Transmission- and reflection-aligned miniaturized filter for hybrid integrated optical micro-platform

This is the authors' abstract. We don't add key points for this paper.

We present hybrid integration of substrate-free, miniaturized spectral thin-film interference filters into a modular optical micro-platform, together with photodiodes, polymer waveguides and coupled to single-mode fiber. All components have edge lengths of few hundreds of micrometers and are assembled on a 6 mm × 16 mm fused silica platform by an automatable precision optics assembly system. The spectral filter is only 16.7 μm thick and it is actively tuned by rotation to meet the desired spectral performance during its assembly. The demonstrated platform functions as a balanced wavelength detector by integration of a long-pass filter with simultaneous on-chip measurement of its transmission and reflection by bare die photodiodes. Tunability of the long-pass filter edge by more than 16 nm in the wavelength range of 968 nm to 984 nm during the assembly was demonstrated. No collimation or other lenses are required on the platform, which is enabled by the implemented technology of substrate-free thin-film filters. We provide a simple numerical approach to analyze the spectral effects due to angle of incidence distribution from beam divergence when combining a thin-film filter with single-mode fiber without collimating lenses. Our spectral measurements of the integrated long-pass filters' transmission and reflection, performed directly on the optical micro-platform, show good agreement with our numerical modeling.