Optical frequency standards operating at 1.55 μm are required for fibre-optic wavelength division multiplexed communication systems and for 'cold start' coherent optical communication. Unfortunately, transitions near 1.55 μm are rare and difficult to probe. One may overcome the difficulties associated with frequency references at 1.55 μm by second harmonic generation (SHG) and locking to Rb D2 line near 780 nm. This reference was already used to stabilize 1560 nm laser diodes using the internally generated second harmonic of diode lasers and by bulk external SHG in KNbO3, however the SHG power levels were in the pW range and the nW range, respectively, hence locking to Doppler broadened line was possible, but the power level was not sufficient for locking to sub-Doppler lines. In order to achieve higher conversion efficiencies, the technique of quasi phasematched (QPM) frequency conversion was used in a 3 cm long periodically-poled LiNbO3 waveguide. The poling, with a period of 14 μm was achieved by applying an electric field and the waveguide was fabricated by annealed proton exchange. The single-pass efficiency for SHG of 1560.5 nm in the waveguide was 120% W-1 at 33°C, with FWHM bandwidth of 0.5 nm. As a light source, a tunable external cavity diode laser, emitting 2.3 mW at 1560.5 nm was used. With a coupling efficiency through the (uncoated) waveguide of 40%, approx.1 μW at 780.25 nm was obtained.
|Number of pages||1|
|State||Published - 1996|
|Event||Proceedings of the 1996 Conference on Lasers and Electro-Optics Europe, CLEO/Europe - Hamburg, Ger|
Duration: 8 Sep 1996 → 13 Sep 1996
|Conference||Proceedings of the 1996 Conference on Lasers and Electro-Optics Europe, CLEO/Europe|
|Period||8/09/96 → 13/09/96|