Using a multimode fiber to measure the spectral phase of ultrafast optical pulses (Conference Presentation)

Abstract

We propose and demonstrate that a multimode optical fiber can be used to measure the spectral phase of ultrafast optical pulses. The speckle pattern formed at the end of a multimode fiber provides a fingerprint which can be used to identify the spectral amplitude and phase of an unknown pulse. We measure both a linear speckle pattern and a non-linear speckle pattern from a multimode fiber. After calibrating the wavelength dependent speckle field formed at the end of the fiber, the linear speckle pattern can be used to reconstruct the amplitude spectrum while the nonlinear speckle pattern can be used to reconstruct the spectral phase. This technique allows for single-shot pulse characterization in a simple experimental setup, while the diversity of spatial and spectral modes contributing to the speckle pattern removes any ambiguities in the sign of the recovered spectral phase. In addition to demonstrating a novel pulse characterization scheme, this work further illustrates the potential of complex photonic structures such as multimode fibers as versatile optical sensing platforms.