| With the development of optical communication technology in recent years, the requirements of communication quality and rate in communication system improve continuously. Compared with direct modulation, external modulation is more suitable for the high-speed optical communication system and receives extensive attention gradually. MZMs (Mach-Zehnder modulators) which is made of lithium niobate is widely used in external modulation system. The electro-optical properties of commercial MZMs are excellent, but the characteristics would be impacted by temperature and other environmental factors, and these factors induce instability of the device. The draft of bias point would increase the bit error rate (BER), and decrease the quality of communication system. In summary, the research of modulator bias control is meaningful.Laser and modulator are the necessary components for optical communication system and research of modulator automatic bias control technique. In traditional algorithm, there would insert a dither signal in the input terminal, and analyze the draft character of the system through the draft curve of the dither signal. The circuit of the system is complex.The paper is mainly about MZM, QPSK modulator circuit control software and the narrow-line width laser circuit control software. The achievements and innovations obtained are as follows:1. The principle of MZM modulation and transmission characteristics is studied systematically in this paper. A software-based and dither-less modulator bias control technique on MCU is proposed in the paper.2. Design and realize the circuit control software of the narrow-line width laser based on MCU. 3. A scheme of dither-less signal modulator circuit control software with MCU is proposed in this paper. A software which controls the parameters of the device is compiled also.4. An experiment platform based on the software is built. Testing the two prototypes and the effectiveness of the bias control algorithm is verified. |
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