Research On Reconfigurable Microwave Photonic Filter Based On PM-PSFBG

Microwave photonics is a multidisciplinary field that studies the interaction between microwave and optical signals.Radio frequency signals can be modulated onto optical signals and directly processed in the optical domain.As an important branch of microwave photonics research,microwave photonics filters have the advantages of low loss,high capacity,wide bandwidth,electromagnetic interference resistance,and reconfigurability.Compared with traditional electronic filters,microwave photonics filters not only inherit the advantages of photonic technology such as large bandwidth and strong electromagnetic interference resistance,but also have higher performance and flexibility.They can realize various types of filters such as single-pass,dual-pass,single-notch,and dual-notch filter,and can be reconfigured as needed during operation.This article focuses on high-performance microwave photonics filters and summarizes the main work as follows:We propose a reconfigurable microwave photonics filter based on a dual-parallel Mach-Zehnder modulator(DPMZM)and a low-birefringence phase-shifted fiber Bragg grating(PS-FBG),also known as a polarization-maintaining phase-shifted fiber Bragg grating(PM-PSFBG).By appropriately setting the DPMZM bias voltage,the DPMZM achieves phase modulation or singlesideband modulation.The modulated optical signal output by the DPMZM is then sent into the PMPSFBG through a circulator.Finally,the orthogonal polarization states reflected by the PM-PSFBG is oriented to have a certain angel relative to the Pol axis,dual-pass,or dual-notch filter response and an enhanced out-of-band suppression and can be obtained.The center frequency of the filter can be adjusted by tuning the laser wavelength.A theoretical model was established and simulated and analyzed,ultimately verified through experiments.We propose and experimentally verify a reconfigurable microwave photonics filter based on a dual-polarization dual-parallel Mach-Zehnder modulator(DPol-DPMZM)and a low-birefringence phase-shifted fiber Bragg grating.By appropriately adjusting the DPMZM bias voltage,it can act as an equivalent phase modulator or single-sideband modulator to achieve passband or notch filter response.The center frequency of the filter can be adjusted by tuning the tunable laser’s wavelength.By adjusting the polarization controller 2(PC2),the two polarization states of the modulated signal are transmitted along the fast and slow axes of the PM-PSFBG,respectively.By aligning the fast and slow axes with the two principal axes of the polarization beam splitter(PBS),we can selectively realize two passbands,two notches,or one passband and one notch response at the two output ports of the PBS.If only one DPMZM is loaded and the polarization state of the single-sideband modulated signal is set to be 45°,the modulated signal is split into two parts that transmit along the fast and slow axes equally.When the polarization direction of the modulated signal transmiting along the fast axis of the PM-PSFBG is oriented to have 135°relative to one principal axis of the polarization beam splitter,the performance-improvement filter response can be obtained by subtracting the filter responses that transmit along on the two principal axes of the PM-PSFBG.