Distributed-Feedback Lasers

Most of the lasers that have been described so far depend on optical feedback from a pair of reflecting surfaces, which form a Fabry-Perot etalon. In an optical integrated circuit, in which the laser diodes are monolithically integrated within the semiconductor wafer, it is usually very difficult to form such reflecting surfaces. They can be formed by etching or cleaving, as described in Chap. 14. However, the planar surface of the wafer is then disrupted, which leads to difficulties in fabricating electrical connections and heat sinks. An alternative approach, which utilizes distributed-feedback (DFB) from a Bragg-type diffraction grating, provides a number of advantages while still utilizing a planar surface geometry.