Photonics-based wireless transmission of 16-QAM signals using feedforward compensation of the frequency and phase noise of free-running lasers

Optical heterodyne-based signal generation offers a promising pathway for sub-THz wireless systems. However, the frequency and phase instability of free-running lasers degrade the quality of wireless signals considerably. We experimentally demonstrate a wireless transmission of 16 quadrature amplitude modulation (16-QAM) signals using feedforward frequency and phase compensation applied to the heterodyned output of two free-running lasers. The frequency and phase fluctuations of optically heterodyned signals are detected by using a 90° hybrid coupler and used to drive an optical IQ modulator for compensation. We successfully transmit 80-Gb/s 16-QAM signals at 132 GHz over a wireless channel, achieving distances of up to 30 m without carrier phase estimation at the receiver.