Single-mode vs. Multimode Transceivers: How Do You Choose?

Most fiber systems use a transceiver, which combines a transmitter and receiver into a single module, using fiber optic technology to send and receive data over an optical network:

• The transmitter converts an electrical input to an optical output from a laser diode or LED source (the light is coupled into the fiber with a connector and transmitted through the fiber cable)
• Light from the end of the fiber cable is coupled to a receiver; a detector converts light into an electrical signal,  which is conditioned for use by the receiving equipment

Digital transmission over optical fiber (Tx = transmitter  Rx = receiver)

Transmitter sources must meet several criteria to work as intended: correct wavelengths, fast enough modulation to transmit data and the ability to be efficiently coupled into fiber. Five types of transmitter sources are commonly used to convert electrical signals into optical signals:

1. LEDs
2. Fabry–Pérot lasers
3. DFB (distributed feedback) lasers
4. DBR (distributed BRAGG reflector) lasers
5. Vertical-cavity surface-emitting lasers (VCSELs)

With so many new speed and technology options in the market, deciding which transceiver types and cabling systems to install isn’t a trivial decision. It’s also important to understand the risks associated with reusing installed fiber cable for cost savings.

What are the differences when comparing singlemode vs. multimode transceivers? Let’s uncover them here.

Distance

In comparing singlemode vs. multimode transceivers, you’ll find that singlemode fiber cabling systems are suitable for long-reach data transmission applications, thanks to low fiber attenuation and low dispersion penalty. Singlemode systems are widely deployed in carrier networks, metropolitan area networks (MANs), and passive optical networks (PONs).

On the other hand, multimode transceivers typically have a shorter reach that is intended for use in small areas or inside a building. Multimode fiber cabling systems are suitable for short-reach interconnects up to a few hundred meters, and have been widely deployed in enterprise data centers and local area networks (LANs).

Multimode fiber (OM3/OM4/OM5) typically has a much larger core 50µm and usually operates at the wavelength around 850nm). Singlemode fiber (OS2) makes use of a smaller core 9µm and operates at the wavelength between 1260nm-1650nm. Singlemode transceiver technology can support fast data transmission speed (i.e. bit rates) and much longer transmission distances.

Multimode fiber and singlemode fiber

Laser Source

When comparing singlemode vs. multimode transceivers in terms of laser source, they each use different types.

Typically used in multimode transceivers, VCSELs are a type of laser diode that offers lower manufacturing and package costs as compared to edge-emitting lasers (another popular laser option). VCSELs can be tested on the wafer level (allowing all individual integrated circuits present on the wafer to be tested for functional defects by applying special test patterns to them) and don’t require a hermetic package. The emission area radius of a typical multimode VCSEL is under 20µm; it can couple very efficiently with multimode fiber that has a core diameter of 50µm.

Edge-emitting lasers, such as Fabry–Pérot, DFB and DBR lasers, are used in singlemode transceivers for different reaches and applications. They have complex layer structures and often require a hermetic package to achieve higher emission power and stable singlemode operation; hence, they are more costly than VCSEL-based transceivers.

Singlemode transmitters can be coupled efficiently with singlemode fiber that has a core diameter of 9µm; however, it has less tolerance to fiber core misalignment as compared to multimode fiber due to its much smaller core size.

Cost

When comparing singlemode vs. multimode transceivers in terms of cost, multimode transceivers are nearly two to three times lower in price as compared to singlemode transceivers. Why? Because singlemode fiber systems cost more to make and are more “fragile” in nature, which makes them more expensive for you to purchase.

Speed

In telecom applications where the fiber cost is high due to long-distance data transmission, singlemode transceivers can support higher speed rates with fast response time, advanced modulation formats and wavelength division multiplexing (WDM) technology.

In datacom environments, both singlemode transceivers and multimode transceivers can accommodate speeds beyond 50G as of today.

Active gear port speed, desired reach and interconnect topology, as well as the total cost of ownership (the futureproof-ness of the fiber cabling infrastructure), should be considered as the main decision criteria.

Where to Go From Here

When evaluating singlemode vs. multimode transceivers, they both have sweet spots to support different data center applications and interconnect architectures. No matter which technology and migration path you choose, a high-quality optical fiber infrastructure will always play an important role in optimizing data center operations by minimizing total cost of ownership.

Whether you’re considering singlemode or multimode, it’s important to note that, although with similar form factors and optical connector interfaces (e.g. SFP+, QSFP+), different types of transceivers aren’t interchangeable, mainly due to differences in laser wavelength and fiber core size – and, more importantly, the designated speed and reach specifications.

Figure transceiver module connections

To build futureproof your fiber infrastructure – whether you’re migrating from 1G to 10G or from 10G to 40G/100G, or you’re already preparing for the migration to 400G – it’s important to find a data center infrastructure partner that provides sustainable, cost-effective solutions, and helps you determine whether singlemode or multimode is the right choice for you. Learn more about Belden’s data center solutions here.