Abstract: Various embodiments of the present invention are directed to optical-based barrier methods and systems for synchronizing processing of two or more threads. In one method embodiment of a barrier method, each thread can be processed by a different processing element. The method comprises transmitting a lightwave along a waveguide that is optically coupled to each of the processing elements. Each processing element that processes a thread turns on diverter capable of diverting substantially all of the lightwave from the waveguide. Each processing element that completes processing of a thread turns off a corresponding diverter. A barrier is reached when all of the processing elements have turned off the corresponding diverters and discontinued diverting a portion of the lightwave from the waveguide.