Coherence phenomena in the phase-sensitive optical parametric amplification inside a cavity

We theoretically and experimentally demonstrate coherence phenomena in optical parametric amplification inside a cavity. The mode splitting in the transmission spectra of a phase-sensitive optical parametric amplifier is observed. Especially, we show that a very narrow dip and peak, which are the shape of a delta function, appear in the transmission profile. The origin of the coherence phenomenon in this system is the interference between the harmonic pump field and the subharmonic seed field in cooperation with dissipation of the cavity.