Stable Optical Frequency Comb Distribution Enabled by Hollow-Core Fibers

Abstract

Over the last two decades, optical frequency combs (OFCs) have enabled some of the most accurate measurements in physics. Distributing light from OFCs via optical fibers could make these high-accuracy measurement tools available more widely, from a few dedicated metrology laboratories to other laboratories and industry. However, the performance of distributed OFCs is strongly limited by impairments of standard single mode fiber (SMF), most notably its thermal sensitivity of chromatic dispersion, for which no compensation technique has been shown to date. To overcome this limitation, use of a new class of optical fiber is suggested here: a hollow core fiber (HCF), which offers more than an order of magnitude lesser such impairment. The measured OFC frequency stability of the optical mode and mode spacing reaches 1.8 × 10−19 and 1.5 × 10−17 at a few thousand seconds, respectively, after transmitting through 7.7 km of HCF. To the best of knowledge, this is the best ever performance for km-lengths of fiber-based OFC distribution. Besides, other HCF advantages over SMF in this application are discussed. Specifically, HCFs offer over an order of magnitude lower thermal sensitivity of propagation delay, several orders of magnitude lower optical nonlinearity, and almost ten times lower chromatic dispersion.