臺大光電所所訊

Wide Field-of-View 3D MEMS LiDAR

Professor Guo-Dung Su

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所蘇國棟教授

Light detection and ranging (LiDAR) sensors are promising for automated transportation to detect the surrounding environment. However, most LiDAR solutions are complex and bulky. By designing a MEMS-mirror-based LiDAR, we can improve the volume constraints, but MEMS mirrors could limit scanning angles. In this newsletter, we show and demonstrate a MEMS LiDAR system to solve the current obstacles. Combining a MEMS mirror and a wide-angle lens into the system, small-volume and large field-of-view (FOV) LiDAR systems can be realized. We use ray tracing optical simulation software to design a pair of aspherical lenses to expand the scanning angle. After the laser beam passes through the wide-angle lens, the FOV can be increased to 104 degrees. The distortion of the wide-angle lens is controlled below 3%, making the scanned image precise to the actual situation. In order to experimentally demonstrate the small-volume MEMS scanning LiDAR, a modular laser rangefinder is used with a MEMS mirror. The entire system of the LiDAR scanner is around 15 cm × 5 cm × 2.5 cm. In the natural light environment for wide-angle LiDAR measurement, the maximum error is less than 2%. Finally, an image processing program is written to convert the scanned data into a 3D point cloud image, and the generated image proves the complete function of the proposed LiDAR.


Fig. 1	Fig. 2

Singlet fission and triplet fusion in amorphous rubrene thin film

Professor Jiun-Haw Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所李君浩教授

Exciton dynamics in amorphous rubrene thin film (100 nm) was investigated by steady and transient photoluminescence measurement. Upon photoexcitation, singlet exciton in rubrene thin film may give light in ~ns range which results in prompt fluorescence in transient measurement. Not only radiative recombination, singlet may also split into the triplets though singlet fission process, and two triplets may fuse back to singlet through triplet fusion process and emit light, which results in delayed fluorescence. Through spectroscopic study, at least three emitting species in this amorphous film were identified with distinct singlet fission, triplet fusion, and triplet hopping rates. It was found that singlet fission and triplet fusion both have direct path. However, singlet fission process could be mediated by charge-transfer (CT)-state which was absent in triplet fusion process.

Fig. 1. Energy transfer routes among singlet, triplet, and CT states.