CWDM BiDi Optics

Due to shortage of available fibers and the increased cost of renting dark fiber, the CWDM BiDi and DWDM BiDi techniques are gaining popularity. In many cases, companies have to rent fiber from a bigger Telco, or the owner of the dark fiber is the national telecom provider which may even be a competitor. Another factor is that CWDM BiDi’s require less fusion splicing and patches. Making pigtails/connectors on the bare fiber can be an important cost factor for a Fttb project.

There are different techniques and possibilities to communicate over one single fiber instead of a traditional dual fiber connection. The most important thing is to know why the ‘normal’ communication cannot be achieved over one single fiber - This is because the normal receiver detects all the light available to it including its’ own back reflection. Every normal UPC patch reflects some light, and if the sender and receiver are on the same fiber, the receiver will get the signal from the other transceiver as well as its’ own back reflection. This is the reason why the normal 100mbit/1G/10G BiDi’s work on two wavelengths.  One side is sending red light and blocking incoming red light, the other side is sending blue light and blocking incoming blue light.

CWDM BiDi explaining lasers

This is a technique which is used worldwide in fiber-to-the-home projects. It will work fine with a single 100mbit/1G/10G connection but not multiple connections. To achieve multiple connections you can use different techniques: currently, there are three proven techniques which are deployed to multiplex multiple channels over one single fiber. These methods include:

-        Using traditional CWDM/DWDM and cross patch

-        Using CWDM BiDi with APC to reduce back reflection

-        Using CWDM BiDi’s which sends two different wavelengths inside one CWDM window

All of the advantages and disadvantages are seen in this presentation. At Solid Optics, we always investigate new products and techniques, and some of them are not mentioned in this presentation. Please contact us with your particular ‘challenge’ and our technical sales team can assist you to develop the best solution to achieve your goals.



Most techniques are based on CWDM - This has to do with the fact that the technique is more stable in outdoor applications with high temperature fluctuations (-40 / +85). We have extensive knowledge and experience with these techniques and are always happy to assist you in determining which will be the best fit for your needs.

The following videos will demonstrate the three different techniques listed above. Here we showcase how to deploy the setups and explain the basic differences of each.

CWDM BiDi with crossconnect CWDM BiDi with APC connectors CWDM BiDi with UPC connectors