This document summarizes the evolution of optical wavelength bands used in fiber optic communication systems, from the original O-band to newer bands like the L-band. It describes technologies like DWDM, CWDM, and TDM that utilize different wavelength bands, and how wavelength bands like the C-band and newer L-band are increasingly important to meet rising bandwidth demands as fiber optic networks expand.

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Fiberstore White Paper | From O to L: The Evolution of Optical Wavelength Bands 1
In optical fiber communications system, several transmission bands have been defined and
standardized, from the original O-band to the U/XL-band. The E- and U/XL-bands have typically
been avoided because they have high transmission loss regions. The E-band represents the water
peak region, while the U/XL-band resides at the very end of the transmission window for silica glass.
Intercity and metro ring fiber already carry signals on multiple wavelengths to increase bandwidth.
Fibers entering the home will soon do the same. Now there are several types of optical telecom
systems have been developed, some based on time division multiplexing (TDM) and others on
wavelength division multiplexing (WDM), either dense wavelength division multiplexing (DWDM) or
coarse wavelength division multiplexing (CWDM). This article may represent the evolution of optical
wavelength bands mainly by describing these three high-performance systems.
Dense Wavelength Division Multiplexing
DWDM systems were developed to deal with the rising bandwidth needs of backbone optical
networks. The narrow spacing (usually 0.2 nm) between wavelength bands increases the number of
wavelengths and enables data rates of several Terabits per second (Tbps) in a single fiber.
These systems were first developed for laser-light wavelengths in the C-band, and later in the
L-band, leveraging the wavelengths with the lowest attenuation rates in glass fiber as well as the
possibility of optical amplification. Erbium-doped fiber amplifiers (EDFAs, which work at these
wavelengths) are a key enabling technology for these systems. Because WDM systems use many
wavelengths at the same time, which may lead to much attenuation. Therefore optical amplification
technology is introduced. Raman amplification and erbium-doped fiber amplifiers are two common
types used in WDM system.
From O to L: The
Evolution of Optical
Wavelength Bands

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Fiberstore White Paper | From O to L: The Evolution of Optical Wavelength Bands 2
In order to meet the demand for “unlimited bandwidth,” it was believed that DWDM would have to
be extended to more bands. In the future, however, the L-band will also prove to be useful. Because
EDFAs are less efficient in the L-band, the use of Raman amplification technology will be
re-addressed, with related pumping wavelengths close to 1485 nm.
Coarse Wave-Division Multiplexing
CWDM is the low-cost version of WDM. Generally these systems are not amplified and therefore
have limited range. They typically use less expensive light sources that are not
temperaturestabilized. Larger gaps between wavelengths are necessary, usually 20 nm. Of course,
this reduces the number of wavelengths that can be used and thus also reduces the total available
bandwidth.

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Fiberstore White Paper | From O to L: The Evolution of Optical Wavelength Bands 3
Current systems use the S-, C- and L-bands because these bands inhabit the natural region for low
optical losses in glass fiber. Although extension into the O and E-band (1310 nm to 1450 nm) is
possible, system reach (the distance the light can travel in fiber and still provide good signal without
amplification) will suffer as a result of losses incurred by use of the 1310 nm region in modern
fibers.
Time Division Multiplexing
TDM systems use either one wavelength band or two (with one wavelength band allocated to each
direction). TDM solutions are currently in the spotlight with the deployment of fiber-to-the-home
(FTTH) technologies. Both EPON and GPON are TDM systems. The standard bandwidth allocation for
GPON requires between 1260 and 1360 nm upstream, 1440 to 1500 nm downstream, and 1550 to
1560 nm for cable-TV video.
To meet the rise in bandwidth demand, these systems will require upgrading. Some predict that
TDM and CWDM (or even DWDM) will have to coexist in the same installed network fibers. To
achieve this, work is underway within the standardization bodies to define filters that block
non-GPON wavelengths to currently installed customers. This will require the CWDM portion to use
wavelength bands far away from those reserved for GPON. Consequently, they will have to use the
L-band or the C- and L-bands and provided video is not used.
Conclusion
In each case, sufficient performance has been demonstrated to ensure high performance for today’
s and tomorrow’s systems. From this article, we know that the original O-band hasn’t satisfied the
rapid development of high bandwidth anymore. And the evolution of optical wavelength bands just
means more and more bands will be called for. In the future, with the growth of FTTH applications,
there is no doubt that C- and L-bands will play more and more important roles in optical
transmission system. Fiberstore offer all kinds of products for WDM optical network, such as
CWDM/DWDM MUX DEMUX and EDFA. For more information, please visit www.fs.com.

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Fiberstore White Paper | From O to L: The Evolution of Optical Wavelength Bands 4
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