Gamma radiation effects on passive silicon photonic waveguides using phase sensitive methods

Radiation effect on silicon photonics chips for space quantum key distribution

Quantum communication satellites have potential for applications in future quantum networks. Photonics integrated chips, due to their compact and lightweight nature, are well-suited for satellite deployment. However, the harsh radiation environment of space can cause permanent damage to these chips, resulting in degraded performance or complete loss of functionality. In this work, we conducted a series of radiation experiments to evaluate the effects of γ rays and high energy protons on quantum key distribution transmitter chips. The results suggest that the insertion loss of the chip is slightly reduced by about 1.5 dB after 100 krad (Si) γ ray irradiation, and further reduced by about 0.5 to 1 dB after 2.39 × 1011/cm2 proton radiation. The half-wave voltages, extinction ratios, and polarization angles are not changed significantly within the measurement error range. Our work proves the feasibility of deploying quantum constellations utilizing terminals based on photonics chips.

Space-qualifying silicon photonic modulators and circuits

Reducing the form factor while retaining the radiation hardness and performance matrix is the goal of avionics. While a compromise between a transistor's size and its radiation hardness has reached consensus in microelectronics, the size-performance balance for their optical counterparts has not been quested but eventually will limit the spaceborne photonic instruments' capacity to weight ratio. Here, we performed space experiments of photonic integrated circuits (PICs), revealing the critical roles of energetic charged particles. The year-long cosmic radiation exposure does not change carrier mobility but reduces free carrier lifetime, resulting in unchanged electro-optic modulation efficiency and well-expanded optoelectronic bandwidth. The diversity and statistics of the tested PIC modulator indicate the minimal requirement of shielding for PIC transmitters with small footprint modulators and complexed routing waveguides toward lightweight space terminals for terabits communications and intersatellite ranging.

Radiation-hardened silicon photonic passive devices on a 3 µm waveguide platform under gamma and proton irradiation

Silicon photonics is considered to be an ideal solution as optical interconnect in radiation environments. Our previous study has demonstrated experimentally that radiation responses of device are related to waveguide size, and devices with thick top silicon waveguide layers are expected to be less sensitive to irradiation. Here, we design radiation-resistant arrayed waveguide gratings and Mach-Zehnder interferometers based on silicon-on-insulator with 3 µm-thick silicon optical waveguide platform. The devices are exposed to ⁶⁰Co γ-ray irradiation up to 41 Mrad(Si) and 170-keV proton irradiation with total fluences from 1×10¹³ to 1×10¹⁶ p/cm² to evaluate performance after irradiation. The results show that these devices can function well and have potential application in harsh radiation environments.

High energy irradiation effects on silicon photonic passive devices

In this work, the radiation responses of silicon photonic passive devices built in silicon-on-insulator (SOI) technology are investigated through high energy neutron and ⁶⁰Co γ-ray irradiation. The wavelengths of both micro-ring resonators (MRRs) and Mach-Zehnder interferometers (MZIs) exhibit blue shifts after high-energy neutron irradiation to a fluence of 1×10¹² n/cm²; the blue shift is smaller in MZI devices than in MRRs due to different waveguide widths. Devices with SiO₂ upper cladding layer show strong tolerance to irradiation. Neutron irradiation leads to slight changes in the crystal symmetry in the Si cores of the optical devices and accelerated oxidization for devices without SiO₂ cladding. A 2-µm top cladding of SiO₂ layer significantly improves the radiation tolerance of these passive photonic devices.