Monolithic optical structures include a plurality of layer with each layer having an isolated optical pathway confined within a portion of the layer. The monolithic optical structure can be used as an optical fiber preform. Alternatively or additionally, the monolithic optical structure can include integrated optical circuits within one or more layers of the structure. Monolithic optical structures can be formed by performing multiple passes of a substrate through a flowing particle stream. The deposited particles form an optical material following consolidation. Flexible optical fibers include a plurality of independent light channels extending along the length of the optical fiber. The fibers can be pulled from an appropriate preform.