All-optical Signal Processing Assisted High Spatial Resolution OFDR

Optical fiber sensing technology has great advantages compared to traditional electronic sensing technology. It can be used in a variety of areas. Based on distributed optical fiber sensing technology, optical frequency domain reflectometry(OFDR) is widely used in various fields because of its high spatial resolution and sensitivity.Large frequency sweeping span and sweeping linearity is needed for high spatial resolution of OFDR system. In order to avoid non-linearly sweeping, external modulation can be used. However, RF signal is limited in the speed and bandwidth due to the electronic bottleneck. Therefore, the linear and continuous optical frequency sweeping bandwidth is restricted at the scale of several GHz. In this work, all-optical signal processing is used to help achieve high performance frequency swept light source.This paper proposes the use of high order sideband modulated by Mach-Zehnder electro-optic modulator as the frequency sweeping light source in OFDR system. Using the N-th order sideband for sweeping can get N times sweeping range of the 1st order sideband. Then, a higher spatial resolution can be obtained through degenerated four-wave mixing process in a highly nonlinear fiber. A corresponding OFDR system is set up. In the experiment, EDFA is used for power amplification. 0.75-cm spatial resolution is obtained with RF frequency sweeping span of 638.4 MHz. The proposed all-optical signal processing method is proved.