All-optical generation of ASK, PSK, and FSK radio-frequency signals

Abstract

In wireless communication networks, the amplitude, phase, and frequency of a radio-frequency (RF) carrier is modulated to carry data signals. Generally, amplitude-shift keying (ASK), phase-shift keying (PSK) and frequency-shift keying (FSK) are served as the basic digital modulation formats. They are also the fundamental modulation schemes to form advanced modulation formats such as quadrature amplitude modulation (QAM) and quaternary phase-shift keying (QPSK). In order to extend the transmission distance of RF signals, radio-over-fiber technique has been proposed. In this context, it is highly desirable to generate ASK, PSK and FSK RF signals directly in the optical domain. In this paper, we report our recent works on the all-optical generation of ASK, PSK, and FSK RF signals based on cross polarization modulation (XPM) effect in nonlinear devices. For the generation of ASK RF signal, single-sideband (SSB) modulation and SSB upconversion is proposed to overcome the fiber chromatic dispersion induced power fading. Moreover, binary PSK RF signal is generated using XPM effect in a highly nonlinear fiber (HNLF). The precise phase shift of the PSK RF signal is independent of the optical power of the control beam. In addition, all-optical FSK RF signal is generated based on ASK to FSK modulation in an HNLF. The significant merit of this all-optical scheme is that the electrical bottleneck can be overcome thanks to the ultra-fast response of the nonlinear media. Thus, the carrier frequency of the phase-coded microwave signal is widely tunable. We have examined our schemes theoretically and experimentally. The proposed all-optical approach has the potential to realize uninterrupted transmission of the RF signals over fiber across different networks to the remote locations.