Tunable Semiconductor Ultrashort Optic al Puse Generator

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The most advanced technology of very large capacity optical communication is the combination of TDM (Time Division Multiplexing) and WDM (Wavelength Division Multiplexing). To test the equipment and components, it is required to develop a high performance optical pulse generator, satiffying conditions (I) pulse width around 1ps, (ii) tuning range 30-100nm. To realize high performance pulse generator, we have investigated three most important issues : (1) stability and chirp charactersitics of external cavity mode-locked semiconductor lasers ; (2) high quality, broad band antireflection coaitn design and fabrication ; (3) realization of tunable mode-locked semiconductor lasers operating at 1.3 and 1.5 um. As for the theory, it was succesfully explained that actively vs. passively mode-locked lasers have red-vs. blue-shift chirp characteristics due to the change of alpha parameters dominated by gain-vs. absorber-region. In addition the tendency of increased chirp due to carrier heating process was predicted. Secondly as for anti-reflection coating, a new design algorithm was proposed : in contrast to the conventional procedure starting with the optical admittance matching condition, the value function of wavelength bandwidth was introduced, and search for the maximum value function in design parmeter space was developed. Experimental trial achieved the band width of 30nm for reflectance less than 10^<-4>. Finally anti-reflection coating was formed for laser chips.Tunability ranging from 1322nm and 1352nm (30nm range) was achieved keeping the pulse width less than 20ps. It is a straightford procedure to compress it to 1 ps using fiber-optic compresser as the present authors have recently demonstrated.