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Can we use sfp multimode on singlemode fiber?

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A few weeks ago, we deliver to our customer singlemode SFP, multimode SFP, singlemode patchcord and multimode patchcord.



The customer tested the SFP and patchcord, then they reported to us that all of multimode SFP have problem. We stayed calm because we were sure that all of our SFP are in the good condition (we tested all SFP before delivery to the customer).

We did a good communication with the customer and found the problem. The problem was very basic, the customer used SFP multimode on singlemode fiber. Let's find why we can't use SFP multimode on singlemode fiber.

We can't use SFP Multimode on singlemode Fiber or vice versa, caused the core diameter of the fiber is different;

Multimode fiber core size = 50 / 62,5 µm

Singlemode fiber core size = 8 - 10 µm

It's impact to light propagation, very little of the multimode light could couple into a too small fiber core.

Let's look the picture below

Conclusion :

  • We must use the correct SFP and fiber
  • If you use SFP Multimode in the singlemode fiber, the vast majority of the light is lost.
  • If you use SFP Singlemode in the multimode fiber, the light still can propagates but start to bounces.