Self-Seeding Gain-Switching Experimental System For Generation Of Wavelength-Tunable Optical Short Pulse And Theoretical Study

Wavelength tunable optical short pulse has great applicable potential in wavelength-division-multiplexed (WDM) and time-division-multiplexed (TDM) optical fiber communications and optical fiber sensors. Simply and reliably generating wavelength tunable optical short pulse is by means of self-seeding while gain-switching of the commercially available Fabry-Perot (F-P) laser diode, which is called self-seeding gain-switching technology. The two main parameters to measure the capability and performance of the self-seeding system are the side-mode suppression ratio (SMSR) of the output single-mode optical pulses and the wavelength-tuning range. This thesis focuses on the establishment of a self-seeding system by gain-switching tuning of F-P laser diode and its analysis in theory. Firstly discussions are carried out on the principle of generating wavelength tunable optical short pulse by self-seeded gain-switched F-P laser diode in frequency and time domains. The high-order mode lock of laser cavity is first expressed to be the matter of fact of self-seeding, as another manner for mode locking. Also a micro dynamic time domain computational frame emphasizing the optical physical process is first presented for computational optical pulse dynamic trace, and used in simulation calculation for two actual experimental systems. All the results in SMSR, the generation process, and the pattern of the optical pulses are shown well consistent with the actual systems. Then, a number of simple, efficient and robust self-seeding experimental systems are established for generating tunable single- and duel-wavelength optical short pulses, resulting in that the output optical pulses have high SMSR within the relatively wide wavelength tuning range. In addition, a self-seeding experimental system applied to gas sensors is first established, and the experimental result shows that the system is with higher sensitivity of measurement. The main innovational contents of this thesis are as follows:1. Establishing and presenting a basic self-seeding experimental system using two optical fiber gratings for producing wavelength-tunable optical short pulses with high SMSR value. A rational optical route structure is the key to the system, which can ensure that the optical coupler introduced is the only for output and the optical feedback (seed of light) is not via the coupler anymore, hence, the seed light has enough power to assure the selected mode strongly competitive. In the external cavity of gain-switched F-P laser diode, two serial connected fiber gratings are used to enhance the wavelength tunable range. The experimental results show that the SMSR value is higher than 32 dB over a wavelength-tuning range of 25.7 nm.An improved experimental system is established installing an erbium-doped fiber amplifier (EDFA) into optical feedback path in the basic experimental system, which significantly intensifies competitive ability of the selected mode, and in turn, makes the output optical pulsereach a very high SMSR value in a larger wavelength tuning range. The results obtained from the system show that the SMSR value of the single mode optical pulses outputted are higher than 40dB and 35dB relatively over a wavelength tuning range of 24nm and 28.2 nm (between 1521.8nm and 1550.0nm).2. Establishing and presenting a basic self-seeding experimental system using the reflection at incidence face of F-P optical filter as output for producing wavelength-tunable optical short pulses; and on this basis developing an improved experimental system by installing an EDFA into optical feedback path.A rational and smart optical route structure is substantial for this system using reflection at incidence face as output, which can divide the transmission and reflection of tunable F-P filter, and select the reflection as system output without the need of a optical coupler to introduce it, in turn, overcome the large insertion loss of an F-P filter and ensure enough power of optical feedback. This system is simple and efficient, and the wavelength of pulses can be tune...