Μm Waveband Research Articles

Watt-Level Diode-End-Pumped Self-Mode-Locked Tm,Ho:LLF Laser

A diode-end-pumped self-mode-locked Tm,Ho:LuLiF4 (LLF) laser is demonstrated for the first time, to the best of our knowledge. At the incident pump power of 3.4 W, the stable self-mode-locked operation of the Tm,Ho:LLF laser was realized without any additional devices in the resonator. Further increasing the incident pump power to 6.8 W, the maximum average output power of 1.07 W was achieved at 2068 nm with a pulse width of 746 ps and a repetition frequency of 468 MHz. The experimental results indicate that the Tm,Ho:LLF crystal is promising to generate the high-power self-mode-locked solid-state laser at 2 μm waveband. The self-mode-locked Tm,Ho:LLF laser has potential applications in optical communication, remote sensing, material process, and nonlinear frequency conversion.

High-speed 4 × 4 silicon photonic plasma dispersive switch, operating at the 2 µm waveband.

The escalating need for expansive data bandwidth, and the resulting capacity constraints of the single mode fiber (SMF) have positioned the 2-μm waveband as a prospective window for emerging applications in optical communication. This has initiated an ecosystem of silicon photonic components in the region driven by CMOS compatibility, low cost, high efficiency and potential for large-scale integration. In this study, we demonstrate a plasma dispersive 4 × 4 photonic switch operating at the 2-μm waveband with the highest switching speed. The demonstrated switch operates across a 45-nm bandwidth, with 10-90% rise and 90-10% fall time of 1.78 ns and 3.02 ns respectively. In a 4 × 4 implementation, crosstalk below -15 dB and power consumption lower than 19.15 mW across all 16 optical paths are indicated. This result brings high-speed optical switching to the portfolio of devices at the promising waveband.

Novel ternary core-shell structure with microwave absorption properties and low infrared emissivity

The development of functional materials with dual characteristics of microwave absorption and low infrared emissivity is vital for protection against magnetic-wave contamination. Currently, both microwave protection and infrared protection technologies are developing rapidly, but simultaneous integration of both has not been extensively investigated. Herein, a new ternary core-shell CoFe2O4@SiO2@ZAO composite dual-functional material was designed and fabricated. The process consisted of coating CoFe2O4 microspheres with ZAO based on SiO2 middle layer prepared through hydrolysis and sol-gel methods. The introduction of ZAO and SiO2 was found conducive to dielectric loss and impedance matching, thereby improving wave absorption. The nano-flower ZAO coating provided low infrared emissivity with a lamellar structure and high carrier concentration in the resulting ternary structure. The rise in ZAO content first enhanced the wave absorption of CoFe2O4@SiO2@ZAO and then decreased while the infrared emissivity declined. Among prepared samples, CoFe2O4@SiO2@ZAO exhibited a minimum reflection loss (RLmin) of −59.31 dB at 10.96 GHz, conducive to effective absorption bandwidth (EAB) of 4 GHz at 2 mm thickness with an infrared emissivity of 0.71 in 8–14 μm waveband. In sum, the novel CoFe2O4@SiO2@ZAO core-shell structure showed attractive properties in terms of compatibility of wave absorption and infrared emissivity, promising for future syntheses of dual-functional materials with improved performance.

Watt-level 1.6 μm dissipative soliton ultrafast laser and external generation of ∼70 fs noise-like pulses for supercontinuum generation

