Abstract A study of optical fibre power metre calibrations is presented based on comparison with fibre-coupled cryogenic radiometry. Three nearly identical cryogenic radiometers are used together with a free-space absolute spectral responsivity measurement facility. The results show that the dominant sources of uncertainty originate not from the radiometers or the transfer standard detector, but from the optical path components used to convey light from the source to the detector. The properties of the optical radiation, defined by wavelength, polarization, and modal quality, together with system components such as optical fibres, fibre switches, fibre splitters, polarization controllers, and external influences including temperature and vibration, limit the achievable uncertainty. Measurements are performed at optical power levels near 100 µW, a regime in which the underlying measurement technology has matured over several decades. The absolute uncertainty ranges from approximately 0.0010 A W −1 to 0.0043 A W −1 , depending on the wavelength and components. The results provide a quantitative basis for assessing the limits of uncertainty reduction in fibre-based optical power measurements and are relevant to future uncertainty analyses of fibre-coupled single-photon detector efficiency in quantum communications and quantum technologies in general.
Abstract A study of optical fibre power metre calibrations is presented based on comparison with fibre-coupled cryogenic radiometry. Three nearly identical cryogenic radiometers are used together with a free-space absolute spectral responsivity measurement facility. The results show that the dominant sources of uncertainty originate not from the radiometers or the transfer standard detector, but from the optical path components used to convey light from the source to the detector. The properties of the optical radiation, defined by wavelength, polarization, and modal quality, together with system components such as optical fibres, fibre switches, fibre splitters, polarization controllers, and external influences including temperature and vibration, limit the achievable uncertainty. Measurements are performed at optical power levels near 100 µW, a regime in which the underlying measurement technology has matured over several decades. The absolute uncertainty ranges from approximately 0.0010 A W −1 to 0.0043 A W −1 , depending on the wavelength and components. The results provide a quantitative basis for assessing the limits of uncertainty reduction in fibre-based optical power measurements and are relevant to future uncertainty analyses of fibre-coupled single-photon detector efficiency in quantum communications and quantum technologies in general.
A system for calibrating single photon detector efficiency that is traceable to the SI through a state-of-the-art classical optical fibre radiometer has been developed and is in the process of being vetted as a calibration service at the National Institute of Standards and Technology (NIST). The method of calibration is direct substitution to power meters relative to NIST's optical fibre cryogenic primary standard and builds on the existing measurement infrastructure for the calibration of optical fibre power meters. Recent improvements to the optical fibre cryogenic radiometer make it more robust and deployable. The traceability of the single photon detector calibration service under development to these classical measurements is discussed, along with a description of the technique used in this calibration service to calibrate the detection efficiency of single photon detectors. Finally, we discuss work on the development of these technologies so that in the future they may be deployable to the point-of- use.
Over the last few years, the National Research Council of Canada (NRC) has been establishing new facilities and improving capabilities in three areas of radiometry: optical power, spectral irradiance, and few-photon measurements. Canada’s realization of the optical radiant power scale now utilizes a new cryogenic electrical substitution radiometer as the primary instrument. With higher cavity absorptance, reduced non-equivalence effects, and a closed-cycle helium cryocooler, this new cryogenic radiometer has significantly contributed to improvements in measurement uncertainties. NRC’s primary spectral irradiance scale has transitioned from a detector based approach to a detector and source based realization. Filter radiometers with spectral responsivity traceable to the cryogenic radiometer and a high temperature blackbody primary light source are implemented in the calibration of transfer standard FEL lamps from 200 nm to 2500 nm. Most recently, NRC has been working to establish a few-photon metrology capability for optical radiometry. The initial goal of this new facility is to measure the detection efficiency of free-space single-photon detectors using a calibrated detector substitution technique. This capability will then be extended to the traceable characterization of NRC on-chip semiconductor quantum dot-based single-photon sources, the evaluation of these sources as new quantum standards, and using entangled photons from these sources for fundamental quantum metrology measurements. Ongoing efforts and details of these new radiometry facilities will be presented.
