We proposed and demonstrated an all-fiber Nonlinear Polarization rotation (NPR) erbium-doped mode-locked laser, which reduces the laser repetition rate to 5.7 MHz based on a Large Mode Area Fiber (LAMF). In addition, the laser 3 dB bandwidth is extended to 86.4 nm by using extra cavity supercontinuum broadening. To the best of our knowledge, this is the first time to obtain a broadband output using such a low repetition rate mode-locked laser. This broadband low repetition rate mode-locked laser signal is then applied to time-stretched Optical Coherence Tomography (OCT). The swept source can achieve an imaging range of more than 85 mm and a sensitivity roll-off of 3.5 dB in OCT. The all-fiber low repetition rate broadband swept source based on time-stretching technology has a compact structure and high stability, and is very promising in the field of frequency measurement and high-resolution OCT.
Precise dispersion measurement is important for various applications, including optical communications, laser cavity design, and nonlinear optics. In this work, we present a dispersion measurement method for the fiber under test inside the Fourier Domain Mode-Locked (FDML) laser by locating the sweet spot regime under the different driving frequencies of the Fabry-Perot tunable filter. The group delay resolution achieved is 2.88 ps, an order of magnitude higher than other dispersion measurement methods based on phase shift or pulse delay. The proposed dispersion measurement method has high resolution and simple configuration, making it promising for measuring the dispersion of special fibers or conventional fibers near their zero-dispersion wavelengths.
A novel scheme for generating ultra-narrow linewidth and ultra-low noise photonic microwave based on simultaneous self-injection locking of dual DFB lasers is proposed and demonstrated. Herein, two narrow linewidth DFB lasers can be independently achieved by Rayleigh backscattering excited in a micro-resonator as feedback for self-injection locking. The 3-dB linewidth of the DFB laser is compressed from 320 kHz to 1.5 kHz, which is narrowed by 2 orders of magnitude. Based on dual narrow linewidth lasers locked to the same micro-resonator, an all-optical high-performance photonic microwave signal is generated by using the optical heterodyne method. The photonic microwave signal with the single sideband phase noise of −102 dBc/Hz and frequency noise of 600 Hz2/Hz is obtained at a frequency offset of 1 MHz for the generated 5.42 GHz microwave. The proposed scheme is also applicable to any other type of lasers such as VCSEL, fiber lasers et al, which provides a new perspective for the generation of ultra-low noise microwave signals.
Thin film lithium niobate (LN) is considered a promising platform for integrated photonics owing to its exceptional electro-, nonlinear-, and acousto-optic properties. In this work, we propose the generation of broadband optical frequency combs in an LN microring resonator by dispersion engineering. We design the structure of the LN waveguide to adjust the effective refractive index of its fundamental mode so that the microring resonator can generate two dispersive waves near the pump light to achieve a broadband optical frequency comb up to 4/5-octave range (about 110 THz). The broadband frequency comb is crucial for future on-chip LN nonlinear photonics applications.
We demonstrate the generation of Kerr frequency combs with controllable intracavity soliton states by seeding the single continuous wave (CW) driven two coupled nonlinear microresonators with a pulsed trigger. The stable one-, two-, or three-soliton frequency comb can be realized deterministically simply by adjusting the pulse intensity of the trigger signal. Numerical simulations show that the generation of the mode-locked soliton frequency combs is robust without going through any instability or chaotic states. These results provide a means for the deterministic and controllable generation of optical Kerr frequency combs on integrated chips.
The statistical dynamics of partially incoherent ultrafast lasers are complex and chaotic, which is significant for fundamental research and practical applications. We experimentally and theoretically reveal the statistical dynamics of the spectral evolutions and correlations in an incoherent noise-like rectangle pulse laser (NLRPL). Based on statistical histogram analysis, the probability distribution asymmetry of the spectral intensity fluctuation is decayed with the wavelength far away from the spectral peak due to the detection noise. The full-spectral correlation values indicate that the spectral similarity between two round trips is exponentially weakened as the round-trip offset increases. By studying the correlation map of spectral components, we find that the area of the high-correlation region is relevant to the pump power, which is reduced by increasing the pump power. The mutual information of the spectra demonstrates that two spectral components with symmetry about the spectral peak have a statistical dependence. Experimental observations and statistical properties can coincide well with theoretical numerical simulations. We reveal the pump-dependent spectral correlation of the NLRPL and provide multiple statistical methods for the characterizations of chaotic dynamics in incoherent light sources.
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