Guide — Fiber Optics
What Is Fiber Optic? How Optical Fiber Works, Types and Uses
What fiber optic means, how light stays trapped inside an optical fiber, the main types of fiber, the wavelengths they use, how fiber compares with copper and where fiber optic cable is used in India.
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- STEP 1Laser turns data into light
- STEP 2Light enters the core
- STEP 3Cladding reflects it back
- STEP 4Detector reads the pulses
Fiber optic technology sends data as pulses of light through hair-thin strands of glass called optical fibers. Light stays inside each fiber's core by total internal reflection, so a fiber optic cable can carry huge amounts of data over long distances with very little signal loss and no electrical interference.
- Fiber optic links carry data as light, not electric current, through strands of glass called optical fibers.
- Light is trapped in the core by total internal reflection, because the cladding around it has a lower refractive index.
- Single-mode fiber, with a core of about 9 µm, serves long-distance telecom; multimode fiber serves short links in buildings.
- Modern single-mode fiber loses only about 0.2 dB per km at 1550 nm, so signals cross tens of kilometres without a boost.
- Most fiber damage in India comes from digging, so buried routes need good records and a survey before excavation.
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What is fiber optic?
Fiber optic technology sends information as flashes of light through glass strands as thin as a hair. An optical fiber is one strand; a fiber optic cable bundles many fibers inside protective layers. Indian telecom paperwork calls the cable OFC; our OFC full form and laying guide covers the civil work, while this page explains the technology.
How does fiber optic work?
Every fiber consists of a core and a cladding. The inner core carries the light. The cladding around it is glass with a slightly lower refractive index, the number that tells you how strongly a material slows light.
When light in the core meets the cladding at a shallow angle, it cannot escape. It bounces back into the core. This is total internal reflection, and it repeats along the whole fiber, so light stays trapped even when the cable bends gently.
For example, with a core index of 1.468 and cladding of 1.463, sin θc = 1.463 ÷ 1.468 ≈ 0.9966, so the critical angle is about 85°. Only light travelling within about 5° of the fiber axis is guided.
What is optical fiber, and what is inside a fiber optic cable?
What is optical fiber made of? Ultra-pure silica glass, drawn into a thread and coated with plastic:
| Layer | Typical size | Job |
|---|---|---|
| Core | About 9 µm | Carries the light |
| Cladding | 125 µm | Keeps light in the core |
| Coating | About 245 µm | Protects the glass |
| Tubes, strength member, jacket | Varies by cable | Protect against pulling, water and rodents |
What are the types of optical fiber?
Each type of fiber suits a different job. The main split is between single-mode and multimode fiber, where "mode" means a path the light can take down the core.
| Feature | Single-mode | Multimode |
|---|---|---|
| Core | About 9 µm | 50 or 62.5 µm |
| Light source | Laser | LED or VCSEL |
| Wavelengths | 1310 and 1550 nm | 850 nm |
| Reach | Long distance, tens of km per span | A few hundred metres at 10 Gbps |
| Jacket colour | Yellow | Orange, aqua or lime green |
| Used for | Telecom, FTTH, railways | Data centres, offices |
In multimode optical fiber, light takes many paths of different lengths, so pulses spread out. Modern multimode cable reduces this with graded index fiber, where the refractive index falls gradually from the centre outward. These laser-optimised types support higher bandwidths; OM3, for example, is rated for about 300 m at 10 Gbps. Single-mode fiber avoids the problem, so long routes in India use single-mode fiber to ITU-T G.652.D.
Which wavelengths do fiber optic links use?
Fiber systems use infrared light in three main windows:
- 850 nm – multimode, short links inside buildings.
- 1310 nm – single-mode, about 0.32–0.36 dB of signal loss per km.
- 1550 nm – single-mode, about 0.19–0.22 dB per km, used for long routes.
Every 3 dB lost halves the optical power, and receivers work within a set range of optical powers. With wavelength-division multiplexing (WDM), dozens of lasers at different wavelengths share one fiber, which is how backbone fiber cables transmit data at terabits per second.
How does fiber optic communication work end to end?
Every link uses the same chain for data transmission:
- Transmitter. A laser diode or LED turns the electrical signal into light pulses.
- Fiber. The pulses travel down the core by total internal reflection.
- Amplifier. On very long routes, optical amplifiers boost the light along the way.
- Receiver. A photodiode turns light back into an electrical signal.
Home FTTH systems such as GPON use a single fiber, with a different wavelength for each direction.
Fiber optic vs copper cable
Copper cables carry data as electric current. Like other electrical cables, copper wire picks up noise and loses signal quickly over distance.
| Point | Fiber optic cable | Copper cable |
|---|---|---|
| Capacity | Terabits per fiber with WDM | Limited |
| Distance | Tens of km | About 100 m for Ethernet |
| Interference | Immune | Picks up electrical noise |
| Lightning surges | Glass does not conduct | Can carry surges |
| Power to devices | No | Yes (PoE) |
Where is fiber optic used in India?
