IEC 61300-3-43:2009

Overview

IEC 61300-3-43:2009 specifies a standardized method to measure the mode transfer function (MTF) of multimode fibre optic sources. The MTF measurement characterizes the launched modal distribution (LMD) - the mode content injected into multimode fibre - and is used to define launch conditions for accurate attenuation and return loss testing of multimode passive components. This first edition (2009) replaces IEC/PAS 61300-3-43 (2006) and is applicable at the operational wavelengths of the system under test.

Key topics and technical requirements

• MTF definition and theory: MTF is derived from the fibre near-field intensity distribution. The standard describes the mathematical relation between the near-field intensity I(r) and the MTF, and how to express results as a normalised mode number (m/M).
• Mode power distribution (MPD): MPD(m) = MTF(m) × m - used to show relative power across mode groups and identify dominant mode ranges.
• Measurement constraints:
  • Modes within a mode group must carry the same power and have random relative phases (mode-continuum approximation).
  • Linewidth requirements to avoid speckle: for a 50 µm core, Δλ > ~0.5 nm at 850 nm and Δλ > ~1.0 nm at 1 300 nm (typical).
  • If line-width is insufficient, temporal averaging (e.g., gentle fibre agitation) can be used; verify azimuthal symmetry by checking MTFs at 45° intervals.
  • The MPD peak should occur at a normalised mode number < 0.8 for valid results.
• Apparatus and procedure: The method uses a near-field imaging system (video microscope) - imaging and condensing lenses, beamsplitter, LED/source, fibre holder with XYZ manipulator, camera, video digitiser, and computer. Procedures cover mounting, optimisation, data acquisition, background subtraction, centroid location, differentiation of intensity profiles, and MTF/MPD computation.
• Alternative method: When fibre profile factor α is unknown, an alternative approach compares the derivative of the test intensity profile to that of a fully-filled reference profile.

Applications and users

• Who uses it: test laboratories, fibre and connector manufacturers, component qualification teams, standards engineers, and network equipment testers.
• Why it’s useful:
  • Establish repeatable launch conditions for attenuation and return-loss tests of multimode passive components (connectors, patch cords, lenses).
  • Diagnose and characterise light source behaviour and modal filling for system performance and interoperability.
  • Support quality control, R&D, and compliance testing for multimode fibre systems.

Related standards

• IEC 61300-1 - Basic test and measurement procedures: general and guidance
• IEC 61300-3-4 - Attenuation measurement procedures
• IEC 60793-1-20 - Optical fibres: measurement methods and test procedures (fibre geometry)

Keywords: IEC 61300-3-43, mode transfer function, MTF measurement, multimode fibre, launched modal distribution, MPD, near-field intensity, attenuation testing, return loss, fibre optic sources.