There are no industry standards for measuring light transmission of a completed fiber optic part.
The amount of transmitted light is influenced by many factors. Typical variables are the types of glass used, the resulting acceptance angle, the purity of each glass, the quality of the fused interface between the core and the clad, the quality of end finishing and part assembly (How tight or loose the fiber pack is).
Consequently, the customer and the vendor should work together to define the requirements and the process used to test and inspect parts. Fiberoptics Technology has been working this way for over 40 years; continuously developing new methods of qualification based on the application. Upon request, we will furnish a transmission curve for each part shipped to validate efficiency.
Be aware of exaggerated claims for light transmission and use the following facts to make an informed decision:
Single Fiber Losses
If you could focus all transmitted light directly on the core of the fiber, a single, perfectly polished fiber starts with a theoretical transmission efficiency of about 92%. Fresnel losses account for 4% at each end.
What are Fresnel Losses?
Light striking the input surface of the fiber will be reflected, rather than continuing through the fiber, even though the incidence angle is within the acceptance angle of the fiber. This phenomena is caused by a difference in refractive indices (light traveling in air with one refractive index, meets the core glass surface, with a different refractive index).
In addition, because light is typically focused on the surface area of the entire fiber, we should also account for cladding losses.
What are Cladding Losses?
Two separate glass types and glass quality are used to manufacture fiber. Core glass is designed to transmit light, while the cladding glass, made to have a different refractive index, is designed to keep the light ray from leaving the fiber once it enters. Cladding glass is not designed to transmit light, so it has a very high attenuation rate. Cladding glass makes up about 15-17% of the total cross sectional area of a fiber.
Very few industrial fiber optic applications use a single fiber. Most customers require a component made from a “bundle” of fibers in a specific configuration. This bundle also has characteristics which contribute to losses.
What are Bundle Losses?
As glass fibers are actually cylinders, when they are grouped together to form a bundle, a space is created between cylinders. Known as interstitial spacing, this wasted area accounts for 9-11% of the total bundle area.
Therefore, a perfectly constructed fiber bundle (no skew, perfectly packed and polished) starts with a transmission efficiency of about 64-68%% (8% fresnel loss, 15-17% cladding loss, 9-11% interstitial spacing loss. When you add in manufacturing process, the maximum practical transmission efficiency is about 60%, before considering attenuation loss. To use this calculator, you have the freedom to type in a new efficiency value if you desire.
The best way to determine efficiency is to test the actual part. If you need accurate information, let us know the size and length of the bundle you are considering. We’ll evaluate performance and supply a curve.
There are no industry standards for measuring light transmission of a completed fiber optic part. Consequently, the customer and the vendor should work together to define the requirements and the process used to inspect the parts.