A difference frequency generation optical transmitter and sum frequency generation optical receiver operating in the mid-infrared wavelength range for use in free space optical satellite communications are described. By using mid-infrared light, the transmitter/receiver can mitigate atmospheric scintillation, scattering, and other non-ideal optical effects in the communication channel. This is achieved through the use of nonlinear optical crystals designed for difference frequency generation in the case of the transmitter and sum frequency generation for the receiver. High-speed modulated communication signals can thus be frequency converted to the mid-infrared wavelength range by a relatively low cost, compact and high-power optical communication system.