The performance of relatively complex photonic integrated circuits (PICs) is now reaching such high levels that the long sought goal of realizing low-cost, –size, -weight, and -power chips to replace hybrid solutions seems to have been achieved for some applications. This tutorial traces some of the evolution of this technology that has led to an array of high-functionality InP-based PICs useful in optical sensing and communication applications. Examples of recent high-performance PICs that have arisen out of these developments are presented.Fundamental to much of this work was the development of integration strategies to compatibly combine a variety of components in a relatively simple fabrication process. For the UCSB work, this was initially based upon the creation of a single-chip widely tunable semiconductor laser that required the integration of gain, reflector, phase-tuning and absorber sections. As it provided most of the elements needed for many more complex PICs, their creation followed somewhat naturally by adding more of these same elements outside of the laser cavity using the same processing steps. Of course, additional elements were needed for some of the PICs to be discussed, but in most cases, these have been added without adding significant processing complexity. Generally, the integration philosophy has been to avoid patterned epitaxial growths, to use post-growth processing, such as quantum-well intermixing to provide multiple bandgaps, rather than multiple epitaxial regrowths, and to focus on processes that could be performed with vendor growth and implant facilities so that only basic clean room processing facilities are required.
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