The photonic crystal was made by using an ion beam to drill a 2D hexagonal array of holes in a layer of indium gallium arsenide phosphide (InGaAsP). The regular spacing of the holes means that only certain wavelengths of light can propagate in the crystal. The holes were 515 nm apart and had a radius of about 180 nm. The crystal was prepared such that one of the holes was "missing" - this defect provided the laser cavity for the device. Photons are trapped in the defect, which is only 0.03 cubic micrometers in size. When cooled to 143 Kelvin, the device emitted pulses of laser radiation with a wavelength of 1.5 microns.