Abstract
An optoelectronic oscillator (OEO) with wideband frequency tunability and stable output based on a bandpass microwave photonic filter (MPF) has been proposed and experimentally demonstrated. Realized by cascading a finite impulse response (FIR) filter and an infinite impulse response (IIR) filter together, the tunable bandpass MPF successfully replaces the narrowband electrical bandpass filter in a conventional single-loop OEO and serves as the oscillating frequency selector. The FIR filter is based on a tunable multi-wavelength laser and dispersion compensation fiber (DCF) while the IIR filter is simply based on an optical loop. Utilizing a long length of DCF as the dispersion medium for the FIR filter also provides a long delay line for the OEO feedback cavity and as a result, optical tuning over a wide frequency range can be achieved without sacrificing the quality of the generated signal. By tuning the wavelength spacing of the multi-wavelength laser, the oscillation frequency can be tuned from 6.88 GHz to 12.79 GHz with an average step-size of 0.128 GHz. The maximum frequency drift of the generated 10 GHz signal is observed to be 1.923 kHz over 1 hour and its phase noise reaches the -112 dBc/Hz limit of our measuring equipment at 10 kHz offset frequency.
Highlights
Featuring extremely low phase noise, high stability and spectral purity, as well as potentially high oscillation frequency, optoelectronic oscillators (OEOs) are of great interest among the research community and have found potential applications in numerous fields such as wireless communication, radar systems, and photonic signal processing [1,2,3,4]
Based on a microwave photonic filter (MPF) implemented by cascading an infinite impulse response (IIR) filter to a tunable finite impulse response (FIR) filter, we have proposed and experimentally demonstrated a low phase noise OEO with wideband tunability and good stability
Due to the multi-tap bandpass FIR filter with a long dispersion medium, which is fed by a multi-wavelength laser, wideband tuning and low phase noise performance are obtained at the same time for the proposed OEO
Summary
Featuring extremely low phase noise, high stability and spectral purity, as well as potentially high oscillation frequency, optoelectronic oscillators (OEOs) are of great interest among the research community and have found potential applications in numerous fields such as wireless communication, radar systems, and photonic signal processing [1,2,3,4]. With high frequency narrowband EBPFs being difficult to manufacture and tune, various alternative schemes for OEOs have been proposed with the motivation to overcome this limitation and bring out the aforementioned advantageous features of the OEO One such improved OEO scheme is the utilization of multi-loop structure which involves combining the high Q factor and larger mode spacing of a long and short feedback loop, respectively [5,6,7,8], easing the stringent requirements on EBPFs. Structures of multiple optoelectronic loops and dual injection-locked OEO loops have been demonstrated in [5, 6] and [7, 8], respectively and all these schemes feature ultra-low phase noise and spurious level. The maximum frequency drift of the generated 10.03 GHz signal is 1.923 kHz over 1 hour and its phase noise reaches the −112 dBc/Hz limit of our measuring equipment at 10 kHz offset frequency
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