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Hybrid optical integrator based on silicon-on-insulator platform

A hybrid optical integrator is a recirculating loop that performs oversampling typically for an analog input using the crossgain modulation (XGM) in a semiconductor optical amplifier (SOA). The modulated input signal changes the gain of the loop through XGM and thus modifies the loop accumulation. This paper presents hybrid optical integrator for an all-optical analog-to-digital converter based on silicon photonics platform. The device consists of silicon waveguides of dimension 220 × 500 nm (thick × width) and approximately 2,800 μm total loop length, input and output grating couplers for 1550 nm signal, directional couplers, and external components (SOA, optical isolator and band-pass filter). All devices are designed for fabrication on the SOI wafer using E-Beam lithography. A theoretical model for the system is developed and simulated with Lumerical software and Matlab that accounts for critical design parameters such as the loop length, coupling coefficient, and gain in the SOA. The 3-dB couplers were designed and loop length was minimized to reduce the propagation loss through the silicon waveguide and increase the sampling frequency. From the simulation, total loss of silicon photonics device at one round trip is approximately 27 dB. The system is characterized for square waves at Giga- Hertz input frequencies. Simulation results show excellent agreement with the theoretical model of leaky integrator. The operation frequency of the integrator can be increased from MHz up to GHz by replacing fiber cable to silicon waveguide, leading to a free-spectral range of approximately 4.17 GHz.