GRaded INdex Film (GRIN)

Working in collaboration with a major European chemical company, Microsharp developed a revolutionary internationally-patented optical diffuser film - termed GRaded INdex (GRIN) film. GRIN films are high performance optical diffuser films with high (92%) optical transmittance and near total polarisation preservation (98-99% laminated, 97-98% unlaminated). The films permit high resolution displays without Moire problems. They enhance both brightness and contrast at specific angles of view. GRIN films are typically 50 microns thick.

The following pictures showing film cross sections demonstrate the variation in local refractive index, which gives rise to the films' optical properties. The geometry of the refractive index variation can be controlled through the manufacturing process.

GRIN film can be included in the backlight, or on the top of the LCD stack, depending on the performance characteristics desired.

GRIN film comes in 3 varieties:

1. Symmetric - accepts an incident narrow light bean and outputs a conical distribution
2. Asymmetric - output is a cone with an elliptical cross-section
3. Off-axis - intended to improve results when original illumination is off-axis, or when viewing is off-axis

A further characteristic of DPI film is that it can be made to have asymmetric properties. This means that the viewing angle in one axis can be increased and the other decreased whilst maintaining the gain of the system:

A unique property of Microsharp GRIN film is its ability to reduce the chromatic dispersion of the LCD when viewed at high angles resulting in a more consistent image.

Applications are mainly in enhancing the performance of flat panel displays, particularly LCDs, to improve viewing angle, but a range of additional applications arise when the film is integrated with other optical materials.

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GRIN 2 Photopolymer

The initial GRIN materials were based upon the Dupont HRF photopolymer series and used a mask to facilitate the initiation of the GRIN tubes. Microsharp have developed a second generation GRIN 2,  called Riffix™ which is based upon their own patented photopolymer system that uses only collimated UV light and no microstructured photomask. These materials offer the ability to enable simple reel-to-reel manufacture and significantly lower costs. 

Several aspects of the GRIN 2 material can be tailored by modifications in:

• the formulation of the initial polymer material
• the thickness of the film
• the precise way the illumination unit is used in its production

The tailoring alters three main variables:

• the mean angle of light direction -from zero to +-30 degree (possibly up to +-40 degrees if suitable light source and material arrangements are used)
• the angle of spread around that mean -from approximately 5 degrees up to 47 degrees
• the degree of light spread asymmetry in the orthogonal directions across the film and along the film

Films have been formulated to have on-axis and off-axis properties and angles of view up to 47 degrees for the symmetric materials.  Samples are available upon request for a small fee.