Designing a next-generation waveguide by geometry

Abstract

Planar lightwave circuits (PLCs) have broad application in areas ranging from space to telecommunications to sensing. For example, PLC technology can be used in optical true-time delays for phased array antennas. These delays make possible a simpler, less-expensive control system and improved performance that could benefit wireless communication in space and air.1 PLCs also have utility in integrated-optic network components, such as optical add-drop multiplexers (OADMs).2 These devices help achieve high system functionality in fiber-to-thehome networks. Finally, PLC techniques can be used for optical sensors and emerging visible applications, since they enable integration of mode filters, interferometric principles, and other optical functions required for compact, highly sensitive and selective devices. Figure 1 gives an overview of optical integration technologies. Integrating functions has several advantages over discrete solutions. Lower costs, mass production, stability, and form factor (footprint area and volume) are all well-known drivers for integration. Achieving integration in the field of optics will require meeting a number of specifications. First, to ensure tight bends and consequently small structures, the technology must offer high contrast in refractive index between the light-guiding layer and the surroundings. Second, there must be a way of correcting for additional losses owing to the greater number of functions. Third, because polarization is so important, there must be a way to control it. Finally, transparency for a large range of wavelengths is essential to guarantee the maximum flexibility required of an industrial standard for integration. We have developed the TriPleX waveguide technology, which is capable of meeting these requirements. It consists of alternating layers of silicon nitride (Si3N4) and silicon dioxide (SiO2) formed by CMOS-compatible low-pressure chemical vapor deposition (LPCVD). TriPleX is fully transparent for wavelengths Figure 1. Examples of optical integration: (from left to right) optical beam forming for phased array antennas, microring resonator filter for R-OADMs, and spiral waveguide for optical sensor. R-OADMs: Reconfigurable OADMs.