A voice optical communication system based on FPGA and acoustic optical modulator(AOM) was proposed to explore the low rate codec algorithm for voice communication. The μlaw algorithm for voice codecs was optimized and then transplanted in FPGA. The communication system, which adopts atmospheric channels, is conducted in double optical path and fullduplex mode. Light sources of the system consist of a high power internal modulated LED and a 637 nm allsolidstate laser which is external modulated by AOM. For performance evaluation, a shortrange communication experiment and a indoor 80 m communication experiment were conducted. In view of the above two cases, the achieved serial communication rate is both 80 kbps, and MOS rate is both higher than 3. However, the bit error rate for the 2 experiments is lower than 0.0001% and 0.0012%, and the call duration is 3 h and 1.5 h, respectively. Experimental results showed the capacity of using the system for low bit rate speech optical communication.