Research On Wide-band Low-spurious Microwave Photonic Frequency Conversion Using Electro-optic Modulators

Wireless Communication techniques makes it convenient to transport information anytime and anywhere, is widely used in communication systems especially on satllites. Howerver, the growing use of radio spectrum requires electronic systems to operate at extended radio-frequency (RF) bands and signal bandwidth, putting forward great challenges to frequency conversion design, which is a crucial function in wireless communication system. Microwave photonic techniques are recently introduced to overcome these limitations due to several inherent advantages, such as potential full-band operation, large instantaneous bandwidth, high RF isolation, low-loss transmission and electromagnetic interference immunity. In the existed works, tunable narrow-band optical filters have to be used to reduce the spurs, raising the implementation complexity. In addition, the works mainly oriented to scheme proposation,while different functions and system performance are needed to be studied and improved.Microwave photonic frequency conversion schemes are proposed to implement wide-band low-spur conversion systems. Optical I/Q modulators are employed instead of conventional Mach-Zehnder modulators to achieve single-sideband carrier-suppressed modulation,saving tunable narrow-band optical filters. Diffrent conversion schemes are also discussed through different detections.Research on microwave photonic I/Q direct-conversion was focused,given the advantage of avoiding image frequency interference and suitable for standard soft-designed radio systems. With 0 GHz to 20 GHz spectral range of modulated radio signal, conversion loss is below 16 dB, noise figure is below 42 dB, spurious free dynamic range is larger than 108 dB/Hz-2/3, which hold in the entire 20 GHz range under test. The performance can be further improved by increasing the laser power, using pre-LNA and low-Vpi optical modulators.A direct-conversion receiver using microwave photonic I/Q mixer was also proposed, demodulating wide-band QPSK signal successfully.The receiver shows mitigated LO leakage and I/Q imbalance, which are recognized as major drawbacks of conventional direct-conversion receivers. The typical amplitude imbalance between I and Q outputs is 0.3 dB and the phase imbalance is 2 degrees. The research provides information about relative techniques and performance for reference and lays the foundation for next step of frequency conversion study.