Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Basic electronic circuits > Modulation technique and the modulator,demodulator and the demodulator > Modulation technique and the modulator

Multi wavelength phase lock frequency and its application in optical network

Author ZouShuMin
Tutor ChiZuo
School Fudan University
Course Communication and Information System
Keywords Multi-Carrier generation Frequency locking Advanced Modulation Mach-Zehnder Modulator Phase Modulator
Type Master's thesis
Year 2012
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With the rapid development of information society and broadband services continue to emerge; the global amount of information grows exponentially. The explosive growth of demand for data services has led the traditional optical network to great development and change. The major developed countries has raised the development of ultra-wideband and high-capacity backbone network transmission technology to the national strategy, Our country also firmly grasps the historical opportunity for update of broadband, high-capacity backbone network and proposed the strategy of China’s national broadband. The ultra-high-speed optical transmission technology over Tb/s capacity development through the use of multi-carrier and multi-band technology is the hot spot of international research.The paper starting from the generation of phase-frequency locking of multi-carrier light source, based on the structure of optical external cavity modulator, and provides a theoretical analysis and numerical simulation for generating multi-carriers with stable frequency interval and smooth amplitude. We first discuss current international popular structure of frequency phase-locked multi-carrier, the theoretical derivation of the system principle, and simulation based on the frequency offset of single-sideband modulator’s output in ring cavity structure. Deduced the principle of multi-carrier generation based on a single Mach-Zehnder Modulator. We analyzed the relationship between the multi-carrier’s flatness with the RF drive voltage and DC bias voltage of Mach-Zehnder modulator, and the relationship of the output multi-carrier’s power with the RF drive voltage and DC bias voltage in detail. We obtained the relationship diagram of three, five and seven carriers’ drive voltage with the flatness and found out of the optimal operating point, and obtained the conditions for getting more carrier numbers. Based on the five carriers’ generation implementation, we proposed a new kind of100Gbit/s all-optical-OFDM transmission system; the generated all-optical-OFDM signal can achieve40km error-free transmission in single-mode fiber without dispersion compensation, the power penalty is less than5dB. Analysis showed that using a single Mach-Zehnder modulator to produce multi-carrier requires a relatively large drive RF voltage and the shortcomings of the system are that the dynamic range is small and unstable. Therefore, concatenating external cavity modulators is proposed to generate multi-carriers. The principles of the system are derived, and the relationship of the multi-carriers’ output performance with the work point of phase modulator and Mach Zehnder modulator is simulated. The results show that the concatenated modulators can generate more of carriers, and Mach Zehnder modulator is use to further trim the multi-carriers’ amplitude jitter caused by the phase modulator, resulting in a flat multi-carrier output, while the concatenated modulators must remain phase locked in order to have better output performance. Based on the structure, we proposed100Gbit/s polarization multiplexed QPSK100km transmission experiment and employed digital coherent demodulation. Besides, we made a comparative experiment between a single wavelength transmission and the multi-wavelength transmission, and experiment verified the concatenated multi-carrier generation, the transmission power penalty of generated multi-carrier is less than0.5dB. Multi-wavelength light source that generated by the concatenated modulator is a promising coherent light source technology in the future Tbit/s optical communication.

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