FWD: breakthroughs in fiber technology

Rohit Khare (khare@w3.org)
Thu, 16 May 1996 12:32:54 -0400 (EDT)

Date: Wed, 15 May 96 04:10:22
From: <jimbell@pacifier.com>

In the April 1996 issue of Fiber Optic Product news, there is an article on
a Lucent Technologies (formerly Bell Labs...no relation...sigh...) product
which wavelength-multiplexes quantity 8, 2.5 Gb/second signals on a single
fiber, for a total of 20 Gb/sec. This is a real, purchaseable system. On
the same page is a somewhat more experimental system, done by Corning and
Siemens, in which eight channels at 10 Gb/sec each were transmitted on a
single Corning fiber.

"Wow", I said. Far faster than the 2.5 Gb/sec transmission that is
currently fairly standard for long-haul fiber trunks.

I wasn't prepared, however, for page 38, in an article titled "Research
Teams Achieve 1 Trillion bits a Second." In fact, three separate groups did
this. I copy the article below.

CP relevance? Well, the justification the government uses to regulate the
airwaves, via the FCC, is that the available bandwidth is limited, which it
is. But that argument has never been true with fiber, at least in theory,
and is becoming even less true in practice. For example, that recent flap
over Internet-based long-distance telephone interconnects (LD companies
don't want competition) is based on the fact that the normal providers of
these services want to get their dime a minute rates come hell or high
water. Sure, that's a might cheaper than it was a decade ago. But with
fiber transmission probably less than 1/100th the cost of older coaxial
transmission systems, per connection, it is unclear why they're even
continuing to meter LD phone calls.

Even if we only consider that 20 Gb/second fiber from Lucent, that is
equivalent to about 300,000 simultaneous voice calls. With a standard,
36-fiber cable, that represents 18x300,000 two-way calls, or about 4.8
million calls. This is probably far greater than the maximum number of
people on LD in the US at any given time, and that's just a single cable trunk.

If we assume that the fiber cable costs $1/meter per fiber, and the cost of
trenching, burial, and interconnects raise this to $10/meter/fiber, and if
we generously assume that the average LD call goes 3000 miles (5,000,000m),
that call occupies 1/150,000th of a $50 million fiber for a few minutes. If
we suppose that the fiber has to gross $100,000,000 per year to pay for
itself, and even if it's only operating at an average 10% load level(both
assumptions are pessimistic, that only works out to a cost of 1.3 cents per
minute per call. That's why these LD phone companies are so scared: If we
can transmit Internet on fiber, that fiber can accept this extra traffic at
very low marginal cost.

Part of article follows:

"Research teams Achieve 1 Trillion bits a second"

Debra Norman, Editor in Chief.

Three research teams achieved their ultimate goal by sending the most
information possible over optical fiber.

The scientists, including a 12-member group from AT&T Research, Bell
Laboratories, Lucent Technologies, reported in post-deadline papers at the
Optical Fiber Conference held recently in San Jose, Calif., that they had
sent one terabit of information over non-zero-dispersion fiber in a second's
time. In short, it is similar to transmitting the contents of 1,000 copies
of a 30-volume encyclopedia in one second. The researchers had not expected
to send that much data until at least the year 2000.

In the paper, the group described a 1 Tb/s transmission experiment that
utilized WDM [wavelength division multiplexing] and polarization multiplexing.

The outputs of 25 lasers were multiplexed using star couplers and waveguide
grating routers. The wavelengths ranged from 1542 nm (channel 1) to 1561.2
nm (channel 25) with 100 GHz channel spacing. All lasers were
external-cavity lasers except for channel 16, which used a DFB laser. Four
of the laser outputs (channels 10,11,17, and 25) were amplified and filtered
before multiplexing. The multiplexed wavelengths were then amplified and
propagated through a polarization beamsplitter to align all the
polarizations. Polarization controllers at the output of each laser allowed
independent polarization control for each source.

The 25 co-polarized wavelengths were split by a 3-dB coupler, separatedly
modulated by LiNbO3 Mach-Zehnder modulators, and then recombined with
orthogonal polarizations in a PBS. The modulators have a small-signal
bandwidth of 18 GHz and built-in polarizers. The 20 Gb/s NRZ drive signals
were produced by electronically multiplexing two 10-Gb/s 215-1 pseudorandom
bit streams using a commercial GaAs multiplexer.

Two other groups from Japan, Fujitsu and Nippon Telephone and Telegraph Co.,
also submitted papers reporting that they reached the terabit mark. All
three groups achieved the record with different experiments.

Scientists from NTT demonstrated 100 Gb/s x 10 channel (1 Tb/s), error-free
-shifted fiber
using a low-noise single supercontinuum WDM source fitted with a newly
developed arrayed-waveguide grating demultiplexer/multiplexer. By fully
utilizing the super-broad bandwidth of the SC spectra over 200 nm, up to 5
Tb/s would be possible.

Fujitsu researchers achieved 1.1 Tb/s (55 wavelengths x 20 Gb/s) WDM
transmission over 150 km of 1.3 mm [?] zero-dispersion singlemode fiber
using preemphasis and dispersion compensating fiber with a negative
dispersion slope. BER [bit error rate] degradation was not observed in any
channel, even without channel-by-channel dispersion adjustment.

[end of quoted portion]

Jim Bell