Biomedical subjects

Mikio Fujiwara

Publications and source records attributed to Mikio Fujiwara.

5 recordsLinked to original sources

PubMed2006

Photon-number-resolving detection at a telecommunications wavelength with a charge-integration photon detector.

We demonstrate multiphoton discrimination at a telecommunications wavelength with the readout frequency of 40 Hz by a charge-integration photon detector (CIPD). The CIPD consists of an InGaAs pin photodiode and a GaAs junction field effect transistor as a preamplifier in a charge-integration circuit, which is cooled to 4.2 K to reduce thermal noise. The quantum efficiency of the CIPD (the detector itself) is 80% for 1530 nm light, and the readout noise is measured as 0.26 electrons at 40 Hz. We can construct Poisson distributions of photocarrier numbers with distinct peaks at each photocarrier number, corresponding to a signal-to-noise ratio of about 3.

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PubMed2005

Ultrahigh-sensitivity high-linearity photodetection system using a low-gain avalanche photodiode with an ultralow-noise readout circuit.

A highly sensitive photodetection system with a detection limit of 1 photon/s was developed. This system uses a commercially available 200-microm-diameter silicon avalanche photodiode (APD) and an in-house-developed ultralow-noise readout circuit, which are both cooled to 77 K. When the APD operates at a low gain of approximately 10, it has a high-linearity response to the number of incident photons and a low excess noise factor. The APD also has a high quantum efficiency and a dark current of less than 1 e/s at 77 K. This photodetection system will shorten measurement time and permit higher spatial and wavelength resolution for near-field scanning optical microscopes.

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PubMed2003

Ultralow-noise near-infrared detection system with a Si p-i-n photodiode.

Noises associated with materials and devices in the readout circuits for a Si p-i-n photodiode have been measured. The dielectric polarization noise of the materials and devices near the gate circuit of the junction field-effect transistor used for the preamplifier determined the photodetection limits of photodiodes with a diameter smaller than several millimeters. We fabricated an ultralow-noise photodetection system, minimizing the polarization noise as much as possible. The readout noises of the system were 10 and 18 electrons in a correlated double sample for 0.1- and 1-mm-diameter Si p-i-n photodiodes at 77 K, respectively.

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PubMed2003

Exceeding the classical capacity limit in a quantum optical channel.

The amount of information transmissible through a communications channel is determined by the noise characteristics of the channel and by the quantities of available transmission resources. In classical information theory, the amount of transmissible information can be increased twice at most when the transmission resource is doubled for fixed noise characteristics. In quantum information theory, however, the amount of information transmitted can increase even more than twice. We present a proof-of-principle demonstration of this superadditivity of classical capacity of a quantum channel by using the ternary symmetric states of a single photon, and by event selection from a weak coherent light source. We also show how the superadditive coding gain, even in a small code length, can boost the communication performance of the conventional coding technique.

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PubMed2003

Development of a gallium-doped germanium far-infrared photoconductor direct hybrid two-dimensional array.

To our knowledge, we are the first to successfully report a direct hybrid two-dimensional (2D) detector array in the far-infrared region. Gallium-doped germanium (Ge:Ga) has been used extensively to produce sensitive far-infrared detectors with a cutoff wavelength of approximately equal to 110 microm (2.7 THz). It is widely used in the fields of astronomy and molecular and solid spectroscopy. However, Ge:Ga photoconductors must be cooled below 4.2 K to reduce thermal noise, and this operating condition makes it difficult to develop a large format array because of the need for a warm amplifier. Development of Ge:Ga photoconductor arrays to take 2D terahertz images is now an important target in such research fields as space astronomy. We present the design of a 20 x 3 Ge:Ga far-infrared photoconductor array directly hybridized to a Si p-type metal-oxide-semiconductor readout integrated circuit using indium-bump technology. The main obstacles in creating this 2D array were (1) fabricating a monolithic Ge:Ga 2D array with a longitudinal configuration, (2) developing a cryogenic capacitive transimpedance amplifer, and (3) developing a technology for connecting the detector to the electronics. With this technology, a prototype Ge:Ga photoconductor with a direct hybrid structure has shown a responsivity as high as 14.6 A/W and a minimum detectable power of 5.6 x 10(-17) W for an integration time of 0.14 s when it was cooled to 2.1 K. Its noise is limited by the readout circuit with 20 microV/Hz(1/2) at 1 Hz. Vibration and cooling tests demonstrated that this direct hybrid structure is strong enough for spaceborne instruments. This detector array will be installed on the Japanese infrared satellite ASTRO-F.

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