| The great demand on information has roused the rapid development of optical communication , how to use the source of the fiber band width effectively has been one of the hottest optoelectronic R & D projects in the world. For the electrons mobility ratio limited , traditional time division multiplexing technique can not reach the highest speed of 40Gbit/s. How to conquer the electric bottle neck and increase the transmission capability , people eyes leave electric multiplexing for optical multiplexing . At present ,there are two optical multiplexing techniques: one is wavelength division multiplexing(WDM) technique ;the other is optical time division multiplexing(OTDM) technique. Although OTDM technique is not very mature and some key devices in OTDM are still studying in the laboratory, the technique becomes the research hotpot all over the world. Recently the devices and system and net in OTDM are developing prodigiously which step toward the utility . In studying the multiplexing technique ,this paper advanced to divide one random signal into two signals via the fiber couplers and control the length difference of the couplers to make a time delay difference between the two signals, then put one signal into the other signal and realized optical signals multiplexed. 4×2.5Gbit/s optical time division multiplexing signal generation system has been developed in our experiment Fiber coupler loop-connecting configuration can realize the same optical signal multiplexing . Due to it's low capability couplers , low cost , easily adjusting for output pulse amplitude and low inserted loss the method becomes a promising optical source for the future high all optical communication. In the experiment we only give the 2×2.5Gbit/s OTDM signal. Based on self-phase modulation and group velocity dispersion, we analyzed the wave shape and pulse chirp of the optical pulse in OTDM. Then we deduced the formula for chirp change with time and length and simulated it . According to theoretic analysis , we measured the wave shape and pulse chirp in OTDM based on FRHSG, in the experiment we got the interference autocorrelation function and the electric-field autocorrelation function of DFB laser pulses before multiplexing and OTDM pulses which transmitted 1km respectively . The result showed that after multiplexed and transmitted 1km the pulses extended 2.8ps and chirp increased about 10GHz, it is up to the theoretic analysis. In the fifth chapter we simulated the ultra-short pulses generation based on the single EAM and the tandem EAM. Measuring the absorption character of EAM, we built the calculation model of pulses generation based on single EAM and tandem EAM , then deduced the calculating formula of extinction ratio and pulse width. analyzed the varying principle of pulse width and extinction ratio according to the modulating condition. In single EAM simulating, we got the pulses which narrowest pulse width is 59.78ps and extinction ratio is more than 20dB. It can be optical pulses source for 10Gbit/s in OTDM. In tandem EAM simulating , we got the pulses which narrowest pulse width is less than 15ps and the extinction ratio is more than that of single EAM. It can be appropriate optical pulses source for 20Gbit/s in OTDM. Otherwise , modulating the phase difference between two EAM, we can change the output pulse width and be more convenient in system application.
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