Data is sent in a fibre optic cable using light pulses.
Fibre optic cables transmit data much like electrical cables, but instead of electrical signals, they use light. This method offers several advantages, including higher bandwidth and resistance to electromagnetic interference. Here's a breakdown of the process:
The Process: From Electrical Signal to Light and Back
The transmission of data through fibre optic cables involves several steps:
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Conversion to Light: At the source, a transmitter converts electrical signals representing data (e.g., voice, video, or computer data) into light pulses. This conversion is typically performed by a semiconductor device, such as a laser diode or an LED (Light Emitting Diode). Laser diodes are generally used for longer distances and higher bandwidth applications due to their more focused and powerful light output.
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Light Propagation Through the Fibre: These light pulses are then injected into the core of the optical fibre. The fibre itself is designed to guide the light over long distances with minimal loss of signal. This is achieved through total internal reflection, where light striking the boundary of the core and cladding (an outer layer of glass with a lower refractive index) is reflected back into the core. This process allows the light to travel along the fibre, even when it's bent or curved.
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Reception and Conversion Back to Electrical Signals: At the receiving end, a receiver detects the light pulses and converts them back into electrical signals. A photodiode, a semiconductor device sensitive to light, is commonly used for this purpose. When light strikes the photodiode, it generates an electrical current proportional to the intensity of the light.
Types of Light Used
- Infrared Light: Fibre optic communication typically uses infrared light, which has a wavelength longer than visible light. This is because optical fibres exhibit lower attenuation (signal loss) at certain infrared wavelengths. Common wavelengths used include 850 nm, 1300 nm, and 1550 nm.
Advantages of Using Light Pulses
- High Bandwidth: Light has a very high frequency, allowing it to carry vast amounts of data. This translates to much higher bandwidth compared to traditional electrical cables.
- Low Signal Loss: Optical fibres have very low attenuation, meaning the signal can travel much farther without needing to be amplified.
- Immunity to Electromagnetic Interference: Light is not affected by electromagnetic fields, making fibre optic cables immune to interference from electrical equipment.
- Security: Fibre optic cables are more secure than electrical cables because it is difficult to tap into them without disrupting the signal.
- Size and Weight: Fibre optic cables are typically smaller and lighter than comparable electrical cables.
Summary
In essence, data transmission via fibre optic cables relies on converting electrical signals into light pulses, guiding these pulses through the fibre using total internal reflection, and then converting them back into electrical signals at the receiving end. This approach offers significant advantages in terms of bandwidth, distance, and immunity to interference.
