Method of qualifying a multimode optical fiber for bandwidth performance

A method of qualifying a multimode optical fiber for bandwidth performance when used with a laser source that excites a modal power distribution (MPD) comprising an optical power in its various mode fields ( i . e . , P source ≅ ∑ i ⁢ c i ⁢ P i smf ) ,

• said multimode fiber having a core surrounded by a cladding and having an input end and an output end, the method comprising the following steps:
• injecting light impulses into the input end of the optical fiber at various radial distances from the center of the core, said light impulses being adapted to excite only a small number of modes of the fiber;
• detecting impulse response data, hi(t), at the output end of the fiber for impulses injected at each of the various radial distances, said impulse response data comprising magnitude and propagation delay of the light impulses;
• storing the impulse response data;
• calculating an impulse response, h(t), of the multimode fiber according to the formula:
• h ⁡ ( t ) = ∑ i ⁢ c i ⁢ h i ⁡ ( t ) ;
• performing a time-domain-to-frequency-domain transformation of the impulse response, h(t), to determine the distribution of optical power as a function of frequency;
• and
• assigning a measure of bandwidth performance to the multimode fiber, said measure being the frequency difference between a pair of band-edge frequencies where the magnitude of the optical power distribution is less than the maximum magnitude of the optical power distribution by a predetermined amount.

A method of qualifying a multimode optical fiber for bandwidth performance when used with a laser source that excites a modal power distribution (MPD) comprising an optical power in various mode fields of the multimode optical fiber, said multimode fiber having a core surrounded by a cladding and having an input end and an output end, the method comprising the following steps:

• measuring a differential mode delay (DMD) characteristic of the multimode fiber;
• estimating from DMD data the delays, τμ, attenuations σμ and pulse widths, γμ, of each mode group μ;
• predicting the impulse response, h(t), of the fiber under excitation by a source with MPD, Psource (μ), according to the equation:
• h ⁡ ( t ) = ∑ μ ⁢ P source ⁡ ( μ ) ⁢ h PMG ⁡ ( t , τ μ , γ μ , σ μ ) ;
• performing a time-domain-to-frequency-domain transformation of the impulse response to determine the distribution of optical power as a function of frequency;
• and
• assigning a measure of bandwidth performance to the multimode fiber, said measure being the frequency difference between a pair of band-edge frequencies where the magnitude of the optical power distribution is less than the maximum magnitude of the optical power distribution by a predetermined amount.