Ultra-Compact and Efficient Microheaters on a Submicron-Thick InP Membrane

Abstract

Energy-efficient electro-optic phase shifters have been widely adopted in the InP material system, but their lengths have been in millimeter scales. The strong thermo-optic effect of InP ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dn/dT = 2.0 \times 10^{-4}\;\text {K}^{-1}$</tex-math></inline-formula> ) can potentially enable compact devices, but it has been hindered by the large heat capacity of the bulky waveguide and inefficient heat transfer to the optical mode. By moving to a sub-micron-thick InP membrane, where the optical modes are more exposed and heat capacity minimized, we report here, to the best of our knowledge, first ultra-compact ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$97\;\mu \text {m}^{2}$</tex-math></inline-formula> footprint), efficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2.26\;\text {mW}/\pi$</tex-math></inline-formula> ) and broadband (100 nm) thermo-optic microheaters in the InP material system. An epitaxially grown layer as part of the waveguide is used as the heating element, enabling maximum heat transfer efficiency. The epitaxial layer structure is designed to be compatible with the membrane photonics platform that includes monolithic amplifiers and lasers. This work could contribute to the further miniturization of monolithic photonic integrated circuits (PIC) that involves phase shifters and amplifiers, and facilitate applications such as optical computing, switching, and sensing.