Generation of a vortex point adjustable vortex array based on decentered annular beam pumping.

An adjustable optical vortex array (OVA) based on decentered annular beam pumping has been demonstrated in an end-pumped Nd:YVO4 laser. This method allows for not only the transverse mode locking of different modes, but also the ability to adjust the mode weight and phase by manipulating the position of the focusing lens and axicon lens. To explain this phenomenon, we propose a threshold model for each mode. Using this approach, we were able to generate optical vortex arrays with 2-7 phase singularities, achieving a maximum conversion efficiency of 25.8%. Our work represents an innovative advancement in the development of solid-state lasers capable of generating adjustable vortex points.

Ultra-High Sensitivity Terahertz Microstructured Fiber Biosensor for Diabetes Mellitus and Coronary Heart Disease Marker Detection.

Diabetes Mellitus (DM) and Coronary Heart Disease (CHD) are among top causes of patient health issues and fatalities in many countries. At present, terahertz biosensors have been widely used to detect chronic diseases because of their accurate detection, fast operation, flexible design and easy fabrication. In this paper, a Zeonex-based microstructured fiber (MSF) biosensor is proposed for detecting DM and CHD markers by adopting a terahertz time-domain spectroscopy system. A suspended hollow-core structure with a square core and a hexagonal cladding is used, which enhances the interaction of terahertz waves with targeted markers and reduces the loss. This work focuses on simulating the transmission performance of the proposed MSF sensor by using a finite element method and incorporating a perfectly matched layer as the absorption boundary. The simulation results show that this MSF biosensor exhibits an ultra-high relative sensitivity, especially up to 100.35% at 2.2THz, when detecting DM and CHD markers. Furthermore, for different concentrations of disease markers, the MSF exhibits significant differences in effective material loss, which can effectively improve clinical diagnostic accuracy and clearly distinguish the extent of the disease. This MSF biosensor is simple to fabricate by 3D printing and extrusion technologies, and is expected to provide a convenient and capable tool for rapid biomedical diagnosis.

1.7 THz tuning range pivot-point-independent mode-hop-free external cavity diode laser.

A novel mode-hop-free (MHF) tunable external cavity diode laser (ECDL) is demonstrated without mechanical pivot-point tuning. By corotating a periscope with an etalon and a narrow band pass (NBP) filter inside an external cavity, the cavity single longitudinal mode selection can be maintained, and continuous tuning can be achieved with optimal synchronization. A MHF continuous tuning range of 1.7 THz has been achieved with a semiconductor gain chip at the wavelength of 652 ± 2 nm experimentally, and the theoretical tuning range can reach over 4.8 THz. The laser linewidth is estimated to be less than 1 MHz (FWHM) by a scanning Fabry-Perot (F-P) and a Michelson interferometer. 1 mW output power with variation of less than 10% in the tuning region of roughly 1.7 THz has been demonstrated.

Solving the overlapped absorbance profile in gas detection by Lorentz distribution solution based on direct absorption spectroscopy method.

A novel method of Lorentz distribution solution (LDS) from overlapped absorbance profile in time domain (incomplete absorbance profile in frequency domain) based on the direct absorption spectroscopy method (DAS) was experimentally demonstrated. It utilized the ratio of the integral in a certain interval on the lower horizontal axis of the Lorentzian profile to the integral in the entire interval on the horizontal axis has a certain relationship and can be expressed by a formula. This method effectively solves the difficulties of extracting gas concentration from incomplete absorbance profile. Formulation and detection procedure were presented, experiments were carried out to prove the method on the extraction of gas concentration from different overlapped absorbance profile and different concentration. Compared with the conventional DAS (C-DAS), the maximum relative errors on the concentration extraction are minimized from 25.55% to 2.64% at different concentration and absorbance profile. Meanwhile, the experimental results show that the obtained gas concentration by LDS presents a good linear relationship while those measured by C-DAS are significantly different.

Progress on Optical Fiber Biochemical Sensors Based on Graphene.

Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors.

2D van der Waals materials for ultrafast pulsed fiber lasers: review and prospect.

2D van der Waals materials are crystals composed of atomic layers, which have atomic thickness scale layers and rich distinct properties, including ultrafast optical response, surface effects, light-mater interaction, small size effects, quantum effects and macro quantum tunnel effects. With the exploration of saturable absorption characteristic of 2D van der Waals materials, a series of potential applications of 2D van der Waals materials as high threshold, broadband and fast response saturable absorbers (SAs) in ultrafast photonics have been proposed and confirmed. Herein, the photoelectric characteristics, nonlinear characteristic measurement technique of 2D van der Waals materials and the preparation technology of SAs are systematically described. Furthermore, the ultrafast pulsed fiber lasers based on classical 2D van der Waals materials including graphene, transition metal chalcogenides, topological insulators and black phosphorus have been fully summarized and analyzed. On this basis, opportunities and directions in this field, as well as the research results of ultrafast pulsed fiber lasers based on the latest 2D van der Waals materials (such as PbO, FePSe3, graphdiyne, bismuthene, Ag2S and MXene etc), are reviewed and summarized.

