The invention is related to an optical device having a housing (1) with a
defined gas atmosphere. The housing includes a wavelength monitor, for
monitoring an optical signal The wavelength monitor includes an etalon (2)
with a gap between two etalon plates. The optical device also has a laser
diode and means for influencing the temperature (3) of the laser diode.
The optical device further includes special means to influence the gas
density in the gap between the etalon plates.
