What are the single mode fiber optic connectors

The emerging demand for higher bandwidth, faster speed connections has significantly fueled the growth of the market for fiber optic cable assemblies, particularly singlemode fiber (SMF) and multimode fiber (MMF). Although these two types of fiber optic cable are widely used in various applications, not everyone knows the exact difference. The following article will focus on the basic construction, fiber spacing, cost, and fiber color to make an in-depth comparison between singlemode and multimode fiber.

definition

Singlemode means that the fiber enables the propagation of one type of light at a time. While multimode means that the fiber can propagate multiple modes. The main difference between singlemode and multimode fibers lies in the fiber core diameter, the wavelength, the light source and the bandwidth.

Core diameter

The singlemode fiber core diameter is much smaller than that of multimode fibers. The typical core diameter is 9 µm, although other fibers are available. And the diameter of multimode fiber cores is typically 50 µm and 62.5 µm, which enables a higher "light gathering ability" and simpler connections. The sheath diameter of singlemode and multimode fibers is 125 µm.

Wavelength & light source

Because of the large core size in multimode fibers, some inexpensive light sources such as LEDs (light emitting diodes) and VCSELs (surface emitting lasers with vertical cavity) that operate at the wavelengths of 850 nm and 1310 nm are used in multimode fiber cables. While singlemode often uses a laser or laser diodes to generate light that is coupled into the cable. And the singlemode fiber wavelength commonly used is 1310nm and 1550nm.

Bandwidth

The bandwidth of multimode fibers is limited by their light mode and the maximum bandwidth is currently 28000 MHz * km of OM5 fiber. While the bandwidth of single-mode fibers is theoretically unlimited, since only one light of one mode is allowed through at a time.

Paint coat

According to the standard definition of the TIA-598C, a single-mode cable is sheathed with a yellow outer jacket and a multimode fiber with an orange or aqua jacket for non-military applications. More details about the color code for fiber optic cables can be found here.

distance

It is known that a single-mode fiber is suitable for applications over long distances, while a multimode fiber is designed for short distances. Then what are the quantifiable differences between singlemode and multimode fibers in distance?

Fiber optic cable type Fiber optic cable spacing

Fast Ethernet 100BA SE-FX 1Gb Ethernet 1000BASE-SX 1Gb Ethernet 1000BA SE-LX 10Gb Base SE-SR 25Gb Base SR-S 40Gb Base SR4 100Gb Base SR10
Single mode fiber OS2 200m 5,000m 5,000m 10km / / /
Multimode fiber OM1 200m 275m 550m (patch cable required for mode conditioning) / / / /
OM2 200m 550m / / / /
OM3 200m 550m 300m 70m 100m 100m
OM4 200m 550m 400m 100m 150m 150m
OM5 200m 550m 300m 100m 400m 400m

It can be seen from the diagram that the spacing of singlemode fibers at a data rate of 1G to 10G is much larger than that of multimode fibers, but OM3 / OM4 / OM5 multimode fibers support a higher data rate. Since the multimode fiber has a large core size and supports more than one light mode, its fiber distance is limited by the model dispersion that is a common phenomenon in multimode step index fiber. This is not the case with singlemode fibers. That is the main difference between them.

Cabling costs

"Singlemode vs. multimode fiber costs" is a hot topic in various IT forums. Many users express their views and focus particularly on the costs of optical transceivers, system costs and installation costs.

Optical transceiver costs

Compared to singlemode transceivers, the price of multimode transceivers is almost two to three times lower. The following table shows FS.COM Cisco Compatible Singlemode Transceivers and Multimode Transceivers as an example.

