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A dual-channel surface plasmon resonance (SPR) sensor, based upon a multimode-single mode-multimode-single mode- multimode (MSMSM) fiber structure, is reported for the simultaneous measurement of temperature and refractive index. One channel is coated with an indium tin oxide-silver layer for refractive index sensing, and the channel is coated with Au and cyclohexane layer for temperature sensing. The experiments show that the sensor provides high sensitivity with values of 3379 nm/RIU across the refractive index range from 1.333 to 1.3699 and −3.163 nm/°C from 40 °C to 90 °C. The cross-sensitivity problem is resolved by the dual-wavelength matrix method. Moreover, the proposed sensor has good stability, low cost, and a compact structure and may be employed in biology, chemistry, and environmental testing. [ABSTRACT FROM AUTHOR]

In this paper, a large mode area photonic crystal fiber (PCF) based on chalcogenide glass A s 2 S 3 with excellent bending resistance and single-mode operation characteristics is proposed.The guiding properties of the PCF are investigated using the full vector finite element method with perfectly matched layers. Numerical results indicate a single-mode bandwidth of 170 nm, covering the wavelength range from 1.1 to 2.8 μ m. The effective mode area exceeds 720 μ m 2 for a wavelength of 2.0 μ m and a bending radius of 10 cm. The bending radius ranges from 7 to 40 cm, 5 to 30 cm, and 3 to 19 cm at the three commonly used operating wavelengths of 1.31 μ m, 1.55 μ m, and 2.0 μ m, respectively. As a result, the designed chalcogenide PCF is bend insensitive and can maintain stable single-mode operation even at different working wavelengths. Moreover, the proposed PCF is easy to fabricate and has potential for application in high power fiber lasers. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) magnetic field sensor with hexagonal lattice is proposed. Magnetic fluid is injected into two air holes for magnetic field sensing. In order to obtain the optimal structure of magnetic field sensor, four types of hexagonal PCF models are discussed and compared. The influence of structure parameters d, d 1 , d 2 , t, D, and Λ on sensing characteristics is analyzed when the PCF-3 is determined. The maximum sensitivity and corresponding resolution can reach 1150 pm/Oe and 0.087 Oe, and figure of merit (FOM) is up to 0.0556/Oe in the magnetic range of 30–150 Oe. The maximum wavelength sensitivity is 25000 nm/RIU, when the range of refractive index (RI) is from 1.420 to 1.450. In addition, the temperature sensitivity is only 65 pm/K, indicating small temperature crosstalk. The proposed sensor has the advantages of large FOM, good linearity and simple structure, enabling accurate measurement of magnetic field, especially suitable for weak magnetic field detection. Good performance makes it applicable to industrial production, military affairs, health and environmental monitoring. [ABSTRACT FROM AUTHOR]

In this paper, we propose a hexagonal photonic crystal fiber (PCF) suitable for broadened mid-infrared supercontinuum generation. The designed PCF has five air-hole rings with three different air holes, arranged in a triangle pattern. The central air hole is filled with G e 10 A s 22 S e 68 and the inner wall of the air hole is coated with A s 2 S 3 . In the mid-infrared wavelength range of 3400 nm to 4500 nm, the supercontinuum bandwidth increases with the increase of the pump wavelength, peak power, and pulse width. When the pump light source with a peak power of 5 kW and the input pulse width is 200 fs, a 10 mm fiber can produce an extremely wide supercontinuum spectrum spanning 6000 nm. In addition, optical parameters including dispersion, confinement loss, effective mode area, and nonlinear coefficients are numerically investigated by the finite element method. The results show that at a wavelength of 4000 nm, the second order dispersion of the fiber is 8.81 × 10 - 27 s 2 m - 1 and the nonlinear coefficient is 972.5 W - 1 km - 1 . The designed photonic crystal fiber is stable, dispersion flat, and can meet the application requirements of obtaining broad supercontinuum spectrum. [ABSTRACT FROM AUTHOR]

In this study, we design a refractive index (RI) sensor using a novel cadmium telluride photonic crystal fiber (TPCF). Based on four-wave mixing (FWM), the changes in RI can be accurately detected, and RI sensing in the mid-infrared region (MIR) can be achieved by detecting wavelength shifts in the Stokes and anti-Stokes spectra caused by the changes in RI of the liquid to be measured. When the pump wavelength of FWM lies in the normal and abnormal dispersion regions of the TPCF, the RI response of the idler frequency wave and the signal wave are analyzed by numerical simulation methods. The simulation results show that the RI sensitivity of the sensor can be as high as 7692 nm/RIU with a linearity is up to 99.9% at the pump wavelength of 3380 nm. To our knowledge, the RI sensing sensitivity of the MIR is presented for the first time in this study by using FWM in the non-silicon PCF. [ABSTRACT FROM AUTHOR]

In this work, a low-loss As2S5 optical fiber with 0.1 dB/m at 1545 nm was designed and fabricated, whose residual birefringence provided an opportunity for investigating the polarization modulation instability (PMI). Using a nanosecond laser operated at ∼1545 nm as the pump source, PMI and the stimulated Raman scattering (SRS) were experimentally investigated in a 3 m As2S5 optical fiber. During the SRS process, the amplified CW signal at 1632 nm and 1633 nm induced the PMI. To the best of our knowledge, this is the first report on the PMI effect induced by the amplified signal in the first-order SRS. The PMI gain was measured to be 24.4 dB at the signal of 1551 nm with the pump power of 20 mW, and the Raman gain was measured to be 31.2 dB at the signal of 1632 nm with the pump power of 41 mW. This investigation on the PMI gain and Raman gain in the As2S5 optical fiber may provide a reference for the development of fiber amplifiers, fiber lasers, and optical communication. [ABSTRACT FROM AUTHOR]

