Application
Notesenko.com

The Relationship between
Insertion Loss and Premium Ferrules
FEBRUARY 2021
Rev. 01

Issued by:EngineeringDepartment

Created by:Andrei Vankov

Application Engineering Note

1.0 Purpose
Senko offers connectors for various fiber optic applications and scenarios. Using highquality components, SENKO connectors can meet IEC, TIA/EIA and the requirementsof GR-326 standards. What is the merit of a fiber optic connector? Fiber optic
connectors main function is designed to terminate the ends of fiber optic cables so they
can be interconnected. Every fiber connection has two most important values aftertermination and interconnection - Insertion Loss (IL) and Reflection or Return Loss (RL).
A higher quality connector will lose less light due to misalignment of the connected
fibers. A fiber optic connector which has lower loss, lower cost, and is easier toterminate is always in demand. Thus, dozens of fiber optic connectors have been
introduced to the market with different standards and applications, but only a few ofthem represent the majority of the market and even fewer stand out in terms quality.
One example of such connectors is a SENKO LC Unibody Premium connector, which isdesigned with super low loss ferrule that made to meet low loss requirements that canbe found in the IEC 61753-1 standard which will be described later in this document.
We will explain what makes SENKO Premium connectors different from the rest.

2.0 Overview
There are two critical parameters in a fiber optic connection. They are the Insertion
Loss, which is defined as the ratio of the optical output power over the optical input
power and is measured in dB. Additionally, Return Loss, which is defined as the ratio oflight reflected back from a connector, to the light launched into the cable within thesame connection also measured in dB.
In the past, ferrule and fiber tolerances were not as tight as they are today to meet thedemand for low insertion losses. To minimize the optical loss a technique called Tuning
was commonly used. Low insertion losses would be obtained by orienting the fiber core
to a certain position, typically it was aligned with the key direction of the connector. By
orienting the fiber core offset (also known as concentricity error) of each ferrule in thesame direction, the total lateral offset between the joining fiber cores can be reduced if
compared with random orientation, thereby reducing the optical loss. This technique isonly effective when the tuned connector is mated with a tuned connector when the fibercores are rotated and placed in the same orientation. Therefore, mating a tuned
connector with a standard one loses all of its advantages of low loss which is common
in the field.
What are the most critical aspects of achieving low insertion loss measurements? Ofcourse, making the assumption that the connectors are clean, free and clear of foreign
particles and defects.

1

Application Engineering Note

The most critical aspects are:•Ferrule hole diameter – The ferrule is the most important component in a fiber optic
connector that ultimately bears responsibility for optical loss values. For a minimum
Insertion Loss, you should use the tightest-tolerance ferrule hole diameter available.
For example, if the typical values for a single-mode fiber glass Outer Diameter (OD)
are 124.5um to 124.9um the desirable ferrule Inner Diameter (ID) should be 125um
to 125.5um.

•Ferrule hole eccentricity – Eccentricity is the linear distance between two similar
parallel shapes. In this case it’s a displacement of true ferrule hole center from its
ideal position. The hole in the ferrule must be perfectly centered. If not, the fiber
cannot be properly aligned.

•Ferrule hole concentricity – The shape of the bore hole must be round and in thecenter of the ferrule. If it has any ovality you deal with another variable called ferrule
hole concentricity: an oval shape instead of perfectly round one, which will not holdan optical fiber in perfect alignment.

Therefore, it’s important to use ferrules considering the above tolerances for optimum
performance.

