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Recent progress in designing optimized microstructured optical fiber spreads an application scenario of optical fiber sensing. In this letter, we demonstrate a novel three-core microstructured optical fiber (TMOF) spliced with single mode fibers (SMFs). Due to low crosstalk and different effective refractive index between three cores in TMOF, multi-beam interference is achieved and verified based on both of experiments and theoretical analysis. In addition, the bending response could also be recorded by the transmission spectrum of TMOF because of the asymmetry of three core effective refractive index. Owing to the consistency of cores responding to temperature changes, the TMOF can effectively suppress the influence of temperature. Theses excellent sensing characteristics indicate the TMOF splicing with SMFs is promising in the field of bending, integrated Mach Zehnder devices and multi-parameter sensing measurement under different temperature.

A microstructure optical fiber (MOF) for co-transmission of signal and power is manufactured to provide power for remote antenna units (RAUs) and make the deployment of central stations fast and flexible. For a high laser damage threshold and a great refractive index difference, the MOF we proposed has a large core and an air ring in cladding pattern with regular holes. To realize high-quality signal transmission and flexible deployment, the MOF is made of pure silica. In this case, material dispersion, nonlinearity effects and bending loss can be restrained. Above all, the MOF with a high optical local capability and multiband optical transmission could be fabricated easily by traditional stack drawing method. Specifically, fiber loss is 2.26 dB/km at 976 nm and 1.44 dB/km at 1550 nm, acquired by the cut-back method. When the MOF was connected to a communication system with a 64-level quadrature amplitude modulation (64-QAM) 4 GHz frequency signal, an error vector magnitude (EVM) of 0.89% to 1.07% was obtained by the receiver. To the best of our knowledge, it is the first time a MOF has achieved co-transmission of signal and power. This work strongly suggests that MOF is applicable for the deployment of communication central station and emergency communication system in the future.

Conventional metal metasurfaces imparting abrupt local phase profiles suffer from strong inherent loss and limited polarizability, leading to low polarization conversion efficiency of electromagnetic fields and insensitive responses with changes of external environment. Here, by adopting lossless silicon nanopillars to constitute a dielectric gradient metasurface, an incident circularly polarized light can be partly converted to a transmitted light of opposite helicity. And the polarization conversion efficiency varies sensitively with the refractive index of surrounding media. Simulation shows that the intensities between 0th and 1st diffraction orders change oppositely with the liquid refractive index, the proposed dual-channel (0th and 1st diffraction orders) average sensitivity reaches 16.134 dB/RIU at a wavelength of 1550 nm. We also analyzed the biosensing characteristics of an ultrathin molecular layer of 30-nm-thick coated on the silicon nanopillars surface. The refractive index sensing utilizing dielectric metasurface that we reported has excellent performance, which has potential applications environmental monitoring, medicine, biochemical sensing, and optical regulations.

A Hollow-core Anti-resonant Fiber (ARF) has many advantages in device applications, such as low cladding density, low nonlinearity, high damage threshold, and excellent polarization characteristics by adjusting the structure and filling a metal. A method of on-line copper coating on the inner hole of hollow-core anti-resonant fiber cladding during drawing is proposed in this paper, and the related polarization characteristic of the ARF is studied. The theoretical and experimental results show that the ARF has good polarization characteristics after coating due to the coupling of copper film and core mode. Polarized light at 860 nm shows the best polarization characteristics. When the ARF is 1 mm, 1.5 mm, and 2 mm in length, its crosstalk is more than 20 dB which works well in communications applications. These characteristics indicate that the ARF coated copper film has a good application prospect in the field of polarization communication.

In this article, we demonstrated the Tm/Al co-doped silica glass fabricated by the laser additive manufacturing technology for the first time. The measurements show that the glass was doped with Tm3+ concentration of 1.64 wt% without any crystallization. The Tm3+ and Al3+ were uniformly distributed, and no additional defects were introduced during the fabrication process. The glass exhibits low hydroxyl content level of 11.56 ppm. Using the prepared silica glass as the core rod, a Tm/Al co-doped photonic crystal fiber (PCF) was fabricated and performed 13.9% slope efficiency with nearly 600 mW output laser power. This novel technology provides an alternative method to fabricate Tm-doped fiber materials with high homogeneity and large core size, promoting the further spread and development of 2 μm fiber lasers.

Surface plasmon resonance (SPR) is a useful phenomenon in many application fields, such as communication and sensing field. In this paper, for the first time, the SPR phenomenon in helical microstructure fiber coated with Ag (HMFA) is analyzed. Compared with untwisted microstructure fiber, multi-wavelength polarizing filtering performance can be achieved. Tunable filtering wavelength of two orthogonal modes can be achieved by adjusting the twisting rate of HMFA. Besides, at a special twisting rate, the SPR mode with the same order can couple with two orthogonal fundamental modes in HMFA, and the jumping point of the refractive index anti-cross of the SPR mode equals to that of the sum of the orthogonal fundamental modes. In addition, the loss anti-crossing point generates at 1.56 μm. These performances indicate that the helical microstructure fiber can effectively improve the characteristics of the SPR in the aspects of multi-wavelength filtering and mode polarization control and show great potentials in the field of communication and the fields related.