Here, we propose a high power dissipative soliton (DS) laser with a central wavelength of ∼1612 nm. The whole laser system includes the mode-locking oscillator and the corresponding master oscillator power amplifier (MOPA). The mode-locking oscillator is a nonlinear amplifier loop mirror (NALM) cavity, which has a net normal dispersion enabling the generation of nJ-level DS pulses. To further enhance the output power of the 1.6 μm DS pulses, the specially-designed MOPA system consisting of multiple-stage single-pass amplifier is constructed, which can amplify the output power to watt level and meanwhile keeps a high suppression ratio to C-band amplified spontaneous emission (ASE). This high power 1.6 μm DS laser will have further applications in biomedical research and material processing. In the amplifier, we observe the automatic evolution of the DS pulses into the noise-like (NL) pulses under high pumping strength. At the maximum pump power, the MOPA system delivers the NL pulses with an output power of over 2 W. The narrowest spike duration is ∼70 fs (fs). This 1.6 μm fs-scale NL laser is a good pump source for generating the mid-infrared supercontinuum without short wavelength region loss. To demonstrate the superiority of this NL laser, a broad supercontinuum from ∼0.87 μm to ∼3.75 μm waveband is achieved with a piece of highly germanium-doped (Ge-doped) fiber.

An Efficient Silicon Grating Coupler for a 2 μm Waveband Based on a Polysilicon Overlay

The short-wavelength mid-infrared spectral range of the 2 μm waveband has the advantages of low transmission loss and broad gain bandwidth, making it a promising candidate for the next optical fiber communication window. It is thus highly desired to develop high-performance silicon photonic components in this waveband. Here, an efficient dual-layer grating coupler was designed on a 220 nm thick silicon-on-insulator based on raised polysilicon to address the low directionality issue. For the fiber tilted at an angle of 10°, the grating coupler’s simulated coupling efficiency reaches 80.3% (−0.95 dB) at a wavelength of 2002 nm. The 1 dB bandwidth is 66 nm. The structure is completely compatible with the standard silicon photonic fabrication process, making it suitable for large volume fabrication.

Optimal Design of Infrared Wavelength‐Selective and Microwave Transmitting Bionic Metasurface

AbstractThe radar and infrared (IR) compatible stealth technology is an important technology in the military field. Inspired by the special triangular‐shaped hairs from the Saharan silver ants, a bionic structure with IR wavelength‐selective emission and large microwave transmission simultaneously is presented. An algorithm based on the combination of Bayesian optimization and finite different time domain method is proposed for optimal design. The proposed structure is an indium tin oxide (ITO)‐hairs/ITO‐film/PET‐substrate structure. The IR wavelength‐selectivity is reached by the hair covered ITO film, and the microwave transmission is realized by patterning gap arrays on continuous films. After optimal calculation, the optimal bionic structure is obtained. The change of the structural parameters of the meta‐atom will lead to a change in microwave transmission. When p = 0.1 mm and w = 0.9 mm, the maximum and minimum transmittivity of the infrared stealth layer (IRSL) in 2–20 GHz are 0.972 and 0.764, respectively, while the estimated emissivity in 3–5, 5–8, and 8–14 µm wavebands are 0.592, 0.730, and 0.373, respectively. It illustrates that the IRSL maintains IR wavelength‐selective emission while maintaining high microwave transmission. This study provides a strategy for bionic structure applied in compatible stealth.

1.7 µm sub-200 fs vortex beams generation from a thulium-doped all-fiber laser.

The pulsed 1.7 µm vortex beams (VBs) has significant research prospects in the fields of imaging and material processing. We experimentally demonstrate the generation of sub-200 fs pulsed VBs at 1.7 µm based on a home-made mode-selective coupler (MSC). Through dispersion management technology in a thulium-doped fiber laser, the stable linearly polarized VBs pulse directly emitting from the cavity is measured to be 186 fs with central wavelength of 1721.2 nm. By controlling the linear superposition of LP11 modes, cylindrical vector beams (CVBs) can also be obtained. In addition, a variety of bound states pulsed VBs at 1.7 µm can also be observed. Our finding provides an effective way to generate ultrashort pulsed VBs and CVBs at 1.7 µm waveband.

SnS2 as a Saturable Absorber for Mid-Infrared Q-Switched Er:SrF2 Laser.

