# Dispersion compensation for hybrid use of G.652 and G.655 fibers

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1. G.652 and G.655 fibers have different dispersion coefficients. To be specific, the dispersion coefficient for G.652 fibers is 17 ps.nm/km and that for G.655 fibers is 4.517 ps.nm/km.
2. When both G.652 and G.655 fibers are used, dispersion of G.652 and G.655 fibers needs to be calculated separately. You can determine the DCM type of a G.652 fiber depending on the G.652 fiber length. The G.652 fiber length can be calculated using the following formula: G.652 fiber length = G.655 fiber length/4.

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Differences between G.653 and G.655 fibers during fiber measurement
1. A G.653 fiber is also called a dispersion shift fiber. The typical parameters of a G.653 fiber in the 1550 nm window are as follows: Attenuation coefficient for the 1310 nm band: < 0.55 dB/km (Currently, the typical value data cannot be obtained yet.) Attenuation coefficient for the 1550 nm band: < 0.35 dB/km (Currently, the value ranges from 0.19 dB/km to 0.25 dB/km.) The zero dispersion point is within the wavelength band from 1525 nm to 1575 nm, and the dispersion coefficient in this wavelength band is less than 3.5 ps/(nm/km). Due to the good performance in the 1550 nm window, G.653 fibers become the optimal choice for single wavelengths and ultra-long-haul transmission. 2. G.655 fibers are non-zero dispersion shift fibers. For G.655 fibers, the zero dispersion point is moved by the specified number of wavelengths from the 1550 nm wavelength so that the zero dispersion point is not within the range of DWDM operating wavelength around the 1550 nm wavelength. The typical parameters are as follows: Attenuation coefficient for the 1310 nm band: < 0.55 dB/km (Currently, the typical value data cannot be obtained yet.) Attenuation coefficient for the 1550 nm band: < 0.35 dB/km (Currently, the value ranges from 0.19 dB/km to 0.25 dB/km.) Dispersion: The absolute value for the dispersion coefficient ranges from 1.0 ps/(nm/km) to 10.0 ps/(nm/km). 3. In conclusion, the attenuation coefficients and CD values do not have obvious limits and they are actually overlapped in the standards. As a result, the specifications of cables vary depending on vendors and the PMD values depend on the cable quality. Therefore, only the preceding parameters cannot help distinguish between G.653 and G.655 fibers. 4. In this case, another parameter, maximum zero dispersion slope, can be used to distinguish between G.653 and G.655 fibers. This parameter is essential to distinguishing fiber types. Each type of fiber has only a typical zero dispersion slope and the value is not fixed. The value changes slightly and varies according to fibers. Use G.653 and G.655 fibers as examples. Zero dispersion slopes of them are as follows: G.653 0.07600 ps/(nm^2.km) G.655-LEAF 0.08365 ps/(nm^2.km) G.655-TWRS 0.04780 ps/(nm^2.km) Therefore, you can distinguish between G.653 and G.655 fibers by measuring zero dispersion slopes of them.

Dispersion differences between the G.652D fiber and other types of G.652 fibers
Question: What are the dispersion differences between the G.652D fiber and other types of G.652 fibers? Analysis: None Answer: The G.652 fiber is known as a non-zero-dispersion shift fiber (NZ-DSF). Currently, it is the most widely used fiber. The G.652 fiber has low attenuation and zero dispersion at 1310 nm operating wavelength and the lowest attenuation but a larger positive dispersion at 1550 nm operating wavelength. The ITU-T further classifies the G.652 fiber into four types: G.652A, G.652B, G.652C, and G.652D. The dispersion coefficients of these fibers are almost the same. 1. G.652A fiber Before the
• ITU-T Recommendation G.652
• released, the G.652A fiber had the parameters most similar to those of the G.652 fiber (in the 1996 edition). This is because the ITU-T recommendation (including the 2000 edition) had no requirements on the polarization mode dispersion (PMD) performance of the G.652A fiber. It should be noted that the 2003 edition made requirements on its PMD. In the past, the highest transmission rate of the G.652A fiber was 2.5 Gbit/s. Now, it can reach 400 km transmission distance in a 10 Gbit/s system, 40 km in a 10 Gbit/s Ethernet system, and 2 km in a 40 Gbit/s system. The G.652A fiber supports the following information: SDH transmission system specified by the ITU-T G.957 STM-16 single-channel SDH transmission system that has an OA, as stipulated in the
• ITU-T Recommendation G.691
• 40 km transmission distance in a 10 Gbit/s Ethernet system 40 Gbit/s transmission rate specified by the ITU-T G.693 2. G.652B fiber Compared with the G.652A fiber, the G.652B fiber extends the attenuation requirements to the L band (1625 nm) and requires a lower PMD. The G.652B fiber can reach over 3000 km transmission distance in a 10 Gbit/s system and 80 km transmission distance in a 40Gbit/s system. The G.652B fiber supports the following information: SDH transmission system specified by the ITU-T G.957 STM-64 single-channel SDH transmission system with OA capabilities specified by the ITU-T G.691 STM-64 WDM system with OA capabilities specified by the ITU-T G.692 STM-256 application specified by the ITU-T G.693 and G.959.1 3. G.652C fiber The G.652C fiber is known as a low water peak or MAN-dedicated fiber. It eliminates loss peak (also called water peak) absorbed by the OH root ions near 1385 nm wavelength, which flattens the loss spectrum and adds 125 wavelength channels with a channel spacing of 100 GHz. The G.652C fiber has the similar attribute and application range with those of the G.652A fiber. However, the G.652C fiber has lower attenuation at 1550 nm wavelength. It can be used for the extended band (E band) and short band (S band) in the range of 1360-1530 nm, which expands the available wavelength range and increases the number of WDM channels. It is a good choice for MAN application.4. G.652D fiber The G.652D fiber integrates the advantages of the G.552B and G.652C fibers. It has the similar attribute and application scope with those of the G.652B fiber and requires the same attenuation with that of the G.652C fiber. The G.652D fiber can be used in the range of 1360-1530 nm (E band and S band) wavelengths. It has bright prospects in the MAN application. For details, see the
• Recommendation ITU-T G.652
• . Suggestion and conclusion: None

