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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]

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 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]

• We demonstrate a passively mode-locked laser operating at 2 um region based on a saturable absorber (SA) of FONPs deposited on the D-shaped fiber (DF). This is the first use of FONPs to achieve mode-locking at 2um. • The mode-locking operates in 1931 nm, the 3 dB bandwidth is 5.9 nm, the repetition frequency is 24 MHz, and the pulse width is 1.29 ps. In addition, the signal-to-noise ratio is ∼67 dB, indicating the stability of the output spectrum. As a unique type of transition metal oxides, ferroferric-oxide nanoparticles (FONPs) have attracted much attention due to their outstanding physical and chemical properties. In this paper, we demonstrate a passively mode-locked laser operating at 2 um region based on a saturable absorber (SA) of FONPs deposited on the D-shaped fiber (DF). FONPs were deposited on DF to form FONP-DF SA devices. As inserted into the thulium-doped fiber laser (TDFL), a mode-locked pulse was realized at 1931 nm. For all we know, this is the first demonstration of FONP-DF SA in fiber lasers at 2 um region. This work fills the gap of FNOP in the realization of 2 um mode-locking and lays the foundation for us to use FNOP-DF for magnetic field sensing in the future. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid-guiding tellurite (TZNLP) photonic bandgap fiber (PBGF) with low confinement loss is presented in this paper. A detailed comparison between the hybrid-guiding tellurite PBGF in which the high-index rods (TLWMN) replace one row of air holes in the radial direction and the all-solid tellurite PBGF has been accomplished. Low confinement loss windows can be achieved in this novel fiber due to the collaborated action of two guiding mechanisms–total internal reflection and antiresonant reflection. [Copyright &y& Elsevier]

In this study, the silver mirror reaction was used to coat the silver film on the surface of self-made microstructured fiber (MSF) to stimulate the surface plasmon resonance effect, and Polydimethylsiloxane (PDMS) with a high thermal-optical coefficient was coated on the silver film as temperature-sensitive material. The MSF with silver and PDMS films was coupled with multi-mode fiber on both sides to form the temperature sensor. In this sensor system, the energy is coupled into the cladding of the microstructure fiber by multi-mode fiber, and the surface plasmon resonance can be further excitated in the MSF. When the temperature of the external environment changes, the refractive index of PDMS will also change. At this time, combined with the surface plasmon resonance effect, a resonant absorption peak corresponding to the temperature appears in the transmission spectrum so that the temperature can be measured quickly and accurately. We found that, in the temperature range of 35 °C to 95 °C, the average temperature sensitivity of the sensor during heating and cooling was −0.83 nm/°C and −0.84 nm/°C, respectively. The advantages of this sensor are the simple structure, convenient operation and good reversibility. The relative sensitivity deviation value (RSD = 0.0059) showed that the sensor has high stability. The temperature sensor based on MSF has favorable prospects for use in fields such as medical treatment, biochemical detection and intelligent monitoring. [ABSTRACT FROM AUTHOR]

The four wave mixing (FWM) characteristics of highly nonlinear tellurite photonic crystal fiber are simulated. The material of tellurite fiber is TeO 2 -Li 2 O-ZnO-P 2 O 5 (TLZP). It is calculated that there are two zero dispersion points at 1590 nm and 3880 nm in tellurite photonic crystal fiber. The linear phase mismatch, the variation of optical signal gain with fiber length and the pump power are calculated at 1538 nm and 3865 nm respectively. The results show that the fiber has good four wave mixing performance near 1550 nm communication window and mid infrared region. [ABSTRACT FROM AUTHOR]

Ultrafast all-optical signal modulation induced by optical Kerr effect (OKE) was demonstrated in an all-solid tellurite photonic bandgap fiber (PBGF) which was designed and fabricated based on TeO2-Li2O-WO3-MoO3-Nb2O5 (TLWMN, high-index rods), TeO2-ZnO-Na2O-La2O3 (TZNL, background), and TeO2-ZnO-Li2O-K2O-Al2O3-P2O5 (TZLKAP, cladding) glasses. At the input of a control pulse with high intensity, OKE occurred in the tellurite PBGF and the transmission bands of the tellurite PBGF shifted. The signal at 1.57 μm transmitting in the fiber core can be ultrafast all-optically modulated by the ultrafast single pulse (200 kW, 200 fs) under OKE, where the modulation speed can reach 50 GHz, faster than some commercial LiNbO3 modulators. The results in this paper can be applied to multi-monitors, local area network, detectors, multi-sources, etc. [ABSTRACT FROM AUTHOR]

In this study, the green up-conversion (UC) fluorescence emission in Er3+/Yb3+/Mo6+ tri-doped tellurite glasses (TeO 2 –ZnO–Li 2 CO 3 –Bi 2 O 3 , TZLB) was explored for temperature sensing. The doping of Mo6+ ions allowed enhanced luminescence at moderate power pumping, avoiding the introduction of undesired laser-induced thermal effects while improving the spectral signal-to-noise ratio. The luminescence characteristics were investigated in detail at different doping molar ratio of Mo6+ ions, and the strongest was observed at 8 mol%. Drawing on tri-doped TZLB glass with the strongest UC emission intensity, a tri-doped TZLB fiber was fabricated and coupled with two multimode fibers (MMFs) via Ultraviolet (UV) adhesive, forming the temperature sensor. The sensor was further encapsulated by a silica tube sealed with Ultraviolet adhesive, overcoming the poor mechanical property of tellurite fiber. The temperature information could be demodulated based on the fluorescence intensity ratio technique. The temperature sensing performance of the tri-doped TZLB sensor was investigated as temperature varied from 258 to 420 K and its repeatability was experimentally verified. The Er3+/Yb3+/Mo6+ tri-doped TZLB has an application prospect in the field of lighting, and the so-based temperature sensor is expected to be applied to thermal detection in the fields of medical diagnostics, environmental monitoring, and optical thermometers, etc. [ABSTRACT FROM AUTHOR]

To this day, the inter-core crosstalk and intra-core crosstalk are potential factors limiting optical fiber transmission over long distances and serious degradation of signal quality in communication systems of multi-core few-mode fibers. To this end, this work proposes a heterogeneous sixteen-core four-mode fiber with two types of refractive index profiles is proposed in this paper, which consists of a graded-index core and a step-index core. After optimization, the four modes can transmit independently and steadily at 1550 nm, and the effective refractive index difference between adjacent modes is more than 1 × 10−3. Under the optimal fiber parameters, the inter-core crosstalk results can be obtained from the research results and are less than −69 dB/km, which reflects the significant effect of the proposed fiber in reducing the inter-core crosstalk. The proposed fiber is the first to use the combination of step-index core and graded-index core so that the inter-core crosstalk of heterogeneous fibers is successfully suppressed at a low level, while providing new ideas and solutions for future research on novel low-crosstalk multi-core few-mode fibers that can be applied to terrestrial and undersea communication systems. • This paper presents a novel sixteen-core four-mode fiber with two types of refractive index profiles. • The inter-core crosstalk of all LP modes is lower than −69 dB/km at 1550 nm. • The effective mode field area and dispersion of the same mode in adjacent cores have small differences. • The number of channels in the sixteen-core fiber reaches 96 and the relative space efficiency is as high as 24. [ABSTRACT FROM AUTHOR]

