Silicon Photonics: Fundamentals and Devices

1.4 The Long-Haul Optical Communication Link

Fiber-optic communication links have spread today over the whole globe like a spider's net. A still larger number of links is being added. Today's fiber-optic links employ dense wavelength division multiplexing (DWDM), in which huge amounts of data carried by hundreds of carrier wavelengths, each modulated at a high bit rate (10 Gb/s or more), are transmitted by a single strand of a fiber. In Section 1.4.1, we shall first discuss the basic link, and the components used 18. In Section 1.4.2, the materials used to grow the devices and the methods of integration of the devices will be pointed out.

1.4.1 Basic Link and Components

Figure 1.4 shows a block schematic of the WDM communication link. Voice, picture, or computer data, in digital format, are impressed on each laser emitting at a particular wavelength (e.g., λ₁). Either the laser may be directly modulated, or an external modulator may be used to impress the signal on the laser beam. A multiplexer combines the modulated signals coming from the bank of lasers, and the combination is transmitted by an optical fiber. After traversing a distance of a few hundred kilometers, the signal becomes attenuated and the digital pulses considerably spread due to material dispersion of the fiber. The combined signal is then regenerated by a regenerator (not shown in Figure 1.4). A photodetector first ...