BIDI is belong single-fiber bidirectional transceiver, only has 1 port, filtering through the filter in the optical transceiver, and finish the emission by 1310nm and reception by 1550nm at the same time, or on the contrary. So this kind of module must be used in pairs. Its biggest advantage is to save fiber resources. The common wavelength of BIDI optical transceiver are TX1310 / RX1550nm; TX1310 /RX 1490nm; TX1550 / RX1490nm.

Introduction:

BiDi transceivers communicate using only one fiber, where traditional communication is with two lines of fiber. To achieve this they use two different wavelengths (colors). For the 10G, these are the 1270nm/1330nm combination. On one side you will have the transceiver which is sending out the 1330nm light and receives the 1270nm light - the other side has the mirror image so the optic will send 1270nm light and receives 1310nm light. The main advantage with these optics is that you can double your speed over a traditional optical fiber pair. You can also build a redundancy over a fiber pair if you use both the fibers with 10G. These 10G Bidi’s can also be used in a CWDM project when you use a MUX with a 1310nm wideband port.

BiDi transceivers are not in the portfolio of the bigger router and switch manufacturers like Cisco/Juniper and Huawei. Because they are so specialized, only companies whose sole focus is optical transceivers supply them. These optics are available in SFP+/SFP10G and in XFP form factors. The basic version can do 20km and there are 40km and 60km models as well. Versions above this are not on the market. The 80km version does not exist because it operates at lower band which has more attenuation then the traditional 1550 band.

Definition:

This new optical transceiver technology allows transceivers to both transmit and receive data to/from interconnected equipment through a single optical fiber. This technology has led to the development of Bi-Directional transceivers, or BiDi transceivers for short.

How BiDi transceivers work:

The primary difference between BiDi transceivers and traditional two-fiber fiber optic transceivers is that BiDi transceivers are fitted with Wavelength Division Multiplexing (WDM) couplers, also known as diplexers, which combine and separate data transmitted over a single fiber based on  the wavelengths of the light. For this reason, BiDi transceivers are also referred to as WDM transceivers.

To work effectively, BiDi transceivers must be deployed in matched pairs, with their diplexers tuned to match the expected wavelength of the transmitter and receiver that they will be transmitting data from or to.

If paired BiDi transceivers are being used to connect Device A (Upstream) and Device B (Downstream), as shown in the figure below, then:

Advantages of BiDi transceivers:

The obvious advantage of utilizing BiDi transceivers, such as SFP+- BiDi and SFP-BiDi transceivers, is the reduction in fiber cabling infrastructure costs by reducing the number of fiber patch panel ports, reducing the amount of tray space dedicated to fiber management, and requiring less fiber cable.While BiDi transceivers (a.k.a. WDM transceivers) cost more to initially purchase than traditional two-fiber transceivers, they utilize half the amount of fiber per unit of distance. For many networks, the cost savings of utilizing less fiber is enough to more than offset the higher purchase price of BiDi transceivers.

There are numerous benefits with BiDi being able to use a single strand of fiber to carry data in both directions rather than multiple strands.

• Double Your Network Capacity:One benefit of BiDi is that is allows you to make full use of all your fiber strands and can therefore double your network capacity. This is because one strand is used to carry information in both directions, for example if you have a six-strand cable you would be able to utilize all six stands rather than three for one direction and three for the other.

• Reliability:Other benefit is increased reliability, single strand solutions are less prone to connection errors due to fewer connections and end points.

• Cost:The most obvious benefit to BiDi however is cost. Costs associated with fiber optic cabling, labor, and material to terminate end points can all be reduced if you are working with a single fiber system. Reducing the amount of fiber needed for a system results in overall cost savings, construction costs can also be avoided since you can increase capacity of existing fibers rather than install new fiber. Finally, the reduced number of terminated fiber strands translates to fewer patch cords and patch panel ports thus a significant cost reduction.

5G networks like 25G/50G BiDis as they can save fiber resources and support the high bandwidth data transmissions. 

And that’s the key to the advantages of BiDi: shorter data transmissions. They are great if they stay within the building, within a data center, on a cell tower. Or from building-to-building and data centers in short distances. 

In many longer distance situations, though, BiDis are a kind of band-aid, a short-term fix. This is because as fiber needs grow, BiDis can't keep up with expanding bandwidth needs. They are good for in-house deployment, not maxing out capacity for devices, not using great bandwidth and will not have a lot of users. 

BiDi in a building is okay, but not always the most conducive for bandwidth growth from tower to tower. 

BiDis are great for what they do, but often passives are better long-term solutions for multiple Ethernet links residing on the same fiber. This is because as needs grow, your fiber network becomes bandwidth intensive than a single Ethernet link. In this situation, BiDi can’t keep up. 

A choice for this would be a passive Mux/Demux solution, using a Mux/Demux filter combo to exponentially increase the number of possible new services (readily available in up to 40 services using DWDM, and 8 services using CWDM). This is a huge advantage as it doesn't require any power for the multiplexers! 

While this also enables you to use standard (dual fiber) transceivers, the higher loss shortens the distance between locations. (It’s really not Voodoo!) 

A single fiber passive solution in Point-to-Point configuration uses 2 wavelengths of WDM per service. This is how you can maximize the number of services using standard dual fiber transceivers on a single fiber strand. This method uses adjacent channel wavelengths to transmit and receive. The advantage of this is it can be used for either CWDM or DWDM network designs. It does not require specialized transceivers because NRZ transceivers generally use non-wavelength receivers. 

