Real-Time Modal Analysis via Wavelength-Swept Spatial and Spectral ( ${S}^{2})$ Imaging

We present a fast implementation of the spatial and spectral imaging (S
²
) technique for a modal analysis of multimode optical fibers. It utilizes a continuously scanning tunable laser source with an InGaAs camera operating at 500 Hz along with inline data processing to increase the measurement repetition rate, by reducing the run up/run down time between two successive scans (about 27 times faster as compared with the previous state of the art). This allows real-time mode content monitoring of a multimode fiber. We illustrate the potential of this tool by collecting an 110000 wavelength S
²
spectrogram of a five mode-group fiber in minutes, and tracking, in real-time, the four LP
₁₁
modes of the same fiber as the launch polarization is rotated.