Fabrication of Low Loss Lithium Niobate Rib Waveguides Through Photoresist Reflow

Abstract

We present lithography and argon plasma etching of lithium niobate on insulator (LNOI) rib waveguides using reflowed photoresist etch masks and 405 nm photolithography. Melting the photoresist at temperatures greatly exceeding its glass transition temperature while minimizing feature distortion through photoresist adhesion control reduces sidewall surface roughness and allows the photoresist to be used both as the pattern mask and the hard etch mask. Waveguide sidewall surfaces exhibiting sub-nm root mean square roughness are fabricated. Dependence of sidewall roughness and angle on feature width, and propagation loss on thermal annealing of the fabricated devices is characterized. Measured quality factors on fabricated microresonators exceed one million. LNOI rib waveguides and resonators with low propagation loss increase nonlinear optical conversion efficiencies and are useful for efficient electro-optic modulation. Photolithography compatible fabrication of low loss LNOI photonic integrated circuits facilitates scalable commercialization.

Mitigating waveguide loss in Ge–Sb–Se chalcogenide glass photonics

“…While the oxide sacrificial layer has been widely deployed as a hard etching mask or for forming special structures [24,25], its application as an etch resist liftoff layer remains rare. Similarly, the use of thermal reflow to reduce surface roughness has mainly been observed in organic materials, such as polymer waveguides and photoresists [26,27]. Although there have been a few reports to reflow chalcogenide glass waveguides, their losses are still much higher than 1 dB cm −1 [23,28,29].…”