Temperature monitoring plays a key role in the kinetics of chemical reaction. In this paper, a sensitive dynamic temperature monitoring sensor based on the rhodamine6G (R6g) film coated anti-resonance fiber (ARF) is proposed. Because of the high thermo-dependent fluorescence intensity of R6g, the ARF coated with R6g film is highly sensitive to the temperature variation, forming the basis of our proposed temperature sensor application. To enhance the temperature monitoring performance and strengthen the florescence intensity, one of the ARF ends spliced a silica ball for reflecting the input signal, and the other end is inserted with two tapered multimode fiber (MMF), acting as bridges for the input of pump light and the output of signal light, respectively. The dual-peak reached the temperature resolution of $3.946\times 10^{-2}\,\,^{\circ }\text{C}$ and $3.991\times 10^{-3}\,\,^{\circ }\text{C}$ with linearity of 0.99914 and 0.99953 respectively. The experiment results show that the output fluorescence and pump light intensity decrease with the increasing temperature. These excellent characteristics demonstrate a highly sensitive dual-peak sensor for temperature calibration with wide potential applications, such as environmental monitoring, mine monitoring and other fields of chemical kinetics.

Many interesting phenomena in twisted fiber have been reported. In this letter, the twisted single-mode fiber (TSMF) was proposed and studied. It was fabricated by CO2 splicer. Experiments and robust cladding modes resonant theoretical model demonstrated it has transmission dips of long-period gratings. Besides, the light in core will scatter into cladding due to disturbance in core. It will cause multimode interference. A tangential direction theoretical model was put forward to test the experiment characteristic, and was in good agreement with experiment results. In addition, some performance of physical parameters, such as temperature and bending loss response of TSMF are also analyzed. The results indicate that TSMF is a good candidate in sensing and the telecommunication fields.

We present the first demonstration of an actively Q-switched orthogonally polarized dual-wavelength Nd:YLF/YVO4 Raman laser to our knowledge. The gain competition of the orthogonally polarized dual-wavelength fundamental laser at 1047 and 1053 nm was ultimately avoided by incorporating two Nd:YLF crystals into two laser resonators. By adjusting the gain or loss difference of two resonators, the pulse synchronization of the orthogonally polarized dual-wavelength Raman laser was realized. Benefitting from the efficient thermal stress and energy-transfer upconversion management of Nd:YLF crystal, a maximum dual-wavelength Raman output power of 4.5 W was obtained with M 2 < 1.8, which contained a 2.5 W Raman component at 1155 nm and a 2.0 W Raman component at 1162 nm, under the incident pump power of 46.1 W and pulse repetition frequency of 5 kHz. The corresponding peak powers were as high as 178.6 and 142.9 kW, respectively. As far as we know, we have increased the orthogonally polarized dual-wavelength Raman average output power by six times.

Due to the air holes in cladding, it is difficult to process for end faces of ytterbium-doped double-cladding microstructured optical fibers. In this paper, we demonstrate the fabricating method of microlenses on ytterbium-doped double-cladding microstructured optical fibers with a CO2 laser to enhance the coupling efficiency. The theoretical and experimental investigation is carried out to study the effect of minor axis semidiameter and major axis semidiameter of ellipsoidal microlenses on coupling efficiency. The coupling efficiency is up to 88%, which is 14.6% higher than that of the perpendicular flat-end microstructured optical fiber using a free space optical path. These results suggest that the proposed end face processing on microstructured optical fibers provides a straightforward solution for the production of microlenses for laser coupling applications in high-power fiber lasers.

In this paper, a novel dual-guided microstructured fiber supporting orbital angular momentum (OAM) mode and linear polarization (LP) mode transmission is proposed to solve the high-volume data transmission. A variety of parameters of the fiber are considered comprehensively under different conditions by using the full-vector finite element method. The results show that the fiber can support 30 OAM modes and 2 LP modes over the whole C wavelength band by making full use of the air-holes to isolate electromagnetic field. The crosstalk between two channels is lower than that previously reported, and the total dispersion is nearly zero and flat. For instance, the isolation parameter of the EH71 mode reaches up to 86.02 dB and the dispersion coefficient varies from − 0.26 to 1.62 ps/(km nm). The large index difference between core and cladding is beneficial to low crosstalk. In addition, this fiber is easier to fabricate, because the preform needs only stacking technique to adjust the structure geometry size. This fiber can be used in short-distance and large-capacity transmission system.

