Double-clad Photonic Crystal Fiber Research Articles

Preparation and optical properties of thulium doped lanthanum aluminum silicate glass photonic crystal fiber

Lanthanum aluminum silicate glass has excellent optical properties, such as high solubility of rare earth ions, good thermal stability, and excellent physicochemical properties. Some of its physicochemical properties are similar to those of silica glass, so it is easy to combine with silica glass to fabricate special optical fibers. It is considered to be an ideal laser glass matrix material. In this paper, a series of Tm<sup>3+</sup> doped lanthanum aluminum silicate glasses with different concentrations for <i>x</i>Tm<sub>2</sub>O<sub>3</sub>-(70–<i>x</i>)SiO<sub>2</sub>-21Al<sub>2</sub>O<sub>3</sub>-9La<sub>2</sub>O<sub>3</sub> (<i>x</i> = 0.2%, 0.4%, 0.6%, 0.8%, 1%, mole fraction) are successfully developed by the traditional high-temperature melting method. Using thulium-doped lanthanum aluminum silicate glass as the fiber core, thulium-doped double-cladding photonic crystal optical fibers are prepared by the stack-and-draw technique and rod in tube method. The core diameter of the thulium-doped lanthanum aluminosilicate glass double-clad photonic crystal fiber is as long as 21.7 μm, the inner cladding diameter is about 119.3 μm, and the outer diameter is about 236.8 μm. The optical properties of thulium-doped lanthanum aluminum silicate glass and its optical fiber are studied experimentally. Under the excitation of a 793 nm laser, the fluorescence bandwidth of thulium-doped lanthanum aluminum silicate glass reaches 223 nm in a wavelength range of 1550–2050 nm. The fiber laser constructed with thulium-doped lanthanum alumino-silicate glass fiber achieves a laser operating at around 2 μm. The fiber laser resonant cavity consists of a pair of dichroic mirrors. The front dichroic mirror has high transmittance for light at 793 nm and high reflectivity (99.9%) for the light within a wavelength range of 1850–2050 nm. The back dichroic mirror has high reflectivity (99.9%) for light at 793 nm and high transmittance (~ 15%) at 2050 nm. Under the experimental conditions in our laboratory, the laser power reaches 253 mW. The highest slope efficiency is 9.67%, which is close to that of the thulium-doped glass fiber laser reported in the literature. It is also found that the central wavelength of fiber laser is shifted toward the longer wavelength with the increase of the optical fiber's length. These results suggest that thulium-doped lanthanum aluminum silicate glass and thulium-doped photonic crystal fiber are suitable for 2-μm fiber laser.

Highly Efficient Yb-Doped Double Clad Photonic Crystal Fiber by Melting Technology

High-power fiber lasers have been developed rapidly since the invention of rare-earth-doped double clad fibers, while the scaling of output power is limited by nonlinear and thermal effects, fiber damage threshold as well. Photonic crystal fiber (PCF) has been used to mitigate this limitation due to large mode area and relatively low core index. In this work, we developed a simplified & flexible method to fabricate Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> doped double-clad (YDDC) PCF for fiber lasers. Systematic simulations and experiments were carried out for fiber characterization and laser performance evaluation. By improving the fabrication process of PCF, the YDDC PCF exhibited good properties, and the laser slope efficiency was measured above 86.8%. It is shown from the results that the proposed PCF fabrication method has huge potentials for applications of high-power fiber lasers.

A readily usable two-photon fluorescence lifetime microendoscope.

A two-photon fluorescence lifetime (2P-FLIM) microendoscope, capable of energetic metabolism imaging through the intracellular nicotinamide adenine dinucleotide (NADH) autofluorescence, at sub-cellular resolution, is demonstrated. It exhibits readily usable characteristics such as convenient endoscope probe diameter (≈2 mm), fiber length (>5 m) and data accumulation rate (16 frames per second (fps)), leading to a FLIM refreshing rate of ≈0.1 to 1 fps depending on the sample. The spiral scanning image formation does not influence the instrument response function (IRF) characteristics of the system. Near table-top microscope performances are achieved through a comprehensive system including a home-designed spectro-temporal pulse shaper and a custom air-silica double-clad photonic crystal fiber, which enables to reach up to 40 mW of ≈100 fs pulses @ 760 nm with a 80 MHz repetition rate. A GRadient INdex (GRIN) lens provides a lateral resolution of 0.67 μm at the focus of the fiber probe. Intracellular NADH fluorescence lifetime data are finally acquired on cultured cells at 16 fps.

