The present invention provides a cylindrical light diffusing device (300)comprising a non-circular core fiber (302) having (i) a fiber core (350) thatprovides a "top hat" core irradiance distribution； (ii) light blocking means(314)that prevent frontal light emisson from distal end of the non-circular corefiber(302)； and (iii) a light diffusing section (308) having a diffusing proximalend(310), a diffusing distal end (312), and internal scattering features (362)distributed within the fiber core (350) of the light diffusing section (308)alongcentral axis (364) of the fiber core (350), wherein the light diffusionsection (308)emits irradiance in a radially symmetric longitudinally "top hat" diffusingirradiance distribution.
