Optical two-tone signal generation without use of optical filter for photonics-assisted radio-frequency quadrupling

Optical two-tone (OTT) signal generation is demonstrated without optical wavelength filtering for wavelength-free operation in radio-frequency (RF) upconversion assisted by photonics. This principle is based on selective polarization manipulation for the optical carrier; the optical carrier's polarization is first tilted, and the carrier is then suppressed using a polarizer. Owing to optimized conditions obtained from theoretical calculation and the high polarization extinction ratio achieving a 25.7-dB carrier suppression, a 40-GHz separated OTT signal is successfully generated by an optical intensity modulator driven by a 10-GHz sinusoidal RF signal. Conversion into a frequency-quadrupled RF signal is also demonstrated experimentally.