Optical fiber is the backbone of modern networks — from the internet backbone that connects cities to the short links inside data centers. Optical Fiber comes in two main categories: singlemode and multimode.
Singlemode fiber features a small core diameter of just 9 µm and allows only one mode of light to propagate. This design minimizes signal loss and supports high-bandwidth applications over long distances. Multimode fiber has a larger core (either 50 µm or 62.5 µm) with multiple light modes. It’s ideal for shorter distances.
What Is Optical Fiber?
Optical fiber is a thin, flexible strand of very pure glass (sometimes plastic) that carries data as pulses of light. Think of it as a tiny, loss‑resistant “light pipe.” Fibers are used everywhere: internet and telecom links, medical imaging, and industrial sensors.
An optical fiber consists of three primary components:
- Core — the center where light travels (made of silica or plastic).
- Cladding — a layer around the core with lower refractive index that keeps light inside via total internal reflection.
- Coating (buffer) — a protective plastic layer that shields the glass from damage and moisture.
Core Types of Optical Fiber
You’ll find two core types of optical fiber: single-mode and multimode. Each type serves distinct applications based on its light transmission characteristics.
Single‑Mode Optical Fiber (SMF)
Very small core (~8–10 µm). Carries one light path (mode). It minimizes dispersion and supports very long distances and very high speeds. Ideal for long‑haul telecom and backbone links.
Multimode Optical Fiber (MMF)
Larger core (50 µm or 62.5 µm). Carries multiple modes of light, which can cause modal dispersion and limits distance. MMF is cheaper to terminate and works well for shorter runs like inside buildings or data centers.
| Feature | Single-Mode Fiber | Multimode Fiber |
| Core diameter | 8–10 μm | 50–62.5 μm |
| Light modes | Single mode | Multiple modes |
| Bandwidth | Very high (up to 100,000 GHz) | Lower bandwidth |
| Distance | Long (tens of kilometers) | Short (up to 1 km approx.) |
| 应用 | Long-haul, high-speed telecom | Short-range, LANs, data centers |
Multimode categories (OM1 → OM5) Quick Guide
Multimode fibers are graded as OM1–OM5. Higher OM numbers mean better performance (higher bandwidth or wavelength flexibility).
| Fiber Type | Core Size (µm) | Bandwidth (MHz·km @850nm) | Max Data Rate | Max Distance (10 Gbps) | Attenuation (dB/km) |
| OM1 | 62.5 | 200 | 10 Gbps | 300 m | 3.5 |
| OM2 | 50 | 500 | 10 Gbps | 550 m | 3.0 |
| OM3 | 50 | 2000 | 40 Gbps | 1000 m | 3.0 |
| OM4 | 50 | Higher than OM3 | 40-100 Gbps | 1500 m | 3.0 |
| OM5 | 50 | Wideband (850-950 nm) | 100 Gbps | Similar to OM4 | 3.0 |
OM1 and OM2
OM1 fibers feature a 62.5-micron core diameter with 200 MHz·km bandwidth at 850 nm wavelength. They support 10 Gbps data rates over distances up to 300 meters with 3.5 dB/km attenuation.
OM2 fibers reduce the core to 50 microns while increasing bandwidth to 500 MHz·km at 850 nm. They maintain 10 Gbps transmission but extend the maximum distance to 550 meters with improved 3.0 dB/km attenuation.
OM3 and OM4
OM3 fibers introduced laser-optimized 50-micron core technology in 2003, achieving 2000 MHz·km bandwidth at 850 nm. They support 10 Gbps over 1000 meters and 40 Gbps up to 400 meters.
OM4 fibers, standardized in 2009, provide enhanced performance with higher bandwidth than OM3. They enable 10 Gbps transmission up to 1500 meters and 40 Gbps operation to 550 meters using engineering rules.
OM5 Wideband Multimode
OM5 fibers, introduced in 2017, feature wideband multimode technology supporting multiple wavelengths from 850-950 nm. They enable wavelength division multiplexing (WDM) for higher aggregate bandwidth using fewer fibers.
OM5 supports duplex transmission at 100 Gbps using two to four wavelengths. These fibers maintain the 50-micron core diameter but optimize chromatic dispersion properties for longer wavelength operation. They are ideal for high-speed applications requiring multiple wavelength transmission.
Single-Mode Fiber Classifications: OS1 vs OS2
OS1 and OS2 fibers share a core diameter of 8–9 µm and a yellow jacket color, but they serve distinct purposes. OS1 fibers use a tight-buffered construction, making them suitable for indoor applications like data centers and campus networks.
They feature an attenuation of ≤1.0 dB/km at 1310 nm and support distances up to 10 km at speeds of 10 Gbps. OS2 fibers employ a loose-tube, gel-filled design for outdoor use, offering lower attenuation of ≤0.4 dB/km at 1310 nm and enabling transmission over 200 km at 100 Gbps.
Fiber Cable Construction: Tight-Buffered vs. Loose-Tube
Optical fiber cables primarily use two distinct construction methods, each optimized for specific environments and performance requirements.
Tight-Buffered Cable
Tight-buffered cables feature a 900 μm buffer coating that directly surrounds each fiber core. This design provides strong protection to the fiber core and cladding.
They’re ideal for indoor applications including LANs, office buildings, and short-distance telco local loops. OS1 single-mode fiber uses tight-buffered construction and supports data rates up to 10 Gbps over distances up to 10 km (6 miles).
