Low-time jitter optical pulses are widely used in precision ranging, photonic microwave generation, optical frequency comb generation, and photonic sampling. In order to obtain highly stable optical pulses at 1560 nm with an ultra-high pulse frequency of approximately 10GHz, a self-regeneratively ultrafast mode-locked laser with a polarization-maintaining fiber cavity is demonstrated in this paper. The laser adopts a section of polarization-maintaining erbium-doped fiber as the gain medium, a lithium niobate phase modulator as the active modulation device, and the rest of the resonant cavity are composed of passive polarization-maintaining fibers. This results in a total ring cavity length of about 10.7 m. The ring cavity can stimulate multiple longitudinal modes under free running conditions. One of these longitudinal mode frequencies is selected through using a self-built clock extraction and recovery module to generate RF signal with a frequency of 10 GHz. The amplified RF signal at 10 GHz drives the phase modulator and modulates the optical field in the cavity, which results in a stable self-regeneratively mode-locked pulse in the entire laser loop. It quickly achieves a stable ultrafast mode-locked state with a low timing jitter without any external RF reference. A pulse frequency of 10.0076 GHz and a pulse width of 3.14 ps were obtained, together with a side-mode suppression ratio of more than 80 dB and a phase noise of about -110 dBc/Hz@10 kHz. The characteristics of this laser, such as long-time stability, repetition rate, and spectral stability, are investigated in detail. Besides, some typical lasing states in experiments are compared and analyzed.
Chip-scale narrow-linewidth lasers have rich applications in sensing, communication, spectroscopy and light detection and ranging (LiDAR). Self-injection locking is one of the most efficient techniques to reduce linewidth significantly. By locking a laser to an external cavity, some amounts of light reflect back into the laser for mode competition, leading to a significant reduction of the lasing linewidth. In this work, we demonstrated a hybrid-integrated laser with a Microring Resonator (MRR) butt-coupled to a Distributed Feedback (DFB) laser. The radius of the MMR is designed to be 442.3 μm, corresponding to a Free Spectral Range (FSR) of about 50 GHz. And the MMR has a quality factor (Q factor) of 3×106 , fabricated in an ultralow loss silicon nitride (Si3N4) waveguide platform. In this way, the frequency noise has been reduced to 12.565 Hz²/Hz at the 10 MHz offset frequency. Finally, 40 Hz intrinsic linewidth and 91.2 kHz integral linewidth are achieved, characterized by a delayed self-heterodyne interferometer.
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