Heterodyne measurement of linewidth, tunability, and frequency synthesis of vertical-cavity surface-emitting laser diode arrays

The linewidth of vertical-cavity surface-emitting lasers (VCSELs) (65 MHz), the tunability of their lasing wavelength (20 AA), and the tunability of the heterodyne beat frequency (65 MHz to 150 GHz) were measured by varying the drive current to the lasers. The ability to control the output wavelength of VCSELs by current and location on the wafer makes it possible to extrapolate tunability over a range from 65 MHz to 3 THz. While the spatial tunability of 3 THz is of interest for wavelength-division multiplexing schemes, the current tunability of 150 GHz is attractive for frequency control and stabilization. The observation of narrow VCSEL linewidths is encouraging for their potential applications in communications.