Figure 1: Examples of defects in ceramic ferrules that result in lateral misalignments.
Note, the images are exaggerated for demonstrative purposes

In fiber optics, to simplify the classical geometry definitions outlined in Figure 1, all threefactors that contribute to a misalignment of the true positioning of the ferrule hole
centered with respect to the outside diameter of the ferrule, referred to a Concentricity
Error.
2Application Engineering Note

In simple terms the concentricity is the degree of deviation of the inner diameter of theferrule hole from the center of the entire circle. The ideal state is zero, that is, no lateral
offset. But in reality, there is an offset where generally single-mode ferrule concentricity
is maintained below 1.0um. The single-mode ferrule requires its insertion loss ≤0.4 dB
per GR-326 when lining up two terminated ferrules, the optical fibers must line up inorder for light to be transmitted from one to another. Any amount of lateral misalignment(where one core is not concentric to another) will contribute to additional optical loss.
In SENKO a ferrule hole concentricity is measured as the difference of inside diameter
center to outside diameter center (ID to OD). In this case the Premium Low Loss value
considered to be ≤0.4 um, the Premium Loss value considered to be ≤0.6 um, and theStandard Loss value considered to be ≤1.0 um.
In addition, one needs to be aware about Random Mating. It is known that when youmate the connector and check the optical insertion loss in random mating scenario, theIL will be higher compared to measuring against a master jumper. A product such as amaster jumper (or reference jumper) and a master adapter should be a jumper and an
adapter that has absolute lowest possible manufacturable tolerances that typicallyachieved by hand selecting components. It is used as a base to measure and define theinsertion loss of the tested product per testing procedures outlined in FOTP-171 andIEC 61300-3-4. It is commonly misunderstood that the IL tested with a master jumper iswhat you should be getting in the connection mating it inside the racks or any other fieldinstallations. When you use a master jumper and master adapter you are measuring
your connection against a nearly perfect ferrule in a nearly perfect adapter. In a realworld environment, it’s very likely that you are not mating against a master jumper nor ina master adapter, but mating to a standard jumper and standard adapter often
manufactured with varying quality and less strict specifications. It is known that aconnector that has a guaranteed IL of 0.5dB against a master jumper can increase IL toas high as 1.00dB or higher in random mating (or roughly double) from the factory
testing. To see the clear difference between a good connector and a bad connector, theRandom mating method that is defined by IEC should be used.

Figure 2 Testing against Master Jumper yields always lower IL due to minimized lateral misalignment between thecores. Note, the images are exaggerated for demonstrative purposes.

3Application Engineering Note

Insertion Loss criteria based on Random mating in the document IEC 61753-1 titledAttenuation of Random Mated Connectors which defines a certain minimum IL value ofrandomly mated connectors in a field setting and categorizes them into four different
grades. It is important to note that the IEC 61753-1 defines connection performance
grades for single-mode and multimode jumpers in a controlled environment. The
standard gives four grades for IL from A (best) to D (worst) and RL, with grades from 1(best) to 4 (worst). Grade “A” is not officially ratified by the IEC document, but most
likely it will have similar optical performance reflected in Table 1 below.

Table 1: IEC 61753-1 Proposed Attenuation Grade Jumpers* Note, Grade A is not specified at time of writing, but assumed to be as shown4

Application Engineering Note

At SENKO, we are continuously pushing the limits with our ferrule technology to achieve
lower losses. When defining your network budget needs, it is important to know what
optical losses are required. While using the top-of-the-line premium ferrules will help
achieve the lowest loss, it may not always be needed. For example, using a Standard
ferrule from the table below you will achieve a Random Mating mean loss of £0.50dB
which may be acceptable for your application.
CONNECTOR TYPEIL AGAINST MASTER

Unibody Premium Low Loss £ 0.05dB Mean/£0.15dB Max£ 0.08dB Mean/£0.20dB Max
Unibody Premium£ 0.12dB Mean/£0.30dB Max
Standard UPC
Table 2: SENKO Ferrule Loss Specifications

IL RANDOM MATINGIL RANDOM TUNED£ 0.12dB Mean/£0.25dB Max£ 0.15dB Mean/£0.30dB Max£ 0.25dB Mean/£0.50dB Max£ 0.02dB Mean/£0.14dB Max£ 0.04dB Mean/£0.17dB Max
N/A

