Photonic temporal differentiator based on polarization modulation in a LiNbO3 phase modulator

A photonic intensity differentiator is proposed based on polarization modulation. The polarization of a continuous wave (CW) optical carrier is rotated in accordance with an RF signal using a LiNbO₃ phase modulator. By properly setting a polarizer at the output of the phase modulator, the absolute value of the time derivative of the input RF signal can be obtained. The proposed scheme is experimentally verified for an 8 Gbits/s pulse train. Although the differentiator performance is sensitive to the frequency-dependent V_pi of the LiNbO₃ phase modulator, the power of the input RF signal as well as the operating optical wavelength can be optimized to get a good performance. The proposed scheme is expected to be able to process higher bit-rate signals when 40 Gb/s optical components are used.