Abstract: A method of free space fibre-to-fibre coupling includes providing a first optical fibre and a second optical fibre spaced apart from one another by a free space distance having a pair of spaced-apart achromatic collimating lenses within the free space distance. Essentially single mode light is launched from the first fibre at a wavelength ? or a range of ?s that provides at least a portion of its light at wavelength(s) below a cut-off wavelength for the first fibre. The first optical fibre and second optical fibre are both <50 m and sufficiently short to provide essentially single mode operation. The essentially single mode light after the launching propagates as free space light through said free space distance and is received by and propagates in the second optical fibre as essentially single mode light.

Abstract: A method of free space fiber-to-fiber coupling includes providing a first optical fiber and a second optical fiber spaced apart from one another by a free space distance having a pair of spaced-apart achromatic collimating lenses within the free space distance. Essentially single mode light is launched from the first fiber at a wavelength ? or a range of ?s that provides at least a portion of its light at wavelength(s) below a cut-off wavelength for the first fiber. The first optical fiber and second optical fiber are both <50 m and sufficiently short to provide essentially single mode operation. The essentially single mode light after the launching propagates as free space light through said free space distance and is received by and propagates in the second optical fiber as essentially single mode light.