Estimation of Rayleigh scattering loss in a double-clad photonic crystal fiber

In this paper the effect of photonic crystal fiber’s structure parameters on Rayleigh scattering was investigated. Rayleigh scattering loss (RSL) has been numerically estimated by average Rayleigh scattering coefficient based on the empirical relations for \(V\) and \(W\) parameters of double-clad photonic crystal fibers (DC PCFs). The dependence of RSL on the two structural parameters—the air hole diameter and the hole pitch was demonstrated. We have shown that RSL depends on the index profiles because of the different optical power confinement factors in every layer of DC PCF. Using these results, the RSL can be optimized by adjusting the fiber parameters—air-hole diameter as well as the air-hole pitch.

Inner cladding influence on mode interaction in symmetry-free photonic crystal fibers under heat load

A further output power scaling of Yb-doped double-cladding photonic crystal fiber lasers, required for practical applications in many industrial fields, is currently prevented by thermal effects, which significantly worsen the beam quality. In this work the mode interaction and, consequently, the single-mode regime of Yb-doped air-silica symmetry-free photonic crystal fibers have been numerically investigated in different heat load conditions using simulation tools based on the finite element method. The effect of the main inner cladding geometric parameters, in particular of the inner cladding dimension, on the guided-mode delocalization has been analyzed, with the aim to identify a design of the large mode area active fiber providing single-mode operation despite the presence of thermal effects. Simulation results have demonstrated that the inner cladding enlargement causes a stronger coupling between core-guided and cladding modes, as well as an increase of the differential overlap between fundamental and first higher-order mode for moderate heat load values. However, the inner cladding influence becomes less important under severe heat load, being the fiber behaviour mainly affected by the thermally-induced refractive index change in the doped core.

Spectral and fluorescence lifetime endoscopic system using a double-clad photonic crystal fiber.

We present a customized small-core double-clad photonic crystal fiber for spectral and fluorescence lifetime measurements of human samples. In this Letter, the new fiber has been characterized on different fluorophores and samples of human brain tumor; a comparison to a bi-fiber homemade system and a commercial fiber probe was made.

High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools.

We present a detailed description of the design, construction, and performance of high-power ultrafast Yb:fiber laser frequency combs in operation in our laboratory. We discuss two such laser systems: an 87 MHz, 9 W, 85 fs laser operating at 1060 nm and an 87 MHz, 80 W, 155 fs laser operating at 1035 nm. Both are constructed using low-cost, commercially available components, and can be assembled using only basic tools for cleaving and splicing single-mode fibers. We describe practical methods for achieving and characterizing low-noise single-pulse operation and long-term stability from Yb:fiber oscillators based on nonlinear polarization evolution. Stabilization of the combs using a variety of transducers, including a new method for tuning the carrier-envelope offset frequency, is discussed. High average power is achieved through chirped-pulse amplification in simple fiber amplifiers based on double-clad photonic crystal fibers. We describe the use of these combs in several applications, including ultrasensitive femtosecond time-resolved spectroscopy and cavity-enhanced high-order harmonic generation.

Four-plate piezoelectric actuator driving a large-diameter special optical fiber for nonlinear optical microendoscopy.

In nonlinear optical microendoscope (NOME), a fiber with excellent optical characteristics and a miniature scanning mechanism at the distal end are two key components. Double-clad fibers (DCFs) and double-clad photonic crystal fibers (DCPCFs) have shown great optical characteristics but limited vibration amplitude due to large diameter. Besides reducing the damping of fiber cantilever, optimizing the structural of the actuator for lower energy dissipation also contributes to better driving capability. This paper presented an optimized actuator for driving a particular fiber cantilever in the view point of energy. Firstly, deformation energy of a bending fiber cantilever operating in resonant mode is investigated. Secondly, strain and stress analyses revealed that the four-plate actuator achieved lower energy dissipation. Then, finite-element simulations showed that the large-diameter fiber yielded an adequate vibration amplitude driven by a four-plate actuator, which was confirmed by experiments of our home-made four-plate actuator prototypes. Additionally, a NOME based on a DCPCF with a diameter of 350 μm driven by four-plate piezoelectric actuator has been developed. The NOME can excite and collect intrinsic second-harmonic and two-photon fluorescence signals with the excitation power of 10-30 mW and an adequate field of view of 200 μm, which suggest great potential applications in neuroscience and clinical diagnoses.