The multi-core few-mode fiber based on space division multiplexing technology is one of the critical ways to address the issue that the current single-mode fiber communication capacity has reached its maximum. However, the energy crosstalk between the cores is an important reason for the deterioration of signal quality. Consequently, this paper designs a nineteen-core seven-mode fiber with more transmission channels, and the auxiliary structures such as trench, high and low refractive index double rings, and air holes can effectively reduce intra-core crosstalk and inter-core crosstalk. After optimization, each core of the nineteen-core fiber can transmit seven LP modes, and the effective refractive index difference between adjacent modes is greater than or equal to 10−3. The optical fiber provides 228 transmission channels for the entire transmission system, the inter-core crosstalk of the highest order LP 41 mode is lower than −30 dB/100 km at 1550 nm. Based on the above, the proposed optical fiber has excellent optical properties and can be applied to data centers, optical sensors, high-speed computer communication networks, and other applications. [ABSTRACT FROM AUTHOR]

We propose a heterogeneous thirteen-core few-mode fiber, which has the excellent characteristics of low crosstalk (XT), large effective mode field area (A e f f) and low dispersion slope (D s l o p e). The double high refractive index ring can precisely control the effective refractive index difference between the LP mode in the core and reduce intra-core XT. The relative spatial efficiency (RSE) of the 13-core 6-mode fiber reaches 33.84, and the number of spatial channels is as high as 130. The inter-core crosstalk is less than −60 dB/km at 1550 nm. The results show that the proposed fiber with low crosstalk and large A e f f is sufficient to satisfy the requirements of long-distance transmission in the future. • A heterogeneous 13-core 6-mode fiber is proposed to reduce inter-core crosstalk while enhancing bending resistance. • Heterogeneous core arrangement can increase the propagation constant difference between adjacent cores. • The maximum differential mode delay for the highest order mode (LP 12) and LP 01 mode is 28 ps/m. • The number of spatial channels of 13-core 6-mode fiber based on space division multiplexing is as high as 130. [ABSTRACT FROM AUTHOR]

• In this study, we first demonstrated a novel saturable absorber (SA) prepared by the deposition of tungsten carbide nanoparticles (WCNs) onto a d -shaped fiber (DF). Combined with a DF, the WCNs-DF SA exhibited high robustness and broadband saturable absorption response. As the same SA was inserted into Er3+ or Tm3+-doped laser cavities, ultrafast pulses were generated with central wavelengths of 1560 nm and 1932 nm. For your reference, a brief summary of the novelty of our work is provided below. • Strong Nonlinear Optical Response. WCNs with an average size of 80 nm were prepared through a hydrothermal method. We proposed the combination of WCNs and DF as a novel optical modulator. The WCNs-DF SA exhibited strong nonlinear optical response at 1560 nm and 2 μm. • Nonlinear Optics and Ultrafast Photonics Applications. As the same WCNs-DF SA was placed into the self-built E/TDFL, ultrafast pulses could be obtained with a central wavelength of 1562 /1932 nm and a pulse duation of 1.28 ps/632 fs. Our results verified that WCNs were promising nonlinear optical modulators for the ultrafast photonics applications. Tungsten carbide nanoparticles (WCNs), as a kind of transition metal carbides, have exhibited extraordinary optoelectronic properties and aroused enormous attention. However, few reports have been focused on the nonlinear properties and relevant devices. In this study, we first demonstrated a novel saturable absorber (SA) prepared by the deposition of WCNs onto a d -shaped fiber (DF). The WCNs with an average size of 80 nm were prepared through a hydrothermal method. Combined with the DF, the WCNs-DF SA exhibited high robustness and broadband saturable absorption response. As the same SA was inserted into Er3+ or Tm3+-doped laser cavities, ultrafast pulses were generated with central wavelengths of 1560 nm and 1932 nm. Our experimental results verified that the integrated WCNs-DF device possessed great potential as a nonlinear optical medium for high-performance ultrafast optical applications. [ABSTRACT FROM AUTHOR]

