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

目前，每根光纤的光纤信号传输容量已超过100gbps，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1500纳米波长范围内半导体激光器的超短脉冲产生。本课题的研究目的是利用任意重复频率的增益开关半导体二极管激光脉冲，通过光纤压缩方案产生高质量的宽带频谱超短光脉冲。我们成功地得到了以下结果。(1)在设计用于100fs以下脉冲产生的光纤压缩器时，考虑光纤中的拉曼效应和高阶色散效应等高阶非线性效应是非常重要的。(2)根据上述设计原则，我们实现了一个较为简单的孤子压缩器，并将其应用于皮秒增益开关激光二极管脉冲。合成宽度为44 fs，这是在1500 nm波长范围内获得的最短脉冲之一。(3)此外，我们构建了非线性光纤环路来消除上述超短脉冲伴随的基座，并成功地获得了基座抑制（>20 dB），从而产生了55 fs的无基座光脉冲。(4)由此产生的脉冲所获得的光谱包含了100 ~ 250 nm的相当宽的光谱，这对于WDM光源来说是非常有吸引力的。因此，我们相信该项目的目标已经实现，我们已经建立了一种技术，可以在1550 nm波长范围内产生低于100 fs的高质量光脉冲。

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.