Wave guiding element and method of manufacture

A method of making an optical waveguide, comprising:

• producing an arrangement of optically transmissive material arranged to provide longitudinal waveguiding with a random transverse distribution of refractive indices effective to localize a transverse extent of conversion light propagating longitudinally in the optical waveguide;
• and
• incorporating a conversion material into the optically transmissive material to generate the conversion light in the optical waveguide by interaction with incident radiation received into the optical waveguide.

A method of making an optical waveguide, comprising:

• producing an arrangement of optically transmissive material arranged to provide longitudinal waveguiding with a random transverse distribution of refractive indices effective to localize a transverse extent of conversion light propagating longitudinally in the optical waveguide,
• wherein the arrangement includes three or more materials of respective distinct refractive indices.