Ape has question. Ape understand not. How is HCF supposed to work from the physical standpoint? If you have a hollow core inside a fiber, the IOR of air < IOR of fiber, so no TIR is possible. Without TIR, the light will be refracting the shit out the air core.
You're right. TIR can't work here. Air core has lower index than glass cladding, so conventional guidance is physically impossible. HCF uses an entirely different mechanism.
The cladding isn't solid glass. It's a photonic crystal that is a periodic microstructure of glass and air holes. This periodicity creates a photonic bandgap: a range of wavelengths that physically cannot propagate through the cladding structure.
Think of it as the optical analog of an electronic bandgap in semiconductors. Just as electrons in the bandgap energy range can't travel through a crystal lattice, photons in the bandgap wavelength range can't enter the cladding.
The cladding becomes a perfect mirror for those wavelengths, trapping light in the hollow core.
So the guiding mechanism is not TIR (index contrast), but Bragg-like reflection from periodic structure.
Quick analogy: TIR is light bouncing off a water-air boundary naturally. Photonic bandgap is light trapped inside a tunnel lined with mirrors.
Ape has question. Ape understand not. How is HCF supposed to work from the physical standpoint? If you have a hollow core inside a fiber, the IOR of air < IOR of fiber, so no TIR is possible. Without TIR, the light will be refracting the shit out the air core.
I think this is a really great question.
You're right. TIR can't work here. Air core has lower index than glass cladding, so conventional guidance is physically impossible. HCF uses an entirely different mechanism.
The cladding isn't solid glass. It's a photonic crystal that is a periodic microstructure of glass and air holes. This periodicity creates a photonic bandgap: a range of wavelengths that physically cannot propagate through the cladding structure.
Think of it as the optical analog of an electronic bandgap in semiconductors. Just as electrons in the bandgap energy range can't travel through a crystal lattice, photons in the bandgap wavelength range can't enter the cladding.
The cladding becomes a perfect mirror for those wavelengths, trapping light in the hollow core.
So the guiding mechanism is not TIR (index contrast), but Bragg-like reflection from periodic structure.
Quick analogy: TIR is light bouncing off a water-air boundary naturally. Photonic bandgap is light trapped inside a tunnel lined with mirrors.
Nice, thank you, great write-up for lesser minds! Does $GLW has a moat here? Or is it still up for grabs with $NOK, for instance?