Photonic crystal fibers (PCFs), providing ingenious microfluidic channels and intense light guidance, have many advantages in the detection of three-dimensional surface-enhanced Raman scattering (SERS). In solid-core PCFs, the light interacts with the sample in the form of an evanescent field, which is weak and limits the SERS detection performance. In this paper, we propose a new mechanism based on avoided crossings between the fiber core mode and the surface mode, which greatly enhances the laser power ratio in the liquid channels and improves the SERS sensitivity. Numerical results show that the intensity in the liquid channels can be increased from 2.8 % to 42 %. To realize this avoided-crossing effect in PCFs experimentally, the silver mirror reaction was optimized which can decorate discrete and densely distributed silver nanoparticles on the hydroxylated surface of the microfluidic channels in less than 15 min. The resulting SERS-active suspended-core PCF has ultra-high sensitivity, with a detection limit of 10−12 M, and an enhancement factor of 1010 for crystal violet solution. It also provides good stability and reproducibility with a relative standard deviation of 4.8 %. This ultra-sensitive and highly reproducible PCF-SERS probe has great potential for application in rapid in-situ detection. • Light interacts with the analyte in the form of surface mode rather than the evanescent field. • The surface mode is enhanced by the avoided crossing effect. • High density Ag nanoparticles were simply formed on the inner surface of the hydroxylated optical fiber. • The SERS performance was greatly improved, with an enhancement factor of 1010 for crystal violet solution. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated the mode-locked pulses at 1560 nm induced by the deposition of M-phase vanadium dioxide nanoparticles (VO 2 (M) NPs) onto the D-shaped fiber (DF) surface. The evanescent wave and VO 2 (M) NPs with longer nonlinear interaction length can be realized. As the VO 2 -DF SA was inserted into the self-constructed erbium-doped fiber laser (EDFL), mode-locked operation was obtained with a central wavelength of 1562 nm and a pulse duration of 1.28 ps. Our work verified the great potential of VO 2 (M) NPs for nonlinear optics and ultrafast photonics applications. [ABSTRACT FROM AUTHOR]

• We successfully fabricated the five mode fiber(5MF) tens of kilometers long and apply it to mode conversion. The optical characteristics of the 5MF has been explored in detail, which confirms that it has low inter-mode crosstalk, large mode field area and low DMGD. • An all-optical fiber-based mode converter is produced by mating together the 5MF with a SMF (G625.D) using the fused tapering technique. And the fundamental mode in the SMF is converted to the five modes (LP 01 , LP 11 , LP 21 , LP 02 , and LP 31) in the 5MF. • The 5MF, mode converters and multiplexers provide a convenient and effective option for constructing the high-capacity mode division multiplexing communication systems. In this work, an all-optical fiber-based mode converter was created by mating a self-made 5-mode fiber (5MF) with a single mode fiber (SMF) using the fused tapering approach. The 5MF was characterized by weakly coupling and large effective mode area with the attenuation of 0.277 dB/km. By controlling the core size during the pre-tapering process, mode conversions of high efficiency were successfully realized between the fundamental mode in the SMF with the five modes (LP 01 , LP 11 , LP 21 , LP 02 and LP 31) in the 5MF. At the wavelength of 1550 nm, the reality normalized coupling efficiencies of the five conversion processes were 0.952, 0.930, 0.990, 0.923 and 0.998, respectively. Moreover, a 5-mode-division multiplexer was produced by cascading the five mode converters in terms of descending order (LP 01 , LP 11 , LP 21 , LP 02 , LP 31). The 5MF, mode converters and multiplexers provide a convenient and effective option for constructing the high-capacity mode division multiplexing communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a temperature-control optical switch is designed based on a conjoined-tubular anti-resonance optical fiber (CTF). The CTF adopts eight pairs of conjoined tubes and four vertical-layout holes were coated with Au to increase the fiber confinement loss (Loss). Toluene was used as transmission medium to injected into the CTF core. The proposed switch produces a Loss difference over 100 dB and ER more than 30 dB. Influence of switch material refractive index and structural parameters on optical switch performance was further discussed. The proposed optical fiber switch has the features of simple structure, small size, broad working wavebands and adjustable operation temperature, which promises broad application prospects in industry, chemistry, biology and other fields. [ABSTRACT FROM AUTHOR]