Dual optical frequency comb using a multi-functional PIC based on fully integrated injection locked gain-switched lasers.

The authors demonstrate and characterise a versatile photonic integrated circuit (PIC) that could serve as a mutually injection locked optical frequency comb (OFC), a 4-channel optical coherent transmitter or a dual optical frequency comb (DOFC). This architecture offers flexibility in terms of its configuration so that it could be adopted to serve the requirements of specific applications. In this paper, we focus on the DOFC configuration, showcasing the ability of this PIC to generate a dual comb with a flexible free spectral range (FSRs) using fully integrated components. Such integration significantly reduces the size of the interrogator compared to other architectures enabling compact, lightweight designs suitable for space-constrained applications. The downconverted radiofrequency (RF) comb generated by heterodyning, on a photodiode, the two phase correlated OFCs exhibits an extremely high amplitude stability with less than 0.4 dB fluctuations over 30 minutes. In the best-case scenario, the resulting RF-DOFC portrays more than 50 lines with a carrier-to-noise ratio (CNR) exceeding 20 dB . The results obtained, with an adaptable PIC, show that such a fully integrated dual comb device, offering a small form factor, displays immense potential to be employed in photonic sensing applications such as spectroscopy, distributed sensing and fibre Bragg grating sensing.