Ryuichiro Goto

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.

Single-polarization operation in birefringent all-solid hybrid microstructured fiber with additional stress applying parts

We demonstrate single-polarization (SP) operation in a birefringent all-solid hybrid microstructured fiber that has additional boron-doped stress-applying parts (SAPs). The stress from the SAPs is added to the stress from the highly germanium-doped high-index regions, and SP operation with more than a 25 nm bandwidth was achieved at the shorter wavelength edge of the second bandgap.

Linearly polarized fiber laser using a point-by-point Bragg grating in a single-polarization photonic bandgap fiber

We present a narrow-linewidth, linearly polarized neodymium-doped fiber laser that incorporates a point-by-point Bragg grating inscribed into the core of a single-polarization all-solid photonic bandgap fiber. The Bragg grating was written within a single-polarization wavelength band of the fiber; thus, the Bragg reflection was polarized. This all-fiber laser produced 7.2 W, linearly polarized output with 25 pm FWHM and 19.6 dB polarization extinction ratio.

UV-induced Bragg grating inscription into single-polarization all-solid hybrid microstructured optical fiber.

We demonstrate a single-polarization all-solid hybrid microstructured optical fiber with a UV-induced Bragg grating. A strong (∼20 dB) UV-induced Bragg grating was inscribed within the 30 nm-wide single-polarization window of the fiber, producing polarized Bragg reflection. The sharp band-edge cutoff allows a large polarization-extinction ratio of the Bragg reflection. The hybrid structure of the fiber enabled minimal UV exposure to the high-index regions and the location of the single-polarization window was maintained after the grating was inscribed.

Point-by-Point Bragg grating inscription into single-polarisation all-solid photonic bandgap fibre

We demonstrate Point-by-Point Bragg grating inscription into the core of a single-polarisation all-solid photonic bandgap fibre. Grating strength of 7.5 dB (>;80% reflectivity) was realised at 1064 nm with linearly-polarised feedback.

Low splice loss solid photonic bandgap fibre and its temperature dependence of filtering wavelength

A low splice loss solid photonic bandgap fibre (PBGF) is realized by deploying a depressed clad layer. The temperature dependence of the filtering wavelength of the PBGF is measured.