A Photonics Approach for Microwave Waveform Generation Based on PM-IM Conversions Using Two Dual-Output Sagnac Interferometers

Abstract

A photonics-assisted scheme for generating various microwave waveforms has been investigated in this paper. In the proposed scheme, two phase modulation to intensity modulation (PM-IM) conversions are realized using two cascaded Sagnac interferometers (SIs) to manipulate light in the optical domain. From the first SI, by adjusting the amplitude of the microwave signal and time delay of the tunable optical delay line (TODL), both half duty cycle square and full duty cycle triangular waveforms can be generated from the photodetector (PD) and balanced photodetection (BPD). Using the second SI and applying microwave signals with appropriate amplitudes and phases, as well as the BPD process, results in full duty cycle sawtooth and reversed sawtooth waveforms. Detailed theoretical analyses are presented and results are verified by simulations. In the simulations, square-, triangular- and sawtooth-shaped (or reversed sawtooth-shaped) waveforms are obtained successfully. To complete the simulation results, the effects of non-ideal microwave hybrid coupler and optical couplers on the performances of the proposed scheme have been studied and no destructive effects were observed. The proposed structure does not include any optical or electrical filters which result in a wide operational bandwidth.

Keywords

• Microwave photonics
• waveform generation
• Sagnac interferometer (SI)
• external modulation
• phase modulation to intensity modulation (PM-IM) conversions