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An internal-and-external-cavity Fabry–Perot interferometer (IECFPI) model was mathematically constructed. Based on the IECFPI configuration, a crosstalk-free fiber optic sensor for simultaneous measurement of refractive index (RI) and temperature was proposed and experimentally demonstrated. The internal cavity was a silica cavity, while the external one consisted of an open cavity and silica cavity. The open cavity was formed by an offset single-mode fiber (SMF) sandwiched between two sections of SMF, and the silica cavity was formed by a well-cleaved SMF. A sensitivity coefficient (SC) matrix of the proposed sensor was used to determine the RI and temperature by monitoring the wavelength shifts of the envelope and fine fringes. The proposed sensor can be used for simultaneous measurement of RI and temperature based on the inverse of the SC matrix. Experimental results demonstrated that the RI sensitivities for the envelope and fine fringes were 1084.9 and 124.2 nm/RIU, respectively. Temperature sensitivities of 3.5 and 9.8 pm/°C were also achieved for the envelope and fine fringes, respectively. The crosstalk between the RI and temperature was thus eliminated. In addition, the proposed sensor has a compact size, simple fabrication, and an all-fiber structure, making it a potential candidate for many applications, such as the food industry and environment monitoring.

We propose and demonstrate a novel and simple wavelength switchable multi-wavelength erbium-doped fiber (EDF) laser based on polarization-dependent loss (PDL) modulation with cascaded fiber Bragg gratings (FBGs) as the wavelength comb filter. PDL is generated and controlled by different polarization angles between the polarization state of each lasing line and the optical fiber polarizer in the laser cavity. The PDL modulation balances the difference between the total loss and the wavelength-dependent lasing gain. The relations among gain, loss, and laser output power under different PDL conditions are numerically analyzed on the basis of a simplified Giles model in an EDF laser system. Results show that multi-wavelength lasing lines can be built up by properly tuning the PDLs in different wavelengths. The amount of lasing lines can be switched by changing the PDL intensity in a certain wavelength. In an experiment, the PDL in that certain wavelength is modulated by utilizing four polarization controllable elements, each of which includes an FBG and a corresponding polarization controller (PC). One PC is used to control the polarization state of the reflected lasing line on the center wavelength of the FBG. A four-wavelength individually switchable EDF laser system is demonstrated by utilizing this wavelength switchable method, in which the switching operation for the single-, dual-, triple-, and four-wavelength laser output is verified. The experimental results are consistent with the theoretical results. All wavelength switching operations are conveniently controlled by merely adjusting the PCs. This simple structure and flexible wavelength switchable operations show that this multi-wavelength EDF laser has great potential in practical applications.

Laser-ultrasonic excitation holds promising prospects in nondestructive testing and structural health monitoring. This paper proposes a multipoint, energy-equal laser-ultrasonic actuator based on multiple peanut-shape (PNS) structures in a single mode fiber link. The PNS structures were fabricated by fiber micro-matching operations using a fiber splicer. The PNSs effectively couple the laser energy from the core mode into the cladding modes in the fiber. Moreover, the coupling ratio can be adjusted by controlling the taper diameter of the PNSs. For energy control, multiple PNS structures are fabricated and connected in order from small to large coupling ratios. Experiments were performed on an actuator with four PNSs of different taper diameters (138.71 $\mu \text{m}$ , 143.42 $\mu \text{m}$ , 158.23 $\mu \text{m}$ , and 180.19 $\mu \text{m}$ ) distributed along a single fiber. With its simple structure, energy control, and multipoint functionality, this all-fiber laser-ultrasonic actuator shows great potential in future multipoint ultrasound applications.

This paper proposes and demonstrates an ultrasensitive refractive index (RI) sensor based on harmonic Vernier effect (HEV) and a cascaded Fabry–Perot interferometer (FPI). The sensor is fabricated by sandwiching a hollow-core fiber (HCF) segment between a lead-in single-mode fiber (SMF) pigtail and a reflection SMF segment with an offset of 37 µm between two fiber centers to form a cascaded FPI structure, where the HCF is the sensing FPI, and the reflection SMF is the reference FPI. To excite the HEV, the optical path of the reference FPI must be multiple times (>1) that of the sensing FPI. Several sensors have been made to conduct RI measurements of gas and liquid. The sensor’s ultrahigh RI sensitivity of up to ∼378000 nm/RIU can be achieved by reducing the detuning ratio of the optical path and increasing the harmonic order. This paper also proved that the proposed sensor with a harmonic order of up to 12 can increase the fabricated tolerances while achieving high sensitivity. The large fabrication tolerances greatly increase the manufacturing repeatability, reduce production costs, and make it easier to achieve high sensitivity. In addition, the proposed RI sensor has advantages of ultrahigh sensitivity, compactness, low production cost (large fabrication tolerances), and capability to detect gas and liquid samples. This sensor has promising potentials for biochemical sensing, gas or liquid concentration sensing, and environmental monitoring.

