Multi-core Photonic Crystal Fiber Research Articles

Seven-core photonic liquid crystal fibers for simultaneous mode shaping and temperature sensing

Through doping liquid crystals into the core region, we propose a kind of seven-core photonic crystal fiber (PCF) which can achieve mode shaping and temperature sensing simultaneously in the communication window of 1.1–1.7 μm. To the best of our knowledge, this is the first time that the function of seven-core PCFs as temperature sensors is investigated. By using the full vectorial finite element method, the characteristics of the fiber with the temperature, such as the effective mode area, the waveguide dispersion, and the confinement loss, are analyzed. This kind of PCF can be competitive in providing temperature sensing in multi-core PCF lasers.

Generation of 110-W sub-100-fs Pulses at 100 MHz by Nonlinear Amplification Based on Multicore Photonic Crystal Fiber

We report a multicore photonic crystal fiber (PCF) amplification system delivering about 110-W laser pulses with a duration of sub-100 fs. This amplifier is seeded by a large mode area (LMA) PCF mode-locked oscillator with a repetition rate of 100 MHz. By a one-stage nonlinear amplification, the pulse energy is scaled up to 1.1 $\mu\text{J}$ . In addition, the amplified pulses can be compressed to as short as 83 fs, corresponding to a peak power of 13 MW. For the multicore fiber used in this letter, the 110-W output average power has already made the mode distribution unstable. The results show that the potential output power of a multicore LMA fiber is mainly limited by the mode instability compared with the accumulated nonlinearity.

A Double-Cladding Seven-Core Photonic Crystal Fiber for Hundred-Watts-Level All-Fiber-Integrated Supercontinuum Generation**Supported by the National High-Technology Research and Development Program of China under Grant No 2013AA031501, and the National Natural Science Foundation of China under Grant Nos 61575075, 61535009 and 61275144.

A seven-core photonic crystal fiber (PCF) is fabricated and shown to possess a Gaussian-like far-field-intensity distribution. The seven-core PCF, designed with double-cladding structure and zero dispersion wavelength at 927 nm, is utilized to build up a 104 W all-fiber-integrated supercontinuum (SC) source with total conversion efficiency up to 74.3%. The average output power of SC can be further scaled based on this multi-core PCF.

The beam combination of multi-core photonic crystal fiber by using the Kagome fiber

Using multi-core photonic crystal fiber (PCF) has advantages of large-mode-area that can support high beam intensity and disperse heat. However, only when the beam profile in far-field and the focal point of in-phase super mode is Gaussian-shaped, the energy can be more concentrated as compared with other shapes. And this beam profile feature limits the applications of multi-core PCF.With the development of optics, there is a practical solution to improve the beam profile of multi-core PCF in which a Kagome fiber is used. This solution is to couple the in-phase super mode source (obtained from multi-core PCF) into Kagome fiber to achieve the beam combination of multi-core photonic crystal fiber, i. e. the beam profile remains to be Gaussian-shaped at any location in the optical field. The Kagome fibers have a novel hollow structure and thus will show some new properties, such as broad optical transmission bands with relatively low loss, no detectable surface modes, and high confinement of light at the core, and these features are suitable for beam combination.In this paper, a Ti: sapphire femtosecond pulsed fiber oscillator, with its center wavelength of 800 nm and output power of 550 mW, is used to pump a piece of seven-core nonlinear PCF, with an efficiency of 19%. EFL of the coupling lens is 18.40 mm and the NA is 0.15. Then the in-phase super mode source can be obtained from the 15 m multi-core PCF, with a broadband spectrum from 700 to 1050 nm. The beam profile of farfield and the focal point of in-phase super mode is Gaussian-shaped and there is a seven-core-shaped pattern at nearfield and other locations in the optical field. In order to combine the beams of multi-core fiber, the in-phase super mode source is coupled into a piece of Kagome fiber, 10 cm long, by using the coupling lens whose EFL is 13.86 mm. Its coupling efficiency is 71% and the output beam profile remains to be Gaussian-shaped at any locations in the optical field; this means that there is no seven-core-shaped pattern. It also transmits broadband spectrum with low loss. Moreover, this experiment also proves that the solution can be used for different multi-core PCFs and can have a higher coupling efficiency, 80%. Thus a reference can be given for high power applications of multi-core PCF, and inspiration may be given to some other frontier fields in fiber optics.

