Cascaded acousto-optical system for modulation of unpolarized light

A cascaded system of two acousto-optical cells is proposed for equalization of multichannel optical signal satisfying coarse wavelength-division multiplexing standard. Two similar acousto-optical modulators for unpolarized light on the basis of 10 degrees-cut paratellurite crystals were used in a free-space gap of a fiber line. The system controlled intensity of several optical carriers in the spectral range from 1200 to 1700 nm. The device was tested in a four-channel regime of operation in the range 1510-1570 nm. Overall optical insertion losses did not exceed -2 dB and less than 1 W electric power per channel was necessary for -20 dB intensity attenuation of the signal in a continuous operation mode. Compensation for birefringence in paratellurite provided diffraction regime that was insensitive to polarization of light. Interchannel crosstalk was less than -10 dB.