Compared to traditional optical fibers, which are designed to transmit light from one end to the other, a multi-point side firing optical fiber can be useful in several applications such as phototherapy, optogenetics brain stimulation and remote sensing. We present the fabrication and characterization of an optical fiber capable of launching light from virtually any point along its circumferential surface by laser micro-ablation. Continuous wave (CW) laser radiation was employed to form a conical-shaped cavity (side window) in the fiber core. Because of the total internal reflection, when the laser beam reached the side window-outside medium interface, the beam was reflected to the side of the optical fiber. A single side window on 730 μm fiber can deliver more than 8% of the total coupled light. Light-firing output can be increased to more than 19% by using femtosecond (fs) laser ablation on smaller optical fiber (65 µm). In addition, the fiber also exhibited 3-dimensional light emission by placing side-windows of various orientations on its axis.
We envision the 65 um-OD multi-point side-firing optical fiber to be employed in optogenetics brain neuron stimulation in vivo. To test the feasibility of this approach, ablated fibers were investigated in agar-based tissue mimicking material (0.5% w/v in water). Successful multi-point side-firing capability has been demonstrated in the tissue phantom with similar refractive index. Furthermore, this experiment was also used to test the side-firing fiber’s mechanical strength in order to optimize the window’s depth.