Abstract: Embodiments of the present invention include a fiber-optic tissue illuminator suitable for illuminating large areas of central and peripheral neural tissue, e.g., in a primate brain. Certain examples of the tissue illuminator have a light delivery surface that may be about two orders of magnitude larger than that of a conventional optical fiber of equal diameter. This illuminator allows for substantially more light to be delivered to brain tissue with no more penetration damage than a conventional fiber. For example, an illustrative illuminator can deliver light over a length of at least 3 mm in neural tissue, such as a macaque cortex, as shown by the presence of a light artifact in the local field potential. An exemplary illuminator can also be used with a previously injected viral vector (e.g., halorhodopsin) of optogenetic applications, like silencing neurons distributed over an extended region (e.g., a 3 mm length) of neural tissue.