With the rapid development of the Internet of Things (IoT), smart devices with both communication and sensing capabilities are playing an increasingly important role in areas such as telemedicine, gesture recognition, and human-computer interaction. Traditional electronic sensors commonly face challenges such as electromagnetic interference, complex configurations and high cost. Compared with electronic sensors, fiber-optic sensors have the advantages of electromagnetic interference immunity and light weight. The optical fiber sensing system based on phase modulation technology mainly relies on the fiber-optic interference structure, which is complex and expensive although it has high sensitivity. Sensing systems based on intensity modulation technology are relatively simple and compact, making them suitable for the development of low-cost devices, but the discrete light sources and detectors limit the further reduction of their system size, hindering the possibility of their high-density and large-scale deployment. Therefore, this study aims to develop an integrated, low-cost optoelectronic platform capable of fiber-optic bending angle sensing and visible light communication (VLC) to meet the demands for multifunctional and compact communication-aware systems in IoT devices.
To address these challenges, a team from Nanjing University of Posts and Telecommunications has built an integrated GaN optoelectronic platform based on the coexistence emission and detection characteristics of InGaN/GaN multi-quantum well (MQW) structure. Such platform monolithically integrates light emission (light-emitting diode, LED) and detection devices (photodiode, PD) with the same quantum well structure, which can be used for fiber-integrated bending angle sensing and VLC. The research results are published in Chinese Optics Letters, Vol. 22, Issue 9, 2024. Fan Shi, Chengxiang Jiang, Li Fang, Zhihang Sun, Jiabin Yan, Hongbo Zhu, Yongjin Wang. A versatile monolithic optoelectronic platform for bending angle sensing and visible light communication [J]. Chinese Optics Letters, 2024, 22(9): 092501
Figure 1 (a) Schematic diagram of a chip-integrated fiber sensing system. (b) Experimental setup of the VLC links for audio and video transmission.
In this study, a GaN optoelectronic chip was designed, utilizing an MQW-based structure to achieve both light emission and detection. By integrating an LED and a PD on a single chip, it enables fiber-optic bending angle measurement and VLC. The chip is spatially integrated with a fiber-optic sensor encapsulated in polydimethylsiloxane (PDMS) to form a miniaturized optical fiber sensing system that can detect the bending angles, as shown in Figure 1(a). When the fiber is bent, the on-chip PD responses to the change in light intensity caused by the bending and generates the photocurrent. Besides, a duplex VLC link is established using the micro-LED as the transmitter and the on-chip PD as the receiver, as illustrated in Figure 1(b).
Experimental results demonstrate that this optoelectronic platform can accurately detect bending angles with high repeatability and stability. For fiber bending sensing, the photocurrent changes by approximately 410 nA as the bending angle varies from 0° to 40°, and the minimum detectable angle is 2°. As to the case of communication, the 3 dB and 10 dB bandwidths of the transmitter are 12 MHz and 42 MHz, respectively. The optical receiver can realize the pseudo-random binary sequence signal reception at the rate of 1 MHz, and the duplex audio and video transmission is verified.
In this study, a compatible micro-nano fabrication process is used to integrate light emission and detection devices on the same GaN chip to construct a VLC system. Dual functions of optical fiber bending angle sensing and VLC are successfully demonstrated by using the change of external environment as optical modulation. The proposed scheme has the advantages of low cost, small size, and easy mass manufacturing, which provides new possibilities for optical sensing and communication systems in IoT devices.
