Calibration of free-space and fiber-coupled single-photon detectors.

We measure the detection efficiency of single-photon detectors at wavelengths near 851 nm and 1533.6 nm. We investigate the spatial uniformity of one free-space-coupled single-photon avalanche diode and present a comparison between fusion-spliced and connectorized fiber-coupled single-photon detectors. We find that our expanded relative uncertainty for a single measurement of the detection efficiency is as low as 0.70% for fiber-coupled measurements at 1533.6 nm and as high as 1.78% for our free-space characterization at 851.7 nm. The detection-efficiency determination includes corrections for afterpulsing, dark count, and count-rate effects of the single-photon detector with the detection efficiency interpolated to operation at a specified detected count rate.

Compact cryogenic self-aligning fiber-to-detector coupling with losses below one percent.

We present a compact packaging technique for coupling light from a single-mode telecommunication fiber to cryogenic single-photon sensitive devices. Our single-photon detectors are superconducting transition-edge sensors (TESs) with a collection area only a factor of a few larger than the area of the fiber core which presents significant challenges to low-loss fiber-to-detector coupling. The coupling method presented here has low loss, cryogenic compatibility, easy and reproducible assembly and low component cost. The system efficiency of the packaged single-photon counting detectors is verified by the "triplet method" of power-source calibration along with the "multiple attenuator" method that produces a calibrated single-photon flux. These calibration techniques, when used in combination with through-wafer imaging and fiber back-reflection measurements, give us confidence that we have achieved coupling losses below 1% for all devices packaged according to the self-alignment method presented in this paper.

Intramural Comparison of NIST Laser and Optical Fiber Power Calibrations.

The responsivity of two optical detectors was determined by the method of direct substitution in four different NIST measurement facilities. The measurements were intended to demonstrate the determination of absolute responsivity as provided by NIST calibration services at laser and optical-communication wavelengths; nominally 633 nm, 850 nm, 1060 nm, 1310 nm, and 1550 nm. The optical detectors have been designated as checks standards for the purpose of routine intramural comparison of our calibration services and to meet requirements of the NIST quality system, based on ISO 17025. The check standards are two optical-trap detectors, one based on silicon and the other on indium gallium arsenide photodiodes. The four measurement services are based on: (1) the laser optimized cryogenic radiometer (LOCR) and free field collimated laser light; (2) the C-series isoperibol calorimeter and free-field collimated laser light; (3) the electrically calibrated pyroelectric radiometer and fiber-coupled laser light; (4) the pyroelectric wedge trap detector, which measures light from a lamp source and monochromator. The results indicate that the responsivity of the check standards, as determined independently using the four services, agree to within the published expanded uncertainty ranging from approximately 0.02 % to 1.24 %.

Connector-induced offsets in optical fiber powermeters.

We discuss issues related to calibration of optical fiber powermeters. The power readings may vary when using various types of fiber connectors, or even the same type of connectors made by different vendors. We study the connector effects by calibrating four types of optical fiber powermeters using six different fiber connectors from four vendors at three wavelengths. We found variations of as much as 12% due to the different reflection properties of the detector windows, connectors, and detectors. We also compared connector measurement results with the data obtained by using open beams.

Nonlinearity of high-power optical fiber power meters at 1480 nm.

We describe a calibration system that measures the nonlinearity of optical fiber power meters (OFPMs) at a maximum power of 0.6 W and a minimum power of 0.2 mW at 1480 nm. The system is based on the triplet superposition method. This system measures the nonlinearity of OFPMs by using correction factors at different powers; the system is an important tool for characterizing OFPMs at high powers in the S band. The measurement uncertainties, typically better than 0.2%, k = 2, associated with the high-power nonlinearity system are also described.