Iodine stabilization of a diode laser in the optical communication band

The iodine molecule has frequently been used as a frequency reference from the green to the near-infrared wavelength region 500 - 900 nm. We describe the frequency locking of the second-harmonic signal of a 197.2-THz 1520.25-nm distributed-feedback diode laser to the absorption lines of the iodine hyperfine structure; a frequency jitter below 0.1 MHz was achieved at a 300-ms time constant. This scheme provides a simple, compact, and high-performance frequency reference in the optical communication band.