Microstructured optical fiber can be used as polarized filters by filling the metal into the air holes in cladding to generate surface plasmon resonance. In this paper, we present a V-type birefringence microstructure optical fiber with embedded dual copper wires that were made by the stack-drawing method, and the dual copper wires were aligned in the vertical direction symmetrically. Through adjusting the fiber structure parameters, we found the fiber can be easily excited strong surface plasmon resonance in the S and L waveband. Then the core mode is completely coupled into the copper wires and generates the surface plasmon resonance in the y-polarized direction, to achieve the purpose of directional filtering. The experimental results are consistent with the theory.

The Mid-infrared waveband plays an important role in the biochemical sensing and material analysis, while the silica glass fiber is rarely used in the mid-infrared region due to the high transmission loss, and most of the silica glass fiber sensors are only used for testing refractive index. In order to achieve both of the concentration and functional groups of biological sample simultaneously, in this paper, we proposed a dual-channel integrated photonic crystal fiber sensor with fluorine-doped tin oxide (FTO) based on the unique optical properties of photonic crystal fibers and FTO. The surface plasmon polaritons (SPP) of FTO in the mid-infrared region has high sensitivity to the refractive index of surrounding material. Theoretical result shows that the confinement loss of the proposed fiber can be close to zero realized by a kind of unique super mode. Meanwhile, it also has a good structural error-tolerant rate, which reduces the difficulty of preparation. These findings have potential to apply the mid-IR waveband to detect multiple physical quantities simultaneously in the biochemical sensing field.

A fiber optics sensor based on the structure of no-core fiber/few-mode fiber coated with a smart hydrogel membrane/no-core fiber, cascading a fiber Bragg grating for temperature monitoring was developed to detect the concentration of Pb2+ in aqueous solution. It is the first time that a phase-modulated fiber sensor is used to measure the concentration of Pb2+ in aqueous solution. When the concentration of Pb2+ changes, the specific adsorption of the hydroxyethyl methacrylate crosslinked hydrogel on Pb2+ will change the refractive index of the sensing membrane, and will shift the interference fringe of the sensor in optical spectrum. The process is simple and friendly to environment, and does not produce any harmful substance. The fiber sensor with high sensitivity of 8.155 × 105nm/(mol/L) and the estimated detection limit of Pb2+ concentration of 2.452 × 10−8 mol/L at the spectral resolution of 0.02 nm. The sensor has the advantages of high concentration resolution, low cost, remote detection ability, etc. It has good application prospect in the detection of Pb2+ concentration.

In this paper, we present a photonic crystal fiber (PCF) filter that it has the advantageous properties of narrow width and single-polarization through the principle of surface plasmon resonance (SPR) by a full-vector modal solver based on the finite element method. Gold nanowire is used as the SPR active metal and be filled into cladding air holes selectively. The proposed PCF can be used as a perfect polarization filter at 1.31 or 1.55 μm from y-polarized mode, respectively, if the appropriate sizes of the cladding air holes are selected. Only 13 nm that the full width at half maximum is able to achieve with one gold nanowire, and when the PCF is filled two gold nanowires, with a length of 1 mm of the designed PCF, the bandwidths with the crosstalk better than 30 dB can reach up to 235 nm, at the wavelength of 1.55 μm. The results indicate that the polarized light in one direction can be filtered out selectively by adjusting diameter of air holes and achieve filtering effect in communication bands.

We demonstrate a new all-fiber laser with Yb-doped double-cladding microstructure optical fiber (MOF) that is fabricated through non-chemical vapor deposition (Non-CVD) technology. In our experiments, both of the seed laser and amplifier are made of the same kind of Yb-doped MOF by spatial light coupling method. The amplifier output power is 5.03 W with a one-stage amplifier when the seed laser power is 1.07 W. The signal power is amplified about five times. These results can provide motivation for the application of Yb-doped MOF. It indicates that all microstructure optical fiber laser has the great potential to provide enormous output power scaling.

With the development communication, polarization filter, as the key components of communication, becomes more and more important. For satisfying various requirements, the paper studies different photonics crystal fiber (PCF) polarizing devices based surface plasmon resonance (SPR). Besides, we have also demonstrated their excellent polarization performance from two aspects of theory and experiment. On one hand, the paper theoretically proposed dual-wavelength single polarizing filter with the broadband of low crosstalk. It could have single polarizing filtering in the dual-wavelength of 1310 and 1550 nm and the polarization direction of optical output is independent of the wavelength of incident light. The polarization direction of emergent light through filter can always keep the core mode in x-polarized direction (x-PCM) in a wide range of wavelength, which increases the difference of confinement loss of core mode in y-polarized direction (y-PCM) and x-PCM, and reduces mutual crosstalk. On the other hand, considering the new communication waveband emerging, we present a V-type birefringence microstructure optical fiber with embedded dual copper wires that were made by the stack-drawing method and the dual copper wires were aligned in the vertical direction symmetrically. Experimental results showed that the fiber can be easily excited strong SPR in the S and L waveband. Then the core mode is completely coupled into the copper wires and generates the SPR in the y-polarized direction, to achieve the purpose of directional filtering.

