Measurement of bending-induced birefringence in a hollow-core photonic crystal fiber.

We report the measurement of bending-induced birefringence in the presence of large intrinsic birefringence in a hollow-core photonic crystal fiber (HC-PCF). The fast axis of bending-induced birefringence was found to be normal to the bending plane, in contrast to the conventional fiber case. The dependence of the induced birefringence on the bending radius was also different from the typical inverse square law. Possibilities and design criteria for polarization controllers using bending-induced birefringence in HC-PCFs are presented.

Wavelength independent all-fiber angle-tunable polarization rotator based on geometric effects.

We propose and demonstrate a simple wavelength independent all-fiber polarization rotator based on purely geometric effects. The device rotates the orientation of an arbitrary input polarization state by arbitrary angle without changing other parameters of the polarization state. The device structure maintains inherent wavelength independence during the tuning process when a non-birefringent single-mode fiber is used.

Optically controlled in-line graphene saturable absorber for the manipulation of pulsed fiber laser operation.

We demonstrate an optically tunable graphene saturable absorber to manipulate the laser operation in pulsed fiber laser system. Owing to the strongly enhanced evanescent field interaction with monolayer graphene, we could realize an efficient control of modulation depth in the graphene saturable absorber by optical means through cross absorption modulation method. By integrating the tunable graphene saturable absorber into the fiber laser system, we could switch the laser operation from Q-switching through Q-switched mode-locking to continuous wave mode-locking by adjusting only the optical power of the control beam. In addition, we realized a hybrid Q-switching of fiber laser by periodical modulation of the absorption of the graphene saturable absorber, where we observed that the repetition rate of the Q-switched laser could be continuously tuned according to the modulation frequency of the applied external signal.

Broadband mode division multiplexer using all-fiber mode selective couplers.

We report an all-fiber mode division multiplexer formed with cascaded mode selective couplers with significantly broadened bandwidth potentially spanning S, C and L band. This was achieved by matching the effective refractive indices over a wide wavelength range for the few mode fiber and the single mode fiber used in the coupler. The multiplexer provides high coupling efficiency (>55% for the worst case) for the 4 spatial modes over the entire wavelength range of 1515-1590 nm. The all-fiber construction provides mechanical stability. Experimental results for the coupling efficiency and the mode extinction ratio for each spatial mode are presented along with the far field radiation patterns.

Mode- and wavelength-division multiplexed transmission using all-fiber mode multiplexer based on mode selective couplers.

We propose all-fiber mode multiplexer composed of two consecutive LP11 mode selective couplers that allows for the multiplexing of LP01 mode and two-fold degenerate LP11 modes. We demonstrate WDM transmission of 32 wavelength channels with 100 GHz spacing, each carrying 3 modes of 120 Gb/s polarization division multiplexed quadrature phase shifted keying (PDM-QPSK) signal, over 560 km of few-mode fiber (FMF). Long distance transmission is achieved by 6×6 multiple-input multiple-output digital signal processing and modal differential group delay compensated link of FMF. The all-fiber mode multiplexer has considerable potential to be used in mode- and wavelength-division multiplexed transmission.

Few-mode fiber multi-parameter sensor with distributed temperature and strain discrimination.

We propose a unique few-mode fiber (FMF)-based multi-parameter optical-fiber sensor for distributed measurement of temperature and strain. We launch a pump and a probe signal through specific linearly polarized modes into a FMF, and monitor the Brillouin frequency shift (BFS) in each mode. By analyzing the temperature and strain coefficients of the BFS of the two lowest order (LP(01), LP(11)) modes, discrimination of temperature and strain are successfully demonstrated, with an accuracy of 1.2°C and 21.9 µÎµ.

Band-rejection filtering based on lossy torsional acousto-optic coupling in a single polarization fiber.

We propose and demonstrate novel band-rejection filtering scheme based on lossy torsional acousto-optic (AO) coupling in a single polarization fiber. Simulation results show that the polarization insensitive notch depth of -30 dB is achievable for a 2-m-long fiber in the state-of-the-art fiber manufacturing technology. More efficient band-rejection in excess of -44 dB could be also feasible in practical fiber length. Good agreement between our numerical simulations and proof-of-principle experiments is obtained in optical communication C-band. The measured notch depth is -29.4 dB for a low loss polarization mode after propagating an AO interaction length of 49.8 cm. The filtered wavelength could be tuned linearly by the variable acoustic transducer frequency with the slope of 0.61 nm/kHz, and the polarization dependence of notch depth was measured to 0.8 dB in our setup. Our experiments confirm the validity and practicality of the approach, and illustrate the in-fiber torsional AO band-rejection filter with simpler device configuration is achievable.

Effect of metal coating in all-fiber acousto-optic tunable filter using torsional wave.