A four-hole tellurite microstructured optical fiber (MOF) was designed and fabricated based on TeO2–Bi2O3–ZnO–Na2O (TBZN), and the fiber loss was 0.1 dB/m@1550 nm. Based on a 3 m tellurite MOF, dispersive wave (DW) generation and evolution was experimentally investigated at the pump wavelengths of 1778 nm, 1812 nm, and 1878 nm. With the increase of the average pump power, DWs trapped by optical solitons were observed at the blue edge wavelength, but their formation became more and more difficult with the pump wavelength shifting far away from the zero-dispersion wavelength. The variation pattern of center wavelengths and peak powers of the fundamental optical solitons and DWs were investigated: the center wavelength distribution satisfied the group velocity matching; the peak power of the fundamental DW gradually exceeded that of the fundamental optical soliton with the increase of the average pump power. Furthermore, using the generalized nonlinear Schrödinger equation, simulation on the generation of DWs and optical solitons was carried out at 1778 nm, 40 mW, the result of which agreed well with the experimental observation. This investigation is instructive for DW applications in tunable laser sources, wavelength conversion, and time frequency metrology. [ABSTRACT FROM AUTHOR]

A temperature sensor based upon a single mode - multimode-single mode – multimode - single mode (SMSMS) fiber structure is experimentally demonstrated. The SMSMS structure is covered by ethanol-glycerol solution, and changing the ratio of ethanol to glycerol changes the temperature sensitivity. A theoretical calculation was developed to characterize the influence of the ethanol-glycerol content upon the sensor performance,. Multimode interference (MMI) occurs between single mode fibers (SMF) and multimode fibers (MMF), and temperature measurements were achieved by monitoring the movement of the interference profile in the transmission spectrum. The results show that covering the SMSMS structure with an ethanol-glycerol solution improves the temperature sensitivity of the sensor. The temperature sensitivity was is 0.700 nm/°C from 30 °C to 80 °C. [ABSTRACT FROM AUTHOR]

This paper reports a double-sided polished microstructured fiber based on the refractive index that simultaneously measures the refractive index and temperature. Two polished planes were introduced into the cladding. A gold film and polydimethylsiloxane are deposited on one side of the plane for temperature measurements, and graphene layers are coated on the surface of the silver film on the other side for refractive index measurements. The finite element method is used to characterize the sensing characteristics of the sensor. The results show that when the liquid refractive index is from 1.36 to 1.4 and the temperature from 70 °C to 110 °C, the maximum sensitivity of the sensor is 15,000 nm/RIU and 8.8 nm/°C, respectively. The double-sided polished structure facilitates the development of multi-parameter measurement sensors for various applications. [ABSTRACT FROM AUTHOR]

A surface-modified D-type photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is reported for application as a polarization filter and refractive index sensor. The gold film is deposited on the surface of the designed fiber structure to stimulate the SPR effect. Through etching, the upper surface of the designed structure forms an angle of 170°. The etching angle changes the distance between the fiber core and the surface of gold film to enhance the local field SPR effect. The designed optical device is numerically simulated using the finite element method (FEM), the mode distribution is studied, and the coupling phenomenon is analyzed. At a wavelength of 1.31 µm, the y-polarization loss is 1307.90 dB/cm, while the loss of x-polarization is 1.13 dB/cm; at 1.55 µm, the y-polarization loss is 1755.19 dB/cm, while the x-polarization loss is only 1.24 dB/cm. In the case of the same structure parameters as the proposed polarization filter, of which communication window is 1.55 µm, the designed structure also serves as a refractive index sensor from 1.330 to 1.365. The average sensitivity of the refractive index sensor is up to 4857 nm/RIU, and the highest sensitivity is 7588 nm/RIU when the refractive index is 1.365. The results show that the reported SPR-based PCF simultaneously implements dual communication window polarization filtering and refractive index sensing. Hence, the designed device has promising applications with good filtering and sensing performance. [ABSTRACT FROM AUTHOR]

In this paper, we propose and experimentally validate passively mode-locked erbium-doped fiber lasers utilizing CNFs as saturable absorbers (SAs). A mode-locked pulse was observed, with a central wavelength of 1562 nm and a bandwidth of 3.56 nm after inserting the CNF film into the ring cavity. The pulse duration and repetition rates are 1.28 ps and 54 MHz, respectively. The maximum output power can reach 1.93 mW. To our knowledge, this is the first report of CNF as SA in erbium-doped fiber lasers. [ABSTRACT FROM AUTHOR]

A D-shaped photonic crystal fiber (PCF) polarization filter and sensor with a standard hexagonal arrangement of pores is designed. The effects of geometric parameters, metal film thickness, liquid refractive index, and optical material refractive index on polarization filtering and sensing characteristics are analyzed by the finite element method (FEM). The proposed PCF shows single-polarization filtering in communication window and has ultra-high corresponding bandwidth. At the 1.55 µm communication window band, the confinement loss of the y-polarized core mode is 819.27 dB/cm, while the x-polarized core mode is only 3.45 dB/cm. The crosstalk (CT) reached a maximum of 708.6 dB in the communication bands, and the corresponding bandwidth reaches 1000 µm when the fiber length is 1 mm. Meanwhile, the D-type PCF is widely used in sensing because it avoids filling the gold film and analyte in the internal pores. The change in the thickness of the mental coating from 39 nm to 22 nm provides the proposed PCF with sensing properties. By reducing the refractive index of fiber material, the maximum sensitivity is 10,741 nm/RIU. When the refractive index measurement range of the analyte is specified from 1.33 to 1.36, the average sensitivity reaches 7313 nm/RIU. Good performance enables the proposed compatible filtering and sensing PCF may be used in a wide range of scenarios. [ABSTRACT FROM AUTHOR]

