Design of a Photonic Integrated Circuit (PIC) for a BOTDR read-out unit

Foundry services for PICs open the way to realize economically complex optical functionality. In the expanding field of fibre sensors Brillouin scattering is a powerful effect for determining strain and temperature distributions along fibres. However, the high cost of the optical circuitry has prevented wide use of this technique. Here a design study is reported for a foundry-based Brillouin Optical Time Domain Reflection (BOTDR) read-out unit with low-cost potential. The circuit contains narrow linewidth tuneable DBR-lasers, photodiodes with an optical mixer for coherent detection, a switchable delay line for frequency tuning and a switching fabric which allows three modes of operation.