As we all know, multimode fiber is usually divided into OM1, OM2, OM3 and OM4. Then how about single mode fiber (SMF)? In fact, the types of single mode fiber seem much more complex than multimode fiber. There are two primary sources for the specifications of single mode optical fiber. One is the ITU-T G.65x series, and the other is IEC 60793-2-50 (published as BS EN 60793-2-50). Rather than referring to both ITU-T and IEC terminologies, we’ll only stick to the simpler ITU-T G.65x in this article. There are 19 different single mode optical fiber specifications defined by the ITU-T, among which G.652 fiber is the most commonly used.
|ITU-T G.652||ITU-T G.652.A, ITU-T G.652.B, ITU-T G.652.C, ITU-T G.652.D|
|ITU-T G.653||ITU-T G.653.A, ITU-T G.653.B|
|ITU-T G.654||ITU-T G.654.A, ITU-T G.654.B, ITU-T G.654.C|
|ITU-T G.655||ITU-T G.655.A, ITU-T G.655.B, ITU-T G.655.C, ITU-T G.655.D, ITU-T G.655.E|
|ITU-T G.656||ITU-T G.656|
|ITU-T G.657||ITU-T G.657.A1, ITU-T G.657.A2, ITU-T G.657.B2, ITU-T G.657.B3|
Among all the single mode fiber types, G.652 fiber is by far the most widely installed single mode fiber optic cable globally. So this fiber category is also known as the standard SMF. G.652 fiber is designed to have a zero-dispersion wavelength near 1310 nm, therefore it is optimized for operation in the 1310nm band and can also operate at 1550 nm. The first edition of G.652 fiber was standardized in 1984 and now it has four subcategories: G.652.A, G.652.B, G.652.C and G.652.D. All the four variants have the same G.652 core size of 8-10 micrometer. Today’s OS2 fibers are generally G.652.C or G.652.D, and the A and B categories are less used. The table below gives the attenuation, macrobending loss, polarization-mode dispersion (PMD), and mode filed diameter (MFD) of G.652 fiber subcategories.
|Attenuation (dB/km)||Less than 0.5 / 0.4 at 1310 / 1550nm||Less than 0.4 / 0.35 / 0.4 at 1310 / 1550 / 1625nm||Less than 0.4 from 1310 to 1625nm, less than 0.3 at 1550nm and at 1383nm, it must be less than that specified at 1310nm, after hydrogen aging.|
|Macrobending loss||Less than 0.5 dB at 1550 nm.||Less than 0.5 dB at 1625 nm.|
|PMD||Less than 0.5 ps/sqrt(km)||Less than 0.2 ps/sqrt(km)||Less than 0.5 ps/sqrt(km||Less than 0.2 ps/sqrt(km)|
|Nominal MFD, min||8.6 µm|
|Nominal MFD, max||9.5 µm|
G.652.D fiber is the most current subcategory of G.652 fiber. What’s the difference between legacy G.652 fiber and G.652.D fiber? Compared with G.652.A fiber and G.652.B fiber, G.652.D fiber eliminates the water peak for full spectrum operation. Conventional G.652.A and G.652.B are not optimized for wavelength-division multiplexing (WDN) applications due to the high attenuation in the E-band region (1360-1460 nm), which is the water peak band. The G.652.D fiber has been developed to specifically reduce the water peak at the 1383nm wavelength range. So G.652.D fiber optic cable can be used in the wavelength regions 1310 nm and 1550 nm, and supporting Coarse WDM (CWDM) transmission.
Figure 1: Difference between legacy G.652 fiber and G.652.D fiber.
Although both G.652.C and G.652.D offer low water peak at 1383 nm, the G.652.D fiber specification shows superior PMD performance than G.652.C fiber, which is 0.2 ps/sqrt(km) in G.652.D vs. 0.5 ps/sqrt(km) in G.652.C.
Unlike zero-dispersion-shifted fiber (G.652) which has a zero-dispersion wavelength at 1310 nm, G.655 fiber is known as non-zero dispersion-shifted fiber (NZDSF) since the dispersion of 1550 nm is close to zero, but not zero. NZDSF overcomes the nonlinear effects in WDM systems, such as four-wavelength mixing (FWD), by moving the zero-dispersion wavelength outside the 1550nm operating window. G.655 fiber is specified at 1550 nm and 1625 nm. It has a small, controlled amount of chromatic dispersion in the C-band (1530-1560 nm), where amplifiers work best, and has a larger core area than G.652 fiber. There are two types of NZDSF, known as (-D)NZDSF and (+D)NZDSF. They have respectively a negative and positive slope versus wavelength. The attenuation parameter for G.655 fiber is typically 0.2 dB/km at 1550 nm, and the PMD parameter is less than 0.1 ps/sqrt(km). Both values are lower than that of G.652 fiber.
Figure 2: Difference between G.652 and G.655.
G.657 fiber is designed to be compatible with G.652 fiber but is less bend-sensitive, which means it produces lower levels of attenuation due to bends. G.657 fiber is split into two parts: category A for access networks and category B for the end of access networks in bending-rich environments. Each category (A and B) is divided into two subcategories: G.657.A1 and G.657.A2, G.657.B2 and G.657.B3. We can see the bending radii of G.652 fiber and different G.657 fibers.
Figure 3: Bend radius difference between G.652 and G.657.
ITU-T G.65x fibers are specified to perform for different applications. The G.652, G.655 and G.657 fibers that we have mentioned above are applied in their areas, and the G.653, G.654 and G.656 fibers are featured in other environments. G.653 fiber is specified at 1310 nm and 1550 nm but with a zero chromatic dispersion slope in the 1550nm region. G.654 fiber is loss-minimized and cut-off shifted at a wavelength around 1500 nm. G.656 fiber is specified at 1460 nm and 1625 nm but with a non-zero chromatic dispersion slope in these wavelength regions. Here’s a comparison among them:
|Name||Other Names||Specified Wavelength (nm)||Applications|
|G.652||Zero-Dispersion/Non-dispersion-shifted fiber, or standard SMF.||1310, 1550, 1625 (C and D excluded)||LAN, MAN, access networks and CWDM transmission.|
|G.653||Dispersion-shifted optical fiber||1310 to 1550||Long-haul single-mode transmission systems using erbium-doped fiber amplifiers (EDFA).|
|G.654||Cut-off shifted optical fiber||1550||Higher bandwidth submarine systems and back haul systems.|
|G.655||Non-zero dispersion-shifted optical fiber (NZDSF)||1550 to 1625||Long-haul systems that use Dense WDM (DWDM) transmission.|
|G.656||Non-Zero dispersion for Wideband Optical Transport fiber||1460 to 1625||Long-haul systems that use CWDM and DWDM transmission over the specified wavelength range|
|G.657||Bending loss insensitive optical fiber for access networks||1260 to 1625||Fiber-to-the-home (FTTH) networks.|
Different single mode optical fibers defined by ITU-T include G.652, G.653, G.654, G.655, G.656 and G.657. Each single mode fiber type has its own area of application and the evolution of these optical fiber specifications reflects the evolution of transmission system technology from the earliest installation of single mode optical fiber through to the present day. Choosing the right one for your project can be vital in terms of performance, cost, reliability and safety.
Related Article: Single Mode Fiber: How Much Do You Know?
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