Dispersion is a factor that causes the axial resolution to decrease in optical coherence tomography (OCT). In this paper, an artificial neural network (ANN) is reported for correcting the dispersion problem. By training a neural network, the dispersion-free spectral signal is predicted only from a given interference spectral signal. First, the dispersion principle of OCT is analyzed. Next, the process for finding the global optimum of dispersion-free spectral signal distribution is described as a training process, and the ANN model is introduced. Lastly, simulation and experiments show that the presented method improves the axial resolution of the system. Accordingly, the ANN model fits the non-linear relationship between input and output, and the spectral response shows the problem of full width at half maximum (FWHM) due to dispersion in OCT which is of great significance. [ABSTRACT FROM AUTHOR]

As a type of carbon-based material, zero-dimensional carbon nano-onions (CNOs), with outstanding physical and chemical properties, have attracted enormous attention. However, the performance of CNOs has not yet been verified in ultrafast photonics. In this work, we demonstrated broadband pulse generation induced by CNO modulators. CNOs were synthesized by the chemical vapor deposition technique with a diameter of ∼45 nm, which presented linear and nonlinear optical response properties. As the fabricated CNO film was embedded into the erbium-doped fiber laser as the saturable absorber, a Q-switched laser operating at 1565 nm was achieved. To further verify the potential of the CNO modulator, we then proposed a combination of CNOs and D-shaped fibers as the optical modulation platform. Ultrafast fiber lasers were achieved at 1562 and 1932 nm with good stability and a high damage threshold, respectively. Our results provide a channel for carbon-based materials in nonlinear optics and ultrafast photonics. [ABSTRACT FROM AUTHOR]

Titanium boride (TiB2), as a kind of metal boride material, has exhibited extraordinary physical and chemical properties. However, few studies have been dedicated to determine their potential for application in nonlinear optics and ultrafast photonics. In this work, we first demonstrate the fabrication of a TiB2 saturable absorber (SA) with broadband absorption covering from 400 to 2500 nm. TiB2 nanoparticles (NPs) with an average size of 200 nm, good stability and high hardness are prepared through a metal-hydrolysis-assisted synthesis method. A Q-switched fiber laser operating at 1559 nm is realized by using a TiB2 film as the SA. By depositing the TiB2 NPs onto the side-polished fiber platform to fabricate the SA, ultrafast fiber lasers at 1.56 and 2 μm can be achieved with pulse durations of 596 and 856 fs, respectively. Our experimental results validate that the integrated TiB2-based devices exhibit great potential as nonlinear optical media for ultrafast optical applications. [ABSTRACT FROM AUTHOR]

Photonic crystal fibers (PCFs) have brought tremendous advancements due to their predominant feature of a peculiar air-hole arrangement in the 2D direction. Functional materials like metals, magnetic fluids, nematic liquid crystals, graphene and so on, are being extensively adopted for integration with PCFs to obtain extraordinary transmission properties. This review takes the development stages of photonic devices based on functional material-infiltrated PCFs into consideration, covering the overview of common materials and their photoelectric characteristics, state-of-art infiltrating/coating techniques, and the corresponding applications involving polarization filtering and splitting devices in optical communication and sensing elements related to multiple-parameter measurement. The cladding airhole of PCFs provides a natural optofluidic channel for materials to be introduced, lightâ€"matter interaction to beenhanced, and transmission properties to be extended, in this case, a lab on a fiber are able to be implemented. This paves the way for the development of photonic devices in the aspects of compact, multi-functional integration as well as electromagnetic resistance. When the PCFs are integrated with the phemomenon of surface plasmon resonance, the property of tunable refractive indices, and the flexible geometry structures, it comes up to some representative researches on polarization filters, multiplexer-demultiplexers, splitters, couplers and sensors. It makes a candidate for widespread fields of telecommunication, signal-capacity, and high-performance sensing. [ABSTRACT FROM AUTHOR]

A Sagnac interferometer based optical fiber ultraviolet (UV) sensor is theoretically proposed and experimentally demonstrated in this work. A layer of ZnO film was deposited upon the surface of a silica no core fiber (NCF) using the magnetron sputtering method. Since the ZnO film was sensitive to UV, the ZnO-coated NCF was introduced into the Sagnac interferometer to help convert changes of the UV irradiance to the wavelength shifts of the interference spectrum. In comparison with the preparation of ZnO nanostructures, the ZnO film had the advantage of simple operation, high deposition rate, good adhesion and stable structure. The influence of the ZnO film thickness on the UV response was investigated, which proved that with the increase of the film thickness, the UV sensitivity decreased gradually. When the ZnO film thickness was 30 nm and the UV irradiance varied from 0 mW/cm2 to 19.95 mW/cm2, the designed sensor had the highest sensitivity of −124.9 pm/(mW/cm2) (R2 = 0.9854) and a detection accuracy of 0.4 mW/cm2. The proposed sensor has competitive sensitivity, high linearity, satisfactory repeatability and stability, which can be expected to conduct high-precision UV sensing in industrial, biomedical and military regions. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-core photonic crystal fiber (PCF) refractive index sensor. And we use the full vector finite element method (FEM) under the anisotropic perfect matching layer (PML) boundary condition to study the effects of various parameters of the sensor on performances. By two airholes which filled with the liquid to be analyzed, the two cores coupled with each other, the refractive index range is 1.36–1.44. Numerical calculations were carried out on the sensor characteristics. The simulation results show that: when the refractive index range is 1.36–1.42, the average sensitivity can be up to 10,315 nm/RIU (refractive index unit), the highest sensitivity can be up to 13,502 nm/RIU when the liquid refractive index is 1.42, the quadratic fitting coefficient R 1 2 = 0.99969. And when the refractive index range is 1.42–1.44, the average sensitivity can be up to 17,980 nm/RIU, the highest sensitivity can be up to 22,380 nm/RIU when the liquid refractive index is 1.44, the quadratic fitting coefficient R 2 2 = 0.99999. The sensor we proposed is suitable for biomolecules and chemistry, as its conventional wide detection range with high sensitivity. Most importantly, a new idea of broadening the detection range is put forward for reference. [ABSTRACT FROM AUTHOR]

