Tomoharu Kitabayashi

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.

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.

30W Q-SW fiber laser

We present an adaptive and robust pulse-operated high power fiber laser, which has an average output power of 30 W. The fiber laser realizes flexible pulse duration without changing a repetition rate and an average power, which is desirable for laser processing, by employing a Q-switched (Q-SW) Master Oscillator Power Amplifier(MOPA). For instance, its pulse duration is controllable in the range of 50 ns to 100 ns at 50 kHz in repetition rate. In addition to the flexible pulse duration, the fiber laser provides high powers, a peak power of 27 kW at 30 kHz in repetition rate and an average power of 30 W at 50 kHz in repetition rate. Large mode area (LMA) fibers and end pumping structure in the laser also contribute the above mentioned features, pulse adaptiveness and high output power. In terms of the robustness of the laser, we employ newly-developed reflection-suppressing pump combiners, which protect pump laser diodes (LDs) from amplified reflected signal light from objectives. All those features make the fiber laser a more practical light source for laser processing.

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.

Novel gain-tilt free L-band EDFA using thulium-doped fiber

We have realized a novel gain-tilt free L-band EDFA using a thulium-doped fiber. This EDFA has a wide input power range of more than 8 dB, a wide temperature range of 65 degreeC without gain-tilt in a wavelength band between 1575 nm and 1610 nm, and a low noise figure of less than 6 dB.

2 kW single-mode fiber laser with 20-m long delivery fiber and high SRS suppression

A 2 kw single-mode fiber laser with a 20-m long delivery fiber and high back reflection resistance has been demonstrated. An Yb-doped fiber with large core size and differential modal gain is used to realize high SRS suppression and single-mode operation simultaneously. The 20 m-long delivery fiber gives flexibility to the design of processing systems. An output power of 2 kW is achieved at a pump power of 2.86 kW. The slope efficiency is 70%. The power of the Stokes light is less than -50 dB below the laser power at the output power of 2 kW even with a 20-m delivery fiber. Nearly diffraction-limited beam quality is also confirmed (M2 = 1.2). An output power of 3 kW is believed to be achieved by increasing pumping power. The back reflection resistance properties of the fabricated singlemode fiber laser is evaluated numerically by the SRS gain calculated from measured laser output spectra and fiber characteristics. The acceptable power of the back reflection light into the fiber core is estimated to be 500 W which is high enough for processing of highly reflective materials. The output power fluctuation caused by SRS and back reflection in materials processing will be well suppressed. Our high power single-mode fiber lasers can provide high quality and stable processing of highly reflective materials.

Over 10-W linearly-polarized single cavity fibre laser at 1180 nm wavelength with slope efficiency of 56 % using Yb-doped polarization-maintaining solid photonic bandgap fibre

We have demonstrated an 1180-nm linearly-polarized single cavity fibre laser with an output power of 10.8 W using an Yb-doped polarization-maintaining solid photonic bandgap fibre. A slope efficiency of 56 % has been achieved.