Comb-Based RF Photonic Filters Based on Interferometric Configuration and Balanced Detection

Abstract

We demonstrate a novel technique to improve radio frequency (RF) performance such as RF gain and noise figure (NF) for comb-based RF photonic filters. While conventional RF photonic links use a dual-output modulator and balanced detection, this RF photonic filter utilizes an interferometric configuration with double sideband suppressed carrier modulation and balanced detection. This technique can simultaneously provide filter tunability, 6-dB RF gain increase, and noise cancellation. The RF gain and NF of the RF photonic filter are improved to approximately 0 and 24 dB, respectively. With the improved RF performance, we perform the tuning of the filter center frequencies from 2 to 8 GHz with no baseband filter response (<−38 dB), no RF power fading, while maintaining good filter shape (sidelobe suppression and stopband attenuation >32 dB).

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

“…1 and 2, respectively, show the configuration and a photo of the dual-comb RF photonic filter using differential detection. This filter configuration is based on our previous work on RF photonic filters reported in [33] and [34]. The novelty of our current implementation is that for the first time, we are able to simultaneously achieve attractive features shown separately in our previous filter designs, such as rapid frequency tuning in [33] and good RF metrics and frequencyindependent RF gain in [34].…”

“…The dual-comb configuration enables high-speed optical delay control and thus results in rapid filter frequency tuning on tens of nanosecond time scales. In addition, double-sideband modulation with suppressed carrier (DSB-SC) modulation and differential detection are used [34]. These techniques significantly suppress intensity noise, generating from the laser and optical amplifiers, and thus provide good RF metrics.…”

“…The polarization-multiplexed signals are passed through a dispersive element and directed to a polarization beam splitter. The single dispersive element with polarization multiplexing is used to provide two nearly identical signal paths for differential detection [34]. Note that the principal axes of the polarization beam splitter following the dispersive element are aligned to have an angle of 45°to the polarization state of the signals coming from either the upper or lower arm of the interferometer.…”

“…Because the MZM generates optical double sidebands, there are two filter passband terms within one filter free spectral range (FSR = 1/T , where T is the filter differential tap delay), pointed out by the ± sign in (1) [34]. In (1), the first phase terms indicate that there are filter passbands due to the differential tap delay (T = ψ 2 ω), originating from the second-order dispersion of the dispersive element.…”

“…Here, for the first time in this dual-comb scheme, we exploit differential detection, increasing RF gain by a factor of two and suppressing common mode intensity noise [20], [34], [35]. In addition, the optimization of the filter configuration using the dual-comb source provides much better RF gain; gain up to ∼1 dB is achieved, which is similar or slightly higher than that obtained with a single-comb source in [34] (e.g., RF gain ∼0 dB). Instead of the previous periodic optical notch filter, here we suppress the filter baseband response by setting the bias point of the Mach-Zehnder modulator (MZM) at Configuration of the RF photonic filter using dual-comb configuration and differential detection.…”