Geometrical optics analysis of the structural imperfection of retroreflection corner cubes with a nonlinear conjugate gradient method

Enhanced lighting on the road surface with TIR-PA optical element on tunnel sidewall

Both the lighting quality and driving safety inside the tunnel have been quite a concern around the world. In this study, a plate with prism array of total internal reflection (TIR-PA) has been designed to enhance the lighting on the road surface inside the tunnel in adherence to traffic safety as well as energy savings. Such optical elements, above the tunnel sidewall, can redirect the rays emitted from both the headlight and lighting devices to the road surface, which supports higher flux on the road. Simultaneously, the simulation is conducted with consideration of practical factors based on the mathematical model and edge-ray principle to attain the effect of the TIR-PA plates. On the one hand, for the rays from the lighting devices, the enhancement rate of illuminance has reached 12.60%-16.58%, which is attributed to TIR-PA plates above the different sidewalls of the Lambertian scattering property. TIR-PA can be suitable for various sidewall materials due to the small effect of illumination reduction. On the other hand, 30.2%-32.2% rays of the headlight source received by the sidewall, due to the effect of TIR-PA plates, are redirected to the driving distance for 27.3-71.9 m, which makes 15.9-31.1m² of road surface brighter. It makes contributions to the improvement of illuminance distribution and drivers' pre-judgment. In the future, broader applications regarding the TIR-PA plates will be explored widely in tunnel lighting systems due to the low production cost.

Measuring corner cube reflectors through ray tracing of a reflected wavefront

The corner cube plays a key role in many advanced optical systems as the critical retrieval component, while the errors such as dihedral deviation will lead to unacceptable results. We present a method to obtain the right-angle plane deviation of the corner cube only by measuring and calculating the normal incident reflection wavefront. The calculation process is an iterative method of ray tracing based on the corner cube reflection process. The three-dimensional shape of the right-angle plane of the corner cube can be obtained accurately by this method. The proposed method is easy to implement and reliable, and it avoids the complicated operation of the traditional measurement method, which can also be applied to the measurement of the errors in the assembly and adjustment process where corner cube reflectors are used.

Compact in-line floating display system using a dihedral corner reflector array

We propose a compact type floating display system using a dihedral corner reflector array. Conventional floating displays using the dihedral corner reflector array usually have a folded configuration which makes the system bulky. The proposed technique achieves the compact in-line configuration using a pair of decentered lenses. The decentered lenses make the effective incident angle to the dihedral corner reflector array be tilted while maintaining the display panel and the dihedral corner reflector array in parallel. The ghost images are also refracted largely by the decentered lenses, being separated from the desired floating images. The proposed technique is verified by optical experiments.

Optical system to display mid-air images on a glossy plane and remove ground images

Mid-air images are formed in the air by the reflection and refraction of light emitted by a light source, which allows the user to view the floating image in real space without wearing special equipment. However, conventional mid-air image optical systems have some weaknesses, such as the need to suitably adjust the height of the viewpoint position depending on its optical arrangement. We propose an optical design that can be installed simply by placing it on a glossy plane, on which an upright mid-air image can be displayed and which is smaller than the existing system.

Flexible corner cube retroreflector array for temperature and strain sensing

Optical sensors for detecting temperature and strain play a crucial role in the analysis of environmental conditions and real-time remote sensing. However, the development of a single optical device that can sense temperature and strain simultaneously remains a challenge. Here, a flexible corner cube retroreflector (CCR) array based on passive dual optical sensing (temperature and strain) is demonstrated. A mechanical embossing process was utilised to replicate a three-dimensional (3D) CCR array in a soft flexible polymer film. The fabricated flexible CCR array samples were experimentally characterised through reflection measurements followed by computational modelling. As fabricated samples were illuminated with a monochromatic laser beam (635, 532, and 450 nm), a triangular shape reflection was obtained at the far-field. The fabricated flexible CCR array samples tuned retroreflected light based on external stimuli (temperature and strain as an applied force). For strain and temperature sensing, an applied force and temperature, in the form of weight suspension, and heat flow was applied to alter the replicated CCR surface structure, which in turn changed its optical response. Directional reflection from the heated flexible CCR array surface was also measured with tilt angle variation (max. up to 10°). Soft polymer CCRs may have potential in remote sensing applications, including measuring the temperature in space and in nuclear power stations.

A flexible corner cube retroreflector (CCR) array based passive dual sensing is demonstrated to measure external stimuli (temperature/mechanical force as weight suspension).

Phase-conjugated directional diffraction from a retroreflector array hologram

A corner cube retroreflector (CCR) consists of three perpendicular flat surfaces and reflects the incident light back to its source.

Truncated corner cubes with near-perfect retroreflection efficiency

By isolating a finite effective volume from a conventional triangular pyramid corner cube, we obtained truncated corner cube structures with greatly enhanced retroreflection efficiency. We explore an optimal truncated corner cube with near 100% retroreflection efficiency based on the expectation that the traveling paths of the optical rays can be localized in the finite effective volume of the structure, and, as a result, truncated corner cubes with perfect efficiency can be produced. As a case study, the retroreflection efficiency of a commercialized 3M truncated corner cube sample is evaluated. Furthermore, it is shown with numerical verification that a truncated corner cube array sheet with near-perfect retroreflection efficiency can be produced.

Quasi-retroreflection from corner cubes with refractive free-form surfaces

Quasi-retroreflection from corner-cube structures with a refractive free-form surface is studied. It is shown that adjustment of the structural parameters of the free-form surface allows control of quasi-retroreflection. Quasi-retroreflection corner-cube array sheets with specified quasi-retroreflection angle are modeled, and their quasi-retroreflection characteristics are analyzed.

Diffraction of transmission light through triangular apertures in array of retro-reflective microprisms

An array of microprisms was described by a model of multiperiod blazed gratings consisting of triangular apertures. The origins of hexagram-shaped diffraction patterns were interpreted based on multiple-beam interference and diffraction array theorem. The relation between zonal/line ghost fringes and imperfectly fabricated array structures was analyzed. Geometrical performance (e.g., the dihedral angle of the microprism) was tested by measuring the features of diffraction patterns of samples from three retroreflective sheeting manufacturers.

Analysis and fabrication of corner cube array based on laser direct writing technology

A detailed analysis of corner cube array (CCA) structure is carried out using the commercially available ray-tracing software ZEMAX. The retroreflective properties of CCA for short-range and long-range propagation are compared. An improved CCA structure with a relatively low structural depth (compared with rectangular CCA) is designed and analyzed. Higher retroreflectance (compared with triangular CCA) at a specific incident angle is proved by ray tracing. Two kinds of CCA structures, including the improved CCA, have been fabricated using laser direct writing technology. The fabrication results are qualified by three-dimensional shape measurement and ray tracing.