Ultrafast Dynamics And All Optical Correlator Of QD-SOA

Optical packet switching (OPS) is one of the main streams of the future all optical networks because it operates the high speed optical packets in the optical domain, which can avoid the optical-electrical-optical conversion and breakthrough the electrical "bottleneck". The key technology for OPS is high-speed all optical signal processing.Compared with the bulk semiconductor optical amplifier (SOA) and the quantum well semiconductor optical amplifier, the quantum dot semiconductor optical amplifier (QD-SOA) is more suitable for the high-speed all optical signal processing due to its outstanding characteristics of temperature low-sensibility, small linewidth enhancement factor, high differential gain, and fast carrier recovery. In this dissertation, we established a multi-level model to investigate the dynamics of the QD-SOA, which includes the rate equations of carriers on every energy level in the conduction band and valence band, the rate equations of the signal photons and the amplified spontaneous emission (ASE) photons based on the spectrum division. Theories and simulations have been detailed performed to study the ultrafast dynamics and all optical correlators based on the QD-SOA.The main topics are briefly described as follow.1. The dependences of the maximal energy efficiency and the optimized active region length on the input power and the saturated power are obtained with both two-level and three-level models. With the spectra division method and the multi-level model, the ASE properties can be discussed in detail accurately, and it shows that the ASE will be more suppressed by higher input signal power.2. The ultrafast dynamics of the QD-SOA have been numerically studied with the gain dynamics, phase dynamics and the frequency chirp of the optical pulse. The dynamic of the phase is faster than that of the gain, and it will advance more with higher input peak power or longer active region. The spectrum will split because of the frequency chirp, and the red-shift decreases and blue-shift increases with higher input peak power.3. QD-SOAs with nonuniform active area are analyzed, it shows that the width non-uniformity can’t matter the characteristics while the average width keeps constant, and only the height non-uniformity will affect the QD-SOA’s dynamics. The modal gain and optical gain are calculated for several different height non-unifomity, and the results demonstrate that the gain of QD-SOA reaches its maximum when the variance of the occupation probability of the electrons on the ground states is minimum for particular height non-uniformity.4. In order to investigate the all optical multi-bit correlator, the transfer function of the QD-SOA Mach-Zehnder interferometer (QD-SOA-MZI) is analyzed, and a few optical logic gates, such as’AND’,’NOT’, and’XOR’, are emulated at500Gbps. The Q factor of the output logic signal increases with increase of the injection current and decrease of the pulse width, and decreases with the increase of the single pulse energy. An8-bits correlator at the bit rate of500Gbps is emulated with a tandem9-stage QD-SOA MZIs. Only one pulse will output at the last bit when all bits of both input signals are identical.5. With the theory of four wave mixing (FWM) and plenty of simulations, the efficiency of FWM in QD-SOA increases apparently with the increase of the pump power, the active region length, and the injection current, and it decreases while the wavelength spacing between the pump and the probe light increases, and the efficiency decreases gently with the increase of the power of the probe light. In the simulations, the logic’XOR’at100Gbps for DPSK signals have been implemented simultaneously at three different wavelengths, as well as the wavelength conversion at100Gbps for RZ-DQPSK and NRZ-DQPSK.6. The gain and phase dynamics of the control signal and probe signal have been discussed in a gain-transparent (GT) QD-SOA. It shows that the amplitude of the probe signal does not experience any change, while the phase of the probe signal is modulated due to the carrier density modulation by the control signal. The higher the power of the control signal is, the larger the phase change of the probe signal is. The switch characteristics of the nonlinear optical loop mirror (NOLM) based on the GT QD-SOA are analyzed with the simulations of all optical format conversion from RZ-OOK to DPSK and from NRZ-OOK to DPSK at250Gbps.