A compact frequency stabilized telecom laser diode for space applications

We report on a Telecom laser diode (LD) frequency stabilization to a narrow iodine hyperfine line in the green range, after frequency tripling process using fibered nonlinear waveguide PPLN crystals. We have generated up to 300 mW optical power in the green range (~514 nm) from 800 mW of infrared power (~1542 nm), corresponding to a nonlinear conversion efficiency h = P3?/P? ~ 36%. Less than 10 mW of the generated green power are used for Doppler-free spectroscopy of 127I2 molecular iodine, and –therefore- for the frequency stabilization purpose. The frequency tripling optical setup is very compact (< 5 l), fully fibered, and could operate over the full C-band of the Telecom range (1530 nm – 1565 nm). Several thousands of hyperfine iodine lines may thus be interrogated in the 510 nm – 521 nm range. We build up an optical bench used at first in free space configuration, using the well-known modulation transfer spectroscopy technique (MTS), in order to test the potential of this new frequency standard based on the couple “1.5 ?m laser / iodine molecule”. We have already demonstrated a preliminary frequency stability of 4.8 x 10-14 ? -1/2 with a minimum value of 6 x 10-15 reached after 50 s of integration time, conferred to a laser diode operating at 1542.1 nm. We focus now our efforts to expand the frequency stability to a longer integration time in order to meet requirements of many space experiments, such earth gravity missions, inters satellites links or space to ground communications. Furthermore, we investigate the potential of a new approach based on frequency modulation technique (FM), associated to a 3rd harmonic detection of iodine lines to increase the compactness of the optical setup.