Provided herein are systems, devices, and methods for improved optical waveguide transmission and alignment in an analytical system. Waveguides in optical analytical systems can exhibit variable and increasing back reflection of single-wavelength illumination over time, thus limiting their effectiveness and reliability. The systems are also subject to optical interference under conditions that have been used to overcome the back reflection. Novel systems and approaches using broadband illumination light with multiple longitudinal modes have been developed to improve optical transmission and analysis in these systems. Novel systems and approaches for the alignment of a target waveguide device and an optical source are also disclosed.