| Optical-microwave mixing technology is developing with the needs of the future wireless-access networks. For this technology, we propose a new approach for photodetector based on non-linear effects realizing microwave-frequency conversion. This technology has many advantages, such as simple structure, feasible operation and low cost. And500MHz intermediate frequency(IF) signal is converted to C-band and Ku-band by direct modulation technology and external modulation technology.The details are described as follows:1. The background and applications of microwave photonics are briefly introduced, the main research is optical-microwave mixing technology belonging to microwave/millimeter wave signal optical processing; Again, the significance of optical-microwave mixing technology is briefly discusses, and finally the research current situation of microwave photonic frequency conversion utilizing photodiode is introduced.2. The characteristics of devices in the optical-microwave mixing link utilizing photodiode are introduced, including Distributed Feed Back (DFB) laser, Mach-Zehnder modulator, photodetector and microwave circulator. We analyze the principle of photodetector based on non-linear effects realizing frequency conversion.3. Design and optimization of the optical-microwave mixing systems are given. In experiments, we use the two ways of direct modulation and external modulation to achieve500MHz IF signal converted to6GHz and16GHz RF carrier, and experimental results show that there are an optimal reverse bias voltage of the photodetector, optimal local oscillating (LO) signal power and IF signal power. By increasing reasonably the power of the optical carrier, the performance of system can be improved. On this basis, baseband signal by20dB noise ratio of IF signal carrying a certain bit rate(32Kbps,lMbps,10Mbps and36Mbps) is transmitted, and this system show good communication performance, the EVM of the correct demodulated signal should be less than15%rms. |
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