Large Mode Area Photonic Crystal Fiber Research Articles

Numerical investigation of a wideband supercontinuum source based on a large-mode-area photonic crystal fiber pumped at 1.3 μm

A numerical investigation was conducted to obtain a supercontinuum spanning about two octaves using a large mode area photonic crystal fiber (PCF) pumped at 1.3 μm. In our study, a 1.3 μm femtosecond laser and a silica-based large mode area PCF were selected as the pump source and nonlinear medium, respectively. The nonlinear Schrodinger equation was solved with split-step Fourier method to simulate the evolution of pulse and the broadening of spectrum. The effect of several parameters including the length of PCF, the pulse width, and the average pump power on characteristics of the output spectrum was studied. The simulation results revealed that the supercontinuum extended from near 600 nm to over 2450 nm at 20 dB with length of 30 cm, pulse width of 100 fs and average power of 12 W, respectively. This work proved this large mode area PCF a potentially excellent medium for supercontinuum source and provided some theoretical guidance for future experiments.

Full-Stokes parameters detection enabled by a non-interleaved fiber-compatible metasurface.

Polarization of the optical field determines the way of light-matter interaction, which lays the foundation for various applications such as chiral spectroscopy, biomedical imaging, and machine vision. Currently, with the rise of the metasurface, miniaturized polarization detectors have attracted extensive interest. However, due to the limitation of the working area, it is still a challenge to integrate polarization detectors on the fiber end face. Here, we propose a design of compact non-interleaved metasurface that can be integrated on the tip of a large-mode-area photonic crystal fiber (LMA-PCF) to realize full-Stokes parameters detection. Through concurrent control over the dynamic phase and Pancharatnam-Berry (PB) phase, different helical phases are assigned to the two orthogonal circular polarization bases, of which the amplitude contrast and relative phase difference can be represented by two non-overlapped foci and an interference ring pattern, respectively. Therefore, the determination of arbitrary polarization states through the proposed ultracompact fiber-compatible metasurface can be achieved. Moreover, we calculated full-Stokes parameters according to simulation results and obtained that the average detection deviation is relatively low at 2.84% for 20 elucidated samples. The novel metasurface exhibits excellent polarization detection performance and overcomes the limitation of the small integrated area, which provides insights into the further practical explorations of ultracompact polarization detection devices.

A computational method for simple design of endlessly all-silica large-mode area photonic crystal fiber for high-power laser applications

A computational method for simple design of endlessly all-silica large-mode area photonic crystal fiber for high-power laser applications

Design and analysis for large-mode-area photonic crystal fiber with negative-curvature air ring

A large mode area photonic crystal fiber (LMA-PCF) under standard fiber size is proposed in this paper. In order to realize large mode field and low bending loss, multilayer negative curvature air ring structure is designed. The finite element method with perfectly matched layer boundaries is used to analyze the performance of PCF. The influence of various parameters of fiber structure on fiber performance is analyzed. Numerical results show that the structure can achieve large mode area with lower bending loss and smaller bending radius in the wavelength range of 1–1.8 µm. Under the condition of a five-layer six-lobed air ring with negative curvature, the mode field area reaches 1358.9 μm2. At the same time, the high-to-fundamental mode loss ratio reaches 331.5. When the bending radius is 15 cm, the bending loss of the fundamental mode is 0.21 dB/m. Within the 360° bending direction, LMA can be realized in all directions and has effective single-mode operation.

Endless Single-Mode Photonics Crystal Fiber Metalens for Broadband and Efficient Focusing in Near-Infrared Range.

The advent of the ‘lab-on-fiber’ concept has boosted the prosperity of optical fiber-based platforms integrated with nanostructured metasurface technology which are capable of controlling the light at the nanoscale for multifunctional applications. Here, we propose an endless single-mode large-mode-area photonic crystal fiber (LMA-PCF) integrated metalens for broadband and efficient focusing from 800 to 1550 nm. In the present work, the optical properties of the substrate LMA-PCF were investigated, and the metalens, consisting of dielectric TiO2 nanorods with varying radii, was elaborately designed in the fiber core region with a diameter of 48 μm to cover the required phase profile for efficient focusing with a high transmission. The focusing characteristics of the designed metalens were also investigated in detail over a wide wavelength range. It is shown that the in-fiber metalens is capable of converging the incident beams into the bright, symmetric, and legible focal spots with a large focal length of 315–380 μm depending on the operating wavelength. A high and average focusing efficiency of 70% was also obtained with varying wavelengths. It is believed the proposed fiber metalens may show great potential in applications including fiber laser configuration, machining, and fiber communication.

