1. National Institute of Standards and Technology (NIST), Boulder, CO, USA. https://www.nist.gov
2. National Physical Laboratory (NPL), Teddington, UK. https://www.npl.co.uk
3. Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany. https://www.ptb.de
4. ITU-T Rec. G.650.2, Definitions and test methods for statistical and nonlinear related attributes of single-mode fibre and cable, Aug 2015
5. TIA-455-191 (FOTP- 191), IEC-60793-1-45 optical fibres-part 1–45: measurement methods and test procedures-mode field diameter, 14 April 2020