Munehisa Fujimaki

Effectively single-mode all-solid photonic bandgap fiber with large effective area and low bending loss for compact high-power all-fiber lasers

An effectively single-mode all-solid photonic bandgap fiber with large effective area and low bending loss for compact high-power all-fiber lasers is fully investigated. The pitch dependencies of effective area, bending loss, and effectively single-mode operation are discussed numerically and experimentally. The calculation results indicate that an effectively single-mode all-solid photonic bandgap fiber with an effective area of more than 500 μm(2) and a bending loss of less than 0.1 dB/m at a bending radius of 10 cm can be realized by choosing optimum fiber parameters. In a fabricated effectively single-mode all-solid photonic bandgap fiber with 48.0 μm core, the effective area of 712 μm(2), the effectively single-mode operation, and the bending loss of less than 0.1 dB/m at a bending radius of 10 cm are achieved simultaneously at 1064 nm.

Fiber fuse phenomenon in hole-assisted fibers

Fiber fuse phenomenon in hole-assisted fibers (HAFs) was investigated. Fiber fuse propagation can be stopped as designing suitable position of air holes in HAF.

Low bending loss and effectively single-mode all-solid photonic bandgap fiber with an effective area of 650 μm 2

A large-mode-area all-solid photonic bandgap fiber with a seven-cell core and five high-index rod rings is investigated. Numerical simulations show that an effective area of more than 500 μm(2), a bending loss of less than 0.1 dB/m at a bending radius of 10 cm and effectively single-mode operation can be achieved simultaneously. A core diameter of 44.8 μm and an effective area of 650 μm(2) at 1064 nm are achieved in a fabricated fiber. Bending loss at 1064 nm is 0.09 dB/m at a bending radius of 7 cm. Effectively single-mode operation is also realized at a bending radius of 10 cm.

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.

Gamma-radiation-induced photodarkening in ytterbium-doped silica glasses

Photodarkening phenomenon in ytterbium (Yb)-doped silica glasses was experimentally investigated by measurements such as electron spin resonance (ESR), X-ray absorption fine-structure (XAFS), and optical transmittance. A predominant increase of Al-oxygen hole center (OHC) was observed for Al-Yb co-doped silica glasses both by the incidence of pump light and by gamma-ray irradiation. It was also recognized that the optical transmission loss similarly increased in both cases. These results indicate that the formation of Al-OHC is the prime cause of the excess loss induced by photodarkening. XAFS measurement indicated that the second-nearest-neighbor atoms around Yb may be related to the mechanism of photodarkening phenomenon.

Defect analysis of photodarkened and gamma-ray irradiated ytterbium-doped silica glasses

Defects in photodarkened and gamma-ray irradiated ytterbium (Yb)-doped silica glasses has been experimentally investigated. The results indicate that the formation of Al-oxygen hole center (Al-OHC) is the prime cause of the photodarkening loss.

1180 nm linearly-polarized fiber laser with high slope efficiency employing low-loss ytterbium-doped polarization maintaining solid photonic bandgap fiber

A linearly-polarized fiber laser operating at 1180 nm was demonstrated using a low-loss ytterbium-doped polarization maintaining solid photonic bandgap fiber. A slope efficiency of 30% was achieved.

Low-loss ytterbium-doped polarization maintaining solid photonic bandgap fiber

A low loss ytterbium-doped polarization maintaining solid photonic bandgap fiber (SPBGF) is fabricated using a new fabrication method. A high efficient fiber laser operated at the low-gain wavelengths is prospected by the fiber.

Bend sensitive wavelength filtering in concentric core solid photonic bandgap fibre

Bend sensitive wavelength filtering property in a concentric core solid photonic bandgap fibre is resented. The property is realised by not only the bandgap effect but mode coupling between the core mode and ring modes.

Experimental and numerical investigation of effective area of all-solid photonic bandgap fiber for high power delivery

The effective area of a large-mode-area all-solid photonic bandgap fiber for high-power delivery is investigated numerically and experimentally. The new evaluation method of the effective area is proposed and discussed.