Silicon-Based Integrated Tunable Fractional Order Photonic Temporal Differentiators

Two integrated fractional-order photonic temporal differentiators based on two Mach-Zehnder interferometer (MZI) structures implemented on a silicon-on-insulator (SOI) platform are designed, fabricated, and experimentally evaluated. The first photonic temporal differentiator employs a multimode interference (MMI) coupler as one of the two 3-dB couplers of the MZI. By changing the polarization state of the input optical signal, the coupling coefficient of the MMI is changed, which leads to the change of the phase shift in the destructive interference wavelength, and a photonic temporal differentiator with a tunable fractional order is implemented. The second photonic temporal differentiator is designed to have two cascaded MZIs, a balanced MZI, and an unbalanced MZI. A phase modulator (PM) is incorporated in one of the two arms of each of the MZIs. The balanced MZI with a PM forms an active tunable coupler, which is used to actively tune the fractional order of the temporal differentiator. The PM in the unbalanced MZI is used to tune the operating wavelength. The two photonic temporal differentiators are designed and fabricated in a CMOS compatible SOI platform, and their performance is evaluated experimentally. The experimental results show that both temporal differentiators can have a tunable fractional order from 0 to 1. In addition, the use of the active temporal differentiator to perform high-speed coding with a data rate of 16 Gb/s is experimentally evaluated.