Optimized Diffuser Design for TN Mode Collimate & Post Diffuse Displays
Original Publication Date: 2002-Jul-01
Included in the Prior Art Database: 2003-Jun-20
Optimized Diffuser Design for TN Mode Collimate Post Diffuse Displays Optimized Diffuser Design for TN Mode Collimate and Post Diffuse Displays Disclosed is an optimized low reflectivity diffuser where a combination of tapered high index light guides surrounded by a low index material containing black particles and an exit planarized surface diffuser only on the ends of the tapered light guides is used where the tapered high index light guides are designed such that light which leaks through the twisted nematic liquid crystal (TN-LC) dark state (beyond about 30 degrees "up" from the display normal) is not transmitted. This can be accomplished by proper design of the tapered high index light guide and the low index surrounding material which contains the black particles. Forming the planarized surface diffuser only on the ends of the light guides has the advantage that manufacturing is simpler and the ambient reflectivity is reduced since the diffuser only covers part of the top surface, i.e. only where it is needed. Further diffusion to achieve the desired output luminance distribution is achieved by the addition of the exit planarized surface diffuser on the top of the light guide. Other forms of planarized surface diffusers, such as those formed by surface holograms for example, can be used. Collimate and post diffuse (CPD) type displays offer potential advantages for wide viewing angle liquid crystal display (LCD) monitors [1,2]. Compared to the current dual-domain in-plane switching (IPS) mode LCD monitors, the region of high contrast (>100:1) extends further off the display normal (to about 60 degrees, depending on the design) and is more symmetric. In a CPD type display, a collimating backlight is used in combination with a TN mode LCD and a low reflectivity exit diffuser. Advantages include the faster electro-optic response of the TN-mode vs. IPS-mode LC which is very desirable for viewing video images to avoid image smearing, lower cost driver chips since a lower voltage is used, and an increased aperture ratio (percent area of the pixel which transmits light) except at very high resolutions (>160 pixels per inch, see ). The increased aperture ratio is desirable since it is difficult to make a collimating backlight which is as efficient as a conventional backlight. It is necessary to collimate the light to about 15 degrees full width half maximum (FWHM).