Ytterbium doped microstructured optical fibers have many advantages for fiber amplifiers. Due to air-clad structures, high-power microstructured optical fiber laser systems require stricter end-facet treatment than that of conventional fiber laser systems. Here, we fabricated microlenses in ytterbium doped double-cladding microstructured optical fibers by a CO2 laser. The surface power density of the MOF tip can be reduced by 2 quantity levels theoretically. The theoretical and experimental investigation is carried out to study effect of minor and major axis semidiameter of ellipsoidal microlenses on coupling efficiency. The experimental coupling efficiency was over 88%. Results indicated that this microlens combines the end cap scheme and pump coupling. The proposed fabrication method is helpful for high mechanical stability, well reproducibility and miniaturization of the high-power rare earth-doped microstructured optical fiber laser systems.

With the rapid development of life science, multi-component detection is necessary. In order to monitor the concentration of the biochemical substances simultaneously, a dual-channel biomedical sensor is proposed in this paper. Due to its sensitivity to the surrounding refractive index, there are many applications in biochemical sensing. Surface plasmons are a coupling of electromagnetic oscillations generated by electromagnetic waves and free electrons at the interfaces between metal and dielectrics. Taking into account the different plasma band of different metals, multiple signal peaks can be generated during detection to achieve multi- peak sensing. In addition, when rough analysis is performed on the analysis sample, In order to avoid the complex process of specific sample extraction, multi-component detection of the sample is necessary. Moreover, research on a micro-structured optical fiber sensor based on the plasmon mode interaction of Au/Ag films has been rarely reported. Therefore, a novel dual-channel sensor is designed considering the flexible characteristics of Photonics crystal fiber (PCF) structure, different plasma bands for Au/Ag, and the necessity of multi- component detection. The numerical results show that the core mode in PCF sensor is affected by the Surface plasmon resonance (SPR) at the Au/Ag interface simultaneously, which makes it possible to monitor multiple substances near the Au/Ag films. Meanwhile, the detection of the positive and negative amplitude sensitivities makes the sensor detection stable and it can eliminate certain external disturbances. Its excellent sensing characteristics are of great application value in environmental monitoring, biochemical sensing, etc.

An ultrahigh sensitive optical fiber sensor for trace detection of Cu2+ concentration in aqueous solution with temperature calibration has been developed in this article. Based on the intermodal interference, the sensor is coated with a hydrogel sensing membrane with specific binding to Cu2+ on the no-core fiber/single mode fiber/no-core fiber structure by using our new spray coating method. The imidazole group in the sensing film combines with Cu2+ to produce chelation, which changes the refractive index of the sensing film. The Cu2+ at trace concentration can be detected by monitoring the displacement of the interference trough. The experimental limit of detection of 3.0×10−12 mol/L can be achieved with the spectral resolution of 0.02 nm. The sensor has also long-term stability of the concentration measurement with the average standard deviation of 1.610×10−12 mol/L over 2 hours observation time and can be compensated the influence of ambient temperature on concentration detection by conducting the temperature calibration. In addition, the sensor has the advantages of strong specificity, simple fabrication and low cost.

We propose a helically twisted pig-nose-shaped core microstructured optical fiber (HPC-MOF) for orbital angular momentum (OAM) mode generation. It comprises seven air-hole rings hexagonally arranged with two air holes and one air-hole ring replaced, forming two cores in a line 3 µm from the fiber center and one ring-shaped core. The fiber is helically twisted along the rotation axis. In this fiber, supermodes in inner dual-core can be coupled to high-order modes in outer ring-core, yielding OAM ring-shaped modes at different certain wavelengths, and various OAM modes at different twist rates were investigated in this paper. We demonstrate the distinct coupling differences of symmetric and antisymmetric supermodes in inner dual-core when the supermode coupled to ring-core mode. A modal matching rule is presented to characterize the coupling differences, which is suitable for describing supermode coupling characteristics in HPC-MOFs. Compared to conventional methods, these properties indicate that the fiber can generate higher-order OAM modes and more easily integrate into all-fiber optical communication systems, with potential in OAM generators, light-controlling devices, and integrated optics applications.

