Hyungsik Lim

Generation of 50-fs, 5-nJ pulses at 1.03 μm from a wave-breaking-free fiber laser

We report the generation of 6-nJ chirped pulses from a mode-locked Yb fiber laser at 1.03 μm . A linear anomalous-dispersion segment suppresses wave-breaking effects of solitonlike pulse shaping at high energies. The dechirped pulse duration is 50 fs, and the energy is 5 nJ. This laser produces twice the pulse energy and average power, and approximately five times the peak power, of the previous best mode-locked fiber laser. It is to our knowledge the first fiber laser that directly offers performance similar to that of solid-state lasers such as Ti:sapphire.

Generation of 2-nJ pulses from a femtosecond ytterbium fiber laser

We report a mode-locked ytterbium fiber laser that generates femtosecond pulses with energies as large as 2.2 nJ. This represents a 20-fold improvement in pulse energy compared with that of previously reported femtosecond Yb fiber lasers. The laser produces pulses as short as 52 fs, which are to our knowledge the shortest pulses to date from a Yb fiber laser. The laser is diode pumped by a wavelength-division multiplexing coupler, which leads to excellent stability.

Control of dispersion in a femtosecond ytterbium laser by use of hollow-core photonic bandgap fiber

We demonstrate the use of photonic bandgap fiber for dispersion compensation in a short-pulse fiber laser. The anomalous dispersion provided by the photonic bandgap fiber enables us to construct a femtosecond fiber laser at 1 micron wavelength without prisms or diffraction gratings. The laser is self-starting and produces 160-fs pulses with 1-nJ energy, and represents a significant step toward all-fiber devices capable of much higher pulse energies.

Low-noise broadband light generation from optical fibers for use in high-resolution optical coherence tomography

Broadband light generation from a single-mode optical fiber was developed for high-resolution optical coherence tomography (OCT). No noise amplification was observed for light broadened by self-phase modulation. The investigation showed that the intensity noise of light broadened by self-phase modulation in a single-mode optical fiber was much lower than that of continuum light from a microstructure fiber (MSF). The spectral width of a femtosecond input laser pulse was successfully broadened by a factor of 11, and a coherence length of 3.7 microm was achieved with this source. The application of light broadened by a single-mode optical fiber and MSF was compared for use in OCT imaging. The results showed that a single-mode fiber with a small core diameter is a useful way to generate low-noise, broadband light for high-resolution OCT imaging.

Practical all-fiber source of high-power, 120-fs pulses at 1 μm

Amplification of femtosecond pulses at 1.03 micrometre in a standard Yb-doped single-mode fiber is reported. A pulse energy of 8 nJ and an average power of 400 mW are obtained, limited by available pump power. To our knowledge these are the highest pulse energy and average power obtained from an integrated, single-mode fiber amplifier. After dechirping, 120-fs, 6-nJ pulses are obtained. A practical fiber-based source with performance comparable with that of a bulk solid-state laser is thus demonstrated, and scaling to substantially higher powers will be possible.

A new capability of cascaded quadratic processes: controllable red and blue shift of femtosecond pulses

We theoretically and experimentally demonstrate the controllable frequency shift of femtosecond pulses in quadratic media in the presence of group velocity mismatch. Applications of this new capability to the compensation of Raman scattering and high-energy pulse compression are discussed.

Environmentally-Stable Femtosecond Ytterbium Fiber Laser with Hollow-Core Photonic Bandgap Fiber

We demonstrate for the first time an environmentally-stable, passively mode-locked ytterbium fiber laser with a hollow-core fiber for dispersion control. The laser generates 1-nJ pulses, which are dechirped to 70 fs.

Wideband light generation from a small core diameter single-mode optical fiber for high-resolution optical coherent tomography

Wideband light generation from a single mode optical fiber was investigated. Investigation showed that spectral structure of light broadened by self-phase modulation was not sensitive to fluctuations of the input pulse energy, and its intensity noise was much lower than that of contimuum light from a microstructure fiber. The spectral width of a femtosecond input laser pulse was successfully broadened by a factor of eleven, and a longitudinal resolution of OCT was improved from 35 to 3.7 μm. The system empoyed a dynamic focusing tracking method to maintain high lateral resolution over a large imaging depth.