Major breakthroughs in silicon photonics often come from the integration of new materials into the platform, from bonding III-Vs for on-chip lasers to growth of Ge for high-speed photodiodes. This report describes the integration of transparent conducting oxides (TCOs) onto silicon waveguides to enable ultra-compact (<10 μm) electro-optical modulators. These modulators exploit the "epsilon-near-zero" effect in TCOs to create a strong light-matter interaction and allow for a significant reduction in footprint. Waveguide-integrated devices fabricated in the Sandia Microfab demonstrated gigahertz-speed operation of epsilon-near-zero based modulators for the first time. Numerical modeling of these devices matched well with theory and showed a path for significant improvements in device performance with high-carrier-mobility TCOs such as cadmium oxide. A cadmium oxide sputtering capability has been brought online at Sandia; integration of these high mobility films is the subject of future work to develop and mature this exciting class of Si photonics devices.
This report describes the research accomplishments achieved under the LDRD Project 'Radiation Hardened Optoelectronic Components for Space-Based Applications.' The aim of this LDRD has been to investigate the radiation hardness of vertical-cavity surface-emitting lasers (VCSELs) and photodiodes by looking at both the effects of total dose and of single-event upsets on the electrical and optical characteristics of VCSELs and photodiodes. These investigations were intended to provide guidance for the eventual integration of radiation hardened VCSELs and photodiodes with rad-hard driver and receiver electronics from an external vendor for space applications. During this one-year project, we have fabricated GaAs-based VCSELs and photodiodes, investigated ionization-induced transient effects due to high-energy protons, and measured the degradation of performance from both high-energy protons and neutrons.
This report describes the research accomplishments achieved under the LDRD Project ''High-Bandwidth Optical Data Interconnects for Satellite Applications.'' The goal of this LDRD has been to address the future needs of focal-plane-array (FPA) sensors by exploring the use of high-bandwidth fiber-optic interconnects to transmit FPA signals within a satellite. We have focused primarily on vertical-cavity surface-emitting laser (VCSEL) based transmitters, due to the previously demonstrated immunity of VCSELs to total radiation doses up to 1 Mrad. In addition, VCSELs offer high modulation bandwidth (roughly 10 GHz), low power consumption (roughly 5 mW), and high coupling efficiency (greater than -3dB) to optical fibers. In the first year of this LDRD, we concentrated on the task of transmitting analog signals from a cryogenic FPA to a remote analog-to-digital converter. In the second year, we considered the transmission of digital signals produced by the analog-to-digital converter to a remote computer on the satellite. Specifically, we considered the situation in which the FPA, analog-to-digital converter, and VCSEL-based transmitter were all cooled to cryogenic temperatures. This situation requires VCSELs that operate at cryogenic temperature, dissipate minimal heat, and meet the electrical drive requirements in terms of voltage, current, and bandwidth.