Misalignment prevention in an external cavity laser having temperature stabilisation of the resonator and the gain medium

1. An external-cavity laser module comprising a thermoelectric cooler comprising an upper carrier plate including an upper surface and being configured to stabilise the temperature of said upper surface, wherein said upper surface has a first length along a main longitudinal direction; a thermally conductive platform in thermal coupling with the upper surface of the thermoelectric cooler and having a second length along said main longitudinal direction; a laser assembly comprising a gain medium for emitting an optical beam into the external cavity, said gain medium being placed in thermal contact with said thermally conductive platform; a thermally conductive intermediate plate arranged between said upper carrier plate and said thermally conductive platform, said intermediate plate being in thermal coupling with both the upper carrier plate and the thermally conductive platform and having a third length along said main longitudinal direction, wherein said third length is smaller than said first length and wherein a mechanical contact between the thermally conductive platform and the upper surface takes place only through said intermediate plate and wherein the ratio between said third length of said intermediate plate and said first length of said upper surface is comprised between 0.5 and 0.65.

2. The laser module of claim 1 , wherein the ratio between said third length of said intermediate plate and said first length of said upper surface is comprised between 0.55 and 0.60.

3. The laser module of claim 1 , wherein said intermediate plate has a thickness not larger than 0.5 mm.

4. The laser module of claim 2 , wherein said intermediate plate has a thickness comprised between 0.05 and 0.4 mm

5. The laser module of claim 1 , wherein said upper surface of said upper carrier plate has a left edge and a right edge along said main longitudinal direction and said intermediate plate is placed on said upper surface at a first distance from the left edge and at a second distance from the right edge, said intermediate plate being placed on said upper surface so as said first distance and said second distance are substantially equal.

6. The laser module of claim 5 , wherein said first distance and said second distance are of at least 2 mm.

7. The laser module of claim 1 , wherein said second length of the thermally conductive platform is larger than said first length and said upper surface of said upper carrier plate has a left edge and a right edge along said main longitudinal direction and said gain medium is placed on said thermally conductive platform at a third distance along said longitudinal direction from said left edge, said third distance being not smaller than 2 mm.

8. The laser module of claim 7 , wherein said third distance is comprised between 3 and 5 mm.

9. The laser module of claim 1 , wherein said intermediate plate comprises a central aperture having a fourth length along said main longitudinal direction, the ratio between said fourth length and the third length of the intermediate plate is of less than about 0.30.

10. The laser module of claim 1 , further comprising a thermally conductive submount onto which said gain medium is placed, said submount being placed on said thermally conductive platform.

11. The laser module of claim 1 , wherein said laser assembly is configured to emit output radiation and said external cavity defines a plurality of cavity modes, said laser module further comprising a grid generator being arranged in the external cavity to define a plurality of pass bands substantially aligned with corresponding channels of a selected wavelength grid, and a tuneable element being arranged in the external cavity to tuneably select one of said pass bands so as to select a channel to which to tune the optical beam.

12. The laser module of claim 11 , wherein said tuneable element is a tuneable mirror functioning also as end mirror of the external cavity and the grid generator is arranged in the laser cavity in the optical path of the laser beam emitted by the gain medium between the gain medium and tuneable mirror, the grid generator being a Fabry-Perot etalon.

13. The laser module of claim 11 , wherein said grid generator and said tuneable element are in thermal contact with said thermally conductive platform.

14. The laser module of claim 11 , wherein the laser assembly is configured to emit output radiation at a laser emission frequency on a single longitudinal mode.

15. The laser module of claim 1 , further including a package defining an enclosure, said package including a base having a surface internal to the enclosure, wherein said thermoelectric cooler is arranged within the enclosure and includes a lower carrier plate being in thermal contact with said internal surface of said base.

16. The laser module of claim 1 , wherein said thermoelectric cooler includes a lower carrier plate and a Peltier cell sandwiched between said upper carrier plate and said lower carrier plate of the thermoelectric cooler.