We present an alternative method of determining the oscillating state of a laser and demonstrate the suitability of relative
intensity noise (RIN) measurements for this purpose.
The experiments were carried out using a two-section DFB laser. Optical and RIN spectra have been recorded and
correlated subsequently. The variation of the maxima of the RIN spectra have been evaluated with respect to intensity and
position in the frequency domain. Varying the frequency, a distinct transition in the above mentioned parameters can be
observed, wich can be correlated clearly to the mode degeneracy at the transition and a dominating oscillating mode below
and above. This delivers a conclusive means of determining the lasing state from RIN spectra.