India had about 42 lakh route km of optical fibre by 2025, and about 6.98 lakh route km was laid in the three years to 31 March 2025. The main uses are:
- Telecom backbones between cities and data centres.
- Mobile towers, where 5G needs dense fiber backhaul; see our 5G fibre backhaul guide.
- Home broadband through FTTH.
- Rural broadband under BharatNet, with over 2.14 lakh gram panchayats service-ready by early 2025; see our BharatNet and FTTH guide.
- Railways and power utilities, for signalling, Kavach and substation control.
What are the disadvantages of fiber optic cable?
- Fragile glass: tight bends raise loss, and crushing can crack a fiber.
- Skilled work: splicing and testing need trained staff and costly tools.
- No power: a fiber cannot feed a camera or phone.
- Digging damage: most outages in Indian cities come from excavators and drills, not from ageing glass.
Who invented fiber optic communication?
In 1966 Charles K. Kao and George Hockham showed that glass fiber could carry signals if loss fell below 20 dB per km; fibers then lost about 1,000 dB per km. Corning reached that target in 1970, and Kao won the 2009 Nobel Prize in Physics. Fiber now carries more than 95% of the world's digital data.
How is buried fiber optic cable protected?
Protection means knowing where cable runs: HDPE ducts, accurate as-built drawings, the Call Before u Dig app, and a ground penetrating radar (GPR) survey before any new trench or bore. Mezux Touch, based in Faridabad, has done this work since 2003, including fiber corridors of 135 km in Bawana, 225 km in the NDMC area and 67 km in Okhla in Delhi. See our OFC route GPR survey and OFC works pages.
Sources
- Physics Today, 2009 Nobel Prize in Physics report, December 2009.
- IEEE Spectrum, "Optical Fiber Pioneer Shares Physics Nobel", October 2009.
- Nature, obituary of Charles Kao by Polina Bayvel, 2018.
- Prysmian and Datwyler G.652.D fibre data sheets.
- Network-Switch, multimode fiber standards OM1–OM5.
- Ministry of Communications reply in Parliament, 31 July 2025.
- Indian Infrastructure, "Fibre Vision", July 2026.
- Rajya Sabha reply on BharatNet, February 2025.
- Mezux Touch project records.
Capt. Manas Verma, Director – Sales, Mezux Touch Pvt. Ltd. He works at two very different altitudes. Above the clouds he is a Boeing 737 type-rated pilot with 500 hours in his logbook; on the ground he is the person contractors, network owners and builders call when they need to know what lies under a road before anyone digs it up. Flying taught him to trust a checklist over a guess, and that is the rule behind every survey he quotes: notice, scan, mark, then dig. Mezux Touch, based in Faridabad, has carried out GPR surveys and trenchless HDD works across India since 2003 with its own equipment and field teams. If he is not at 35,000 feet, he is probably talking about what sits two metres below your site.
More guides on fibre networks
Questions about fiber optic technology
Is fiber optic the same as OFC?
Yes, in practice. OFC means optical fibre cable, the cable that carries fiber optic signals; Indian tenders say OFC, product sheets often say fiber optic cable.
Why is fiber optic faster than copper?
Signals in both travel at a large fraction of the speed of light. Fiber wins because it carries far more data, loses less over distance and ignores electrical noise.
Can a fiber optic cable carry electricity?
No. Glass does not conduct, so fiber is safe near power lines and does not carry lightning surges into equipment.
Does bending damage a fiber optic cable?
Bending tighter than the minimum radius in the data sheet leaks light and can crack the glass. Bend-insensitive G.657 fiber suits tight corners in homes.
Does Mezux lay fiber optic cable?
Yes. Mezux Touch surveys fiber routes with GPR and, as a separate scope, lays duct, blows cable and splices fiber with its own crews.
Related survey categories
Fibre route survey in Indian cities
- Fibre route survey in Delhi
- Mumbai OFC route scanning
- Bengaluru duct route survey
- Chennai fibre corridor survey
- Hyderabad OFC route check
- Kolkata fibre route survey
- Pune duct route scanning
- Ahmedabad OFC corridor survey
- Gurugram fibre route check
- Noida OFC route survey
- Jaipur duct route survey
- Lucknow fibre corridor scanning
Send your fibre route for a survey quote
What to send for an exact quote
- Start and end points of the route, or a KML
- District and site type
- Survey type: standard or L-section
- When you want the crew on site
Minimum 4 km · GST extra · ₹1,00,000 project minimum outside Delhi NCR · 25–50% off above 100 km.
What happens next
- Scope check – we confirm route length, crossings and L-section need.
- Written quote – rate, slab, minimums, extras and a day-by-day programme.
- Mobilisation – our own crew and systems on the agreed date.
