Basic Electro-Optics Modulation

At the exit plane of the crystal of length /, these electric field components become 

The effect of the retardation plate on the e-o crystal is to impart a further phase shift [e.g., % 2 phase shift for a quarter wave (A74) plate] on the y component. The total phase shift between the y and x components thus becomes 

The electric field components after the retardation plate become 

By suimning the components of E and Ey on the transmission axis of the output polarizer (along 7), a straightforward analysis gives the output intensity 

The intensity of the output beam from the output polarizer thus varies according to the value T, which is electrically controlled through the phase shift imparted by the electro-optic crystal, r(.jystai. 

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FIGURE 32 Basic electro-optic modulator configurations. 

Figures 23-28 show the process of producing basic circuit elements of vertically stacked circuits. The use of the three lithographic masking techniques mentioned results in very low loss transitions between optical circuits in different vertical stacks. These techniques can also be used to fabricate the low loss electro-optic modulator configuration shown in Figs. 29 and 30.

Equations (2.27), (2.28), (2.29) and (2.30) show that nonlinear optical effects in organic r-conjugated molecules (i.e. electric field dependent polarizablity) are basically due to electronic rearrangements so it is expected that organic molecules exhibit extremely fast response times leading to the possibility of electro-optic modulation in frequency domains that are prohibited for inorganic crystals presently available in the market. 

Fig. 10.11 Basic setup for evaluating electro-optic shutter/modulator characteristics (open condition shown). Reproduced with permission from [131]. Cop5uight 1999, John Wiley Sons...

Figure 5 shows typical responses for this particular sample (0.5% sphere volume fraction). A basic difference in the electro-optical behavior of spherical compared to anisometric particles is the linear response at low field intensity. The modulated signal follows the frequency of the applied field with a phase difference of —90°. With an increase in frequency the ac component relaxes, changing in both amplitude and phase and passing to double frequency, while the dc component changes... 

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