Photonic integrated circuit optical parametric oscillators

Optical parametric oscillators (OPOs) are versatile nonlinear optical devices for wavelength generation from the visible to the mid-infrared. Recently, OPO research has merged with photonic integrated circuits (PICs) in the advancement of miniaturized, on-chip light sources utilizing second-order ( χ (2) ) or third-order ( χ (3) ) nonlinearities. This mini-review of PIC-based OPOs begins with an overview of their history, applications, and underlying physics. We then discuss χ (2) and χ (3) implementations in depth, highlighting material and device platforms, recent breakthroughs, and key engineering strategies across different wavelength regions. Finally, we outline future directions in PIC OPO technology and its application to spectroscopy, sensing, quantum optics, and photonic computing.