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The PLQY of emissive Cs4PbBr6 NCs increases greatly with the induction of water.

This work presents a gas-liquid sensor based on chalcogenide etched-tapered fiber (ETF) functionalized with graphene oxide film. Unlike the preparation of conventional tapered fiber sensors, the core diameter of the optical fiber of this gas-liquid sensor was kept constant, and part of its cladding was removed via the chemical corrosion method that the fiber optic modes were the invariant. The energy distribution of transmission mode in the original fiber and tapered fiber is simulated respectively, and obtained the conclusion that the tapered fiber structure has higher sensing sensitivity. The sensors could detect VOCs such as formaldehyde (HCOH) and butane (C4H10) in the mid-infrared band. Results showed that the ETF sensor had a high detection sensitivity of both HCOH solution (2.6731 a.u./mg·mL−1) and C4H10 gas (0.2773 a.u./vol.%). A layer of graphene oxide (GO) film was coated on the ETF to further improve the sensitivity of the sensor. The GO coated etched-tapered fiber (GO-ETF) sensor’ sensitivity was substantially improved owing to the strong hydrophilicity and biocompatibility of GO which can absorb bioactive molecules. The high detection sensitivity of both solution and gas were 4.5091 a.u./mg·mL−1 and 0.4812 a.u./vol.%, respectively, which were 1.69 and 1.74 times higher than that of the sensor without a coating of GO film. The results further showed that the sensor had a rapid response speed, low detection limit, good repeatability, and stability.

The complete removal of the impurities like Se-H in Se-based chalcogenide glasses has been challenging in the development of highly transparent chalcogenide glass fiber. In this paper, several purification methods, including dynamic distillation, static distillation, and combined distillation method, were adopted with an aim of purifying arsenic selenide glass with ultra-low content of the impurities. The experimental results demonstrated that the Se-H can be completely eliminated in the arsenic selenide glass host and fiber without the introduction of any chloride. We further explored the applications of such low loss and Se-H-free chalcogenide glass fiber in the mid-infrared. It was found that, using such a Se-H free fiber, a flattened supercontinuum spectrum above the -30 dB level from 1.2 to 13 µm was generated from the Se-H free fiber with a 5.5 µm laser pumping. The sensitivity was found to be improved 5.1 times for CO

As the Bragg fiber can guide light by tuning the structure parameters of claddings, it is possible to improve the ability of laser-power transmission in the mid-infrared with effective omnidirectional reflection, but it usually suffers from the disturbance of the air core and functional bandgap. Here, the structural parameters of three pairs of periodic cladding layers were optimized by the plane wave expansion method, and the thickness of each layer is 3.36 µm, consisting of Ge20As20Se15Te45 and As2S3 glasses with a refractive index contrast of Δn = 0.8. The simulation results showed that a wide bandgap of 1.2 µm can be realized in the fiber after structural optimization. Then, a fiber preform was prepared via an improved stacked extrusion based on seven thickness-compensated glass plates. The experimental results show that the all-solid Bragg fiber has three pairs of uniform periodic cladding and an extra-large core. The superior optical fiber structure can also be well maintained in the whole fiber length, and the average ratio of each cladding thickness to the fiber diameter is kept nearly at 3:100. Finally, the fiber loss at 1.55 µm and 2.94 µm is 12 dB/m and 18 dB/m, respectively. In all, such a well-structured all-solid chalcogenide Bragg fiber would pave a new way to develop high-quality laser transmission or optical sensors in mid-infrared.

The S-band polymer-based waveguide amplifier has been fabricated, but how to improve the gain performance remains a big challenge. Here, using the technique of establishing the energy transfer between different ions, we successfully improved the efficiency of Tm3+:3F3→3H4 and 3H5→3F4 transitions, resulting in the emission enhancement at 1480 nm and gain improvement in S-band. By doping the NaYF4:Tm,Yb,Ce@NaYF4 nanoparticles into the core layer, the polymer-based waveguide amplifier provided a maximum gain of 12.7 dB at 1480 nm, which was 6 dB higher than previous work. Our results indicated that the gain enhancement technique significantly improved the S-band gain performance and provided guidance for even other communication bands.

In this study, (1 + 1) × 1 side-pump couplers made of tellurite fibers were fabricated and investigated. The whole optical design of the coupler was established on the basis of ray tracing models and validated by experimental results. By optimizing the preparation conditions and structural parameters, the tested component achieved a coupling efficiency of 67.52% and an insertion loss of 0.52 dB. To the best of our knowledge, this is the first time a tellurite-fiber-based side-pump coupler was developed. The fused coupler presented will simplify many mid-infrared fiber lasers or amplifier architectures.

