| 摘要 |
A phase modulator includes a lower layer (30) of glass or silicon substrate containing a 1-D array of pixels (32) formed from either ITO or aluminium respectively. The substrate is covered by an upper glass plate (36) coated uniformly with ITO to make one large transparent electrode. Polymer-dispersed LC composite material (38) is sandwiched between these layers, the polymer-dispersed material containing a nematic LC (with positive dielectric). Figure 4a shows the director configuration within the droplets (40) in the field-off condition. This type of droplet director configuration is known as bipolar. In the absence of an electric field the bipolar axis of each droplet is assumed to be randomly oriented. The direction of this axis is assumed to be determined by a slight elongation of the droplet which results in the bipolar axis along the long axis, and/or the random pinning of the director on the interior surface of the droplet. Light impinging on this material may encounter small enough scattering centres to be suitable for Rayleigh scattering. An applied electric field couples to the LC dielectric anisotropy and exerts an electric torque on the directors. This is balanced by an elastic torque generated by the distortion of the director pattern away from its equilibrium position. The balance of these two forces determines an equilibrium position of the director and a rotation of the bipolar axis towards an orientation normal to the plane of the SLM. The device is thus able to provide an analogue modulation of the refractive index, and hence phase delay, encountered by incoming light. Figure 4b shows the final switch configuration in which voltages of different magnitudes have been applied to different pixels (42) to produce several different regions (44) of PDLC, with different switch states, and hence a phase pattern suitable to defract light into first order spot with high efficiency. |
