Simulation studies for the design and manufacturing of optical sensors and white light emitting devices
In this study, three dimensional ray tracing simulations are used as a tool for the design and manufacturing of optical sensors and white LED devices. Key experimental results and independent experimental results are used to verify the simulation results and a satisfactory agreement is obtained.
In the optical sensor technology, it is required to understand the pattern of propagation of light and the relationship between the collected signal and the detected objects. The Monte Carlo simulation results show for the first time that the response of the optical sensor for detecting particles in suspension depends not only on the concentration but also on the particle size, optical path length, and the optical properties of a particle. Sensor performance limit greatly depends on particle size and optical path length. Simulation results show that the sensor response is more sensitive to the concentration of smaller particle sizes than particle sizes. Single expression for the sensor response to the change of particle concentration of different sizes is presented. The simulation results are compared with individual experimental results to verify the accuracy of the simulations and a satisfactory agreement is obtained.
Light propagation in an LED package experiences similar phenomena as in an optical sensor for sediment-concentration measurement: reflection, scattering, and absorption. In the LED packaging, the LED device should have high external quantum efficiency and should provide different patterns of the output light so that it can serve for different applications. The efficiency of an LED device depends on many factors: LED chip structures (size, shapes, and surface types), types of the reflector cup (specular or diffuse), cup geometries, lens geometries and dimension, and optical properties of encapsulant such as refractive indices and transmittance. The simulation results show that the high negative deformed angle chip (HNDA-chip) has a higher light output than other structures. Texturing the top surface can improve the light output in a conventional LED structure but it reduces the efficiency of the HNDA-chip (the highest light extraction structure). For the HNDA chips, the circular-base chips have the highest LEE, i.e., significantly higher than that of square-, pentagonal- and hexagonal-base cubic chips. The light output of the LED package can be improved with a high extraction lens structure. A high extraction lens with the light output having a low viewing angle is presented. It can provide up to 287% higher in the power output within the viewing angle of 10 degree compared to a conventional LED package.
In phosphor-conversion white LEDs (pc-WLEDs), the efficiency and light output also depends on other parameters including phosphor particle sizes, phosphor placements and geometries, separation distance between the phosphor layer and the LED chip, phosphor concentration, and optical properties of phosphor materials. It is shown for the first time that the package with low phosphor concentration has an advantage over the high phosphor concentration package. It is also found that a WLED package with phosphor particles with the size range between 10μm and 20 μm has a higher luminous efficacy.
Improving the performance of optical sensors and LED and WLED devices while maintaining or reducing the manufacturing cost is important. The results in chapter 2 are significant in designing a particle-concentration sensor with high sensitivity and accurate measurement. The findings in LED studies are important for the development of materials such as phosphor materials for WLED devices and encapsulants. (Abstract shortened by UMI.)