The physical limits of fiber optics

I might assume that this is similar to that of a uWave wave guide.

The wider dimension has to exceed 1/2 wave length, so

for visible light, this works out to be 275nm.

Actually, its probably worse due to the fact that your biological tubes

are not good reflectors.

They are dielectric discontinuities / poor reflectors.

The angle of incidence for TIR to take place

limits what goes on in the tube, so

its probably a lot larger than 1/2 wave in width.

Single mode comm grade optical fiber is in the 60um area for 1.5u IR.

Hi you are absolutely right.

Only in the infrared and visible it is preferred to take the circular waveguides.

These have 4µm diameter for the visible.

So with xrays there will be smaller diameters. (See SPIE.org for literature)

These diameters will enable longdistance waveguides (more than 100km without repeater in the IR).

Some electromagnetic radiation is leaking from smaller holes so light can be transmitted through holes of a few nanometer size but only very limited energy.

This is used in the optical nearfield microscope where optical lateral resolution can be much better than the wavelength.

RHABE

The wider dimension has to exceed 1/2 wave length, so

for visible light, this works out to be 275nm.

Do you have to reduce the wavelength by a factor n, the index of refraction?

The limiting wavelength to diameter ratio is; pie : 1 = 3.14... The wavelength can then be lower than the limit.