Akira Shirakawa

87 W, narrow-linewidth, linearly-polarized 1178 nm photonic bandgap fiber amplifier.

High-power narrow-linewidth photonic bandgap fiber amplifier was demonstrated. In order to suppress stimulated Brillouin scattering, the seed linewidth was broadened by applying a random phase noise with an electro-optical modulator. A factor of 15 in terms of Brillouin gain suppression can be theoretically expected. An 87 W linearly-polarized (11 dB PER) and narrow-linewidth (780 MHz FWHM) output was obtained.

Large-mode-area hybrid photonic crystal fiber amplifier at 1178 nm

Amplification of 1178xa0nm light is demonstrated in a large-mode-area single-mode ytterbium-doped hybrid photonic crystal fiber, relying on distributed spectral filtering of spontaneous emission at shorter wavelengths. An output power of 53xa0W is achieved with 29xa0dB suppression of parasitic lasing. Further power scaling is limited by parasitic lasing.

Self-focusing in multicore fibers

Self-focusing is the ultimate power limit of single mode fiber amplifiers. As fiber technology is approaching this limit, ways to mitigate self-focusing are becoming more and more important. Here we show a theoretical analysis of this limitation in coupled multicore fibers. Significant scaling of the self-focusing limit is possible even for coupled multicore fibers if the out-of-phase mode is chosen. On the other hand the in-phase mode can - depending on the coupling strength - be prone to instabilities.

A 98 W 1178 nm Yb-doped solid-core photonic bandgap fiber oscillator

A high-power ytterbium-doped solid-core photonic bandgap fiber laser directly oscillating at 1178xa0nm is reported. The sharp-cut bandpass distributed filtering effect of photonic bandgap fiber can suppress amplified spontaneous emission (ASE) in the conventional high-gain spectral region. The oscillator is composed of a high reflection fiber Bragg grating spliced with a 39xa0m gain fiber and a Fresnel fiber end surface. A model based on rate equations is investigated numerically. A record output power of 98xa0W is achieved with a slope efficiency of 54%. The laser linewidth is 0.5xa0nm. The spectrum at 98xa0W indicates that ASE and parasitic lasing are suppressed effectively.

High-peak power pulse amplification by SRS-suppressed photonic bandgap fiber

We report Yb-doped photonic bandgap fiber amplifier generating 19 kW nanosecond pulses without stimulated Raman scattering by long-wavelength cut distributed filtering. Modulation instability due to the huge anomalous waveguide dispersion around the cutoff was observed.

Delay line coherent pulse stacking

We show a novel approach to coherent pulse stacking at 1.5μm. We use phase preshaping of a symmetric 47 MHz pulse train to combine pulses next to each other and in turn reducing the repetition rate to 23.5 MHz.

Spectrally-filtering photonic bandgap fiber lasers

Photonic bandgap fiber lasers are realizing new laser spectra and nonlinearity mitigation that a conventional fiber laser cannot by distributed spectral filtering. The recent our works will be reviewed and the future will be discussed.

Coupled multicore fibers in the high power regime: Impact of core size mismatch

The impact of core diameter mismatch in multicore fibers in the context of the Kerr nonlinearity is analyzed. A mismatch decreases the stability of the even mode. The odd mode is unaffected.

High-power Single-Frequency Fiber MOPA Based on FRA and PBGF Amplifier at 1178 nm

87 W CW single-frequency lineally-polarized signal amplification was obtained in a photonic bandgap fiber amplifier with suppressing SBS by linewidth broadening. The broadening was obtained via a phase modulator driven by a white Gaussian noise.

Femtosecond Mode-Locked Nd3+-doped Ba(Zr,Mg,Ta)O3 Ceramic Laser

We report efficient CW laser operation and first femtosecond mode-locked laser operation of transparent Nd3+:Ba(Zr,Mg,Ta)O3 ceramic. The disordered crystalline system exhibits the characteristic broadband absorption and fluorescence spectra suitable for ultrashort pulse lasers.