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**My understanding of SFP functionality. **

SFP is an “interface” between 2 parts of a device.

SFP is a transceiver There are input and output, electrical to optical or optical to electrical. SFP includes a laser diode and photodiode.

Optical fibre connects 2 SFP module via LC connector.

If output signal of SFP is electrical, how can it be connected via optical fibre?

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An SFP module isn't a complete interface - it's just the last part of a physical-layer interface, forming the Physical Medium Dependent (PMD) sublayer between the Physical Medium Attachment (PMA) and the medium.

If output signal of SFP is electrical, how can it be connected via optical fibre?

As you've stated, a transceiver consists of a transmitter (e.g. a laser) and a receiver (e.g. a photodiode) for the used medium. For optical media, those components convert the electrical signal from the SFP socket to an optical one and vice versa.

Of course, transceivers also exist for twisted-pair copper cable which may or may not require active transcoding inside the SFP module (e.g. from 1000BASE-X to 1000BASE-T) and the ubiquitous direct-attach cables (DAC) with affixed twinax cabling.

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  • I am trying to understand if SFP is used in optical satellite terminals. 1, 2. These terminals have optical fibre inside I am sure. They transmit optical signal. A transmit device/telescope should be connected with other parts via optical fibre. Nov 24 at 9:49
  • Theoretically possible but very unlikely, given that SFPs are intended for low(er)-power, fiber-based optical and that satellite tech needs to be highly optimized (power, weight, radiation hardening, longevity).
    – Zac67
    Nov 24 at 9:55
  • What can be used to connect electrical and optical parts? Nov 24 at 12:59
  • Sorry, this site is about about professionally managed networks in a business environment, see the help center - for engineering satellites Space Exploration might be more appropriate.
    – Zac67
    Nov 24 at 13:05
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    @NoelMiller, there are also SFPs that are not optical. We often use 10/100/1000Base-T SFPs, and even 10GBase-T SFP+s when devices are in the same closet, only using optical for distant devices.
    – Ron Maupin
    Nov 24 at 15:30

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