We fabricate a series of reconfigurable waveguide interferometers using laser machining techniques and charac- terize them classically. The 3D nature of the ultrafast laser writing technique allows for the fabrication of unique multi-arm interferometers not possible in planar platforms. We demonstrate selectivity between multiple phase shifters in a single interferometer by patterning the chip surface using picosecond laser ablation in a separate step. Microfluidic elements for making practical measurements on-chip are incorporated by machining channels within the substrate to interact with waveguide modes. Our results provide a path toward practical implementation of quantum metrology protocols requiring multiple interferometer arms and tunable phases.
We perform a rigorous characterisation of multiport waveguide circuits. These devices were fabricated using an ultrafast laser inscription process which permits uniquely three-dimensional circuit fabrication not possible using standard lithographic means. To infer device manipulation of an arbitrary input state of light (i.e. intensity and phase transformations), we perform device interrogation with coherent input states. We demonstrate that the inscription process, and output from coherent state interrogation combined with a maximum likelihood estimation algorithm, provide a rapid prototyping system for waveguide circuits acting on quantum states of light. This opens the way for more advanced multiport structures exploiting additional paths, input states and arbitrary phase relationships.