Loose-Tube Cable
Loose-tube cables contain multiple 250 μm coated fibers inside large, rugged, oversized tubes that are either gel-filled or dry. The fibers “float” inside these tubes, allowing expansion and contraction with temperature changes while improving protection against moisture and physical stress.
You must use fan-out kits for termination due to the bare fiber ends. These cables are designed for outdoor, long-distance applications including telecom backbones, direct burial, and harsh environments. OS2 single-mode fiber uses a loose-tube design, supporting speeds up to 100 Gbps and distances up to 200 km (124 miles).
Key Performance Characteristics
You evaluate optical fiber performance using wavelength, bandwidth, attenuation, and dispersion metrics.
- Wavelengths: SMF commonly uses 1310 nm and 1550 nm for long distances. MMF typically uses 850 nm (and 1300 nm) for short links.
- Attenuation: Loss of signal per kilometer (dB/km). Lower is better. SMF has very low attenuation (≈0.2 dB/km at 1550 nm). MMF attenuation at 850 nm is higher.
- Dispersion: Causes pulses to spread and limits distance/speed. Modal dispersion dominates MMF; chromatic dispersion affects SMF at long distances and high bitrates.
Practical Guidelines for Choosing the Right Fiber Type
- Use single‑mode when you need long distances, future‑proofing for very high bandwidth, or when budget allows higher‑cost transceivers. Good for carrier networks, long backbone links, and data center interconnects.
- Use multimode for short runs inside buildings, within data centers, or campus LANs where transceiver cost and ease of use matter most. OM3/OM4 are excellent choices for modern data centers.
- Choose bend‑insensitive fibers (e.g., G657 variants for SMF) if you’ll route fiber in tight spaces or ducts.
Future-Proofing Your Network
- If your budget permits and you expect rapid growth or frequent upgrades, consider single‑mode for backbone routes — it has the longest useful life.
- For campus and in‑building links, OM4 (or OM5 when WDM is desirable) balances cost and upgradeability.
- Standardize connectors and testing procedures (loss budget, OTDR traces) so future moves/adds/changes are predictable.
Common mistakes to avoid
- Mixing fiber types without proper transceivers/adapters (e.g., blindly connecting SMF transceivers to MMF) — this can prevent links from working.
- Underestimating connector and patch‑panel loss when calculating budget.
- Choosing legacy OM1/OM2 for new, high‑speed installations — upgrading later is costly.
Seetronic optical-fiber recommendations
Seetronic’s optical-fiber range offers industrial-grade, low‑loss pre‑assembled cables, rugged IP65/67 stainless‑steel plugs & sockets (2‑ and 4‑channel), and useful accessories (dust covers, adapters, fan‑out kits) that map directly to common project needs.
View Seetronic Optical Fiber product details or request a custom quote.
Frequently Asked Questions
What are the main types of optical fibers?
The two main types are singlemode and multimode fibers. Singlemode fiber has a small core (8–10 µm) and supports long-distance, high-speed data transmission. Multimode fiber has a larger core (50–62.5 µm) and is ideal for shorter distances, such as within data centers or enterprise networks.
What is singlemode fiber used for?
Singlemode fiber is designed for long-distance, high-bandwidth applications. It supports speeds up to 100,000 GHz and is commonly used in telecommunications, backbone networks, and high-speed data links over distances of several kilometers or more.
What is multimode fiber used for?
Multimode fiber is best for short-distance applications, typically under 1 km. It is widely used in local area networks (LANs), data centers, and enterprise environments due to its lower-cost transceivers and easier light coupling compared to singlemode fiber.
What are OM1, OM2, OM3, OM4, and OM5 fiber types?
These are multimode fiber grades with different performance levels. OM1 and OM2 support up to 1 Gbps and are considered legacy. OM3 supports 10 Gbps up to 300m, OM4 extends this to 550m, and OM5 enables wavelength division multiplexing for higher bandwidths, supporting up to 100 Gbps.
What are OS1 and OS2 singlemode fibers?
OS1 and OS2 are singlemode fiber classifications. OS1 is tight-buffered for indoor use, with attenuation ≤1.0 dB/km. OS2 uses a loose-tube, gel-filled design for outdoor applications, offering lower attenuation (≤0.4 dB/km) and supporting longer distances—up to 200 km at 100 Gbps.
How does attenuation affect fiber performance?
Attenuation measures signal loss over distance. Lower attenuation means better performance. Singlemode fiber has very low attenuation (~0.2 dB/km at 1550 nm), ideal for long hauls. Multimode fiber has higher attenuation (~10 dB/km at 850 nm), limiting its use to shorter distances.
What is the difference between tight-buffered and loose-tube cables?
Tight-buffered cables have a protective coating around the fiber, making them suitable for indoor use. Loose-tube cables allow fibers to “float” inside tubes, providing better moisture and temperature resistance for outdoor and long-distance applications.
How do I choose the right fiber optic cable?
Consider distance, bandwidth, environment, and budget. Use singlemode for long-distance, high-speed needs. Choose multimode for shorter, cost-sensitive applications. Also evaluate specific requirements like jacket type, connectors, and future network upgrades to ensure optimal performance.
Why is fiber optic cable better than copper?
Fiber offers higher bandwidth, lower latency, and less signal loss over distance compared to copper. It supports faster data rates, is immune to electromagnetic interference, and provides a more future-proof solution for high-demand applications like cloud computing and telecommunications.
What is total internal reflection in optical fibers?
Total internal reflection is the principle that allows light to travel through the fiber core with minimal loss. Light reflects off the core-cladding boundary, enabling efficient data transmission over long distances at speeds close to the speed of light.
