G.652.D vs G.657.A1 & G.657.A2 Singlemode Fibre Differences (2024)

What does the term singlemode fibre cover?

Various types of fibre under the “singlemode” umbrella

On hearing the term “singlemode fibre”, the first thing that comes to mind for many of us is the core size of 9/125µm and it being used to transmit at a wavelength of 1310nm. However, the fibre also has to meet many other criteria which vary depending on type of singlemode fibre.

Below we discuss the various types and how they differ.

The main definition for singlemode fibre

ITU-T G.652.D

Unless specifically stated, it is commonly accepted among networking professionals that when requesting singlemode fibre cables they will conform to ITU-T (International Telecommunication Union Telecommunication) G.652.D.

This standard is applicable to both singlemode OS1 and OS2 cables and describes the geometrical, mechanical and transmission attributes of the cable and ensures that the cable can be used in the operating wavelengths around 1310nm and 1550nm.

There are also other variations of G.652 (A to C) which are now considered to be legacy fibre standards because they do not support the full range of modern-day requirements such as Coarse Wavelength Division Multiplexed (CWDM) transmission or Wavelength Division Multiplexing (WDN).

Types of singlemode fibre

ITU-T G.657

However, with the demand for ever higher fibre density and the constraints this creates, it is becoming more common for networking professionals to require singlemode fibre that performs in more constrained areas with tighter cable routing and reduced bend radii.

When this is the case, singlemode fibre meeting the G.657 (characteristics of a bending-loss insensitive single-mode optical fibre and cable) standard may be required. G.657.A1 or G.657.A2 are typically requested although there are other standards. Cables meeting either of these standards are often referred to as Bend Insensitive (BI) or Reduce Bend Sensitive (RBS) fibre cable.

Are G.652 and G.657 compatible?

G.652.D, G.657.A1 and G.657.A2 all have the same physical size with internal and external core diameters of 9μm and 125μm, respectively.

This means that cables defined under all three standards are completely compatible with each other.

G.657 categories

The ITU standard splits cables into two categories of G.657: category A for access networks and category B for short distances at the end of networks where space is at even more of a premium.

Within categories A and B, G657 is split further into:

G.657.A1 and G.657.A2
G.657.B2 and G.657.B3

Most environments related to data and telco applications typically do not require cables to perform to category B so we only discuss category A cables below.

G.657.A1 vs G.652.D

A key difference between G.657.A1 and G.652.D is the minimum bend radius a cable can be bent without the cable causing a network to experience failures.

G.657.A1 has a bend radius of 10mm without impacting performance. Whereas G.652.D has a larger minimum bend radius of 30mm.

Note these bend radius are for single singlemode cables in the initial manufactured form with just their primary buffered coating and before they are given outer sheaths or put into multicore constructions as these changes to the cable will also affect the minimum bend radius.

As such, thicker sheath cables or larger multicore cable constructions typically do not use G657.A1 or A2 cores as the limiting factor on the bend radius is the physical limitations of the cable construction and not the glass core.

G.657.A1 vs G.657.A2

G.657.A2 is also compliant with G.652.D while having a tighter minimum bend radius of 7.5mm, compared to 10mm for G.657.A1.

Because of its tighter bend radius and compliance with G.652.D, G.657.A2 is popular for use in tighter spaces within high density patching fields in data centres. Many of our customers from larger telecommunication companies also ask for G.657.A2 for the same reason.

When using G.657.A2, it is recommended that the smallest cable sheath diameter is used so the sheath does not restrict the cables minimum bend radius. Similarly, short booted connectors are also specified as often the tightest bend is at the connection point. For similar reasons of maintaining performance and maximising the benefit of using G657.A2 fibre, these cables are made with a lower loss ferrule and polished to give an IL (typical) <0.15dB and <0.20dB (Max).

G.657.B2 and G.657.B3

Category B of G.657 has an even tighter bending radius than category A. B2 has a minimum bend of 7.5mm and B3 has 5mm, the lowest radius available for singlemode fibre patch cables.

Cost of singlemode G.657.A1 and G.657.A2 fibre patch leads

The production costs vary for singlemode fibres made to the different standards. Cables with a tighter bend radius tend to cost more due to the volumes produced and the higher specification required.

Our typical price for a 1m LC to LC singlemode duplex (1.8mm) cable with short boots is as follows:

It can be seen that as the cables get longer the price differential gets bigger.

Our low loss patch cords stock in different bend insensitive fibres all have a typical insertion loss of 0.15d/b.

Get in touch

If you have more questions about singlemode fibre, or any other requirements, can contact our team by phone, online chat or email on the details below.