All-optical tunable comb filters using ytterbium doped fibers and an LPG pair

We have demonstrated a new type all-optical tunable comb filter by using a long-period fiber gratings(LPG) pair spliced with an ytterbium doped fiber. When the 25.5cm long ytterbium doped fiber was used with the ytterbium doping concentration of ~0.82at%, the wavelength channel spacing and the isolation between channels were 0.7nm and 16-21dB, respectively, between 1545nm and 1555nm. Also, the optical comb filter was tuned up to `1.53π' phase shift at the launched pump power of 56mW with the LD at 976nm.