Hidemi Tsuchida

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.

Cross-phase-modulation-based wavelength conversion using intersubband transition in InGaAs/AlAs/AlAsSb coupled quantum wells

We report an ultrafast cross phase modulation (XPM) effect in intersubband transition (ISBT) of InGaAs/AlAs/AlAsSb coupled quantum wells, where the ISBT absorption of a transverse-magnetic mode pump signal induces phase modulation of a transverse-electric mode probe signal. Using waveguide-type ISBT devices, we have achieved XPM-based 10 Gbit/s wavelength conversion with a power penalty of 2.53 dB. Also, we propose XPM-based signal processing circuits for gate switching and modulation format conversion.

Frequency Stabilization of AlGaAs Semiconductor Laser Based on the 85Rb-D2 Line

The frequency of an AlGaAs semiconductor laser was stabilized by using the linear absorption spectrum of the 85Rb-D2 line. By controlling the injection current, the frequency stability of 3.0×10-10σ1.4×10-12 was obtained for 10 msτ500 s. First observation of the saturated absorption spectrum of the 85Rb-D2 line is demonstrated, which can be used as a frequency reference to improve the frequency stability.

40-Gb/s optical clock recovery using an injection-locked optoelectronic oscillator

A 40-Gb/s optical clock recovery is demonstrated using an injection-locked optoelectronic oscillator (OEO). Injection locking is achieved by directly coupling a return-to-zero optical data stream to a photodiode in the OEO. This scheme is advantageous in its simple configuration, wavelength-independent operation, and wide locking range. The pulsewidth and root-mean-square jitter of the recovered clock are 9.8 ps and 283 fs (10 Hz-18.6 MHz), respectively. Furthermore, subharmonic clock recovery from a 160-Gb/s optical time-division-multiplexed data stream is achieved using the same configuration.

All-optical demultiplexing of 160–10Gbit∕s signals with Mach-Zehnder interferometric switch utilizing intersubband transition in InGaAs∕AlAs∕AlAsSb quantum well

We have developed a Mach-Zehnder interferometric all-optical switch employing intersubband transition in an InGaAs∕AlAs∕AlAsSb-coupled double quantum well waveguide. The recently discovered cross-phase modulation phenomenon was utilized as the switching mechanism; the nonlinear index of refraction for transverse electric polarized light is induced by intersubband optical excitation using transverse magnetic pump light. We demonstrate the demultiplexing operation of 160Gbit∕s data signals to 10Gbit∕s using this switch. At the input control pulse energy of 8pJ, the demultiplexed signals showed an extinction ratio better than 10dB, and an error-free demultiplexing was achieved.

Frequency Stabilization of AlGaAs Semiconductor Laser to the Absorption Line of Water Vapor

The absorption spectrum of water vapor in the (2, 1, 1) vibration-rotation band has been observed by using an AlGaAs semiconductor laser around 0.82 µm. The laser frequency was stabilized to one of the absorption lines by controlling the injection current. A frequency stability of 1.9×10-9≧σ≧1.1×10-11 was obtained for 10 ms≦τ≦500 s.

Gated-mode single-photon detection at 1550 nm by discharge pulse counting

Gated-mode single-photon detection using an avalanche photodiode is characterized by charge and discharge pulses, which are attributable to capacitive behavior. In this letter, the discharge pulse rather than the photon-induced avalanche pulse is counted in single-photon detection, in order to reduce after pulses. A demonstration adopts an indium–gallium–arsenide avalanche photodiode operating at 1550 nm. After-pulse probability per gate is evaluated at a repetition frequency of 5 MHz.

Stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short PPLN waveguide

We demonstrate a stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short periodically-poled lithium niobate (PPLN) waveguide. Full quantum state tomographic measurement performed on the photon-pairs has revealed a very high state purity of 0.94, and an entanglement fidelity exceeding 0.96 at the low-rate-regime. At higher rates, entanglement quality degrades due to emission of multiple-pairs. Using a new model, we have confirmed that the observed degradation is largely due to double- and triple-pair emissions.

Simple technique for improving the resolution of the delayed self-heterodyne method

A new technique is proposed and demonstrated for improving the resolution of the delayed self-heterodyne method for laser spectral linewidth measurement. The delay time between two laser beams is increased by the use of multipass transmission in an optical fiber ring interferometer containing a frequency shifter. This technique does not require a longer fiber or complicated curve fitting of the observed spectra.

A 1550 nm Single-Photon Detector Using a Thermoelectrically Cooled InGaAs Avalanche Photodiode

We report a gated-mode single-photon detector sensitive to 1550 nm radiation using a thermoelectrically cooled InGaAs avalanche photodiode. At the operation temperature of 238 K, we have obtained a quantum efficiency of 24.3% with a dark-count probability per gate of 9.4×10-5.