Low-Phase-Noise Ultra-Wide Arbitrary Waveforms Generation Using a Wideband Injection-Locked Optoelectronic Oscillator

We propose and demonstrate a photonic approach to generating low-phase-noise ultra-wide arbitrary waveforms based on a wideband injection-locked optoelectronic oscillator (OEO). A seed wideband microwave signal from an external microwave source is injected into the OEO loop. When the period of the seed signal is equal to the round-trip time of the loop, injection locking works and a continuous-wave wideband microwave signal, of which the center frequency and bandwidth are identical to that of the seed signal, is generated by the OEO. Thanks to the long fiber loop, the phase noise of the generated wideband microwave signal is highly improved. To increase the bandwidth of the generated signal, photonic-assisted microwave frequency multiplication is leveraged, and an ultra-wide bandwidth is resulted. By tuning the seed signal in terms of center frequency, bandwidth, and frequency pattern, the generated ultra-wide microwave signal is also tuned correspondingly. An experimental demonstration is performed in which a high-speed dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM) is incorporated. The upper X-polarized DDMZM is used to realize the OEO loop; the lower Y-polarized DDMZM is employed for frequency multiplication. When a seed linearly chirped signal with a bandwidth of 3 GHz is injected, a same microwave signal is generated, of which the phase noise is measured to be -124 dBc/Hz@10 kHz, more than 20 dB improvement compared to that of the seed signal, and a frequency stability with an Allan deviation is 3.72 × 10^-12@1s, almost the same as that of the seed signal. With the use of photonic-assisted frequency multiplication, a frequency-quadrupled signal with a bandwidth as broad as 12 GHz is also generated. By tuning the seed microwave signal, fully tuning of the ultra-wide microwave waveforms is also experimentally demonstrated. In particular, by controlling the loop gain, microwave pulses with different duty cycles are generated. Our proposed approach combines the distinct advantages of photonic generation in terms of low phase noise and ultra-wide bandwidth, and of electronic generation in term of fully tuning, which takes a big step forward practical application.