Abstract: A wavelength tunable cavity includes a first reflecting unit adapted to at least partially reflect a beam of electromagnetic radiation towards a second reflecting unit, adapted to at least partially reflect a beam of electromagnetic radiation back towards said first reflecting unit, both reflecting units providing resonance modes of said electromagnetic radiation within said cavity, wherein an optical path of said beam within said cavity is defined in length by said first and second reflecting unit, a grating arranged within said optical path of said beam reflected by said first reflecting unit, said grating adapted for tuning the wavelength of said beam, wherein said at least one second reflecting unit is rotatable about an axis by at least 360 degrees along a circle path with respect to said grating, said circle path including at least a portion arranged to intersect with said beam, which is redirected by said grating.