078: Fiber optic cables – Overview

Fiber-optic cable (optical fiber) is a network cable used to carry the light signals along a transparent medium and consists of different parts:

1- Core:

• • Glass
  • Plastic

2- Cladding layer: glass with lower refractive index

Due to the lower refractive index of the outer layer (cladding) compared to the inner layer (core), light signal does not enter the cladding and reflects into the core back. Therefore, under the radiated angle, light signal travels along the cable.

Note1: This light is near infrared wavelength (850 to 1500 nm).

Note2: Light reflection takes place when the angle of incidence for light is greater than critical angle.

3- Protective layer:

• • Coating
  • Strengthening fibers
  • Cable jecket
    • PVC: Polyvinyl chloride
    • PE: Polyethylene
    • PUR: Polyurethane
    • PBT: Polybutylene terephthalate
    • PA: Polyamide

Fiber-optic cable types (ISO/IEC 11801):

1- SMF (Single mode fiber): Typically two fibers, diameter of 8.3 to 10 um (microns), wavelength of 1310 or 1550 nm

2- MMF (Multi mode fiber):  Typically two fibers, diameter of 50 to 100 um, wavelength of 850 or 1300 nm
Multi mode cables are manufactured in OM1, OM2, OM3, OM4 and OM5 types.

• OM1 (1989): orange jacket, LED source, 62.5 um diameter, 100 Mb/s to 10 Gb/s, Application up to 300 meters
• OM2 (1998): orange jacket, LED source, 50 um diameter, 1 to 10 Gb/s, Application up to 600 meters
• OM3 (2002): aqua jacket, VSCEL source, 50 um diameter,10 to 100 Gb/s, Application up to 300 meters
• OM4 (2009): aqua jacket, VSCEL source, 50 um diameter, 40 to 100 Gb/s, Application up to 550 meters
• OM5 (2014): lime green jacket, VSCEL source, 50 um diameter, 40 to 100 Gb/s

3- POF (Plastic optical fiber): Similar to multimode

Note3: Transmission rate in single mode is up to 50 times more than multi-mode.

Fiber optic system components:

1. Transmitter: Translate coded electronic pulse information to coded light pulses (light emitting diode (LED) / injection laser diode (ILD))
2. Receiver: light sensitive receiver convert the light pulses to electronic pulses back.

Note4: Converting of electronic pulse to light pulse means translation of 1 and 0 to ON and OFF.

So using light pulses in fiber-optic cables instead of electronic pulses in copper cables brings us a lot of advantages and some disadvantages as well. Below some of them can be enumerated:

Advantages:

• Longer distance of data transferring because of lower signal loss
• Higher carrying capacity (bandwidth) due to operation at higher data rates
• Higher speed (Up to gigabits)
• Immune to interference (resistance to electromagnetic noise)
• Occupies less space due to smaller dimensions

Disadvantages:

• Price of fiber cable and installation material - up to now - is higher than copper type.

Note5: Type designation code for fiber-optic cables according to VdS shows the exact specification of cables.