Three dimensional amplitude modulation and demodulation technology based on independent dual sideband optical communication system

Abstract

This article proposes the use of Three Dimensional Amplitude Modulation (TDAM) and demodulation techniques in independent dual sideband systems without increasing the modulation order of the carrier amplitude. This system generates two columns of random binary sequences digitally. One is modulated with 3D-8QAM at −13 GHz, and the other is modulated with 3D-8QAM at 29 GHz with half amplitude. Then, the three dimensions x, y, and z of the three-dimensional signal are modulated onto the carriers $\cos \left(\omega t\right)$, $\sin \left(\omega t\right)$ and $\cos \left(\omega t\right)\ast \sin \left(\omega t\right)$, respectively, so that the left and right independent sidebands are superimposed in the IQ modulator. At the receiving end, two independent sideband signals are received through a single photodiode (PD). After PD square law conversion, a three-dimensional 8TDAM signal is synthesized, and then separated and demodulated by a digital signal processing (DSP) to obtain two separate three-dimensional signals. The simulation results show that the system can successfully achieve 8 Gbaud independent 8TDAM signal 20 km SSMF transmission, with an HD-FEC threshold of 3.8 × 10⁻³ and an error rate of 7 %. The system has demonstrated that three-dimensional signals can be transmitted independently in both sidebands, greatly simplifying the system structure, further reducing implementation costs, and improving spectral efficiency. The highest spectral efficiency can reach 3.692bit/s/Hz.