Definitions of 850nm and 1310nm

Definitions of 850nm and 1310nm

The modal characteristics of 50nm and 1310nm wavelengths in optical fiber transmission are analyzed, clarifying that 850nm is typically used for multimode fibers (such as OM1/OM2/OM3), while 1310nm is mainly used for single-mode fibers (such as G.652/G.657). The selection criteria for different wavelengths in communication systems are explained by analyzing the correspondence between wavelength and fiber type, transmission principles, and typical application scenarios.

I. Fiber Mode Characteristics at 850nm and 1310nm

1. 850nm: The Mainstream Wavelength for Multimode Fiber

- Specific Value: 850nm is the typical operating wavelength for multimode fiber (MMF). Common fiber types are OM1 (62.5/125μm), OM2/OM3/OM4/OM5 (50/125μm).

- Professional Reference: According to ISO/IEC 11801 and TIA-492AAAC standards, the bandwidth of the 850nm window can reach 1 GHz·km (OM3) or 4.7 GHz·km (OM5).

- Explanation of Principle: Due to the short wavelength of 850nm, the propagation path of light within the fiber core varies greatly, easily exciting multiple modes (i.e., multimode transmission), making it suitable for short-distance, high-speed communication (such as data centers).

2. 1310nm: The Standard Wavelength for Single-Mode Fiber

- Specific Value: 1310nm is the zero-dispersion wavelength for single-mode fiber (SMF). Typical fibers are G.652D (mode field diameter 9.2μm) and G.657 (bending-resistant).

- Professional Reference: ITU-T G.652 specifies a dispersion coefficient of ≤3.5 ps/(nm·km) at 1310nm, suitable for long-distance transmission.

- Explanation of Principle: The 1310nm wavelength is relatively long, supporting only a single fundamental mode transmission (single-mode), avoiding multimode dispersion problems, making it suitable for metropolitan area networks or backbone networks.

II. Extended Analysis: Wavelength and Fiber Matching Logic

1. Why Does Wavelength Affect Modes?

- The normalized frequency (V-number) of the fiber determines the number of modes: the formula is V = 2πa/λ·NA (where a is the core radius and NA is the numerical aperture). 850nm, due to its small λ and large V-number (V > 2.405), allows multimode; 1310nm, due to its large λ and small V-number (V < 2.405), only supports single-mode.

2. Comparison of Other Common Wavelengths

- 1550nm: The second window for single-mode fiber, with lower loss (0.2 dB/km), used for ultra-long distances (such as submarine cables).

- 1300nm vs 1310nm: Often used interchangeably in industry terminology; actual technical documents use 1310nm as the standard (ITU-T standard).

III. Application Scenarios and Selection Recommendations

1. Typical Applications of 850nm Multimode Fiber

- Short-distance, high-speed: e.g., data center 40G/100G SR4 (OM3/OM4 transmission 70-100 meters).

- Cost-priority: Multimode fiber transceivers are cheaper than single-mode ones.

2. Typical Applications of 1310nm Single-mode Fiber

- Long-distance, low-power: e.g., telecommunications access networks (GPON uplink wavelength 1310nm, transmission 20 km).

- Future expansion: Single-mode fiber is compatible with WDM technology, supporting capacity upgrades.

Summary: The choice between 850nm and 1310nm depends on distance, bandwidth, and cost. Multimode fiber (850nm) is suitable for short-distance, cost-effective scenarios, while single-mode fiber (1310nm) is the inevitable choice for long-distance transmission.