Cryogenic primary standard for optical fibre power measurement

Abstract

NIST has completed commissioning a new, state-of-the-art cryogenic primary standard for optical fibre power measurement and calibration. It establishes for the first time, a direct traceability route between the device under test and primary standard. Two silicon micromachined planar detectors, with vertically aligned carbon nanotube absorbers, thin film tungsten heaters and superconducting resistive transition edge temperature transducers, form the basis of the radiometer. Magnetic phase change thermal filters ensure noise-free operation at 7.6 K. Measurement repeatability below 50 ppm is routinely achieved during a measurement cycle of 30 min. The system operates at a nominal radiant power level of 200 µW (−7 dBm). The expanded measurement uncertainty at k = 2 is 0.4%, a 20% improvement on NIST's current optical fibre power Calibration and Measurement Capability.The performance of the new standard was established by comparing it to our current standard, using four transfer detectors, at nominal wavelengths 850 nm, 1295 nm and 1550 nm. The comparison agreed within the combined expanded measurement uncertainty of 0.6%. Whilst the new standard is intended primarily to service the telecommunications industry, it is limited in use only by available sources and optical fibre.

Meta-study of laser power calibrations ranging 20 orders of magnitude with traceability to the kilogram

“…Measurement repeatability below 50 ppm is routinely achieved during a measurement cycle of 30 minutes. The expanded measurement uncertainty is currently 0.4% [11]. However, work in progress is reducing the uncertainty sources and we expect to soon achieve a relative expanded uncertainty of less than 0.1 % [12].…”

“…The statistical uncertainty component of power meter "b" (𝑢 𝑏,𝑠𝑡𝑎𝑡 2) is already contained in 𝑢 𝐾 𝑎,𝑏 as seen in Equation (11). As an example, we have used this approach to quantify the uncertainty of our singlephoton avalanche photodiode (SPAD) power meter with a traceability chain through the LOCR where KSPAD,LOCR= KSPAD,SiTrapKSiTrap,OFPMKOFPM,LOCR.…”

“…The uncertainty on γ x and η x must be included in the uncertainty of the comparison factor K a,b . In both the specific case of equation ( 1) or the most general case of equation (10), the comparison factor is a ratio. Its uncertainty indicates only the repeatability of the ratio of the powers reported by the two meters in question, not the full uncertainty of either power meter.…”

“…Since (C.5) As described in the main body of the paper, the comparison factor for a power meters 'a' and 'b' can be found even when they operate at different powers and or wavelengths. This requires comparison to an intermediate (transfer) power meter 'x' with a spectral responsivity ratio η x and a power non-linearity factor γ x described by equations ( 8) through (10). This mediated comparison factor (C.7) The transitive relationship of equation (C.6) allows any two power meters to be virtually compared if there is an unbroken chain of comparisons between them, Finally, we can use the power reported by power meter 'a' to produce an estimated power value referenced to power meter 'b'.…”

“…At the opposite end of the power range, we have used radiation pressure to measure the power of CW lasers approaching 100 kW [18][19][20]. Our lowest-uncertainty system, which is based upon a cryogenic cavity radiometer (LOCR), is now in the process of being replaced by a planar-absorber-based optical fiber cryogenic radiometer (OFCR) [11]. This minimizes the traceability chain and will eventually lead to lower uncertainties in optical fiber power measurement.…”