Dual-valley transmission spectrum based on periodically poled lithium niobate with a structure defect

We observe the symmetrical dual-valley spectrum in periodically poled lithium niobate (PPLN) with a defect in the middle employing electro-optic effect. When the external electric fields are applied, light satisfying phase-matching condition (λ
₀
) will undergo polarization rotation and then turn back. However, the polarization states of wavelength at λ
₀
±Δλ will be changed at the end of the sample due to phase mismatching. A dual-valley transmission spectrum is thus obtained. Moreover, the depth of the valley could be tailored with different electric fields on the y-surface of the sample.