Working Principle of Fiber Optics

The working principle of fiber optics is based on total internal reflection of light.

01 Fiber Optic Dispersion

Causes of Dispersion

In fiber optics, the light signal consists of various components. Due to the different propagation speeds of signal frequency components or mode components, a delay difference occurs among them after transmitting through the fiber optic for a certain distance. This delay difference leads to waveform distortion and pulse broadening, known as fiber optic dispersion.

Impact of Dispersion

The presence of fiber optic dispersion causes distortion and broadening of transmitted signals, resulting in inter-symbol interference. To ensure communication quality, it is necessary to increase the inter-symbol interval, i.e., reduce the signal transmission rate, limiting the communication capacity and transmission distance of fiber optic systems.

Types of Dispersion

Dispersion in fiber optics can be classified into mode dispersion, material dispersion, waveguide dispersion, and polarization dispersion.

02 Fiber Optic Loss

Fiber optic loss refers to the decrease in optical power of a light signal after transmission through the fiber optic due to factors such as absorption and scattering.

Absorption Loss

Intrinsic absorption: inherent absorption of fiber optic material itself. Impurity absorption: absorption of light by impurities in the fiber optic.

Scattering Loss

Linear scattering; non-linear scattering; imperfect structure scattering.

Other Losses

Microbending loss, etc.

Fiber optics are flexible and can be bent. However, excessive bending alters the transmission path by converting transmission modes into radiation modes. This causes some light to penetrate the cladding or leak out through the cladding, resulting in loss. Bending with a radius greater than 5-10 cm produces negligible loss.

03 Advantages of Fiber Optic Communication

1. 1.Enormous Communication Capacity: A single fiber optic can transmit 10 billion voice channels simultaneously. Successful experiments have achieved simultaneous transmission of 500,000 voice channels, surpassing traditional coaxial cables, microwaves, etc., by several thousand to several hundred thousand times.

2. 2.Long Relay Distance: Fiber optics have an extremely low attenuation coefficient. With appropriate optical transmission, reception devices, optical amplifiers, forward error correction, and RZ coding modulation technology, relay distances exceeding several thousand kilometers can be achieved, compared to 1.5 km for traditional cables and 50 km for microwaves.

3. 3.High Security: Fiber optics offer strong resistance to electromagnetic interference and industrial interference due to their quartz-based composition. The transmission of light signals in fiber optics is unaffected by electromagnetic fields, making it resistant to electromagnetic and industrial interference. The signal transmitted in fiber optics is less susceptible to eavesdropping, enhancing security.

4. 4.Versatility: Fiber optics are immune to external strong electromagnetic field interference, corrosion-resistant, and more.

5. 5.Compact Size and Lightweight

6. 6.Abundant and Cost-Effective Raw Materials: Fiber optics, composed mainly of quartz, are non-conductive and not influenced by electromagnetic fields, making them highly resistant to electromagnetic and industrial interference. This characteristic makes signals transmitted through fiber optics difficult to eavesdrop, enhancing security.

7. 7.Small Volume and Light Weight: Fiber optics are compact and lightweight, providing ease of installation and handling.

8. 8.Abundant and Inexpensive Raw Material Sources: The primary component of fiber optics is quartz, which is readily available and cost-effective.