Μm-band Laser Research Articles

High-efficiency 1.6 μm-band fiber laser based on single Er3+-doped tungsten tellurite glass with high mechanical strength through tailored glass network

In this study, the correlation between the Raman structure, thermal stability, and mechanical properties of TeO2-ZnO-La2O3–WO3 glasses with varying WO3 contents are systematically established. By exploring the critical point in the transformation process of glass network structural units, the optimal glass components of 74TeO2-12ZnO-5La2O3–9WO3 glass possess the maximum thermal stability (158 °C) and the highest mechanical properties at the same time. The maximum Vicker hardness and Young's modulus of the optimal glass can reach up to 4.007 GPa and 56.212 GPa, which are higher than those of the well-known TeO2-ZnO-Na2O (TZN) and TeO2-ZnO-La2O3 (TZL) glasses. Furthermore, the 0.5 mol% Er3+-doped glass at this critical point (TZLW-0.5Er) exhibits a higher laser figure of merit (54.29 × 10−21 cm2 ms), a larger laser gain bandwidth value (116 nm) and higher emission cross-sections at 1600 nm (2.52 × 10−21 cm2) and 1625 nm (1.06 × 10−21 cm2) than other host glasses. Finally, high-efficiency laser outputs at 1600 and 1625 nm based on TZLW-0.5Er glass fiber are successfully achieved by simulation. These results show the greater practical potential of TZLW-0.5Er glass with higher mechanical strength compared to TZN and TZL fibers for the 1.6 μm-band laser.

Simultaneous transmission of multi-format signals in the mid-infrared over free space

Mid-infrared (MIR) light within the 3–5 μm spectrum offers distinct advantages over the 1.5 μm band, particularly in adverse atmospheric conditions, rendering it a favorable option for free-space optical (FSO) communication. The transmission capacity within the 3–5 μm band is relatively low due to the immature state of its devices. In this study, we demonstrate multi-format signals FSO transmission with a total of 40 Gbps capacity in the 3 μm band, utilizing our developed MIR transmitter and receiver modules. These modules facilitate wavelength conversion between the 1.5 μm and 3 μm bands through the utilization of difference-frequency generation (DFG) effect. The MIR transmitter effectively produces three MIR signals: On-Off Keying (OOK), Binary Phase Shift Keying (BPSK), and Quadrature Phase Shift Keying (QPSK) optical signals. The generated MIR power is 7.8 dBm, covering a wavelength range from 3.5864 to 3.5885 μm. The MIR receiver regenerates the three format signals with a power of −29.6 dBm. Relevant results of regenerated signal demodulation have been collected in detail, including bit error ratio (BER), constellation diagram, and eye diagram. The required powers for the 10 Gbps OOK, BPSK, and QPSK are −37.82, −40.24, and −39.4 dBm at BER of 1 × 10−6. It is expected to further push the data capacity to the terabit-per-second level by adding more 1.5 μm band laser sources and using wider-bandwidth chirped nonlinear crystals.

150 Gbps multi-wavelength FSO transmission with 25-GHz ITU-T grid in the mid-infrared region.

The 3∼5 µm mid-infrared (mid-IR) light has several exceptional benefits in the case of adverse atmospheric conditions compared to the 1.5 µm band, so it is a promising candidate for optical carriers for free-space communication (FSO) through atmospheric channels. However, the transmission capacity in the mid-IR band is constrained in the lower range due to the immaturity of its devices. In this work, to replicate the 1.5 µm band dense wavelength division multiplexing (DWDM) technology to the 3 µm band for high-capacity transmission, we demonstrate a 12-channel 150 Gbps FSO transmission in the 3 µm band based on our developed mid-IR transmitter and receiver modules. These modules enable wavelength conversion between the 1.5 µm and 3 µm bands based on the effect of difference-frequency generation (DFG). The mid-IR transmitter effectively generates up to 12 optical channels ranging from 3.5768 µm to 3.5885 µm with a power of 6.6 dBm, and each channel carries 12.5 Gbps binary phase shift keying (BPSK) modulated data. The mid-IR receiver regenerates the 1.5 µm band DWDM signal with a power of -32.1 dBm. Relevant results of regenerated signal demodulation have been collected in detail, including bit error ratio (BER), constellation diagram, and eye diagram. The power penalties of the 6th to 8th channels selected from the regenerated signal are lower than 2.2 dB compared with back-to-back (BTB) DWDM signal at a bit error ratio (BER) of 1E-6, and other channels can also achieve good transmission quality. It is expected to further push the data capacity to the terabit-per-second level by adding more 1.5 µm band laser sources and using wider-bandwidth chirped nonlinear crystals.