All-fiber-optic vector magnetometer based on nano-magnetic fluids filled double-clad photonic crystal fiber

We demonstrate a compact all-fiber-optic vector magnetometer based on Mach-Zehnder interferometer by utilizing nano-magnetic fluid filled double-clad photonic crystal fiber (DC-PCF). The magnetic fluid (MF) serving as sensing elements is injected into the micro-channel-arrays of DC-PCF. The magnetometer is constructed by splicing a section of MF-filled DC-PCF between two standard single mode fibers forming a high stable all-fiber structure without any additional sealed capillary. The vector magnetometer has the capability of simultaneous measurement of magnetic field intensity and orientation by monitoring a specific dip wavelength shift or transmission loss of Mach-Zehnder interference spectrum. The magnetometer with response sensitivities of 114.5pm/mT, 1.79dB/mT (X-axis) and 41.9pm/mT, 0.52dB/mT (Y-axis) at two particular orthogonal magnetic field orientations was fabricated and investigated.

Characterization of fiber ultrashort pulse delivery for nonlinear endomicroscopy.

In this work, we present a detailed characterization of a small-core double-clad photonic crystal fiber, dedicated and approved for in vivo nonlinear imaging endomicroscopy. A numerical and experimental study has been performed to characterize the excitation and collection efficiencies through a 5 m-long optical fiber, including the pulse duration and spectral shape. This was first done without any distal optics, and then the performances of the system were studied by using two kinds of GRIN lenses at the fiber output. These results are compared to published data using commercial double clad fibers and GRIN lenses.

Analysis of the Modal Content Into Large-Mode-Area Photonic Crystal Fibers Under Heat Load

Yb-doped double-cladding photonic crystal fibers are one of the key enabling factors for the development of high-power fiber lasers, due to their capability to provide a very large-mode-area together with the effective suppression of high-order modes, while allowing strong pump absorption and efficient conversion. Thermal effects are currently considered as the main bottleneck for future power scaling; since beyond a certain average power, they allow guidance of high order modes and energy transfer to them, causing a sudden degradation of the beam quality. In this paper, the effects of the heat load on the modes of double cladding fibers are thoroughly analyzed with a full-vector modal solver based on the finite-element method with integrated steady-state heat equation solver. Fibers with different inner cladding designs are compared to provide a deeper understanding of the mechanisms beyond the mode reconfinement and coupling. The influence of the fiber design on the robustness of the single-mode regime with respect to fiber heating has been demonstrated, providing a clear picture of the complex interaction between modes. On the basis of simulation results it has been possible to group fiber modes into three families characterized by peculiar reaction to heating.

Ytterbium Fiber Laser Based on a Three Beam Optical Path Mach-Zehnder Interferometer

In this letter, a switchable ytterbium doped double cladding photonic crystal fiber (Yb-doped-DCPCF) laser based on a three optical path Mach-Zehnder interferometer (MZI) is presented. Here, the MZI with three-beam path was achieved by fusion splicing a segment of an Yb-doped-DCPCF between two pieces of single mode fibers. Moreover, in the proposed laser arrangement, the Yb-doped-DCPCF segment is acting simultaneously as the MZI and also as the gain medium. This laser can be switched to emit a single or double line by controlling the polarization state and it operates within the range from 1028 to 1033 nm. In addition, the laser emission has a linewidth of 0.07 nm and a single-mode suppression ratio of 40 dB. Finally, it is shown that the fiber laser arrangement is compact and robust and that requires a relativity simple fabrication procedure.

