OM1 vs OM2 vs OM3 vs OM4 vs OM5 Fiber: Multimode Fiber Types Explained

Source: Dev.to

Basics of Multimode Fiber: Why Need to Divide OM Levels?

In short‑distance high‑speed communication scenarios such as data centers and local area networks, multimode optical fiber plays an important role due to its low cost and easy installation. In the face of ever‑escalating bandwidth requirements, multimode optical fiber is also constantly improving. The differences and specific application scenarios of different multimode optical fibers are introduced in detail below.

Core Principles and Optical Signal Transmission Mechanism

The core characteristic of multimode fiber is that the core is thicker. The core diameter of multimode optical fibers is usually 50 µm or 62.5 µm. As the name suggests, multimode fiber allows multiple optical transmission modes to exist simultaneously. When the light beam emitted by the source enters the fiber core, rays with different incident angles propagate along different paths. This multimode transmission is significantly different from the single‑path transmission of single‑mode fiber and introduces the technical challenge of modal dispersion.

Modal Dispersion and Bandwidth Limitation

Modal dispersion is the primary factor that limits the performance of multimode fibers. Because light enters at multiple angles, different propagation modes travel at different axial velocities. As these modes arrive at the far end at different times, pulse broadening and signal distortion occur, as shown in the figure below.

Taking the early OM1 fiber as an example, its bandwidth‑distance product at 850 nm is only 200 MHz·km, which cannot meet the requirements of modern 10 Gigabit Ethernet. Subsequent OM grades have gradually improved bandwidth performance by optimizing the fiber core structure. The commonly used OM4 fiber now has a bandwidth‑distance product of 4700 MHz·km at 850 nm, supporting 10 Gbps signal transmission over 550 m.

OM Grading Standard

The classification of OM levels originates from the TIA/EIA‑492 standard system and is updated as optical communication technology evolves.

Major breakthroughs

• OM2 – reduced core to 50 µm and optimized the gradient‑index profile, increasing the 850 nm bandwidth to 500 MHz·km.
• OM3 – matched the narrow spectral characteristics of VCSEL sources, enabling 10 Gbps transmission.
• OM4 – further refined preform manufacturing and coating materials, nearly doubling bandwidth over OM3.
• OM5 – designed for future high‑speed scenarios, supports short‑wave division multiplexing (SWDM) across 850‑953 nm, allowing four parallel channels on a single fiber.

Full Analysis of Technical Parameters from OM1 to OM5

OM1 Fiber Optic

• Core / Cladding: 62.5 µm / 125 µm (step‑index or gradient)
• Typical Light Source: LED
• Bandwidth: 100 Mbps at 850 nm (short distances)
• Limitations: Low bandwidth, limited to 100 Mbps; 1300 nm use is impractical due to LED inefficiency.

OM2 Fiber Optic

• Introduced: 1998
• Core / Cladding: 50 µm / 125 µm (gradient‑index)
• Bandwidth Improvement: ~40 % reduction in modal dispersion vs. OM1
• Performance: 1 Gbps up to 550 m at 850 nm
• Typical Applications: Data‑center distribution rooms, campus backbone links.

OM3 Fiber Optic

• Key Feature: “Effective Mode Bandwidth” concept; optimized for VCSEL sources.
• Performance: 10 Gbps up to 300 m at 850 nm.
• Impact: Enabled the 10 Gbps era in data‑center interconnects.

OM4 Fiber Optic

• Enhancement: More precise preform manufacturing; 2.35× bandwidth of OM3.
• Performance:
  • 10 Gbps up to 550 m
  • 100 Gbps up to 150 m (vs. 100 m for OM3)
• Compatibility: Backward compatible with OM3, easing upgrades.

OM5 Fiber Optic

• Standardization: Proposed 2014, ANSI/TIA‑492AAAE (2016), ISO/IEC naming.
• Wavelength Range: 850 nm – 953 nm (supports SWDM).
• Capability: Single‑fiber 4‑channel wavelength transmission, reducing cabling density.
• Mechanical Improvement: Minimum bend radius reduced from 15 mm to 7.5 mm, suitable for high‑density environments.