Wavelength tuning speed in semiconductor ring lasers using on-chip filtered optical feedback

Wavelength tunable and switchable lasers are widely used in telecommunication networks as they allow flexible wavelength division multiplexing, fast optical signal routing, and all-optical signal processing. In this work, we characterize the wavelength switching speed of a tunable semiconductor ring lasers using filtered optical feedback. Semiconductor ring lasers nowadays are promising sources in photonic integrated circuits because they do not require cleaved facets or mirrors to form a laser cavity. They are interesting from a nonlinear dynamics point of view due to the existence of two counter propagating modes that interact with each other which allows semiconductor ring lasers to be used as all-optical switches and as all-optical memories. The wavelength of the semiconductor ring laser is controlled by a feedback section which consists of two arrayed waveguide gratings, four semiconductor optical amplifiers and waveguides to connect the different components. The filtered optical feedback is realized by employing the two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback strength of each wavelength channel independently. The switching is achieved by changing the currents injected in the semiconductor optical amplifier gates. Experimentally, we observe a wavelength transition time of 5 ns. However, we also noticed a non-negligible delay in the switching process. We discuss this delay time and the different parameters which have an effect on it. We can numerically reproduce the experimental results using rate equations taking into account the effect of spontaneous emission. The simulations also demonstrate that the wavelength transition time and the delay can be further decreased by controlling the phase in the feedback section and by increasing the strength of the feedback.