CWDM refers to Coarse Wavelength Division Multiplexing, a process of combining multiple singlemode wavelengths into a single fibre optic cable. Depending on the transmitters, receivers and transceivers used, signals can be transported in either or both directions simultaneously. Each wavelength can be used to transport a different audio, video or data stream, or a combination of all three in the case of audio and data embedded in an SDI signal. The ITU- G.692.2 standard defines eighteen wavelengths from 1270nm to 1610nm, with a channel spacing of 20nm, which can be used within a CWDM system.
Fibre-ready Lynx yellobrik modules are fitted with an SFP (Small Form factor Pluggable) 'cage' into which can be plugged an SFP optical module. They can be readily installed or hot-swapped without tooling or opening the yellobrik module.
Note that there are several, incompatible, SFP pin connection protocols and quality and reliability varies enormously between SFP manufacturers. It is therefore recommended that only Lynx Technik SFPs are used with yellobrik modules.
CWDM Building Blocks
There are three basic building blocks in a CWDM system, CWDM fibre transmitters (or transceivers), optical multiplexers / de-multiplexers and receivers.
Transmitters
As the optical channel separation is quite small (20nm), CWDM transmitters and transceivers are specifically designed with a narrow spectral response (transmission peaks) to avoid cross channel interference. Although some non-CWDM SFPs may appear to offer the same wavelengths (1310nm and 1550nm are frequently used for simple two-channel, bi-directional systems), it is vital that CWDM compatible transmitters are used throughout multi-channel CWDM systems. Non-CWDM types have a much less tightly-controlled spectral peak, which is likely to cause adjacent channel interference.
Lynx Technik offer SFP fibre optic transmitter and transceiver modules, covering all 18 wavelengths for use with the yellobrik modules, offering 40km range at 3GBit/s SDI. (80km versions are also available; please contact Technical Support for details).
Lynx yellobrik SFP fibre optic CWDM transmitter and transceiver modules may also be used to replace the non-CWDM modules originally supplied in many yellobriks to extend the original 10km transmission range, or to add a multiplex capability as systems evolve. Please contact Technical Support to check compatibility.
Multiplexers, De-multiplexers
Lynx Technik yellobrik optical multiplexers/de-multiplexers combine or separate the various CWDM wavelengths onto, or from, a single fibre. They are bi-directional devices with up to nine input/output ports; each port is designated for use with a particular wavelength so must be matched to the SFP transmitter wavelength. Lynx yellobrik MUX/DEMUX components are passive so require no power and all have UPG (upgrade) or expansion ports allowing them to be combined to enable up to 18 signals in a single fibre. See Lynx Yellobrik CWDM Optical Multiplexers.
Receivers
All Lynx yellobrik singlemode SFP optical receivers are suitable for wavelengths between 1260 and 1620nm, so may be used to detect and convert the output from any CWDM or non-CWDM transmitter, whether used in a multiplexed or point-to-point system. See the 'Fibre Receiver Options (RX) For yellobrik Utility Modules' section in 'Lynx Yellobrik Fibre Optic SFP Modules - TX, RX and TR (Non-CWDM)'.
The Lynx Technik guides to Fibre and CWDM are available for download at www.canford.co.uk/Technical .
OH-TX-4 - Fibre CWDM SFP Transmitter Options For yellobrik TX Modules - Single channel
Eighteen, single-channel, SFP modules with LC simplex connection, each transmitting a single CWDM wavelength (1270 to 1610nm). Power output: -1dBm. Range: 40km at 3GBit/s SDI.
OH-TT-4, OH-TT-12G - Fibre CWDM SFP Transmitter Options For yellobrik TT modules - Dual channel
Nine modules for use typically with the OTT 1842 dual-channel 3G-SDI to fibre transmitter. The SFP module utilises both channels of the LC duplex connection to transmit two wavelengths from the CWDM range (1270 to 1610nm), one on each fibre. Wavelengths in each module are adjacent in the CWDM spectrum, i.e. 1270nm and 1290nm, 1310nm and 1330nm etc. Power output: -1dBm per channel. Range: 40km at 3Gbit/s SDI.
OH-TR-4 - Fibre CWDM SFP Transceiver Options For yellobrik TR Modules
Eighteen modules for use typically with the OTR 1840 3G-SDI to fibre transceiver, OET 1540 Ethernet transceiver or ODT 1540 serial and GPI transceiver. The SFP module utilises both channels of the LC duplex connection, one to transmit a single CWDM wavelength, the other as a broadband receiver. Power output: -2dBm. Transmitter range: 40km at 3Gbit/s SDI. Receiver wavelength: 1270 - 1610nm. Sensitivity: -3dBm to -23dBm.