The application of coherent detection to indoor optical free-space communications is considered here. Analytical expressions are derived for a wide line-of-sight (W-LOS) optical link which determine the coverage area and the required photo-detection area given different binary digital transmission schemes and a given bit rate. The coverage area is maximised for systems using both metal-semiconductor-metal (NISM) and PIN photo-detectors. Results show that MSM photo-detectors, due to their inherently lower capacitance per unit photo-detection area, result in a greater coverage area than their PIN counterparts. To demonstrate the viability of implementing coherent detection indoors, a 200 Mb/s LOS optical link which uses coherent detection is also reported.
Jafar, M., O'Brien, D. C., Stevens, C. J., & Edwards, D. J. (2008). Evaluation of coverage area for a wide line-of-sight indoor optical free-space communication system employing coherent detection. IET Communications, 2(1), 18-26. https://doi.org/10.1049/iet-com:20060225