We report a passively Er3+-doped mode-locked fiber laser based on repetition rate multiplication, in which a three-stage Mach Zehnder interference structure is employed as a repetition rate multiplier. The initial soliton pulses are generated from a ring cavity with a fundamental repetition rate of 102.70 MHz, which is a seed laser. When the intrinsic frequency of repetition rate multiplier is almost aligned with a variable optical delay line, the initial repetition rate output from a seed laser, is lifted from 100.20 MHz to 801.03 MHz. This result demonstrates a method to achieve high repetition rate (> 500 MHz) pulse lasers, which avoids the limitation of cavity length on the repetition rate.
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.
The spectral range of the optical frequency comb (OFC) generated by electro-optic modulators (EOMs) is limited by the modulation depth. In this paper, an on-chip system based on a Si3N4 waveguide is built to broaden a 12.5 GHz electrooptic comb (EO-comb). A numerical simulation is carried out to demonstrate the nonlinearities of self-phase modulation (SPM), Raman soliton self-frequency shift, and dispersive wave generation dominating the spectral broadening of the EO-comb in the waveguide.
CMOS based Kerr soliton frequency comb has been demonstrated as the most promising multi-wavelength onchip light source. In this work, basic parameters of a Si3N4 micro-ring resonator (MRR) are characterized via the assistance of a fiber ring resonator and the calibration of a gas cell. Besides, by using of an auxiliary laser to suppress thermal dragging dynamics in dissipative soliton comb formation, a stable 100GHz Kerr soliton frequency comb generation is achieved.
The exciton complexes in two-dimensional materials have long fascinated scientists and researchers for their mechanisms in fundamental photo-physics. And it is well established that the evolution of defect bound excitons in twodimensional semiconducting TMDs brings largely unexplored opportunities for tailoring their optoelectronic properties. Yet thus far, the properties of defect bound excitons of TMDs have been rarely investigated. In this work, the intrinsic properties of defect bound excitons in aged CVD-grown monolayer WS2 are experimentally studied by the steady-state photoluminescence measurement. Specifically, the photoluminescence mapping experiment is conducted to demonstrate the spatial distribution of the defect bound excitons, whose spectral feature is located ~0.2 eV below the neutral free Aexcitons. Additionally, the power-dependent photoluminescence experiment is applied to investigate the behavior of the defect-state photoluminescence and a significant nonlinear dependence of defect bound excitons on excitation power is revealed. Furthermore, we directly observed the disappearance of defect-state photoluminescence by exposing sample to high laser power irradiation, which can be explained by the enhanced desorption process of molecules physiosorbed on surfaces under laser irradiation. The results of our work provide a comprehensive understanding for the defect bound excitons in monolayer tungsten disulfide, which is essential in promoting the development of defect engineering about two-dimensional semiconducting TMDs and may pave the way for tailoring the performance of the optoelectronic device.
In this work, few layers of Bi2Se3 is chemically treated, in which the AuCl3 solution is used for oxidation reaction to form p-doping, and BV solution (benzyl dichloride) is put to form n-doping to change material properties. We used pumpprobe system to verify the effect of doping on Bi2Se3 materials. In addition, the nonlinear saturable absorption of the material is also controlled. Through the I-scan test, we found that the saturable absorption has diverse responses to different wavelengths and doping conditions. By doping, the Fermi level of the material can be adjusted to control the saturable absorption of the material, which can be applied to the mode-locked laser. The weakened saturable light intensity can make the mode-locked pulse easier to generate.
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