Stand-off detection of ethanol gas in turbulent state using a 1.7 μm/1.5 μm near-infrared spectroscopy system

Considering that the stand-off detection of ethanol gas is significant for monitoring ethanol-free occasions, we propose and experimentally demonstrate a 1.7 μm/1.5 μm near-infrared spectroscopy system. Then based on the generated laser signals and the system, the ethanol gas and ethanol solution was stand-off detected and researched. Firstly, we measured the absorption characteristics of ethanol solution in the near-infrared band for wavelength selection. Secondly, the Tm-doped fiber laser in the system was achieved based on a ring cavity and a customized FBG; its output laser wavelength was 1728.45 nm. The linewidth of the 1.7 μm band signal was about 0.18 nm and the side mode suppression ratio (SMSR) was about 57 dB. Thirdly, ethanol gas and ethanol solution were stand-offs detected using the established 1.7 μm/1.5 μm near-infrared spectroscopy system. The concentration of ethanol solution was measured by 1.7 μm band laser, and the R-Square of the linear fit was 0.98. However, the concentration of ethanol gas in a turbulence state cannot be easily measured due to scintillation. Therefore, we detected the ethanol gas a turbulence state using a 1.7 μm/1.5 μm dual-band system, R-Square of the linear fit was 0.83 when the power jitter variance was 2.35. the experimental results offer a technical reference for stand-off detection of ethanol gas.

10-Watt-Level 1.7 μm Random Fiber Laser with Super-High Spectral Purity in a Cost-Effective and Robust Structure

The 1.7 μm band eye-safe laser sources have recently received lots of attention thanks to the development of various applications. Although a variety of lasing configurations operating in this band have been demonstrated, one still needs to seek a good candidate for particular applications with a reasonable compromise between the relative performance targets (e.g., stability, output power, and spectral purity) and the construction cost. Here, we demonstrate a high-power 1694 nm random fiber laser (RFL) in a cost-effective structure pumped by a high-powered 1565 nm RFL. The maximum output power reached the 10 W level, and the output showed extremely low-intensity fluctuations for both the short-time and long-time regimes. Meanwhile, an excellent spectral purity as high as 26.9 dB was also realized. This work provides one of the most attractive approaches for constructing high-performance 1.7 μm band laser sources for practical applications.

Low threshold and high spectral purity 1.7 μm random fiber laser based on hybrid gain

1.7 μm band lasers have shown great potential in various applications including gas monitoring and pumping mid-infrared lasers. However, due to the lack of an effective gain mechanism, the lasing performance of current sources in this band, in terms of the threshold, the spectral purity, as well as the reliability, is still inferior to their counterparts at ∼1 μm or ∼1.5 μm and hinders their actual applications. Here, we propose the first demonstration of an efficient 1.7 μm random fiber laser with hybrid gain in a common cavity structure to the best of our knowledge. In the hybrid gain approach, the lasing threshold is greatly reduced benefiting from the active gain of thulium fiber, while the optical efficiency is dramatically boosted accompanied by the nonlinear gain of stimulated Raman scattering. Besides, the optimized cavity design based on two backward pumped half-open cavities can produce a completely pure 1.7 μm lasing for the whole power scaling range. This work enriches the gain mechanism of the 1.7 μm band laser and provides high spectral purity and low lasing threshold as well as excellent robustness for realistic applications.

Mid-infrared 2.8 µm band laser output and pulse modulation

The mid-infrared 2.8 µm band laser has broad application value and development prospects in the fields of medicine, biology, military and remote sensing. At present, MIR 2.8 µm band lasers are mainly produced by solid-state lasers, fiber lasers, semiconductor lasers and chemical lasers, etc. The pulse modulation methods for this band lasers include electro-optical Q-switching, acousto-optic Q-switching, passive Q-switching, mechanical Q-switching and FTIR Q-switching, etc. The main technical difficulty lies in the discovery and utilization of high-performance and high-quality Q-switching new materials. In this paper, the output methods and pulse modulation methods of 2.8 µm band laser are summarized, and its development situation and existing problems are analyzed and prospected.

Preparation of Ho3+/Tm3+ Co-doped Lanthanum Tungsten Germanium Tellurite Glass Fiber and Its Laser Performance for 2.0\u2009\u03bcm