A femtosecond soliton erbium-doped fiber ring laser with the symmetrical saturable absorber (SA) of graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) is proposed and proved. Based on the nonlinear multimode interference (NL-MMI) effect of SA, the fiber laser achieved femtosecond soliton mode-locking operation and repetition rate tuning. The duration of soliton was 364 fs at 1562.5 nm and repetition rate was tunable from 10.29 MHz to 763.36 MHz. In the structure of SA, a short step index multimode fiber (SIMF) was inserted between two graded index multimode fibers (GIMFs) to generate more high-order modes, adjust the self-focusing length, and improve operation stability of mode-locked fiber laser. The SA also has the advantages of immunity to the external environment variation, high damage threshold and inoxidizability, which make the laser operate stably for a long time.

A high-sensitivity fiber-optic strain sensor, based on the Vernier effect and separated Fabry–Perot interferometers (FPIs), is proposed and experimentally demonstrated. One air-cavity FPI is used as a sensing FPI (SFPI) and another is used as a matched FPI (MFPI) to generate the Vernier effect. The two FPIs are connected by a fiber link but separated by a long section of single-mode fiber (SMF). The SFPI is fabricated by splicing a section of microfiber between two SMFs with a large lateral offset, and the MFPI is formed by a section of hollow-core fiber sandwiched between two SMFs. By using the Vernier effect, the strain sensitivity of the proposed sensor reaches $\text{1.15 nm/}\mu \varepsilon $ , which is the highest strain sensitivity of an FPI-based sensor reported so far. Owing to the separated structure of the proposed sensor, the MFPI can be isolated from the SFPI and the detection environment. Therefore, the MFPI is not affected by external physical quantities (such as strain and temperature) and thus has a very low temperature cross-sensitivity. The experimental results show that a low-temperature cross-sensitivity of $\text{0.056 } \mu \varepsilon /^ {\circ }{\text{C}}$ can be obtained with the proposed sensor. With its advantages of simple fabrication, high strain sensitivity, and low-temperature cross-sensitivity, the proposed sensor has great application prospects in several fields.

We theoretically and experimentally demonstrate an all-fiber multi-channel ultrasonic sensor using a switchable fiber Bragg gratings (FBGs) filter in an erbium-doped fiber laser (EDFL). The FBGs are not only used as the filter to determine the laser wavelength, but also as the sensing element to induce the intensity response of the lasing line via cavity loss modulation from the ultrasound-induced relative spectral shift of the matched FBGs. The switchable FBGs filter consists of a tuning FBG and several sensing FBGs. Multi-channel ultrasound detection is achieved via this filter by tuning an FBG to scan the spectra of multiple sensing FBGs. The ultrasonic-detection channel can be flexibly and efficiently switched via tuning the tunable FBG to match with any one of the sensing FBGs. A novel dynamic response model of the EDFL based on wavelength-dependent gain is proposed and developed to study the effects of different spectrally matched FBG positions and the consistency of the ultrasound response of each detection channel. The theoretical results show that the optimal sensing position is at the overlapping regions of spectra when the slope of the FBGs is greatest and the laser power is relatively high. Meanwhile, the consistency of the ultrasound response for each detection channel is influenced by the laser-resonance condition of the EDFL and can be optimized by adjusting the laser-cavity loss. Such theoretical results are well-verified experimentally. This sensor-laser-integrated system achieves high ultrasonic detection response since cavity-loss modulation is related to the amplifying effect of the laser. Using this method, an eight-channel switchable ultrasonic-sensing system has been demonstrated, covering nearly a 16-nm spectral range. By further controlling the cavity loss in the laser system, the consistency of ultrasonic response of each detection channel was optimized. The proposed all-fiber system has multiple- detection channels in a single laser system and consistent ultrasonic-detection response at each channel; it shows great potential for fiber-optic-ultrasonic-detection applications.

