Kuniharu Himeno

Low-bending-loss single-mode fibers for fiber-to-the-home

Recent progress on low-bending-loss single-mode optical fibers for fiber-to-the-home (FTTH) is reviewed. Designing and manufacturing for three types of fibers-a step-index-profile fiber, a trench-index-profile fiber, and a holey fiber-are discussed. The trench-index-profile fibers and the holey fibers are confirmed to be candidates for indoor wiring because of their low bending losses, as well as splice losses.

Boundary element method for analysis of holey optical fibers

By using a full-vector boundary element method (BEM) based on a formulation in terms of transverse magnetic field components, holey fibers (HFs) are numerically analyzed. The BEM provides very accurate solutions with an extremely small number of unknowns. Not only the characteristics of all-silica HFs, but also those of hole-assisted lightguide fibers and field-confined HFs, are investigated and compared with each other.

A novel temperature-insensitive long-period fiber grating using a boron-codoped-germanosilicate-core fiber

Long-period fiber gratings are promising components as gain equalizers for erbium-doped fiber amplifiers, band rejection filters and sensors. It has been reported that these devices have a high temperature sensitivity, typically 0.05 nm//spl deg/C at room temperature. Judkins et al., showed a method to eliminate the temperature sensitivity by optimizing the refractive-index profile of the host fiber. In this paper, we show a novel method to compensate the temperature sensitivity using a boron codoped germanosilicate core fiber as a host fiber.

Population inversion factor dependence of photodarkening of Yb-doped fibers and its suppression by highly aluminum doping

We have confirmed that the photodarkening of Yb-doped fiber (YbDF) has the second-power dependence on a population inversion factor. The photodarkening of a newly developed highly aluminum-doped YbDF has been significantly suppressed

Multimode fibers for compensating intermodal dispersion of graded-index multimode fibers

This paper proposes a novel type of multimode dispersion compensation fiber (MM-DCF) by which the intermodal dispersion of multimode fibers (MMFs) can be effectively compensated. A theoretical model that precisely calculates the group velocities of a target MMF and its MM-DCF and the power coupling between the two fibers is applied to confirm the proposal presented here. As a demonstration of the operation of the MM-DCF, an MMF optimized for transmission at a wavelength of 850 nm is compensated by the MM-DCF, and its overfilled launch bandwidth at a wavelength of 1300 nm is enhanced from 0.62 to 2.56GHz/spl middot/km.

Birefringent all-solid hybrid microstructured fiber

We report the characterization of a birefringent all-solid hybrid microstructured fiber, in which the core-modes are guided by both the photonic bandgap (PBG) effect and total internal reflection (TIR). Due to the twofold symmetry, modal birefringence of 1.5 x 10(-4) and group birefringence of 2.1 x 10(-4) were measured at 1.31 microm, which is in the middle of the second bandgap. The band structure was calculated to be different from conventional 2-D PBG fibers due to the 1-D arrangement of high-index regions. The bend loss has a strong directional dependence due to the coexistence of the two guiding mechanisms. The fiber has two important properties pertinent to PBG fibers; spectral filtering, and chromatic dispersion specific to PBG fibers. The number of high-index regions, which trap pump power (by index guiding) when the fiber is used in cladding-pumped fiber lasers, is greatly reduced so that this fiber should enable efficient cladding pumping. This structure is suitable for linearly-polarized, cladding-pumped fiber lasers utilizing the properties of PBG fibers.

Cladding-Pumped Yb-Doped Solid Photonic Bandgap Fiber for ASE Suppression in Shorter Wavelength Region

We demonstrate suppression of amplified spontaneous emission at 1030 nm in a cladding-pumped ytterbium-doped solid photonic bandgap fiber. This fiber should play an important role for a high power fiber laser lasing around 1180 nm.

Basic Study on an Antenna Made of a Transparent Conductive Film

The radiation characteristics of a monopole antenna that consists of one-half of a bow-tie dipole antenna, made of optically transparent conductive thin film and mounted above a ground plane, are investigated. The antennas performance is measured for several films with different sheet resistivities. It is found that the gain lowering of the antenna caused by material resistance decreases from 4.4 dB to 0.2 dB at 2.4 GHz and the efficiency of the antenna increases from 46% to 93% at the same frequency, as the sheet resistivity decreases from 19.8 Ω/□ to 1.3 Ω/□. The antenna is analyzed by the moment method. A wire-grid model with resistance loading on every discretized wire is applied. The analyzed results agree with the experimental values very well.

Over 10 W Output Linearly-Polarized Single-Stage Fiber Laser Oscillating Above 1160 nm Using Yb-Doped Polarization-Maintaining Solid Photonic Bandgap Fiber

We propose an all-fiber linearly-polarized single-stage fiber laser oscillating above 1160 nm employing a low-loss Yb-doped polarization-maintaining solid photonic bandgap fiber (Yb-PM-SPGF) as a laser source for a yellow-orange frequency-doubling laser. We also present a new fabrication method for Yb-PM-SPBGF to reduce fiber attenuation in its photonic bandgap for increasing laser output power and improving slope efficiency. The attenuation of a fabricated Yb-PM-SPBGF is below 20 dB/km at 1180 nm, which is as low as that of a conventional Yb-doped fiber. All-fiber linearly-polarized single-stage fiber laser oscillating at 1180 nm using the fabricated Yb-PM-SPBGF is demonstrated. ASE and parasitic lasing in the wavelength range from 1030 nm to 1130 nm are suppressed and eliminated thanks to the filtering effect of the fiber. A 10.8 W output power is successfully achieved with a slope efficiency of 56% and a conversion efficiency of 50% by high-power 976 nm pumping. A spectral width of less than 0.05 nm, a polarization extinction ratio of more than 20 dB and nearly diffraction limited beam quality in output light are achieved. These results indicate that our proposed fiber laser can realize a compact and high-power yellow-orange frequency-doubling laser.

Evaluation of High-Power Endurance of Bend-Insensitive Fibers

We examined high power endurance of single-mode fibers including bend-insensitive fibers. The bend-insensitive fibers have effective suppression of fiber-temperature increase under tight bending. Trench index profile does not influence on threshold powers for fiber fuse propagation.