Ho3+/Tm3+ co-doped 50TeO2-25GeO2-3WO3-5La2O3-3Nb2O5-5Li2O-9BaF2 glass fiber is prepared with the rod-tube drawing method of 15 μm core diameter and 125 μm inner cladding diameter applied in the 2.0 μm-infrared laser. The 2.0 μm luminescence properties of the core glass are researched and the fluorescence intensity variation for different Tm3+ doping concentration is systematically analyzed. The results show that the 2.0 μm luminescence of Ho3+ is greatly influenced by the doping concentration ratio of Ho3+ to Tm3+ and that the maximum fluorescence intensity of the core glass can be obtained and its emission cross section can reach 0.933 × 10−21 cm2 when the sensitized proportion of holmium to thulium is 0.3 to 0.7 (mol%). Simultaneously, the maximum phonon energy of the core glass sample is 753 cm−1, which is significantly lower than that of silicate, gallate and germanate glass and the smaller matrix phonon energy can be conductive to the increase 2.0 μm-band emission intensity. The continuous laser with the maximum laser output power of 0.993 W and 2051 nm -wavelength of 31.9%-slope efficiency is output within the 0.5 m glass fiber and the experiment adopts 1560 nm erbium-doped fiber laser(EDFL) as the pump source and the self-built all-fiber laser. Therefore, the glass fiber has excellent laser characteristics and it is suitable for the 2.0 μm-band laser.

Tm3+/Yb3+ co-doped tellurite glass with silver nanoparticles for 1.85 μm band laser material

Tm3+/Yb3+ co-doped tellurite glasses with different silver nanoparticles (Ag NPs) concentrations were prepared using the conventional melt-quenching technique and characterized by the UV/Vis/NIR absorption spectra, 1.85 μm band fluorescence emission spectra, transmission electron microscopy (TEM) images, differential scanning calorimeter (DSC) curves and X-ray diffraction (XRD) patterns to investigate the effects of Ag NPs on the 1.85 μm band spectroscopic properties of Tm3+ ions, thermal stability and structural nature of glass hosts. Under the excitation of 980 nm laser diode (LD), the 1.85 μm band fluorescence emission of Tm3+ ions enhances significantly in the presence of Ag NPs with average diameter of ∼8 nm and local surface Plasmon resonance (LSPR) band of ∼590 nm, which is mainly attributed to the increased local electric field induced by Ag NPs at the proximity of doped rare-earth ions on the basis of energy transfer from Yb3+ to Tm3+ ions. An improvement by about 110% of fluorescence intensity is observed in the Tm3+/Yb3+ co-doped tellurite glass containing 0.5 mol% amount of AgNO3 while the prepared glass samples possess good thermal stability and amorphous structural nature. Meanwhile, the Judd-Ofelt intensity parameters Ωt (t = 2,4,6), spontaneous radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of relevant excited levels of Tm3+ ions were determined based on the Judd-Ofelt theory to reveal the enhanced effects of Ag NPs on the 1.85 μm band spectroscopic properties, and the energy transfer micro-parameters and phonon contribution ratios were calculated based on the non-resonant energy transfer theory to elucidate the energy transfer mechanism between Yb3+ and Tm3+ ions. The present results indicate that the prepared Tm3+/Yb3+ co-doped tellurite glass with an appropriate amount of Ag NPs is a promising lasing media applied for 1.85 μm band solid-state lasers and amplifiers.

All-fiber Q-switched operation of thulium-doped silica fiber laser by piezoelectric microbending

We demonstrate an all-fiber Q-switched laser operation in the 2 µm region on the basis of a dynamic periodic microbend and pulsed-pump configuration. A single-mode thulium-doped silica fiber is pumped by 1.6 µm-band laser diodes, and the dynamic loss is introduced in the fiber ring resonator by the periodic microbend that is electrically controlled with a piezoelectric actuator. When the voltage-off period of the piezoelectric actuator is set at 20 µs for the pump power of 120 mW, the output pulse power is measured by 420 mW with a pulse width of 1.3 µs.

Effects of wavelength on boron nitride ablation by a transversely excited atmospheric CO2 laser

Laser ablation processing for a reaction sintered cubic boron nitride (cBN) by a transversely excited atmospheric CO2 laser was found to be strongly affected by the laser wavelength. The ablation threshold of the cBN was 3 J/cm2 at 9.3 μm for the 9R(10) branch but 18 J/cm2 at 10.8 μm for the 10P(38) branch since the 9.3 μm laser pulse is resonantly absorbed by the transverse optical phonons. Although the reflectance of the cBN surface is very high, it was efficiently ablated by the 9.3 μm laser irradiation. Hot pressed hexagonal BN samples were also ablated by a 9 μm band laser as well as a 10 μm laser, however, a boron rich layer was left on the ablated surface.

Erratum: Highly efficient optical fibre amplifier pumped by a 0.8 μm band laser diode

Erratum: Highly efficient optical fibre amplifier pumped by a 0.8 μm band laser diode

Highly efficient optical fibre amplifier pumped by a 0.8 μm band laser diode

A highly efficient Er-doped fibre amplifier pumped by GaAlAs laser diodes is reported. Using a low Er-cluster content fibre with a high numerical aperture, the EDFA attains 39 dB signal gain for double LD pumping and 30 dB for single LD pumping at 1.536 μm. A maximum gain coefficient of 1.3 dB/mW was achieved at the 0.827 μm pump band.