As the increase of environment and conservation consciousness in recent years, green-lighting concept begins attracting
much attention of the people in our country; particularly, the exploration of daylight lighting system is an obvious
example. However, in this nature-light lighting system, versatile optical couplers are required to guide and dissipate
sunlight into different indoor spaces to produce assistant illumination, and their coupling efficiencies directly affect the
whole efficiency of the lighting system. Thus, they play an important role in the daylight lighting system. To obtain high
efficient optical couplers, this thesis, other than investigating various used Y-branch couplers, proposes another new type
of coupler, which has a positive- or negative-arc Y-branch structure to split a light-beam into two beams or to combine
two light-beams into one beam with high efficient light output. From optical simulation results, it can be seen that the
output efficiency of this symmetrical Y-branch coupler with positive or negative arc can reach above 90%, no matter it is
used as a combiner or splitter. Furthermore, this thesis also goes through an investigation of the Y-branch output field
distribution and an improved arc design; the coupling efficiency between the coupler and an externally connected optical
fiber can be promoted.
In many photovoltaic (PV) or sunlight-illumination systems, solar trackers are always essential to obtain high energy/flux concentration efficiency, and that would lead to increase cost and extra power consumption due to the complex structure and heavy weight of the trackers. To decrease the cost while without sacrificing efficiency, a Fresnellens concentrator incorporated with a simple and cheap shutter, which consists of high reflective mirrors instead of conventional trackers, is proposed in this paper to provide solar tracking during the daytime. Thus, the time-variant and slant-incident sunlight rays can be redirected to vertically incident upon the surface of the Fresnel lens by appropriately arranging mirrors and swinging them to the proper slant angles with respect to the orientation of sunlight. The computer simulation results show that power concentration efficiency over 90%, as compared with the efficiency of directly normal incident sunlight, can be achieved with the mirror reflectance of 0.97 and for any solar incident angle within ±75 degrees to the normal of the Fresnel lens. To verify the feasibility and performance of the concentrator with the proposed shutter, a sunlight illumination system based on this novel structure is demonstrated. Both computer simulation and practical measurement results for the prototype of the sunlight illumination system are also given to compare with. The results prove the simple and high efficient shutter applicable to general PV or sunlight-illumination systems for solar tracking.