We demonstrate the absorption-based fiber humidity sensors working near 1950 nm wavelength which is a strong water absorption peak. No additional coating of humidity-sensitive material is needed for the proposed relative humidity (RH) fiber sensors. Two sensor structures including a taper fiber and a microfiber knot resonator are fabricated. For the taper fiber sensor, upto 0.18 mW/% RH sensitivity has been achieved via direct power measurement. For the fiber knot sensor, the RH variations induce both extinction ratio change and wavelength shift. The optical spectra of the fiber knot resonator under different RH are measured, and the extinction ratio and wavelength shift sensitivity are measured to be 0.034 dB/% RH and 10 pm/% RH, respectively. The response time for the tapered fiber is 1.13 s for RH increasing from 28.6% to 53.4% and 2.27 s for the reverse operation. The microfiber knot sensor can respond in 0.8 and 1.55 s accordingly. The sensor performance for the two structures is also investigated under different temperatures from 25 °C to 45 °C and the results indicate negligible impact from the temperature variations. We believe the simple fabrication and low cost of the sensor will make it potential and practical for the RH measurement.

We propose and demonstrate a multi-point, self-adaptive fiber ultrasonic sensor based on fiber Bragg gratings (FBGs). The sensor is constructed from matched FBG pairs (FBGPs) and a tunable optical filter in a fiber ring laser. FBGPs with different Bragg wavelengths are used as both the comb filter to produce potential lasing lines and the ultrasonic sensing elements. The ultrasonic signal is directly detected by monitoring the intensity response at each laser channel to the cold-cavity loss modulation from the spectral shift of matched FBGPs. The laser channel between the FBGPs is actively switched using the tunable optical filter, thereby achieving multi-point and switchable detection yet avoiding mode competition in the lasers. Meanwhile, to achieve self-adaptability, the two FBGs of the FBGP are fixed side by side at the same location of the structure such that both FBGs respond similarly to static strain and temperature variation. The multi-point system is promising for the robustness in the practical applications because it is insensitive to static strain ranging over 1400 μ ϵ and temperature variation from 20 °C to 50 °C, respectively.

This study experimentally demonstrates a high-sensitivity fiber-optic relative humidity (RH) sensor based on sensitivity amplification and a reduction mechanism, employing an internal–external Fabry–Perot cavity (IEFPC) Vernier effect and a chitosan film as a Fabry–Perot (FP)-sensing cavity. The proposed sensor is constructed using cascaded FP interferometers comprised of an air cavity formed by a hollow-core fiber (HCF), a chitosan cavity, and an air–chitosan hybrid cavity. The chitosan cavity is fabricated by dipping the HCF into a chitosan solution to form a thin chitosan film. Thus, the thickness of the chitosan film could be controlled precisely based on dipping time and capillary effect. As the optical path lengths of an air–chitosan hybrid cavity and an air cavity are similar, the IEFPC Vernier effect is generated, amplifying the air–chitosan hybrid cavity’s low sensitivity to the chitosan cavity’s high sensitivity. The experimental results agree with the theoretical analysis, supporting the fact that the sensor’s sensitivity is related only to the thickness of the chitosan film. The sensitivity of the sensor reaches up to 7.15 nm/% RH, ranging 40%–92% RH at 25°C. Fabrication of the proposed sensor is cost-effective. The proposed sensor also exhibits superior stability performance, a low-temperature cross-sensitivity of 0.0068% RH/°C, and repeatable fabrication. The proposed IEFPC Vernier effect model functions well for cascaded cavities, which plays a guiding role in the sensitivity improvement of such a structure within a fiber-optic sensing context.

A Q -switched mode-locked square noise-like pulse (QMLSNLP) is generated in a nonlinear polarization rotation passively mode-locked fiber laser. When the pump power changes from 154 mW to 414 mW, the frequency of the Q -switched envelope varies from 21.7 kHz to 38.9 kHz, while the duration of the Q -switched envelope decreases from 5.1 µ s to 3.2 µ s , correspondingly. In the meantime, QMLSNLP keeps the fundamental repetition rate constant, and the pulse duration increases from 3.4 ns to 6.7 ns. By inserting different lengths of single-mode fiber into the ring cavity, the evolutions of QMLSNLP are measured and analyzed. According to the cavity parameters and experimental results, impacts of the cavity length on QMLSNLP are investigated in detail.

We designed an erbium-doped fiber laser based on a semiconductor saturable absorber mirror. The switch of Q-switched mode-locking and continuous-wave mode-locking was obtained by adjusting the pump power.

