BUBBLES could soon be steering your phone calls and e-mail around the
world鈥攁nd doing so faster and more reliably than ever before, thanks to
the invention of optical telephone exchange switches that don鈥檛 have any moving
parts.
In today鈥檚 telephone exchanges, electronic switches route phone calls or data
connections to their destinations. But to do the same to light beams requires
switches with moving parts, such as arrays of minuscule mirrors. Engineers fear
that it will be difficult to align these tiny moving parts precisely enough, and
that they will wear out quickly.
Now Agilent Technologies in California and phone company NTT in Tokyo have
separately invented compact optical switches with no moving parts. Both devices
consist of a flat substrate criss-crossed by stripes of a different material,
which form the light-carrying channels. Like optical fibres, the stripes confine
light because their refractive index is higher than that of the surrounding
material.
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Where the light-carrying stripes cross, they intersect with fluid-containing
channels. The fluid has the same refractive index as the stripes, so light
usually passes straight through them. However, if the fluid at the intersection
is replaced by a lower refractive index bubble鈥攖he light is reflected.
In Agilent鈥檚 switch, the bubble is created when the fluid in the channels is
vaporised by a tiny heater. Technology adapted from inkjet printers allows
precise control of temperature at the junction, says David Andersen, research
manager at the company鈥檚 optical networking division in Santa Clara, California.
鈥淭he device is operated very close to the vapour temperature of the fluid,鈥� he
says, so a bubble can form or disappear within 10 milliseconds. The fluid
channels are sealed within the device.
NTT uses two heaters to move a permanent bubble back and forth. This makes it
possible to create switches in which bubbles will remain in one place until
power is applied, whereas in Agilent鈥檚 design, power is needed to maintain the
bubble.
Karl Kissa of JDS Uniphase, a Connecticut optics company, says the
fluid-switch technology has promise. 鈥淚t鈥檚 simple and is based on existing
technology,鈥� he comments.
