Semiconductor laser diodes (LDs) are great candidates for space laser communications, but most LDs do not have adequate radiation hardness to operate in a high-radiation environment like space.

Zhao et al. reviewed recent studies investigating how different types of radiation affect LDs, including neutrons, gamma rays, protons, and electrons. They summarize how LD performance and behavior changes with radiation conditions, and methods researchers have used to enhance LD radiation hardness.

The team found that nanoscale quantum dot LDs typically exhibit superior radiation tolerance compared to quantum well LDs and other LDs that work on the bulk scale. This behavior is due, among other factors, to the enhanced confinement of carriers and less active area that can interact with radiation particles.

“Quantum dot LDs have significant potential for space applications,” author Chao Zhao said. “Damage to quantum dot LDs may also be recovered fully or partially over time via forward bias annealing or thermal annealing. However, the QD lasers may not necessarily operate at faster speeds than QW lasers. We are also looking for speed improvements in QD lasers and other LDs that can balance high-speed operation and radiation hardness.”

Zhao says the merits described in the paper are important to consider for harsh environments beyond space, such as nuclear power plants. The mechanisms outlined in the review are also applicable to other optoelectronics components used in space communications — such as photodiodes, modulators, and amplifiers — since they are equally susceptible to radiation-induced effects.

“More efforts should be devoted to studying the radiation hardness of other optoelectronic components and the global system architecture of space laser communications,” Zhao said.

Source: “Radiation hardness of semiconductor laser diodes for space communication,” by Manyang Li, Chao Shen, Zhenyu Sun, Bo Xu, Chao Zhao, and Zhanguo Wang, Applied Physics Reviews (2024). The article can be accessed at https://doi.org/10.1063/5.0188964.