Tunable laser having low intra-cavity chromatic aberrations

A tunable laser source based on a tunable external-cavity laser, the tunable laser source comprising:

• two reflective surfaces to form a laser cavity therebetween;
• an active waveguide for amplifying laser light propagating in the laser cavity;
• a tunable wavelength-selective filter within the laser cavity for selecting the emission wavelength of the tunable external-cavity laser within a tuning range;
• a collimating lens system for collimating the optical beam out of the active waveguide for propagation in the laser cavity;
• wherein said collimating lens system comprises:
• an imaging lens defining an image plane, said imaging lens inducing a positive chromatism within said tuning range;
• and
• a collimating lens for collimating the optical beam coming from the image plane, said collimating lens comprising a complex lens inducing a negative chromatism within said tuning range so as to at least partially compensate for the positive chromatism induced by the imaging lens, wherein said collimating lens comprises a doublet lens having a first converging lens element made of a first material having a first constringence and a second diverging lens element made of a second material having a second constringence, wherein a value of said first constringence is greater than that of said second constringence.