Ultra-broadband spontaneous parametric downconversion in periodically poled lithium niobate and electro-optic tuning of the optical parametric oscillation

We demonstrated an electro-optically tunable ultra-broadband singly resonant ns-optical parametric oscillator (OPO) based on a periodically poled lithium niobate crystal (PPLN) with a three-segment structure. The ultra-broadband parametric gain was obtained by precise selection of the pump wavelength and the poling period to match the group velocities of the signal and idler. Selected wavelengths in the broadband parametric signal and idler gain spectrum generated by the first segment was amplified in the third segment. This selection could be electro-optically controlled by applying a variable dc electric field in the middle single-domain segment. A singly resonant OPO cavity was then constructed and the output signal wavelength could be tuned from 1.373 to 1.749 mu m (corresponding idler tuning range from 2.863 to 1.972 mu m) by changing the electric field from -6.5 to +5.0 kV/mm. Electro-optic tuning facilitated fast wavelength switching for the OPO to span the entire near-infrared spectral region. This is the largest electro-optic tuning range observed to our knowledge.