Wavelength demultiplexers based on finite photonic lattices

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Abstract
Demand for densely packed wavelength demultiplexers has increased due to the rapid developments in information systems and sensing for biomedical and space applications. The required miniaturisation is problematic due to the crosstalk in high-density photonic circuits, while the feature size complicates design at sub-micrometer wavelengths. As a solution, we propose wavelength demultiplexers based on wavelength-dependent self-imaging in linearly coupled finite optical lattices. The novel semi-analytical design allows for intuitive and efficient control of their spectral characteristics, notably the bandwidth control by changing the number of waveguides in the lattice. The principle is validated using femtosecond laser fabrication of visible/near-infrared demultiplexers in borosilicate glass. The insertion loss did not exceed 0.43 dB with 0.1–0.15 dB for most devices and the crosstalk was lower than 30 dB. The applicability of the proposed design to other fabrication platforms and wavelength ranges is demonstrated by numerical simulations of silicon-on-insulator demultiplexers at telecom wavelengths with highly competitive insertion loss and crosstalk of 0.13 dB and −82 dB, respectively.

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