Transverse mode locking of different frequency-degenerate families based on annular beam pumping.

Optical vortex arrays have been achieved in an end-pumped Nd:YVO4 laser pumped by an annular beam. Spontaneous transverse mode locking of Laguerre-Gaussian modes in different frequency-degenerate families has been obtained by merely adjusting the pump power. A maximum output power of 0.88 W and optical conversion efficiency of 13.6% are achieved for optical vortex arrays. Optical vortex arrays formed in different frequency-degenerate families of Laguerre-Gaussian modes can be actively controlled by the position of the axicon. This work provides a way to research transverse mode locking of Laguerre-Gaussian modes in different frequency-degenerate families based on annular beam pumping.

Design and optical characterization of an efficient polarized organic light emitting diode based on refractive index modulation in the emitting layer.

Luminescent liquid Crystal (LC) material is regarded as the most promising material for polarized organic light emission due to their intrinsic characteristics including orderly alignment and luminescence. Nevertheless, the optical extraction efficiency of LC based organic light emitting diodes (OLEDs) devices still requires significant effort and innovation towards real-world applications. In this paper, we propose the design of a highly linearly polarized light-emission from OLEDs with integrated refractive index nanograting in the emissive layer (EML) based on photo aligned luminescent liquid crystal material. The simulation results indicate that the geometrically optimized polarized device yields an external quantum efficiency (EQE) up to 47% with a polarized ratio up to 28 dB at a 550 nm emission wavelength. This conceptual design offers a new opportunity to achieve efficient polarized organic luminescence, and it is (to the best of our knowledge) the first approach that enhances the light extraction of OLEDs based on luminescent liquid crystal via index grating in the EML.

Highly efficient and broadband mid-infrared metamaterial thermal emitter for optical gas sensing.

Development of a novel, cost-effective, and highly efficient mid-infrared light source has been identified as a major scientific and technological goal within the area of optical gas sensing. We have proposed and investigated a mid-infrared metamaterial thermal emitter based on micro-structured chromium thin film. The results demonstrate that the proposed thermal light source supports broadband and wide angular absorption of both TE- and TM-polarized light, giving rise to broadband thermal radiation with averaged emissivity of ∼0.94 in a mid-infrared atmospheric window of 8-14 µm. The proposed microphotonic concept provides a promising alternative mid-infrared source and paves the way towards novel optical gas sensing platforms for many applications.

Comparison of the sagittal profiles among thoracic idiopathic scoliosis patients with different Cobb angles and growth potentials.

BACKGROUND: Previous studies have demonstrated that pelvic incidence and sacral slope are significantly greater in idiopathic scoliosis patients compared with normal adolescents. However, whether these sagittal parameters are related to the progression of scoliosis remain unknown. The present was designed to determine the differences in the sagittal profiles among thoracic idiopathic scoliosis patients with different potentials for curve progression. METHODS: Ninety-seven outpatient idiopathic scoliosis patients enrolled from June 2008 to June 2011 were divided to three groups according to different Cobb angles and growth potentials: (1) non-progression of thoracic curve group, Risser sign of 5 and Cobb's angle < 40°; (2) moderate progression of thoracic curve group, Risser sign of 5 and Cobb's angle ≥ 40°; and (3) severe progression of thoracic curve group, Risser sign ≤ 3 and Cobb's angle ≥ 40°. All patients underwent whole spinal anteroposterior and lateral X-ray in standing position, and the sagittal parameters were measured, including thoracic kyphosis, lumbar lordosis, sacral slope, pelvic incidence, and pelvic tilt. RESULTS: The average thoracic scoliosis Cobb's angle in the non-progression group was significantly less than that in the moderate progression group (P < 0.01) and severe progression group (P < 0.01), but there was no statistical difference in the average thoracic scoliosis Cobb's angle between the severe progression group and moderate progression group. The average thoracic kyphosis angle in the severe progression group (9° ± 4°) was significantly smaller than that in the non-progression group (18° ± 6°, P < 0.01) and moderate progression group (14° ± 5°, P < 0.05). No statistical differences were present in the average lumbar lordosis, sacral slope, pelvic incidence, and pelvic tilt among the three groups. CONCLUSIONS: Thoracic hypokyphosis is strongly related with the curve progression in thoracic idiopathic scoliosis patients, but not pelvic sagittal profiles.