C. Lin

Multiple-reflection-induced intensity noise studies in a lightwave system for multichannel AM-VSB television signal distribution

In a lightwave system used for transmission and distribution of multichannel AM-VSB (amplitude-modulated vestigial side-band) television signals, the dependence of multiple-reflection-induced intensity noise on laser diode linewidth, fiber jumper length, modulation index, and the number of connectors is studied. The noise is investigated for systems both with and without optical amplifiers. The requirements on the reflectance of fiber connectors/splices, the maximum number of connectors, and the usable optical amplifier gain are discussed.<<ETX>>

Polarization statistics of crosstalk-induced noise in transparent lightwave networks

In transparent lightwave networks, small component-crosstalk imperfections are known to generate interferometric noise levels that are significant under the worst case of matched signal and crosstalk polarizations, but vanish for orthogonal polarizations. We show that, contrary to intuition, performance under random polarizations is skewed toward worst-case, and that deployed networks must accordingly be designed for it.<<ETX>>

Self-regulating WDM amplifier module for scalable lightwave networks

By placing a set of pump-shared, gain-compressed, amplifying fibers in parallel between a multiplexer pair, one obtains a simple WDM gain module suitable for large transparent multiwavelength networks. Systems employing such modules self-adjust for transparency on a channel-by-channel basis without servo-loops. >

A widely tunable erbium-doped fiber laser pumped at 532 nm

A tunable erbium-doped fiber laser with a very wide continuous-tuning range (1522-1567 nm) is discussed. The wide tuning range was achieved using an aluminum/erbium-doped fiber; the aluminum codoping is known to broaden the gain spectrum substantially. The tunable fiber laser has a ring laser configuration utilizing an inline tunable etalon as the tuning element. Continuous tuning over 45 nm in the spectral range of 1522-1567 nm was achieved with 80 nW of pumping at 532 nm, using the second harmonic of a Nd:YAG laser as the pump source.<<ETX>>

Direct detection of closely spaced optical FM-FDM Gb/s microwave PSK signals

A modulation scheme combining microwave phase-shift-keyed (PSK) and optical frequency modulation (FM) techniques is used in a two-channel optical frequency-division-multiplexed (FDM) system. Optical filtering and FM demodulation are carried out by a tunable fiber Fabry-Perot etalon. A transmission rate of 2 Gb/s and a channel spacing of less than 30 GHz are achieved with a crosstalk level of about -25 dB. This work shows that the modulation technique of combining optical FM/FDM and RF/microwave subcarrier multiplexing is transparent to either digital or analog signals. The modulation technique not only avoids the low-frequency nonuniform FM response problem, but also facilitates close optical channel spacing.<<ETX>>

An 11 Gbit/s, 151 km transmission experiment employing a 1480 nm pumped erbium-doped in-line fiber amplifier

By using an in-line erbium-doped fiber amplifier with a net gain of 20.5 dB, it was possible to transmit an 11 Gb/s NRZ signal over 151 km of dispersion-shifted fiber. The bit rate distance product of 1.66 Tb/s-km obtained for a single-laser link with optical amplifiers experiment is a substantial improvement over the previous record of 1.03 Tb/s-km. The measurements indicate that new systems optimization procedures, as well as the incorporation of additional optical isolators, are required in order to assure stable operation with minimum system degradations.<<ETX>>

A high-gain, high-output saturation power erbium-doped fiber amplifier pumped at 532 nm

An erbium-doped fiber amplifier with a high small-signal gain of 42 dB at the gain peak of 1536.4 nm, a pumping efficiency of 1.6 dB/mW, and an output saturation power of 10 dBm is obtained with a pump power of 60 mW at 532 nm using the second harmonic of a Nd:YAG laser as the pump source. These experimental results indicate that diode-laser-pumped mini-Nd:YAG lasers with intracavity frequency-doubling have an output power at 532 nm of 100-150 mW that can be of great interest for practical system applications using high-gain, high-output-power erbium-doped fiber amplifiers.<<ETX>>

Optical amplifiers for WDM systems and networks

The emergence of practical fiber-amplifier chains has raised the prospect of transparent lightwave networks, in which signals travel from source to destination through a sequence of intermediate nodes without optoelectronic conversion. When such networks employ multiple wavelengths, however, some of the most substantial new research challenges are those posed by the amplifier chains themselves. Such networks suffer from accumulating inter-channel power-spread, from sensitivity to inter-amplifier loss variations, and from transient cross-saturation, as the network undergoes reconfiguration. The authors describe two different approaches to address these problems.<<ETX>>

Multiple angle-tuned étalon filters for optical channel selection in wavelength-division multiplexed and optical frequency-division multiplexed direct-detection transmission systems

We propose and demonstrate the use of multiple angle-tuned in-line Fabry-Perot etalon filters for tunable optical channel selection in wavelength-division multiplexed and optical frequency-division multiplexed direct-direction fiber transmission systems. Feasibility is experimentally demonstrated with two stacked identical etalons [free spectral range (FSR) of 74 nm with a finesse of 50 for each etalon] and with two stacked nonidentical etalons (FSR of 8 and 2 nm, respectively, with a finesse of 76 for both etalons). The stacked etalons are used to select the individual modes of a multilongitudinal-mode semiconductor laser output in the 1550-nm region. The method allows the selection of tens or possibly hundreds of closely spaced optical channels, because the reduction of channel spacing to much less than 1 mm is feasible, and the resultant FSR of stacked nonidentical etalons can be made much larger than their individual FSR’s.

Link-budget optimization in multichannel AM-VSB/QAM lightwave video trunking system with erbium-doped fiber amplifiers

We discuss the CNR performance and optical link-budget optimization in 1550-nm EDFA-based video lightwave transmission systems for video trunking applications. The operating point of the in-line EDFAs was determined by balancing the requirement for achieving a targeted CNR and a largest-possible link-budget. In addition, a 120-km multichannel AM-VSB/256-QAM video lightwave trunking system using two in-line EDFAs was demonstrated. At the optimum plus 3-dBm EDFAs input optical power, the 1550-nm AM/QAM video lightwave trunking system offers an AM CNR greater than 49-dB with CSO and CTB distortions less than minus 65- dBc as well as nearly error-free 256-QAM transmission. The overall system link-budget was greater than 35-dB.