Reconfigurable and Tunable Flat-Top Microwave Photonic Filters Utilizing Optical Frequency Combs

Abstract

We demonstrate reconfigurable and tunable flat-top microwave photonic filters based on an optical comb source and a dispersive medium. Complex taps allowing flexible and tunable filter characteristics are implemented by programming the amplitude and phase of individual comb lines using an optical line-by-line pulse shaper. First, we implement a flat top filter by applying positive and negative weights across the comb lines, then tune the filter center frequency by adding a phase ramp onto the tap weights.

Rapidly Tunable Dual-Comb RF Photonic Filter for Ultrabroadband RF Spread Spectrum Applications

“…5(f). The stopband attenuation level difference of 7.5-13 dB between simulation and measurement may be caused by imperfect amplitude and phase errors in the control of the taps [32]. For different filter passbands, the RF gain is >0 dB with 1-dB variation.…”

“…This advantage is achieved because of the finite impulse response filter design, with filter coefficients easily controlled by the programmable pulse shaper. We have experimentally demonstrated the programmability of the filter passband in the single-comb filtering scheme using a single photodetector [16], [32]. However, RF performance metrics, e.g., RF gain, were not investigated in these studies.…”

“…Fig. 5(a), (c), and (e) shows optical spectra at the output of pulse shaper1 for flat-top, Gaussian, and Sinc (with Kaiser window [32], [43]) shapes, respectively. The output comb shapes of both pulse shapers are close to identical.…”

“…The EO comb source [22]- [29] provides one good choice for the dispersivetapped delay line schemes [16] because it can provide many dozens of evenly spaced optical frequencies with gigahertz repetition rate, good spectral flatness, high coherence, and low noise. In conjunction with a programmable pulse shaper that enables precise control of the individual filter taps, programmable filters with arbitrary amplitude and phase responses can be realized [16], [30]- [32]. Although not adopted here, it is worth noting that through self-phase modulation-based spectral broadening of the EO comb in a highly nonlinear fiber, the number of optical comb lines and hence filter taps can be further increased, as in recent demonstrations of RF photonic phase filters with over 160 filter taps [30], [31].…”

Reconfigurable Filter-free Sinc-shaped RF Photonic Filters Based on Rectangular Optical Frequency Comb

“…Compared to its electrical counterpart, this approach is favored due to the broad bandwidth and low losses rendered by optical fibers, as well as arbitrary RF filter shape empowered by lineby-line shaping of the optical frequency comb [2,3]. For instance, highly selective rectangular RF filter shape has been demonstrated using programmable pulse shapers to tailor optical frequency comb [4] or slice ASE source [5]. From a communication perspective, sinc-shaped RF photonic filters may offer great potential to high-speed orthogonal frequency division multiplexing (OFDM), optimizing the spectral efficiency among electrical, optical, and wireless applications.…”