双包层太赫兹光子晶体光纤的传输特性

双包层太赫兹光子晶体光纤的传输特性

Research on ytterbium-doped photonic crystal fiber amplifier for the femtosecond fiber laser

We report on a single-stage, high-repetition photonic crystal fiber amplifier working at 1030 nm seeded by a femtosecond fiber laser, which generates an output with average power of 2.23 W at a repetition rate of 49.5 MHz and a 3 dB spectral width of 5 nm, corresponding to a pulse energy of 45.2 nJ. After amplification, the spectrum of the femtosecond laser is broadened. A home-made, ytterbium-doped, double-clad photonic crystal fiber fabricated by laser sintering technology combined with a solution doping method with a core diameter of only 24 μm is used as the power amplifier medium. The spectral characteristics as well as the suppression of amplified spontaneous emission are discussed in detail. Experiment confirms that the amplified spontaneous emission becomes negligible with increasing incident seed power and no obvious nonlinear effects arise in this experiment. These results can provide motivation for the application of ytterbium-doped photonic crystal fiber and can provide a potential application for the high-power, all-fiber laser in the future.

Double-cladding rectangular-lattice birefringence photonic crystal fiber with elliptical air holes

We proposed a novel design of photonic crystal fiber with the characteristics of high birefringence and zero dispersion. The structure of the photonic crystal fiber is composed of the rectangular lattice with double-cladding and there is an elliptical air hole in the core of the photonic crystal fiber which has the same size with the holes of inner ring. Simulation results show that the elliptical air hole in the core can enhance the performance of mode birefringence and control the properties of chromatic dispersion at the same time. We obtain the high birefringence B = 2.1 × 10−3 and B = 2.9 × 10−3 at the wavelength of 1.31 and 1.55 μm respectively and the zero dispersion point at the wavelength of 1.31 μm. The proposed photonic crystal fiber with high birefringence and zero dispersion will be important in the applications of polarization maintaining transmission systems.

双包层平坦色散光子晶体光纤的设计与性能研究

双包层平坦色散光子晶体光纤的设计与性能研究

Symmetry-Free Tm-Doped Photonic Crystal Fiber With Enhanced Mode Area

Thulium-doped fiber lasers have recently attracted a growing interest because of the possibility to combine emission around 2 μm with the high beam quality and compactness provided by the fiber medium. A key factor for power scaling of these devices, especially if operation in the short- and ultrashort-pulse regime is desired, is the availability of active fibers capable of joining large effective area and robust single-mode guiding. The strong thermo-optic effect originating from the large quantum defect of Tm ions hinders the possibility to easily find a design with such features, strongly improving the confinement of high-order modes and shrinking the mode area of the fundamental one. In this paper, a rod-type double-cladding photonic crystal fiber with inner cladding properly designed without any mirror symmetry in the cross-section is presented, and its guiding properties are thoroughly analyzed by means of numerical simulations, taking into account the effects of thermally-induced refractive index change. The results have shown that, with a careful choice of the structural parameters, the proposed fiber is capable of ensuring effective high-order mode suppression and effective area up to 3800 μm 2 when operating under heat load of about 300 W/m.

Low Loss Splicing Between Double-Clad Fiber and Photonic Crystal Fiber Using Graded Index Fiber Lens

A novel approach of splicing between photonic crystal fiber (PCF) and double-clad fiber is demonstrated with the utilization of graded index fiber (GIF) and coreless fiber as fiber lens. The light beam in large core double-clad fiber is first enlarged by coreless fiber and then focused by GIF to match the small core PCF to realize the low loss splicing. The splicing losses versus the length of GIF, coreless fiber as well as the air hole collapsed region were investigated theoretically and experimentally. Through tailoring the length of GIF and coreless fiber precisely, a splicing loss as low as 0.5 dB was finally achieved between double-clad fiber and PCF with the mode field diameters of 18.7 and 3.9 μm, respectively. To the best of our knowledge, this is the first time to achieve such a low splicing loss between double-clad fiber and PCF.

Design and fabrication of a holey fiber microfluidic device with transverse micro-channel

