Biomedical Engineering Reference
In-Depth Information
2.2.7 Optical Control of Passive Devices:
Dielectric Resonator Oscillator
The DRO is used more readily as its benefits are realized. Some of the advan-
tages of the DRO over other oscillators are reduced phase noise, higher effi-
ciency, and lower susceptibility to microphonics. Figure 2.15 shows a simple
depiction of a DRO circuit. Notice that the dielectric resonator is placed in
close proximity to the output stripline that affects the feedback characteris-
tics of the FET oscillator. The resonator couples magnetically to the feedback
path and the distance between the resonator and the microstrip line deter-
mines the amount of coupling.
Optical control can be achieved by adding a photoconductive sample on
top of the dielectric resonator material. Once illuminated, the conductivity of
the photoconductor increases that alters the magnetic coupling of the dielec-
tric resonator resulting in a frequency shift of the DRO.
2.2.7.1  Illumination Effects on Dielectric Resonator Oscillator
Two effects of illumination on DROs are discussed. First, frequency tuning,
or shifting, is reviewed as with the IMPATT and TRAPATT diodes. Also, FM
modulation of the DRO is discussed. Experimental results on other illumina-
tion induced effects are still in development.
2.2.7.2  Experimental Results: Optical Tuning
Experiments were performed on a 10.2 GHz DRO. Illumination was provided
by three sources: white light, a HeNe laser with a power output of 5 mW at
630 nm, and a GaAs LED with a power output of 1 mW at 850 nm. The white
Fiberoptic cable
LED
Photoconductor
Dielectric resonator
FET
FIGURE 2.15
Optical tuning of the dielectric resonator.
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