Dual-wavelength single polarizing filter has many important applications in the field of optical communication. Based on the principle of surface plasma resonance, a kind of dual-wavelength single polarizing filter with the broadband of low crosstalk was proposed in the paper by adopting good polarization characteristics of photonic crystal fiber. It could have single polarizing filtering in the dual-wavelength of 1310 and 1550 nm and the polarization direction of optical output is independent of the wavelength of incident light. The polarization direction of emergent light through filter can always keep the core mode in x-polarized direction (x-PCM) in a wide range of wavelength, which increases the difference of confinement loss of core mode in y-polarized direction (y-PCM) and x-PCM, and reduces mutual crosstalk. Meanwhile, the theoretical result also showed that the wavelength location and intensity of loss peak of polarizing mandrel are only affected by the air holes adjacent to fiber core and metal film and have little correlation with the structural parameters of other air holes, which ease the difficulty level of preparing filter based on photonic crystal fiber. Under certain structural parameters, the confinement loss of y-PCM could reach 265.04 dB/cm in 1310 nm and 230.5 dB/cm in 1550 nm. The half-width of confinement loss in the wavelength of 1310 nm is only 12 nm, while the loss of x-PCM is much smaller than that in y-PCM.

A pure silica core photonic crystal fiber with multicoating layers for high refractive index (RI) sensing is proposed. Au is used as the active plasmonic material. Tantalum pentoxide is deposited on Au in order to prevent the oxidation and further enhance the evanescent field. The simulation was preformed through the full-vector finite element method (FEM), and the results show that the proposed fiber sensor can obtain the average wavelength sensitivity of 9180 nm/RIU with the analyte RI range of 1.40-1.44, corresponding to the resolution of 1.09 × 10-5 RIU. Moreover, the maximum amplitude sensitivity of 1739.26 RIU-1 with resolution of 5.75 × 10-6 RIU are also obtained. The designed sensor can be a potential candidate for microfluidic analyte detecting.

A novel surface plasmon resonance (SPR) sensor based on ring-core microstructured optical fiber with silver film is presented in this paper. Field leakage from the ring core to the central metal film excites plasmon polaritons. Through numerical simulation with the finite-element method, we found that fundamental modes and one of second-order modes have strong interaction with surface plasma modes. Analyzing coupling characteristics, results show that high sensitivity using linear fitting and narrow full-width at half-maximum (FWHM) can both be acquired in these two modes, which contributes to the highest value of figure of merit reaching 2203. The proposed model with two air-hole rings is easy to fabricate in the real operation. Finally, influences of different metal and geometrical parameters on sensing performance are also discussed for optimization further.

Second-harmonic generation (SHG) near ultraviolet wavelengths is experimentally demonstrated by coupling femtosecond pump pulses into the normal dispersion region far away from the zero-dispersion wavelength of the fundamental mode in a silica photonic crystal fiber (PCF) fabricated in our laboratory. When the pump pulses with average input power $P_{\mathrm {av}}$ of 500 mW and center wavelength $\lambda _{\mathrm {p}}$ of 820 nm are used, the maximum conversion efficiency $\eta _{\mathrm {SH}} ^{^{^{}}}$ of the second harmonics centered at 410 nm can be up to $1.6\times 10^{-6}$ , corresponding to the output power $P_{\mathrm {SH}}$ of 520 nW. By measuring $P_{\mathrm {SH}}$ at different PCF lengths and studying the temporal dependence of $P_{\mathrm {SH}}$ , it is confirmed that the physical mechanism of SHG is dominated by surface nonlinearity polarization, which is resulted from the local inhomogeneities in the silica core region and at the core-air-silica cladding interface of PCF. Finally, a theoretical model is established to analyze the nonlinear optical process.

In this paper, a novel multi-orbital-angular-momentum multi-ring micro-structured fiber (MOMRMF) is proposed for the first time. This compact MOMRMF is presented with 19 rings, each ring supporting 36 modes (34 of them are OAM ones i.e., 684 channels in total) over the whole C wavelength band (1520–1580 nm). Due to the large refractive index difference between silica and air, the effective refractive index ( n eff ) differences between the adjacent eigenmodes are all larger than 10 −3 , which is practically impossible to gain in other traditional high-density OAM fibers fabricated by modified chemical vapor deposition (MCVD) method. Compared with the trench-assisted multi-OAM multi-ring fiber (TA-MOMRF), the lower-level inter-ring crosstalk in the designed MOMRMF also can be achieved by the air hole-assisted. It is believed that both the high-density and low-level crosstalk make such a fiber of great potential in the space-division multiplexing (SDM) system.

In this paper, we propose a novel microstructure fiber with annular core for transmitting optical orbital angular momentum (OAM), and the OAM modes are calculated under different structure parameters of the fiber. Compared with the previous hollow step-index ring fiber, the proposed fiber brings higher refractive index contrast between the ring core and the cladding region by using only the single material of silica. The designed fiber can support more well-separated OAM modes with both thin and thick rings. Simulation results show that the novel microstructure ring fiber is promising to be applied in fiber-based OAM multiplexing in order to improve communication capacity.

