Study On Wavelength Monitoring And Control Of Monolithic Tunable Semiconductor Lasers

Widely tunable semiconductor lasers are considered to be the key components in the next generation dynamic optical networks where the length of the optical bursts or packets ranges from 100 ns to 10 ms at standard ITU-T wavelengths. Stabilization of these devices is essential for applications in both static optical networks and future OBS/OPS networks. One stabilization technique uses feedback signal derived from a reference optical filter such as a fiber Bragg grating, an arrayed waveguide grating or a stable Fabry-Perot etalon to counteract the frequency drift by tuning the phase section current. In this thesis, fast wavelength monitoring and control of widely tunable lasers using wavelength locking loop are investigated and the work mainly consists of the following parts.The structure and wavelength tuning principle of tunable semiconductor lasers have been analyzed, and then the theory of the wavelength moniroring and control system have been studied. The thermal wavelength drift caused during switching operation are analyzed, we also clarify the mode-hop-free condition for muti-section DBR tunable semiconductor lasers. Based on optics and modern control theory, we propose a continuous-time linear theoretical model of wavelength locking loops(WLLs) for tunable transmitter stabilization. The performance of the WLLs will be analyzed first from a theoretical point of view, followed by more accurate numerical simulations, finally the optimal P.I.D coefficients of the loop are derived by numerical simulation. The relation between the P.I.D coefficients and wavelength locking performance are investigated, and the effects of the loop bandwidth on locking performance are discussed in this thesis. A FPGA based electronic board has been designed and used for wavelength monitoring and control of SGDBR lasers. Fast wavelength locking of the SGDBR laser has been implemented by FPGA programme, and the accuracy, long-term stabilization and speed of locking are measured experimentally.The simulation and experimental results can provide guidance for the design of the wavelength stabilization circuits for tunable transmitters in future OPS/OBS networks.