speed Transceiver Transceiver description price price difference
1GSinglemode SFP Cisco GLC-LH-SMD Compatible 1000BASE-LX / LH SFP 1310nm 10km DOM Transceiver US $ 7.00 US $ 1.00
Multimode SFP Cisco GLC-SX-MMD Compatible 1000BASE-SX SFP 850nm 550m DOM Transceiver US $ 6.00
10GSinglemode SFP + Cisco SFP-10G-LR Compatible 10GBASE-LR SFP + 1310nm 10km DOM Transceiver US $ 24.00 US $ 6.00
Multimode SFP + Cisco SFP-10G-SR Compatible 10GBASE-SR SFP + 850nm 300m DOM Transceiver US $ 24.00
25GSinglemode SFP28 Cisco SFP-25G-LR-S Compatible 1310nm 10km US $ 59.00 US $ 20.00
Multimode SFP28 Cisco SFP-25G-SR-S Compatible 850nm 100m US $ 39.00
40GSinglemode QSFP + Cisco QSFP-40G-LR4 Compatible 40GBASE-LR4 and OTU3 QSFP + 1310nm 10km LC DOM Transceiver US $ 279.00 US $ 240.00
Multimode QSFP + Cisco QSFP-40G-SR4 Compatible 40GBASE-SR4 QSFP + 850nm 150m MTP / MPO DOM Transceiver US $ 39.00
100 GSinglemode QSFP28 QSFP28 Cisco QSFP-100G-LR4-S 100GBASE-LR4 1310nm 10km Compatible Transceiver US $ 499.00 US $ 400.00
Multimode QSFP28 QSFP28 Cisco QSFP-100G-SR4-S Compatible 100GBASE-SR4 850nm 100m Transceiver US $ 99.00

From the table we can see that the price difference increases sharply with increasing speed.

System costs

Singlemode fibers are generally targeted for longer distance applications, requiring fiber transceivers with lasers that operate at longer wavelengths with smaller spot sizes and generally narrower spectral widths. These transceiver characteristics in connection with the need for more precise alignment and tighter plug tolerances with smaller core diameters lead to significantly higher transceiver costs and overall higher connection costs for single-mode fiber connections.

Manufacturing methods for VCSEL-based transceivers that are optimized for use with multimode fibers are easier to manufacture into array devices and are less expensive than corresponding single-mode transceivers. Despite the use of multiple fiber tracks and multi-transceiver arrays, there are considerable cost savings compared to singlemode technology with single or multi-channel operation via simplex-duplex connections.

Installation costs

Singlemode fiber often costs less than multimode fiber. If you're building a 1G fiber network that you eventually want to expand to 10G or faster, the cost savings on single-mode fiber will save you about half the price. While the multimode OM3 or OM4 fiber increases the cost of SFP modules by 35%. Singlemode optics are more expensive, but the labor cost of replacing the multimode fiber is significantly higher, especially if the OM1 - OM2 - OM3 - OM4 follow. If you're ready to buy used Ex-Fiber Channel SFPs too, the price of 1G singlemode will drop through the ground. If you are on a budget and need 10G short links, economy at the last check still supports multimode. Keep these economics in mind, however, as history suggests that the singlemode premium will go down.

Frequently asked questions about single-mode vs. multimode fiber

Q: What is a better singlemode or multimode fiber?

A: As mentioned earlier, single-mode fiber and multimode fiber cable have their own specific advantages in terms of cost and applications. It is best to choose the fiber that is most suitable for your applications.

Q: Can I mix singlemode and multimode fiber?

A: The answer to this question is "no". Multimode fiber and singlemode fiber have different core sizes, and so do the number of modes of light they transmit. If you mix the two fibers or connect them directly to each other, you will lose a large part of the optical losses, which will cause a connection to rattle or break. Remember, you should never mix different types of wiring at random.

Q: Can I use a multimode transceiver on a single mode fiber?

A: In general, the answer is no. Large optical losses occur when a multimode transceiver is connected to a single-mode fiber. However, the opposite will work. For example, 1000BASE-LX singlemode SFP can work on multimode fiber optic cables using mode conditioning fiber optic cables. Fiber optic media converters can also sometimes be used to resolve such problems between single-mode transceivers and multimode transceivers.

Q: Singlemode vs. Multimode Fiber: Which Should I Choose?

A: When deciding between single-mode and multimode fiber optic cables, the first factor to consider is the fiber spacing, which you actually need. In a data center, for example, multimode fiber optic cables are sufficient for a distance of 300-400 meters. For applications that require a distance of up to several thousand meters, the singlemode fiber is the best choice. And for applications that can use both single-mode and multimode fiber optic cables, other factors such as cost and future upgrade requirements should be considered when making your choice.

Summary

The single-mode fiber optic cabling system is suitable for long-range data transmission applications and is widely used in carrier networks, MANs and PONs. The multimode fiber optic cabling system has a shorter range and is widely used in businesses, data centers, and LANs. Whichever system you choose, it is an important task for any network designer to choose the one that best suits your network needs based on total fiber costs.