one can lock an exponentially large amount of information, in order to make it inaccessible to unauthorized users without the key. Quantum data locking presents a resource-efficient alternative to one-time pad encryption which requires a key no shorter than the message. We report experimental demonstrations of quantum data locking scheme originally proposed by DiVincenzo et al. [Phys. Rev. Lett. 92, 067902 (2004)] and a loss-tolerant scheme developed by Fawzi, Hayde, and Sen [J. ACM. 60, 44 (2013)]. We observe that the unlocked amount of information is larger than the key size in both experiments, exhibiting strong violation of the incremental proportionality property of classical information theory. As an application example, we show the successful transmission of a photo over a lossy channel with quantum data (un)locking and error correction.

A thin-gold-film-covered titanium transition edge sensor is newly developed for highly reliable optical photon detection. The aim of the gold film is to prevent a formation of a surface oxidation layer (typically 2.8 nm) on titanium that causes severe degradation of the titanium superconductivity. Optical properties for the gold-covered titanium TES embedded in an optical cavity are calculated, and we find that the maximum absorptance and absorption bandwidth will be reduced with increasing a thickness of the gold film. However, more than 99% absorptance can be possible for the gold (10 nm in thickness) and titanium (30 nm) if 11 dielectric layers are used in an anti-reflection coating. A depth profile of a chemical state for the fabricated device was analysed by an X-ray photoelectron spectroscopy. The profile shows no evidence of TiO2 existence in photoelectron spectrum. Superconducting critical temperature covered with the 10 nm gold were in the range of 200 mK to 320 mK depending on the titanium thickness of 18 nm to 26 nm.

This study quantitatively compared lower limb motility of normal subjects and those requiring Support Level 1 (support_1). We developed a wireless inertial sensor with an embedded triaxial accelerometer and angular velocity sensor. Six normal elderly subjects and ten elderly subjects who were classified as support_1 by the Japanese care insurance system participated in the study. We attached the wireless motion sensors to the center of the lower back and both thighs of the subjects. The subjects were then asked to walk 10 m and perform a stepping exercise. For the evaluation, the cadence, pitch angle, and pitch angular velocity of the thigh autocorrelation function and root mean square (RMS) on the lower back were calculated. The autocorrelation coefficient function for the support_1 subjects was smaller than for the normal subjects, while the RMS was larger in support_1. These differences indicated that the gait and balance abilities of the support_1 subjects were poorer than those of the normal subjects. This suggests that our wireless motion sensor is useful for assessing the motility of the lower limbs while walking and climbing steps. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(12): 37–45, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11430

Photon number resolving detectors based on titanium-transition edge sensors with high speed and high quantum efficiency have been developed for quantum sensors in the fields of quantum information and quantum radiometry. The two devices optimized at wavelengths of interest showed 81% and 64% system detection efficiencies at 850 nm and 1550 nm, respectively. The response speed of the device optimized for a high counting operation is 190 ns, which corresponds to a counting rate over 1 MHz.

A model describing spectral supralinearity for a silicon photodiode in the near-infrared region is presented. This theoretical model is based on the internal quantum efficiency model of the photodiode using Shockley-Read-Hall recombination, which depends on the inner structure parameters of the photodiodes. Comparing the experimental results with the theoretical calculation results, the model enables us to quantitatively predict the starting power level, shape, and wavelength dependence of the supralinearity for a silicon photodiode. This model contributes to high-accuracy measurements over wide optical power ranges and various incident wavelengths.