To obtain better filtering characteristics and transmission performance, an asymmetric gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) was designed and investigated. The surface plasmon mode is generated by coating gold film to the inner walls of two liquid-filled holes along the y polarization direction. Three air holes with different diameters are introduced near the core which break the symmetry of the primary fiber structure and make the resonance wavelengths of the x polarization and y polarization of the core mode well separated. The filtering performances are evaluated with the finite element method (FEM) based software. The numerical simulation shows that the confinement loss of y polarization is as high as 1375.94 dB/cm at 1.55 µm, while the x polarization loss is only 10.45 dB/cm. Furthermore, the crosstalk (CT) has a maximum of 1186.06 dB in the communication bands when the length of the fiber is 1000 µm. In the range from 1.1 µm to 2 µm, the bandwidth of the filter is approximately 900 nm. The asymmetry of the structure and liquid filling of gold-coated holes enhance the coupling strength of the filter. Meanwhile, the higher confinement loss, crosstalk and wider bandwidth may have useful applications for polarization filters with significance for the design of other filters. [ABSTRACT FROM AUTHOR]

A Sagnacinterferometer-based magnetic field sensor is theoretically proposed and experimentally demonstrated by taking advantage of the high birefringence of an asymmetric four-hole fiber (AFHF) as well as the sensibility of magnetic fluid (MF) to magnetic field. A variation in the magnetic field intensity would induce a change in the RI of MF, leading to a birefringence change of MF-filled AFHF and resulting in a shift of the interference spectrum. The magnetic field sensing can be realized by monitoring the spectral shift. The proposed sensor has a high sensitivity of 226.2 pm/Gs (2.96 ∼ 89 Gs) with a measurement accuracy of 0.221 Gs, accompanied with competitive linearity, good repeatability and stability. In addition, it is insensitive to ambient temperature disturbance. The proposed sensor can be used in industry, biomedicine, aerospace and other fields which require a magnetic field measurement with high precision and good stability. [ABSTRACT FROM AUTHOR]

We propose a dual-channel surface plasmon resonance (SPR) sensor based on hollow-core fiber (HCF) for the simultaneous measurement of the liquid refractive index (RI) and ambient temperature. The simultaneous monitoring of two parameters can effectively realize the temperature compensation of liquid RI measurement. One channel is coated with a silver film to sense the liquid RI, the other channel is coated with a gold film and polydimethylsiloxane (PDMS) to sense the ambient temperature, and the cross sensitivity of the multi-parameter measurement is solved using the dual-wavelength matrix method. The sensing performance of the proposed sensor is investigated both theoretically and experimentally, which proves that it can achieve high sensitivity in a relatively wide measurement range. The experiment shows that the liquid RI sensitivity is as high as 2400.079 nm/RIU in the RI range of 1.3333–1.3770, and the temperature sensitivity is −1.29 nm/°C in the temperature range of 40 °C–90 °C. This work provides a new scheme for the multi-parameter measurement, and the proposed sensor has the advantages of simple and compact structure, low cost, wide measurement range and high sensitivity, which promises broad application prospects in the simultaneous monitoring of liquid RI and temperature. [ABSTRACT FROM AUTHOR]

In this work, a tellurite microstructed optical fiber (TMOF) was designed and fabricated by 78TeO2-5ZnO-12LiCO3-5Bi2O3 (TZLB) glass, which provided an opportunity for investigating the stimulated Raman scattering (SRS) and four wave mixing (FWM). Using a nanosecond laser operated at 1545 nm as a pump signal, mid-infrared cascaded SRS was observed. At 60 mW, the continuous-wave (CW) signal gain was as high as 10.46 dB. During the FWM process, with the CW signal wavelengths changing from 1547 nm to 1560 nm, a maximum conversion efficiency (CE) of −27.05 dB was obtained. The SRS and FWM in the TMOF were numerically simulated, and the obtained results agreed well with the experiment. To the best of our knowledge, it was the first time to demonstrate simultaneously SRS and FWM in a TMOF. The proposed TMOF of extremely high nonlinearity can be exploited for the development of multifunctional multiplexing devices of Raman amplifiers and wavelength converters, and is expected to meet the increasing requirements of high-performance all-optical devices. [ABSTRACT FROM AUTHOR]

