Vertical-cavity surface-emitting lasers (VCSELs) present many attractive properties, such as surface emission, circular and low divergent output beam. Single-transverse mode VCSELs (SM-VCSELs) are preferred optical sources for small chip-scale atomic sensors, including atomic clocks, magnetometers, and gyroscopes. VCSEL is required to work at high temperatures with single-mode and high output power in the application of nuclear magnetic resonance gyroscope (NMRG).

In a study published in Optics Express, a research group led by Prof. NING Yongqiang from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) proposed a novel designed VCSEL. By optimizing the oxide layer position, the single-mode high power operation of the device is realized.  

In the traditional VCSEL structure, the radial effective refractive index difference Δ_neff is generally 0.006, leading to the light mode being strictly restricted inside the oxide aperture. In this novel designed VCSEL, the losses of different transverse modes are almost the same, resulting in high order transverse modes are easy to maser. The novel design reduces the effective refractive index difference Δ_neff of VCSEL to 0.002, which leads to more extension of the high-order transverse mode beyond the oxide aperture with high loss. Therefore, the novel VCSEL can maintain single-mode high power operation.

The novel designed VCSEL achieved a maximum single-mode output power of 4.1mW with side-mode suppression ratio of 41.68 dB at 80°C. Because of its excellent device performance, the novel VCSEL was applied in a NMRG system as pump source and satisfactory test results were obtained. 

This research result opens up a new possibility for the study of high-power single-mode VCSEL at high temperature, and its successful application in the prototype of NMRG promotes the further development of quantum precision measurement technology.