Self-homodyne interferometric detection in 2×4 optical hybrid for free-space optical communication

The time-delay self-homodyne interferometric detection used in 2×4 90° optical hybrid for free-space optical communication is presented. An asymmetric Mach-Zehnder interferometer splits the received signal into two paths and recombines these two signals after a optical path difference. A balanced receiver follows the interferometer as a multiplier. The modulation contrast in the interferometer depends on the interference of identical wave-fronts, not on the quality of the wave-front itself. So it does not require wave-front compensation techniques, a local oscillator laser nor does it need frequency locking. The scheme can eliminate the effect of wave-front deformation on coherent detection in free-space optical communication effectively.