In a panel discussion at the recent Level123 Terabit Optical and Data Networking conference, Kim Roberts, senior director coherent systems at Ciena, shared his thoughts about the future of optical transmission.
Final part : Optical transmission in 2020
"Four hundred Gigabit and one Terabit are not going to start in long-haul"
Kim Roberts, Ciena
Kim Roberts starts on a cautionary note, warning of the dangers when predicting the future. "It is always wrong," he says. But in his role as a developer of systems, he must consider what technologies are going to be useful in 2020.
The simple answer is cheap, flexible optical spectrum and coherent modems (DSP-ASICs).
Since DSP-ASICs will become cheaper and consume less power as they are implemented using the latest CMOS processes, they will migrate from their initial use in long-haul/ regional networks to the metro and even the campus. "Four hundred Gigabit and one Terabit are not going to start in long-haul," says Roberts.
Traditionally, the long-haul network has been where new technology is introduced since it is the part of the network where premium prices can first be justified. "It is not going to start there; it won't have that reach," he says. Instead 400 Gigabit-per-second (Gbps) and one Terabit wavelengths will start over medium reaches - 500-700km - once they become more economical.
One consequence is that when going distances beyond medium reach, more spectrum will be required. "You'll have to light up more fibres [for long-haul], whereas in metro-regional you can put more down one fibre," says Roberts.
The current trend of greater functionality and intelligence being encapsulated in an ASIC will continue but Roberts does not rule out a new kind of optical device delivering a useful function. "It can happen quite suddenly - optical amplifiers happened really suddenly." That said, he does not see any such candidate optical technology for now.
The trends Roberts does expect through to 2020 are as follows:
- Optical pulse shaping: Technologies such as optical regeneration and optical demultiplexing have existed in the labs. But such techniques are not spectrally efficiency and are hot, large and expensive, he says. As a result, he does not expect them to become economical for commercial products by 2020.
- Photonic Switching: Optical burst switch, optical label switching, optical packet switching, all will not prove themselves to be economical by 2020. "Optics is not the right answer in the medium term," says Roberts.
- Optical wavelength conversion, optical logic, optical CDMA and optical solitons are other technologies in Roberts' view that will not be economical by 2020.
What Roberts does identify as being useful through 2020 are:
- Low loss, high dispersion, low non-linearities fibre: "New fibres from the likes of Sumitomo and Corning allow the exploitation of coherent modems," says Roberts. "High dispersion is good, it is your friend: it helps minimise non-linearities." This was not an accepted view as recently as 2005, he says, but now it is well accepted.
- Low cost, heat and noise, high-powered optical amplifiers: "This is a fairly simple function, let's just make them better and better," he says.
- Low cost, frequency-selective switching: This refers to taking a wavelength-selective switch (WSS) and getting rid of the ITU grid; making the WSS more flexible while lowering its cost and size.
- Coherent modems: As mentioned, these will improve in efficiency in terms of bits/s/dollar as well as higher performance in terms of decibels (dBs), reach and spectral efficiency. "Polishing these [metrics]," says Roberts.
Roberts admits that his useful items listed are not exciting, radical breakthroughs: "I think we are in an interval of improving on the trends we already have until there is some breakthrough."
Part 1: The capacity limits facing optical networking
Part 2: Optical transmission's era of rapid capacity growth
Further reading on photonic switching:
Packet optical transport: Hollowing the network core