I was having a discussion with a friend of mine about fiber and he said that he has GBICs that support both Single-mode and Multi-mode fiber in the same device. At first I thought, no way, that can't be, that doesn't make any sense.
My thinking was this:
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Single-mode uses a laser while Multi-mode uses an LED to generate the signal. This would require two significantly different devices to generate the signal.
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The core sizes are drastically different between Single-mode and Multi-mode. SM being 9 micron and Multi-mode 62.5 or 50 micron.
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Wouldn't the photo receiver (or whatever they use) be very different and have trouble dealing with the two different types of signal.
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It doesn't really make much sense from an administration stand point to me. I mean I understand the idea of plugging something in and having it just work no matter what, but anyone who is plugging in this stuff should probably know the difference and how to identify which fiber is what type. Wouldn't it be more cost prohibitive to jam these two different technologies into one small GBIC?
So, I looked it up and according to CISCO the Cisco GLC LH SM SFP GBIC is an example of one that "is able to work with both single-mode and multi-mode fiber". So I suppose I am wrong.
My question is, is this true, has anyone used one of these MM/SM GBICs? When did they start making these and why did they start making these?
Best Answer
The particular GBIC you're referring to requires the use of a mode-conditioning patch cord when connected to a multi-mode fiber cable. The GBIC doesn't really "support" multi-mode fiber, per se, but rather this patch cord provides the necessary optical "distortion" to make the modulation work properly over a multi-mode fiber.