A Liquid-Crystal Video Stereoscope With High Extinction Ratios, A 28 % Transmission State, And One-Hundred-Microsecond Switching

Thomas J. Haven

doi:10.1117/12.940116

16 June 1987 A Liquid-Crystal Video Stereoscope With High Extinction Ratios, A 28 % Transmission State, And One-Hundred-Microsecond Switching

Thomas J. Haven

Author Affiliations +

Proceedings Volume 0761, True Three-Dimensional Imaging Techniques & Display Technologies; (1987) https://doi.org/10.1117/12.940116
Event: OE LASE'87 and EO Imaging Symposium, 1987, Los Angeles, CA, United States

Abstract

A liquid-crystal pi-cell is an ideal choice for fabricating a video stereoscope because it can switch between states at speeds that approach vertical blanking times on a standard display monitor. Initial applications, although very good compared with alternative technologies, revealed several areas for improvement. First, extinction ratio measurements made from 470 to 630 nanometers varied between 20:1 and 35:1. This range of ratios falls far short of dichroic polarizer capability. Second, a noticeable color shift can occur in the transmissive state as the image is rastered down the screen. For instance, a white image can appear bluish white at the top and yellowish near the bottom. The problems associated with less than perfect extinction ratios are due to boundary-layer optics of the liquid-crystal device and with the drive waveforms applied to the liquid-crystal device. The coloration in the transmissive state occurs because the switching time from the extinction state to the transmission state is 2 to 4 msec, which exceeds typical submillisecond vertical blanking times. A second compensating liquid-crystal cell was introduced to cancel the two extinction-state problems. The compensating cell arrangement also allows simultaneous cell switching without changing the net optical state of the device. By pre-switching both cells prior to vertical blanking, a drive scheme was devised that allows less than 100 Asec switching to either the extinction or transmis-sion state. Although increased by two to three times, extinction ratios still failed to meet expectations. However, the double cell arrangement accentuated substrate index mismatches that accounted for the last bit of light leakage. Correcting this problem brought the extinction values near the limits of the polarizers and improved the transmission state to 28% .

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Thomas J. Haven "A Liquid-Crystal Video Stereoscope With High Extinction Ratios, A 28 % Transmission State, And One-Hundred-Microsecond Switching", Proc. SPIE 0761, True Three-Dimensional Imaging Techniques & Display Technologies, (16 June 1987); https://doi.org/10.1117/12.940116

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