Measurement and compensation of residual group delay in a multi-core fiber for lensless endoscopy

We present a new experimental concept suitable for partially compensating the inter-core group delay dispersion in a multi-core fiber (MCF). First we map out the group delays of all 169 single-mode cores of a MCF using phase-shifting spectral interferometry and find the group delays distributed with standard deviation 123 fs in a 30 cm long MCF. We then detail and apply the compensation scheme based on two wavefront shapers with which we narrow the group delay distribution to 65 fs. These results are relevant for lensless endoscopes employing femtosecond excitation, and we quantify the performance gain in a lensless endoscope with 150 fs laser pulses as excitation and discuss possible generalizations of the concept. (C) 2015 Optical Society of America