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.

Low bending loss and effectively single-mode all-solid photonic bandgap fiber with an effective area of 650 µm2.

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.

A large effective area multi-core fiber with an optimized cladding thickness.

The cladding thickness of trench-assisted multi-core fibers was theoretically and experimentally investigated in terms of excess losses of outer cores. No significant micro-bending loss increase was observed on multi-core fibers with the cladding thickness of about 30 µm. The tolerance for the micro-bending loss of a multi-core fiber is larger than that of the single core fiber. However, the cladding thickness will be limited by the occurrence of the excess loss on outer cores. The reduction of cladding thickness is probably limited around 40 µm in terms of the excess loss. The multi-core fiber with an effective area of 110 µm(2) at 1.55 µm and 181-µm cladding diameter was realized without any excess loss.

Selective mode excitation and discrimination of four-core homogeneous coupled multi-core fiber.

Coupled modes of homogeneous coupled multi-core fiber are selectively excited and discriminated utilizing the difference of equivalent propagation angle. To quantatively evaluate the extinction ratio (selectivity) of adjacent modes, a new mode discrimination technique is developed by measuring the visibility of far-field patterns under small change of wavelength of the launching beam. The peak angles of discriminated far-field patterns show a strong correlation with the incident angle of the launching beam, which means that the coupled modes were selectively excited and discriminated.

Observation of a propagation mode of a fiber fuse with a long-period damage track in hole-assisted fiber.

We examined the fiber-fuse propagation characteristics in hole-assisted fibers (HAFs) when the diameter of an inscribed circle linking the air holes was almost the same as the diameter of the melted area caused by the fiber fuse. We observed a new propagation mode for the fiber fuse in HAF with a damage track whose period was approximately 30 times longer than that in conventional single-mode fiber. We also made the first observation of a new threshold power (upper threshold) for the fiber fuse.