Abstract
A novel photonic approach for multi-format signal generation based on a frequency-tunable optoelectronic oscillator (OEO) is proposed using a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) integrated in the DP-QPSK modulator is properly biased to serve as an equivalent phase modulator, which functions in conjunction with a phase-shifted fiber Bragg grating (PS-FBG) in the OEO loop as a high-Q microwave photonic band-pass filter. The lower DP-MZM in the DP-QPSK modulator injected by the oscillation signal functions as a frequency multiplier, a phase-coded microwave signal generator or an optical frequency comb generator, respectively, with different signal injection methods. An experiment is performed. When the lower DP-MZM serves as a frequency multiplier, tunable frequency-doubled and quadrupled microwave signals up to 40 GHz are generated without using an optical notch filter; and if it functions as a phase-coded microwave signal generator, fundamental and frequency-doubled binary phase-coded microwave signals are generated with a tunable frequency. Furthermore, tunable five-line optical frequency combs are also generated using the compact system without an external RF source. The performance of the generated signals is also investigated.
Highlights
Microwave photonics, an interdisciplinary area which combines the worlds of radiofrequency (RF) engineering and optoelectronics, has been a topic of interest over the past few decades
The upper dual-parallel Mach-Zehnder modulator (DPMZM) integrated in the dual-polarization quadrature phase shift-keying (DP-QPSK) modulator is properly biased to serve as an equivalent phase modulator (e-PM), which functions in conjunction with a phase-shifted fiber Bragg grating (PS-FBG) in the optoelectronic oscillator (OEO) loop as a high-Q microwave photonic band-pass filter (MWP-BPF), whereas the lower DP-MZM in the DP-QPSK modulator injected by the oscillation signal functions as a frequency multiplier, a microwave phase-coded signal generator or an optical frequency comb generator, respectively, with different settings
A fundamental oscillation signal with a frequency from about 7.5 GHz to 12.5 GHz is generated in the OEO loop, which is used as the reference signals for frequencydoubled and quadrupled microwave signal generation up to 40 GHz, for fundamental and frequency-doubled binary phase-coded microwave signal generation up to 17 GHz, and for five-line optical frequency comb generation with a frequency spacing to 12.5 GHz
Summary
An interdisciplinary area which combines the worlds of radiofrequency (RF) engineering and optoelectronics, has been a topic of interest over the past few decades. High-frequency microwave signals, phase-coded microwave signals and optical frequency combs are all able to be generated using external modulation with a RF reference, whereas OEOs provide an effective solution for low phase noise RF signal generation, which is a promising technique to offer reference signals with high performance. The upper dual-parallel Mach-Zehnder modulator (DPMZM) integrated in the DP-QPSK modulator is properly biased to serve as an equivalent phase modulator (e-PM), which functions in conjunction with a PS-FBG in the OEO loop as a high-Q microwave photonic band-pass filter (MWP-BPF), whereas the lower DP-MZM in the DP-QPSK modulator injected by the oscillation signal functions as a frequency multiplier, a microwave phase-coded signal generator or an optical frequency comb generator, respectively, with different settings. The frequencytunable range can be greatly increased by using PD and EA with a larger operating bandwidth
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