A novel light source for coherent anti-Stokes Raman scattering (CARS) microspectroscopy based on degenerate four-wave mixing (DFWM) is experimentally demonstrated in a photonic crystal fiber with two adjacent zero dispersion wavelengths. When the pump pulse wavelengths are changed from 780 to 800 nm and the average input powers $P_{{\mathrm{av}}}$ are increased from 300 to 500 mW, the central wavelengths $\lambda _{\mathrm{as}}$ and $\lambda _{s}$ of the generated anti-Stokes and Stokes waves are tunable from 660 to 606 nm and 953 to 1177 nm, respectively. In addition, the corresponding frequency difference between the pump and Stokes beams is in the range of 2331–4002 cm $^{-1}$ , which covers a wide range of vibrational Raman spectra of the biological and chemical samples. The feasibility of the proposed DFWM-based light source is demonstrated through measuring the CARS spectrum of the ethanol sample.

We experimentally report a high-order-mode (HOM) suppression effect which may bring dips in transmission spectrum of a large-size (with core diameter > 10 µm) six-hole helical microstructured fiber (HMSF). Firstly, we performed rigorous theoretical analysis in helical frame to demonstrate that high loss peaks do not appear in fundamental mode. However, this phenomenon suppressed at special wavelengths is due to coupling rather than the interference between HOMs and air filling mode (AFM). For simplicity, we also proposed a more efficient equivalent structure model which may save much time in simulations based on tangential optical fiber analysis. Theoretical results agree well with experimental results. Furthermore, we introduce a method to effectively manipulate the suppression wavelength by rotating the HMSF axially (without changing the fixed structure parameter). Based on several characteristics of HMSF, we also point its potential in applications such as high-energy laser, optical communication, mode filters and so on.

Helically twisted microstructured optical fibers have wide application prospects in the field of optical vortex communications. In this paper, the optical performance of supermodes in helical dual-core microstructure fiber (DCMF) is analyzed. Compared with the untwisted case, the fundamental odd modes in helical DCMF (HDCMF) carry the orbit angle momentum (OAM). Besides, the confinement loss of fundamental supermodes (FSMs) carrying the same order OAM in HDCMF increases sharply at special wavelength. It shows that HDCMF can be used as an OAM filter. These excellent characteristics shows HDCMF can be a good candidate in the fields of communication and functional devices.

A helical Yb3+-doped three-core microstructure fiber (YTMF) amplifier is proposed in this paper, so as to solve the problem of generation and transmission of the orbital angular momentum (OAM) beams. The fiber is composed of three Yb3+-doped cores with a regular triangle shape and a longitudinal helical structure. The experimental results show that the 1064nm laser can be amplified due to the fluorescence amplification characteristics of the doped material Yb3+. Furthermore, theoretical analysis indicates the modes in YTMF at 1064nm, which is located in the amplified wavelength, can support nine modes carrying OAM. Therefore, the related experiments were performed and verified that the transmission modes can respectively carry 1, 2, and 3-order OAM at 1064nm in different coupling cases. These excellent properties indicate that the combination of doped materials and helical fiber provide favorable conditions for the generation and amplification of OAM, which provides a basis for the further development of OAM beams in the field of quantum communication and dense space division multiplexing.

In this work, Tm:YAG (Tm: Y 3 A l 5 O 12 ) ceramic-derived multimaterial fiber was fabricated by using the molten core method, which has a high gain per unit length of 2.7 dB/cm at 1950 nm. To our knowledge, this is the highest gain per unit length at 2 µm band in similar Tm:YAG-derived multimaterial fibers. A distributed Bragg reflector (DBR) fiber laser was built based on a 10-cm-long as-drawn fiber. The achieved 1950 nm laser, which has a maximum output power of ∼ 240 m W and a slope efficiency of 16.5%, was pumped by a self-developed 1610 nm fiber laser. What is more, an all-fiber-integrated passively mode-locked fiber laser based on the 10-cm-long as-drawn fiber was realized. The mode-locked pulses operate at 1950 nm with duration of ∼ 380 p s , and the repetition rate is 26.45 MHz. The results described here indicate that the Tm:YAG ceramic-derived multimaterial fiber with high gain per unit length has promising applications in 2 µm all-fiber fiber lasers.

Based on the surface plasmon resonance of metal and anti-resonant principles of hole-core microstructure optical fiber (MSF), in this Letter, we demonstrate a MSF microfluidic sensor that combines silver film and hole-core MSF to achieve the sensitive real-time monitoring of refractive indices and components. The large hole core is a common channel for guiding light and flowing measured liquid. Because of the interaction between light and continuous flow measured liquid, the component and refractive indices can be simultaneously monitored by the characteristic absorption wavelength and the surface plasmon resonant peak position, respectively. These results indicate that the MSF microfluidic sensor is an ideal multi-parameter measurement optical sensor.

Double-air-cladding Tm3+-doped silica fiber with a large core is fabricated by stacking capillaries method. By the excitation at 1064 nm, the optical properties of this fiber doped with 0.1 mol% Tm3+ are studied. The blue and near-infrared emissions around 473 and 793 nm are experimentally observed. In addition, the up-conversion mechanism of Tm3+ in glass is investigated. The results show that the Tm3+-doped fiber with a large core can be used as the potential optical material for the high power fiber laser which operates at the blue and near-infrared wavelengths.