Whether G.652 fibers can be used for NS4 boards
G.652 fibers can be used if the door of the cabinet housing the NS4 boards can be properly closed.

Differences between dispersion compensation for G.652 and G.655 fibers in the 10G system of the OptiX OSN 6800
The typical dispersion coefficient of G.652 single-mode long wavelength optical fibers (SMF) is 17 ps/nm.km (the value in actual use is 20 ps/nm.km). Generally, the dispersion coefficient of a single span exceeds 40 km. Therefore, dispersion compensation is required. The typical dispersion coefficient of G.655 single-mode long wavelength optical fibers is 4.5 ps/nm.km (the value in actual use is 6 ps/nm.km), which is transmitted in G.655 fibers. The dispersion-limited distance is 800/6 = 130 km. (Note: The dispersion limit is 700/6 = 115 km in China). Dispersion compensation distance = transmission distance (L) �?OTU dispersion limited distance + engineering margin

Differences between G.653 and G.655 fibers in fiber measurement
Question: Fiber measurement is usually required in engineering commissioning of 40G WDM and 10G WDM systems. In guide documents, parameters to be measured are attenuation, CD value, and PMD value. In practice, zero dispersion slope is also an important parameter that must be measured. This parameter can be used to distinguish between G.653 fibers and G.655 fibers. Analysis: Understanding how to distinguish between G.653 fibers and G.655 fibers through fiber measurements is important because the two types of fibers require different incident optical power. G.653 fibers impose strict requirements on incident optical power. If incident optical power does not meet specified requirements, non-linear effects are serious, which results in a high bit error rate (BER), low optical signal-to-noise ratio (OSNR), or even a service interruption. Root cause: None Answer: The specifications of the two types of fibers are as follows: 1. The G.653 fiber is also called dispersion-shifted fiber. Its typical specifications are as follows: In the 1310 nm window, the attenuation coefficient is 0.55 dB/km and no typical value is available currently. In the 1550 nm window, the attenuation coefficient is 0.35 dB/km and the value is usually within the range of 0.19 dB/km to 0.25 dB/km. The zero dispersion point is in the range of 1525 nm to 1575 nm and the dispersion coefficient in this range is smaller than 3.5 ps/(nm/km). G.653 fibers have optimal features in the 1550 nm window and therefore are preferred for single-wavelength and ultra long-haul transmission. 2. The G.655 fiber is also called non-zero dispersion-shift fiber (NZDSF). The zero dispersion point is moved several wavelengths away from 1550 nm so that the zero dispersion point is not in the working wavelength range near 1550 nm. Its typical specifications are as follows: In the 1310 nm window, the attenuation coefficient is 0.55 dB/km and no typical value is available currently. In the 1550 nm window, the attenuation coefficient is 0.35 dB/km and the value is usually within the range of 0.19 dB/km to 0.25 dB/km. The dispersion coefficient absolute value is between 1.0 to 10.0 ps/(nm/km). 3. According to the preceding specifications, the attenuation coefficient and CD value of G.653 fibers are not very different from those of G.655 fibers. Actually, the value range of the attenuation coefficient and CD value of G.653 fibers overlaps with that of G.655 fibers. The actual specifications of fibers are determined by manufacturers. The PMD value depends on the quality of fibers. Therefore, you cannot distinguish between G.653 and G.655 fibers using only these parameters. 4. In this case, another parameter called maximum zero dispersion slope can be used to distinguish between G.653 and G.655 fibers. This parameter is essential to distinguishing fiber types. Each type of fiber has only a typical zero dispersion slope and the value is not fixed. The change of the value, however, is very small and this parameter is fiber-specific. Take G.653 and G.655 fibers as examples. Zero dispersion slopes of them are as follows: G.653: 0.07600 ps/(nm^2·km) G.655-LEAF: 0.08365 ps/(nm^2·km) G.655-TWRS: 0.04780 ps/(nm^2·km) You can distinguish between G.653 and G.655 fibers by measuring zero dispersion slopes of them.

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