Acousto-Optics, Optical Computing, and Signal Processing - Applied Optics Fundamentals and Device Applications - page 116

TI indiffused LiNbO 3 waveguide

Zero
beam
dump
diode

0.2 cm

GaAlAs
Laser
diode

140 Element
photodiode
array

400 MHz
Transducer
array

1.2 cm

2.72 cm

FIGURE 3.14
Westinghouse design for advanced IOSA.

the waveguide at the other end. Geodesic lenses were formed by single-point
diamond turning to >0.5 μm tolerances. The lenses had an insertion loss of
about 2 dB. With >5% of the input light diffracted by the SAW's, the mea-
sured dynamic range was around 40 dB. A 400 MHz bandwidth centered at
600 MHz was scanned by dividing the 140 pels into 20 groups of 7 each.
A resolution of 4 MHz was achieved. The clock rate was 5 MHz, providing
simultaneous pulse detection for 0.3-3.0 μs pulses separated in frequency
by 20 MHz. The maximum RF power fed into the transducers was 60 mW.
It is interesting to point out that the HeNe laser, emitting 100 μW, is near
the power threshold of optical damage in LiNbO 3 . The authors pointed out
that performance could be greatly enhanced by using a longer wavelength
semiconductor laser, due to the increasing damage threshold with increas-
ing wavelength in LiNbO 3 . For comparison, bulk-type receivers have been
built with 1 GHz of bandwidth, 1MHz of resolution, and 40 dB of dynamic
range; however, wider bandwidth can potentially be achieved with the inte-
grated optical spectrum analyzer using multiple arrays of tilted transducers
or chirped transducers.

3.9 NonreceiverIntegratedOpticBraggCellApplications
Other applications of AO Bragg cells must be split into 1-D and 2-D cases,
because IO implementations can only be 1-D. Only those systems realizable
in IO technology will be mentioned. The space-integrating and the time-
integrating correlators are shown in Figures 3.15a and b, respectively. These
are 1-D devices. In the space-integrating correlator, “the received signal g ( t )
is fed into the Bragg cell at P 1, which is illuminated at the correct angle.
Lenses L 1 and L 2 image plane P 1a onto plane P 1b . A slit filter at P 2 performs