2025超高規模与人工智能數據中心模擬徑向（MFD）研究報告

Prologue This white paper continues our series aimed at clarifying the technical nuances of deployingsingle-mode optical fiber in modern, large-scale data centers. These environments include This installment focuses on Mode Field Diameter (MFD), a crucial yet often overlooked fibercharacteristic that influences installation, performance, and testing methodologies. By addressingMFD and the associated implications, the paper seeks to clarify fiber’s intricate properties to benefit Applications inside the data center: MFD plays a significant role in transmission efficiency at the1310 nm wavelength inside the data center. For more information on single-mode bend -Single Mode Fiber Bend Requirements in the Data Center This series will also explore the significance of micro-bending in deploying ultra-high fibercount cables. Contributors Keith SullivanDirector of Stategic Innovation, AFL Alan KeizerSenior Technology Advisor, AFL Ben AthertonTechnical Author, AFL Paige JamesDesign Manager, AFL David TanisSenior Product Line Manager, AFL What is MFD and Why Does It Matter? MFD represents the diameter of the area through which light propagates in a single-mode fiber. Step index single mode optical fibershowing core in cladding structure Specifically, MFD is the diameter of the circle at which the optical intensity has fallen from its peak valueat the center of the core to a prescribed minimum value of intensity (decreased by 1/e2, where e is thebase of the Natural Logarithm). The MFD of a fiber is somewhat larger than the physical core, increasing at longer wavelengths anddecreasing when the refractive index difference of the core and the cladding increases. For example, a MFD directly influences several key optical properties: Bend Sensitivity Larger MFD fibers are more sensitive to bending losses. In these fibers, the light is less tightlyconfined, resulting in more power being carried in the lower index cladding. This leads to greater Insertion Loss (IL) A small amount of optical power may be lost when joining or splicing fibers with different MFDs.This loss is small for fibers conforming to the ITU-T standards listed below. Testing Implications MFD differences can influence Optical Time Domain Reflectometer (OTDR) measurements, yieldingfalse or misleading increases in light power levels, referred to as “Gainers”, and conversely erroneousdecreases in light power levels, referred to as “Exaggerated Losses”. This discrepancy arises becauseOTDR measurements depend on backscattered light, which is determined by the material propertiesof the glass and the optical intensity. A smaller MFD leads to higher intensity and increased MFD has less impact on these properties: Dispersion MFD has no impact on polarization mode dispersion and has only a small influence on chromaticdispersion. Due to small values of both material and waveguide dispersion at this wavelength, Return Loss (RL) MFD difference at a connection does not contribute to RL. The very small amount of power loss dueto MFD difference at a joint dissipates in the cladding and not reflected. MFD in Fiber Standards Industry standards define allowable nominal values and tolerance ranges for MFD. Within a singlesupplier’s product range, MFD can vary within these tolerances. Key standards include: -ITU-T G.652 (Standard Single-mode Fiber)– Typical MFD: 8.6-9.5μm + 0.6μm.-ITU-T G.657 (Bend-insensitive Fiber)– MFD: range of nominal values 8.6-9.2μm, tolerance + 0.4μm. Internationally, IEC 60793 2 50 is aligned with ITUT- G.652. European national standards (e.g. the ENversions of IEC 60793) also reference these criteria. In the United States, TIA/EIA 60793 references the performance and characteristics defined by theITU-T documents. Telcordia GR 20 sets performance requirements for optical fiber that are consistent Cabled fiber standards referencing G.652 include ISO/IEC 11801 and TIA/EIA 568. MFD Mismatch: Homogeneous vs. When splicing or connecting fibers with different MFDs, an MFD mismatch occurs. This mismatch may arise from variations in the typical MFD of fiber in the following scenarios: -A single fiber type from one manufacturer with an MFD mismatch within the allowable range of+ 0.4μm (homogeneous).-Different fiber types from the same manufacturer, with either different nominal values or different Regardless of the MFD mismatch source, all mismatches across the three scenarios are standards-compliant and fully interoperable. Quantifying IL Whether by fusion splicing or use of separable connectors, joining two fibers with different MFDs resultsin inefficient coupling. Copyright © 2025 AFL. All rights reserved.The joint insertion loss, IL, may be expressed with this formula:IL =-10Log10(4MFD12MFD1.Agrawal, G. P. Fiber-Optic Communication Systems (4th ed., Wiley, 2010)2.Keiser, G. Optical Fiber Communications (5th ed., McGraw-Hill, 2011) MFD mismatch loss is an expression of inefficient coupling of two waveguides and doe