Since surface plasmon resonance (SPR) provides quick response and high sensitivity to environmental substances, it is recognized as a powerful technique for toxic gas detection system [1–3]. Although already reported SPR gas sensors have achieved a high sensitivity at the ppm level, the adsorption of vapor molecules relies only on the affinity of the planar surface of the sensitive membrane. In terms of adsorption efficiency, a planar adsorber element is less advantageous because the specific surface area is small. It is expected that the sensitivity of the SPR gas sensor could be improved by introducing a porous structure to the sensor surface. However, in order to excite SPR at optical frequencies, materials are limited to Ag or Au on account of the dielectric permittivity to achieve wavenumber matching. These noble metals are stable both chemically and physically, and fabrication of a nano-sized porous structure on these metals has been difficult. In this letter, a meso-porous membrane of a noble metal on which SPR can be excited is reported. The adsorption of water vapor on the membrane is observed from the SPR signal, and the dimension of the porous structure is validated by the Kelvin’s capillary condensation theory. The meso-porous structure proposed in this study is based on the surface profile of a two-dimensional colloidal crystalline structure (CCS) of mono-sized nanoparticles. By utilizing this as a substrate for metallic vapor deposition, a metal film with a surface profile consisting of a number of nano-sized pores and grooves is realized. The crystalline structure is fabricated utilizing the self-assembling behavior of colloidal polymer nanoparticles spread on a hydrophilic glass slide [4]. First, a glass slide is washed carefully with a sponge containing surfactant, and then rinsed couple of times with pure water and organic solvent for degreasing. After rinsing, it is dried by blowing N2 gas over it. Due to the cleaning, the surface of the glass slide obtains a hydrophilic property. In the next stage, a colloidal aqueous solution of polystyrene nanospheres is dropped onto the cleaned surface of the stationary glass slide. As the thickness of the suspension layer becomes smaller than the diameter of the colloidal particles, owing to the evaporation, the particles are forced to attract each other due to capillary force. When the solvent is completely evaporated, the particles form a closely packed hexagonal crystalline structure on the surface of the glass slide. The crystalline structure of the nanoparticles intrinsically possesses nano-sized grooves and cavities of high aspect ratio at the interface of constitutive particles. As illustrated in Fig. 1a, each particle in the crystalline structure has contact points with the neighboring particles every 60 of the azimuth angle. The cross-sectional profile of the contact point of the two particles, expressed by the line A–B, shows a cycloidal surface profile as depicted in Fig. 1b. The width of the wedge-shaped groove gradually decreases and finally becomes zero numerically in the limit. This means that an ultimate porous structure is realized at the contact points. In addition, a small quasi-triangular cavity is T. Numata (&) Y. Otani N. Umeda Faculty of Engineering, Tokyo University of Agriculture and Technology, Nakacho 2-24-16, Koganei, Tokyo 184-8588, Japan e-mail: t-numata@cc.tuat.ac.jp J Mater Sci (2007) 42:1050–1053 DOI 10.1007/s10853-006-1285-z

We report localized thermal processing using a laser-trapped and heated metal nanoparticle. A metal nanoparticle trapped by a focused, continuous wave (CW), near-infrared laser was heated by photothermal conversion and acted as a remotely controllable nanosized thermal tool for processing a workpiece. We demonstrated the processing of a glass substrate with an optically trapped gold nanoparticle (diameter 200 nm) irradiated by a Nd:YAG laser (λ = 1.064 µm, CW). Laser irradiation caused local melting of the substrate and a crater-like nanosized imprint on the substrate, demonstrating thermal nanoprocessing of an optically transparent material. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

According to development of optical engineering, the measurement accuracy of optical components and materials has become more important. For example, birefringence in polymer thin film is an essential issue for development of liquid crystal display. In this study, after a PVA (poly vinyl alcohol) film was embedded by photopolymer and cut by ultramicrotome, a cross-sectional birefringence distribution of cut film was observed by birefringence contrast scanning near-field optical microscopy (B-SNOM). As a result, three dimensional birefringence ratios were calculated and birefringence of parallel to stretching direction was larger than that of vertical one. This result shows that cross-sectional birefringence distribution is yielded by inhomogeneous distribution of molecular alignment in film material according to asymmetry stretching.

The sensitivity of an optical dew sensor is enhanced by the use of the surface plasmon resonance (SPR) of a periodic Ag nanostructure. As the temperature of an SPR-excited Ag nanostructure decreases, vaporous water molecules condense and adsorb onto hydroxyl groups formed on the Ag surface. A redshift of 40 nm in absorption peak wavelength was observed owing to the amount of adsorbed water molecules due to the temperature. An SPR signal occurs at temperatures higher than the theoretical dew point and shows the sensitivity improvement of the optical dew sensor by the proposed SPR technique.

