Optimization Of Tunable Laser Devices

With the development of information technology, the research and deviceof tunable laser attended climax around 2000. In static application, thewavelength of tunable laser can be fixed in using process, and will not changewith time. This can make it to be substitute of source laser, and can be used indense wavelength division multiplex (DWDM) transiting system. Tunablelaser can act as the store of several fixed wavelength laser or flexible sourcelaser. In dynamic application, tunable laser whose wavelength can changeregularly in using, enhance the flexibility of the optical network. All theapplications need that tunable laser have wider tuning range. In order to solvethe question, we have done some work and receive some conclusions. First, we explained the physical model of semiconductor laser thatincluded electricity equation, wave equation, thermal conduction equation andcoupled wave equation, and introduced the method of energy band analyzingand the calculating method of band offset. This was base of simulating andoptimizing. We put forward a simplified analyzing method in which tunable lasercould be devised by section. In simulating and analyzing of active layerstructure, we calculated the gain spectrum by energy band theory. Through theanalyzing of the efficiency of light transfer in laser, we could choose betterwaveguide layer. By analyzing the external cavity sampled grating structure,we could calculate the tuning range of tunable laser. The wider ranging and flat gain spectrum was important in tunable laser.Conventional single well laser and symmetrical multi-quantum well laserwere difficulty to achieve the request. We adopted a novel multi-quantum well,asymmetrical multi-quantum well (AMQW). In this well, the material ofevery well was different, so the energy band of every well was different, too.This make the out light wavelength and gain of every well different. The totalgain of the laser equal every gain of single well fitting result. We usedGaxIn1-xAs1-yPy material system acting as wells and barriers of active layer.Though adjusting component and parameters of every layer and using energyband theory, we could draw the gain spectrum of every well. The total gain 52吉林大学硕士学位论文spectrum could be calculated by fitting single well gain spectrum. Throughcalculating and comparing, we put forward a four-layer AMQW structure. Thebarrier material was In0.775Ga0.225As0.65P0.3. The two-fringe thickness was150? ,and the middle thickness was 50?.The well material was respectivelyIn0.775Ga0.225As0.8P0.2, In0.775Ga0.225As0.72P0.28, In0.775Ga0.225 As0.685P0.315 andIn0.775Ga0.225As0.65P0.35 which were all 100?. Using this active layer structurewe could receive flat and wide ranging gain spectrum whose tuning range isabout 300nm. When we chose the material of waveguide, we thought over the latticematching, light transmitting efficiency, and the influence of laser performance.We calculated light transmitting efficiency of two kind of waveguide material,In0.775Ga0.225As0.489P0.511 and In0.92Ga0.08As0.175P0.825. The first efficiency was60%, and the other was 47%. We also analyzed the threshold current and L-Irelation of the lasers whose waveguide material was In0.775Ga0.225As0.489P0.511and In0.92Ga0.08As0.175P0.825 respectively. In the laser whose waveguidematerial was In0.775Ga0.225 As0.489P0.511, the threshold current was 17.3 mA, andslope coefficient of L-I curve was 25.95% (W/A). In the laser whosewaveguide material was In0.92Ga0.08As0.175P0.825, the threshold current was110.63 mA, and slope coefficient of L-I curve was 10.84% (W/A). By takinglight transmitting efficiency and the influence of threshold current and L-Icurve slope coefficient into account, we used In0.775Ga0.225As0.489P0.511 actingas the waveguide material. In external tuning section, we used sampled grating to receive thewavelength tuning function of tunable laser. We analyzed...