High capacity optical transmission arrangement

#The present invention relates generally to the field of optical communications and in particular to a high capacity, dense wavelength-division-multiplexed (DWDM) transmission arrangement.

#The capacity of dense wavelength division multiplexed optical fiber communication systems is expanding rapidly due, in large part, to the demand created by voluminous amounts of data traffic and the Internet. Long-haul commercial DWDM systems, which are generally based upon silica erbium-doped fiber amplifiers (EDFA's), are limited to a capacity of much less than 1 Tb/s due to the limited bandwidth of the EDFA's.

#Experimental long-haul transmission exhibiting 32×10 Gb/s capacity using wide band silica EDFA's was reported by Y. Sun et al., in an article entitled “Transmission of 32-WDM 10 Gb/s Channels over 640 km using Broad-band, Gain-Flattened Erbium-Doped Silica Fiber Amplifiers”, that appeared in IEEE Photon. Technol. Lett., Vol. 9, No. 12, pp. 1652-1654 in 1997. The channel spacing for the arrangement was 100 GHz, which corresponds to an ITU standard. Subsequently, a transmission exhibiting 50×10 Gb/s capacity was reported by H. Tagu et al., in an article entitled “A half Tbits/s (50×10.66 Gb/s), over 1600 Km Transmission Experiment using Widely Gain-flattened EDFA Chain”, at ECOC 97 in Edinburgh, UK, Paper PD, pp. 13-16, 1997. In that experiment, the spacing between amplifiers was 50 km—a much more suitable distance for such applications as trans-oceanic links. For terrestrial applications however, longer spans are preferable to further reduce the number of amplifiers in the transmission path.

#FIG. 1 is a schematic view of a wide band optical amplifier useful in the present inventive arrangement;

#FIG. 2 is a schematic view of our exemplary wide-band transmission arrangement according to the present invention;

#FIG. 3 is a graph showing the accumulated fiber dispersion vs. distance for our inventive arrangement;

#FIG. 1 illustrates the basic principle of our wide band, optical fiber amplifier that is used within our high-capacity transmission arrangement. The wide band amplifier shown there 100, is divided primarily into two sections namely, a first common section 102 and a second, split section 104. Briefly stated, optical signals enter the common section 102 of the wide band optical amplifier 100. The signals are then split into two (or more) independent bands and each of these independent bands is then directed into separate branches of the second, split section 104. In parallel, the independent bands may be amplified within these separate branches and then subsequently re-combined into an output signal. Optionally, the re-combined output signal may be further amplified or otherwise processed into output section 106.

#Based upon this principle, a wide-band optical amplifier may be implemented. With continued reference to FIG. 1, optical signals enter the wide band optical amplifier 100 through input port 108 and exit from output port 166, with the output port 166 being “downstream” of the input port 108. Components 110-112 are optical isolators, 120-130 are erbium-doped amplifier fibers, 140-143 are wavelength-selective optical fiber couplers or “WDMs” for coupling pump radiation 144-147 into the amplifier fibers, 131-138 are gain equalization filters (GEFs), 160 is an attenuator, and 150-151 are a demultiplexer and a multiplexer, respectively. Optical isolators, attenuators, GEFs, WDMs, multiplexers, and demultiplexers are generally known, some of which are commercially available. Those skilled in the art know that it is conventional, but optional, to place optical isolators respectively upstream and downstream of an EDFA.

#As can be seen from FIG. 1, all entering optical signals pass through the common section 102 where they may be amplified prior to splitting. In this exemplary structure, the signals are split into three sub-bands through the action of demultiplexer 150. More specifically, the signals are shown split into a short wavelength (S-band), a middle wavelength band (M-band—also known as the conventional or C-band) and a long wavelength band (L-band), each corresponding to a branch of the split section 104. As may now be apparent, this splitting of the optical signals into multiple bands permits the separate, parallel amplification of the bands.