All-fiber-photonics-based ultralow-noise agile frequency synthesizer for X-band radars

We propose and demonstrate an agile X-band signal synthesizer with ultralow phase noise based on all-fiberphotonic techniques for radar applications. It shows phase noise of-145 dBc∕Hz(-152 dBc∕Hz) at 10 kHz(100 kHz) offset frequency for 10 GHz carrier frequency with integrated RMS timing jitter between 7.6 and 9.1 fs(integration bandwidth: 10 Hz–10 MHz) for frequencies from 9 to 11 GHz. Its frequency switching time is evaluated to be 135 ns with a 135 pHz frequency tuning resolution. In addition, the X-band linearfrequency-modulated signal generated by the proposed synthesizer shows a good pulse compression ratio approximating the theoretical value. In addition to the ultrastable X-band signals, the proposed synthesizer can also provide 0–1 GHz ultralow-jitter clocks for analog-to-digital converters(ADC) and digital-to-analog converters(DAC) in radar systems and ultralow-jitter optical pulse trains for photonic ADC in photonic radar systems.The proposed X-band synthesizer shows great performance in phase stability, switching speed, and modulation capability with robustness and potential low cost, which is enabled by an all-fiber-photonics platform and can be a compelling technology suitable for future X-band radars.

Widely tunable ultra-narrow-linewidth dissipative soliton generation at the telecom band

Ultra-narrow-linewidth mode-locked lasers with wide wavelength tunability can be versatile light sources for a variety of newly emergent applications.However,it is very challenging to achieve the stable mode locking of substantially long,anomalously dispersive fiber laser cavities employing a narrowband spectral filter at the telecom band.Here,we show that a nearly dispersion-insensitive dissipative mode-locking regime can be accessed through a subtle counterbalance among significantly narrowband spectral filtering,sufficiently deep saturable absorption,and moderately strong in-fiber Kerr nonlinearity.This achieves ultra-narrow-linewidth(a few gigahertz)nearly transform-limited self-starting stable dissipative soliton generation at low repetition rates(a few megahertz)without cavity dispersion management over a broad tuning range of wavelengths covering the entire telecom C-band.This unique laser may have immediate application as an idealized pump source for high-efficiency nonlinear frequency conversion and nonclassical light generation in dispersion-engineered tightly light-confining microphotonic/nanophotonic systems.