Low-noise mode-locking in a GHz repetition rate Tm3+-doped fiber laser.

We demonstrate a GHz repetition rate mode-locked Tm3+-doped fiber laser with low noise. Based on a home-made Tm3+-doped barium gallo-germanate fiber with reduced dispersion, a broad optical spectrum of mode-locking is achieved, and its amplified spontaneous emission quantum-limited timing jitter is largely suppressed. Besides, we carefully investigate the influence of the intracavity pump strength on the noise performance of the mode-locked pulses and find that manipulating the intracavity pump power can be an effective method for optimizing the timing jitter and relative intensity noise (RIN). Particularly, RIN, which originated from the relaxation oscillation, can be effectively suppressed by 33 dB at offset frequencies of >1 MHz. The integrated timing jitter and RIN are only 7.9 fs (10 kHz-10 MHz) and 0.05% (10 Hz-10 MHz), respectively.

Enabling long-cycling aqueous sodium-ion batteries via Mn dissolution inhibition using sodium ferrocyanide electrolyte additive.

Aqueous sodium-ion batteries (AIBs) are promising candidates for large-scale energy storage due to their safe operational properties and low cost. However, AIBs have low specific energy (i.e., <80 Wh kg-1) and limited lifespans (e.g., hundreds of cycles). Mn-Fe Prussian blue analogues are considered ideal positive electrode materials for AIBs, but they show rapid capacity decay due to Jahn-Teller distortions. To circumvent these issues, here, we propose a cation-trapping method that involves the introduction of sodium ferrocyanide (Na4Fe(CN)6) as a supporting salt in a highly concentrated NaClO4-based aqueous electrolyte solution to fill the surface Mn vacancies formed in Fe-substituted Prussian blue Na1.58Fe0.07Mn0.97Fe(CN)6 · 2.65H2O (NaFeMnF) positive electrode materials during cycling. When the engineered aqueous electrolyte solution and the NaFeMnF-based positive electrode are tested in combination with a 3, 4, 9, 10-perylenetetracarboxylic diimide-based negative electrode in a coin cell configuration, a specific energy of 94 Wh kg-1 at 0.5 A g-1 (specific energy based on the active material mass of both electrodes) and a specific discharge capacity retention of 73.4% after 15000 cycles at 2 A g-1 are achieved.

Broadband high-gain Tm3+/Ho3+ co-doped germanate glass multimaterial fiber for fiber lasers above 2 µm.

High-gain Tm3+/Ho3+ co-doped optical fibers are urgently desired for high-repetition-rate mode-locked fiber lasers at >2 µm. Here, Tm3+/Ho3+ co-doped germanate glass with low hydroxyl (OH-) content was prepared by the conventional melt-quenching method combined with the reaction atmosphere procedure (RAP) dehydration technique. The doping concentrations of Tm2O3 and Ho2O3 are 2.5 mol.% (7.1 wt.%) and 0.25 mol.% (0.7 wt.%), respectively. Thanks to the high Tm3+ doping (7.1 wt.%) and low energy transfer efficiency (19.8%) between Tm3+ and Ho3+ ions, it enables achieving broadband and high-gain performance in the 2 µm region. Then a silicate-clad Tm3+/Ho3+ co-doped germanate core multimaterial fiber was successfully drawn by using the rod-in-tube method, which has a broadband amplified spontaneous emission (ASE) with a full width at half-maximum (FWHM) of 247.8 nm at 2 µm. What is more, this new fiber has a high gain per unit length of 4.52 dB/cm at 1.95 µm. Finally, an all-fiber-integrated passively mode-locked fiber laser was built by using this broadband high-gain fiber. The mode-locked pulses operate at 2068.05 nm, and the fundamental repetition rate is up to 4.329 GHz. To the best of our knowledge, this is the highest fundamental repetition rate for the all-fiber passively mode-locked fiber laser above 2 µm. These results suggest that the as-drawn multimaterial fibers with broadband high-gain characteristics are promising for high-repetition-rate ultrafast fiber lasers.

Manipulating the polarization dynamics in a >10-GHz Er3+/Yb3+ fiber Fabry-Pérot laser.

In this work, we report on the vector and scalar soliton dynamics that result from inevitable fiber birefringence in an 8-mm Er3+/Yb3+ fiber based Fabry-Férot (FP) laser that has a free spectral range of up to 12.5 GHz. The generation of polarization-evolving vector solitons can largely degrade the performance of application systems, and the underlying mechanisms and manipulation technologies are yet to be explored. To realize the transition from vector to scalar (linearly polarized) state, we here incorporate the polarization selection effect (PSE) in the simulation model and the numerical results verify that only a small amount of PSE is sufficient for manipulating the soliton dynamics. It also reveals that, prominent polarization-dependent intensity discrimination can be acquired via geometry-induced oblique incidence to the Bragg mirror of the semiconductor saturable absorber mirror (SESAM), and we obtain switchable operating states by tilting the SESAM in the experiments. These efforts create a feasible method to manipulate high-repetition-rate pulse and may shed light on understanding the dissipative soliton dynamics in ultrafast fiber FP lasers.