Torsional mode acousto-optic tunable filter (AOTF) is demonstrated using a metal-coated birefringent optical fiber for an improved robustness. The changes in acoustic and optical properties of a metal-coated birefringent optical fiber induced by the thin metal coating were analyzed experimentally and theoretically. The filter wavelength shift is successfully explained as a result of combined effect of acoustic wavelength change and optical birefringence change. We also demonstrated a small form-factor configuration by coiling the fiber with 6 cm diameter without performance degradation. The center wavelength of the filter can be tuned >35 nm by changing the applied frequency, and the coupling efficiency is higher than 92% with <5 nm 3-dB bandwidth.

Mode division multiplexed optical transmission enabled by all-fiber mode multiplexer.

Mode division multiplexed optical transmission enabled by all-fiber mode multiplexer is investigated. The proposed all-fiber mode multiplexer is composed of consecutive mode selective couplers. It multiplexes or demultiplexes LP01, LP11, LP21, and LP02 modes simultaneously. We demonstrate successful transmission of three spatial modes with 120 Gb/s PDM-QPSK signals over 15 km of four mode fiber by using 6x6 MIMO digital signal processing.

Characterization of distributed modal birefringence in a few-mode fiber based on Brillouin dynamic grating.

We propose and demonstrate generation of Brillouin dynamic grating (BDG) in a few-mode fiber (FMF) with a Gaussian pulse pump and a counterpropagating continuous wave pump in LP01 mode. Brillouin optical time-domain analysis (BOTDA) is achieved by launching a third Gaussian pulse probe in LP11 mode. With coherent detection and time-domain analysis on the backreflected probe signal, the modal birefringence of the FMF is characterized via the distributed BDG with high spatial resolution and high accuracy.

Spectral shaping of an all-fiber torsional acousto-optic tunable filter.

Spectral shaping of an all-fiber torsional acousto-optic (AO) tunable filter is studied. The technique is based on the axial modulation of AO coupling strength along a highly birefringent optical fiber, which is achieved by tailoring the outer diameter of the fiber along its propagation axis. Two kinds of filter spectral shaping schemes-Gaussian apodization and matched filtering with triple resonance peaks-are proposed and numerically investigated under realistic experimental conditions: at the 50-cm-long AO interaction length of the fiber and at half of the original fiber diameter as the minimum thickness of the tailored fiber section. The results show that the highest peak of sidelobe spectra in filter transmission is suppressed from 11.64% to 0.54% via Gaussian modulation of the AO coupling coefficient (κ). Matched filtering with triple resonance peaks operating with a single radio frequency signal is also achieved by cosine modulation of κ, of which the modulation period determines the spectral distance between two satellite peaks located in both wings of the main resonance peak. The splitting of two satellite peaks in the filter spectra reaches 48.2 nm while the modulation period varies from 7.7 to 50 cm. The overall peak power of two satellite resonances is calculated to be 22% of the main resonance power. The results confirm the validity and practicality of our approach, and we predict robust and stable operation of the designed all-fiber torsional AO filters.

Diagnosis of Leucocytozoon caulleryi infection in commercial broiler breeders in South Korea.

This report confirms a recent outbreak of a Leucocytozoon caulleryi infection in a commercial broiler breeder flock in South Korea. Seven, 18-day-old broiler breeders (Gallus gallus) were necropsied following a history of depression, sudden death, and subcutaneous hemorrhages. On necropsy, subcutaneous hemorrhages were identified in the wings and legs, pectoral and thigh muscles, thymus, epicardium, pancreas, and kidneys. On histopathology, there were numerous schizonts and merozoits of a Leucocytozoon sp. noted in the heart, spleen, liver, kidneys, thymus, and bursa of Fabricius. Molecular analysis of the mitochondrial cytochrome oxidase b confirmed that the causative agent was Leucocytozoon caulleryi. Although L. caulleryi was diagnosed previously in South Korea, there had been no reports of L. caulleryi over the past several decades.

Prevalence and characterization of Salmonella species in entire steps of a single integrated broiler supply chain in Korea.

The purpose of this study was to investigate the distribution of Salmonella species in an integrated broiler supply chain in Korea. A total of 1,214 samples from various steps of an integrated broiler production company including broiler breeder farms, broiler farms, broiler trucks, slaughterhouse, and retail chicken meats were collected and investigated. Salmonella was detected in 195 of the samples. The highest prevalence of Salmonella was observed in broiler transporting trucks (71.43%), followed by the slaughterhouse (63.89%) and broiler farms (16.05%). Salmonella Hadar was the most frequently isolated serotype (83.08%). All Salmonella Hadar isolates investigated in this study with pulsed-field gel electrophoresis showed the same XbaI pulsed-field gel electrophoresis pulsotype.

Intermodal stimulated Brillouin scattering in two-mode fibers.

