EVERY phone call or Internet data transfer requires electrical switches to send it to the right place. But this slows everything down, especially optical signals. The only way to speed things up is to use light rather than electrons to control where the signals go.
When an optical signal reaches a telephone exchange, the signal has to be 鈥渢ranslated鈥� into electricity before it can be sent to its destination鈥攜our phone, for example. But the delay in converting from light to electricity, and then back to light again, slows the network down. So the race is on to make telephone exchange switches that are controlled by light (快猫短视频, 26 May 2001, p 25, and 1 April 2000, p 10).
Now a group in Florida has found a novel way to switch light using chemicals, delegates to the American Chemical Society conference in Orlando heard last week. Fran莽isco Raymo and Silvia Giordani at the University of Miami predict that one day they鈥檒l be able to make tiny light-controlled switches the size of organic molecules.
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The key components of their system are two quartz cells. The first is used to split the light signal into three beams of distinct wavelengths. It does this using three different fluorescent molecules: anthracene, naphthalene, and tetracene. Each wavelength can be thought of as carrying a separate phone call.
The second cell holds a solution of a spiropyran, an organic chemical whose complex molecules assume one of three different forms when hit by visible light, ultraviolet light or when acid is added. Each form of the molecule absorbs a different one of the three signal wavelengths.
The three light beams produced by the first cell enter the second quartz cell, which then either blocks or lets them through. For example, if you shine visible light on the spiropyran molecules in this cell they switch to the state that soaks up only the light beam emitted by one of the three fluorescent molecules in the first cell. This corresponds to blocking one phone call and allowing the other two to pass through. A different pair of light beams can be allowed through by shining UV light on the spiropyran molecules instead, and the third combination gets through when you add an acid.
It means the team can use three inputs鈥攙isible light, UV light and acid鈥攖o control which pair of phone calls gets through at any one moment. A series of such assemblies could be used to steer a particular beam to an output fibre by selectively blocking others. Although the solutions are held in quartz cells, the same principles should apply at the molecular level, say Raymo and Giordani, allowing for miniaturisation.
But this early stage is still a long way from the dream of an 鈥渁ll-optical鈥� switch. Massive challenges remain, not least of which is finding ways around using an unwieldy acid additive. And no one knows how to 鈥渨ire up鈥� molecules on the nanoscale to make the miniature switches the researchers envisage. For now, the team is working out how to embed the chemicals in a solid, such as glass, rather than in solution, as a first step towards making all-optical switching a reality.