# Should optical cables be water tight? Geometric optics

• carnivalcougar
In summary, the physical principle of total internal reflection is used in optical cables to allow light to travel through the core of the cable without passing through the cladding. The critical angle of incidence for light passing from glass to air and glass to water are calculated to be 41.8° and 62.457° respectively. Based on this, it can be concluded that optical cables should be water tight to ensure efficient transmission of light through the core.
carnivalcougar

## Homework Statement

Explain the physical principle of total internal reflection used by optical cables. Calculate the critical angle of incidence that corresponds to a refracted angle θair = 90
Next, calculate the critical angle for a bare glass fiber submerged in water nH2O = 1.33.

Should optical cables be water tight?

n1sinθ1=n2sinθ2

## The Attempt at a Solution

2. As the angle of light passing from glass to air increases with respect to the normal line, the refracted light bends further away from the normal line. At the critical angle, the refracted light will not pass through the glass but will travel 90° along the surface of the glass. An optical cable works because light travels through the core of the cable which has a higher index of refraction than the cladding surrounding the core. The angle of light is always greater than the critical angle so the light is always reflected from the cladding. This allows the light to travel great distances.
Θcr of θair = 90° is sin-1 (nr/ni) = sin-1 (1/1.5) = 41.8°
Θcr of θH2O = 90° is sin-1 (nr/ni) = sin-1 (1.33/1.5) = 62.457°

I'm just having trouble with the last question. I think that optical cables should be water tight because the critical angle for glass to water is greater than that of glass to air. This means that the light will have total internal reflection at angles greater than 41.8 which is easier to achieve than angles greater than 62.457.

That sounds right to me.

1 person

## 1. Should optical cables be water tight?

Yes, optical cables should be water tight. Water can cause damage to the delicate components inside the cable and affect the transmission of light signals. Therefore, it is important for optical cables to be water tight in order to ensure efficient and reliable data transfer.

## 2. Why is it important for optical cables to be water tight?

Optical cables contain glass or plastic fibers that transmit light signals. Water can seep into the cable and create small cracks or bubbles, which can interfere with the transmission of light. This can lead to loss of data or a decrease in signal strength, affecting the overall performance of the cable.

## 3. What happens if optical cables are not water tight?

If optical cables are not water tight, water can seep into the cable and cause damage to the internal components. This can result in interruptions or disruptions in data transfer, leading to slow or unreliable connections. In extreme cases, it can even cause the cable to fail completely.

## 4. Can optical cables be made water tight?

Yes, optical cables can be made water tight. Manufacturers use various methods such as tight enclosures, water-resistant materials, and protective coatings to ensure that the cables are water tight. Some cables also come with waterproof connectors to prevent water from entering at the connection points.

## 5. Are all optical cables water tight?

No, not all optical cables are water tight. Some cables are designed for indoor use and may not have the necessary properties to make them water tight. It is important to check the specifications of the cable to ensure that it is suitable for use in wet or outdoor environments.

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