Flat fiber: the flexible format for distributed lab-on-a-chip

Integrated optical devices offer dense, multifunctional capability in a single robust package but are rarely considered compatible with the fields of remote or distributed sensing or compete in the long-haul with conventional 'one-dimensional' fibers. Here we aim to change that by introducing a 'flat-fiber' process that combines the advantages of of existing low-cost fiber drawing with the functionality of planar lightwave circuits in a novel hybrid format. Adapted from MCVD fiber fabrication, our preforms are deposited and collapsed into a rectangular geometry before drawing, resulting in extended lengths of mechanically flexible flat-fiber material with a photosensitive germanium-doped planar core. Direct UV writing is then used to create arrays of channel waveguides within the core layer, using a 5μm focused laser spot that literally 'draws' refractive index patterns into the flat fiber as it moves. Having recently demonstrated simple building blocks for integrated optical circuits in millimeter-wide flat-fibers (including; channel waveguides, power junctions and splitters, and planar Bragg gratings), our next step is to incorporate structured windows at strategic points along the fiber to allow fluidic access to the evanescent field for local refractive-index-based chemical measurements. By taking this approach, we hope to extend beyond the limitations of traditional planar and fiber substrates, allowing exotic material compositions, device layouts, and local sensing functions to be distributed over extended distances with no coupling or compatibility concerns in highly functional distributed lab-on-a-chip devices.