Augmented and Virtual Reality Systems - pág.51

In either configuration, the eye itself serves as the last element in the optical chain, with the retina serving as the display surface (Bhakta et al., 2014).

Figure 4.6 A Texas Instrument DLP digital micromirror device uses the retina of the human eye as the last element in the optical chain of a head-mounted display.

DMDs represent one of the fastest display technologies in existence. The speed of color refresh and low latency, the high resolution for such a small form factor (a 0.3-inch array diagonal enables a 1280 × 720 image), flexible illumination direction, and low power requirements make DMD an ideal imaging solution for head-mounted displays

Liquid Crystal on Silicon Microdisplay

Liquid Crystal on Silicon (LCoS) imaging technology is a cross between LCD and DLP technologies. As explained earlier in this section, an LCD is composed of an array of cells containing liquid crystal molecules sandwiched between two sheets of polarizing material with one cell (subdivided into red, green, and blue sections) representing one pixel. The state of each pixel is modulated by controlling the phase of the liquid crystal molecules and thus, the passage of light. This makes the LCD a «transmissive» technology. In comparison, DLP displays use an array of individually controlled micromirrors (each representing one pixel) that reflect sequentially projected light from an RGB source. The state of each pixel is modulated by tilting the mirror, making this a «reflective» technology.

As shown in Figure 4.7, an LCoS device is a combination of both transmissive and reflective technologies. Constructed on a silicon wafer overlaid with a highly reflective coating, LCoS uses nematic or ferroelectric liquid crystal to modulate field sequential colored light reflected off this backplane.