In this work, a new method was explored for developing temperature and relative humidity (RH) optical fiber sensors based on surface plasmon resonance (SPR). A SPR optical fiber sensor coated with carboxymethyl cellulose (CMC) and polydimethylsiloxane (PDMS) was proposed for the simultaneous measurement of RH and temperature. The sensor was fabricated by connecting two no-core optical fibers (NCFs) using multimode optical fibers (MMFs). Metal films were deposited on the surface of NCFs and further coated with CMC and PDMS. CMC coating was used for RH sensing based on the change of refractive index (RI) caused by water absorption; PDMS coating was used for temperature sensing based on its RI change with temperature. Univariate analysis showed that there was very weak interaction between RH and temperature measurement. For RH sensing, the sensitivities were −1.230 nm/RH%, −2.932 nm/RH% and −0.431 nm/RH% when RH were 50%~65%, 65%~70% and 70%~80%, respectively; for temperature sensing, the sensitivity was −2.213 nm/°C at 10 °C~50 °C. The proposed sensor can not only respond to both temperature and RH variation, but also compensate the cross sensitivity between the two parameters. It is simple in structure, easy to manufacture and efficient in the simultaneous detection of temperature and RH, which promises great application prospects in the fields of agriculture, food industry, biological field and other production activities. [ABSTRACT FROM AUTHOR]

As a member of the MXene family, tungsten carbide (WC), with its unique physical structure and excellent optical properties, possesses enormous development potentials in ultrafast optoelectronics. In this letter, A WC film saturable absorber (SA) is successfully demonstrated to induce passive Q-switching in an erbium-doped fiber laser (EDFL). The WC nanoparticles (NPs) are synthesized by a hydrothermal method. Stable Q-switched pulses are generated at 1558 nm with a threshold pump power of 141 mW, after inserting the prepared WC film into the EDFL ring cavity. As the pump power ranges from 141 mW to 193 mW, the repetition rate increases from 32.34 kHz to 35.8 kHz, while the pulse duration decreases from $5.5~\mu \text{s}$ to $4.16~\mu \text{s}$. When the pump power reaches a maximum power of 193 mW, the corresponding maximum pulse energy and output power are 81 nJ and 2.9 mW, respectively. To our best knowledge, this is the first report of utilizing WC as SA to achieve Q-switched pulses. Our research results provide a new reference for the realization of pulsed laser using MXene materials and reveal that WC has immense applications in nonlinear optics and ultrafast laser technology, which greatly broadens the frontier of materials for optoelectronic techniques. [ABSTRACT FROM AUTHOR]

A Fabry-Perot interferometer (FPI) temperature sensor was proposed by splicing a self-made hollow core anti-resonance fiber (HC-ARF) between two single mode fibers (SMFs). The HC-ARF was 2 mm long and one SMF was 20 mm in length. The SMF end face was coated with an Au film. When temperature varied from 45 °C to 85 °C, a sensitivity of 81.1 pm/°C was obtained at the waveband of 1550 nm∼1555 nm. When temperature varied from 35 °C to 95 °C, a sensitivity of 138.8 pm/°C was obtained at the waveband of 1571 nm∼1581 nm. Theoretical analysis suggested that the sensitivity of this proposed sensor can be easily adjusted by varying the length of the Au-coated SMF via the Vernier effect, which was confirmed by a subsequent experiment where the SMF length was varied from 20 mm to 170 mm. This work offers a simple sensitivity control method, and the proposed sensor is easy to manufacture, compact in structure, and convenient in performance control, which can be applied for a wide range of biological and chemical applications. [ABSTRACT FROM AUTHOR]

We theoretically proposed the concept of temperature sensing using the soliton self-frequency shift (SSFS) effect in a fluorotellurite microstructured fiber (FTMF) which had one ring of six alcohol-infiltrated air holes. The glass material for the fiber core was 70TeO2–20BaF2–10Y2O3 and the cladding AlF3–BaF2–CaF2–YF3–SrF2–MgF2–TeO2. Based on SSFS effect, temperature sensing in the mid-infrared (MIR) region was achieved by detecting the wavelength shift of solitons with the variation of temperature. Using a 2800 nm fiber laser with a pulse width of 131 fs as the pump light and a 0.5-m-long FTMF as the nonlinear media, the temperature sensing sensitivity could be as high as 2.09 nm/°C. To the best of our knowledge, this is the first study concerning temperature sensing in the MIR region by drawing on SSFS effect in a non-silica FTMF. [ABSTRACT FROM AUTHOR]

The metal‐to‐insulator transition behavior and the fast and reversible phase transition behavior in vanadium dioxide (VO2) have attracted widespread attention to study various potential applications. However, few studies have been focused on its nonlinear properties and applications in the pulsed laser field. Here, the authors report the design and synthesis of monoclinic nano‐VO2(M) saturable absorber with broadband absorption which spans the entire near‐infrared region, and high optical nonlinearity which is much higher than those of carbon nanomaterials, gold nanocrystals, and Cu1.8S nanocrystals, as measured in the same condition. The nano‐VO2(M) optical modulators are integrated into the fiber laser cavities, and demonstrate wideband Q‐switching operations at 1, 1.56, and 2 µm and mode‐locking operation at 2 µm, with a pulse duration of 765 fs. This work first reveals the outstanding nonlinear optical properties of nano‐VO2(M) and lays a foundation for its development in advanced nonlinear optical and photonic devices. [ABSTRACT FROM AUTHOR]

In this paper, a carboxymethyl cellulose (CMC)/graphene oxide (GO) composite film-coated humidity sensor was proposed based on thin-core fiber Mach-Zehnder interferometer (TCMZI). A segment of thin-core fiber (TCF) was spliced between two segments of single-mode fiber (SMF), and the TCF cladding was first corroded with hydrofluoric acid and then coated with a layer of CMC/GO film via optical driven deposition method. The relative humidity (RH) sensing characteristics of the sensor were experimentally investigated by observing the wavelength shift of resonant dips in the transmission spectrum, which showed that the CMC/GO composite film-coated TCMZI has good repeatability and stability in the measurement of humidity. A maximum average humidity sensitivity of −75.6 pm/%RH was obtained in the RH range of 35%-80%, nearly 2.048 and 3.237 times higher than that of CMC and GO single film coated ones. To the best of our knowledge, this is the first report on using the CMC/GO composite film for humidity measurement, and its excellent performance is expected to be extended to humidity sensitization of more fiber-optic sensors. The proposed sensor has the advantages of simple structure, easy fabrication, low cost, good stability and high performance, which can be applied to the fields of bio-chemical and medicine. [ABSTRACT FROM AUTHOR]

