Pigtailed nonconfocal spherical mirror Fabry-Perot tunable filter with FSR over 40 nm

摘要

The non-confocal spherical mirror Fabry-Perot resonator is capable of having very high finesse and stability. However, the higher-order cavity modes (HOCM) of the non-confocal resonator must be controlled to attain any useful performance. Precision mode-matching collimators and/or an intra-cavity aperture is suggested and demonstrated here to diminish the HOCM. Mode-matching collimators at both input and output port of the resonator are recommended to achieve higher HOCM depression ratio, better long-term stability and a pigtailed in-line structure. A preliminary filter with mode-matching collimators at both input and output port of the cavity has shown a finesse of 100, HOCM depression ratio of 25 dB, insertion loss of 3.5 dB and a free spectrum range over 40 nm at 1.5 $mu@m band.