Two-dimensional (2D) materials own unique band structures and excellent optoelectronic properties and have attracted wide attention in photonics. Tin disulfide (SnS2), a member of group IV-VI transition metal dichalcogenides (TMDs), possesses good environmental optimization, oxidation resistance, and thermal stability, making it more competitive in application. By using the intensity-dependent transmission experiment, the saturable absorption properties of the SnS2 nanosheet nearly at 3 μm waveband were characterized by a high modulation depth of 32.26%. Therefore, a few-layer SnS2 was used as a saturable absorber (SA) for a bulk Er:SrF2 laser to research its optical properties. When the average output power was 140 mW, the passively Q-switched laser achieved the shortest pulse width at 480 ns, the optimal single pulse energy at 3.78 µJ, and the highest peak power at 7.88 W. The results of the passively Q-switched laser revealed that few-layer SnS2 had an admirable non-linear optical response at near 3 μm mid-infrared solid-state laser.

Synthesis of La2NiO4 by the molten salt method and its infrared radiation properties

The layered perovskite structure material La2NiO4, which is a material with better infrared radiation properties, was synthesized successfully at 950 ºC and above by the molten salt method. The emissivity values of La2NiO4 were all above 0.973 in the 3–5 µm waveband, which was due to the narrow band gap, and those in the 8–14 µm waveband were all above 0.987. The force constants of La2NiO4 were calculated, and it was proven that higher infrared emissivity in the 8–14 µm waveband corresponds to lower force constants. In addition, the high temperature chemical stability of La2NiO4 was studied and it was found that no chemical reactions occurred in La2NiO4at high temperature. The infrared emissivity of La2NiO4 treated at 1400 ºC was tested. The results showed that the maximum attenuation rate of infrared emissivity was less than 0.40%, indicating that La2NiO4 still had excellent infrared radiation properties after heat treatment.

Dual-wavelength passively Q-switched Ho:GdVO4 self-Raman laser operating at 2473 nm and 2520 nm.

A dual-wavelength passively Q-switched Ho:GdVO4 self-Raman laser in the 2.5 µm wave band was demonstrated with Cr:ZnS as a saturable absorber. Synchronized dual-wavelength pulsed laser outputs at 2473 nm and 2520 nm were acquired, corresponding to Raman frequency shifts of 808 cm-1 and 883 cm-1, respectively. The maximum total average output power of 114.9 mW was obtained at an incident pump power of 12.8 W with a pulse repetition rate of 3.57 kHz and a pulse width of 16.36 ns. The maximum total single pulse energy was 32.18 µJ, corresponding to a total peak power of 1.97 kW. The power ratios of the two Raman lasers can be controlled by varying the incident pump power. To the best of our knowledge, this is the first time a dual-wavelength passively Q-switched self-Raman laser in the 2.5 µm wave band has been reported.

Infrared radiation properties of La3Ni2O7 and performance of the La3Ni2O7-based coating considering the effect of thermal reactivity

Materials with excellent infrared radiation properties are important for preparing infrared radiation coatings that are applied in industrial furnaces, to improve the efficiency of heating equipment. To find a new material with better infrared radiation performance, La3Ni2O7, a layered perovskite structural material, was prepared by the sintering method, and its infrared radiation performance was studied in detail. It was found that La3Ni2O7 has excellent infrared radiation properties, and the measured emissivity values at the 3–5 μm waveband were above 0.970, which was determined by its narrower forbidden bandwidth. Furthermore, La3Ni2O7-based coatings on clay brick substrates were prepared. The thermal behavior of the coatings, from room temperature to 1400 °C, was studied using thermogravimetry and differential scanning calorimetry (TG-DSC). The results indicated that a series of reactions occurred for the coatings at temperatures higher than 1000 °C. Furthermore, the coatings were heated in a muffle furnace at 1000 °C, 1100 °C, and 1200 °C, for 60 min to study the effect of thermal reactivity on the infrared radiation performance of the coatings. The results showed that at high temperatures, although the thermal reactivity led to a phase change for the coatings, the change had little effect on the emissivity. Above 1100 °C, La3Ni2O7 starts to decompose into La2NiO4 and NiO, and above 1200 °C, the La2NiO4 content is above 50%, implying that the decomposition product La2NiO4 plays a key role in maintaining the high emissivity of the coatings. The emissivity of La2NiO4 specifically fabricated was tested and it was found that its emissivity was above 0.970. Furthermore, thermal shock resistance tests of the coatings were conducted. The results showed that the transition layer was formed by the chemical reactions between La3Ni2O7 and the oxides in the substrate, which plays a positive role in prolonging the service life of the coating.

