Exploiting few mode-fibers for optical time-stretch confocal microscopy in the short near-infrared window

Dispersive fiber is well-regarded as the most viable candidate for realizing efficient optical time-stretch process--an ultrafast spectroscopic measurement technique based on the wavelength-to-time mapping via group velocity dispersion (GVD). Despite optical time-stretch has been anticipated to benefit a wide range of high-throughput biomedical diagnoses, the lack of commercially-available dispersive fibers which can operate in the "biomedically-favorable" short near-infrared (~800 nm - 1100 nm) range hinders practical time-stretch-based biomedical spectroscopy and microscopy. We here explore and demonstrate the feasibility of using the standard telecommunication single-mode fibers (e.g. SMF28 and dispersion compensation fiber (DCF)) as few-mode fibers (FMFs) for optical time-stretch confocal microscopy in the 1 μm range. By evaluating GVD of different FMF modes and thus the corresponding time-stretch performances, we show that the fundamental modes (LP(01)) of SMF28 and DCF, having sufficiently high dispersion-to-loss ratios, are particularly useful for practical time-stretch spectroscopy and microscopy at 1 μm, without the need for the specialty 1 μm SMF. More intriguingly, we also show that the higher-order FMF modes (e.g. LP(11)) could be excited and utilized for time-stretch imaging. Such additional degree of freedom creates a new avenue for optimizing and designing the time-stretch operations, such as by tailored engineering of the modal-dispersion as well as the GVD of the individual FMF modes.