Design of Multicore Photonic Crystal Fibers to Generate Cylindrical Vector Beams

We propose a method to generate cylindrical vector beams (CVBs) using a specially designed multicore photonic crystal fiber (PCF). In a PCF with six cores arranged symmetrically around the fiber axis, the light fields in the cores present different polarization states, promising the compositions of vector modes. By introducing small defect airholes in the cladding region and enlarging airholes around the cores to control the mode polarizations, azimuthally and radially polarized modes are obtained separately with low propagation loss and high mode selectivity. In addition, the operation wavelength range of the vector beams can be tuned simply by adjusting the diameters of air-holes inside the cladding defect. The far fields of the fiber outputs are studied as well, which show perfect CVBs with hollow-core intensity profiles. The PCF-based CVB-generator could make the applications of vector beams much more convenient by extending it into the all-fiber structure.

Design of large-mode-area multi-core photonic crystal fibers with low confinement loss and dispersion

Through doping high refractive index materials into the core region, we propose a kind of large-mode-area multi-core photonic crystal fiber (MCPCF) with low confinement loss and dispersion. The fiber is designed numerically by using the full vectorial finite element method (FEM) and the characteristics of the fiber such as effective mode area, confinement loss and dispersion are investigated. The MCPCF exhibits large effective mode area, ultralow confinement loss and dispersion in the communication window of 1–1.6 μm. The MCPCF can be used as matrix fibers in high power fiber lasers with the requirements of high thermal damage threshold and low nonlinear effects.

Flat-topped hollow laser beams can be obtained by using the multi-core photonic crystal fiber mixed with GeO2

In this paper, we design a photonic crystal fiber (PCF) which can generate a flat-topped hollow laser beam. The PCF is considered to add six special fiber cores doping with GeO2. The six special fiber cores arrange in hexagon structure. By solving Maxwell's equations with the perfect matched layer (PML) boundary conditions, we find the beam can be adjusted to some extent. Through simulation analysis we can obtain the following points: if we change the inner and outer fiber cores of the PCF or the molar percentage of doping GeO2, the laser intensity distribution of the flat-topped hollow laser beam can be influenced, but there is little influence on the size of dark spot (DSS) and the width of annular beam (Wr). While if we change the size and spacing of cladding air holes of the PCF, the DSS and Wr of flat-topped hollow laser beams can be influenced. Such result well meets our designed needs to gain high quality flat-topped laser beam with various DSS. Namely the flat pattern of obtained flat-topped hollow laser beams has a lower peak intensity in comparison with Gaussian model, and in the red part of the visible and near infrared wave band, the limit losses of the proposed PCF is low, and it also has the independent characteristics of six fiber cores, these properties help flat-topped laser beam effectively reduce the heat effect when trapping the active biological molecules. This doped PCF has simply structural design and is more easily prepared than the liquid filling one, so it has stronger practical applications.

Large mode area OmniGuide fiber with superconductor-dielectric periodic multilayers cladding

An OmniGuide fiber consisting of superconductor–dielectric cladding periodic multilayers is investigated. The theoretical results of the OmniGuide fiber are presented and compared with that of multicore photonic crystal fiber and step-index fiber. The large mode area and low loss with small bending radius are observed by the OmniGuide fiber.

Fiber-laser monolithic coherent beam combiner based on multicore photonic crystal fiber

A monolithic coherent combiner scheme for combining multiple fiber lasers based on a photonic crystal fiber is described. Beam propagation method (BPM) simulations show that the beam combiner efficiency can reach 96% for a 4×1 combiner, 94% for an 8×1 combiner, and 91% for a 16×1 combiner, provided the fiber lasers are phase matched. In addition, a 2×1 intensity polarization combiner is proposed and simulated through full vectorial BPM, yielding a combining efficiency of 95%. This concept can lead to a rugged and efficient combiner for multiple fiber lasers.

