Abstract
Microwave photonic bandpass filters (MPBPFs) are important building blocks in radio-frequency (RF) signal processing systems. However, most of the reported MPBPFs fail to satisfy the stringent real-world performance metrics, particularly low RF insertion loss. In this paper we report a novel MPBPF scheme using two cascaded integrated silicon nitride (Si3N4) ring resonators, achieving a high link gain in the RF filter passband. In this scheme, one ring operates at an optimal over-coupling condition to enable a strong RF passband whilst an auxiliary ring is used to increase the detected RF signal power via tuning the optical carrier-to-sideband ratio. The unique combination of these two techniques enables compact size as well as high RF performance. Compared to previously reported ring-based MPBPFs, this work achieves a record-high RF gain of 1.8 dB in the passband, with a high spectral resolution of 260 MHz. Furthermore, a multi-band MPBPF with optimized RF gain, tunable central frequencies, and frequency spacing tunability is realized using additional ring resonators, highlighting the scalability and flexibility of this chip-based MPBPF scheme.
Highlights
Microwave photonic filters (MPFs) eliminate unwanted interference and channelize the signal of interest, which play an important role in numerous applications such as RF receivers [1], as well as enabling optoelectronic oscillator (OEO) [2]
We have demonstrated a Microwave photonic bandpass filters (MPBPFs) based on cascaded silicon nitride ring resonators, exhibiting key features of high gain, low noise figure, and large spurious free dynamic range (SFDR)
The comprehensive theoretical model for ring-resonator-based MPBPF was established, and the RF gain to full width at half magnitude (FWHM) ratio of the filter is for the first time introduced and optimized
Summary
Microwave photonic filters (MPFs) eliminate unwanted interference and channelize the signal of interest, which play an important role in numerous applications such as RF receivers [1], as well as enabling optoelectronic oscillator (OEO) [2]. In [5,6], the combined use of an intensity modulator and a ring resonator based on one-to-one spectrum mapping from the optical filter response to RF domain was demonstrated. In order to improve the extinction ratio, phase-modulator-based ring resonator approaches using RF interference cancellation was reported [7,8,9,10,11]. In [7,8,9,10], an MPBPF using a silicon-on-insulator (SOI) ring resonator as an optical notch filter to achieve phase modulation to intensity modulation conversion was proposed. In [11], a MPBPF with a 3 dB bandwidth of 0.673∼2.798 GHz based on a Si3N4 ring resonator and phase modulation was demonstrated
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