  Reconfigurability of integrated photonic chips plays a key role in current
experiments in the area of linear-optical quantum computing. We demonstrate a
reconfigurable multiport interferometer implemented as a femtosecond
laser-written integrated photonic device. The device includes a femtosecond
laser-written $4\times 4$ multiport interferometer equipped with 12
thermooptical phase shifters, making it a universal programmable linear-optical
circuit. We achieve a record fast switching time for a single nested
Mach-Zender interferometer of $\sim10$ ms and quantitatively analyse the
reconfigurability of the optical circuit. We believe, that our results will
improve the current state of quantum optical experiments utilizing femtosecond
laser-written photonic circuits.