Threshold reduction of GHz-repetition-rate passive mode-locking by tapering the gain fiber.

Passively mode-locked fiber lasers with GHz repetition rates have recently attracted significant attention in frontier research areas, including frequency-comb spectroscopy, coherent optical communication, photonic radar, micromachining, etc. In general, the threshold of passive mode-locking increases with the fundamental repetition rate, which is inversely proportional to the cavity length, and this sets a limit on the scalability of the fundamental repetition rate. To overcome this issue, here we propose to reduce the threshold of continuous-wave mode-locking (CWML) by precisely tapering the gain fiber, which can enhance the power density incident on the semiconductor saturable absorber mirror. Assisted by the analysis of guiding property, an experimental scheme is established for tapering standard Yb-doped fibers (125 µm cladding diameter), and tapered Yb-doped fibers with different waist diameters can be fabricated. Using a tapered Yb-doped gain fiber with waist cladding diameter of 90 µm, we are able to achieve CWML with a fundamental repetition rate of 3.3 GHz, and reduce its mode-locking threshold by 31%. More importantly, the optical spectrum of the CWML is found to be broadened with the waist diameter reduction of the gain fiber, which is beneficial for generating shorter transform-limited pulses. The efforts made in this work can provide a promising route to realize stable high-repetition-rate mode-locked fiber lasers with moderate levels of pump power.

>10†GHz femtosecond fiber laser system at 2.0†µm.

We demonstrate a high-power 2.0-µm fiber laser system delivering femtosecond pulses with a fundamental repetition rate of >10 GHz, the highest value so far, to the best of our knowledge. The seed is a self-started fundamentally mode-locked Tm-doped fiber laser that has excellent power and spectral stabilities. The laser system can provide an average power of >600 mW, and the use of soliton-effect-based pulse compression allows the achievement of a pulse duration of 163 fs, leading to a compression factor of ∼ 13. It is anticipated that this new high-power femtosecond fiber laser with a 10-GHz-level fundamental repetition rate can serve as a promising light source for various applications, including laser surgery, micromachining, frequency comb spectroscopy, and nonlinear frequency conversion.

4.3†GHz fundamental repetition rate passively mode-locked fiber laser using a silicate-clad heavily Tm3+-doped germanate core multimaterial fiber.

We report a silicate-clad heavily Tm3+-doped germanate core multimaterial fiber that is successfully drawn by using a rod-in-tube method. This new fiber has a high gain per unit length of 6.11 dB/cm at 1.95 µm, which is, to the best of the authors' knowledge, the highest gain per unit length reported so far for Tm3+-doped glass fibers. By virtue of this high-gain glass fiber, an all-fiber-integrated passively mode-locked fiber laser with a fundamental repetition rate up to 4.3 GHz is demonstrated. Remarkably, the generated pulse operating at 1968 nm exhibits a signal-to-noise ratio of >76 dB in the radio-frequency domain. These results suggest that the silicate-clad heavily Tm3+-doped germanate core multimaterial fiber can act as a key building block for high repetition rate mode-locked fiber lasers at 2 µm.

SERS-based cascade amplification bioassay protocol of miRNA-21 by using sandwich structure with biotin-streptavidin system.

In our bioassay protocol, the Ag@4MBA@DNA-biotin probes were synthesized by linking biotin-modified DNA and 4-mercaptobenzoic acid-covered Ag nanoparticles, and the Si@Ag@anti-digoxin/digoxin-DNA substrate was fabricated by immune linking of digoxin-DNA and anti-digoxin immobilized on a Ag-coated wafer. Then, the probes, miRNA-21 and the substrate were constructed into a "sandwich structure" to detect the variation in the SERS signals with respect to miRNA-21 concentrations. Next, streptavidin and extra probes were alternately introduced to implement the cascade amplification of the SERS signal to increase the detection sensitivity. The results show that the limit of detection (LOD) with cascade amplification is remarkably improved from 97.81 pM to 38.02 fM, which is three orders of magnitude higher than the original data without cascade amplification. Furthermore, the SERS-based cascade amplification mechanism was analyzed and is attributed to the "hot spots effect" of the noble metal nanostructure. The biotin-streptavidin (B-S) system was introduced into the SERS detection platform, and the novel SERS-based cascade amplification bioassay protocol has significant creativity for the detection of nucleic acids.