Abstract: An apparatus for generating an FSK-modulated optical signal has an optical two-filter FSK super-heterodyne receiver. The optical signal has two different polarization conditions that are orthogonal to one another. Due to the two-filter receiver and orthogonal conditions, polarization-independent reception is possible. Conversion of the polarized, optical signal into the optical signal having the orthogonal polarization conditions is accomplished by a switching device. Each condition has a corresponding bit status of a data signal. The data signal effectively controls the polarizatiion of the optical signal. Hence, the frequency boost can be freely selected while maintaining excellent bandwidth characteristics and optimum sensitivity.