Ultrahigh-sensitivity infrared detection system using an InGaAs p-i-n photodiode with low dielectric polarization noise.

We developed a highly sensitive infrared photodetection system using an InGaAs p-i-n photodiode. The temperature and data sampling rate dependences of the readout noise were measured to determine the optimum temperature for low-noise detection. The optimum temperature for sampling rates below 100 Hz was 100 K, and the readout noise at 1 Hz was 2.5 e. The readout noise at 1 MHz and 140 K was 49.4 e. The light detection limit of the system was 8.2×10(-19) W at a wavelength of 1.3 µm. The spectral noise densities of a readout circuit were measured in order to determine the origin of noise.

Ultrahigh-sensitivity single-photon detection with linear-mode silicon avalanche photodiode.

We developed an ultrahigh-sensitivity single-photon detector using a linear-mode avalanche photodiode (APD) with a cryogenic low-noise readout circuit; the APD is operated at 78K. The noise-equivalent power of the detector is as low as 2.2x10(-20)W/Hz(1/2) at a wavelength of 450nm. The photon-detection efficiency and dark-count rate (DCR) are 0.72 and 0.0008counts/s, respectively. A low DCR is achieved by thermal treatment for reducing the trapped carriers when the thermal treatment temperature is above 100K.

Measurement and simulation of the effect of snowfall on free-space optical propagation.

We measured the time variation of a received laser signal level during snowfall over a distance of 72 m. The signal level dropped sharply for up to 10 ms when a snowflake crossed the laser beam. The probability distribution of the variation due to snowfall was calculated by assuming it to be the linear superposition of the light diffracted by snowflakes. The measured distributions could be reproduced by assuming reasonable snowflake size distributions. Furthermore, the probability distributions due to snowfall over a 1 km distance were calculated, and the expected bit errors during snowfall and the transmitted beam sizes were evaluated.

Ultralow-noise readout circuit with an avalanche photodiode: toward a photon-number-resolving detector.

The charge-integration readout circuit was fabricated to achieve an ultralow-noise preamplifier for photoelectrons generated in an avalanche photodiode with linear mode operation at 77 K. To reduce the various kinds of noise, the capacitive transimpedance amplifier was used and consisted of low-capacitance circuit elements that were cooled with liquid nitrogen. As a result, the readout noise is equal to 3.0 electrons averaged for a period of 40 ms. We discuss the requirements for avalanche photodiodes to achieve photon-number-resolving detectors below this noise level.

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.

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.