Optical reflection characteristic-based emissivity analysis of a pyramid array flat-plate blackbody for remote sensor calibration.

The flat-plate blackbody (FPB) is the core device in infrared remote sensing radiometric calibration for providing accurate infrared radiation energy. The emissivity of an FPB is an important parameter that directly affects calibration accuracy. This paper uses a pyramid array structure based on the regulated optical reflection characteristics to analyze the FPB's emissivity quantitatively. The analysis is accomplished by performing emissivity simulations based on the Monte Carlo method. The effects of specular reflection (SR), near-specular reflection (NSR), and diffuse reflection (DR) on the emissivity of an FPB with pyramid arrays are analyzed. In addition, various patterns of normal emissivity, small-angle directional emissivity, and emissivity uniformity are examined under different reflection characteristics. Further, the blackbodies with the NSR and DR are fabricated and tested experimentally. The experimental results show a good agreement with the corresponding simulation results. The emissivity of the FPB with the NSR can reach 0.996 in the 8-14 µm waveband. Finally, the emissivity uniformity of FPB samples at all tested positions and angles is better than 0.005 and 0.002, respectively. The standard uncertainty of experimental measurement of waveband emissivity and spectral emissivity are 0.47% and 0.38% respectively, and the simulation uncertainty is 0.10%.

Direct Emission of Two-Color Vortex Beams at 1.0 μm and 1.5 μm Wavebands From an All-Fiber Laser

In this letter, we demonstrated an all-fiber laser that can simultaneously radiate dual-color vortex beams by incorporating a dual-channel mode-selective coupler (DC-MSC) into the laser cavity. By optimizing the phase-matching condition between LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes, wavelength-dependent mode coupling could be observed. In this case, a broadband mode conversion with two isolated bands can be achieved, which totally covers the gain bands of ytterbium and erbium ion, enabling the simultaneous generation of vortex beams (VBs) at 1.06 μm and 1.55 μm wavebands. With intra-cavity mode conversion and polarization controlling, a coaxial two-color VB is transmitted directly from the laser cavity, providing a more compact dual-beam light source for subsequent vortex nonlinear frequency conversions, such as wavelength extension to the red light and the mid-infrared (3 μm) wavebands.

Efficient 1.55 and 2 μm Dual‐Band SOI Grating Coupler for Light Coupling and On‐Chip Wavelength Division (De)multiplexing

Efficient fiber‐chip couplers operating at distinct wavelength bands are key components to combine or split different optical bands for emerging data transmission and nonlinear applications. Herein, a dual‐band silicon‐integrated grating coupler (GC) operated at 1.55 and 2 μm wavebands is designed and demonstrated. The proposed device can simultaneously couple 1.55 and 2 μm wavebands light into the in‐plane waveguides at the same incident angle. Numerical simulations indicate that coupling efficiencies (CEs) are −2.5 and −3.9 dB for center wavelengths at 1561 and 1979 nm, respectively. The dual‐band GC is experimentally demonstrated on a commercially available 340 nm silicon‐on‐insulator wafer. The fabricated dual‐band GC with center wavelengths of 1559 and 1968 nm obtains CEs of −4.9 and −6.4 dB, with 3 dB bandwidths of 81 and 80.4 nm, respectively. Also, the first proof‐of‐concept demonstration of 10 Gb s−1 wavelength division multiplexing transmission at 1.55 and 2 μm waveband is presented based on the fabricated dual‐band GC.

