Figure 14: Characteristics of a DFB photonic crystal fire laser. The grating is written by a 2-photon process which avoids the need for hydrogen loading. The top shows a schematic of the setup and a profile of the measured laser output. Center is the characteristic power curve—inset shows the doped section illuminated with white light. Bottom shows the laser operates single polarization. The measured linewidth by self-heterodyne is <50 kHz [17].