Hyo Sang Kim

All-fiber acousto-optic tunable notch filter with electronically controllable spectral profile.

We demonstrate a novel all-fiber acousto-optic tunable notch filter based on coupling to cladding modes in a single-mode fiber. The device has the advantage of low loss (<0.1 dB) and low polarization dependence. By coupling input light to multiple cladding modes by use of multiple acoustic waves, we achieved an electronically controllable variable spectral profile without a significant coherent cross-talk problem.

Actively gain-flattened erbium-doped fiber amplifier over 35 nm by using all-fiber acoustooptic tunable filters

We demonstrate an actively gain-flattened erbium-doped fiber amplifier (EDFA) using an all-fiber gain-flattening filter with electronically controllable spectral profiles. A good gain flatness ( 35 nm) is achieved for a wide range of operational gain levels as well as input signal and pump powers.

Longitudinal mode control in few-mode erbium-doped fiber lasers

We report an approach to the control of the longitudinal mode structure in erbium-doped fiber lasers that uses saturable absorbers and the spatial hole-burning effect in the laser cavity. Two- and three-mode fiber lasers are successfully demonstrated, and the laser output properties are compared with theoretical calculations.

Dynamic gain equalization of erbium-doped fiber amplifier with all-fiber acousto-optic tunable filters

Summary form only given. In this work, we demonstrate a dynamic gain equalization of an EDFA by employing an all-fiber active filter with low loss and low polarization dependence as a mid-stage gain-flattening element. In contrast to other active gain clamping schemes, such as pump-power adjustment or all-optical feedback loop, that ensure gain flatness only at a particular gain level, our dynamic approach enables us to achieve a good gain flatness ( 35 nm) at a wide range of operational gain levels as well as input signal and pump powers. Our gain-flattening filter consists of two all-fiber acousto-optic tunable filters (AOTFs) in series.

Narrow-bandwidth all-fiber acoustooptic tunable filter with low polarization-sensitivity

We demonstrate a narrow-bandwidth acoustooptic tunable filter with very low polarization-sensitivity using a dispersion-compensating fiber that has a large group index difference between the core and the cladding modes with a specific stress distribution. The 3-dB bandwidth of the filter is 0.8 nm with the interaction length of 10 cm, and the polarization-dependent center-wavelength splitting is 0.04 nm at the wavelength around 1550 nm. The origin of the low polarization-dependence is successfully explained through the analysis on the stress field in the fiber.

Square ring laser diode with MMI coupler cavity

A square ring laser diode is designed and fabricated in which a multimode interference 3-dB coupler operates as an output coupler and a ring resonator simultaneously. This merged structure allows a shorter cavity length and a lower loss in the output branching. Lasing in the ring cavity is confirmed and the spectra are also measured.

Narrow-bandwidth acousto-optic tunable filter with low polarization dependence

We demonstrate a narrow-bandwidth all-fiber acousto-optic tunable filter with low polarization dependence using a dispersion compensating fiber. The 3-dB bandwidth at 10-dB notch was 0.66 nm, and the polarization-dependent wavelength shift was 0.04 nm.

Few-mode erbium-doped fiber laser using saturable absorber

Summary form only given. In summary, a long Fabry-Perot Er-doped fiber laser with a few modes was demonstrated by using the combination of a saturable absorber and the position control of the gain medium. We believe that the mode selection method we describe here can provide useful light sources for many optical systems.