Quantum cascade offers 'two for one' laser

17 Jun 2002

A semiconductor laser that emits light at two different wavelengths, depending on the polarity of the bias voltage, has been developed by scientists at Lucent Technology's Bell Labs.

This quantum cascade laser produces light at 6.3 micrometres when driven in one direction and 6.5 micrometres when the voltage is reversed.

Conventional semiconductor light emitters are polar and only work when the drive voltage is of the correct polarity.

In contrast, quantum cascade lasers are made by controlling the thickness rather than the composition of the semiconductor layers. This gives the right energy gaps for optical transitions between quantum states.

Quantum cascade lasers are not polar, but reversing the voltage normally alters the energy level structure so that they do not emit light. The researchers have tailored the design so that reversing the drive voltage excites another set of lasing energy levels and gives a different wavelength.

The researchers say that the new type of laser could benefit applications such as trace gas analysis by differential absorption spectroscopy. It also offers the option of 'two lasers for the price of one'. The findings are published in the 22 October 1999 issue of the journal Science.

SH