In 1870, people watched a performance of buckets. Two buckets on the stage were put together one by one. The upper bucket opens a small hole from which water can flow into the lower bucket and bend in the process. To the audience's surprise, the sun also bends with the water - a phenomenon later known as "total internal reflection". The performer on the stage is John Dindal, one of many scientists trying to control the most obvious form of energy, light.


Entering the Photon Age
For decades, researchers have been working to find a way to control light and apply it to the transmission and processing of information. This field of research is called photonics. At the same time, electronics has assumed this role. In recent years, due to the comprehensive development of photolithography, molecular beam epitaxy and chemical vapor deposition, scientists have been able to produce nanostructured devices and control the flow of light. Optical packages (photons) are expected to be ideal for maintaining Moore's law.


Origin of Integrated Optical Path
The goal of the researchers'research on Photonics is to provide an analog of an electronic integrated chip, which can use photons to perform all the required computational processes while saving space and time. Researchers call this technology photonic integrated circuit (PIC), which can integrate different optical elements on a single board. In principle, the chip should be able to perform various optical operations, such as focusing, splitting, isolation, polarization, coupling, modulation and (ultimately) detection of light.


Development of Optical Elements for PIC
Researchers have studied the different optical components that make up the full-function PIC, and determined that the way to make the light source is through laser, which can transmit the narrow-band light source to the integrated chip module. As for optical fibers, they can transmit light from one end to another thousands of meters away. Next comes the most common component of PIC: optical waveguide, which can connect different components on the substrate.


The input coupler is used to effectively couple the light from the laser or fiber to the optical waveguide on the substrate, and the directional coupler is used to control the optical coupling between the two parallel optical waveguides. Then the ring resonator came into being. It acts as a filter (that is, it supports only one narrowband frequency) and can couple two optical waveguides in opposite directions.