Evolution of Optical Wavelength Bands

As fiber optic networks have developed for higher speeds, longer distances, and wavelength-division multiplexing (WDM), fibers have been used in new wavelength ranges, namely "bands". Fiber transmission bands have been defined and standardized, from the original O-band to the U/XL-bands. This article will mainly illustrate the evolution of the typical fiber transmission bands used for different optical telecom systems.

Among these bands, the O-band, also called the Original-band, was the first band used in optical telecommunication because of the small pulse broadening (small dispersion); Single-mode fiber transmission began in the "O-band" just above the cutoff wavelength of the SM fiber developed to take advantage of the lower loss of the glass fiber at longer wavelengths and availability of 1310nm diode lasers.

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. The E-band (water-peak band) has not yet proven useful except for CWDM. It is probably mostly used as an extension of the O-band but few applications have been proposed and it is very energy-intensive for manufacture. The E-band and U/XL-bands usually are avoided because they correspond to high transmission loss regions.

To take advantage of the lower loss at wavelength of 1550nm, fiber was then developed for the C-band. The C-band is commonly used along with the development of ultra-long distance transmission with EDFA and WDM technologies. As transmission distances became longer and fiber amplifiers began being used instead of optical-to-electronic-to-optical repeaters, the C-band became more important. With the advent of DWDM (dense wavelength-division multiplexing) which enables multiple signals to share a single fiber, the use of C-band was expanded.

With the development of fiber amplifiers (Raman and thullium-doped), DWDM system was expanded upward to 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 multiple wavelengths simultaneously, which may lead to much attenuation. Therefore optical amplification technology is introduced.

Despite great expectations, the number of installed systems using all-Raman solutions worldwide can be counted on one hand. 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 1485nm.

Although CWDM is now considered as a low-cost version of WDM that has been in use, most do not work over long distances. The most popular is FTTH PON system, sending signals downstream to users at 1490nm (in S-band) and using low cost 1310nm transmission upstream. Early PON systems also use 1550 downstream for TV, but that is being replaced by IPTV on the downstream digital signal at 1490nm. Other systems use a combination of S, C and L bands to carry signals because of the lower attenuation of fibers. Some systems even use lasers at 20nm spacing over the complete range of 1260nm to 1660nm but only with low water peak fibers.

Although various wavelength bands of the O-, S-, C- and L- bands have come into use with the explosive expansion of the traffic in recent years, the optical fiber amplifiers for the O- and S-band wavelengths were not realized for many years because of many technical hurdles. C- and L-band most commonly used in fiber optic networks will play more and more important roles in optical transmission system with the growth of FTTH applications.

Originally published at http://www.china-cable-suppliers.com

Installation Guide to CWDM MUX/DEMUX System

CWDM MUX/DEMUX System Overview

Coarse Wavelength Division Multiplexing (CWDM) is a wavelength multiplexing technology for access networks. It is designed to increase fiber optic network capacity without adding additional fibers. The wavelengths of CWDM channels range from 1270nm to 1610nm with 20nm spacing, which allows the use of cost-effective lasers. CWDM MUX/DEMUX system is a passive, optical solution to increase the flexibility and capacity of existing fiber lines in high-speed networks. By adding more channels into available fibers, the CWDM MUX/DEMUX system enables greater versatility for data communications in ring, point-to-point, and multipoint topologies for both enterprise and metro applications.

CWDM MUX/DEMUX System Components

All CWDM system components are passive and require no power supplies. They consist of the rack mount chassis, a set of CWDM MUX/DEMUX and CWDM OADM (Optical Add/Drop Multiplexing) modules with color-coded ports. The CWDM MUX/DEMUX takes 4 or 8 different wavelength channels and multiplexes them onto one common fiber cable for transmission to the network. Then it demultiplexes the channels it receives from the network and sends each channel to a different device. Multiple modules may be chained through the expansion port on the four-channel modules. Thus it increases flexibility and enables growth for evolving networks.

The CWDM OADM module can add or drop CWDM channels into an existing backbone ring. It provides the ability to drop one CWDM channel from the network fiber, while allowing all other channels to continue pass to other nodes. Similarly, the drop/insert module removes an individual channel from the network fiber, however, it also provides the ability to add that same channel back onto the network fiber. The drop/insert module supports two paths (east and west) for dropping and adding, so that network viability is maintained in a ring topology, even if a break occurs in the ring.

CWDM MUX/DEMUX System Installation Guide

Step1: Mount the system chassis on the rack. The CWDM rack-mount chassis can be mounted in a standard 19-inch cabinet or rack. Make sure that you install the rack-mount chassis in the same rack or an adjacent rack to your system so that you can connect all the cables between your CWDM MUX/DEMUX modules and the CWDM SFP transceivers.

Step2: Install the CWDM MUX/DEMUX modules. First loose the captive screws on the blank of module panel and remove the panel. Then align the module with the slot of the chassis shelf and gently push the module into the slot. Finally, ensure that you line up the captive screws on the module with the screw holes on the shelf and tighten them up.

Step3: Install CWDM SFP transceivers. Since each channel has a specific wavelength, transceivers must comply with the right wavelengths. Each wavelength must not appear more than once in the system. Device pairs must carry transceivers with the same wavelength.

Step4: Install the CWDM MUX/DEMUX to the switch. After inserting the CWDM SFP transceiver into the switch, single-mode patch cables are used to connect the transceiver to the CWDM MUX/DEMUX module.

Step5: Connect the CWDM MUX/DEMUX pairs. In a CWDM MUX/DEMUX system, multiplexer and demultiplexer must work in pairs. Two strands of single-mode patch cables are needed in the duplex MUX/DEMUX module and one strand for the simplex one. Simply insert single-mode cables from your system equipment to the appropriate port on the CWDM MUX/DEMUX or OADM module.

Conclusion

CWDM MUX/DEMUX system is an attractive solution for carriers who need to upgrade their networks to accommodate current or future traffic needs while minimizing the use of valuable fiber strands. With CWDM technology, you can accommodate Ethernet and SONET on a single fiber that enables converged circuit/packet networks at high demand access sites. Besides, CWDM MUX/DEMUX can work seamlessly with transceivers to optimize link length, signal integrity and network cost, thus becoming a single rack-mount solution for enhanced design, power and space efficiency.

 Source: http://www.china-cable-suppliers.com/