Optical integration and silicon photonics: A view to 2021
LightCounting’s report on photonic integration has several notable findings. The first is that only one in 40 optical components sold in the datacom and telecom markets is an integrated device yet such components account for a third of total revenues.
Another finding is that silicon photonics will not have a significant market impact in the next five years to 2021, although its size will grow threefold in that time.
By 2021, one in 10 optical components will be integrated and will account for 40% of the total market, while silicon photonics will become a $1 billion industry by then.
Integrated optics
“Contrary to the expectation that integration is helping to reduce the cost of components, it is only being used for very high-end products,” says Vladimir Kozlov, CEO of LightCounting.
He cites the example of the cost-conscious fibre-to-the-home market which despite boasting 100 million units in 2015 - the highest volumes in any one market - uses discrete parts for its transceivers. “There is very little need for optical integration in this high-volume, low-cost market,” he says
Where integration is finding success is where it benefits device functionality. “Where it takes the scale of components to the next level, meaning much more sophisticated designs than just co-packaged discrete parts,” says Kozlov. And it is because optical integration is being applied to high-end, costlier components that explains why revenues are high despite volumes being only 2.4% of the total market.
Defining integration
LightCounting is liberal in its definition of an integrated component. An electro-absorption modulated laser (EML) where the laser and modulator are on the same chip is considered as an integrated device. “It was developed 20 years ago but is just reaching prime time now with line rates going to 25 gigabit,” says Kozlov.
Designs that integrate multiple laser chips into a transceiver such as a 4x10 gigabit design is also considered an integrated design. “There is some level of integration; it is more sophisticated than four TO-cans,” says Kozlov. “But you could argue it is borderline co-packaging.”
LightCounting forecasts that integrated products will continue to be used for high-end designs in the coming five years. This runs counter to the theory of technological disruption where new technologies are embraced at the low end first before going on to dominate a market.
“We see it continuing to enter the market for high-end products simply because there is no need for integration for very simple optical parts,” says Kozlov.
Silicon photonics
LightCounting does not view silicon photonics as a disruptive technology but Kozlov acknowledges that while the technology has performance disadvantages compared to traditional technologies such as indium phosphide and gallium arsenide, its optical performance is continually improving. “That may still be consistent with the theory of technological disruption,” he says.
There are all these concerns about challenges but silicon photonics does have a chance to be really great
The market is also developing in a way that plays to silicon photonics’ strengths. One such development is the need for higher-speed interfaces, driven by large-scale data centre players such as Microsoft. “Their appetite increases as the industry is making progress,” says Kozlov. “Six months ago they were happy with 100 gigabit, now they are really focused on 400 gigabit.”
Going to 400 gigabit interfaces will need 4-level pulse-amplitude modulation (PAM4) transmitters that will provide new ground for competition between indium phosphide, VCSELs and silicon photonics, says Kozlov. Silicon photonics may even have an edge according to results from Cisco where its silicon photonics-based modulators were shown to work well with PAM4. This is where silicon photonics could even take a market lead: for 400-gigabit designs that require multiple PAM4 transmitters on a chip, says LightCounting.
Another promise silicon photonics could deliver although yet to be demonstrated is the combination of optics and electronics in one package. Such next-generation 3D packaging, if successful, could change things more dramatically than LightCounting currently anticipates, says Kozlov.
“This is the interesting thing about technology, you never really know how successful it will be,” says Kozlov. “There are all these concerns about challenges but silicon photonics does have a chance to be really great.”
But while LightCounting is confident the technology will prove successful sooner of later, getting businesses that use the technology to thrive will require overcoming a completely different set of challenges.
“It is a challenging environment,” warns Kozlov. “There is probably more risk on the business side of things now than on the technology side.”
Sckipio improves G.fast’s speed, reach and density
Sckipio has enhanced the performance of its G.fast chipset, demonstrating 1 gigabit data rates over 300 meter of telephone wire. The G.fast broadband standard has been specified for 100 meters only. The Israeli start-up has also demonstrated 2 gigabit performance by bonding two telephone wires.
Michael Weissman
“Understand that G.fast is still immature,” says Michael Weissman, co-founder and vice president of marketing at Sckipio. “We have improved the performance of G.fast by 40 percent this summer because we haven’t had time to do the optimisation until now.”
The company also announced a 32-port distribution point unit (DPU), the aggregation unit that is fed via fibre and delivers G.fast to residences.
G.fast is part of the toolbox enabling faster and faster speeds, and fills an important role in the wireline broadband market
The 32-port design is double Sckipio’s current largest DPU design. The DPU uses eight Sckipio 4-port DP3000 distribution port chipsets, and moving to 32 lines requires more demanding processing to tackle the greater crosstalk. Vectoring uses signal processing to implement noise cancellation techniques to counter the crosstalk and is already used for VDSL2.
