Holey Optical Fibers Research Articles

Semiconductor material photonic crystal fiber for mid-infrared supercontinuum generation

In this paper, Al0.24Ga0.76As based holey optical fiber is designed for coherent supercontinuum generation. It is mainly simulated for optical characteristic of lattice microstructures. For computational studies, the introduced design is composed of five loops of air vents with circular and elliptical structures. Flat and anomalous dispersion in the mid-infrared range has been achieved by obtaining a high nonlinear Kerr coefficient 5402 W−1 km−1 at the pump wavelength of 3.25 µm from the proposed microstructure fiber. Thereby, the expansion of the supercontinuum spectrum from 1.70 µm to 8.5 µm has been obtained. With the help of the high effective refractive index at the pump wavelength and the small effective mode region, proper supercontinuum spectrum (SC) is generated. The range of the spectrum of supercontinuum based on fiber length, pump duration and pump energy is simulated. Applications of this work will be advantageous in bio-medical, optical sensing, and wavelength conversion.

Design and Electromagnetic Analysis of Microstructured Holey Optical Fibres with Stepwise Random-Air-Hole Distributions in Concentric Cladding Layers

Design and Electromagnetic Analysis of Microstructured Holey Optical Fibres with Stepwise Random-Air-Hole Distributions in Concentric Cladding Layers

Optofluidic Dye Lasers Based on Holey Fibers: Modeling and Performance Analysis

Holey optical fibers with air-filled openings can be turned into unconventional optofluidic components by selectively introducing a suitable liquid into their internal holes. Enhanced interaction between the light guided by the fiber and molecular species suspended in the confined liquid then forms the basis for designing unique optofluidic devices—filters, sensors, or lasers—whose operating characteristics are extremely sensitive to minute changes in the liquid composition. We present a comprehensive mathematical analysis of dye lasers based on suspended-core and hollow-core fibers, with aqueous solution of Rhodamine B dye injected into the internal holes of the fibers acting as the gain medium. Our model consists of coupled first-order differential equations that characterize the population of lasing levels and the variation of pump and signal laser powers along the fiber length in the steady state. We obtain optimum operating conditions of the proposed holey fiber dye lasers, such as the optimum fiber length and dye concentration, and compare their performance to conventional dye jet lasers. We conclude that the fiber variant of dye laser using the hollow-core fiber is superior in terms of low lasing threshold and high slope efficiency. The presented theoretical framework can find applications in designing practical holey fiber dye lasers serving as fiber-based alternatives of conventional dye jet lasers as well as novel biological/chemical sensors and bio-lasers.

Finding Propagation Constants of Leaky and Degenerate Modes Using Simultaneous Transcendental Equations of Holey Optical Fibers

This paper presents a simple solution to simultaneous transcendental equations of propagation constants for leaky and degenerate modes. Using a block version of the Sakurai–Sugiura method (SSM) and a criterion for distinguishing physical solutions from spurious ones, we solved a nonlinear matrix equation formulated by the multipole method in a two-dimensional cylindrical coordinate system. Numerical examples showed that we can obtain accurate propagation constants and extract field distributions of leaky and degenerate modes of holey fibers without imposing symmetry. In addition, the condition numbers of the eigenvalues are efficient criteria for distinguishing solutions computed by the block version of the SSM.

An experiment-based comparative investigation of correlations for microtube gas flow

An experimental system was built to measure the gas (nitrogen and helium) flow characteristics in circular microchannels with diameters of 50, 20 and 5 μm. The Reynolds number of the flow was controlled in the large range of 15 to 2550. The highest Mach number could reach a magnitude of 0.625 and the highest Knudsen number was over 0.021. Four available empirical correlations were comparatively studied, in terms of the influence from compressibility and rarefaction. The accuracy of each correlation was investigated, and qualitative explanations were given according to the essence of fluid dynamics. The compressibility is found to be the dominant parameter in the experiments carried out. The results obtained by gas flow in holey optical fibres are helpful for the design of micro-scale pulse tube cryocoolers.

Performance analysis of a micro-scale pulse tube cryocooler based on optical fiber regenerator

The newly-developed holey optical fiber in photo-communication technology is introduced to the pulse tube cryocooler (PTC), exploring its feasibility as the regenerator. The influences of regenerative materials, as well as the influences of regenerator geometry, frequency, working pressure and input power were analyzed by calculating with a model based on thermoacoustic theory. The results from the simulation demonstrate that compared with the conventional stacked stainless steel screen, the utilization of optical fiber has the potential in increasing the coefficient of performance (COP) of a micro-scale PTC, as large as 0.136 at 80K. Further calculation shows the influence of working parameters on the performance of a micro-scale PTC with the optimized geometries.

Optical properties of IR-emitting centres in Pb-doped silica fibres

The first fibre preforms with a Pb-doped silica core, free of other dopants, have been produced using chemical vapour deposition. The preforms have been used to fabricate holey optical fibres. The spectroscopic properties of the fibres have been studied in detail in the range 400 — 1700 nm: we have measured the optical loss, constructed a three-dimensional luminescence excitation — emission graph and determined the decay time for the major luminescence peaks.

