| With the progress of Internet and communication technology, communication networks gradually develop toward high efficiency, fast, low cost and large capacity. All optical network can overcome the O/E/O electronic transfer bottleneck, improve the optical fiber bandwidth utilization effectively, and lead to lower cost, larger information capacity. As an important component of all optical network, QD-SOA has many advantages, such as higher gain, lower line width enhancement factor, smaller threshold current characteristics and so on. The QD-SOA is widely used in wavelength converters and logic devices. All optical wavelength converters and all-optical logic devices have become an important part in all-optical network. Extinction ratio(ER) and Q factor can well reflect the quality of the output wave and can be used as a measure of the performance of wavelength converter, half-subtracter and half-adder. The main contents of this paper are as follows:1. All optical network and all optical network technology are introduced. The concept of quantum dots and the working principles of QD-SOA are discussed. A wavelength converter and logic operation devices based on QD-SOA are introduced.2. The Newton method and the fourth order Runge Kutta method used to solve the rate equations are simply introduced. With the help of static model and dynamic model of QD-SOA, static gain changed with injected optical power under different injection current and length of the active region is analyzed, and the distribution of carriers in the active region is studied. The simulation results show that higher gain can be got with the increase of the injection current and the length of the active region, the distribution of the carrier concentration in the active region is gradually reduced, and the output optical power is increased by a certain period.3. The function of the wavelength conversion is realized according to the XGM of QD-SOA. The change trend of ER and chirp of the wavelength converter is studied by changing injection current, pump power, probe power, line width enhancement factor and pump pulse width. The simulation results show that larger extinction ratio and smaller chirp can be obtained by selecting the appropriate size of the pump power, probe power, injection current, line width enhancement factor and pump pulse width, which means better waveform can be got.4. Half-subtracter logic operation function can be realized based on the XGM of QD-SOA. The output Q factor and ER can well reflect the difference between the logic “1” and logic “0” in the output light waves, the larger difference is easy to get better waveform. The smaller difference between the logic “1” is, the more perfect the waveform is. So the ER and Q factor can be used as a measure of the performance of half-subtracter. The appropriate value of input optical power can be found which lead to the higher value of ER and Q factor by changing the pump power, probe power,injected current density and pulse width. The simulation results show that better performance of half-subtracter can be obtained when we choose 14 d Bm as the pump power,-9dBm as the probe power, 22A/ cmK as injected current density, 2 ps as pulse width.5. Half-adder logic operation function can be realized based on the XGM of QD-SOA. The output ER and Q factor can well reflect the difference between the logic “1” and the logic “0” of output waveform, which makes ER and Q factor good standards to measure performance of the half adder. The larger value of ER and Q factor can be obtained through changing the input pump power, probe power, injected current density and pulse width according to simulation based on half adder structure. The results show that the better output waveform can be realized by choosing 15 d Bm as the pump power,-9dBm as the probe power, 22A/ cmK as injected current density, 2ps as pulse width, which means better performance of half adder. |
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