All-Fiber-Integrated High-Power Supercontinuum Sources Based on Multi-Core Photonic Crystal Fibers

The obstacles of power scaling the supercontinuum (SC) source based on single-core photonic crystal fiber (PCF) are analyzed. The combination of high-power fiber lasers and multi-core PCFs would be a feasible method to obtain an all-fiber-integrated high-power broadband SC source (covering visible range). In this paper, we present a comprehensive study of high-power SC generation in multi-core PCFs. Comparative experiments are performed by using a high-power pulse-repetition-rate-tunable picosecond fiber laser to pump two kinds of home-made seven-core PCFs. The influences of PCF structure (fiber dispersion property) and pulse repetition rate (pulse peak power) on the SC generation in multi-core PCFs are investigated in detail. When the picosecond fiber laser at a pulse repetition rate of 1.9 GHz is adopted as the pump, 116 W SC spanning from 800 to 1700 nm is generated in 1# seven-core PCF. Also 64 W visible SC spanning at least 500-1700 nm is demonstrated in 2# seven-core PCF at a pump pulse repetition rate of 480 MHz. The potential of extending the spectral range and scaling the output power for the SC source based on multi-core PCFs are analyzed and discussed.

Gaussian-Like Mode Field Generated in a Seven-Core Photonic Crystal Fiber for Low Loss Splicing by Air Hole Collapse Technique

Multicore photonic crystal fiber is an important research direction to realize high-power supercontiuum. We report two post processing methods based on air hole collapse technique to generate Gaussian-like mode field in a seven-core photonic crystal fiber (SCPCF) for low loss splicing. By heating and collapsing all air holes in the meantime, the mode field of SCPCF becomes more concentrated and the valleys between separated core modes become much flatter. Another method to generate Gaussian-like mode field is selectively collapsing the central air holes between the seven cores, which can form an integrated larger core. Theoretical simulation results are confirmed by experiment and both methods are used to decrease mode field mismatch between SCPCF and double clad fiber with splicing losses as low as 0.46 and 0.22 dB, respectively.

Analysis of supermode and structural characteristics of octagonal multicore photonic crystal fiber with large effective mode area and low confinement loss

An octagonal multicore photonic crystal fiber is proposed. The supermode and its far field distribution have been analyzed by using the full-vector finite element method. In the condition of in-phase supermode, the influences of different wavelengths, air filling fraction, and air hole diameter between cores on normalized intensity of cores are studied. The equal intensity distribution of cores in the output plane is realized. Finally, the effects of changing the air hole diameter between different cores on the effective mode area and confinement loss are investigated. The results show that the effective way to change the relative intensity between cores is to resize the air holes between different cores. If this parameter is changed, a better intensity distribution with large effective mode area and low confinement loss for propagation is obtained.

Scaling the mode instability threshold with multicore fibers.

Mode instabilities (MIs) have quickly become the most limiting effect for the average power scaling of nearly diffraction-limited beams from state-of-the-art fiber laser systems. In this work it is shown that, by using an advanced multicore photonic crystal fiber design, the threshold power of MIs can be increased linearly with the number of cores. An average output power of 536 W, corresponding to 4 times the threshold power of a single core, is demonstrated.

Visible supercontinuum generation in dual-concentric-core-like photonic-crystal fiber

We report the visible supercontinuum (SC) generation in the double zero dispersion multi-core photonic crystal fiber (PCF), pumped by picosecond pulses from Yb-doped fiber laser. Such a dual-concentric-core-like PCF provides two closely spaced zero-dispersion wavelengths (ZDW). The redshift solitons will be canceled out at the vicinity of the second ZDW, and the steady solitons will cause considerable dispersive waves at the edges of the output SC which spans from 550 to 1700 nm at an average pump power 1 W. Moreover, the optical field is transferred from the inner core to the outer core. Experimental results agree well with the theoretical calculations.

