RF photonic channelizers can overcome limitations of conventional electronic methods for analysis of wideband RF spectral content. Here, we will present a recent progress on the RF photonic channelizer systems that are based on optical parametric combs. These systems can analyze very wide RF bandwidths exceeding 100GHz, therefore providing essential capability for the applications demanding a wide-bandwidth spectral analysis. The RF channelizers being presented utilize parametric processes in the highly non-linear fiber mixers to generate a large number of RF signal copies in the optical domain. Two different implementations for generation of RF signal copies will be presented and compared: one using a parametric multicasting and another utilizing a direct comb modulation. Generation of optical combs spanning more than 10THz will be shown. We will also present two distinct system architectures for RF photonic channelizer system: one employing a periodic optical filter such as Fabry-Perot etalon to select channels from the signal comb, and another one utilizing a coherent detection between a frequency-locked signal comb and a parametrically generated local oscillator (LO) comb. The second scheme gives benefit of providing both in-phase and quadrature (I/Q) information on channelized intermediate frequency (IF) signals. We will present a system with 32 implemented channels using a filtered scheme and a 32-channel coherent system with a full-field detection implemented on one tunable channel. Sensitivity and dynamic range as well as benefits of both system architectures will be discussed.
A photonic microwave signal generator is assembled utilizing self-oscillation and bidirectional modulation in a LiNbO3-phase modulator. The generated frequency is determined by the round trip of an outer and an inner fiber cavity, in addition to a narrow bandpass electrical filter in the feedback loop. A Faraday mirror reflects the light in the outer fiber cavity, and the polarization shift enhances the stability of the oscillation. Light is detected in the inner cavity, using a photodetector followed by a filter and a high power electrical amplifier. The modulator is thereby driven at several Vπ by the detected output signal. In our experiment, the oscillation is locked on 10 GHz, but generate harmonic frequencies which are extracted through narrowband Brillouin amplification. The output of the system is thus only dominated by two frequencies in the optical domain, separated by arbitrary harmonic of the oscillator frequency. This technique is shown for generation of 60 GHz microwaves, limited mainly by the amount of phase-shift that can be achieved in the modulator. It is a simple technique that does not require an electrical signal generator, or any electronics faster than 10 GHz.