Tunable laser with linewidth suppression for optical frequency standards working in telecommunication bands

In this work we present a laser source working in telecommunication wavelength band useful for construction of an optical frequency standard at 1540 nm. These standards are usually defined through a saturated absorption spectroscopy technique where acetylene gas is used as the absorption medium. Because the linewidth of absorption lines of acetylene are very narrow (several hundred kHz) it needs the laser with linewidth below the level of several kHz. We present a single-mode laser diode with a planar lightwave circuit (PLC) that includes a Bragg grating as the primary laser source. It has mode hop free tunable range up to 5 GHz of optical frequency at the operational wavelength 1540.577 nm. The linewidth of the laser is better than 3 kHz for short term period. But the laser absolute frequency is influenced by a flicker noise that could be suppressed. We used unbalanced Michelson fiber interferometer with 1 km long arm to suppress frequency noise of the laser. We provided the signal processing with PID servo loop with the laser current control. We suppressed the noise around the laser linewidth by -60 dB up to 33 kHz of Fourier frequency. The noise properties of the stabilized laser have promising stability for the optical frequency standard using an acetylene saturated absorption technique as a reference.