We experimentally demonstrate a wavelength-switchable noise-like pulse (NLP) with modulation sidebands in an erbium-doped mode-locked fiber laser. The central wavelength of NLPs can be switched from 1530.2 to 1558.8 nm due to the birefringence filtering effect based on nonlinear polarization rotation. The corresponding pulse durations are 656 and 613 fs, respectively. As the total pump power increases to 700 mW, the modulation sidebands of NLPs can be observed by adjusting the polarization controller appropriately. The formation of modulation sidebands is caused by cross-phase modulation-induced modulation instability.
We propose a new optical engine that supresses stray light to address the problems of high stray background light and low star point simulation in traditional star simulators and offer an experimental proof that the new design provides higher contrast. Our design incorporates an optical collimator with a modulation frequency transfer function (MTF) greater than 0.6 at a cut-off frequency of 60 lp/mm that meets star point identification requirements. Experimental results show the background noise of the high contrast star simulator to be well suppressed, providing a 3.16-fold reduction in stray light compared with a traditional system.
We have experimentally obtained dispersion-managed solitons with sidebands in a passively mode-locked thulium-doped fiber laser. The stable single soliton with sidebands can be converted into two soliton pulses at the pump power of 867 mW with appropriate settings of the polarization controllers (PCs). By increasing the pump power and cautiously adjusting the PCs, the three, four, and five soliton pulses with nonuniform intensity operate with stability in the cavity due to the global soliton interaction caused by unstable continuous waves. Furthermore, the soliton bunch can be observed at the pump power of 1 W. The position of solitons in the soliton bunch is random with a fixed separation that is controllable by changing the linear phase delay. Our work gives insight into the dynamics of multipulse dispersion-managed solitons in a 2-μm mode-locked fiber laser.
The stretched pulse has narrower pulse duration and high pulse energy than conventional soliton, so that the stretched pulse can improve the potential application values of 2 μm mode-locked fiber laser in remote sensing, mid-infrared source, material processing and other applications. In this paper, the dispersion management method is adopted to accurately manage the dispersion in the cavity using a commercial ultra-high numerical aperture fiber and a common single-mode fiber. Based on the nonlinear polarization rotation technology to achieve mode-locking, when the pump power is set to 645 mW, the polarization controller is adjusted to achieve stretched pulse output with a de-chirped pulse duration of 581 fs. The center wavelength is 1939.26 nm and the 3-dB bandwidth is 21.8 nm. The repetition rate is 28.9 MHz and the signal to noise ratio is 54.21 dB. At the maximum pump power, the direct output power of the resonant cavity is 9.98 mW, and the corresponding single pulse energy is 0.34 nJ.
We report the experimental results of various soliton molecules in a passively mode-locked thulium-doped fiber laser based on nonlinear polarization rotation (NPR) technology. Not only stable single solitons but also soliton molecules can be observed in the same cavity. With the increase of the pump power, soliton triplets composed of three solitons can also be observed. It is found that the ratio of the pulse separation to the pulse width is less than 5, which indicates that the direct soliton interaction leads to the formation of bound states. On the other hand, the effect of the dispersive wave is to suppress the random relative phase change between the solitons and leads to phase-locking. Meanwhile, we analyzed the complex nonlinear interactions that form soliton molecules and enriched the nonlinear dynamics of soliton molecules at 2-μm.
In this paper, we experimentally demonstrated a free space optical communication system transmission based on continuous wide-spectrum laser at 10Gbit/s over 1km simulated atmospheric channel. The wide-spectrum laser is part of supercontinuum generated by using a self-made picosecond mode-locked laser based on Raman gain solution effect to pump a dispersion compensation fiber which dispersion coefficient are D=-135ps/nm ⋅ km@1550nm. A 10Gbit/s NRZ signal was then modulated on the wide-spectrum laser and transmitted into a tunable simulated atmospheric turbulence pool which can simulate atmospheric turbulent intensity up to 0.59cm of coherent length. Scintillation intensities and bit error rates of transmission based on wide-spectrum laser and narrow linewidth laser were compared. The results show that communication sensitivity reached -10.98dBm at FEC limit. which has 1.53dB improvement comparing with FSO communication system using narrow linewidth laser under weak turbulent condition.
We report a low coherence supercontinuum source with high-repetition rate and compare its spectral width and coherence under conditions of different pump pulse. The repetition rate of supercontinuum source is 4GHz and the spectrum width of supercontinuum is nearly 400nm. The supercontinuum spectral width and coherence under different pump pulse duration were compared, which indicates that with the same pump power, as the pump pulse duration increases, the width and coherence of the supercontinuum both decreases. We also compare the coherence of the supercontinuum with different pump power, as the pump power increases, the coherence of the supercontinuum deteriorates. The coherence of supercontinuum is related to pulse width and power of injected pulse.
In this paper, we use a pulse trigger to manipulate soliton-fission in supercontinuum generation process by modulation instability (MI) in ~picosecond pump scheme and we demonstrate the prior performance of generated supercontinuum compared to non-trigger situation. A distributed feedback (DFB) laser is modulated into a pulse source with a high repetition rate of 4GHz by pulse amplitude modulation (PAM) and an adiabatic soliton compression (ASC) method is used to compress pulse width from 8.2ps to 3.3ps. It is observed that threshold of SC generation is relatively lower when the trigger is used. As pump light coupled with pulse trigger launch into a 400m high non-linear dispersion-shifted fiber (HNL-DSF), the generated supercontinuum is nearly 100nm wider in redshifted side and exhibit better stability than untriggered one.
The transmission characteristics of 384 Gbit / s free-space laser link with dense wavelength division multiplexing (DWDM) are demonstrated, with channel spacing of 100 GHz. We use a simulated atmosphere channel with a tunable weak turbulence, and bit error rate (BER) curves of back-to-back transmission, which are measured and contrasted, respectively. To our knowledge, it is the first demonstration in the research of DWDM-DP-QPSK high-speed free-space optical (FSO) transmission in an atmospheric channel with tunable turbulence. For 100 GHz channel spacing, receiving sensitivities can be −33.6, −32.7, and −32.1 dBm for 300, 336, and 384 Gbit / s DWDM-PM-QPSK signals, respectively, at BER of 3.8 × 10 − 3 (FEC limit). In comparison with −37.6, −36.1, and −35.1 dBm for B2B case, the power penalties are 4, 3.4, and 3.0 dB, respectively. This study indicates that high-speed coherent DWDM-DP-QPSK FSO transmission is feasible.