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9 December 2015 Time-gated digital phase conjugation for two-photon excitation microscopy through multimode optical fibers
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Proceedings Volume 9792, Biophotonics Japan 2015; 97920X (2015)
Event: SPIE/OSJ Biophotonics Japan, 2015, Tokyo, Japan
The large number of modes supported by multimode optical fibers potentially allows the transmission of larger amounts of information compared to single mode fibers. However, when pulsed light is transmitted through multimode fibers, the spatio-temporal profile of the incident beam is altered upon propagation, leading to a highly scrambled spatial profile and a broadened temporal duration due to modal and material dispersion. We present a digital phase conjugation method to counter-propagate through a multimode optical fiber only a group of modes of similar propagation constants which interfere constructively at a single location at the other side of the fiber, generating a spatially focused pulse. Since only modes with the same speed are excited, temporal broadening due to modal dispersion is suppressed, preserving the ultrashort duration of the propagating pulse. Using this technique, we experimentally demonstrate the transmission of focused pulses of 500 fs through a 30 cm length, 200 micrometer core step-index multimode fiber. Additionally, using a graded-index fiber, which allows the propagation of a larger number of modes of the same speed than a graded index fiber (hence a better focusing capability), we have been able to deliver and scan high-intensity focused femtosecond pulses. Moreover, based on the described principle, we demonstrate for the first time two-photon excitation imaging through a multimode optical fiber.
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Edgar E. Morales-Delgado, Salma Farahi, Ioannis N. Papadopoulos, Demetri Psaltis, and Christophe Moser "Time-gated digital phase conjugation for two-photon excitation microscopy through multimode optical fibers", Proc. SPIE 9792, Biophotonics Japan 2015, 97920X (9 December 2015);

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