Shutters, PLZT

The optical shutter described above can function as a voltage-controlled colour filter. The PLZT is again of the slim-loop quadratic variety, and the polarizer-PLZT-analyser configuration as for the shutter. 

Thin PLZT films deposited by, for example, sputtering are too thin (< 1 /im) to achieve the necessary retardation for transverse mode optical devices. There is, however, potential for films having thicknesses in the range typically 2-25 /mi. If these can be successfully and economically produced then they offer potential for a variety of devices including optical shutters, modulators and displays. 

The films can be grown by various methods (see Section 3.6.9). G.H. Haertling and G.C. Robinson [10] describe the production of 6 /nn thick (9/65/35) PLZT films on sapphire substrates by an automated repeated dipping/firing process. The dipping solution consisted of the acetates of the metal ions, La, Zr, Ti and Pb. The films were the basis of a successful shutter and display based on the principles described above (see Sections 8.21 and 8.33). 

A special class of materials that is also ferroelectric are electrooptic ceramics. Materials such as lanthanum-modified lead zirconate titanate (PLZT) produce excellent electrooptic devices. These polycrystalline ceramics exhibit voltage-variable behavior—that is, they can be switched from optically transparent to opaque by the application of voltage. Most of these devices, which are used for shutters, modulators, and displays, are processed by hot pressing to full density. Experiments in many laboratories are being carried out to tape-cast these materials into thin sheets. The main problem encountered to date has been the ability to sinter to full density. The use of nanosized powders has helped in this regard. The ability to tape-cast large sheets could open a wide variety of applications for these materials. 

A second approach involves using PLZT with the same composition as that of the optical shutter discussed above, and using an electric field to induce FE-AFE phase transitions. This method uses the same element structure as in Figure 7.1.27, but instead of using light exposure to write a pattern on... 

Figure 8.35 Principle of an optical shutter based on an electro-optic PLZT ceramic plate (Moulson and Herbert, 2003). Reprinted with permission from Wiley-Blackwell Ltd, Oxford, UK.

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