Electro-Optics - Applied Optics Fundamentals and Device Applications - page 29

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FIGURE 2.16
Shift in the DRO resonant frequency as a function of IA LED output power.

light source shifted the DRO center frequency by 5 MHz and also lowered
the power by 1 dB. A total of 1 W/cm 2 of light output power was used. A
0.4 MHz frequency shift was obtained using the HeNe laser, and a 0.5 MHz
shift was seen with the GaAs LED. In addition to a constant intensity illu-
mination, the light sources were varied in intensity to determine their effect
on frequency shift. Results showed a linear relationship between frequency
shift and light intensity as shown in Figure 2.16 [36].

2.2.7.3 FM Modulation

FM modulation experiments were performed using an AM-modulated LED
as the coupling mechanism to the photosensitive sample. Modulation rates
of 130 MHz were observed; however, higher rates could have been achieved
if the LED would not have limited the rate.

2.2.8 Applications of Optical Control

Applications of devices controlled by optical means are diverse and con-
stantly increasing. A description of some common applications provides a
better understanding of why much of the research has taken place.
One very important area for utilization optically controlled devices is in
phased array radar systems. Phased arrays radars have many emitting ele-
ments (sometimes >10,000) on a planar surface. These emitting elements
allow the antenna pattern to be electrically steered very quickly but, in
order for the pattern to be correct, the phase and frequency of each one of