This article presented an investigation of nonlinear temperature sensing based on soliton self-frequency shift (SSFS) in an in-house fabricated microstructured optical fiber (MOF), and the sensing performance was evaluated by detecting the peak wavelength shift of soliton with the variation of temperature. Both theoretical simulation and experimental research were carried out and there was a good correspondence between the two results. The experimental sensitivity was as high as 0.451 nm/°C at 400 mW with a resolution of 0.2653 °C. Our work is a proof of concept of the optical fiber nonlinear phenomenon of SSFS to sensing technology. This temperature sensor does not involve additional fiber modification, and it has potential applications in biomedical, security, and harsh industrial environment. [ABSTRACT FROM AUTHOR]

According to Faraday rotation effect and Fresnel reflection theory, a novel magnetic field intensity sensor is theoretically proposed and experimentally demonstrated by introducing a 6.4-cm-long tellurite (76.5TeO2-6BiO3-11.5Li2O-6ZnO) no core fiber (TBLZ NCF) into the loop of Sagnac interferometer. The large Verdet constant of TBLZ NCF will bring about an apparent Faraday rotation angle in magnetic field sensing, and the large refractive index difference between TBLZ and silica fibers makes the Fresnel reflection more obvious. The designed sensor demonstrates a sensitivity of 13.51 pm/Gs with an accuracy of 1.47 Gs in the measuring range of 0–380 Gs. It has satisfactory linearity, repeatability, and stability, and does not require additional utilization of expensive magnetic field sensitive materials, exhibiting great application potential. [ABSTRACT FROM AUTHOR]

We present a novel D-shaped photonic crystal fiber sensor with double loss peaks based on surface plasmon resonance. The proposed sensor has a lot of better characteristics for refractive index detection compared with single-peak sensor. It is worth noting that the trough of the loss spectrum keeps unchanged as the analyte refractive index increases, which indicates that this sensor is extremely stable. In addition, numerical simulation shows that the average wavelength sensitivity can reach 29,000 nm/RIU and the maximum resolution is as high as 3.45 × 10−5 RIU. Furthermore, the coupling theory between fundamental mode and the surface plasmon polarization (SPP) mode is investigated in this paper. It is found that there is obvious competition between the resonant modes. This study has enlightening significance for us to understand the generation mechanism of polarization-entangled quantum photo source. [ABSTRACT FROM AUTHOR]

In hard rock deep-hole blasting excavation, blastholes are rarely utilized due to the clamping effect of the lower rock, which affects excavation progress and restricts the development and application of deep-hole blasting technology. Cut blasting is a key to improving excavation speed. In this paper, a new cutting method designating the two-step cutting technology was presented. The blasthole was divided into upper and lower sections without changing the blasthole layout. The upper section was detonated first, creating sufficient free surface for the lower section, which was detonated secondly. This created a larger cavity and improved blasthole utilization. Results showed good blasting effects for two-step cutting technology through theoretical analysis and engineering applications. The blasthole utilization rate was 96.1% when the upper and lower specific charge ratio = 0.78. This paper provides a good reference for resolving the low blasthole utilization problem in deep-hole blasting of vertical shafts within a hard rock. [ABSTRACT FROM AUTHOR]

Multi parameter measurement and device miniaturization are the development trend of optical fiber sensors. Here we propose a compact dual channel surface plasmon resonance (SPR) fiber sensor which can measure the liquid refractive index (RI) and ambient temperature in real time. This sensor coats metal and polydimethylsiloxane (PDMS) on the side of a no-core D-shaped fiber: the channel for measuring the liquid RI is covered by silver film, and the channel for temperature sensing is covered by gold film and PDMS. The sensing sensitivity is analyzed by finite element method. When the liquid RI is within 1.33~1.44 and the temperature is within 0~180 °C, the corresponding maximum spectral sensitivity is 12530 nm/RIU and −3.465 nm/°C, respectively. The sensor has wide detection range, compact structure and temperature compensation function, which is suitable for environmental monitoring and high-precision sensing. [ABSTRACT FROM AUTHOR]

Due to the unique optical properties and good thermal stability, GeAsSeTe microstructured optical fiber (MOF) offers tremendous opportunity for applications in mid-infrared range (MIR). In this article, we design a CS2-filled GeAsSeTe MOF whose core, inner and outer cladding adopt Ge15As25Se15Te45, Ge20As20Se17Te43 and Ge20As20Se15Te45 glass, respectively. Highly efficient four-wave mixing (FWM) is realized and ultrabroadband optical parametric gain is obtained. By analyzing the central parametric gain bandwidth change with the temperature variation, this CS2-filled GeAsSeTe MOF is proved to be highly sensitive concerning temperature sensing, the sensitivity being as high as 2.32nm/°C from −80°C to 45°C. Such high temperature sensing property have key prominence for developing optical fiber temperature sensor in MIR region based on FWM. To the best of our knowledge, this is the first study to propose temperature sensing in the MIR by drawing on central parametric gain bandwidth of FWM change in a GeAsSeTe MOF. [ABSTRACT FROM AUTHOR]

