Δ-Σ変調方式による空間光伝送装置の研究開発

概要

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This paper describes development of a free space optical communication system with the delta-sigma modulation scheme. The delta-sigma modulater can convert analog signals into 1 bit digital signals whose SNR against the quantum noise is equal to maltibit AD converters by means of over sampling and noise shaping. Constructed second-order delta-sigma modulator has 256 over sampling ratio that causes the same ability of 18-bit AD converters, and has 16 kHz band width from dc to 16 kHz. The 1 bit digital signal obtained by the second-order delta-sigma modulator drives a 780 nm-diode laser. The laser beam is passed through the atmosphere over 30m and disturbed by the atmospheric turbulence. To reduce the effect of the atmospheric turbulence on the optical digital signal, we use a comparator in the receving circuit to clear the smeared digital signal. The SNR is 37.56 dB without the comparator, while it is 45.26 dB with the comparator.
福山大学の論文