Research On All-optical Logic Devices Based On QD-SOA

As an important form of optical fiber communication, all-optical network can meet the requirements of high data transmission. Because the active region is composed of quantum dots,the quantum dots semiconductor optical amplifier (QD-SOA) shows fast gain recovery and has been widely used in optical amplification and optical conversion. Besides the wavelength converter, the QD-SOA can be used as a component of the logic gate device. According to the different modulation, all-optical logic device based on QD-SOA was divided into three kinds.The QD-SOA logic gate using cross phase modulation (XPM) has the characteristics of large extinction ratio and small chirp compared with other modulation of QD-SOA. The main contents of this paper are as follows:1. According to the theory of QD-SOA, the static and dynamic models of the QD-SOA are established. The laws of carrier concentration and optical field changes are got by Newton iteration method and fourth-order Runge-Kutta method. And this is the right basis of QD-SOA wavelength conversion and logic device.2. Based on the QD-SOA, the wavelength conversion’s characteristics of QD-SOA-XPM are studied. Both noninverting and inverting conversion and phase change characteristics of XPM are analyzed. By changing the injected current, inverting conversions are achieved successfully. When I1 and I2 are 40mA, the converted waveform is a positive phase output,when I1 is 40mA, I1 is 10mA, the output waveform is inverted output. Besides, the regulation of phase change is analyzed starting from the change of carrier concentration.3. Based on the QD-SOA-XPM, the logic OR gate is simulated. The effects on performance of injection current, τw2 。 pump power, pulse width, gmax and the length of active region are studied. According to the simulation analysis, we can get: when increasing the injection current,reducing the τw2 and the gmax, the Q factor and extinction ratio can improved, when increasing the pump power, the pulse width and the length of active region, the change trends of Q factor and extinction ratio are opposite. So the appropriate pump power, pulse width and the length of active region should be selected by balancing Q factor and extinction ratio.4. Based on the QD-SOA-XPM, the all-optical half adder using XOR gate and AND gate is realized. The influences of injection current, τw2 , pulse width, gmax and the length of active region on the performance of half adder are studied. Through the simulation analysis the conclusions are obtained: reducing the τw2, the pulse width and the gmax , reducing the length of active region in the blade can improve the contrast ratio and the pattern effect. But for the external current, the changes of the contrast ratio and the pattern effect are inverted, so the parameters must be selected properly.5. Based on the QD-SOA-XPM, the all-optical half subtracter is simulated, P01/P11 is introduced as the parameter to measure the performance of half subtracter, Through simulation the injection current, τw2 , the pulse width,gmax , the length of the active region influence the performance of the half subtracter. So the better input parameters are obtained. Specifically,when the injection current is 50mA, the pulse width is 0.5ps, the gmax is 1800 m-1, and the active region length is 1.8mm, the performance of all-optical half subtracter is improved.