Metalenses can be used as standalone single elements or incorporated as one component of a subassembly that also includes other non-metalens optical elements. A ray-based design approach allows the co-design of a hybrid system with metalenses and conventional optics. Such a ray-based design approach is applicable to both polarization-sensitive and -insensitive designs. We validate the ray-based design approach with polarization-sensitive designs.
Metalenses can be used as standalone single elements or incorporated as one component of a subassembly that also includes other non-metalens optical elements. Because of the sub-wavelength length scale of the meta-atoms, ray-based methods for analysis and optimization may not be considered appropriate. However, by treating the imparted phase appropriately, ray-based methods can be used to design and analyze optical systems that incorporate one or more metalenses. These methods can be applied to imaging systems or illumination systems composed solely of metalenses, or systems that incorporate a mix of metalenses and conventional refractive, reflective, or diffractive optical elements. There are two pieces of information that are required by the ray trace: i) the ray directions following the metalens, and ii) the amount of energy that the ray carries. The distribution of the meta-atoms in the metalens can be used to determine ray directions and Fourier analysis allows for estimation of the energy carried by the rays. The method relies on having access to the imparted phase (from an EM solver, say) that can be accessed during the ray trace. This approach allows for workflows that are familiar to lens designers—even those without experience designing metalenses—while offering results that are in excellent agreement with more rigorous wave-based analyses. This approach is applicable to both polarization-insensitive and polarization-sensitive designs. In this paper, we discuss the design approach and offer design examples.
To meet the growing demand for design automation of metalens with inverse design capability, Synopsys has developed a powerful and user-friendly multi-domain design tool, MetaOptic Designer (MOD), that can handle lenses with subwavelength features. The optimization algorithm employs the well-known adjoint method, which can easily handle millions of design variables. The forward propagation is done by the efficient Fourier transform, also called angular spectrum method. The transfer function of each metalens is characterized by a parametric BSDF databases built with RCWA or FDTD. Application examples include achromatic metalens, large FOV metalens, reflective metalens, chiral hologram, and hybrid optical system.
A fully automated solution for designing metalens/metasurface systems has been developed to optimize the parameter values of each meta-atom on each metasurface based on the given inputs and desired targets. Unlike traditional design approaches, which are based on a given phase profile for a particular incident condition, inverse design can generate the optimum layout and its simulation results automatically based on a limited set of inputs from designers. The knowledge required of designers is minimized significantly. Hence, designers at different levels of expertise, including undergraduate students, can use this software solution to design metalens systems quickly.
The components in optical projectors are becoming increasingly smaller due to the need for increased output resolution and the desire for small form-factor devices. One such component is Liquid Crystal (LC) panels, that utilize periodic micro-lens arrays which become more sensitive to diffractive effects as the period becomes near/sub wavelength. This paper explores the diffraction effects within these systems through numerical modeling. Traditionally Ray tracing techniques have been used for analyzing projection systems and has led to significant improvements in illumination uniformity and efficiency. However, increasingly complex projector designs that incorporate smaller geometric features like micro/nano lens arrays, including coherent diffraction and interference effects arising from such structures, cannot be handled by ray-tracing approaches alone. Rigorous electromagnetic (EM) wave optics based techniques, such as finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA) which solve Maxwell’s equations must be used. These rigorous EM techniques, however, have difficulty in analyzing the larger projector structures due to computational resource limitations. We use a mixedlevel optical simulation methodology which unifies the use of rigorous EM wave-level and ray-level tools for analyzing projector performance. This approach uses rigorous EM wave based tools to characterize the LC panel through a Bidirectional Scattering Distribution function (BSDF) file. These characteristics are then incorporated into the ray-tracing simulator for the illumination and imaging system design and to obtain the overall performance. Such a mixed-level approach allows for comprehensive modeling of the optical characteristic of projectors, including coherent effects, and can potentially lead to more accurate performance than that from individual modeling tools alone.
Ray-tracing (RT) has long been the workhorse technique for analyzing light-emitting diode (LED) dies and packages and has led to significant improvements in extraction efficiency and beam shaping. However, to achieve further enhancements, nano-/microscale features such as patterned substrates and surface textures have been explored. The coherent effects arising from these near/subwavelength features are difficult to include in the RT of the packaged device. We show that under certain conditions these effects can have a significant impact on LED performance, especially if back-reflectors are present. Furthermore, we demonstrate that coherence must be accounted for even in structures that would otherwise be considered as having relatively large feature sizes, such as gratings with periods many times the wavelength. We present comparisons between the optical responses of prototypical periodically patterned substrates modeled with RT alone and with a mixed-level approach that combines RT and rigorous electromagnetic simulation, such as rigorous coupled wave analysis and finite-difference time-domain. Several examples with varying lateral periods are computed with both methods. It is shown that these results may differ, and that these differences can be significant if back reflection is present. We conclude that a mixed-level approach is an efficient and accurate method to model light extraction in modern LEDs.
Over the last two decades, extensive research has been done to improve light-emitting diodes (LEDs) designs. Increasingly complex designs have necessitated the use of computational simulations which have provided numerous insights for improving LED performance. Depending upon the focus of the design and the scale of the problem, simulations are carried out using rigorous electromagnetic (EM) wave optics-based techniques, such as finite-difference time-domain and rigorous coupled wave analysis, or through ray optics-based techniques such as Monte Carlo ray-tracing (RT). The former are typically used for modeling nanostructures on the LED die, and the latter for modeling encapsulating structures, die placement, back-reflection, and phosphor downconversion. This paper presents the use of a mixed-level simulation approach that unifies the use of EM wave-level and ray-level tools. This approach uses rigorous EM wave-based tools to characterize the nanostructured die and generates both a bidirectional scattering distribution function and a far-field angular intensity distribution. These characteristics are then incorporated into the RT simulator to obtain the overall performance. Such a mixed-level approach allows for comprehensive modeling of the optical characteristic of LEDs, including polarization effects, and can potentially lead to a more accurate performance than that from individual modeling tools alone.
Over the last two decades there has been extensive research done to improve the design of Organic Light Emitting Diodes (OLEDs) so as to enhance light extraction efficiency, improve beam shaping, and allow color tuning through techniques such as the use of patterned substrates, photonic crystal (PCs) gratings, back reflectors, surface texture, and phosphor down-conversion. Computational simulation has been an important tool for examining these increasingly complex designs. It has provided insights for improving OLED performance as a result of its ability to explore limitations, predict solutions, and demonstrate theoretical results. Depending upon the focus of the design and scale of the problem, simulations are carried out using rigorous electromagnetic (EM) wave optics based techniques, such as finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA), or through ray optics based technique such as Monte Carlo ray-tracing. The former are typically used for modeling nanostructures on the OLED die, and the latter for modeling encapsulating structures, die placement, back-reflection, and phosphor down-conversion. This paper presents the use of a mixed-level simulation approach which unifies the use of EM wave-level and ray-level tools. This approach uses rigorous EM wave based tools to characterize the nanostructured die and generate both a Bidirectional Scattering Distribution function (BSDF) and a far-field angular intensity distribution. These characteristics are then incorporated into the ray-tracing simulator to obtain the overall performance. Such mixed-level approach allows for comprehensive modeling of the optical characteristic of OLEDs and can potentially lead to more accurate performance than that from individual modeling tools alone.
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