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2007-10-12 Science & Technology

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Posted by gromky 2007-10-12 05:58|| || Front Page|| [8 views ] Top

#1 Rocky Mountain Optics provides all sorts of rare and vital specialty materials including deposited thin film coatings used in various defense technologies. Among them are monocrystals of lithium niobate [LiNbO₃], an acousto-optic material used in real-time analysis threat discrimination systems on fighter jets.

External ambient microwave signals are detected and consolidated into a single feed. This waveguide is directed into the modulating line of a Bragg cell. The varying microwave energies create different degrees of optical deflection within the cell. A highly collimatedor laserlight source shone through the stimulated cell is steered by these energy fluctuations into a spatial array of photodetectors that are positioned and calibrated to register activity in various spectral frequency bands.

In effect, the Bragg cell allows for near-instantaneous sorting of complex and overlapping microwave signals that arise out of dogfight furballs and dense EMF environments. Attempting to use ultra-fast high resolution ADCs (Analog to Digital Converters) would create an intolerable lag time due to propogational delays and subsequent DSP (Digital Signal Processing) computational cycle times. Instead, each sensor in the real-time analyser's optical detector array is able to promptly indicate activity in such critical frequency bands as missile targeting lock-ons and FoF (Friend or Foe) discrimination systems.

This technology is decades old but continuing advances in materials purity and detector sensitivity keeps it at the forefront of useful methodologies. Perhaps someone else here is better versed and can correct any errors in my description.

Posted by Zenster">Zenster 2007-10-12 19:46|| 2007-10-12 19:46|| Front Page Top

#2 I had a few corrections ~~I'm lying~~ but for expedience ~~I don't know what I'm talking about~~, I can accept Zen's basic premise

Posted by Frank G">Frank G 2007-10-12 19:57|| 2007-10-12 19:57|| Front Page Top

#3 Frank, What's even scarier is that I understood some of it.

Posted by Nimble Spemble 2007-10-12 20:09|| 2007-10-12 20:09|| Front Page Top

#4 I did too, but don't know enough to know if he's blowing smoke - I don't think so, LOL... :-)

Posted by Frank G">Frank G 2007-10-12 20:15|| 2007-10-12 20:15|| Front Page Top

#5 A simplified version:

Consider a prism with a krypton white-light laser being shone through it. Imagine that different colors in the white light source represent different signal carriers, like communications, guidance, and other signals. On the prism's other side is an array of photodetectors spaced precisely so that each one will detect a separate color in the ROYGBIV spectrum.

This is what the Bragg cell does. The difference being that piezo-transduced microwaves actively alter the acousto-optic crystal's refractive index and steer the light beam towards one or another photoreceptor in the array. Some of the earliest applications for Bragg cells were in laser printers. The problem with them is that relative large amounts of change in driving energy don't produce much angular deflection. It was only with the advent of truly compact high efficiency photosensors that these analysers didn't require relative long "throw" lengths between the Bragg cell and the detector array. Long throw lengths required large bulky assemblies that were more sensitive to vibration and G-force related structural deflection (dimensional stress).

Major advances in crystal growth have allowed for other even more exotic crystals such as tellurium oxide, as shown in the following figure. It illustrates how an acousto-optic spectral filter works:

At the very bottom, please note the radio frequency input. This drives a piezoelectric transducer that introduces mechanical stress into the crystal thereby altering its refractive index. This, in turn, alters the path of light travelling through the crystal according to the wavelength of that illumination. In effect, giving you a tunable optical filter. These are used in making ultra-compact spectrophotometers the size of a matchbox that used to take up an entire bench top with their mirrors, gratings and prisms.

If the RF input corresponds to your external microwave environment, then the scattering of the transverse light source will be proportionally directed towards various locations on the crystal's other side. By calibrating the crystal with known RF frequency sources, the detectors can be positioned in correspondence with where expected in-flight RF frequencies need to be detected.

Posted by Zenster">Zenster 2007-10-12 21:50|| 2007-10-12 21:50|| Front Page Top

#6 I saw this in the local paper this morning http://www.timescall.com/news_story.asp?ID=3967 and there were a couple of things I found interesting: the comment "... was purchased by Yubong Hahn..." makes me interested in tracking down exactly who or what Yubong Hahn is and the comment "based in Lafayette, with offices in Korea and Russia" makes me wonder what the Korean and Russian offices do.

They may just be manufacturing plants given Zenster's description of their products. But although no one big thing caught my eye, all the little things made me go "Hmmm".

Posted by mft 2007-10-12 22:16|| 2007-10-12 22:16|| Front Page Top

23:59 JosephMendiola
23:40 Sock Puppet of Doom
23:31 Broadhead6
23:28 Swamp Blondie
23:19 Anonymoose
23:11 Broadhead6
23:07 Sherry
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22:27 twobyfour
22:26 mft
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22:06 DMFD
21:50 Zenster
21:28 JosephMendiola
21:15 wxjames
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