A compact frequency stabilized telecom laser diode for space applications

Abstract

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 η = P3ω/Pω ~ 36%. Less than 10 mW of the generated green power are used for Doppler-free spectroscopy of 127 I2 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 µm laser / iodine molecule". We have already demonstrated a preliminary frequency stability of 4.8 x 10 -14 τ -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 3 rd harmonic detection of iodine lines to increase the compactness of the optical setup.

Rubidium Vapour-cell Frequency Standards : Metrology of Optical and Microwave Frequency References

“…A compact laser system for the stabilisation at 2051 nm (B2 line) using a HC-PCF filled with pure CO 2 was developed by Schilt et al [146], a relative frequency stability of 7 • 10 −10 is demonstrated for time scales ranging from 1 s up to 1000 s. More recently, a laser system based on NICE-OHMS instrumentation and frequency stabilisation on the acetylene 1531 nm and 1538 nm demonstrated relative frequency stability at the order of 10 −11 at 1 seconds of integration time, averaging down as 1/ τ up to 8 • 10 −13 at 240 s of integration time [147]. Finally, a laser system based on a frequency tripled Telecom laser diode at 1542 nm frequency stabilized to the narrow iodine hyperfine lines (at ≈ 514 nm) were reported by Philippe et al [148]. They used a 20-cm long multipass iodine cell and they demonstrate a relative frequency instability of 4.8 • 10 −14 averaging down as 1/ τ up to 6 • 10 −15 at 50 s. However, these two last publications do not present frequency stability at 1572 nm which result into a wavelength gap of 34 nm for [147] and 30 nm for [148].…”

“…Finally, a laser system based on a frequency tripled Telecom laser diode at 1542 nm frequency stabilized to the narrow iodine hyperfine lines (at ≈ 514 nm) were reported by Philippe et al [148]. They used a 20-cm long multipass iodine cell and they demonstrate a relative frequency instability of 4.8 • 10 −14 averaging down as 1/ τ up to 6 • 10 −15 at 50 s. However, these two last publications do not present frequency stability at 1572 nm which result into a wavelength gap of 34 nm for [147] and 30 nm for [148]. Moreover, long-term frequency instability for integration times longer than one day for a frequency stabilized laser at 1572 nm is abstent to our knowledge.…”