Abstract
An optical true time delay device is demonstrated that
is capable of supporting 112 antennas with 81 different delays (${>}6$ bits) in a volume $16' \times 5' \times 4'$ including
the box with electronics. It uses a free-space design based on the White cell,
and alignment is made simple, fast, and robust by the use of slow-tool diamond
turning of many optics on a single substrate. Pointing accuracy of the 12
objective mirrors is better than 10 $\mu$rad, and surface roughness is ${\approx}45$ nm RMS. Delays vary from 0 to
25 ns in 312.5 ps increments. Short delays are implemented using delay rods
of high refractive index, and long delays using folded mirror trains. Total
insertion loss from fiber to detector was 7.82 dB for the no-delay path, and
10.22 dB for the longest lens train. A three-state tip-style MEMS micromirror
array is used to select among the delays, with tilt angles ${\pm}1.4^{\circ}$ plus flat, and switching
time ${<}100\ \mu$s for the entire array. An InP wideband optical combiner photodetector
array converts the optical signal to RF with 20 GHz bandwidth. The unit survived
temperature cycling 0 to 50 C and random vibration on three axes (9.84 g RMS)
with no degradation of signal.
© 2011 IEEE
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