Optical fibre communications systems, such as those used in telephone
networks and internal links in computers, could be made much cheaper by
a new type of semiconductor laser. Researchers at AT&T Bell Laboratories
in Maryhill, New Jersey, say the zone laser, or Z-laser, is the first that
can focus itself.
Like lasers in laser printers and compact disc players, the Z-laser
generates light from the excitation of electrons in an 鈥榓ctive鈥� layer of
semiconducting material just below its surface. But almost all other semiconductor
lasers on sale today feed the light out of the active layer sideways in
a ribbon about a micrometre wide which must then be focused by a lens. Lining
this up to an optical fibre makes up to 80 per cent of the cost of setting
up an optical link.
However, the Z-laser is a surface emitter: its light escapes upwards
through the semi-conductor. Grooves can be cut in the upper layer to create
interference patterns in the infrared light, focusing it by diffraction
to a relatively large spot, 8 micrometres across. This should be much easier
to join to an optical fibre, reducing setup costs.
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