Problems 231 Input 3 dB coupler Figure 3.80 A 3 dB coupler with the two outputs connected by a piece of fiber. An overview of optical detectors and receivers can be found in [Per08]. The tutorial article by Spanke [Spa87] is a good review of large switch architec- tures for optical switches. See also [MS88] for a good collection of papers on optical switching and [Clo53] for the original paper on the Clos switch architecture. The classic book by Bene [Ben65] is the authoritative reference for the mathematical s theory of large switch architectures developed for telephony applications. A very accessible survey of mechanical switches can be found in [Kas95, Chap- ter 13]. Several papers [NR01, LGT98, Nei00, Ryf01, Lao99, WSF06] describe