Programmability in femtosecond-laser-written integrated circuits is commonly achieved with the implementation of thermal phase shifters patterned from a single gold film on a trenched substrate. To increase the compactness, we propose two improvements to this technology. Firstly, we report thermal phase shifters with a photolithography process based on two different metal films. Secondly, we show a novel curved isolation trench design that allows for a significant reduction in the optical length of integrated circuits. These results pave the way toward the fabrication of femtosecond-laser-written photonic circuits with a steep increase in terms of layout complexity.
