60 dB Dynamic range single-shot spectral measurements of spontaneous modulation instability

The dispersive Fourier transform (DFT) [1] uses optical fibre dispersion to separate the spectral components of a noisy incident signal to allow real-times spectral measurement using a photodetector and oscilloscope. DFT has now become a standard tool in ultrafast laboratories to study ultrafast dynamics of complex transient phenomena including optical rogue waves [1] and Kerr-lens mode-locking [2]. The dynamic range of DFT, however, is limited to typically only 20 dB due to the usual 8-bit analog-to-digital converter of the oscilloscope. Here, we demonstrate an unbalanced dual path mechanical streak camera capable of resolving single shot spectra with 60 dB dynamic range. We use this technique to detect spectrally, for the first time, the collision of breathers in noise-seeded modulation instability (MI) whose spectral signature is manifested in the wings of the spectrum below the 30 dB level, and which are not captured by the standard DFT technique.