Integrated interrogator circuits for fiber optic sensor network in generic InP photonic integrated circuit technology

Together with the development of fiber optic sensor networks the accurate and reliable operation of dedicated readout instruments became a critical issue. After years of optimizing the interrogating devices the use of photonic integrated circuits (PICs) has opened a new era of highly reliable, compact and versatile devices offering additionally advantages of low power consumption and cost-optimized design. Considering the most commonly deployed fiber Bragg grating (FBG) based sensor systems/networks, typically two PICs-based solutions for interrogators may be used: an arrayed waveguide grating (AWG) spectrometer with a broadband SLED source or a set of tunable laser sources with a photodiode detector. Among commercially available PIC technologies the InP platform has a substantial advantage as it allows fabrication of both passive devices (waveguide circuitry) as well as active devices (photodiodes and light sources) in the same technological process. In this work we investigate two different layouts of AWG-based integrated interrogators fabricated in generic technology of indium phosphide. We analyze the influence of crosstalk between AWG channels on operation of the device and possibility of interrogating narrow-band FBG reflection peaks as well as the influence of input polarization state on the AWG response, which is of fundamental importance for proper operation of an integrated FBG interrogator. As there is no polarization control elements available at present in the offer of generic InP technology providers we discuss the possibility of using off-chip solutions exploiting additional fiber-optic components. As a possible alternative to AWGbased interrogators, we discuss also the possibility of using integrated tunable lasers for FBG interrogation.