Liquid Crystal on Silicon (LCOS)

Liquid Crystal on Silicon or LCOS technology has been around for decades. Only a few years ago did the technology get far enough to see a real application – big screen projection TV. Today you can see LCOS at work in televisions such as Sony’s SXRD. LCOS operates on two basic technology principles. First, the ability to lay down liquid crystals on a microchip semiconductor, and for each crystal to be controlled as independent pixels, and 2nd the liquid crystal material’s properties in relation to light. More on that 2nd principle. LCOS operates using polarized light. Light has two polarizations, “P” and “S.” Your common sunglasses use cross polarizers to shade the sun from your eyes. Well, with liquid crystal material, the crystals either rotate or switch the light’s polarization and reflect it or it does not change the polarization – depending on how the molecules are aligned.

Typically, if the molecules are aligned one direction – that pixel will be “on.” Meaning, light hitting that pixel (say “S”) light, will be reflected and rotated to “P” and will pass through a polarizer and form a projected image (using projection optics). A pixel in the “off” position, that is to form a dark pixel on the screen, will have the molecules aligned the opposite direction. These pixels will reflect the “S” light but will not change it’s polariziation. That “S” light will then be reflected by the polarizer away from the projection optics and away from the screen.

LCOS has potential for cell phone projection. The LCOS technology for pico projection requires very bright LED’s or lasers in the case of laser holographic technology. LCOS also requires a good polarizer that can split the “S” and “P” lights – otherwise known as beam splitter. Drawbacks for LCOS are the cost of the chip, the 50% loss of light due to the separation of “S” and “P,” and the need for projection optics.