We propose a communication system of Circular Polarization Shift Keying (CPolSK) with homodyne coherent detection in free-space optical (FSO) communication with Gamma-Gamma atmospheric turbulence channel. The system need no polarization coordinate alignment, thus the complexity is reduced. Meanwhile, we derived the closed bit error rate (BER) expression of the system compared with the coherent on-off keying (OOK) system. Simulation results show that CPolSK with homodyne system is highly insensitive to the phase noise and BER performance is greatly promoted compared to OOK modulation, the signal-to-noise ratio (SNR) of receiving is reduced about 8dB when the system has the same BER performance under same conditions.
A novel solution of frequency locking based on beat frequency detection in homodyne coherent receiver is presented and experimentally demonstrated. The beat frequency detection, using two beat frequency signals generated by a balance detector module, is easily to eliminate the noise introduced during long distance transmission. Furthermore, FPGA, as the core of the control unit, is adopted to change the resulting frequency of OVCO on the basis of the frequency deviation. The proposed scheme is tested more efficiency and higher stability than the previously single path feedback loop.
We propose a detection scheme called Stokes vector direct detection (SV-DD) to realize high electrical spectral efficiency and cost-effective optical communication , which is more suitable than coherent detection for short-reach. At reception, the signal is detected in Stokes space.SV-DD is different from conventional DD technique in the parts of not requiring polarization tracking or narrow band optical filtering for carrier extraction. 2nd-order nonlinearity due to photodetection is a fundamental limitation for DD. The conventional SV-DD systems use 2*4 coupler in the receiver, it makes 2nd-order nonlinearity much serious since there are four photodetections or two balance photodetections. In this paper, we experimentally demonstrate the SVDD scheme in single-carrier system using a 3*3 coupler with three photodetections in the receiver.
In this paper, we mainly introduce a novel measurement system of the polarization extinction ratio(PBSBC system). Here, because the main optical components of the system is PBS and PBC, so we call this system PBSBC system. First of all, we introduce the principle of method of measuring the polarization extinction ratio by drawing a circle on the Poincare. Secondly, we present the system block diagram of PBSBC system, and design an experimental system to theoretically and experimentally investigate the performance of this system though the multiple groups of experimental data collected under the same condition. Finally, we could show that it is compatible with the analysis in PBSBC system.