An optical system comprising: an optical fiber core array (104; 204; 300) having a collection end (107; 207; 306), a transition region (108; 208), and an output end (109; 209; 308), the optical fiber core array (104; 204; 300) being formed of a plurality of optical fibers (106; 206; 302) each having a core, a cladding, and a fiber jacket, the optical fiber core array being configured to receive an illumination beam at the collection end (107; 207; 306) and convert the illumination beam into a plurality of propagation beams propagating within the plurality of optical fibers (106; 206; 302) and output at the output end (109; 209; 308); wherein the collection end (107; 207; 306) of the optical fiber core array (104; 204; 300) consists of (i) bare cores of the plurality of optical fibers (106; 206; 302) that, on the collection end, are cleaned of any jacket and cladding materials and placed flush against one another and organized in a fixed collection array having a collection plane for receiving an incoming illumination beam and (ii) a coating (608; 658) surrounding an outer surface of the fixed collection array of the bare cores and extending the length of the collection end (107; 207; 306), wherein the collection end (107; 207; 306) of the optical fiber core array (104; 204; 300) is designed to allow cross talk of light between bare cores in order to induce or enhance randomization of light; wherein the transition region (108; 208) extends from the collection end (107; 207; 306) and comprises the cores of the plurality of optical fibers (106; 206; 302) each surrounded by a respective cladding; wherein the output end (109; 209; 308) extends from the transition region (108; 208) and comprises the cores of the plurality of optical fibers (106; 206; 302) each surrounded by the respective cladding and a respective fiber jacket for transmitting the illumination beams as a plurality of parallel output beams; and a plurality of photodetectors positioned to receive the plurality of parallel output beams. an optical fiber core array (104; 204; 300) having a collection end (107; 207; 306), a transition region (108; 208), and an output end (109; 209; 308), the optical fiber core array (104; 204; 300) being formed of a plurality of optical fibers (106; 206; 302) each having a core, a cladding, and a fiber jacket, the optical fiber core array being configured to receive an illumination beam at the collection end (107; 207; 306) and convert the illumination beam into a plurality of propagation beams propagating within the plurality of optical fibers (106; 206; 302) and output at the output end (109; 209; 308); wherein the collection end (107; 207; 306) of the optical fiber core array (104; 204; 300) consists of (i) bare cores of the plurality of optical fibers (106; 206; 302) that, on the collection end, are cleaned of any jacket and cladding materials and placed flush against one another and organized in a fixed collection array having a collection plane for receiving an incoming illumination beam and (ii) a coating (608; 658) surrounding an outer surface of the fixed collection array of the bare cores and extending the length of the collection end (107; 207; 306), wherein the collection end (107; 207; 306) of the optical fiber core array (104; 204; 300) is designed to allow cross talk of light between bare cores in order to induce or enhance randomization of light; wherein the transition region (108; 208) extends from the collection end (107; 207; 306) and comprises the cores of the plurality of optical fibers (106; 206; 302) each surrounded by a respective cladding; wherein the output end (109; 209; 308) extends from the transition region (108; 208) and comprises the cores of the plurality of optical fibers (106; 206; 302) each surrounded by the respective cladding and a respective fiber jacket for transmitting the illumination beams as a plurality of parallel output beams; and a plurality of photodetectors positioned to receive the plurality of parallel output beams.