Wavelength-division-multiplexing fiber coupler based on bending-insensitive holey optical fiber

A wavelength-division-multiplexing (WDM) coupler has been made with a bending-insensitive holey optical fiber (HOF) by using the fused biconical tapered (FBT) method. The transmission band of the proposed HOF WDM coupler could be easily tuned by adjusting the pulling length during the FBT process. Interestingly, it was observed that the air-hole structure of the HOF should be maintained to have the property of a WDM coupler. As the air holes collapse, the HOF WDM exhibits high-pass-filter-like properties. The cross-sectional scanning electron microscope images of the implemented HOF WDM coupler are presented along with the light intensity distribution measured at the coupling region of the coupler. The proposed HOF couplers may also find applications in optical coarse WDM systems and optical fiber sensors.

Flexible Curled Optical Cord for Bending-Insensitive Optical Imaging Delivery

In the application of optical imaging technologies to the biomedical field, the flexible optical cord is one of the key components used to deliver the reflected optical signal from the internal biological tissue to the biomedical imaging system. However, the conventional optical fibers suffer from a critical wiring limitation, which results in severe power losses under a small bending radius that is less than a few centimeters. In this paper, we demonstrate that holey optical fibers with 18 air holes in cladding have negligible bending loss under a minimum bending radius of 3 mm. Excellent bending insensitivity of the holey fibers can effectively reduce the device size and space, which will be highly beneficial to the flexible endoscopic common-path optical coherence tomography system. A curled optical cord, similar to a curled telephone cord, is specially designed and fabricated to accommodate access of the imaging probe to the biological target at flexible distances. The curled optical cord displays excellent optical properties of a much lower bending loss and better optical imaging quality, but the attenuation and insertion losses are still the same as that of a conventional single-mode fiber-based optical cord.

背向切割法测量高双折射多孔光纤拍长

Based on the cutback method,an experimental system has been set up to measure the beat-length of high-birefringence(hi-bi) optical fiber. The least-square fitting is adopted to process data. The restriction to the cut length of fiber is relaxed and the measurement range of beat length is extended, so that the cutback method can be suitable for the short beat-length measurement of hi-bi holey optical fiber.

采用基本空间充填模式的掺铒多孔光纤分析

Erbium-doped holey fiber with hexagonal lattice was modeled by using effective index method. In order to calculate the equivalent step index of the periodic structure of the cladding holey optical fiber, all-vectorial fundamental space filling mode approach was utilized. By using EH11 mode, we have numerically solved the rate equations of a three-level pumping scheme for a fiber laser. The obtained results have shown a good agreement with the other experimental results, recently. The results have predicted amplifiers with gain efficiencies as high as 10 dB/mW. OCIS codes: 060.2310, 060.2410, 060.2320, 140.3500, 140.4480. doi: 10.3788/COL20080609.0644. In erbium doped fiber amplifiers (EDFAs), to obtain high gain efficiency one needs to use fibers with high numerical aperture (NA) to achieve the maximum population inversion of the erbium ions. It is useful to confine the erbium ions to the central part of the core to enforce the pumping light propagating with the fundamental HE11 mode [1,2] . Germanium-doping, which is used in the core of high NA fiber, reduces the emission bandwidth of the Er 3+ ions and limits its concentrations. This results in narrower gain bandwidths and increases the device

Behavior of Random Hole Optical Fibers under Gamma Ray Irradiation and Its Potential Use in Radiation Sensing Applications

Effects of radiation on sensing and data transmission components are of greatinterest in many applications including homeland security, nuclear power generation, andmilitary. A new type of microstructured optical fiber (MOF) called the random hole opticalfiber (RHOF) has been recently developed. The RHOFs can be made in many differentforms by varying the core size and the size and extent of porosity in the cladding region.The fibers used in this study possessed an outer diameter of 110 μm and a core ofapproximately 20 μm. The fiber structure contains thousands of air holes surrounding thecore with sizes ranging from less than 100 nm to a few μm. We present the first study ofthe behavior of RHOF under gamma irradiation. We also propose, for the first time to ourknowledge, an ionizing radiation sensor system based on scintillation light from ascintillator phosphor embedded within a holey optical fiber structure. The RHOF radiationresponse was compared to normal single mode and multimode commercial fibers(germanium doped core, pure silica cladding) and to those of radiation resistant fibers (puresilica core with fluorine doped cladding fibers). The comparison was done by measuringradiation-induced absorption (RIA) in all fiber samples at the 1550 nm wavelength window(1545 ± 25 nm). The study was carried out under a high-intensity gamma ray field from a 60Co source (with an exposure rate of 4x104 rad/hr) at an Oak Ridge National Laboratory gamma ray irradiation facility. Linear behavior, at dose values less than 106 rad, was observed in all fiber samples except in the pure silica core fluorine doped cladding fiber which showed RIA saturation at 0.01 dB. RHOF samples demonstrated low RIA (0.02 and 0.005 dB) compared to standard germanium doped core pure silica cladding (SMF and MMF) fibers. Results also showed the possibility of post-fabrication treatment to improve the radiation resistance of the RHOF fibers.