This paper proposes a novel refractive index profile design based on few-mode fibers (FMFs) which can support 4 linear polarization (LP) modes. We first present a FMF whose core is dually assisted by a nano-hole (NH) and a high-index-ring (HIR), and then substitute the dual assistance by an innovative graded concave HIR (GC-HIR) assisted structure. Using the finite element method (FEM), the parameters of the NH-HIR and GC-HIR optical fiber are adjusted to investigate their respective minimum effective refractive index difference (minΔneff), which is 2.012 × 10−3 for the former, and 2.532 × 10−3 for the latter. Both optical fibers have a significant improvement on the crosstalk suppression effect, and the GC-HIR optical fiber is even better. The proposed GC-HIR FMF with special refractive index profile has potential application prospects in mode division multiplexing (MDM) optical fiber communication system, and can provide theoretical foundation for the design and analysis of subsequent optical fibers and key components. [ABSTRACT FROM AUTHOR]

In this paper, multi-pair cross-phase modulation instability (XPMI) induced by multiple modes was experimentally observed in the deep normal dispersion regime of a tellurite high birefringence microstructured optical fiber (HBMOF) fabricated based on 76.5TeO2-6Bi2O3-11.5Li2O-6ZnO (TBLZ) glass. At the pump wavelength of 1062.7 nm three modes were emitted, whose modal birefringence was on the order of >10−5, providing a good platform for the multi-pair XPMI generation. During the experimental investigation, a picosecond laser was adopted as the pump source, and a three-pair XPMI induced by the three modes was observed in the deep normal dispersion regime of the tellurite HBMOF. This work May provide reference for the development of multi-wavelength fiber amplifiers and all-optical modulators. [ABSTRACT FROM AUTHOR]

A double-clad single-mode tellurite optical fiber (DC-SMTOF) with a loss of 0.5 dB/m @1545.1 nm was fabricated based on the TeO2–ZnO–Li2O–Bi2O3 (TZLB) material. During the fiber drawing process, a low level of residual birefringence was produced, which gave a chance for the investigation of the polarization modulation instability (PMI). With a nanosecond laser operated at 1545.1 nm as the pump source, the PMI effect in the DC-SMTOF was investigated using different fiber length and different average pump power. This investigation of the PMI generation in non-silica optical fibers may provide guidance for the generation of the highly repetitive optical pulse train. [ABSTRACT FROM AUTHOR]

A biocompatible and robust fiber surface plasmon resonance (SPR) temperature sensor was fabricated based on an alcohol-filled hollow-core fiber. The fabrication process of this designed sensor included Ag film coating, liquid injection, and fusion splicing, which was low cost and efficient. Due to the high refractive index sensitivity of the SPR effect and the high thermal optical coefficient of alcohol, the designed sensor performed well in temperature sensing, whose linear sensitivity reached as high as 1.16 nm/°C in the range of 35.5 °C–70.1 °C. Being small in size, low in fabrication cost, and highly sensitive in performance, this sensor is suitable for temperature detection during biological and chemical reactions and has the potential to realizing multiparameter or distributed temperature measurement. [ABSTRACT FROM AUTHOR]

A novel curvature sensor was proposed based on a dual-core photonic crystal fiber (PCF) that was spliced between two single-mode fibers (SMFs). The sensor sensitivity was investigated both analytically and experimentally, and the influence of the PCF length and temperature on the sensor performance was also analyzed. The results showed the sensor had different sensitivity with different bending direction and its highest sensitivity can reach 10.14 nm/m−1. It also showed great insensitivity to temperature interference. Being of simple structure and good mechanical strength, this curvature sensor has great application potential in various fields, such as architecture, machinery, robot, wearable sensor, and so on. [ABSTRACT FROM AUTHOR]

A D-shaped photonic crystal fibre filled with liquid crystal was demonstrated as an amphibious sensor for detection of both temperature and refractive index, when combined with plasma materials. Specifically, the optical component is implanted into a complete optical system ensuring modulation of the external electric field. When the refractive index of the external solution changes from 1.0 to 1.6, the y-polarised mode has a loss spectrum with a wavelength sensitivity of up to 2275 nm/RIU, and the corresponding amplitude sensitivity is −88.2RIU−1. When the perceived temperature changes from 15°C to 50°C, the temperature of the sensor is correspondingly expressed as the maximum wavelength sensitivity of 9.09 nm/°C and the amplitude sensitivity of −0.311°C−1. In addition, the actual micro-operation processes have been studied in detail, such as polishing depth, coating thickness and coating method. This provides practical ideas for real-time sensing analysis that requires harsh environments. [ABSTRACT FROM AUTHOR]

Semiconducting polymer dots (Pdots) have attracted much attention due to their outstanding optical properties. However, the potential of Pdots in laser technology is rarely studied. Here, we first report the benzobisthiadiazole (BBT)-based Pdot as a single broadband nonlinear saturable absorber (SA) for passively Q-switched fiber lasers at 1, 1.5, and 2 μm. The Pdot-SA possesses a strong saturable absorption, a broadband nonlinear optical response, and a large modulation depth. Once the Pdot-SA is integrated into the ytterbium-, erbium-, and thulium-doped fiber laser cavities, stable Q-switched operations are observed at the central wavelengths of 1036, 1561, and 1951 nm. Our results verify that the Pdots are promising nonlinear media for Q-switched pulse generation, and highlight the potential of Pdots for relevant nonlinear optical applications. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a high sensitivity refractive index (RI) sensor with D-shaped structure covered with gold and graphene film. Specifically, the effect of structural parameters on the stability of fiber sensor is analyzed. In our research, it have been found that the sensor we proposed is not very sensitive to the change of structure parameters on the premise of ensuring the sensing precision. This advantage means that the requirements for machining errors are reduced. Further probing shows that the proposed sensor shows a maximum wavelength interrogation sensitivity of 4391nm/RIU with the dynamic refractive index range from 1.33 to 1.39 and a maximum amplitude sensitivity of 1139RIU− 1 with the analyte RI = 1.38 in the visible region. The corresponding resolution are 2.28 × 10− 5 and 8.78 × 10− 6 based on the methods of wavelength interrogation and amplitude-(or phase-) based method. These characteristics of compact sensing architectures, simple to fabricate, and high sensitivity open the possibility of using this type of sensor in biological applications. [ABSTRACT FROM AUTHOR]

