That sounds sort of like what they must have been doing.

But, they were quite clear that it was a "Quartz" thermometry
unit, and that the crystals were quartz.

And, this was before solid state IR laser diodes, around 1982.
Each temperature measuring module was plug in, and about 3/4 inch
by 5 inches, by 8 inches in size... maybe a little smaller.

Whatever they did was stable, needed no alignment when the plugins
were moved in the chassis, and had no external adjustments.

-Chuck Harris

Attila Kinali wrote:
On Sun, 20 Jul 2014 15:57:24 -0400
Chuck Harris <[email protected]> wrote:

I initially thought that it might be a transmission sort of effect, where
the light intensity changed with temperature, but its total lack of sensitivity
to being in a liquid, kind of makes that unlikely.

Nope, it's a path length difference system.
There is a small, temperature dependend crystal at the tip.
The device measures the optical length of this crystal.

See: http://www.emeraldinsight.com/content_images/fig/0870260309013.png

I'm sure there are other ways as well, like using distributed fiber
gratings (a change in length means a change in "resonant" frequency/wavelength)
but i have no references for such (though, i haven't searched either)

                        Attila Kinali

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