Geometrical birefringence in square-lattice holey fibers having a core consisting of a multiple defect

Geometrical birefringence in circular- and elliptical-hole square-lattice holey optical fibers having a core consisting of a multiple defect is investigated. The effect of unidirectional extension of the core area on the birefringence of these holey fibers (HFs) is discussed. We demonstrate that, as expected, a high birefringence can be induced in circular-hole HFs by unidirectional extension of the core area. In contrast, the maximum birefringence of elliptical-hole HFs, the holes of which have their major axes parallel to the long axis of the core, is achieved in a core structure that has a single defect. We also found that for elliptical holes having their major axes orthogonal to the long axis of the core, an exchange of the fast and slow modes occurs between the two orthogonally polarized fundamental modes by birefringence compensation.

Microscopic spacial effect on the dispersion polymerization in scCO 2

We report for the first time the microscopic spacial effect on the dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO 2). A variety of different-sized high-pressure vessels including microstructured holey optical fiber were employed to conduct the polymerization reactions. The molecular weights of the polymer products indicate that the function of the stabilizer and the process of chain growth are not significantly influenced. However, the SEM images show a gradual loss of the controlled morphology for the polymer products in reactors of dimension less than 1 mm under the same reaction conditions. This study provides a better understanding of the mechanism of the dispersion polymerization progress and gives a very important caution on the performance of microreactors.

How the pitch of a holey optical fiber affects its lightguide properties

This paper discusses how scaling (increasing) the transverse dimensions of a holey optical quartz fiber affects its lightguide properties. It is established that a limiting pitch exists, and that, when this is exceeded, the lightguide properties of a holey optical fiber are weakened.

Simulation of the properties of microstructured optical fibers

A new method for calculating the radiation loss and chromatic dispersion of leaky modes propagating in microstructured (holey) optical fibers (MOFs) with circular air-filled channels is proposed and implemented numerically. It is shown that the results are in good agreement with both the known numerical data and with the experimental data obtained for two types of fabricated MOFs that contain, respectively, 30 and 60 channels.

Brillouin characterization of holey optical fibers

We report the results of detailed measurements on the Brillouin frequency shift (BFS), gain bandwidth, and gain coefficients of several small-core holey optical fibers (HFs) of both uniform and axially varying structural characteristics and compare these with measurements on more conventional fibers. Our measurements show that the BFS of HFs is first-order proportional to the modal index for light propagating along the fiber and is thus extremely sensitive to its precise structural parameters. Our results highlight the possibility of using distributed Brillouin scattering measurements to perform nondestructive structural characterization of HFs, and the possibility of producing Brillouin-suppressed HFs using controlled structural variation along the fiber length.

Temperature-independent strain sensor made from tapered holey optical fiber

A large-mode-area holey fiber was tapered to a point in which the airholes collapsed, and its dependence on temperature and strain was studied. The transmission spectrum of such a fiber exhibits a series of peaks owing to the interference between the modes of the solid taper waist. We found that the interference peaks shifted to shorter wavelengths as the taper was elongated. However, the peaks were insensitive to temperature. The fabrication and advantages of our novel wavelength-encoded temperature-independent strain sensor compared with other optical fiber strain sensors are discussed.

Holey optical fiber with circularly distributed holes analyzed by the radial effective-index method.

We analyze a holey fiber that consists of a circular distribution of air holes by the radial effective-index method. By this method, we show that the holey fiber is a leaky structure and its extended single-mode operation is governed by the differential leakage loss between the first two modes of the fiber. The effects of the hole size and the hole separation on the leakage losses of the first two modes are calculated. The leakage loss of the fundamental mode of the fiber is found to be comparable to that of a conventional holey fiber that has a hexagonal distribution of air holes.

Understanding bending losses in holey optical fibers

Extremely large mode area fibers that are single-moded over a broad wavelength range can be created using holey fiber technology. However, as with any fiber, the largest mode areas that are practically feasible are ultimately determined by bending losses. It is therefore essential to gain an understanding of the factors that influence bend loss in these fibers in order to form accurate predictions that can facilitate improved bend loss design. Here, we present the first detailed study of transition loss and pure bend loss in a holey fiber, and consider the impact of the fiber structure. A theoretical model is derived that retains the full refractive index profile of a holey fiber. This approach is used to predict the bend loss in large mode area holey fibers and is validated through comparison with experimental data. For the fibers under study here, we demonstrate that pure bend loss is the dominant component of macro-bend loss and that the hole configuration within the cladding can strongly influence this loss.