In this report, we present a design of holey fiber structure with six air holes in the cladding and a transverse microfluidic channel intersecting the silica core for liquid detection purpose. The simulation results suggest an improved refractive index sensitivity of the proposed structure compared to that of a single mode fiber with similar transverse channel. The proposed holey fiber structures are fabricated and characterized. Full Text: PDF References J.C. Knight, J. Arriaga, T.A. Birks, A. Ortigosa-Blanch, W.J. Wadsworth and P.St.J. Russell, "Anomalous dispersion in photonic crystal fiber", IEEE Photon. Technol. Lett. 12, 807 (2000) CrossRef D.J.J. Hu, P. Shum, G. Ren and C. Lu, "Hole-assisted lightguide fibers with small negative dispersion and low dispersion slope", App. Opt. 47, 5061 (2008) CrossRef P.St.J. Russell, P. H&ouml;lzer, W. Chang, A. Abdolvand and J. C. Travers, "Hollow-core photonic crystal fibres for gas-based nonlinear optics", Nature Photonics, 8, 278 (2014) CrossRef D. J. J. Hu, P. Shum, C. Lu and G. Ren, "Dispersion-flattened polarization-maintaining photonic crystal fiber for nonlinear applications", Opt. Comm. 282, 4072 (2009) CrossRef K. Milenko, D. J. J. Hu, P. P. Shum, T. Zhang, J. L. Lim, Y. Wang, T. R. Wolinski, H. Wei and W. Tong, "Photonic crystal fiber tip interferometer for refractive index sensing", Opt. Lett., 37, 1373 (2012) CrossRef D. J. J. Hu, Y. Wang, J. L. Lim, T. Zhang, K. Mileńko, Z. Chen, M. Jiang, G. Wang, F. Luan, P. P. Shum, Q. Sun, H. Wei, W. Tong and T. R. Woliński, "Novel Miniaturized Fabry&ndash;Perot Refractometer Based on a Simplified Hollow-Core Fiber With a Hollow Silica Sphere Tip", IEEE Sensors Journal, 12, 1239 (2012) CrossRef M.T. Myaing, J.Y. Ye and T.B. Norris, "Enhanced two-photon biosensing with double-clad photonic crystal fibers", Opt. Lett., 28, 1224 (2003) CrossRef D. J. J. Hu, J. L. Lim, M. K. Park, L. T.-H. Kao and Y. Wang, "Photonic Crystal Fiber-Based Interferometric Biosensor for Streptavidin and Biotin Detection", IEEE J. Sel. Top. Quant. Electron., 18, 1293 (2012) CrossRef D. J. J. Hu, J. L. Lim, Y. Cui, K. Milenko, Y. Wang, P. P. Shum and T. Wolinski, "Fabrication and Characterization of a Highly Temperature Sensitive Device Based on Nematic Liquid Crystal-Filled Photonic Crystal Fiber", IEEE Photonics Journal, 4, 1248 (2012). CrossRef Y. Cui, P.P. Shum, D. J. J. Hu, G. Wang, G. Humbert and X.-Q Dinh, "Temperature Sensor by Using Selectively Filled Photonic Crystal Fiber Sagnac Interferometer", IEEE Photonics Journal, 4, 1801 (2012) CrossRef D. J. J. Hu, P.P. Shum, J.L. Lim, Y. Cui, K. Milenko, Y. Wang and T. Wolinski, "A Compact and Temperature-Sensitive Directional Coupler Based on Photonic Crystal Fiber Filled With Liquid Crystal 6CHBT", IEEE Photonics Journal, 4, 2010 (2012) CrossRef Dinish U. S, Chit Yaw Fu, Kiat Seng Soh, Ramaswamy Bhuvaneswari, Anil Kumar and Malini Olivo, "Highly sensitive SERS detection of cancer proteins in low sample volume using hollow core photonic crystal fiber", Biosensors and Bioelectronics, 33, 293 (2012) CrossRef K. Zhou, Z. Yan, L. Zhang, and I. Bennion, "Refractometer based on fiber Bragg grating Fabry-P&eacute;rot cavity embedded with a narrow microchannel," Opt. Express 19, 11769-11779 (2011). CrossRef J. Petrovic, Y. Lai, and I. Bennion, "Numerical and experimental study of microfluidic devices in step-index optical fibers", Appl. Opt. 47, 1410-1416 (2008). CrossRef

Modeling thermo-optic effect in large mode area double cladding photonic crystal fibers

The impact of thermally-induced refractive index changes on the single-mode (SM) properties of large mode area (LMA) photonic crystal fibers are thoroughly investigated by means of a full-vector modal solver with integrated thermal model. Three photonic crystal fiber designs are taken into account, namely the 19-cell core fiber, the large-pitch fiber (LPF) and the distributed modal filtering (DMF) fiber, to assess the effects of the interplay between thermal effects and the high-order mode (HOM) suppression mechanisms exploited in order to obtain effectively SM guiding. The results have shown significant differences in the way the SM regime is changed by the increase of heat load, providing useful hints for the design of LMA fibers for high power lasers.