In this case, standard dual fiber CWDM or DWDM transceivers will work when matched to the appropriate passive multiplexer. This can add up to 8 (CWDM) or 40 (DWDM) services and can span distances of up to 80km (i.e., the rated distance of the optical transceiver). 

Cisco BiDi:

Cisco 40-Gbps QSFP BiDi transceiver reduces overall costs and installation time for customers migrating data center aggregation links to 40-Gbps connections.As a result of data center consolidation, server virtualization, and new applications that require higher data transport rates, the data center network is shifting to 10 Gbps at the access layer and 40 Gbps at the aggregation layer. A broad portfolio of high-performance and high-density 10- and 40-Gbps Cisco Nexus Family switches is available at attractive prices for this transition. However, to support 40-Gbps connectivity, data center architects are challenged by the need for a major upgrade of the cabling infrastructure, which can be too expensive or disruptive to allow data centers to quickly adopt and migrate to the 40-Gbps technology.Cisco solves this problem with innovative 40-Gbps Quad Small Form-Factor Pluggable (QSFP) bidirectional (BiDi) technology that allows reuse of existing 10-Gbps fiber infrastructure for 40-Gbps connections.

How Many BiDi Module Types?

The common types of BiDi transceivers used in today's networks are 1G/10G BiDi SFPs. The most common optical wavelengths for this transceiver are 1310/1490 nm, 1490/1550 nm, and 1310/1550 nm. They are designed for 1/10 GB deployment and can reach up to 80km distance. BiDi variants are also available for the form factor XFP X2 for 10G, GBIC for 1G.

The 25G SFP28 BiDi transceiver supports connections up to 10km over single-mode fiber and uses LC connectors. The wavelengths are 1330TX/1270RX and 1270TX/1330RX.

The 100G QSFP28 BiDi CWDM4 transceiver supports connections up to 2km over single-mode fiber and uses LC connectors. The wavelengths are 1271 nm, 1291 nm, 1311 nm, and 1331 nm.

The 40GBase QSFP+ BiDi has two 20G channels that support connections up to 100 meters on OM3 MMF and up to 150 meters on OM4 MMF. It uses an LC Duplex connector and the wavelength is 850nm. QSFP+ BiDi is a cost-effective solution for a 10G to 40G upgrade.

Why BiDi Module?

This single fiber BiDi transmission gradually becomes a popular and cost-effective solution for today's data center and IT infrastructure because of its unbeatable advantages:

•  

  Double Your Network Capacity– One benefit of BiDi is that it allows you to make full use of all your fiber strands and can therefore double your network capacity. This is because one strand is used to carry information in both directions, for example, if you have a six-strand cable you would be able to utilize all six stands rather than three for one direction and three for the other.

•  

  Reliability – Another benefit is increased reliability, single strand solutions are less prone to connection errors due to fewer connections and endpoints.

•  

  Cost – With the reduction of fiber strands by half, the number of patch cords and patch panel ports can be reduced accordingly, as well as reducing the amount of tray space dedicated to fiber management.

Where BiDi Modules Are Used?

BiDi modules are usually deployed in applications like access PON networks deployment P2P (point-to-point) connection, Digital Video, and Closed Circuit Television (CCTV) applications. They can be installed on servers, switches, routers, OADM to provide high speed and stability optical transmission systems, and Metropolitan Area Networks (MAN). In addition, 25/50G BiDi transceivers are welcomed by 5G networks since they can save fiber resources and support high bandwidth, ultra-low latency, and high reliability for data transmissions.

What Can BiDi Transceiver Achieve

• 40G connectivity becomes more reliable with BiDi transceiver technology. Your servers need it, your applications and users demand it, and your competitors are working to deliver it.

• BiDi transceiver can reduce the cost of fiber cabling infrastructure since it requires less fiber cable and less fiber patch panels. On the other hand, BiDi transceiver also makes it possible to save more precious space in data centers.

Working Principle of BiDi SFP

Compared to traditional SFP transceiver, BiDi SFP are deployed in matched pairs. One for the upstream (“U”) direction, and the other for the downstream (“D”), each part is transmitting at a different wavelength. We could get intuitive understanding of how BiDi SFP works from the image below. The two wavelengths utilized in this example are 1310 nm and 1550 nm. (1310 nm/1550 nm or 1550 nm/1310 nm are commonly used wavelengths in BiDi SFP). Typically, the upstream or “U” transmits at the shorter of the two wavelength — 1310 nm, while the downstream or “D” the longer wavelength — 1550 nm.

Main Differences Between BiDi SFP and Traditional SFP

The primary difference between BiDi SFP and traditional two-fiber SFP transceiver is that BiDi SFP is fitted with wavelength division multiplexing (WDM) couplers, also known as diplexer, which combine and separate data transmitted over a single fiber based on the wavelengths of the light. That’s why BiDi SFP has only one port, while the traditional SFP module is generally with two ports. One is TX for the transmitting port, and the other is RX for receiving port. The following picture shows different port structures of common Cisco SFP and BiDi SFP.

Conclusion:

BiDi transceivers can be produced either with SC or LC simplex port, that is used both transmission and receiving. By offering a standard, hot swappable electrical interface, it can support a wide range of physical media, from copper to long-wave single-mode optical fiber, at lengths of hundreds of kilometers. The most typical wavelength combination is 1310/1490, 1310/1550 and 1490/1550.

Please click to check more related concepts: