A backlight unit is constructed by laying out a plastic optical fiber (POF) in a curved trench fabricated in a light-guide plate. First, the light leaks out of the POF at curved sections and enters the plate. Next, the light is extracted from the plate by some microstructures fabricated on the surfaces of the plate. Coupled to a laser diode, its optical power can be efficiently and uniformly delivered over a large area via the POF. In this experiment, we fabricated a 10 cm×10 cm×3 mm prototype unit with off-the-shelf components. It becomes see-through when the space around the POF is filled with index-matching oil. One can build an arbitrary-shaped planar light source by tiling multiple cells and connecting them by a POF. The light inside the POF is depleted as it propagates downstream. This can be compensated by decreasing the radii of curvature. Microstructures on the light-guide plate can distort the passage of ambient light. For a see-through unit, we can distribute them sparsely and/or use absorbers. A see-through backlight unit is a relatively unexplored device, and it might pave the way for new applications.
A concentrator photovoltaic system can be built by coupling a lens array to a branched planar waveguide, which has one end with a solar cell attached and the other end divided into multiple branches. A right-angle prism is attached to each branch end, redirecting the focused sunlight into the waveguide via total internal reflection so that the light propagates inside the waveguide. With an appropriate design, the light leakage from the waveguide can be made negligible. Our ray-tracing simulations show that the ratio of the optical power exiting the waveguide to an optical power entering the lens-array is close to 87%, with the loss being mostly due to the Fresnel reflections at the lens (8%) and prism surfaces (3%). We can increase geometric concentration by cascading tapered waveguides. The number of cascades should be limited so that the light leakage from the tapered portions remains insignificant. A secondary optical element on each prism would collimate the light, easing this limitation, as well as making the system thinner. The absorption in the waveguide material imposes an inherent limit on the number of cascades and the concentration factor.
We propose a concentrator photovoltaic system based on a planar waveguide. Here, the waveguide has one stem at one end and the other end is divided into multiple branches. A right-angle prism is attached to each end of the branches. A lens-array is stacked on the waveguide such that each prism is placed near a focal point of a corresponding lens. Its 45-degree slope leads the focused sun light into the waveguide via total internal reflection. The light propagates inside the waveguide and its intensity increases at each branching point. A solar cell is coupled to the end of the stem for photoelectric conversion. The branched portion can be either straight or curved. In both cases, according to our ray tracing simulations, the light loss inside the waveguide becomes negligible when we set the focal length of the lens larger than a certain value. For example, this value is 300mm for a 5mm-thick, 150mm-long straight waveguide coupled to a lens-array with a lens diameter of 90mm. This number is reduced to 220mm for a curved waveguide. It is further
reduced to 100mm when we assume 100% reflection at the 45-degree slope. In these cases, the efficiency defined as the ratio of the optical power exiting the waveguide to one entering the lens-array is close to 87%. The major loss
mechanism is the Fresnel reflections at the lens surfaces (8%) and the prism surfaces (3%). The rest is mostly due to the
absorption by the material assumed for the waveguide (PMMA) (1-2%).