Abstract
This paper presents a detailed investigation on the cause of ripples in the frequency response of a microwave photonic phase shifter implemented using a 90° hybrid coupler. It was found that an unwanted radio frequency (RF) modulation sideband is generated at the modulator output due to the 90° hybrid coupler amplitude and phase imbalance. This resulted in phase shifter output RF signal amplitude variation and phase deviation. Experimental results demonstrated that incorporating an optical filter in the phase shifter structure can reduce the amplitude variation and phase deviation from 4.2 dB to 2.2 dB and from ±12° to ±3.8°, respectively, over a wide frequency range. A comparison of the loss and the dynamic range of the microwave photonic phase shifter implemented using a 90° hybrid coupler with a conventional fiber optic link is also presented.
Highlights
Controlling the amplitude, frequency, and phase of a radio frequency (RF) signal in an optical domain has attracted significant interest
Experiments were set up to investigate the ripples in the frequency response of a microwave photonic phase shifters (MPPSs) and to verify that using a low cost optical filter can improve MPPS frequency response performance
Was connected after the laser source. It was formed by two dual-parallel Mach Zehnder modulator (DPMZM), a 90◦ polarization rotator, and a polarization beam combiner (PBC)
Summary
Controlling the amplitude, frequency, and phase of a radio frequency (RF) signal in an optical domain has attracted significant interest. This is because microwave photonic signal processors can overcome inherent electronic limitations including limited bandwidth, electromagnetic interference, and limited tunability [1]. The MPPSs implemented using a 90◦ hybrid coupler can be operated over a wide frequency range, which is only limited by the coupler bandwidth. They suffer from the problem of ripples in the phase shifter output amplitude and phase response, causing output RF signal amplitude variation and phase deviation
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