Originally posted by Andrew Hamilton
That is very interesting.
I looked up Lithium niobate and found that it produces birefringence (or double refraction) that is proportional to the electric field it is exposed to (according to one website) thus it splits any ray of light into rays two rays of light when it refracts a ray of light.
But wouldn’t that mean that a lens made of this s ...[text shortened]... hus making it impossible to produce a single clear well focused image at the back of the camera?
Hang on; I just read at: http://en.wikipedia.org/wiki/Lithium_niobate
“…Lithium niobate has negative UNIAXIAL birefringence which depends slightly on the stoichiometry of the crystal and on temperature
…” (my emphasis)
So I looked up “UNIAXIAL” and got:
“…Having one direction along which double refraction of light does not take place…”
So this appears to answer my question -the answer being that ALL the light of a light ray of a given wavelength is NOT split into two but ALL of it is diffracted into the SAME direction.
But now I am confused; if there is “one direction along which double refraction of light does not take place” then in what sense is it “double refraction”!!!? -this appears to be a logical contradiction to me that makes me wonder if I have somehow completely misunderstood something here.
And what does the “negative” mean in the term “negative UNIAXIAL birefringence”?
I would also like to know what kind of voltage would be needed to change the refractive index of a refocusable lens made of Lithium niobate enough to have useful amount of refocusing? -I mean, are we talking about less than one volt or hundreds of volts or what?
And is there any good technical reason why refocusable lenses made of Lithium niobate are not used much (are any used at all?) other than problems with fabrication and manufacturing cost?