Abstract
A dual-channel phase-tunable down converter with local oscillator (LO) frequency doubling is proposed by using a commercial dual-polarization dual-drive Mach-Zehnder modulator (DP-DMZM) and a specially designed dual-channel phase modulator (DP-PM). A radio frequency (RF) signal is injected to one of sub-DMZMs in the DP-DMZM, and a LO signal modulates another sub-DPMZM. An optical bandpass filter (OBPF) is used to filter out the unwanted sidebands, and only the +2nd-order LO and +1st-order RF sidebands are remained and output to the DP-PM. The DP-PM is composed by two parallel PMs with different modulation efficiency between orthogonal polarizations. Each bias voltage of the DP-PM can linearly vary the phase shift between the RF and LO modulated optical sidebands. After detected by a photodetector, the down converted signal with doubled LO frequency and dual-channel phase shift can be obtained. The principle of the proposed link is verified and the experiments are carried out. The experimental results show that the average spur suppression ratio of the down-converted signals is 29.15 dB. The spurious-free dynamic range (SFDR) of the down converter is 103.94 dB·Hz2/3. The continuous and dependent dual-channel phase shift with the full range of 360° can be experimentally achieved. The proposed down converter integrates multiple function in a link, and has the merit of high electrical purity and convenient operation.
Highlights
Frequency conversion and tunable phase shift are two significant functions in the modern communication transmitter and receiver
The experimental microwave photonics link (MPL) of the down conversion with local oscillator (LO) frequency doubling and dual-channel phase shift is carried out according to Fig. 1
The radio frequency (RF) signal is launched to the DMZM-1, the LO signal is introduced to the DMZM-2
Summary
Frequency conversion and tunable phase shift are two significant functions in the modern communication transmitter and receiver. Microwave photonic phase shifter is proposed based on a dual-parallel Mach-Zehnder modulator (DPMZM) [14] or a dual-polarization dual-drive MZM (DP-DMZM) [15]. In these methods, the bias voltage of the sub-MZM is tuned to realize 360° phase shifting. A photonic-assisted microwave hybrid combiner is designed by a DP-DPMZM and an optical bandpass filter (OBPF) [29] In this link, the phase shift and power ratio of the microwave signals can be tuned continuously and flexibly. The sub-harmonic sideband of LO signal and the adjustment of bias voltage of modulator are used to realize the frequency doubling and tunable phase shifting, respectively. The suppression ratio of the down conversion signal averagely reaches 29.15 dB, and the performance of spurious-free dynamic range (SFDR) is measured at 103.94 dB·Hz2/3
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