CWDM multiplexers are passive devices that merge light of multiple datastreams of different wavelengths (i.e. colors) to a single mode COMMON (COM) fibre per direction.
As CWDM multiplexers are totally passive devices they do not care what kind of signals are connected to them in terms of optical power or data-rate/type as long as they match the CWDM multiplexer port wavelengths.
Normally CWDM multiplexers include both band-limited CWDM inputs / output as well as wide-band UPGRADE (or AUX) ports.
CWDM input ports must match the transmitted wavelength and the spectral band width of the transceiver that feeds it.
CWDM output ports have the individual different wavelengths filtered and can connect to any transceiver receiver (all transceiver inputs are wide-band and therefore rely on an upstream CWDM de-multiplexer to untangle the different wavelengths (i.e. colors).

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UPGRADE (or AUX) ports are essentially non-filtered ports that can be connected to any wide- or CWDM narrow band transceivers.
But they do not protect the user from not overriding some of the CWDM specific wavelengths in use in the multiplexer.
Care must be taken to only connect the UPGRADE ports for colors that are not in use on the multiplexers CWDM ports.

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CWDM is always single mode and CWDM passive multiplexers attenuate optical power more than regular fiber cables and connections.

Single mode transceivers and fiber cables can either be multi-signal WDM, CWDM or DWDM multiplexed or single-signal wide-band.

SFP Transceivers in General:
SFP transceivers are small modules that connect electrically to a host device and provide optical input and output to connect via fiber cables to another device.

Electrically the SFP module must match the host device in electrical consumption, thermal management and a profile matching the data that is fed to/from the host device.

Optically the SFP must match the cable gauge (single or multi-mode), power budget (launch power vs receive sensitivity must be within range with all optical losses) and the wavelength if optical multiplexing is used.

Even though SFP transceivers are mechanically compatible they cannot be guaranteed to work unless tested and supported by the manufacturer of the host device.

Using FreeSpeakII (FSII) and Single-Mode Fiber Connection via CWDM passive multiplexers:
FreeSpeakII BASE-II basestation, FSII-SPL splitters, and E-IPA-HX cards running in E1 fiber-mode (Eclipse version 12.1 and higher) allow fiber connectivity.
For single mode connectivity Clear-Com offers the HLI-SMFO transceiver which can be used with these devices. These transceivers are tested and supported by Clear-Com.
The HLI-SMFO operates on standard bandwidth, centered on 1310 nm which is compliant with WDM multiplexing and overlaps the lower CWDM wavelengths 1270-1450nm

This allows the HLI-SMFO to be connected to UPGRADE (or AUX) ports of CWDM multiplexers as long as;

• CWDM ports 1270nm to 1450nm are not used

• Optical Power Budget /attenuation between transmitter and receiver is less than 12dB (connections, cables, multiplexers)
  Note: Maximum optical attenuation is a factor of the SFP transceivers!

Please note:
Clear-Com does not sell or support WDM, CWDM or DWDM transceivers for E1 based FreeeSpeakII systems.
Any third party transceivers, which cannot be guaranteed to be supported by Clear-Com, need to support OC-3/SONET/100Mb datarates.
Use of third-party SFP transceivers or other SFP electrical components with FreeSpeakII E1 based systems is not recommended or supported by Clear-Com and can void warranty if found to be root cause of system damage.