ABSTRACT
A laser can also have multiple longitudinal modes, with multiple peaks shown in its output optical spectrum and multiple lasting optical field patterns inside its cavity. With special designs, however, one is able to leave only one surviving longitudinal mode by eliminating all other resonances inside a cavity. A laser with such a cavity is therefore called a single longitudinal mode (SLM) laser. Many SLM laser structures have been proposed and demonstrated; a few dominant structures survived and became popular products on today's market. This chapter discusses the grating-assisted lasers and the coupled-cavity lasers, respectively, covering their structures and working mechanisms, governing equations describing the device physics processes, and numerical simulation results on device performance. It describes the recent development on SLM, by showing a few advanced structures for emerging demands, their operating principles, the measured prototype device performance, in contrast to numerical simulation results.
