Researchs On The Integration Of External Modulators And Automatic Bias Control Algorithm

With the development of optical communication technology in recent years, requirements of communication quality and rate in communication system improve continuously. Compared with direct modulation, the external modulation for high-speed communication:receives extensive attention gradually. In external modulation system, MZMs (Mach-Zehnder modulators) made of lithium niobate are most applied widely. MZMs have excellent electro-optical properties, but the impact of temperature and other external factors would lead to drifting of bias operating point. Then the bit error rate (BER) would increase and the quality of optical communication system will be effectted directly. In summary, there is important practical significance on the research of modulator bias control.Modulator and laser are the necessary link for optical communication system and research of modulator automatic bias control technique. With low integration and poor stability, the traditional research platform would cause inaccurate results. Therefore, high integration of the platform becomes basis of the algorithm research, which leads to high practical and industrial value.The paper relies on MZM, QPSK modulator automatic bias control technique and the designs of source integrated prototype and QPSK optical modulation integrated prototype. 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 LabVIEW is proposed and it’s also one of the innovations of the paper. After verifying, the technique guarantees the performance of bias control, reduces the complexity of circuit, and is unlimited to modulation formats.2. An integrated narrow-linewidth laser prototype is designed and implemented. The PC software designed based on Lab VIEW achieves instrument Control. Taking advantage of Lab VIEW is another innovation of the paper.3. An integrated QPSK external modulator solution is proposed. Utilizing multiple techniques such as Lab VIEW, data acquisition, C language, etc. the integrated QPSK optical modulator prototype is designed and implemented. The modulator automatic bias control technique is applied in integrated QPSK optical modulator prototype and the PC software designed based on LabVIEW achieves instrument Control.4. A test platform is set up to verify optical communication system which is made of designed integrated narrow-linewidth laser prototype and integrated QPSK optical modulator prototype. The platform tests the function of prototypes and proves the validity and practical significance of the integration of the system under high-speed signal modulation rate at10Gbit/s and20Gbit/s.