Improved designs for short wavelength amplification based on a thulium-doped Ta2O5 waveguide

Abstract This study aims to design a thulium-doped Ta2O5 amplifier for short wavelength amplification at 1.7 µm waveband. The waveguide width of the proposed design is theoretically optimized to ensure the condition of single mode guidance and the appropriate width must be less than 3.2 µm. Finite element method based edge element is applied to compute the optical field distribution of the fundamental mode across the waveguide length and to find the values of the overlapping factor and the effective mode field area of the proposed waveguide. The numerical results display that 0.83 and 6.8 µm2 are the computed values of the overlapping factor and the effective mode field area, respectively at 1.72 µm wavelength. The amplification performance of a Tm:Ta2O5 amplifier is presented based on the rate equations and the power distribution equations. The effects of the waveguide length and the pump power are investigated on the signal amplification at 1.72 µm wavelength. The simulation results reveal that about 25 dB small signal gain and 8.7 dB noise figure could be achieved at 1.72 µm wavelength when pumped with only 100 mW pump power at 1630 nm wavelength. As a result, it is possible to achieve an efficient laser and amplifier source at the 1.7 µm waveband based on a Tm:Ta2O5 waveguide.

Broadband long-wave infrared high-absorption of active materials through hybrid plasmonic resonance modes

Broadband high absorption of long-wavelength infrared light for rough submicron active material films is quite challenging to achieve. Unlike conventional infrared detection units, with over three-layer complex structures, a three-layer metamaterial with mercury cadmium telluride (MCT) film sandwiched between an Au cuboid array and Au mirror is studied through theory and simulations. The results show that propagated/localized surface plasmon resonance simultaneously contribute to broadband absorption under the TM wave of the absorber, while the Fabry–Perot (FP) cavity resonance causes absorption of the TE wave. As surface plasmon resonance concentrates most of the TM wave on the MCT film, 74% of the incident light energy is absorbed by the submicron thickness MCT film within the 8–12 μm waveband, which is approximately 10 times than that of the rough same thickness MCT film. In addition, by replacing the Au mirror with Au grating, the FP cavity along the y-axis direction was destroyed, and the absorber exhibited excellent polarization-sensitive and incident angle-insensitive properties. For the corresponding conceived metamaterial photodetector, as carrier transit time across the gap between Au cuboid is much less than that of other paths, the Au cuboids simultaneously act as microelectrodes to collect photocarriers generated in the gap. Thus the light absorption and photocarrier collection efficiency are hopefully improved simultaneously. Finally, the density of the Au cuboids is increased by adding the same arranged cuboids perpendicular to the original direction on the top surface or by replacing the cuboids with crisscross, which results in broadband polarization-insensitive high absorption by the absorber.

High-efficiency mode-locked erbium-doped ZBLAN fiber laser around 2.8 µm by directly depositing Bi2S3 particles onto a cavity mirror.

Mid-infrared (MIR) pulsed lasers near a 3µm waveband show great potential for the high absorption of water molecules and many important gas molecules. A passively Q-switched mode-locked (QSML) E r 3+-doped fluoride fiber laser with a low laser threshold and high slope efficiency around a 2.8µm waveband is reported. The improvement is achieved by depositing bismuth sulfide (B i 2 S 3) particles onto the cavity mirror directly as a saturable absorber and using the cleaved end of the fluoride fiber as output directly. -QSML pulsesbegin to appear with the pump power of 280mW. The repetition rate of the QSML pulses reaches a maximum of 33.59kHz with the pump power of 540mW. When the pump power is further increased, the output of the fiber laser switches from the QSML to the continuous-wave mode-locked operation with the repetition rate of 28.64MHz and the slope efficiency of 12.2%. The results indicate that B i 2 S 3 is a promising modulator for the pulsed lasers near a 3µm waveband, which paves the way for further development of various applications in MIR wavebands, including material processing, MIR frequency combs, and modern healthcare.

