OM stands for Optical Multimode, a specific designation used for fiber optic cable specifications. It denotes a type of optical fiber primarily designed for shorter-distance data transmission within buildings, data centers, and local area networks (LANs).
Understanding OM Fiber Optic Cable
Fiber optic cables are categorized into different types based on their core diameter, light source, and performance capabilities. OM is one such designation for multimode fiber, distinguishing it from OS (Optical Singlemode) fiber. The core distinction lies in how light travels through the fiber:
- Multimode Fiber (OM): Has a larger core diameter (typically 50 or 62.5 micrometers), allowing multiple light rays (modes) to travel through it simultaneously. This larger core makes it easier to couple light into the fiber using less expensive light sources like LEDs or Vertical Cavity Surface Emitting Lasers (VCSELs). However, due to modal dispersion (light rays traveling different paths and arriving at slightly different times), multimode fiber is limited in bandwidth and distance compared to singlemode fiber.
- Singlemode Fiber (OS): Has a much smaller core diameter (typically 8-10 micrometers), allowing only a single path or "mode" of light to propagate. This eliminates modal dispersion, enabling higher bandwidth and significantly longer transmission distances, often used for long-haul networks and high-speed data links over many kilometers. Singlemode fiber typically uses laser diodes as light sources.
The Significance of OM Numbers
The letters "OM" are always followed by a number (e.g., OM1, OM2, OM3, OM4, OM5). These numbers are critical as they denote different generations and performance specifications of multimode fiber. Each OM standard is designed to support various data rates, wavelengths, and transmission distances, along with specific attenuation characteristics.
As the numbers increase, the fibers generally offer higher bandwidth, lower attenuation, and support faster data rates over longer distances, primarily due to improvements in the fiber's manufacturing and optimization for laser-based light sources (VCSELs).
Here's a breakdown of common OM types:
| OM Type | Core Diameter (µm) | Primary Light Source | Common Applications & Distances (e.g., 10GbE) | Key Characteristics |
|---|---|---|---|---|
| OM1 | 62.5/125 | LED | 100 Mbps (2 km), 1 GbE (275 m), 10 GbE (33 m) | Older standard, less common for new installations. Good for legacy low-speed applications. |
| OM2 | 50/125 | LED | 1 GbE (550 m), 10 GbE (82 m) | Also an older standard. Improved performance over OM1 but still limited for high-speed Ethernet. |
| OM3 | 50/125 | Laser-Optimized (VCSEL) | 10 GbE (300 m), 40 GbE (100 m), 100 GbE (100 m) | First "laser-optimized" multimode fiber. Widely used for data centers and campus backbones for 10 Gigabit Ethernet and higher. Aqua jacket. |
| OM4 | 50/125 | Laser-Optimized (VCSEL) | 10 GbE (550 m), 40 GbE (150 m), 100 GbE (150 m) | Enhanced OM3, offering extended reach for 10GbE, and supporting 40GbE and 100GbE over longer distances. Aqua jacket. |
| OM5 | 50/125 | Laser-Optimized (VCSEL) | 40 GbE (150 m), 100 GbE (150 m), 200/400 GbE (100 m) | Also known as Wide Band Multimode Fiber (WBMMF). Designed to support Shortwave Division Multiplexing (SWDM4) for multiple wavelengths, allowing more data over fewer fibers. Lime green jacket. |
Practical Applications and Benefits of OM Fiber
OM fiber is a popular choice for various applications due to its cost-effectiveness and ease of installation compared to singlemode fiber, particularly for shorter distances.
- Data Centers: Widely used for connecting servers, storage, and networking equipment within racks and across rows, supporting high-speed links like 10 Gigabit Ethernet (10GbE), 40GbE, and 100GbE.
- Enterprise Networks: Ideal for backbone connections within office buildings, campus networks, and local area networks (LANs) where distances are typically less than a few hundred meters.
- Storage Area Networks (SANs): Connecting storage devices and servers for high-speed data transfer.
Key Benefits:
- Cost-Effective: Multimode transceivers (like VCSELs) are generally less expensive than singlemode lasers, reducing the overall cost of network deployment.
- Easier Termination: The larger core size makes multimode fiber easier to work with, allowing for simpler and quicker termination and splicing processes.
- Higher Port Density: For shorter distances, multimode solutions can sometimes enable higher port densities in network equipment.
While OM fibers are excellent for short-to-medium distances, understanding the specific OM type is crucial to ensure compatibility with network equipment and to meet the required data rates and distance limitations of your application.
