Single- mode cable is a cable with a single strand of optical glass fibre with diameter of 8.3 to 10 microns. Compared to multi-mode fibres, the light is narrower and has a higher bandwidth. Compared to Multi-mode, Single-mode has a considerably smaller core. The result is a thinner light wave that travels down the cable without being distorted. The core of the Multi-mode is 50 to 100 microns larger than the Single-mode. Due to the bulkier nature of its light, light waves are scattered widely along the cable. For short distances, this won't be an issue, but for distances longer than one kilometer, it may result in light distortion at the distant end and insufficient data transfer. Although it is possible to install multi-mode on a single-mode transceiver, it is highly recommended to use a compatible device.
What if you have to connect Multi-mode and Single-mode?
When trying to mix up the installation it’s highly advisable to pay attention to the device’s specifications which can be found in the device’s data sheet.
The main thing to remember when attempting to install multi-mode fibre on a single mode installation is to use a mode conditioning patch cable. This cable has been designed and developed to provide a convenient method of connecting multi-mode fibre optic cables to 1000BASE-LX optical modules. Mode conditioning cables offer the option of calibrating multi-mode fibres using single mode single core modules. They are constructed as duplex patch cords and therefore do not require any additional components. The requirement for such patch cords is the default nature of 1000BASE-LX modules to emit 1310nm light along a single fibre. If a normal multi-mode fibre is used with a single-mode transceiver module instead of a mode conditioning jumper, the single-mode transceiver module will emit light directly at the centre of the cable, resulting in the generation of multiple optical signals and thus confusing the receiving module. Mode modulation jumpers eliminate this problem by allowing single mode emission to be off-centre from the multi-mode fibre. This solution provides emission similar to typical LED emission. While it is possible to mount a multi-mode fibre to a single-mode module, the larger light wave of a multi-mode module, typically 62.5 microns, would not allow for another way of transmitting into a 9 micron fibre. This would result in a loss of at least 85% of light.
The main things to understand when using these types of cable are:
- Mode conditioning jumpers require MC cables to be connected on each side of the installation.
- When using equipment with LC or SC connectors, it is important to remember that the single-mode part of the cable must be connected to the transmission side of the equipment and the multi-mode part of the cable must be connected to the receiving side of the equipment.
Please note that the quality of this solution is not the best. Depending on the bandwidth, the transmission distance on multi-mode fibres is limited.
Therefore, it is always recommended to use multi-mode or single-mode fibre optic patch cables to match the transceiver in order to obtain the best connection quality.