Non-cyclic geometric phase-induced output coupler for optimum out-couple power in optical parametric oscillators

We present a Geometric phase (GP)-based Sagnac anti-resonant ring (ARR) interferometer mirror (GP-mirror) for achieving tunable optimum output coupling in continuous wave (CW) doubly resonant optical parametric oscillator (DRO). The DRO is designed using a nonlinear crystal MgO: PPsLT of 30 mm length and a grating period of 7.97 µm with a GP mirror in one arm of the standing wave cavity. The GP mirror is constructed using a quarter wave-plate (λ/4), half wave plate (λ/2), and quarter wave-plate(λ/4) at +45◦, θ, -45◦ with respect to vertical polarization, respectively. The DRO output transmission can be varied continuously from 0.6% to 50%, attaining optimum output coupling of 1.4% for maximum power extraction of 2.45 W when pumped with an incident power of 5 W at 47◦C crystal temperature at signal and idler wavelength of 1054 nm and 1074 nm, respectively. The maximum pump depletion of 89% is obtained with a conversion efficiency of 49%. The transmission througha GP-based mirror delivers the tunable optimum output power across the tuning wavelength range > 90 nm. This showcased GP-mirror concept presents an avenue for enhancing the capabilities and management of coherent sources adjustable across various spectral ranges and across all time scales, ranging from continuous-wave to ultrafast femtosecond domains.