The many-core design research community has shown high interest in optical crossbar on chip for more than a decade. Key properties of optical crossbars, namely (1) contention-free data routing, (2) low latency communication, and (3) potential for high bandwidth through the use of wavelength division multiplexing, motivate several implementations of this type of interconnect. These implementations demonstrate very different scalability and power efficiency abilities depending on three key design factors: (1) network topology, (2) considered layout, and (3) insertion losses induced by the fabrication process. In this paper, the worst-case optical losses of crossbar implementations are compared according to the factors mentioned earlier. The com-parison results have the potential to help many-core system designer to select the most appropriate crossbar implementation according to, for instance, the number of IP cores and the die size.