Fig. 1. (a) Schematic of Fourier domain mode-locked optoelectronic oscillator (FDML OEO) enabled by chip-integrated thin-film lithium niobate phase modulator and electrically tuned micro-ring resonator. LD, laser diode; PC, polarization controller; MRR, micro-ring resonator; EDFA, erbium doped fiber amplifier; DCF, dispersion compensation fiber; PD, photodetector; LNA, low noise amplifier; AFG, arbitrary function generator. (b) The operation principle of the PM-IM conversion enabled MPF. (c) Microphotograph of the fabricated chip and MRR.

Fig. 2. Characterization of the MRR. (a) The measured transmission spectrum of the MRR. Inset: a zoom-in-view of the transmission spectrum of a resonance peak. (b) The wavelength shift of a resonance peak as the applied DC voltage varies. (c) The peak wavelength of the MRR resonance as a function of the applied DC voltage extracted from (b).

Fig. 3. Measurement of the voltage response rate of the MRR. (a) Illustration of the MRR response rate measurement. Red denotes the driving signal applied to the MRR, black denotes the center frequency of the laser incident on the MRR, and yellow, purple, and green denote the notch of the MRR corresponding to different moments t1, t2, and ti, when the MRR is modulated. (b) The experimental setup for measuring the response rate of MRR. LD, laser diode; PC, polarization controller; AFG, arbitrary function generator; OSC, oscilloscope; APD, avalanche photodetector. (c) The temporal width of the notch as a function of the frequency of the driving signal applied to the MRR. Blue denotes the experimental results, and red denotes theoretical results. Inset: a zoom-in-view of the curves from 2 MHz to 5 MHz. (d–i) Temporal waveforms of the APD output (blue) and the driving signal applied to MRR at 1 MHz. (d-ii) Zoom-in-view of the notch’s temporal waveform. (e-i) Temporal waveforms of the APD output (blue) and the driving signal applied to MRR at 3 MHz. (e-ii) Zoom-in-view of the notch’s temporal waveform.

Fig. 4. (a) Measured spectrum of the generated LCMW with a scanning bandwidth of 8.5 GHz from 17.7 GHz to 26.2 GHz (the span of the electrical spectrum analyzer is 10 GHz). (b) Zoom-in-view of the spectrum at around 22.003 GHz with a 2 MHz span. (c) Measured optical spectrum of the generated LCMWs with a bandwidth of 8.5 GHz.

Fig. 5. Experimental results of the FDML OEO. (a) The temporal waveforms of the generated LCMW with a scanning bandwidth of 8.5 GHz (green) and the sawtooth wave signal applied to the MRR (orange). (b) Spectrogram of the generated LCMW with a bandwidth of 8.5 GHz. (c) Linear fit of the frequency sweep of a single period. (d) Autocorrelation of the generated LCMW. Inset: zoom-in view of the LCMW autocorrelation.

Fig. 6. Tuning of the scanning bandwidth and the center frequency of the integrated FDML OEO. (a) Spectra of the generated LCMWs with a scanning bandwidth from 3.85 GHz to 8.5 GHz at a center frequency of 22.5 GHz. (b) Spectra of the generated LCMWs with a scanning bandwidth of 3.85 GHz at center frequencies from 18.55 GHz to 23.59 GHz.

Fig. 7. Measured phase noise of the FDML OEO. (a) Measured phase noise curves of the oscillations at 20 GHz (pink), 21 GHz (red), 22 GHz (orange), 23 GHz (cyan), 24 GHz (green), and 25 GHz (blue) from the OEO with a loop length of 500 m, as compared with that of a 20 GHz signal from a commercial microwave source (Keysight E8257D). (b) Measured phase noises of the OEO at a frequency-offset of 10 kHz for various frequencies extracted from (a).