A controllable fabrication of flat absorber dual-layer coating with electric shielding on 6061 aluminum alloy by PEO with nanoparticles additive

In spacecraft, thermal control coatings with anti-static functionality are vital for electronic packages to ensure proper operation of devices and instruments while preventing the reduction of component lifetime due to extreme temperatures or electrostatic discharge. However, simultaneously integrating thermal control and static charge dissipation into one coating remains a huge challenge. Herein, a dual-layer black coating composed of an Al2O3-In2O3-P2O5-SiO2 glass bottom layer embedded with crystalline indium tin oxide (ITO) and a top layer with ITO and carbon nanotubes (CNTs) as sealed conductive and radiative components grows in situ on the 6061 aluminum alloy surface using a modified PEO method with nanoparticles additive under special parameters, experiencing one-step liquid-plasma-assisted particle deposition and sintering (LPDS) process. During the LPDS process, the addition of CNTs to the electrolyte promotes the deposition and sintering of ITO nanoparticles on the bottom layer, resulting in the transition from a single-layer coating to a dual-layer coating. CNTs with high absorption/emissivity assisted further by the infrared-trapping effect of the micro/nanostructure lead to flat absorber dual-layer coating. The black coating offers both high solar absorptance (~0.93) in the 0.2–2.5 μm waveband and infrared emissivity (~0.94) in the 3–20 μm waveband. Notably, CNTs with high aspect ratio connect the ITO nanoparticles to form a complete conductive channel on the coating surface, thus eliminating in-plane charges. At only 1.27 × 102 Ω, the surface resistivity of the dual-layer coating is five orders of magnitude lower than that of the single-layer Al2O3 coating (1.15 × 107 Ω). Such an all-in-one design provides a feasible and sustainable strategy for anti-static black products in space applications.

Silicon MMI-based power splitter for multi-band operation at the 1.55 and 2 µm wave bands

Multimode interference (MMI)-based power splitters are fundamental building blocks for integrated photonic devices consisting of an interferometer structure. In order to forestall the 'capacity crunch' in optical communications, integrated devices capable of operating in multiple spectral bands (e.g., the conventional telecom window and the emerging 2 µm wave band) have been proposed and are attracting increasing interest. Here, we demonstrate for the first time, to the best of our knowledge, the realization of a dual-band MMI-based 3 dB power splitter operating at the 1.55 and 2 µm wave bands. The fabricated power splitter exhibits low excess losses of 0.21 dB and 0.32 dB with 1 dB bandwidths for 1500-1600 nm and 1979-2050 nm, respectively.

Enhanced near- and mid-infrared radiation property of MgCr2O4 by doping with Cu ions

MgCr2O4 is one of promising candidate to develop high near- and mid-infrared emissivity materials for industrial furnaces energy-saving, and its infrared emissivity property will be improved by doping Cu ions. The results show that Cu ions can be doped into the spinel lattice by solid-state sintering, and the single phase Mg1-xCuxCr2O4 (0.1 ≦ x ≦ 0.4) radiation materials were prepared at 1200 °C. With the increase of the molar ratio of Cu ions from 0.1 to 0.4, their near- and mid-infrared emissivity all increase. The average infrared absorptivity of Mg0·6Cu0·4Cr2O4 is 0.81 in the wavelength range of 0.8–2.5 μm, and the average infrared emissivity of Mg0·6Cu0·4Cr2O4 is 0.94 in the wavelength range of 2.5–13 μm. Compared with MgCr2O4, the average infrared absorptivity in 0.8–2.5 μm waveband and emissivity in 2.5–13 μm waveband of Mg0·6Cu0·4Cr2O4 increased by 224% and 35% respectively. Cu ions in Mg1-xCuxCr2O4 had a mixed valence with Cu2+ and Cu+ valence state, and the forbidden bandwidth of MgCr2O4 decreased with doping Cu ions, which were responsible for the increase of near- and mid-infrared radiation of MgCr2O4 with doping Cu ions.