Tunable fibre-coupled multiphoton microscopy with a negative curvature fibre.

Abstract

Negative curvature fibre (NCF) guides light in its core by inhibiting the coupling of core and cladding modes. In this work, an NCF was designed and fabricated to transmit ultrashort optical pulses for multiphoton microscopy with low group velocity dispersion (GVD) at 800nm. Its attenuation was measured to be <0.3dBm(-1) over the range 600-850nm and the GVD was -180±70fs(2) m(-1) at 800nm. Using an average fibre output power of ∼20mW and pulse repetition rate of 80MHz, the NCF enabled pulses with a duration of <200fs to be transmitted through a length of 1.5m of fibre over a tuning range of 180nm without the need for dispersion compensation. In a 4m fibre, temporal and spectral pulse widths were maintained to within 10% of low power values up to the maximum fibre output power achievable with the laser system used of 278mW at 700nm, 808mW at 800nm and 420mW at 860nm. When coupled to a multiphoton microscope, it enabled imaging of ex vivo tissue using excitation wavelengths from 740nm to 860nm without any need for adjustments to the set-up.