ABSTRACT
The advantage of silicon photonics is its potential for large-scale integration. The key enabler there is the very high index contrast: as discussed in the previous chapter, light can be conned into a submicron waveguide code and guided in bends with radii of only a few micrometers. In addition, the potential of wafer-scale processing, integration of active components, electronics, and even III-V semiconductors (topics discussed further in this book). However, the submicron waveguide core introduces a signicant problem of its own: coupling light into and out of the chip to the outside world. The standard for transporting light at telecom wavelengths is single-mode ber where the optical mode has a mode-eld diameter of 10.4 μm at 1550 nm and 9.2 μm at 1310 nm. This is illustrated in Figure 3.1. When joined together at the interface, coupling efciency from one waveguide to the other is of the order of 0.1% (−30 dB).
