MSOs Find New Optical Tech Opens Way Out of Fiber Crunch

January 5, 2012 – With surging bandwidth requirements threatening to outstrip the capacity of cable operators’ installed fiber resources, the prospect of having to add fiber is prompting new thinking about optical technology, including speculation that it may soon be time to abandon traditional amplitude modulation transmission in favor of all-digital links.
 
But a spate of innovations in AM optics on the part of InnoTrans Communications is convincing at least some MSOs that they may be able to get more out of existing fiber than seemed possible until very recently. “Our message to the industry is you don’t have to base new decisions on old assumptions,” says InnoTrans CEO Mani Ramachandran. “A lot of people are responding to that message.”

One unnamed case in point is a top tier MSO which has gone so far as to contract with InnoTrans as a sole source for ongoing optical network enhancements. While it’s common practice to tap multiple sources for such equipment, the company’s engineers have concluded there’s nowhere else to turn for the capabilities it is looking for, Ramachandran says.

“They were using our technology just for fiber reclamation,” he adds, in reference to the ways in which the full-spectrum multiple wavelength capabilities of the firm’s Chromadigm transmitters can be used to free up fiber for new uses, such as commercial applications. “Now they have moved to using Chromadigm for all their new downstream transport requirements, whether it’s for fiber deep, RFoG (RF over Glass) or node splitting. They’re engaged in a lot of activity along these lines, so this is a big pump up.”

Over the past year InnnoTrans has experienced a brisk increase in business across the U.S. and Canada as operators confront the competing needs of ever more narrowcast services and an expanding commercial services business for more fiber transport capacity. Most pressing on the residential customer side is the need to go beyond the node segmentation capabilities of traditional AM fiber systems, says George Vasilakis, vice president of sales and business development at InnoTrans.

“The need to get to smaller service groups to support narrowcast requirements is pressing the limits of traditional segmentation technology,” Vasilakis says. “With our system you can go to eight full-spectrum wavelengths in both forward and reverse directions over a single fiber at distances of up to 65 Km.”

The move to full-spectrum optical transmission, which means all the analog and digital broadcast signals are combined with all the narrowcast signals onto a single wavelength, contrasts with the traditional approach in node segmentation where a high-power 1310 nanometer transmitter is used to deliver broadcast signals to the node over a single fiber while multiple wavelengths operating at 1550 nm. are used to deliver narrowcast signals to each node or node segment. InnoTrans officials say that their solution overcomes the operational and bandwidth limitations of the overlay approach at comparable costs of implementation.

A key factor in cost reduction is InnoTrans’ ability to use off-the-shelf 1550 directly modulated transmitters without having to select for very low noise parameters. The company employs proprietary electrical and optical processing techniques that produce an exceptionally high optical modulation index (OMI), which equates to a higher signal-to-noise performance at a given level of optical power than would otherwise be the case.

Equally vital to InnoTrans’ high performance parameters is the fact that the firm’s technology also mitigates chirp and clipping, which, respectively, refer to unintended frequency modulation of each amplitude-modulated optical signal and third-order distortion bursts caused by QAM stacking on each wavelength.

The combination of these techniques not only enables the high-density packing of wavelengths bearing the full spectrum of downstream and upstream channels used in cable HFC networks. Ramachandran says these techniques also eliminate the need to fix distances precisely or purchase receivers precisely tuned to the performance parameters of the optical signal at a given node.

“Our technology avoids the headache of customizing for every part of the network,” he says. “Sometimes residential or industrial growth occurs where it hasn’t been predicted. You want to be able to address that without having distance issues. You want to tell the businesses you’re serving, ‘We can operate anywhere you want.’”

In its latest product innovation, InnoTrans has combined all its techniques along with field-based optical amplification to create a strand-mounted optical hub it’s calling the “I-Hub,” which can be used to replace existing hubs and to lower the costs of adding new nodes for both HFC plant extensions and all-fiber extensions via RFoG. “With the I-Hub you can cover a region with fiber runs of up to 80 Km,” Ramachandran says.

A variety of I-Hub field-hardened modules encased in strand-mountable housing can support optical amplification, optical switching, return recover and re-transmission as well as passive wavelength multiplexing and demultiplexing for a variety of networks. For example, a fully configured I-Hub with full-band loading of four wavelengths per fiber will support a total of 16 nodes in both the downstream and upstream directions.

Or the I-Hub can be used for upstream aggregation where stacking of multiple upstream QAMs on each wavelength will support up to 72 node returns, Vasilakis notes. “Operators’ inability to aggregate and extend further on optical returns has been a big limiting factor for HFC and RFoG,” he says.

Where RFoG is concerned, the I-Hub can be the point of passive regeneration where wavelengths dedicated to the all-fiber service area can be amplified and spliced onto individual fibers and then further split in the field to extend service to hundreds of end users. “The ability to launch RFOG from the I-Hub allows you to greatly extend the reach into new service areas, which is what operators want to do with RFoG,” Vasilakis says.