Evaluation of the performance of coherent optical communications commercial DSP ASICs in low earth orbit radiation environments

Abstract

Coherent optical communications systems on satellites have the potential to contribute meeting to world-wide data capacity demand. Digital signal processing (DSP) application specific integrated circuits (ASICs) for coherent optical communications systems, first developed in 2008 with current capabilities of over 100 Gbps for commercial terrestrial applications, are a key technology needed for space-based applications. However, in order to develop coherent optical communications systems for space applications, the performance of these commercial ASICs must be evaluated with consideration of the radiation effects from the space environment. This work investigates the performance of the Inphi CL2001OA1 optical coherent DSP ASIC in a low earth orbit (LEO) radiation environment and assesses whether this ASIC could be a viable option for a coherent optical communications system on a LEO spacecraft. The approach consists of simulation and experiment. First the radiation environment is modeled for three sample LEO orbits: International Space Station (ISS) orbit, 800 km polar orbit, and 1000 km 0° inclination, for 1-year, 5-year, and 10-year mission durations. Total ionizing dose (TID) requirements were determined for each mission and used to experimentally evaluate the TID tolerance of the CL20010A1. The CL2001OA1 on an evaluation board system (EVK) is modeled and simulations with Stopping Range In Matter (SRIM) program are used to simulate 64.0 MeV protons penetrating through the system. The SRIM simulations are used to calculate the proton energy levels entering the silicon active region of the CL2001OA1 and to determine the proton energy level sufficient for depositing ionizing dose in the active region and penetrating through the active region. The simulations determine the lower threshold of proton energy level needed for experimental testing. Two proton test campaigns of the CL2001OA1-EVK were completed at UC Davis Crocker Nuclear Laboratory (CNL) and Tri-University Meson Facility (TRIUMF) using energy levels of 64.0 MeV and 480 MeV, respectively. The CL2001OA1 ASIC survived and experienced no performance degradation from TID exposure up to 170 krad(Si). The measured CL20010A1 single event effect (SEE) cross section was 2.46x10-⁹ cm² at the 64 MeV proton energy level and 3.82x10-¹⁰ cm² at the 480 MeV proton energy level. The SEE cross section data from the proton test campaigns was used to calculate the CL20010A1 SEE rate for the sample LEO missions. The SEE cross section results were compared to the results from previous studies on proton-induced SEEs of other Complementary Metal Oxide Semiconductor (CMOS) devices with silicon active regions. Mitigation strategies against LEO radiation effects for the CL2001A1 are considered, such as spot shielding, strategic placement in spacecraft, incorporation of protective electronic devices in the circuit system design, and programming periodic CL20010A1 resets or full system power cycles. Expansion of this work, such as additional proton radiation test campaigns at different energy levels below 64.0 MeV and between 64.0 MeV and 480 MeV as well as heavy ion test campaigns to assess SEEs induced by heavy ions from galactic cosmic rays (GCRs) and solar energetic particles (SEPs), would provide additional insights on potential effects of the LEO radiation environment on the CL20010A1. Heavy ion test campaigns would provide SEE cross section data, which could be used to calculate the expected heavy-ion induced SEE rate for a given LEO mission. This work serves as an initial step toward the development of a DSP coherent optical communications transceiver for LEO satellite applications.