Abstract

Portable optical frequency standards are interesting in metrology and in other applications (optical sensing, telecommunication, etc.). Laser frequency stabilization has been widely investigated using saturated absorption spectroscopy (SAS) on acetylene and iodine vapor cells, often combined with frequency modulated spectroscopy techniques [1,2]. The increased availability of hollow core (HC) fibers allowed to investigate the realization of a portable optical frequency standard based on a gas-filled HC fiber [3,4]. The stability of a laser-locking scheme based on SAS techniques strongly depends on the ratio between the strength and the linewidth of the absorption line addressed. Gas-filled HC fibers introduced clear advantages (longer interaction length and higher light intensity) that results in a stronger signal with respect to the conventional bulk vapor cells, but the smaller mode field diameter (MFD) increases the transit-time broadening effect, ending with a larger linewidth that limits the stability. Therefore, the investigations have been mostly oriented on the fibers with larger core size, suggesting the Kagome fiber (typical core diameter ~ 60 µm) as the best HC fiber design to address to the detriment of the HC photonic crystal fibers (HC-PCFs), because of their typical smaller core diameter (less than 20 µm) [4].

© 2015 IEEE