G.fast
“G.fast is part of the toolbox enabling faster and faster speeds, and fills an important role in the wireline broadband market,” says Julie Kunstler, principal analyst, components at market research firm, Ovum.
G.fast achieves gigabit rates over copper by expanding the usable spectrum to 106 MHz. VDSL2, the current most advanced digital subscriber line (DSL) standard, uses 17 MHz of spectrum. But operating at higher frequencies induces signal attenuation, shortening the reach. VDSL2 is deployed over 1,500 meter links typically whereas G.fast distances will likely be 300 meters or less.
Another issue is signal leakage or crosstalk between copper pairs in a cable bundle that can house tens or hundreds of copper twisted pairs. Moreover, the crosstalk becomes greater with frequency. The leakage causes each twisted pair not only to carry the signal sent but also noise, the sum of the leakage components from neighbouring pairs. Vectoring is used to restore a line's data capacity.
G.fast can be seen as the follow-on to VDSL2 but there are notable differences. Besides the wider 106 MHz spectrum, G.fast uses a different duplexing scheme. DSL uses frequency-division duplexing (FDD) where the data transmission is continuous - upstream (from the home) and downstream - but on different frequency bands or tones. In contrast, G.fast uses time-division duplexing (TDD) where all the spectrum is used to either send data or receive data.
Using TDD, the ability to adapt the upstream and downstream data ratio as well as put G.fast in a low-power mode when idle are features that DSL does not share.
“There are many attributes [of DSL] that are brought into this standard but, at a technical level, G.fast is quite fundamentally different,” says Weissman.
One Tier-1 operator has already done the bake-off and will very soon select its vendors
Status
Sckipio says all the largest operators are testing G.fast in their labs or are conducting field trials but few are going public.
Ovum stresses that telcos are pursuing a variety of broadband strategies with G.fast being just one.
Some operators have decided to deploy fibre, while others are deploying a variety of upgrade technologies - fibre-based and copper-based. G.fast can be a good fit for certain residential neighbourhood topologies, says Kunstler.
The economics of passive optical networking (PON) continues to improve. “The costs of building an optical distribution network has declined significantly, and the costs of PON equipment are reasonable,” says Kunstler, adding that skilled fibre technicians now exist in many countries and working with fibre is easier than ever before.
“Many operators see fibre as important for business services so why not just pull the fibre to support volume-residential and high average-revenue-per-user (ARPU) based business services,” she says. But in some regions, G.fast broadband speeds will be sufficient from a competitive perspective.
“One Tier-1 operator has already done the bake-off and will very soon select its vendors,” says Weissman. “Then the hard work of integrating this into their IT systems starts.”
And BT has announced that it had delivered up to 330 megabit-per-second in a trial of G.fast involving 2,000 homes, and has since announced other trials.
“BT has publically announced it can achieve 500 megabits - up and down - over 300 meters running from their cabinets,” says Weissman. “If BT moves its fibre closer to the distribution point, it will likely achieve 800 or 900 megabit rates.” Accordingly, the average customer could benefit from 500 megabit broadband from as early as 2016. And such broadband performance would be adequate for users for 8 to 10 years, he says
Meanwhile, Sckipio and other G.fast chip vendors, as well as equipment makers are working to ensure that their systems interoperate.
Sckipio has also shown G.fast running over coax cable within multi-dwelling units delivering speeds beyond 1 gigabit. “This allows telcos to compete with cable operators and go in places they have not historically gone,” says Weissman.
Standards work
The ITU-T is working to enhance the G.fast standard further using several techniques.
One is to increase the transmission power which promises to substantially improve performance. Another is to use more advanced modulation to carry extra bits per tone across the wire’s spectrum. The third approach is to double the wire's used spectrum from 106 MHz to 212 MHz.
All three approaches complicate transmission, however. Increasing the signal power and spectrum will increase crosstalk and require more vectoring, while more complex modulation will require advanced signal recovery, as will using more spectrum.
“The guys working in committee need to find the apex of these compromises,” says Weissman, adding that Sckipio believes it can generate a 50 to 70 percent improvement in data rate over a single pair using these enhancements. The standard work is likely be completed next spring.
Sckipio says it has over 30 customers for its chips that are designing over 50 G.fast systems, for the home and/ or the distribution point.
So far Sckipio has announced it is working with Calix, Adtran, Chinese original design manufacturer Cambridge Industries Group (CIG) and Zyxel, and says Sckipio products are on show in over 12 booths at the Broadband World Forum show.