BROADBAND SPECTRUM ULTRASHORT PULSE GENERATION WITH ARBITRARY REPETITION FREQUENCY EMPLOYING SEMICONDUCTOR LASERS

最近，每根光纤的光纤信号传输容量超过了几个100Gbps，超过了1Tbps。支持这些趋势的是波分复用和光时分复用技术。在这些技术中，最重要和最基本的问题之一是从1500 nm波长范围的半导体激光器中产生超短脉冲。本研究项目的目的是实现一种方法--利用光纤压缩方案，从具有任意重复频率的增益开关半导体激光器脉冲中产生高质量的宽带超短光脉冲。我们已经成功地取得了以下成果。(1)我们发现，在设计用于亚100ps脉冲产生的光纤压缩器时，必须考虑光纤中的高阶非线性效应，如光纤中的拉曼效应和高阶色散效应。(2)根据上述设计准则，我们实现了一个比较简单的孤子压缩器，并将其应用于皮秒增益开关激光二极管脉冲。在1500 nm波长范围内获得了44fS的合成脉冲宽度，这是迄今为止获得的最短的脉冲之一。(3)此外，我们还构建了非线性光纤环路来消除上述超短脉冲所伴随的基座，并获得了成功的基座抑制(&gt；20分贝)，得到了合成的55fs无基座的光脉冲。(4)在所产生的脉冲中获得的光谱包含100-250 nm的相当宽的光谱，这对于WDM光源是很有吸引力的。我们相信，该项目的目标已经达到，我们已经建立了一种在1550 nm波长范围内产生低于100飞秒的高质量光脉冲的技术。

Recently, the capacity of fiber-optic signal transmission per an optical fiber is more than several 100 Gbps and exceeding 1 Tbps. What have supported these trends are the wavelength division multiplexing and optical time division multiplexing techniques. In those techniques, one of the most important and fundamental issues is ultrashort pulse generation from semiconductor lasers in the 1500 nm wavelength range. The aim of this research project is to implement a method-to generate broadband spectrum ultrashort optical pulse of high quality by means of fiber-optic compression schemes out of gain-switched semiconductor diode laser pulse having arbitrary repetition frequencies. We have succeeded in the getting the following results. (1) We found out that it is important to take into account the higher order nonlinear effects like the Raman effect and the higher order dispersion effects in optical fibers when we design fiber optic compressors for sub-100 fs pulse generation. (2) According to the above guideline for the design, we implemented a rather simpler soliton compressor and applied it to pico-second gain-switched laser diode pulses. Resultant width of 44 fs was obtained, which is one of the shortest pulses ever obtained in the 1500 nm wavelength range. (3) Furthermore, we constructed nonlinear optical fiber loops to eliminate the pedestals accompanying the ultrashort pulses in the above, and have obtained successful pedestal suppression (>20 dB), which has given resultant 55 fs pedestal free optical pulses. (4) The optical spectra obtained in the pulses thus generated were found to contain fairly broadband spectra of 100 to 250 nm, which are quite attractive for the WDM optical source. We believe thus the goal of the project has been reached and we have established a technology to generate sub-100 fs high quality optical pulses in the 1550 nm wavelength range.