Comb self-referencing
ID: comb-self-referencing
Comb self-referencing compares two parts of one optical frequency comb. Coherent broadening supplies an octave, a factor of two in frequency. Second-harmonic generation doubles a red tooth; a photodiode detects its beat with an original blue tooth.[ref]
Introduction to Self-reference Comb Laser by Comblaser Laboratory, Department of Physics, National Central University. Introduction to Self-reference Comb Laser, Fig.1 explanation
Applying the tooth formula givesThe doubled branch carries , while the original high-frequency branch carries : their difference retains exactly one offset.
Read the tooth spacing and offset through separate electronic signals
. Original functional comb self-referencing scheme. Solid optical paths bring doubled red light and original blue light to one detector. Dashed electronic paths connect both readouts to a common reference and feedback controls. Actuators can affect both parameters. Details.
The displayed difference uses the order doubled tooth minus original tooth. An ordinary electronic frequency counter returns a nonnegative beat magnitude; spectral selection and known electronic shifts must identify whether it represents , , or a shifted version. Coherent broadening, overlapping photon polarization, spatial alignment and temporal overlap are required. Merely producing a broad patch of colored light does not establish a usable offset signal.
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