On the apodized integrated Bragg grating as a binary generator in SI-MZI circuits comprising double closed-loop interferometer

The spectral response of four Mach–Zehnder Interferometers (MZIs)-based silicon photonic circuits integrated with/without apodized corrugated waveguide gratings comprising common feature of two serially connected closed-loop interferometers (CLIs) was investigated theoretically and experimentally. These CLIs with serial connection naturally alter the phase of signal in nonlinear manner and effectively produce a noisy signal. The apodized corrugated waveguide design was optimized to ensure side-lobe suppression, and used as a part of CLI arm in photonic circuits. The interferometers with balanced and/or unbalanced arms were examined to control phase modulation in a constructive manner. Analyses revealed that positioning four apodized corrugated waveguides in balanced arms of two closed-loop MZIs critically governs phase modulation constructively to produce spectra with sine waves over the wavelength range of ~ 1540–1550 nm. This region with discriminating frequency and obvious sine shape property is unique, and can be interpreted as the symbol “1” and the rest of the spectrum with noisy feature can present the symbol ‘0’ in a binary system.