Compact pulsed thulium-doped fiber laser for topographical patterning of hydrogels

We report the generation of high energy 2 μm picosecond pulses from a thulium-doped fiber master oscillator power amplifier system. The all-fiber configuration was realized by a flexible large-mode area photonic crystal fiber (LMA-PCF). The amplifier output is a linearly-polarized 1.5 ns, 100 kHz pulse train with a pulse energy of up to 250 μJ. Pulse compression was achieved with (2+2)-pass chirped volume Bragg grating (CVBG) to obtain a 2.8 ps pulse width with a total pulse energy of 46 μJ. The overall system compactness was enabled by the all-fiber amplifier design and the multi-pass CVBG-based compressor. The laser output was then used to demonstrate high-speed direct-writing capability on a temperature-sensitive biomaterial to change its topography (i.e. fabricate microchannels, foams and pores). The topographical modifications of biomaterials are known to influence cell behavior and fate which is potentially useful in many cell and tissue engineering applications.

272 W quasi-single-mode picosecond pulse laser of ytterbium-doped large-mode-area photonic crystal fiber

A large-mode-area (LMA) ytterbium-doped photonic crystal fiber (PCF) with core NA of 0.034 and core diameter of 50 μm was made by the stack-and-draw technique. The core is formed by Yb3+/Al3+/F−/P5+ co-doped silica glass containing 0.09 mol% Yb2O3 with an absorption coefficient at 976 nm up to 3.2 dB/m. The core glass with homogeneous distribution of Yb3+ ions and refractive index difference of 4 × 10−4 compared with pure silica was prepared by the sol-gel method and heat homogenization at 2000°C. Laser power amplification of this LMA PCF was studied using a seed source of 21 ps pulse duration and 48.7 MHz repetition rate at 1030 nm wavelength. With pump power of 520 W, a maximum 272 W (266 kW peak power) quasi-single-mode laser output with M2 of 2.2 was achieved in a 4.7 m fiber length bent at a diameter of 47 cm with slope efficiency of 52%, and no obvious mode instability, stimulated Raman scattering, or thermal damage on the end facet of the fiber were observed.

Optimal Design of Large Mode Area Photonic Crystal Fibers Using a Multiobjective Gray Wolf Optimization Technique

A new multiobjective optimization framework is presented for designing large mode area photonic crystal fibers (LMA-PCFs) with effective single-mode operation in the bent state. For optimizing the structure, we utilize the multiobjective gray wolf optimizer (MOGWO) to maximize the effective mode area (EMA) and the bending loss of higher order modes (HOMs), while minimizing the fundamental mode (FM) loss. The simulation results demonstrate that this framework enables us to improve the EMA by a factor of 1.26 and increase (decrease) the bending loss of the HOMs (the FM) by a factor of 7 (17), compared to the nonoptimal design. In addition, we investigate the dependence of the optical characteristics of the optimized LMA-PCFs on the wavelength and the bending radius. We found that some optimal structures are highly wavelength dependent and are not suitable for wideband applications. Furthermore, we found that the HOM loss is very sensitive to the bending radius. The proposed framework is comprehensive and can be employed to find a broad range of optimal designs for a wide range of applications.

Design and analysis for a bend-resistant and large-mode-area photonic crystal fiber with hybrid cladding.

In this paper, an asymmetric large-mode-area photonic crystal fiber (LMA-PCF) with low bending loss at a smaller bending radius is designed. The finite-element method with a perfectly matched layer boundary is used to analyze the performance of the PCF. To achieve LMA-PCF with low bending loss, the air holes with double lattice constants and different sizes at the core are designed. Numerical results show that this structure can achieve low bending loss and LMA with a smaller bending radius at the wavelength of 1.55μm. The effective mode area of the fundamental mode is larger than 1000 μm2 when the bending radius is ≥10 cm. The bending loss of the fundamental mode is just 0.0113dB/m, and the difference between the fundamental and high-order modes of the bending loss is larger than 103 when the bending radius is 10cm. Simulation results show this novel PCF can achieve LMA and have effective single-mode operation when the bending orientation angle ranges in ±110°. This novel photonic crystal has potential application in high-power fiber lasers.

Manipulating refractive index, homogeneity and spectroscopy of Yb3+-doped silica-core glass towards high-power large mode area photonic crystal fiber lasers.

Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb3+-doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb3+/Al3+/F-/P5+-co-doped silica core-glass (YAFP), which is prepared by modified sol-gel method developed by our group and highly suitable for fabricating high power LMA PCF amplifiers. By controlling the doping combinations of Al3+/F-/P5+ in Yb3+-doped silica glass,it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb3+. The spectroscopic properties of Yb3+ ions have not deteriorated by the co-doping of F- and P5+ in YAFP glass compared with that of Yb3+/Al3+ co-doped silica glass. A large-size (⌀5 mm × 90 mm) YAFP silica-core glass rod with low average RI difference of 2.6 × 10-4 (with respect to pure silica glass), and low radial and axial RI fluctuations of ~2 × 10-4, was prepared. A LMA PCF with 50 µm core diameter was obtained by stack-capillary-draw techniques using YAFP core glass. Its core NA is 0.027. An average amplified power of 97 W peaking at 1030 nm and light-light efficiency of 54% are achieved from a 6.5 m long PCF in the pulse amplification laser experiment. Meanwhile, quasi-single-mode transmission is obtained with laser beam quality factor M2 of 1.4.

Evaluating optical properties of real photonic crystal fibers with compressed sensing based on non-subsampled contourlet transform

A real photonic crystal fibers (PCFs) evaluation approach based on compressed sensing with non-subsampled contourlet transform (NSCT) and the total variation model is proposed for modeling optical properties of the real PCFs. The classical images of a commercial large mode area PCF and polarization-maintaining PCF are used to verify the effectiveness of the proposed method. Experimental results demonstrate that the cross section images of real PCFs are rebuilt effectively by using only 36% image data for evaluating the optical properties with the same accuracy as by 100% data. To the best of our knowledge, this is the instance of applying the compressed sensing with the NSCT and total variation to reconstruct the cross section images of PCFs for quickly evaluating the optical properties of real PCFs without the requirement of long fiber samples and expensive measurement apparatuses.

Design of triangular core LMA-PCF with low-bending loss and low non-linearity for laser application

In this paper we characterize the design of a simple large-mode area photonic crystal fiber (LMA-PCF) with low bending loss and low non-linearity. The finite element method (FEM) with perfectly matched boundary layer (PML) is used to investigate the guiding properties. According to simulation the characterized four ring fluorine doped triangular core LMA-PCF achieves 1500µm2 effective mode area with a low bending loss of10-5dB/km at the wavelength of 1.064µm and at a bending radius of 40cm which is suitable for high power fiber laser.

PCF Modal Interferometer Based on Macrobending for Refractive Index Sensing

We experimentally demonstrated a photonic crystal fiber (PCF)-based modal interferometer with macrobending for the detection of analyte refractive index (RI). The interferometer consists of a section of large mode area PCF spliced between single mode fibers (SMFs), i.e., SMF-PCF-SMF structure. The PCF is subjected to macrobending of the order of cm $^{-1}$ and its modal properties for different values of macrobending radii have been analyzed using finite-element method. Experimental results show that this simple and compact interferometer has low temperature and power dependence but its RI sensitivity is found to be as high as 258 nm/RIU for a curvature of 0.36 cm $^{\mathrm {\mathbf {-1}}}$ (which is 165% higher than zero curvature) with a resolution $3.9 \times 10^{\mathrm {\mathbf {-5}}}$ RIU.

Inline Microcavity-Based PCF Interferometer for Refractive Index and Temperature Sensing

We report an inline Fabry–Perot interferometer based on photonic crystal fiber (PCF) with microcavity as refractive index and temperature sensor. The interferometer consists of a section of large mode area PCF spliced with single mode fibers on one side, whereas a microcavity is fabricated on the other side of PCF. The formation of the microcavity reduces the period of the interference pattern thereby providing distinctiveness to the measurement. Experimental results show that this simple, compact, and highly stable inline interferometer has temperature sensitivity of 12 pm/°C and a refractive index sensitivity of $\sim 30$ nm/RIU along with a resolution of $3 \times 10^{-4}$ RIU $^{-1}$ .

Monolithic Fiber Lasers Combining Active PCF With Bragg Gratings in Conventional Single-Mode Fibers

Novel monolithic fiber laser architectures utilizing large mode area (LMA) photonic crystal fiber (PCF) and fiber Bragg gratings (FBG) in conventional single-mode fibers (SMF) are presented. The main challenge is to address high cavity losses arising from the intrinsic 18-fold mode-field mismatch between the SMF and the active LMA PCF. Employing an all-fiber, robust and reproducible mode-field matching approach based on graded-index multimode fibers, we numerically and experimentally demonstrate that the SMF-to-LMA PCF coupling can be more than three-fold improved. This MFA approach is further implemented in monolithic fiber laser cavities combining FBGs in SMF and active LMA PCF. We demonstrate that cavity losses can be significantly mitigated when using appropriate MFAs resulting in a substantial increase of the laser output performances.

