Young-Suk Lee

Robust dual-wavelength ring-laser based on two spectrally different erbium-doped fiber amplifiers

The authors demonstrate simultaneous lasing at two wavelengths in a fiber ring-laser containing two erbium-doped fiber amplifiers with different spectral characteristics. The lasing wavelengths were selected by a filter combination. For certain wavelength pairs, the ring co-lased even if the loss at one wavelength increased by 8 dB relative to the loss at the other one, while a 1-dB change was enough to prevent co-lasing in a ring with two similar amplifiers. The increased robustness-to-loss variations is a consequence of the overall spectral gain inhomogeneity that results from combining two amplifiers with different gain spectra. The concept is also applicable to dual-wavelength transmission.

Experimental characterization of a dynamically gain-flattened erbium-doped fiber amplifier

We have designed and experimentally characterized an erbium doped fiber amplifier (EDFA) which possesses a wavelength-independent gain spectrum, independent of the operating level of the gain (dynamic gain flatness), and without requiring any gain-level-dependent control of any parameters. In the wavelength range 1542-1552 nm, the gain was flat to within the experimental uncertainties of /spl plusmn/0.3 dB even as the gain level changed by 17 dB. The EDFA was based on a low-Al-content alumino-germanosilicate EDF and a Mach-Zehnder filter. We believe that this type of EDFA, which has not been demonstrated before, can significantly simplify the design of amplified wavelength-division multiplexing (WDM) transmission systems and increase the robustness of long-distance WDM transmission.

Analysis of AC gain tilt in erbium-doped fiber amplifiers

We analyze theoretically and experimentally the dependence of AC gain tilt variations on gain variations in homogeneously broadened erbium-doped fiber amplifiers. Theoretically, we find that this dependence can be evaluated from the fibers absorption spectrum. This is experimentally verified for gain variations induced by a pump-power reduction. For AM CATV, AC gain tilt variations limit how much the gain can vary before composite second order distortions become too large. From this point of view, for an erbium-doped alumino-germanosilicate fiber, an operating wavelength between 1542-1555 nm is more suitable than other ones in the long wavelength range of the EDFA, normally considered for AM CATV.