ABSTRACT
The intersatellite microwave photonics link with an optical preamplifier is affected by third-order intermodulation distortion under dual-tone modulation and pointing errors due to beam wander, which would greatly degrade the link performance. An exact analytical expression for signal-to-noise and distortion ratio (SNDR) is derived considering the signal fade caused by the pointing errors of transceiver. It is shown that, given the desired SNDR and the rms random pointing jitter, an optimum modulation index of Mach-Zehnder modulator exists that minimizes laser output power. Moreover, an optimized model for laser output power and modulation index is established. The effects of the optical preamplifier gain and noise figure on the optimum link performance are also examined. Numerical results show that the minimum laser output power required to achieve the desired SNDR is more sensitive to the preamplifier noise figure. For an SNDR of 20 dB, doubling the preamplifier noise figure results in an 8.95 dB increase in minimum laser output power at the rms pointing jitter of 0.5 µrad.
ABSTRACT
An optical preamplifier is utilized to improve the signal-to-noise and distortion ratio (SNDR) of intersatellite microwave photonic links employing a Mach-Zehnder modulator under dual-tone modulation. The resulting SNDR at an appropriate direct current (DC) bias phase shift is additionally investigated without small-signal approximation in order to optimize the performance of all the links. It is observed that the most limiting factor degrading the SNDR performance is changed, and the fundamental power is seen to increase more compared with the power of third-order intermodulation (IM3) plus noise due to the optical preamplifier. Thus, SNDR can be improved with respect to the case of a nonoptical preamplifier. For the preamplifier gain of 20 dB and noise figure of 3 dB, an increase of about 24 dB in optimum SNDR is accessible. In addition, the optimum DC bias phase shift is found to be insensitive to the preamplifier gain and noise figure, while the optimum SNDR is sensitive to the preamplifier gain and noise figure.
ABSTRACT
An exact analytical expression of the signal-to-noise ratio (SNR) for an intersatellite microwave photonics link with an optical preamplifier is derived considering the signal fade caused by the pointing errors of the transceiver, and an optimized model for laser output power and direct current (DC) bias phase shift of the Mach-Zehnder modulator is established. It is shown that, given the desired SNR and the root mean square (rms) random pointing jitter, an optimal DC bias phase shift exists that minimizes laser output power. The effects of the optical preamplifier parameters on the minimum laser output power and optimal DC bias phase shift are also examined. Numerical results show that the preamplifier noise figure determines the minimum laser output power needed to achieve the desired SNR but affects the optimal DC bias phase shift little. For a SNR of 20 dB, doubling the preamplifier noise figure results in a 6.36 dB increase in minimum laser output power for rms pointing jitter of 0.4 µrad.