Chalcogenide glass (ChG) optical fibers have excellent transmission performance in the mid-infrared range, and microstructured devices prepared on ChG fibers play an important role in the field of infrared sensing and optical integration. In this study, high-quality chalcogenide optical fibers were prepared, and grating structures were produced on their end surfaces. An easy-to-use FC cable was first prepared and polished to high flatness with the surface roughness of less than 0.08 μm. 1- and 2-D diffraction gratings were then prepared on the end surfaces of the chalcogenide fibers via femtosecond laser line-by-line direct writing technology. The ChG fiber end surface gratings prepared with optimized femtosecond laser parameters exhibited high diffraction efficiency and clear diffraction pattern, indicating that they had excellent optical performance. The performance of the grating was tested by using a laser source with wavelengths covering the visible to the near-infrared regions. This measurement showed that the first-order diffraction efficiency of the grating on the end face could reach close to 50% at 1550 nm.

We have prepared a novel fiber consisting of three different glasses with W-type double-cladding structure and constant core-to-cladding ratio by the extrusion method. An ultra-high numerical aperture (NA ≥ 2.17) indicates that this fiber has a good capability of collecting and confining light in a wide wavelength range. The lowest fiber loss is approximately 1.7 dB/m at 6.1 μm. Supercontinuum spectrum covering 1.6 μm to 10.85 μm at a bandwidth of −30 dB has been demonstrated in a 21 cm long fiber pumped by 5 μm laser. This chalcogenide fiber has high-NA and W-type double-cladding structure, and thus shows great potentials in the field of high power laser delivery, high efficiency imaging and high-capacity signal transmission in the mid-infrared.

We have developed an innovative extrusion with double peeling-off process to fabricate chalcogenide (GhG) preform, with an aim to remove the defects, such as bubbles, oxidation, and particles that always induce large optical losses in ChG glass fibers. As a result, none of the defects is found in the core-cladding interface of the fiber. The loss in a wavelength range of 5.5–8.2 μm is generally lower than 1 dB/m, with a minimum value of 0.2 dB/m at 6.3 μm. Moreover, a flat mid-infrared (MIR) supercontinuum (SC) spectrum spanning from 1.4 μm to 13.7 μm is generated in an 18 cm-long Ge-As-Se ChG fiber, accompanied with a highest spectrum flatten ratio of 72.4%.

A fast-response mid-infrared gas sensor based on a chalcogenide suspended-core fiber with microchannels fabricated by a tightly focused femtosecond laser pulse was demonstrated. Chalcogenide four-hole suspended-core fiber was fabricated by extrusion and exhibited the lowest transmission loss of 1 dB/m at 4.7 μm. The 50-μm-diameter solid core in the suspended-core fiber was protected by an outside solid jacket to avoid other environmental factors, such as dust and liquid pollution and touch damage. To increase gas filling rate, we introduced microchannels on the side of the suspended-core fiber by femtosecond laser writing to allow gases to enter into the fiber and fully interact with the core. The distribution, shape, and size of the channels could be controlled by laser writing technology. The engineered technique showed the advantage of increased minor loss in the suspended-core fiber. Methane gas sensing utilizing evanescent wave in the core was carried out in the prepared suspended-core fiber with several hundred microchannels. The methane sensitivity was 100 ppm, and the response time was estimated to be less than 20 s.

We reported on a polarization beam splitter based on a novel chalcogenide dual-core photonic crystal fiber. The glass matrix of the optical fiber is Ge10As22Se68. We used computerized numerical control precision drilling methods to manufacture preforms. Then the preform was drawn into an optical fiber with a regular hole structure. The maximum extinction ratio reached -32.76 dB with a 26.27 mm-long optical fiber. Numerical results show that the shortest working length of the designed polarization beam splitter is 636 µm. In addition, the modeling analysis based on the actual structure shows that the theoretical value is consistent with the measured value.

Encapsulating quantum dots (QDs) into a transparent glass matrix can not only increase their stability but also explore new luminescence properties. Herein, erasable

High quality large-core As Se chalcogenide fiber was fabricated via a novel extrusion method to peel off the out-layer of the core glass, and thus all the defects, such as deformations, interface bubbles between the core and cladding can be eliminated effectively. The raw materials were purified by the dynamic distilling and the glasses were prepared by the melt-quenching method. The preform was prepared by an improved isolated stacked homemade extrusion (ISE) machine. The fibers coated with polymer protection were drawn out with a core diameter of ∼240 μm. The core/cladding ratio of the fiber were kept approximately 1:2, and the optical loss was generally lower than 1.5 dB/m in a wavelength range of 5.6–9.7 μm, with a minimum value of 0.6 dB/m at 8.3 μm. The calculated fiber numerical aperture was approximately 0.55. Supercontinuum (SC) generation experiments of fiber at different wavelengths and pump powers were performed. A flattened SC spectrum can be obtained in this large-core fiber with femtosecond pumping.

In this paper, we described the fabrication and polishing characteristics of the end-faces of highly stable physical contact type chalcogenide optical fiber connectors. The effects of downforce pressure, polishing duration, and polishing fluid on the polishing process with abrasive grit size of 0.02 μm were investigated, and the final polishing parameters were determined. The surface roughness Ra was approximately 20 nm in the fiber area, and the average fiber roughness of the core region (10 μm × 10 μm) was about 3 nm, which were measured by the profilometry and atomic force microscope. Finally, the optical performance was analyzed in terms of the insertion loss of 1 dB and return loss of -18 dB.