Question : Problem: media converter Allied Telesyn MC 101-XL

I have bought an Allied Telesyn media converter model MC 101-XL (802.3u). This media converter has one port for fiber (100FX) and one port for 100baseT. Normally on the fiber port you are supposed to use multimode fiber. I was wondering if you can not use single mode fiber on that port? The 100baseFX 802.3u standard should be ok to use with either single or multimode fiber...at least that's what I think. I do not care about the distance. The problem I have is that my building is wired with single mode, and I have already bought the media converter. I asked Allied if I can use this media converter with single mode..they told me no. I do not understand why not? The converter is 802.3u compliant..so 100FX should be working on either type of fiber? Allied did not say why but they told me to use another media converter they sell..I want to know if someone (independant)could explain why I can not use multimode and single fiber with this media converter? Thanks

Answer : Problem: media converter Allied Telesyn MC 101-XL

Single-mode and multi-mode fiber is not interchangable. The smaller diameter of the single-mode fiber requires lasers to drive the light, but the larger diameter multi-mode can use LED's.