Uncertainty change in length conversion affected by change in environmental parameters

The national standard of length in Japan changed to a femtosecond optical frequency comb (FOFC) in July 2009. The center frequency of the FOFC standard is 1560 nm, which is in the transmission band (C-band) of the communication optical fiber. Thanks to this fact, through the communication fiber networks, an FOFC can be delivered to everywhere at anytime. That means everyone at everywhere may access the high-accuracy length standard via communication fiber networks at anytime. An FOFC is a stabilized pulse laser. In other words, an FOFC is a phase-coherent combination of several hundreds of thousands of wavelengths. Therefore, this fact means that there are several hundreds of thousands of different wavelengths and their combination, adjacent pulse repetition interval length (APRIL), which can be used as a length scale. Based on this idea, we proposed the APRIL-based method. APRIL-based length measurement method uses an APRIL (the physical length associated with the pulse repetition period) as a ruler for measuring distance. In this work, we show how the uncertainty in length conversion is affected by the change in environmental parameters via the sensitivity coefficients of refractive index under an actual experimental environment.