This paper describes the laser manipulation of metal nanoparticles and dielectric particles by fiber-optic laser tweezers with a microspherical focusing lens. In this manner, a small ball lens attached to the end of the core focuses light guided through a single-mode optical fiber. Numerical electromagnetic analysis of the microfocusing structure showed the possibility of metal nanoparticle trapping with this method. An effective focus allows metallic particles located in the path of the focused light to be attracted to the center of the beam path and to be two-dimensionally trapped on a substrate. In the experiment, manipulation of Au nanoparticles with diameters of 40, 100, and 200 nm was demonstrated. In addition to metallic samples, manipulation of dielectric particles with 1 and 3 µm diameters was also demonstrated using the same configuration, showing the extended capability of the fiber-optic laser manipulator.

The response non-uniformities of laser beam profiling cameras were investigated experimentally at near-infrared laser wavelengths. A uniform-irradiance light source with near-infrared laser wavelengths, and also a visible wavelength as comparison, was constructed for testing several different commercially available beam profiling cameras. The response signals of all charge-coupled device (CCD)-type sensors showed a strong dependence on the irradiant wavelength. The pixel-to-pixel non-uniformity of CCDs at 1064 nm increased rapidly with the reduction of exposure time, whereas that of CMOS sensors was maintained independently of these parameters. The characteristics of CCDs were discussed in terms of charge leakage effect, which is a likely source of these phenomena.

Broadband light sources play essential roles in diverse fields, such as high-capacity optical communications, optical coherence tomography, optical spectroscopy and spectrograph calibration. Although a nonclassical state from spontaneous parametric down-conversion may serve as a quantum counterpart, its detection and characterization have been a challenging task. Here we demonstrate the direct detection of photon numbers of an ultrabroadband (110 nm FWHM) squeezed state in the telecom band centred at 1535 nm wavelength, using a superconducting transition-edge sensor. The observed photon-number distributions violate Klyshko's criterion for the nonclassicality. From the observed photon-number distribution, we evaluate the second- and third-order correlation functions and characterize a multimode structure, which implies that several tens of orthonormal modes of squeezing exist in the single optical pulse. Our results and techniques open up a new possibility to generate and characterize frequency-multiplexed nonclassical light sources for quantum info-communications technology.

Ultrabroadband photon-number-resolving detection is demonstrated for parametric fluorescence ranging over 150 nm in the telecom window, using a Ti transition edge sensor. Our results violate Klyshko's classical limit for even photon numbers.

Spectral supralinearity of silicon photodiodes in visible light was investigated. The experimental spectral supralinearity results were compared with the calculation results using a device simulator, PC1D that includes the front surface recombination parameters, and these comparison results were in reasonable agreement for a silicon photodiode. These comparison results show that supralinearity in visible light clearly occurs with a front surface charge density of more than 1012 cm−2 and the included parameters are adequate for quantitatively predicting the internal quantum efficiency of silicon photodiodes.

Porous nickel–phosphorus (NiP) black surfaces exhibit excellent low reflectance in the visible and near-IR regions. Through use of a model of the surface morphology and composition, the reflectance was numerically simulated by a three-dimensional finite-difference time-domain method to determine the origin of the low reflectance. In agreement with experimental results, the simulations showed a spectrally flat, quite low reflectance of

A transition edge sensor (TES) is one of superconducting photon detectors, which has a photon number resolving ability in light pulses. The TES device is a kind of calorimeters operated at an extremely low temperature, and the energy of the photons is measured as a resistance change in a superconducting transition region of the TES. The advantages of the TESs are an excellent energy resolution and a high quantum efficiency. However a response speed is limited due to slow thermal recovery time. To overcome this, we fabricated new TES devices which are based on a titanium superconductor. The critical temperature of our titanium films is around 410 mK, which greatly improves the thermal recovery time. The observed decay time constant of response signals to the light pulses is around several hundreds of ns, that make it possible to operate the devices at a counting rate over 1 MHz. The photon number resolving power is 0.35 eV(FWHM) for a 5 μm size device even at the high operating temperature. The system quantum efficiency is 65 % by embedding the TES films in an optical structure with a high reflection dielectric mirror and an anti-reflection coatings fabricated by an ion beam assisted sputtering method. These features are very promising for high speed photon number resolving applications in the quantum information field.

