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

近来，每根光纤的光纤信号传输容量超过几百Gbps并且超过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波长范围内的半导体激光器产生超短脉冲。本研究的目的是实现一种利用光纤压缩技术从具有任意重复频率的增益开关半导体二极管激光脉冲中产生高质量的宽带光谱超短光脉冲的方法。我们成功地取得了以下成果。(1)我们发现，当我们设计用于产生亚100 fs脉冲的光纤压缩器时，考虑光纤中的高阶非线性效应如拉曼效应和高阶色散效应是很重要的。(2)根据上述设计原则，我们实现了一个相对简单的孤子压缩器，并将其应用于皮秒增益开关半导体激光脉冲。获得了44 fs的合成宽度，这是在1500 nm波长范围内获得的最短脉冲之一。(3)此外，我们还构造了非线性光纤环，以消除上述超短脉冲中伴随的噪声，并获得了成功的基座抑制（>20 dB），这产生了55 fs的无基座光脉冲。(4)发现在由此产生的脉冲中获得的光谱包含100至250 nm的相当宽的光谱，这对于WDM光源是相当有吸引力的。我们相信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 fs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.