In this paper, an Ytterbium-doped V-shape photonic crystal fiber (Yb-VPCF) with low dispersion and high nonlinearity is designed and fabricated in our laboratory. Through coupling femtosecond pulses into the fundamental mode of Yb-VPCF, the tunable anti-Stokes signals at the visible wavelength are efficiently generated based on the phase-matching four-wave mixing. When the pump wavelength is changed from 810, to 820, and to 830 nm and the input average power is increased from 0.4, to 0.5, and to 0.6 W, respectively, the anti-Stokes signals are generated within the wavelength range of 562–477 nm. The wavelength-tunable range is over 100 nm, and the maximum power ratio of anti-Stokes signal at 477 nm and the residual pump at 830 nm can be up to 23.9:1. The anti-Stokes signals generated can be used as the ultrashort pulse sources for ultrafast optoelectronics and spectroscopy.

For the first time, the fundamental mode of a dual-mode photonic crystal fiber (PCF) is suppressed by the index-matching between the core and cladding modes. The PCF designed proposes a new solution of selective excitation of second-order modes. The simulation results demonstrate that the confinement loss of the fundamental mode is higher than 1 dB/m, while the second-order modes are lower than 10 −4 dB/m in the C+L waveband. The high feasibility and low wavelength dependence make the fiber of great potential in the mode-division multiplexing (MDM) transmission.

We report optical properties and fabrication of hollow core fibers in our lab for optical pumped fiber gas laser. A width transmission window in near infrared spectral region is obtained in octagram hollow core fiber.

We investigate the temporal evolution of photodarkening effect in ytterbium-doped large-mode-area photonic crystal fiber and discuss its mechanism. The results show the great influence of photodarkening on lasing properties.

In this Letter, we demonstrate experimentally for the first time, to the best of our knowledge, discrete ultraviolet (UV) wavelength generation by cascaded intermodal FWM when femtosecond pump pulses at 800 nm are launched into the deeply normal dispersion region of the fundamental guided mode of a multimode photonic crystal fiber (MPCF). For pump pulses at average input powers of Pav=450, 550, and 650 mW, the first anti-Stokes waves are generated at the visible wavelength of 538.1 nm through intermodal phase matching between the fundamental and second-order guided mode of the MPCF. The first anti-Stokes waves generated then serve as the secondary pump for the next intermodal FWM process. The second anti-Stokes waves in the form of the third-order guided mode are generated at the UV wavelength of 375.8 nm. The maximum output power is above 10 mW for Pav=650 mW. We also confirm that the influences of fiber bending and intermodal walk-offs on the cascaded intermodal FWM-based frequency conversion process are negligible.

Deep-ultraviolet (UV) second-harmonics (SHs) have important applications in basic physics and applied sciences. However, it still remains challenging to generate deep-UV SHs especially in optical fibers. Here, for the first time, we experimentally demonstrate the deep-UV SH generations (SHGs) by combined degenerate four-wave mixing (FWM) and surface nonlinearity polarization in an in-house designed and fabricated air-silica photonic crystal fiber (PCF). When femtosecond pump pulses with average input power Pav of 650 mW and center wavelength λp of 810, 820, 830, and 840 nm are coupled into the normal dispersion region close to the zero-dispersion wavelength of the fundamental mode of the PCF, the anti-Stokes waves induced by degenerate FWM process are tunable from 669 to 612 nm. Then, they serve as the secondary pump, and deep-UV SHs are generated within the wavelength range of 334.5 to 306 nm as a result of surface nonlinearity polarization at the core-cladding interface of the PCF. The physical mechanism of the SHGs is confirmed by studying the dependences of the output power PSH of the SHs on the PCF length and time. Finally, we also establish a theoretical model to analyze the SHGs.

High concentration Tm3+-doped La 2 O 3 -Al 2 O 3 -SiO 2 photonic crystal fibers are firstly fabricated by the stack-and-draw technology. The fiber core Tm3+-doped La 2 O 3 -Al 2 O 3 -SiO 2 glass is prepared by the conventional melt-quenching technique. The optical properties including the absorption property, fluorescence property and laser performance of the Tm3+-doped photonic crystal fibers are experimentally investigated. The results suggest that Tm3+-doped La 2 O 3 -Al 2 O 3 -SiO 2 photonic crystal fibers have potential applications in high power fiber laser operating at 2μm.

