Generation of triangular waveforms based on a microwave photonic filter with negative coefficient.

Wei Li,Wei Yu Wang,Wen Hui Sun,Wen Ting Wang,Ning Hua Zhu

doi:10.1364/oe.22.014993

Abstract

We report a novel approach to generating full-duty-cycle triangular waveforms based on a microwave photonic filter (MPF) with negative coefficient. It is known that the Fourier series expansion of a triangular waveform has only odd-order harmonics. In this work, the undesired even-order harmonics are suppressed by the MPF that has a periodic transmission response. A triangular waveform at fundamental frequency can be generated by setting the bias of a Mach-Zehnder modulator (MZM) at quadrature point. However, it is found that a broadband 90° microwave phase shifter has to be used after photodetection to adjust the phases of odd-order harmonics. Alternatively, a frequency doubling triangular waveform can be generated by setting the bias of the MZM at maximum or minimum transmission point. This approach is more promising because the broadband microwave phase shifter is no longer required in this case but it is more power consuming. The proposed approach is theoretically analyzed and experimentally verified.

Highlights

In recent years, there has been a growing interest in the photonic generation of triangular waveforms because of its applications in all-optical signal processing and microwave signal manipulation, e.g. optical frequency conversion, pulse compression, doubling of optical signals, and signal copying [1,2,3]
We have theoretically and experimentally demonstrated a novel approach to generating a fullduty-cycle triangular waveform based on a microwave photonic filter (MPF) with negative coefficient
The undesired harmonics are removed by the MPF with periodic transmission response, while the desired ones are well kept

Summary

Introduction

There has been a growing interest in the photonic generation of triangular waveforms because of its applications in all-optical signal processing and microwave signal manipulation, e.g. optical frequency conversion, pulse compression, doubling of optical signals, and signal copying [1,2,3]. We propose and experimentally demonstrate a new method to generating full-duty-cycle triangular waveforms based on a microwave photonic filter (MPF) with negative coefficient. Triangular waveforms at fundamental frequency can be generated by biasing the MZM at the quadrature point. Frequency doubling triangular waveforms can be generated by biasing the MZM at the maximum or minimum transmission point. This method is more promising since the broadband 90° microwave phase shifter is no longer required but it is more power consuming because the required power of the input sinusoidal microwave signal is more than that in the previous case. The frequency tunable range of the generated triangular waveforms are mainly limited by the bandwidth of the devices used in our experiment

B P 90o D

10 GHz 20 GHz

Conclusion