In-phase mode selection of 18-core photonic crystal fiber based on Talbot resonator

An effective mode selection is important for the multi-core photonic crystal fiber (PCF) to obtain good output. Talbot cavity is popular to lock the in-phase mode, but few satisfactory experimental results have been reported. In this paper, a dual-Talbot cavity with reflected mirrors on each side of PCF is designed to lock the in-phase mode. The design gains the advantage of in-phase mode against out-of-phase mode. What’s more, it can weaken the influence brought by the imperfect end facet of the fiber. The corresponding theoretical analyses and the experiment are taken. The experimental results suggest that the dual-Talbot cavity improves the capacity of mode selection.

Coupled Energy Measurements in Multi-Core Photonic-Crystal Fibers

Abstract This paper outlines a measurement method of properties of microstructured optical fibers that are useful in sensing applications. Experimental studies of produced photonic-crystal fibers allow for a better understanding of the principles of energy coupling in photonic-crystal fibers. For that purpose, fibers with different filling factors and lattice constants were produced. The measurements demonstrated the influence of the fiber geometry on the coupling level of light between the cores. For a distance between the cores of 15 μm, a very low level (below 2%) of energy coupling was obtained. For a distance of 13 μm, the level of energy transfer to neighboring cores on the order of 2-4% was achieved for a filling factor of 0.29. The elimination of the energycoupling phenomenon between the cores was achieved by duplicating the filling factor of the fiber. The coupling level was as high as 22% in the case of fibers with a distance between the cores of 8.5 μm. Our results can be used for microstructured-fiber sensing applications and for transmission-channel switching in liquid-crystal multi-core photonic fibers.

Research of Numerical Simulation for Multi-Core Photonic Crystal Fiber Couplers

In this paper, multi-core photonic crystal fiber couplers are characterized and numerically simulated with Mangan et als theory and beam propagation method. We propose a kind of 1×3 multi-core photonic crystal fiber couplers with broadband characteristics and the identical split ratio within the range from 1300nm to 1800nm. If the proper length of the couplers is chosen, light couple intensity is completely the same by periphery there-core fiber with broadband characteristics. It provides a theoretical basis for the practice of multi-core photonic crystal fiber couplers.

A surface plasmon resonance sensor based on a multi-core photonic crystal fiber

A surface plasmon resonance (SPR) sensor based on a multi-core photonic crystal fiber (PCF) is presented in this paper. There is only one analyte channel positioned in the center of the PCF cross section, rather than several closely arranged analyte channels around the central core. So the design of this sensor not only reduces the consumption of gold and samples, but also effectively avoids the interference between neighboring analyte channels. Optical field distributions of this fiber at different wavelengths and the sensing properties of this sensor are theoretically analyzed and discussed using finite element method (FEM). Simulation results confirm that both the thickness of metallic layer and the fiber structural parameters have significant effect on sensing performance. The amplitude sensitivity of the sensor is found to be 1.74×10−5 RIU, and the spectral sensitivity is 3300 nm/RIU, corresponding to a resolution of 3.03×10−5 RIU. Finally, in order to achieve PCF-SPR sensing characteristics, an experiment design scheme based on spectroscopic detection method is proposed.

Multicore Photonic Crystal Fiber Based 1 × 8 Two-Dimensional Intensity Splitters/Couplers

This study uses the beam propagation method to propose a new design of multicore photonic crystal fiber-based 1 × 8 two-dimensional splitters. An optical signal at a wavelength of 1.55 μm inserted into the central core is equally divided into eight other cores, each with 12.5% of the total power. In addition, the physical behavior of the coupling characteristics is obtained using coupled mode analysis. Numerical simulations demonstrate that the optical signal can be divided equally in a photonic crystal fiber structure having dimensions of 60 μm × 60 μm × 5.35 mm.

Numerical analysis of photonic crystal fiber with chalcogenide core tellurite cladding composite microstructure

Kinds of photonic crystal fibers with chalcogenide core tellurite cladding composite microstructure are proposed. The multi-core photonic crystal fiber can reach the higher nonlinearity coefficient and the larger effective mode area. The small single-core photonic crystal fiber has a very high nonlinearity coefficient. At the wavelength λ = 0.8 μm, the nonlinearity coefficient can reach 31.37053 W−1·m−1, at the wavelength λ = 1.55 μm, the nonlinearity coefficient is 11.19686 W−1·m−1.