Seong Joon Ahn

Demonstration of highly efficient flat-gain L-band erbium-doped fiber amplifiers by incorporating a fiber Bragg grating

A flat-gain output of 13.5 (15.5) dBm is obtained over 30 nm in the L-band with only a 97 (130)-mW pumping of a 980-nm laser diode. Such highly efficient flat-gain L-band erbium-doped fiber amplifiers are achieved by simply adding a regular fiber Bragg grating. An efficient and simple gain-clamping operation is also demonstrated.

Analysis on the channel power oscillation in the closed WDM ring network with the channel power equalizer

Channel power oscillations in an optically amplified wavelength-division-multiplexed (WDM) ring network have been analyzed to reveal the oscillation dynamics and governing parameters of the chaotic behavior. The WDM ring round-trip frequency determined by the closed ring network span length and the speed of the channel power equalizer were found to be the two main factors defining the network stability. Spectral analysis shows that the formerly unresolved chaotic ring network behavior can be understood in terms of mode-locking-like instability which takes a closed WDM ring network as a loss-modulated laser.

Reference level free multichannel gain equalization and transient gain suppression of EDFA with differential ASE power monitoring

We demonstrate a novel means of gain flatness monitoring and control of a multichannel gain flattened erbium-doped fiber amplifier (EDEA), which does not require a gain dependent reference level for the feedback loop. Using the difference of amplified spontaneous emission/probe powers extracted from the edges of the gain-flattened bandwidth, gain flatness monitoring, equalization, and transient gain suppression can be achieved regardless of the steady-state gain value of an EDFA. This approach eliminates the need of elaborate measurements for the determination of control parameters for each application, making it possible to use the same circuitry for different amplifiers. Measurements show flatness control within 0.03 dB/10 nm, at the same time the suppression of time-dependent gain excursion to below 0.2 dB.

Incorporation of a fiber Bragg grating to improve the efficiency of a 1580-nm-band tunable fiber ring laser.

An efficient and tunable 1580-nm-band erbium-doped fiber ring laser is achieved by injection of amplified spontaneous emission in a conventional band by a fiber Bragg grating into the gain medium. The insertion of the fiber Bragg grating reduces the lasing threshold to 25%. The tuning range is 1560-1610 nm; the side-mode suppression ratio is better than 65 dB.

Link-control gain clamping for a cascaded EDFAs link using differential ASE monitor

We propose a novel scheme for the suppression of gain excursion in a cascaded erbium-doped fiber amplifiers (EDFAs) link. By applying the differential amplified spontaneous emission monitoring method on link-control gain clamping, it is possible to achieve gain clamping for the whole link irrespectively of the control-signal wavelength and characteristics of individual amplifiers. The suggested algorithm/circuitry does not require predefinition of the injected signal power and operates independently of the wavelengths of control/data signals to the EDFA, enabling its application to different amplified links under distinct design parameters.

Demonstration of 52-nm gain bandwidth over 2400 km (540 dB loss) with gain-equalized low-noise wide-band EDFA's

We successfully demonstrate the compensation of 540-dB transmission loss over 52-nm gain bandwidth by using acoustooptic tunable filters in conjunction with silica-based low-noise wide-band amplifiers. A signal-to-noise rate of over 17 dB (optical) over the whole gain bandwidth has been achieved with very small gain variation (4.3 dB), which corresponds to only 0.8% of the total accumulated gain in the 30 erbium-doped fiber amplifier link.

Widely tunable S/S+ band thulium-doped fiber laser locked to 50-GHz ITU-T grid

In this study, we demonstrate an S/S+ band discretely tunable thulium-doped fiber laser (TTDFL), locked to the 50-GHz ITU-T grid. By optimizing the inversion dynamics of the thulium-doped fiber while using a dual-wavelength (1.4 and 1.5 /spl mu/m) pumping scheme, 66.2 nm of tuning range (1452.2-1518.4 nm) that cover most of the thulium bandwidth, and more than 6.7 dBm of output power were obtained. By controlling the temperature of the fine grid filter, we also stabilized the output frequency of the TTDFL to within /spl plusmn/2 pm.

Design parameters of dispersion decreasing fiber based OTDM source: quasi-adiabatic higher-order soliton compression from sinusoidal input signal

We propose a new scheme for generating a pedestal-free, femtosecond soliton pulse train by utilizing quasi-adiabatic high order soliton pulse evolution in dispersion decreasing fiber in conjunction with the intermediate pedestal suppression stage. A compression factor over 250 was achieved from 10 GHz sinusoidal input, to 207 fs soliton pulse train.

Analysis on the network oscillations in the amplified WDM ring network-dependency on the channel power equalizer speed and network span length

Chaotic lasing effect in a closed cycle in optically amplified ring network with channel power equalizers (CPE) has been simulated to reveal the dynamics of WDM ring network oscillation, WDM ring round-trip frequency, combined with the RC-time constant of channel power equaliser (CPE), determine oscillation behavior of the network.

Demonstration of 540-dB loss compensation over 52 nm gain bandwidth with wideband erbium-doped fiber amplifiers

To increase the transmission capacity of a wavelength-division multiplexed (WDM) system, numerous works concentrated on the extension of erbium-doped fiber amplifier (EDFA) bandwidths. Recent reports showed that ultra-wide bandwidths, wider than 80nm were possible by using both the C-band (1550nm band) and L-band (1580nm band). System experiments showed the possibility of their application to real systems. In spite of the large bandwidth of the single ultra-wideband EDFA, bandwidth-distance products on the demonstrations limited to less than 24K nm-km (55.6nm/spl times/400km, 40nm/spl times/600km). The key issues are how to maintain the flat gain with transmission distance increase and how to achieve low noise figure for L-band EDFAs. In the work, we demonstrate a 124K nm-km (52nm/spl times/ 2400nm) transmission of 51 channels at 17dB of the optical signal to noise ratio (OSNR), by employing a low-noise wideband amplifier in conjunction with an all-fiber acousto-optic tunable filter. We have employed a re-circulating EDFA loop which consists of acousto-optic modulators, a single mode fiber, an attenuator, an isolator, a polarization scrambler, and an wideband EDFA (WEDFA).