Optical refractometer constitutes the core element for many applications, from determining the purity and concentration of pharmaceutical ingredients to measuring the sugar content in food and beverages, and the analysis of petroleum. Here, we demonstrated the monolithic integration of light-emitting diodes (LEDs) and photodetectors (PDs) to fabricate ultracompact refractometers with a chip size of 475 × 320 μm2. The light emission and photodetection properties of the devices containing the same InGaN/GaN multi-quantum wells have been characterized, confirming that the PD can respond to the emission of the LED. The flip-chip assembly of the chip enables the exposed sapphire substrate to be in direct contact with the solution, and the refractive index sensing capability governed by the change of critical angle and Fresnel reflection at the sapphire/solution interface has been investigated. The processing of the optically smooth surface of sapphire and the integration of high-reflectance distributed Bragg reflector beneath the devices facilitate the amount of light received by the PD. The monolithic chip is capable of detecting solutions with a refractive index ranging from 1.3325 to 1.5148 RIU and exhibits a sensitivity of 7.77 μA/RIU and a resolution of 6.4 × 10–6 RIU at the LED current of 10 mA. Rapid real-time responses of 33.9 ms for rise time and 34.7 ms for fall time are obtained in the detected photocurrent, thereby verifying the feasibility of the chip-scale refractometer.
Airflow sensors are an essential component in a wide range of industrial, biomedical, and environmental applications. The development of compact devices with a fast response and wide measurement range capable of in situ airflow monitoring is highly desirable. Herein, we report a miniaturized optical airflow sensor based on a GaN chip with a flexible PDMS membrane. The compact GaN chip is responsible for light emission and photodetection. The PDMS membrane fabricated using a droplet-based molding process can effectively transform the airflow stimuli into optical reflectance changes that can be monitored by an on-chip photodetector. Without the use of external components for light coupling, the proposed sensor adopting the novel integration scheme is capable of detecting airflow rates of up to 53.5 ms−1 and exhibits a fast response time of 12 ms, holding great promise for diverse practical applications. The potential use in monitoring human breathing is also demonstrated.
The design and fabrication of a vertically stacked red–green–blue (RGB) light-emitting diode (LED) with novel, to the best of our knowledge, wavelength-selective distributed Bragg reflectors (DBRs) are demonstrated. The two DBRs are optimized to achieve selective reflectance in the RGB spectral region through theoretical calculations and simulation modeling. The insertion of optimal DBRs into the stack structure can effectively reflect downward emission from the upper chip without filtering the emission from the lower chips, thereby increasing the luminous efficiency for white emission with a color temperature range of 3000–8000 K by 1.6–7.4%. The optical performances of stacked devices with and without DBRs are thoroughly studied, verifying the effectiveness of the proposed wavelength-selective DBR structure.
Pressure sensing based on high-sensitivity and fast-response photonic devices is essential for various transient and dynamic processes in diverse fields. Therefore, a miniaturized device being capable of precise and reliable detection is highly desired for the development of optical pressure sensors. Here, we develop a compact pressure sensor, showing a sensitivity of 1 μA/kPa and a fast response time of <10 ms, based on a III-nitride photonic chip combined with a PDMS membrane on submillimeter-scale footprints. The emitter and detector are monolithically integrated on a GaN-on-sapphire chip consisting of InGaN/GaN multiquantum wells, enabling quantitative readout for pressure sensing. Self-assembled polystyrene nanospheres are embedded in the PDMS layer and function as an opal-based photonic crystal, transforming the received mechanical signals into optical signals which can be precisely determined through recorded photocurrent. This underlying mechanism of angle-dependent reflective characteristics via the photonic bandgap effect is well fitted by our theoretical simulation. Sensors with opal films embedded at different vertical positions are fabricated, and their corresponding performance is systematically studied and compared through a series of pressure loading/unloading tests. The demonstrated high repeatability, stability, and durability of the developed chip-scale optical pressure sensor, paving the way for its widespread usage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.