Radiometric calibrations of fibre-coupled single photon detectors are experiencing growing demand, especially at the telecommunication wavelengths. In this paper, the radiometric calibration of a fibre-coupled superconducting nano-wire single photon detector at the telecom wavelength 1.55 µm by means of well-characterized synchrotron radiation is described. This substitution method is based on the unique properties of synchrotron radiation and the Metrology Light Source, the dedicated electron storage ring of the Physikalisch-Technische Bundesanstalt, and is suitable for fibre-coupled single photon detectors. The Metrology Light Source is used as a light source with a high dynamic range of the radiant power to bridge the radiometric gap occurring in the transition from radiant power measurements and the counting of photons with single photon detectors. Very low uncertainties below 2% have been achieved in the measurement of the detection efficiency of a fibre-coupled superconducting nano-wire single photon detector.
We show a setup for characterising the efficiency of a single-photon-detector absolutely and with a precision better than 1%. Since the setup does not rely on calibrated devices and can be implemented with standard-optic components, it can be realised in any laboratory. Our approach is based on an Erbium-Doped-Fiber-Amplifier (EDFA) radiometer as a primary measurement standard for optical power, and on an ultra-stable source of spontaneous emission. As a proof of principle, we characterise the efficiency of an InGaAs/InP single-photon detector. We verified the correctness of the characterisation with independent measurements. In particular, the measurement of the optical power made with the EDFA radiometer has been compared to that of the Federal Institute of Metrology using a transfer power meter. Our approach is suitable for frequent characterisations of high-efficient single-photon detectors.
InGaAs/InP single-photon detectors are today the most frequently used detectors for fibre-based Quantum Key Distribution (QKD) [1,2]. The performance of the QKD-systems greatly depends on the optical properties of its detector, such as quantum efficiency, dead time, dark counts, gating rate, etc., which need to be metrologically characterized to fully grantee the QKD network security. Therefore, several European National Metrological Institutes (NMIs) are putting today great efforts in developing novel measurement methods and calibration facilities, which allow to perform the traceable characterisation of single-photon detectors by using reference standards [3, 4]. From the metrological, and specifically radiometric, point of view, the detection efficiency of the single-photon detector is the main parameter that needs to be traceable to the primary standard for optical power (i.e. the cryogenic radiometer), which is maintained by most of the NMIs. Recently, four European NMIs have carried out a pilot comparison on the detection efficiency of a free-running InGaAs/InP single-photon detector, which main purpose has been to provide a snapshot of the measurement capabilities of the four European NMIs in the field of photon counting detection. The comparison was carried out in the framework of the EMPIR project 14IND05 “Optical metrology for quantum-enhanced secure telecommunication (MIQC2)” at the telecom wavelength of 1550 nm by using different reference standards with independently traceability chains. The results of this comparison, including the different experimental setups, the measurement methods, the traceability chain and the uncertainty evaluation of each participant, will be presented in this conference. References: [1] Akihisa Tomita, et al., “High speed quantum key distribution system”, Optical Fiber Technology, 16, Issue 1, 55-62 (2010). [2] Damien Stucki, et al., “Photon counting for quantum key distribution with peltier cooled InGaAs/InP APDs”, Journal of Modern Optics, 48, Issue 13, 1967-1981 (2001). [3] M. López, et al, “Detection efficiency calibration of single-photon silicon avalanche photodiodes traceable using double attenuator technique, Journal of Modern Optics 62, S21 – S27, 2015. [4] G. Porrovecchio, et al., “Comparison at the sub-100 fW optical power level of calibrating a single-photon detector using a high-sensitive, low-noise silicon photodiode and the double attenuator technique”, Metrologia 53, 1115-1122 (2016).
We will present our current efforts on single photon quantum metrology using high-efficiency superconducting detectors and high-efficiency single-photon sources based on spontaneous parametric downconversion. Optical power measurements based on single photon counting could establish a quantum standard for optical power calibration in the future. At NIST we are pursuing the development of single photon sources and single photon detectors for metrology, quantum and classical applications. As part of these efforts, we are pursuing the establishment of a measurement service for the calibration of single photon detectors. We present how our calibration is tied to the calibration of our transfer standard optical fiber power meters. Using the beamsplitter method, we have implemented a fiber-coupled and free-space measurement system. Also, we have developed testbeds and measurement protocols for the characterization of single photon sources and single photon detectors. We will review several methods, which allow for the characterization of the spatial and spectral degree of freedom in spontaneous parametric downconversion.