Monolithically integrated active passive waveguide array fabricated on thin film lithium niobate using a single continuous photolithography process

TL;DR

This paper presents a monolithic integration method for active and passive thin film lithium niobate photonics using a single photolithography process, enabling low-loss interfaces and integrated waveguide amplifiers.

Contribution

The work introduces a tiled substrate approach for monolithic integration of active and passive lithium niobate photonics with a single fabrication step.

Findings

Interface loss as low as 0.26 dB

Demonstrated four-channel waveguide amplifier

Achieved net gain of ~5 dB at 1550 nm and ~8 dB at 1530 nm

Abstract

We demonstrate a robust low-loss optical interface by tiling passive (i.e., without doping of active ions) thin film lithium niobate (TFLN) and active (i.e., doped with rare earth ions) TFLN substrates for monolithic integration of passive/active lithium niobate photonics. The tiled substrates composed of both active and passive areas allow to pattern the mask of the integrated active passive photonic device at once using a single continuous photolithography process. The interface loss of tiled substrate is measured as low as 0.26 dB. Thanks to the stability provided by this approach, a four-channel waveguide amplifier is realized in a straightforward manner, which shows a net gain of ~5 dB at 1550-nm wavelength and that of ~8 dB at 1530-nm wavelength for each channel. The robust low-loss optical interface for passive/active photonic integration will facilitate large-scale high performance photonic devices which require on-chip light sources and amplifiers.