Reliable laboratory transmitter with submegahertz linewidth

An external-cavity transmitter configuration is introduced using a semiconductor laser at 1.3 μm wavelength, a spherical reflector for laser mode selection and a semitransparent Au-coated GRIN-rod lens for linewidth reduction. At 1.45 mW output power a linewidth of 700 kHz and a laser sidemode suppression of 30 dB is achieved.