We report on some efforts to improve a quantum efficiency of titanium‐based optical superconducting transition edge sensors using the multi‐layered absorption structure for maximizing photon absorption in the Ti layer. Using complex refractive index values of each film measured by a Spectroscopic Ellipsometry, we designed and optimized by a simulation code. An absorption measurement of fabricated structure was in good agreement with the design and was higher than 99% at optimized wavelength of 1550 nm.

An optical dew point sensor based on plasmonic resonance effect of Ag nanoparticle array is described. Plasmonic response from Ag nanostructure allows sensing subtle change of refractive index according to adsorption of H 2 molecules.

A laser manipulation technique for metal nanoparticles using an optical fiber has been developed. A micro ball lens adhered onto the flattened end of the optical fiber focuses a light beam propagated through a core. An object is trapped in the focused beam. An electromagnetic field distribution was numerically simulated for validation of the focusing lens. Calculation including an Au nanoparticle indicated that the laser trapping would be possible with this method. In the experiment, trapping of Au particles with diameter of 200nm was achieved by using a light source (Nd-YAG: 1064nm). The maximum trapping efficiency attained in the focal region was estimated to be 5.4fN/mW. Additionally, the fixation of a manipulated particle onto a glass substrate was also demonstrated. With intensifying the laser power, a laser-trapped particle is fixed on the substrate. By repetition of the procedure of laser manipulation and fixation, alignment of Au nanoparticles was achieved.

Energy resolution (ΔE), recovery time (τeff), and quantum efficiency (QE) are some of the most important single photon-counting detector parameters. New applications in the quantum optics field place extreme demand on detector performances that go beyond the capabilities of established single-photon detectors. Unfortunately, it is hard to reach best results for all these parameters at the same time. Concerning transition-edge sensors (TESs) as single photon detectors, ΔE and τeff are directly and inversely proportional to the transition temperature Tc, respectively. Moreover, the geometrical optical coupling between illuminating fiber and detector, the device material and the characteristics of the optical cavity or the antireflection coating, drastically influence the QE and in some cases also the ΔE. Previous TESs fabricated by Istituto Nazionale di Ricerca Metrologica were characterized by very high energy resolution (0.18 eV) but high τeff and low QE. In this work, we present a Ti/Au TES with higher Tc (300 mK) that, using the optical alignment system implemented by AIST, shows an optimization of these important parameters, energy resolution of 0.26 eV, recovery time of 186 ns, and a quantum efficiency of 50% without using any optical structure deposited on the detector.

We have realized a high-detection-efficiency photon number resolving detector at an operating wavelength of about 850 nm. The detector consists of a titanium superconducting transition edge sensor in an optical cavity, which is directly coupled to an optical fiber using an approximately 300-nm gap. The gap reduces the sensitive area and heat capacity of the device, leading to high photon number resolution of 0.42 eV without sacrificing detection efficiency or signal response speed. Wavelength dependent efficiency in fiber-coupled devices, which is due to optical interference between the fiber and the device, is also decreased to less than 1% in this configuration. The overall system detection efficiency is 98%±1% at wavelengths of around 850 nm, which is the highest value ever reported in this wavelength range.

We have fabricated Niobium-based superconducting single photon detector (Nb-SSPD) for realizing high detection efficiency and fast reset time. The Nb-SSPD consisted of a 7 nm-thick and 200 nm-wide Nb meander line and exhibited the critical temperature and critical current density of 4 K and 4.6×105 A/cm2, respectively. The Nb-SSPD was coupled to an optical fiber, and the reset time of 2.5 ns was observed with illumination of laser pulses at 1550 nm wavelength.