Characterization of stimulated Brillouin scattering (SBS) in an elliptic-core two-mode fiber is experimentally demonstrated. The LP(01) or LP(11) mode is selectively launched to a fiber under test by a mode-selective coupler as a Brillouin pump, and the Brillouin gain spectra are analyzed for different mode pairs of the pump and probe waves. Intermodal SBS between counterpropagating LP(01) and LP(11) modes is observed, and the efficiency is measured to be about 58% of that of the SBS between the LP(01) modes.

Subharmonics and chaos generation in all-fiber phase modulator: experimental and theoretical analyses with simulation.

We report the results of experimental observation and theoretical analysis of the generation of subharmonic and chaotic signals in a harmonically driven all-fiber phase modulator (PM). When a PM constructed with optical fiber wrapped around a piezoelectric cylinder is driven at high amplitude, we identified that the fiber itself moves with subharmonic frequencies while the piezoelectric cylinder maintains harmonic motion. A theoretical model is presented that is a modification of the model for a bouncing ball on an oscillating table. Some key physical parameters for the model are identified. Potential origins for the discrepancy between the experimental and theoretical analyses are discussed. Ways to suppress the nonlinear effect are also discussed.

Cross-protective immune responses elicited by a Korean variant of infectious bronchitis virus.

Infectious bronchitis virus (IBV) infections cause great economic losses to the poultry industry worldwide. IBVs continuously evolve by developing mutations in antigenic sites; therefore, an IBV vaccine that provides broad cross-protection can be a highly relevant and practical method in IBV control strategies. Although some IBV vaccine strains are known to provide protection against multiple IBV serotypes, in general commercially available IBV vaccine strains provide protection against antigenically related viruses but not distinct heterologous viruses. In the present study we characterized the Korean variant IBV K40/09 strain with regard to its immunogenicity and protective efficacy against seven currently circulating IBV serotypes. Three-week-old specific-pathogen-free chickens were intraocularly immunized with the IBV K40/09 strain at 10(3.5) 50% egg infective dose (EID50). Three weeks after immunization all the birds were challenged with seven different strains at 10(4.5) EID50. Chickens immunized with the IBV K40/09 strain showed significantly high levels of protection against all challenge viruses at the trachea and kidney levels. Our results suggest that IBV K40/09 could be useful to ensure IBV vaccine effectiveness owing to its cross-protective ability. Therefore, the IBV K40/09 strain merits consideration as a vaccine candidate to prevent infection as well as the spread of new IBV strains and many IBV variants that have been reported worldwide.

Toward higher-order passive harmonic mode-locking of a soliton fiber laser.

We report >13 MHz/mW pump power efficiency in increasing the repetition rate of passive harmonic mode-locking by engineering the soliton pulse energy in Er fiber lasers incorporating carbon nanotube saturable absorber. Stable pulses with a ∼5 GHz repetition rate and 40 dB of super-mode suppression are demonstrated with only ∼400 mW pump power in a single-clad fiber laser.

Measurement of the entanglement between photonic spatial modes in optical fibers.

We experimentally demonstrate the entanglement of spatial modes between two photons propagating through separate few-mode optical fibers. Quantum states over the two lowest-order spatial modes are measured with highly efficient spatial-mode analyzers based on acousto-optics. Quantum state tomography verifies the entanglement of the spatial-domain Bell state.

Mode-locking and Q-switching in multi-wavelength fiber ring laser using low frequency phase modulation.

We describe experimental investigation of pulsed output from a multi-wavelength fiber ring laser incorporating low frequency phase modulation with large modulation amplitude. The Erbium-doped fiber (EDF) ring laser generated more than 8 wavelength channels with the help of a phase modulator operating at 26.2 kHz and a periodic intra-cavity filter. For most cases, the laser output is pulsed in the form of mode-locking at 5.62 MHz and/or Q-switching at harmonic and sub-harmonic of the phase modulation frequency. Chaotic pulse output is also observed. The behavior of the output pulses are described as functions of pump power and phase modulation amplitude. The relative intensity noise (RIN) value of a single wavelength channel is measured to be under -100 dB/Hz (-140 dB/Hz beyond 1.5 GHz).

Design of waveguide grating with ultrafast tunable index contrast.

A long-period waveguide grating (LPWG) with a tunable index contrast is proposed. The design features a simple configuration that consists of a two-mode waveguide formed on periodically poled lithium niobate with an angle with respect to its domain wall and a traveling-wave electrode. In the design, the electrical traveling wave introduces a periodic change in the refractive index of waveguide, which functions as a long-period waveguide grating that couples between symmetric and anti-symmetric core modes. The index contrast of grating can be controlled by the traveling-wave intensity. For application to ultrafast device, structural parameters satisfying velocity and impedance matching conditions are numerically calculated.