#Spectral comb sound reference signals series#

Under injection locking, the auxiliary laser acquires the spectral properties of the comb mode and constitutes the desired filtered and amplified output signal. It has been successfully reported for OFCs with mode spacing of 10-GHz or higher as well as with sub-GHz repetition rate combs and down to 56 MHz using a frequency-selective Brillouin amplifier that amplifies an individual comb line while efficiently suppressing the others. Injection locking of a continuous-wave (cw) laser by the comb mode of interest is an alternative method to extract a single comb mode that offers such a high control bandwidth. However, a fast frequency control of the auxiliary laser is needed to properly imprint the comb line spectral properties to the scanning laser. The method is similar to a concept commonly used in comb-assisted spectroscopy, where a single-mode tunable laser is locked to a mode of an OFC to accurately scan an absorption line of a molecular species. The most direct approach is to phase-lock an auxiliary single-mode laser to the comb mode. Therefore, other methods have been developed to isolate and amplify a single frequency component from a comb spectrum. However, this makes the system much more complex and poorly tunable if the comb line to be extracted needs to be switchable. After repetition rate multiplication, a line of the resulting comb can be isolated more easily using a conventional optical bandpass filter.

#Spectral comb sound reference signals series#

This can be achieved either with a combination of Fabry-Perot optical cavities of different free spectral ranges or with an interleaver system made of a series of fibered or free-space unbalanced Mach-Zehnder interferometers. A possible 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 ultra-low-noise microwave generation by optical-to-microwave frequency division realized with fs-laser frequency comb. Furthermore, extracting and amplifying a single line of a comb with a sub-GHz mode spacing is rather challenging, as no suitable conventional optical filter (e.g., based on thin films or gratings) with a sufficiently narrow bandwidth is commercially available. Moreover, they also require a high optical power in this specific mode, which is most often not directly available from an OFC. This is the case for instance for optical frequency references for differential absorption lidar (DIAL) systems or for optical frequency synthesizers. Among the variety of applications of frequency combs, some make essentially use of only one particular component of the comb spectrum. Self-referenced combs deliver absolute optical frequencies that benefit many research fields. Optical frequency combs (OFCs) from femtosecond mode-locked lasers represent a powerful tool in time and frequency metrology as they provide a direct and phase-coherent link between the optical and microwave spectral domains.