Based on following tested zero dispersion wavelength data of different sample of same model, we conclude that it is G.655 fiber, more specifically it should be truewave "-" (truewave-negative) fiber : Zero dispersion wavelength: 1584.040nm, dispersion slope at zero dispersion wavelength: 0.0804 ps /(nm2*km), spool length: 25.088km, tested by our local dispersion-test contractor at last pdf link below (see spool 7 in test report), with GN Nettest dispersion receiver FD440 RX and transmitter FD440 TX, in July 2013. We believe this “DXD” type fiber made in 1998 is same but improved model of “DXC’ fiber (made in 1996), see “DXC” fiber details at Store product code: FSC-NZDSF-SPOOL-007C and FSC-NZDSF-SPOOL-007D. It can work with truewave plus fiber together for average zero dispersion in ultra long haul fiber transmission, this fiber combination is also called dispersion-management fiber. The following message is from http://www.olson-technology.com/mr_fiber/Fiber_Types.htm NZ-DSF was developed to counteract the FWM limitations of DSF. The idea is to move lambda0 to either end of the 1550 nm band, thus ensuring that all of the wavelength channels have slightly different optical speeds in the fiber. Common brands are TrueWave Classic (Lambda0 < 1530 nm), TrueWave Plus (Lambda0 = 1497 nm), TrueWave RS (Lambda0 < 1452 nm) by Lucent, and SMF-LS (Lambda0 > 1560 nm) by Corning. The advantage that these fibers have over DSF is a compromise solution of a slightly lower degree of integrated dispersion compensation for a higher tolerance to non-linear distortion effects. Available with positive dispersion (+D) NZ-DSF and negative dispersion (-D) NZ-DSF. The following message is from last pdf link below: -------------------------------------------------------------------------------------- The first generation of Truewave fiber was originally developed in 1993 by ATT. Since then, the Truewave family has evolved under the Lucent brand. After the TW-AT&T, the next member of the family was named Truewave Classic (TW-C). In the data sheet below, we notice a slightly higher CD coefficient and a slightly reduced dispersion slope compared to the TW-AT&T. Following the TW-C, Lucent introduced the Truewave Plus (TW+). Even in this case the CD properties have been modified. The rest of the optical parameters are left unchanged. The Truewave evolution continued with the introduction of major changes in the Truewave Reduced Slope (TW-RS), which, according to Lucent, represent the largest part of installed Truewave. The TW-RS is characterized by a higher CD and shows a decrease of about 36% in the dispersion slope. These two properties translate in a performance improvement for high-density DWDM applications. The latest member of Truewave family, the Truewave Reach, has been introduced in 2002. The TW Reach is a fiber optimized for application in the S, C and L band and for Raman assisted amplification. (The datasheet is currently not available). --------------------------------------------------------------------------------------- It is ITU G.655 fiber, see ITU G.655 fiber info at 3rd pdf link below.