Tian, J.J.; Liu, Y.J., and Yin, Z.D., 2020. Relationship between coastal foreign direct investment & industrial upgrading of China under the condition of the Belt and Road initiative. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 695–699. Coconut Creek (Florida), ISSN 0749-0208.At present, the issuance of the relationship between foreign direct investment & the transformation and upgrading of domestic industrial structures has been controversial under the condition of the construction of the “Belt and Road” of China. Based on the data from 2008 to 2018, the VAR model is applied for studying the interrelationship between foreign direct investment in sixty four countries along the “Belt and Road” and the transformation and upgrading of domestic industrial structures according to the experience since China has joined in Word Trade Organization (“WTO”); and it is found that in this kind of countries, the direct investment is without any statistical significance on the industrial upgrading of China so far; nevertheless, the industrial restructuring of China still in turn accelerates the going out intention of companies and promotes direct investment in this kind of countries.

The orbital angular moment (OAM) of light has been proved to be useful in plenty of applications. By transmitting the OAM of the focused light field to a particle, it will be orbited around the optical axis. Therefore, it is necessary to study the OAM distribution of the focused light field used to manipulate the particles. In this application, the widely used paraxial approximation is no longer sufficient due to the tightly focused beam. We employ the higher-order Poincaré sphere to represent the Laguerre–Gaussian (LG) beams with arbitrary polarization. Then the Rayleigh–Sommerfeld integral method and the q -parameter method are used to derive the analytical expression of the light field on the focal plane. Based on this, the OAM density expression of the tightly focused LG beam is derived. In the numerical simulation, we study and analyze the unique intensity distributions and OAM distributions of tightly focused linear polarized, radial polarized, and circular polarized LG beams. The results could be leveraged to further explore the applications of the polarized vortex beam.

A photo-invertible helical cholesteric superstructure was constructed by doping a novel chiral fluorescence photoswitch and a static dopant with opposite handedness into a nematic host. The handedness of circularly polarized luminescence can be reversibly inverted accompanied by a positive-negative change of luminescence dissymmetry factor values upon alternate light irradiations.

A rapid and precise phase-retrieval method based on Lissajous ellipse fitting and ellipse standardization is demonstrated. It only requires two interferograms without pre-filtering, which reduces its complexity and shortens the processing time. The elliptic coefficients obtained by ellipse fitting are used for ellipse standardization. After compensating phase-shift errors by ellipse standardization, the phase distribution is extracted with high precision. It is suitable for fluctuation, noise, tilt-shift, simple and complex fringes. This method is effective for the number of fringes less than 1. The reliability of the method is verified by simulations and experiments, indicating high accuracy and less time consumption.

In this paper, we employ a symmetrical graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) structure as artificial saturable absorber to achieve mode-locked operation in an Erbium-doped fiber laser. After optimizing the cavity length, pump power and orientation of polarization controller, noise-like pulse (NLP) is built in anomalous dispersion region experimentally. It is worth noting that except for the traditional NLP, a special NLP with unique features is obtained whose temporal and spectral properties are different from the known case on NLP reported before. According to the experimental results, we also acquire and compare properties of subpulse within NLP envelope with the change of pump power. Last but not least, harmonic of the peculiar NLP is found under appropriate cavity conditions.

A severe infectious disease characterized by nephritis, hepatitis and splenitis has attacked goslings around Shandong province in China since 2016. A novel chicken-origin avian orthoreovirus (ARV) was isolated with LMH cells from affected goslings named Reo/Goose/SDPY/1116/17 (SDPY-ARV) strain, and the infection was successfully reproduced experimentally. The ARV-SDPY full genome sequencing was conducted using Next-Generation Sequencing (NGS) technique on Illumina HiSeq platform. The complete genome of SDPY-ARV was 23,427 bp in length and consist of 10 dsRNA segments ranged from 1192 bp (S4) to 3958 bp (L1) which encoding 12 viral proteins. Genomic sequence analysis showed that the SDPY-ARV strain is in the same branch with broiler, pheasant-origin ARV isolates, and shares 51.8–96.2% of nucleotide identity of σC gene with them; while only 49.3–50.3% with waterfowl isolates. In addition, the occurrence of 10 segments genetic reassortment of SDPY strain is confirmed among the PA15511, the 1733 and the PA13649 strains from America. In conclusion, the causative agent of gosling hemorrhagic necrotic hepatitis and nephritis occurring in China is a novel chicken-origin goose orthoreovirus.

