NONLINEAR OPTICAL ELEMENT

PROBLEM TO BE SOLVED: To provide a nonlinear optical element which considerably reduces a component of unnecessary signal light superposed on converted light to be able to minimize crosstalk regardless of the increase of output when performing wavelength conversion in cascade difference frequency generation. SOLUTION: With respect to a multi-period QPM-LN element, a domain polarized in one direction and another domain adjacent to the domain and polarized in the opposite direction are considered as one pair, and a length of each pair is denoted as D. It is considered that a ratio Δ/D (called duty radio) of an occupancy area Δ of the domain polarized in one direction in a pair to the length D of the pair is controlled by a prescribed function f(z) with respect to all pairs. A hyperbolic tangent function is used as the function f(z), and a phase function (z) is optimized so that a peak value η(l) of SHG light becomes flat. COPYRIGHT: (C)2010,JPO&INPIT