Hyang Kyun Kim

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.

Dynamic erbium-doped fiber amplifier based on active gain flattening with fiber acoustooptic tunable filters

We describe the first demonstration of a dynamic erbium-doped fiber amplifier (EDFA) based on automatic feedback control of active gain equalizing filters. The filters are all-fiber acoustooptic tunable filters capable of generating controllable filter shapes. Wide dynamic-range gain/power control is achieved with <0.6-dB signal ripple over 30 nm in various operating conditions. We also show, by numerical simulation, an important advantage of the dynamic EDFA over a conventional EDFA in cascaded structures.

Transmission of directly modulated 2.5-Gb/s signals over 250-km of nondispersion-shifted fiber by using a spectral filtering method

We demonstrate 250-km nondispersion-shifted fiber transmission of directly modulated 2.5-Gb/s signals. The chirping-induced power penalty is reduced by using a spectral filter whose transmission peak is tuned to mark wavelength of the modulated laser output. A well-known intensity modulation with a sufficiently high extinction ratio is used to suppress the intersymbol interference induced by nonuniform frequency modulation response of semiconductor lasers. The observed results are explained theoretically by using eye closure penalty.

Dynamic gain and output power control in a gain-flattened erbium-doped fiber amplifier

We demonstrate an erbium-doped fiber amplifier (EDFA) that has a flat-gain spectrum over an 18-nm band and a constant per-channel output power regardless of the input powers and the number of channels. The gain flatness and the constant output are obtained by changing the laser diode pump power and the attenuation of the voltage-controlled attenuator (VCA) dynamically. The response times of pump control circuit and attenuator control circuit are 650 ns and 9 ms, respectively. The power excursion of surviving channel in an EDFA with fast control circuit is /spl sim/1% of that without fast control circuit when channels are added or dropped.

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.

Dynamic erbium-doped fiber amplifier with automatic gain flattening

We demonstrate, for the first time to our knowledge, a dynamic EDFA based on automatic active gain flattening. Wide-dynamic-range gain/power control is achieved with <0.6 dB signal ripple over 30 nm in various operating conditions. We also show a significant advantage of the dynamic EDFA over conventional one in cascaded structures.

Influence of the span loss variation in cascaded EDFA's on the receiver dynamic range in WDM systems

Influences of the gain or the span loss variations in cascaded EDFAs on the receiver dynamic range are investigated for WDM systems and compared the results with single channel systems. The optical power dynamic range of the receiver additionally required in the WDM system is approximately proportional to the number of cascaded EDFAs and the span loss margin. The slope coefficient is about 0.12 dB/EDFA/(dB in the span loss margin) when the channels are allocated in the region of 1545-1557 nm. The increment of optical power dynamic range becomes smaller for the channels allocated near 1545 mm.

Polarization and modal properties of rare-earth-doped fiber lasers

The polarization and modal properties of fiber lasers are theoretically and experimentally analyzed. The polarization properties of the fiber laser is advantageously applied to a novel form of fiber laser sensor.

Efficient and low-noise operation in a gain-flattened 1580 nm band EDFA

The power conversion efficiency of 35% and the noise figure of 5.1 dB are obtained in the 1580-nm band erbium-doped fiber amplifier (EDFA) composed of the first stage backward pumped at 980 nm and the second stage backward pumped at 1480 nm.

Simplification of the EDFA gain spectra utilizing gain slope compensating filter

We propose the use of gain slope compensating filter to simplify the EDFA gain spectra. The proposed gain slope compensating filter (GSCF) exhibits the loss which increases or decreases monotonically with wavelength which is easily implemented by using directional coupler techniques.