A section of birefringent optical fiber spun at a slowly varying spin-rate from zero to a high value, or vice versa, behaves as a fiber-optic quarter wave plate in polarization transforms. Despite this similarity in SOP transforms with its bulk-optic counterpart which is narrow-band, this invention works on an entirely different mechanism that favorably makes the invention broad-band. Using different spin-rate functions, the invention is extended to include broad-band fiber-optic half wave, full wave, and fractional wave plates, capable of performing polarization transforms like the respective bulk-optic counterparts. Fabrication of the invented broad-band fiber-optic wave plates can be performed in the conventional way by using a birefringent preform drawn by a fiber-drawing tower incorporated with a variable-speed spinner on top of the setup. A nonconventional way is to use the moving microheater technique, devised by the same inventor, using a length of birefringent fiber as the starting material. The invention finds immediate and potential applications in all-fiber optical circuitry, an electric current sensing architecture for example, wherein circular light is used along with linear light.