In this study, we propose and demonstrate a multipoint fiber-optic laser-ultrasound transducer based on fiber waist-enlarged tapers (WETs), which are fabricated by taper fusing two single-mode fibers. The WET structure can effectively extract some of the light energy from the fiber core and transfer it to the cladding to form a series of higher-order modes that can be used to excite ultrasound waves. The light energy in the cladding can be absorbed and converted into ultrasound waves by the photoacoustic composite coating on the fiber near WET. The coupling efficiency of the WET is dependent upon its taper length and, therefore, can be easily controlled by the splicer during fabrication. Thus, by controlling coupling efficiencies of the WETs, a multipoint laser-ultrasound actuator with a balanced signal strength can be obtained. We constructed a prototype of the actuator and successfully generated ultrasound waves with balanced strengths at four points by connecting four WETs with coupling ratios of 25.24%, 32.25%, 49.52%, and 90.62% in a fiber link. This multipoint laser-ultrasound actuator is simple to fabricate and provides a balanced ultrasonic signal strength, and thus, has various potential applications in fiber-optic active ultrasound testing technologies.

A wavelength tunable, dark pulse, and bright pulse-switched dual-wavelength fiber ring laser is reported. Through adding high nonlinear optical fiber as a nonlinear medium in the fiber ring cavity, the double-wavelength dark-bright pulse pair can be formed. The separation of dark-bright pulse pair can be achieved by polarization beam splitter. The dark pulse and bright pulse with orthogonal polarization correspond to different wavelengths, respectively. Then, via tunable optical filter and polarization controller to filter out the wavelength we need and adjust the polarization, we achieved the interconversion of dark pulse and bright pulse in the same wavelength and the tunableness of wavelengths of dark pulse and bright pulse in our laser.

In 2017, an emerging disease outbreak with high mortality in goslings occurred in China. A novel goose astrovirus was isolated and identified as the causative agent of this disease. Genomic analysis revealed that this virus strain was significantly distinct from published astrovirus strains.

A severe infectious disease characterized with gout, haemorrhage and swellings of kidneys has affected goslings around the major goose-producing regions in China since November 2016. A Novel goose-origin astrovirus (AStV), designated as AStV/SDPY/Goose/1116/17 (AStV-SDPY) strain, was isolated from diseased goslings, and experimental reproduction of gout was successful using the AStV-SDPY strain. Additionally, the AStV-SDPY was conducted for its full genome sequencing characterization using next-generation sequencing (NGS) technique on Illumina HiSeq platform. A complete genome of the AStV-SDPY was 7,252 nt in length and encoded three viral proteins. Phylogenetic analysis revealed that AStV-SDPY strain belongs to an independent branch of avian astroviruses, and the nucleotide homology among AStV-SDPY and other classic avian astrovirus strains was only 48.8%-68.2%. Results of above data indicated the causative agent of the gosling gout occurring in China is a novel divergent goose astrovirus.

A high sensitivity humidity fiber sensor based on all-agar Fabry–Perot (FP) interferometer is proposed and experimentally demonstrated. The sensor is fabricated by filming a thin layer of moisture-sensitive agar to single mode fiber with end dipping method. Due to the all-agar FP cavity structure, both the size and the RI changes of agar film in the swelling effect are fully utilized to induce the frequency shift, the sensor exhibits a high sensitivity of 4.20 nm/%RH, with relative humidity (RH) ranging from 25%RH to 95%RH at 25 °C. Moreover, owing to the short FP cavity, $7.10~\mu \text{m}$ , the proposed sensor provides a short response time less than 340 ms with the humidity level changed from 64.0%RH to 74.2%RH. The proposed sensor also exhibits other superior performances in terms of good stability, low cost, and easy fabrication. Such good characteristics make the proposed sensor a good candidate for practical applications.

A high-sensitivity Fabry–Perot interferometer (FPI) strain sensor based on a concave-core photonic crystal fiber (CPCF) was proposed and demonstrated. The FPI was formed by directly splicing a CPCF to a standard single-mode fiber. The CPCF was fabricated by cleaving a high-numerical-aperture solid-core photonic crystal fiber under axial tension using a traditional fiber cleaver. An FPI strain sensor with a cavity length of 4.85 μ m and a strain sensitivity of 31.58 pm/ μ ϵ was successfully produced. The sensor also demonstrated a low temperature sensitivity of 0.653 pm/°C, reducing the cross-sensitivity between tensile strain and temperature. The benefits of the proposed sensor include simple fabrication, high strain sensitivity, and low temperature cross-sensitivity, making it attractive for practical applications.

