Singlemode vs. Multimode - Fiber Optic Cable Types

While single-mode fiber (SMF) and multimode fiber (MMF) cables are widely used in a variety of applications, the differences between single-mode and multimode fiber can be confusing. This article will provide an in-depth comparison of single-mode and multimode fiber types, focusing on their basic construction, fiber distances, cost, fiber colors, and more.

Comparison between singlemode and multimode

Single-mode fiber transmits only one mode of light at a time. Multimode fiber transmits multiple modes. The main differences between single-mode and multimode fiber lie in core diameter, wavelength and light source, bandwidth, jacket color, transmission distance, and cost.

Core diameter

Single-mode fiber has a much smaller core diameter than multimode fiber. While other types exist, single-mode fiber typically has a core diameter of 9 µm. Multimode fiber, on the other hand, typically has core diameters of 50 µm and 62.5 µm, which allows for greater light-gathering capabilities and simplifies connections. The cladding diameter of both single-mode and multimode fiber is 125 µm.

Multimode fiber has higher attenuation than single-mode fiber because its core diameter is larger. Single-mode fiber has a very narrow core, so light passing through these fibers does not reflect as many times, keeping attenuation to a minimum.

Wavelength and light source

Due to the larger core size of multimode fiber, low-cost light sources such as LEDs (light-emitting diodes) and VCSELs (vertical-cavity surface-emitting lasers) operating at wavelengths of 850nm and 1300nm are commonly used. Single-mode fiber, on the other hand, typically uses lasers or laser diodes to generate the light injected into the cable. Common single-mode fiber wavelengths are 1310nm and 1550nm.

Bandwidth

The bandwidth of multimode fiber is limited by its optical mode. The current maximum bandwidth is 28000MHz*km for OM5 fiber. The bandwidth of single-mode fiber is theoretically unlimited because it only allows one optical mode to pass at a time.

Color sheath

According to TIA-598C, for non-military applications, the outer jacket of single-mode fiber is yellow, and the outer jacket of multimode fiber is orange or light green. Click here for more details on fiber optic cable color codes .

Singlemode and multimode fiber working distance

It is well known that singlemode fiber is suitable for long-distance applications, while multimode fiber is suitable for short-distance transmission. So, what are the quantifiable differences in transmission distance between single-mode fiber and multimode fiber?

As you can be seen from the chart, at data rates from 1G to 10G, single-mode fiber has a much greater transmission distance than multimode fiber , but OM3/OM4/OM5 multimode fiber supports higher data rates. Because multimode fiber has a larger core size and supports multiple light modes, its transmission distance is limited by modal dispersion, a common phenomenon in multimode step-index fiber. This does not occur with single-mode fiber, representing a fundamental difference between the two. Furthermore, OS2 single-mode fiber can support longer transmission distances in 40G and 100G links, a fact not listed in the table.

Singlemode Cost vs. Multimode Cost

The cost of single-mode fiber vs. multimode fiber has been a hot topic on forums. Many people have expressed their opinions, focusing primarily on optical module costs, system costs, and installation costs.

Optical transceiver cost

Compared with singlemode optical modules, multi-mode optical modules are nearly two to three times cheaper. The following table uses Fibermart-compatible Cisco single-mode and multi-mode optical modules as examples.

As can be seen from the table, as the speed increases, the price difference increases significantly.

System cost

Single-mode fiber is typically suitable for long-haul applications, but fully utilizing its essential properties requires transceivers equipped with lasers operating at longer wavelengths, with smaller spot sizes and generally narrower spectral widths. These transceiver characteristics, combined with the need for higher-precision alignment and tighter connector tolerances for smaller fiber core diameters, significantly increase transceiver costs and overall interconnect costs for single-mode fiber interconnects.

The manufacturing methods of VCSEL-based transceivers are optimized for multimode fiber, making them easier to manufacture in arrays and lower in cost than equivalent single-mode transceivers. Despite the use of multiple fiber channels and multiple transceiver arrays, single-mode technology still offers significant cost savings in simplex-duplex connectivity compared to single-mode technology operating in single or multi-channel configurations. Multimode fiber systems offer the lowest system cost and upgrade path to 100G for standards-based indoor applications using parallel fiber interconnects.

Installation costs

Single-mode fiber generally costs less than multimode fiber. If you're building a 1G fiber network and hope to eventually scale up to 10G or faster speeds, the cost savings from single-mode fiber can roughly halve the price. Meanwhile, the SFP module cost for multimode OM3 or OM4 fiber increases by 35%. Single-mode fiber is more expensive, but so is the labor cost of replacing multimode fiber, especially after transitioning from OM1 to OM2, OM3, and finally OM4. If you're willing to consider used Fibre Channel SFPs, the price of single-mode 1G can drop significantly. If you have the budget and need 10G connections over short distances, the economics still favor multimode. However, keep an eye on these economics, as historical experience suggests the price premium for single-mode fiber will decrease.

Frequently Asked Questions about Single-Mode Fiber and Multimode Fiber

Q: Which type of fiber is better, single-mode or multimode?

A: As mentioned above, single-mode fiber and multimode fiber each have their own advantages in terms of cost and application. There is no single-mode fiber that is superior or inferior. Simply choose the fiber that best suits your application.

Q: Can I mix single-mode and multimode fiber types?

A: The answer to this question is "no." Multimode fiber and single-mode fiber have different core sizes and transmit different numbers of light modes. Mixing these two types of fiber or directly connecting them together will result in significant optical loss, causing link jitter or interruption. Remember, never mix different types of cables.

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

A: Generally speaking, the answer is no. Connecting a multimode optical module to a single-mode fiber will result in significant optical loss. However, the reverse is also true. For example, a 1000BASE-LX single-mode SFP can operate over a multimode fiber cable by using a mode-conditioned fiber cable. Sometimes, a fiber media converter can also be used to resolve this issue between single-mode and multimode optical modules.

Q: Single-mode vs. multimode fiber optic cable types: Which should I choose?

A: When choosing between single-mode and multimode fiber, the primary consideration is the actual fiber transmission distance you require. For example, in a data center , multimode fiber is sufficient for transmission distances of 300-400 meters. However, for applications requiring transmission distances of several kilometers, single-mode fiber is the best choice. In applications where both single-mode and multimode fiber can be used, other factors should also be considered, such as cost and future upgrade requirements.

Summary

Comparing single-mode fiber and multimode fiber reveals the following: Single-mode fiber cabling systems are suitable for long-distance data transmission and are widely deployed in carrier networks, metropolitan area networks (MANs), and passive optical networks (PONs). Multimode fiber cabling systems offer shorter transmission distances and are widely deployed in enterprise networks, data centers, and local area networks (LANs). Regardless of which method you choose, selecting the solution that best suits your network needs based on the total fiber cost is a crucial task for every network designer.