Measurement of group velocity dispersion in a solid-core photonic crystal fiber filled with a nematic liquid crystal.

Liquid crystal-filled photonic crystal fibers (PCFs) are promising candidates for electrically tunable integrated photonic devices. In this Letter, we present group velocity measurements on such fibers. A large mode area PCF, LMA8, was infiltrated with the liquid crystal mixture, E7. The measurements were performed with an interferometric setup. The fiber exhibits several spectral transmission windows in the visible wavelength regime that originate from the bandgap guiding mechanism. The dispersion of these windows is very unusual compared to typical fibers. Our measurements show that it can change from -2500 ps km(-1) nm(-1) to +2500 ps km(-1) nm(-1) within a spectral range of only 15 nm. This leads to multiple zero dispersion wavelengths in the visible wavelength range.

Tunable picosecond SESAM mode-locking ytterbium-doped double-clad LMA PCF oscillator

A picosecond tunable ytterbium-doped double-clad fiber oscillator with semiconductor saturable absorber mirror (SESAM) mode-locking large mode area (LMA) photonic crystal fiber (PCF) is demonstrated. Without any tunable elements in the oscillator, we obtain self-starting mode locking ytterbium-doped fiber oscillator tunable over 35.5nm. The center wavelength in the ranges from 1028.5nm to 1064nm with excellent beam quality is achieved by proper adjusting the polarization beam splitter (PBS), half-wave plate (HWF) and SESAM in the laser cavity. The output power ranges from 0.76W to 1.01W at the different center wavelengths under the same incident pump power. A narrow spectral bandwidth with only 0.25–0.5nm and pulsed duration with 7.9ps have been obtained at the different center wavelengths. The repetition rate has been measured to be about 45.9MHz, which has a slight change for the different center wavelengths.

Optical and laser properties of Yb3+-doped Al2O3–P2O5–SiO2 large-mode-area photonic crystal fiber prepared by the sol–gel method

Yb3+, Al3+ and P5+ co-doped silica glass with the composition of 0.05Yb2O3–2.0Al2O3– 1.0P2O5–96.95SiO2 (mol%) was prepared by the sol–gel method. Using this glass as the fiber core, the corresponding large-mode-area (LMA) photonic crystal fiber (PCF) was drawn by the stack-capillary-draw technique. Spectral properties of the silica glass chip and LMA PCF are discussed. Pumped with a 976 nm laser diode, the PCF fiber achieved the highest laser output power of 34.6 W at ∼1040 nm, with a slope efficiency of 62%. To the best of our knowledge, this is the highest laser output power report on Yb3+-doped silica LMA PCF prepared by the sol–gel method.

基于粉末烧结技术制备镱铝共掺大模场光子晶体光纤

Based on powder sintering technology,Yb3+/Al3+ co-doped silica rods are prepared,and the concentration of Yb3+ is up to 12 000 ppm(wt).Then,with the Yb3+/Al3+ co-doped silica rods as core materials,highly doped Large-mode-area Photonic Crystal Fibers(LMA-PCF) are fabricated by stack-draw method.The mode area can reach 550 μm2,and the mode field diameter is 26 μm.The results indicate that the fiber has a broad absorption band in the near infrared wavelength(850~1 033 nm),and the main peak is at the wavelength of 976 nm where the absorption loss is higher than 10 dB/m;when the fiber is pumped by the laser with a wavelength of 971 nm,there exists a Gaussian fluorescence peak in the wavelength range of 1 150~1 125 nm,with a peak value of 1 088 nm and a half-line width of 45 nm.

Novel large mode area photonic crystal fibers with selectively material-filled structure

A novel large mode area (LMA) photonic crystal fibers (PCFs) are proposed in this paper. LMA is obtained by selectively material-filled structural PCFs in which six air-holes near the center are filled with high refractive index material. It provides a new method to design and realize LMA PCFs. The transmission characteristics such as effective mode areas, chromatic dispersion, and confinement losses are investigated and also the influences of structure parameters are numerically analyzed by employing the full vectorial finite element method (FEM). Numerical results demonstrate that effective mode area can improve, small and flat dispersion is achieved, and confinement losses are still acceptable by applying our novel selectively material-filled technology. Compared with the traditional method achieving LMA, it has perfect performances and it is simple and easy to fabricate.