A novel magnetic field sensing system based on surface plasma resonance (SPR) optical fiber sensor and filled with magnetic fluid (MF) is proposed and demonstrated for the first time. In the magnetic field SPR optical fiber sensor, SPR is excited by Ag as metallic material and MF is filled into the capillary sealed with epoxy glue, which utilizes the tunable refractive index (RI) of MF, and the transmission spectrum will change with different magnetic field intensities. The magnetic-optic effect of MF and the high RI sensitivity of optical fiber SPR sensor are utilized to enhance the sensitivity of the novel magnetic field sensor significantly. In the experiment, the performances of the magnetic field sensing system are tested by applying different measured magnetic fields. The final results indicated that a sensitivity of 303 pm/Gs is achieved. Compared with other optical fiber magnetic field sensors, the advantages of the proposed sensor in this paper are simple structure, small in size, easy to make, low cost, high sensitivity, and anti-interference. [ABSTRACT FROM AUTHOR]

A dual communication band single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance is presented in this paper. Numerical simulation results demonstrate that the resonance strength of x- and y-polarized direction can reach 569.83 and 719.25 dB.cm−1 simultaneously at the communication wavelength of 1.31 and 1.55 µm. By filling liquid analyte, the confinement loss of x- and y-polarized direction can simultaneously reach 831.7 and 580.53 dB.cm−1 at the wavelength of 1.31 and 1.55 µm. Furthermore, when the fibre length L is equal to 700 µm, the peak value of the crosstalk can reach 493.86 and −323.67 dB at the same time at the wavelength of 1.31 and 1.55 µm, and when the length of the fibre L is 400 µm, the bandwidths of the crosstalk better than 20 dB and less than −20 dB are about 160 and 210 nm, respectively. These performances make it an ideal candidate for designing dual-band polarization filter equipment. [ABSTRACT FROM AUTHOR]

The evolution Raman effect in a single-mode tellurite fiber (SMTF) was investigated by pumping a nanosecond laser operated at ~1545 nm. With the increase of the average pump power, inverse Raman scattering (IRS) effect was first observed in a 2.5-m-long SMTF, which induced a steadily growing second-order Raman Stokes that finally exceeded the first-order Raman Stokes. When the length of the SMTF was reduced to 0.5 m, no IRS effect was obtained due to the lower Raman gain. [ABSTRACT FROM AUTHOR]

The filtering characteristics and applications of photonic crystal fibers being selectively infiltrated with one aluminum rod were investigated based on the finite-element method. The aluminum rod being selectively infiltrated into one cladding air hole acted as a defect core and generated surface plasmon polaritons on its surface. As the phase matching condition was satisfied, the light transferring in fiber core coupled to the surface of the aluminum rod and the confinement losses of core modes experienced an abrupt increase. The filtering characteristics could be modified by adjusting the fiber structure parameters, such as diameters of air holes and the aluminum rod. Two applications of the photonic crystal fibers being selectively infiltrated with one aluminum rod were studied. First, a polarization filter with ultrabroad bandwidth was designed based on the cascaded resonances between fiber core modes and surface plasmon polariton modes. The bandwidth of the polarization filter was as broad as 600 nm covering wavelengths from 1.4 to 2.0 μm. Second, an intensity-type refractive index sensor was designed based on the filtering characteristics. The output power ratio and sensitivity increased as the refractive index of analyte increases and reached to 3.91 dB and 128 dB/RIU in x-polarized direction at the analyte refractive index of 1.37, respectively. [ABSTRACT FROM PUBLISHER]

Multiwalled carbon nanotubes have been widely used as mechanical reinforcement fillers for polymers during the past few decades. However, high electrical conductivity of raw multiwalled carbon nanotubes hampers their application in some fields demanding not only good mechanical properties and/or high thermal conductivity but also electrical insulation. In this research, carboxyl functionalized multiwalled carbon nanotubes and organically modified montmorillonite were introduced to prepare epoxy nanocomposites with anhydride as curing agent. The obtained epoxy nanocomposites possessed improved impact toughness, and the electrical insulation was maintained. Compared to the volume resistivity of the raw multiwalled carbon nanotubes (0.6 wt%)/epoxy nanocomposites, the volume resistivity of the organically modified montmorillonite/carboxyl functionalized multiwalled carbon nanotubes (0.6 wt%)/epoxy nanocomposites increased more than four order of magnitude. These excellent properties were attributed to the synergistic effect of carboxyl functionalized multiwalled carbon nanotubes and organically modified montmorillonite on toughening epoxy, as well as the suppression of electron transport by multiwalled carbon nanotubes surface modification and the organically modified montmorillonite layer in the multiwalled carbon nanotubes conductive network. The effects of adding nanofillers on the dielectric constant and dielectric loss values of epoxy nanocomposites were also studied. This work has demonstrated the feasibility of using multiwalled carbon nanotubes as mechanical reinforcement fillers, while simultaneously giving electrical insulation in the polymer nanocomposites. [ABSTRACT FROM AUTHOR]