In order to establish specification base for high performance grade connectors, SENKO
performed a study per an IEC61300-3-34 standard Examinations and measurements –Attenuation of random mated connectors:
Scenario 1 - Testing Jumpers with premium ferrules against Master Jumpers.
Scenario 2 - Testing Jumpers with premium ferrules against Jumpers with premiumferrules.
This would in turn represent a random mating scenario. A quantitative analysis using
theory of probability was employed. First estimating expected losses based on therequired mechanical tolerances for ferrule fiber hole diameter and concentricity error.
The results were compared and determined at what ferrule tolerance threshold the loss
differences are minimized between the two scenarios.
For theoretical values the following calculations were considered when estimating IL
due to lateral misalignments.
The equation used:#!

IL (dB) = -10 log 𝑒 !" , where 𝑈 = $%
χ = core misalignment;'.)'*,.-.*

ωo = α(0.65 + + ".$ + + & )5Application Engineering Noteωo –single mode fiber (SM) spot size determined empirically with α as a fiber coreradius and V as a normalized frequency – dimensional number used to describe thecharacteristics of SM fibers, depending of refractive indexes of fiber core/cladding.
Theoretical calculations were analyzed and correlated to an actual data set in order todevelop ferrule required dimensional tolerances that satisfy the Grade B condition inTable 1. Below in Figure 3 is empirical data that shows the optical losses for thepremium LC/APC ferrules that make Scenario 1 and Scenario 2 relatively close.
IL @1310nm Random, Mean 0.09dB

0. 00250.
00. 507500. .11250.
10. 5
17500. .2
2250.
2
0. 5
27500. .3
3250.
3
0. 5
3750.
4

00.025
0.05
0.075
0.1
0.125
0.15
0.175
0.2
0.225
0.25
0.275
0.3
0.325
0.35
0.375
0.4

IL @1310nm Against Master, Mean 0.05dB

Figure 3: Test data of Premium 1.25mm LC/APC connectors against Master (Mean 0.05dB) and Random mating

against each other (Mean 0.09dB).

During the study, it was determined that the fiber, and especially, the ferrule
dimensional consistency was the key element in achieving low IL results. As seen in
Table 2, the ferrule ID tightness and the concentricity value play an important role inachieving low losses. Through a series of experiments, SENKO has developed
optimum specifications for the ferrules that exhibit premium optical losses in randommating scenarios, and yet can be relatively cost effective. SENKO emphasizes that inorder to achieve this result manufacturing processes of jumper assemblies must be also
under strict control and compliant to GR-326-CORE requirements in order toconsistently produce the polished ferrule geometry and desired IL results that are
required in today’s high-end fiber optic cabling market.
Total

Pass (IL<=0.25dB)

Pass Rate >97%

Average<0.12dB

1310nm1550nm1310nm1550nm1310nm1550nm1310nm1550nm

360

360

360

360

100.00%100.00%

0.06

0.05

Table 3: LC in Random mating with ferrule ID 125.0-125.8um and concentricity ≤0.3um

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Application Engineering Note

The ferrules with the Premium Loss will have slightly higher concentricity (0.5um vs0.3um) and thus are expected to have a slightly higher IL averages without tuning. WithSenko Premium connectors by adding the ferrule tuning technique it is possible toexceed the Grade B Loss requirements.

3.0 Conclusion
SENKO offers a range of specifications including Premium Low Loss, Premium, andStandard connectors that offer varying loss specifications. At SENKO we encourage ourcustomers to purchase quality connectors that offer the tightest tolerances for ferrule
hole diameter, ferrule hole concentricity, and ferrule hole eccentricity, but also whatmeets your optical budget needs.
To achieve the best results, it is important to note that the fiber itself should havecore/cladding concentricity close to zero and factory termination processes must be GR326-CORE compliant. When your manufacturing processes use connectors that meetstringent tolerance requirements, you are positioned to build world-class fiber optic
cable assemblies that deliver performance and long-term reliability. We suggest you
contacting SENKO representative if you have any additional questions.

7Application Engineering Note8