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

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 integrationof passive/active lithium niobate photonics. The tiled substrates composed ofboth active and passive areas allow to pattern the mask of the integratedactive passive photonic device at once using a single continuousphotolithography process. The interface loss of tiled substrate is measured aslow as 0.26 dB. Thanks to the stability provided by this approach, afour-channel waveguide amplifier is realized in a straightforward manner, whichshows a net gain of ~5 dB at 1550-nm wavelength and that of ~8 dB at 1530-nmwavelength for each channel. The robust low-loss optical interface forpassive/active photonic integration will facilitate large-scale highperformance photonic devices which require on-chip light sources andamplifiers.