Light Modulator Technology And Its Applications In Optical Label Switching Network And The Rof System

Internet, B-ISDN and multimedia services enhance the requirements of optical transmission with respect to bit rate and bandwidth. As one of the key technologies for high speed optical communication system, novel modulation format has been attracting attention. Transmitter with higher spectral efficiency, better tolerance against nonlinearity and simple structure is targeted by researchers in the field. The research on novel modulation formats involves all aspects in the whole high speed optical communication system and network. The works in the dissertation include novel CSRZ modulation technologies with better transmission performance, combined amplitude and phase modulation technologies and related applications in optical label switching network and millimeter-wave radio over fiber system.1. A scheme to generate pulse-width tunable carrier suppression return zero (CSRZ) signal with LiNbO₃ modulator and optical time delay interferometer based on optical interference principle is proposed, and mathematic calculations and experimental demonstration are achieved. Experimental results show that the CSRZ signal with pulse-width of 48ps has best transmission performance, compared to others with different pulse-widths. Moreover, it is found that the duty cycle of CSRZ pulse could be changed from 53% to 66% by adjusting the amplitude of incoming electrical signal, but at the same time extinction ratio goes down and transmission performance is deteriorated.2. Theoretical calculation for receiver with time delay line interferometer used to demodulate star 16QAM (ASK-8DPSK) is performed. In addition, transmission property is analyzed in the scheme to generate millimeter-wave vector modulation signal, in which parallel amplitude modulation and phase modulation are utilized, and the transmission distance as a function of radio carrier frequency and bit rate of data under dispersion circumstance is also given.3. Four wave mixing (FWM) effect is proposed to realize loading, erasing and switching operations for optical label with DPSK format by use of its phase information processing function, and it is demonstrated for optical packet using ASK/DPSK for payload/label multilevel modulation by simulation. Furthermore, a novel scheme to generate optical packet using ASK/DPSK for payload/label serial modulation is described, in which rectangular pulse is used to modulate the bias of LiNbO₃ modulator and the optical carrier is modulated only for one time. Research results indicate that optical label switching can be realized by utilizing FWM effect, but the extinction ratio as well as the tolerance to error bit of combined amplitude and phase modulated signal are both deteriorated, therefore, the times of label switching and corresponding network capability are limited.