Self-powered circularly polarized light detector based on asymmetric chiral metamaterials

Circularly polarized light (CPL) is the next big thing in the development of detection devices. It has found extensive applications in numerous fields, including biomedical diagnosis and image processing. The electric field vector in CPL travels along helical trajectories and can be decomposed into two distinct linearly polarized components. Typically, CPL can be classified into two main categories based on the trajectories of the electric field vectors: left-handed and right-handed. To date, numerous methods, such as combining different optical elements in conventional optics, have been devised for distinguishing circularly polarized light. Unfortunately, most of these methods are complex and inconvenient, thus not suitable for practical applications. Therefore, developing alternative CPL detection methods has been the focus of recent research.

Chiral metamaterials are promising candidates for circularly polarized light detection. It has recently gained popularity amongst researchers owing to its unique properties like circular dichroism and Raman optical activity. Over the past few years, numerous devices based on chiral metamaterials for CPL detection have been extensively researched. Among them, self-powered devices have attracted significant research attention due to their adaptability and economy than external-powered devices. Self-powered photodetectors based on a combination of semiconductors and chiral metamaterials have been successfully used to detect CPL with improved optical absorption.

Despite the good progress, different factors affecting the performance of these devices have not been fully explored. Recent research revealed that the performance of these devices highly depends on the magnitude of the photocurrent. Additionally, improving responsivity, responsible for high performance in conventional photodetectors, has remained a great challenge. On this account, Hunan University scientists: Mr. Zhihua Yin, Mrs. Xuemeng Hu, Mr. Jianping Zeng, Mr. Yun Zeng and Professor Wei Peng designed a self-powered and optimized circularly polarized light detector based on chiral metamaterials. Their objective was to detect CPL at zero bias through the photocurrent direction. Their research work is currently published in the Journal of Semiconductors.

In their approach, three different optimized self-powered photodetector devices based on chiral interdigital structures with asymmetric chiral metamaterials were developed. Chiral interdigital electrodes enabled the distinction of the direction of the CPL electric fields via photocurrent direction without the need for external bias. Through simulations, their characteristics and performance were discussed and compared with those of the conventional photodetectors. The authors also investigated the underlying physical mechanism of hot electrons under circularly polarized light illumination.

Results showed that the detector could easily detect the direction of circularly polarized light electric fields even at low responsivity, resulting in their high performance than the conventional devices. At a wavelength of 1322 nm, the responsivity of the device was reported to be approximately 1.9 mA/W, and was considered sufficient to distinguish the circularly polarized light. Three different self-powered devices with electrode structures were successfully presented and analyzed.

In summary, the authors reported a new circularly polarized light detector based on asymmetric chiral metamaterials. Compared to the conventional detectors, it exhibited significantly improved performance. This was attributed to its capability to detect the rotating direction of circularly polarized light at weak responsivity, unlike conventional detectors whose performance linearly related to the responsivity. Based on the simulation results, the self-powered detector improved the performance for distinguishing circularly polarized light at low responsivity. In a statement to Advances in Engineering, Professor Wei Peng said their study potentially advance the applications of the proposed detector in numerous fields such as optical communication.