Taro Itatani

Titanium-based transition-edge photon number resolving detector with 98% detection efficiency with index-matched small-gap fiber coupling

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.

Self-starting mode-locked femtosecond forsterite laser with a semiconductor saturable-absorber mirror.

We report on a self-starting mode-locked femtosecond Cr:forsterite laser pumped by a diode-pumped Nd:YVO(4) laser. The mode locking is initiated by a semiconductor saturable-absorber mirror (SESAM). We also present the measured group delay of the forsterite crystal and the SESAM.

High Electron Mobility Metal–Insulator–Semiconductor Field-Effect Transistors Fabricated on (111)-Oriented InGaAs Channels

Metal–insulator–semiconductor field-effect transistors (MISFETs) were fabricated on the (111)A surface of In0.53Ga0.47As for the first time. Al2O3 gate dielectrics were formed by atomic layer deposition on sulfur-stabilized InGaAs surfaces. The MISFET on (111)A demonstrated channel mobility higher than that on (100), achieving more than 100% improvement with respect to Si even at a high surface carrier concentration.

Intense Terahertz Pulses from Large-Aperture Antenna with Interdigitated Electrodes

We fabricated a large-aperture photoconductive terahertz (THz) emitter array on a semi-insulating GaAs substrate. The device was composed of seven 1 cm2 photoconductive antenna units having microstructured interdigitated electrodes with 10 µm lines and spaces. By illuminating it with amplified femtosecond optical pulses, a large THz field comparable to that obtained from conventional large-aperture photoconductive antennas was obtained at a bias voltage as low as 30 V. The coherent superposition of the output of the seven units was observed.

Femtosecond Cr:forsterite laser with mode locking initiated by a quantum-well saturable absorber

We studied a mode-locked Cr:forsterite laser pumped by a diode pumped Nd:YVO/sub 4/ laser. Both the Kerr lens mode locking and the semiconductor saturable absorber initiated mode locking have been demonstrated. Using our measured dispersion data of the forsterite crystal, together with our dispersion compensation technique, we obtained 20-fs pulses for the pure Kerr lens mode locking and 36-fs pulses for semiconductor saturable absorber initiated mode locking, respectively.

Photon number resolving detection with high speed and high quantum efficiency

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.

Development of quantum hall array resistance standards at NMIJ

An experimental device of quantum Hall array resistance standards with a nominal value close to 10 kOmega on the i = 2 plateau and a parallel array of two Hall bars have been developed. The latter array clearly shows quantized Hall resistance of a quarter value of the von Klitzing constant, RK on the i = 2 plateau.

Correlation between channel mobility improvements and negative V th shifts in III–V MISFETs: Dipole fluctuation as new scattering mechanism

Channel mobility µ<inf>eff</inf> for InGaAs MISFETs is improved by using the (111)A surface orientation and (NH<inf>4</inf>)<inf>2</inf>S treatment. These µ<inf>eff</inf> improvements are associated with negative shifts in V<inf>th</inf> and V<inf>fb</inf>. We propose that carrier scattering by fluctuated dipoles at the MIS interfaces contributes to µ<inf>eff</inf> for the III–V MISFETs. For the InP MISFETs, the effects of the interface dipoles are not apparent due to their inferior interface quality.

Titanium Superconducting Photon-Number-Resolving Detector

High-efficiency photon-number-resolving detectors have been developed using titanium-based transition-edge sensors. Device performances have been evaluated with respect to the response photon distribution, dark count, and timing jitter. In the analysis of the photon statistics, the observed detection probabilities were consistent with Poisson distributions. From a comparison of the measured distribution with theory, 98% detection efficiency was deduced at 850 nm. The dark count probability of the device is less than 10-6, corresponding to a dark count rate of 0.6 Hz. The timing jitter is 25 ns, the best value ever reported (to our knowledge) in transition-edge sensors used for optical photon measurements.

FEMTOSECOND CR:FORSTERITE LASER DIODE PUMPED BY A DOUBLE-CLAD FIBER

We present a compact, all-solid-state femtosecond Cr:forsterite laser. The laser is pumped by diodes through a double-clad fiber. Kerr-lens mode locking is initiated and stabilized by a semiconductor saturable-absorber mirror with a single InGaAs quantum well. This system generates transform-limited 80-fs pulses near 1.3microm . An average power of 68 mW with fluctuation of much less than 1% is obtained with 3.8 W of absorbed pump power. The stability, efficiency, compactness, and potential for scaling to higher power of this system make it an attractive short-pulse source for applications.