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Optical Routers
April 29, 2013
Mechanical systems are generally slow, they require frequent
maintenance, they're subject to
wear, and they often have a
short lifetime. After
vacuum tubes were replaced by
transistors,
electronic systems became more reliable than mechanical systems, they didn't need maintenance, and they were far less expensive.
Although the
signals switched were
electrical, the
US telephone switching system of the early
twentieth century was mechanical.
Stepping relays would convert the
pulses from
rotary dials to connections between
wires. When transistor technology had reached a critical performance point, the
telephone company began the phase-out of mechanical switching components.
Bell Labs is located in
New Jersey, having moved from the
Bell Laboratories Building in
New York City in 1966. New Jersey had become a hotbed of telephone company activity at that time.
Bell Telephone field-tested its first electronic switching system, the
1ESS switch, in
Succasunna, New Jersey, less than a
mile from my house, in 1965.
The Succasunna, New Jersey, Post Office, on a fine spring day in 2013.
Succasunna was the site for the field test of the 1ESS telephone switching system, starting May, 1965, somewhat coincident with the move of Bell Labs from New York City to New Jersey.
(Photo by the author.)
Succasunna is the word for "black rock" in the
language of the region's
Native Americans. The black rock in this case is
iron-bearing
magnetite, which is abundant in the area. I wrote about New Jersey magnetite in a
previous article about
Thomas Edison's venture into
iron mining (Edison's Iron Mine, September 20, 2010).
Although the 1ESS switching system replaced the rotary relays, it still contained miniature
reed relays to switch the connections.
Transistors at the time couldn't tolerate the
high voltages carried on telephone lines. Although the
speech signals of
POTS (plain-old-telephone-service) are less than a
volt, there are 48 volts present to determine the hook status of the
telephone handset; and a
ring signal of 90 volts, 20
Hz,
alternating current superimposed on the
DC hook voltage.
The interesting thing about
standards is that they linger for too long a period. My residential telephone service comes to me via a
fiberoptic cable, but there's a big box in my
cellar that converts
digital signals to the high voltages traditionally used by telephones. While antique telephones used the 90 volt signal to ring a mechanical bell, the telephones in my house use this voltage to generate a tone signal.
As my home example shows, world communications are migrating to
optical fiber, even in "
the last mile." Often along the course of a message, light signals are converted to electrical signals, switched to another channel, and then converted to optical signals again. This is quite a roundabout way of doing things. It would be far more efficient to just
route the light.
This fact was noted by Bell Labs scientists many years ago, and I attended quite a few presentations about their solution. This was a peak period for
microelectromechanical systems (MEMS) devices, so their solution involved miniature
mirrors popping out of
substrates to change the direction of light signals. It worked, it was
high-tech, but it took a lot of
circuit area, a lot of
chemical processing, it was mechanical, and it was not implemented.
Now, an international
research team comprised of members from
Harvard University,
Singapore's Nanyang Technological University, the
Singapore Institute of Manufacturing Technology, and
Nankai University,
China, have developed a
nanoscale optical router based on
surface plasmon polaritons excited in a
nanostructured metal surface layer.[1-3] I wrote about
plasmons in nanostructured metal layers as a means of increasing
solar cell efficiency in a
previous article (Light Trap, January 7, 2013). The
principal investigator of this study was
Federico Capasso, a
Professor of
Applied Physics at Harvard and a Bell Labs Alumnus.
A circularly-polarized light beam is split into two components by a surface plasmon array.
The splitter is an array of herringbone slits in a gold layer.
(A portion of a Harvard University image by Jiao Lin and Samuel Twist.)
Plasmon control of light is not new, but the typical structure used in the past was a
grating, which is not that efficient. The surface layer of the Harvard device is a thin sheet of
gold perforated with a
herringbone pattern of slits.[2] Since the pattern elements are smaller than a
wavelength of light, it would be easy to integrate such structures onto integrated circuits.[2]
The surface plasmon polaritons, created by incident light, are waves in the
electron sea that exists in metals, and they inherit the
polarization of the light source.[2-3] A perpendicularly incident light wave will be be sent in different direction depending on its polarization (see figure). The polarization can be
linear,
left-hand circular, or
right-hand circular.[2] As
Andrey E. Miroshnichenko and
Yuri S. Kivshar of the
Australian National University remarked in a perspective on this research, this is a somewhat unexpected property of surface plasmons.[3]
Plasmonic waves in the Harvard University optical router. Left, left-hand circularly polarized light is routed only to the left; center; linearly polarized light sent both left and right; right, right-hand circularly polarized light is routed only to the right. These images were obtained with a near-field scanning optical microscope. (Harvard University image by Jiao Lin and Balthasar Müller.)
This research was supported by the
U.S. Air Force Office of Scientific Research,
A*STAR of Singapore, the
National Natural Science Foundation of China, and other sources.[2]
References:
- Jiao Lin, J. P. Balthasar Mueller, Qian Wang, Guanghui Yuan, Nicholas Antoniou, Xiao-Cong Yuan and Federico Capasso, "Polarization-Controlled Tunable Directional Coupling of Surface Plasmon Polaritons," Science, vol. 340 no. 6130 (April 19, 2013), pp. 331-334.
- Caroline Perry, "Physicists find right (and left) solution for on-chip optics," Harvard School of Engineering and Applied Sciences Press Release, April 22, 2013.
- Andrey E. Miroshnichenko and Yuri S. Kivshar, "Perspective- Applied Physics, Polarization Traffic Control for Surface Plasmons," Science, vol. 340 no. 6130 (April 19, 2013), pp. 283-284.
Permanent Link to this article
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