Refractive Index Explained: Basics, Plots, and Database

This page covers the basics of refractive index, including plots of the refractive index of silicon and glass. It also mentions a refractive index database link.

Refractive index is the ratio of the speed of light in free space to the speed of light within the medium being measured. The refractive index value is always greater than or equal to one.

Refractive Index, $n = c/v$

Where:

• $n$ is the refractive index
• $c$ is the speed of light in a vacuum
• $v$ is the speed of light in the medium

Total Internal Reflection

Total internal reflection, according to Snell’s Law, is defined as follows:

$n_1 * sin(φ_1) = n_2 * sin(φ_2)$

Where:

• $n_1$ is the refractive index of the first medium
• $n_2$ is the refractive index of the second medium
• $φ_1$ is the angle of incidence
• $φ_2$ is the angle of refraction

If $φ_2 = 90$ degrees, then internal reflection takes place.

$φ_1 = sin^{-1}(n_2/n_1)$

Total internal reflection will occur if the angle of incidence ($φ_1$) is greater than or equal to the critical angle ($φ_c$):

$φ_c = sin^{-1}(n_2/n_1)$

All information within an optical fiber is transmitted using the principle of total internal reflection. Furthermore, all information is carried within the core of the fiber. The cladding does not support any information transmission.

Refractive Index Plots

Here are plots illustrating the refractive index of glass and silicon:

Image alt: refractive index of glass

Image alt: refractive index of silicon

The figures above show how the refractive index varies with wavelength.

The graph for glass (optical glass type: BK7) shows the refractive index varying between approximately 1.56 and 1.48, depending on the wavelength. The graph for silicon shows the refractive index varying between approximately 1.4 and 1.55.

Refractive Index Database

The refractive index data presented here is derived from the “refractiveindex.info” website. This website provides a database for various glass types, including:

• Optical (BK7, BAF10, BAK1, FK51A, LASF9, SF5, SF10, SF11, etc.)
• Multipurpose (fused silica, soda lime, schott)
• Display glass
• Infrared glass
• Ophthalmic glass
• And more