Fig. 3: Experimental evaluation of the locking ratio.
a Power Spectral Density (PSD) of the output signal of cavity 1 as function of the laser wavelength at a 5.5 dBm input power. The fundamental peak of the modulation is observed ranging in between 0.1 MHz and 2 MHz over 420 pm. b PSD of the optical output signal of the two coupled cavities for the same input power as in Fig. 3a. Extra features appear at specific laser wavelengths where the two optical resonances overlap (width of the two resonances are highlighted with black and green rectangles on the right). The blue arrow highlights λL = 1573.88 nm, where the overlap begins. The orange arrow highlights λL = 1574 nm, the first 1:1 locking ratio. c Evolution of the locking ratio of the as function of the wavelength, it is commonly referred to as the devil’s staircase. d Arnold tongue representation of the locking values. The colored part of this graph refers uniquely to the region where the two resonances overlap. The different locking values are highlighted with different colors. The red dotted rectangle refers to the locking regions extension of (b, c).
