• Current Optics and Photonics
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• v.7 no.6
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• pp.732-737
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• 2023

A high-power Yb-doped femtosecond (fs) fiber laser at a repetition rate of 1.83 GHz is reported. By employing a 5-stage repetition rate multiplier, the repetition rate of the mode-locked master oscillator was multiplied from 57.1 MHz to 1.83 GHz. The ultrashort pulse output at 1.83 GHz was amplified in a two-stage Yb-doped fiber amplifier, leading to >100 W of fs laser output with a pulse duration of 290 fs. The theoretical pulse width along the fiber was simulated, showing that it was in good agreement with experimental results. Further improvement in power scaling is discussed.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.33-36
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• 2009

Laser ablation with femtosecond lasers is highly promising for microfabrication of materials. Also, the high peak power of femtosecond lasers could induce a multiphoton absorption to ablate transparent materials. Similar results have also been were obtained in the case of optical fibers. In this paper, we present our experimental results of femtosecond laser microstructuring of optical fiber and its applications to microelectronic components and fiber optic devices. Finally, we directly produced micro holes with femtosecond laser pulses in a single step by moving an optical fiber in a preprogrammed structure. When water was introduced into a hole drilled from the bottom surface of the optical fiber, the effects of blocking and redeposition of ablated material were greatly reduced and the aspect ratio of the depth of the hole was increased. We have presented circular and rectangular-shaped holes in optical fiber.

• Current Optics and Photonics
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• v.7 no.6
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• pp.708-713
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• 2023

A robust all-fiber nonlinear amplifying loop-mirror-based mode-locked femtosecond laser is demonstrated. Power-dependent nonlinear phase shift in a Sagnac loop enables stable and power-efficient mode-locking working as an artificial saturable absorber. The pump power is adjusted to achieve the lowest intensity noise for stable long-term operation. The minimum pump power for mode-locking is 180 mW, and the optimal pump power is 300 mW. The lowest integrated root-mean-square relative intensity noise of a free-running mode-locked laser is 0.009% [integration bandwidth: 1 Hz-10 MHz]. The long-term repetition-rate instability of a free-running mode-locked laser is 10^-7 over 1,000 s averaging time. The repetition-rate phase noise scaled at 10-GHz carrier is -122 dBc/Hz at 10 kHz Fourier frequency. The demonstrated method can be applied as a seed source in high-precision real-time mid-infrared molecular spectroscopy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.137-138
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• 2008

• Journal of the Optical Society of Korea
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• v.17 no.2
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• pp.117-129
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• 2013

We briefly review the recent progress in passively mode-locked fiber lasers (PMLFLs) based on semiconductor saturable absorber mirrors (SESAMs) and discuss the detailed characterization of a SESAM-based, passively mode-locked erbium-doped fiber (EDF) laser operating in the 1.5-${\mu}m$ spectral range for various configurations. A simple and compact design of the laser cavity enables the PMLFL to generate either femtosecond or wavelength-tunable picosecond pulses with high stability as the intra-cavity filtering method is altered. All the cavities investigated in our experiments present self-starting, continuous-wave mode-locking with no Q-switching instabilities. The excellent stability of the source eventually enables the wavelength-tunable PMLFL to be used as a master oscillator for a power-amplifier source based on a large-core EDF, generating picosecond pulses of >10-kW peak power and >100-nJ pulse energy.

• Journal of the Optical Society of Korea
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• v.1 no.2
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• pp.110-115
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• 1997

We report effcient cascaded Raman generation and signal amplification at 1.3.mu.m achieved in a ring resonator constructed solely from fiber components, i.e. fusion WDM couplers. Low-loss single-mode fiber with moderate $GeO_2$ content (18 mole %) is used as an active medium and pumped by a Nd:YAG laser at 1.064.mu.m. In a resonant cascaded geometry, this generates the third Stokes line at 1.24.mu.m, which acts as a pump for signal wavelength around 1.3.mu.m. A DFB laser operating at 1.315.mu.m is used to provide an input signal. An output signal powers up to 20 dBm (100 mW) with a 28 dB Raman gain are attained, where the Nd:YAG pump power is 3.4 W. It is also shown experimentally that it is important to use optical filters to suppress feedback from the resonator, permitting high Raman gain and good signal quality.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.249-250
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• 2011

• Current Optics and Photonics
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• v.6 no.4
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• pp.407-412
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• 2022

We report on a diode-laser-pumped mode-locked Yb:KGW laser system, which delivers ultrashort pulses down to 89 fs at a repetition rate of 63 MHz, with an average power of up to 5.6 W. A fiber-coupled diode laser at 981 nm, operated with a compact driver, is used to optically pump the gain crystal via an off-axis parabolic mirror. A semiconductor saturable-absorber mirror is used to initiate the pulsed operation. Laser characteristics such as the pulse duration, spectrum bandwidth, and output power are investigated by varying the intracavity dispersions via changing the number of bounces between negative-dispersive mirrors within the cavity. Short pulses with a duration of 89 fs, a center wavelength of 1,027 nm, and 3.6 W of output power are produced at a group-velocity dispersion (GVD) of -3,300 fs². As the negative GVD increases, the pulse duration lengthens but the output power at the single-pulse condition can be enhanced, reaching 5.6 W at a GVD of -6,600 fs². Because of pulse broadening at high negative GVDs, the highest peak intensity is achievable at a moderate GVD with our system.