The design and construction of a predictable quantum efficient detector (PQED), suggested to be capable of measuring optical power with a relative uncertainty of 1 ppm (ppm = parts per million), is presented. The structure and working principle of induced junction silicon photodiodes are described combined with the design of the PQED. The detector uses two custom-made large area photodiodes assembled into a light-trapping configuration, reducing the reflectance down to a few tens of ppm. A liquid nitrogen cryostat is used to cool the induced junction photodiodes to 78 K to improve the mobility of charge carriers and to reduce the dark current. To determine the predicted spectral responsivity, reflectance losses of the PQED were measured at room temperature and at 78 K and also modelled throughout the visible wavelength range from 400 nm to 800 nm. The measured values of reflectance at room temperature were 29.8 ppm, 22.8 ppm and 6.6 ppm at the wavelengths of 476 nm, 488 nm and 532 nm, respectively, whereas the calculated reflectances were about 4 ppm higher. The reflectance at 78 K was measured at the wavelengths of 488 nm and 532 nm over a period of 60 h during which the reflectance changed by about 20 ppm. The main uncertainty components in the predicted internal quantum deficiency (IQD) of the induced junction photodiodes are due to the reliability of the charge-carrier recombination model and the extinction coefficient of silicon at wavelengths longer than 700 nm. The expanded uncertainty of the predicted IQD is 2 ppm at 78 K over a limited spectral range and below 140 ppm at room temperature over the visible wavelength range. All the above factors are combined as the external quantum deficiency (EQD), which is needed for the calculation of the predicted spectral responsivity of the PQED. The values of the predicted EQD are below 70 ppm between the wavelengths of 476 nm and 760 nm, and their expanded uncertainties mostly vary between 10 ppm and 140 ppm, where the lowest uncertainties are obtained at low temperatures.

The generation, measurement, and manipulation of light at the single-and few-photon levels underpin a rapidly expanding range of applications. These range from applications moving into the few-photon regime in order to achieve improved sensitivity and/or energy efficiency, as well as new applications that operate solely in this regime, such as quantum key distribution and physical quantum random number generation. There is intensive research to develop new quantum optical technologies, for example, quantum sensing, simulation, and computing. These applications rely on the performance of the single-photon sources and detectors they employ; this review article gives an overview of the methods, both conventional and recently developed, that are available for measuring the performance of these devices, with traceability to the SI system. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

The predictable quantum efficient detector (PQED) is intended to become a new primary standard for radiant power measurements in the wavelength range from 400 nm to 800 nm. Characterization results of custom-made single induced junction photodiodes as they are used in the PQED and of assembled PQEDs are presented. The single photodiodes were tested in terms of linearity and spatial uniformity of the spectral responsivity. The highly uniform photodiodes were proved to be linear over seven orders of magnitude, i.e. in the radiant power range from 100 pW to 400 µW. The assembled PQED has been compared with a cryogenic electrical substitution radiometer with a very low uncertainty of the order of 30 ppm. Experimental results show good agreement with the modelled response of the PQED to optical radiation and prove a near unity external quantum efficiency.

The spectral responsivity of a predictable quantum efficient detector (PQED) is calculated based on the responsivity of an ideal quantum detector and taking into account reflection losses from the surface of the photodiode and internal charge-carrier gains/losses inside the diode. The internal quantum deficiency (IQD) is obtained from simulations with the PC1D software using the material data of the produced PQED photodiodes. The results indicate that at room temperature the predicted IQD of the PQED is close to zero with an uncertainty of about 100 ppm over the visible range. It is further concluded that a primary standard of visible optical power with an uncertainty of approximately 1 ppm is achievable using the PQED at low temperatures.

Ikonen, E. (2017). Predictable quantum efficient detector based on n-type silicon photodiodes. Metrologia, 54(6) AbstractThe predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO 2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al 2 O 3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatiallyOriginal content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.

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.

In this paper, we present a new substitution method based on the unique properties of synchrotron radiation and of the Metrology Light Source (MLS), the dedicated electron storage ring of the PTB. The MLS is used as a light source with a dynamic range of its photon flux of 11 orders of magnitude to bridge the gap in optical power measurement between a cryogenic electrical substitution radiometer and a single photon detector. Two single photon avalanche diodes were calibrated at 651 nm with combined relative uncertainties of 0.17% and 0.16% traceable to a primary standard, a cryogenic electrical substitution radiometer.

The 'Metrology for Industrial Quantum Communication Technologies' project (MIQC) is a metrology framework that fosters development and market take-up of quantum communication technologies and is aimed at achieving maximum impact for the European industry in this area.MIQC is focused on quantum key distribution (QKD) technologies, the most advanced quantum-based technology towards practical application. QKD is a way of sending cryptographic keys with absolute security. It does this by exploiting the ability to encode in a photon's degree of freedom specific quantum states that are noticeably disturbed if an eavesdropper trying to decode it is present in the communication channel. The MIQC project has started the development of independent measurement standards and definitions for the optical components of QKD system, since one of the perceived barriers to QKD market success is the lack of standardization and quality assurance.