In this paper, we demonstrated experimentally the intermodal four-wave mixing effect by launching femtosecond pulses centered at 1550 nm into deeply normal dispersion region in the fundamental guided-mode of an air-silica photonic crystal fiber with two zero dispersion wavelengths. When intermodal phase-matching condition is satisfied, the energy of the pump waves at 1550 nm in the fundamental guided-mode is converted to the anti-Stokes waves around 1258 nm and Stokes waves around 2018 nm both in the second-order guided-mode. When femtosecond pulses at input average power P av of 90 mW are propagated inside 22-cm-long photonic crystal fiber, the conversion efficiencies η as and η s of the anti-Stokes and Stokes waves generated are 8.5% and 6.8%, respectively. We also observed that the influences of the fiber bending and walk-off effect between the fundamental and second-order guided-modes on intermodal four-wave mixing-based frequency conversion process are very small.

In this work, we proposed a feasible method to prepare the Bi/Al co-doped silica glass by using laser additive manufacturing technology. Bi was uniformly doped into the silica matrix. The hydroxyl content of the glass sample was measured to be 29.36 ppm. Using an 808 nm laser diode as the excitation source, a broadband near-infrared emission from 1000 to 1600 nm was obtained. The emission peak was centered at 1249 nm, and the corresponding FWHM was more than 400 nm. The results show that the laser additive manufacturing technology is promising to fabricate highly homogeneous Bi-doped core materials with broader emission band, which is beneficial to solving the communication capacity crunch and promotes the development of fiber communication in the upcoming fifth and sixth generation systems.

Higher-order solitons are formed by coupling femtosecond pulses into the fundamental mode of a highly nonlinear silica photonic crystal fiber (HNL-SPCF) fabricated in our laboratory. It is experimentally observed that the higher-order solitons break up into a series of stable and broadband discrete fundamental solitons at the mid-infrared wavelength longer than 2000 nm through the process of soliton self-frequency shift due to the perturbations induced by the higher-order dispersive and nonlinear effects. The maximum soliton red-shift and the tunable wavelength range can be up to 1600 nm and over 400 nm, respectively. The nonlinear dynamic processes of femtosecond pulse breakup are consistent with the solution of the generalized nonlinear Schrodinger equation. This multiple stable and broadband mid-infrared wavelengths generated in such an HNL-SPCF can be used as all-fiber multiwavelength ultrashort pulse sources for multiphoton microscopy and ultrafast photonics.

The broadband blue-shifted dispersive waves (DWs) are efficiently generated by the diffraction-arrested solitons in a photonic crystal fiber (PCF) designed and fabricated in our laboratory. By optimizing the pump parameters and the fiber length, the DWs can be used as the pump pulses for the high resolution coherent anti-Stokes Raman scattering (CARS) microscopy. The CARS microscopy based on the broadband DWs can be an attractive tool for simultaneously measuring the vibrational dephasing times of multiple Raman modes of the biological and chemical samples with the C–H and O–H stretch vibration resonances of 2700–3000 cm−1 and 3000–3750 cm−1.

A microstructure optical fiber with Yb 3 + /Al 3 + co-doped glass core is fabricated using high-temperature laser sintering process combined with stack-capillary-draw technology. No crystal is observed in the core glass and its fluorescence lifetime is measured to be 1.31 ms. The bonding features of glass and fiber, together with the structure of fiber core and cladding, are provided and analyzed. Moreover, the uniform element distributions and the axial stress profiles show a highly symmetrical variation trend which is in good agreement with the intensity distribution of Raman signal in Micro-Raman mapping. Excited by 976-nm LD, the laser slope efficiency of microstructure optical fiber reaches up to 72.5 % at 1032 nm. The near-field beam intensity distribution of fiber laser with spectrum FWHM of 8 nm exhibits an excellent laser beam quality. This work strongly suggests Yb 3 + /Al 3 + co-doped silica preform fabricated by high-temperature sintering method is applicable for the field of high-power laser.

A surface plasmon resonance (SPR) sensor with two orthogonal open loops based on microstructured optical fibers (MOFs) is introduced. The interaction between core mode and surface plasmon polariton (SPP) mode produced by two different metal films is studied. Full vector finite element method is used to analyze the coupling and sensing characteristics. The results show that there are three loss peaks near the Au/Ag film, and multi-peak calibration is achieved. Because of the positive and negative sensitivity of the amplitude, the sensor has strong anti-interference capability when the external environment changes. The sensor can detect the refractive index between 1.37 and 1.40, and the working wavelength is between 1600 nm and 2400 nm. Because the sensor has some excellent characteristics, it can be used in biochemical sensing, environmental detection, and other related fields.

In this paper, a double-cladding Tm3+/Al3+ co-doped photonic crystal fiber (PCF) is fabricated with stacking and drawing technology based on laser sintering technology (LST) for the first time. The absorption, emission and loss properties of glass and fiber are studied experimentally, and the laser performances of fiber with different lengths are analyzed. The results demonstrate that Tm3+/Al3+ co-doped large-mode-area PCF fabricated based on laser sintering technology is potential materials for developing 2 μm high power fiber laser.