Abstract
We present a detailed frequency noise analysis of a feedforward scheme used to faithfully transfer the spectral properties of an individual line of an optical frequency comb spectrum to a single-mode laser and in this way indirectly amplify it, which is applicable to any arbitrary comb mode spacing. In contrast to previously reported implementation of the feedforward method for a similar purpose, we present a more thorough noise study, including the measurement of the additive noise of the setup. The reported experimental investigation was performed using two low-noise ultrafast mode-locked lasers with different repetition rates (~ 1 GHz and 250 MHz) and show a faithful transfer of the comb mode frequency noise to the auxiliary laser with a sub-radian additive phase noise integrated from 1 Hz to 1 MHz. We discuss the present limitations of the method that is able to transfer optical comb lines with sub-Hz linewidth and propose simple improvements.
Highlights
Optical frequency combs (OFCs) from femtosecond modelocked lasers represent a powerful tool in time and frequency metrology as they provide a direct and phasecoherent link between the optical and microwave spectral domains
* Correspondence: pierre.brochard@unine.ch 1Laboratoire Temps-Fréquence, Institut de Physique, Université de Neuchâtel, CH-2000 Neuchâtel, Switzerland Full list of author information is available at the end of the article solution to this issue may be to first enlarge the comb mode-spacing to the multi-GHz range using a pulse repetition rate multiplier (PRRM) as frequently used in ultralow-noise microwave generation by optical-to-microwave frequency division realized with fs-laser frequency comb [3, 4]
The additive frequency noise of the feedforward scheme was separately characterized. It cannot be assessed from the simple subtraction of the Frequency Noise Power Spectral Density (FN-PSD) measured for the initial comb line and transferred to the auxiliary laser, as these two curves are very close to each other at a fairly high noise level, so that their difference would be very sensitive to any small measurement imprecisions
Summary
Optical frequency combs (OFCs) from femtosecond modelocked lasers represent a powerful tool in time and frequency metrology as they provide a direct and phasecoherent link between the optical and microwave spectral domains. * Correspondence: pierre.brochard@unine.ch 1Laboratoire Temps-Fréquence, Institut de Physique, Université de Neuchâtel, CH-2000 Neuchâtel, Switzerland Full list of author information is available at the end of the article solution to this issue may be to first enlarge the comb mode-spacing to the multi-GHz range using a pulse repetition rate multiplier (PRRM) as frequently used in ultralow-noise microwave generation by optical-to-microwave frequency division realized with fs-laser frequency comb [3, 4].
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