Method to identify time delay of chaotic semiconductor laser with optical feedback

We propose a power spectrum analysis method to directly identify the time delay of a chaotic semiconductor laser with optical feedback. By measuring the radio frequency (RF) power spectrum of the chaotic laser and performing an inverse Fourier transform, we can easily unveil all the time delay signatures, regardless of whether the chaotic output is induced by single or multiple feedback. This method successfully retrieves the two time delay signatures from the power spectrum of a semiconductor laser with double-cavity feedback.