We propose and demonstrate a fiber sensor for simultaneous temperature and strain measurements. The proposed sensor is implemented by a cascaded-cavity Fabry–Perot (FP) fiber interferometer. The two cascaded FP cavities comprise a micro-air-cavity in a hollow-core tube fiber and a micro-silica-cavity in a standard single-mode fiber. To separate the interference spectrum of each FP cavity, the total spectrum is filtered in the frequency domain through band-pass filters, whose central frequencies were predesigned based on the relationship between the spatial frequency and free spectral range of each FP cavity. The different cross-sectional areas and thermal-optic coefficients of the two FP cavities confer different sensitivities to temperature and strain. Both parameters were measured simultaneously by tracking the wavelength shifts in the filtered interference spectra of the FP cavities. Moreover, the temperature–strain cross-sensitivity was compensated by solving a sensitivity-coefficient matrix equation for the two cavities, using the calibrated temperatures and strains. Other advantages of the proposed sensor are simple fabrication and an all-fiber structure. Owing to these properties, the proposed sensor is potentially applicable to real sensing applications.

Versatile structures of wavelength-dependent bound solitons are obtained based on nonlinear polarization rotation (NPR) mode-locked technology in an anomalous-dispersion fiber laser. After optimizing the intra-cavity birefringence and finely adjusting the operating wavelength of the laser, both the conventional soliton and loosely bound-state soliton pairs can be generated and switched under different operating wavelengths. With the evolution of bound state, the spectral interference fringes show significant changes and the temporal separation between bound solitons varies accordingly. Altering initial settings of laser parameters, wavelength-dependent multiple-soliton bound states are also found experimentally. Moreover, the formation and evolution mechanism of the bound states are explored and analyzed in this work.

The formation and evolution of dip-type spectral sidebands are numerically and experimentally researched in a soliton fiber ring laser passively mode locked by the nonlinear polarization rotation (NPR) technique. We provide a theoretical model that can predict the positions of dip-type sidebands, and point out that the formation of the dip-type sidebands is due to the local destructive interference effect between the soliton and dispersive waves induced by the periodic soliton perturbations in the laser cavity. The expression describing the position of dip-type sidebands is strictly deduced, which indicates that the positions of dip-type sidebands on the spectrum can be changed with the pulse width variation. The reliability of the theoretical model of dip-type sidebands is verified by experiments and simulations; both the experimental observations and numerical simulations can well confirm the theoretical predictions.

A switchable and tunable multiwavelength erbium-doped fiber laser is proposed and demonstrated based on a two-stage Lyot filter and intensity-dependent loss (IDL) effect induced by a nonlinear optical loop mirror (NOLM). The proposed laser can achieve multi-parameter individually tuning functions, such as adjusting the channel-spacing, number, and spectral-range of lasing line. The channel spacing can be switched via adjusting the beam's polarization in the Lyot filter among 0.53, 0.78, and 1.56 nm. Meanwhile, the number and the spectral range of the multiwavelength lasing line can be independently controlled by IDL modulation through the combination of adjusting pump power and the birefringence in the loop of the NOLM. The individual tuning method of the proposed laser on each specific output characteristic provides more convenience and practicality to the applications.

In this paper, we investigated the mode splitting in subwavelength grating metamaterial ring resonators caused by the break of rotational symmetry, which can be leveraged to detect 25 nm diameter single nano particle.

Two novel chiral fluorescent photoswitches bearing unsymmetric α-cyanothienylethene as emissive/photosensitive scaffold and bridged binaphthyl moieties as chiral entities are synthesised. The effects of the position of cyano group in switch 8 and 9 on the photoluminescence and photoresponsive properties of them in organic solvent and cholesteric liquid crystals (Ch-LCs) are explored. Both of these two photoswitches undergo partial reversible Z/E photoisomerisation accompanied by changes in fluorescence intensity under the light irradiations in both organic solvent and LC media. However, fluorescence quantum yields of switch 8 are much higher than those of switch 9. Meanwhile, the initial helical twisting power (HTP) value of switch 8 in LC media is much higher than that of switch 9, which is ascribed to their distinct geometries arising from different positions of cyano group on the C=C bond in them. Moreover, the switch 8-doping Ch-LC system exhibits more fast response and better reversible switching behaviours compared to Ch-LC system containing switch 9. Finally, simultaneous photoswitching of the reflection colour and fluorescence intensity in the Ch-LC sample is demonstrated. This work provides an idea for designing chiral fluorescent photoswitches with advanced photoluminescence and photoswitching characteristics.

We propose to place subwavelength segments in the evanescent field region of strip waveguide to reduce grating strength. Millimeter-long grating is designed which is essential to the implementation of large aperture optical phased arrays.