Scientists from Bell Labs, the research and development arm of Lucent Technologies, have built a semiconductor laser that may have numerous applications, ranging from advanced optical communications to sensitive chemical detectors and ‘lasers on a chip’.
The device uses a photonic crystal, a highly engineered material with superior optical properties made in collaboration with scientists from the New Jersey Nanotechnology Consortium, California Institute of Technology and Harvard University.
The new laser is a quantum cascade (QC) laser - part of a class of high-performance semiconductor lasers. QC lasers are made by stacking ultra thin layers of standard semiconductor materials (such as those used in photonics) on top of each another. Varying the layer thicknesses allows the wavelength at which the laser will emit light to be selected. This allows for the laser to be custom designed.
When electricity flows through a QC laser, electrons fall down an energy “staircase,” and a photo of infrared light is emitted whenever an electron hits a 'step'. These photons are reflected back and forth inside the semiconductor stimulating the emission of other photons. This process results in amplification that enables high output power from a small device. Although they are commercially available QC lasers cannot emit laser light through the surface of the device.
Bell Labs have overcome this by using the precise light-controlling qualities of a photonic crystal to create a QC laser that emits photons perpendicular to the semiconductor layers. The result is a laser that emits light through its surface. Photonic crystals are materials with repeating patterns spaced very close to one another. These separations are comparable to the wavelengths of light.
Using electron beam lithography at the New Jersey Nanotechnology Consortium, the researchers superimposed a hexagonal photonic crystal pattern on the semiconductor layers that made the QC laser. The final laser was only 50 micrometers across, or about half the diameter of a human hair.