The Offset Frequency Tracking Of Two Semiconductor Lasers And The Use In Frequency Modulation Coherent Optic Communication

Electromagnetic wave communication started when the first wireless system was invented by Marconi in 1895. However, we had to wait about one hundred years to realize a similar technology in the lightwave frequency region. The invention of laser in 1960 and two technology innovations in 1979 low loss silica fiber and semiconductor lasers operating at room temperature-promoted the development of fiber-optic transmission systems. The development of high-speed long-haul fiber optic transmission systems has led to the formation of domestic and international trunk networks. The installed fiber cables in local loop plants provide multimedia communication services including broadband video. However, present lightwave communication systems do not fully utilize the fruitful potential of lightwave. ramely the capacity of extremely high frequency electromagnetic information carrier waves. The frequency of lightwaves used for fiber-optic transmission is about 200THz. and the frequency bandwidth of the fiber low loss region is about 2OTHz. Recent developments of narrow spectrum width semiconductor laser and planer optical waveguide devices offer us the possibilities for a new generation of lightwave-based communication systems. Based on the measuring and analyzing of basic performance of new narrow linewidth, integrated external cavity semiconductor lasers, a semiconductor laser current driver the modulation of part and a feedback fiber loop for offset frequency tracking was designed. The offset frequency tracking of two semiconductor lasers was succeed by heterodyne detection structure. The results show that the accuracy is within 1MHz, the frequency acquired rang is 300MHz, the frequency tracking range is about 1 Gl-z, modulating the signal lascr with variable polse pattem generation demodulating themodulated signal with frequency discriminatof, a heterodyne,coherent optical signal transmission system including frequencymodulation and demodulation was set up which demonstrating theinfOrmation transmission progress including information transmittingtransmission and demodulation recovery.