Insertion Loss

AboutDesigning fiber optic test equipment for 20 years
Specialize in measuring Insertion Loss and Return Loss
Tailor test equipment to the needs of the customer
We take pride in simplifying the test and m e a s u r e m e n t
process for our customers to help increase efficiency

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Insertion Loss Overview
What is insertion loss
Where does it come from?
Single mode
Multimode fibers
Launch conditions in multimode fiber

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Insertion Loss
§ Insertion loss (IL) in fiber optic cables is the amount of light lostwith respect to the light going into the fiber optic cable§This is a value that typically is expressed in decibels (dB)𝑷𝒊𝒏𝑰𝑳 𝒅𝑩 = 𝟏𝟎 ∗ 𝑳𝑶𝑮 𝑷§

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𝒐𝒖𝒕

A decrease in 50% power is about 3dB of insertion loss

Where Does Insertion Loss Occur?
§ There are two main sources of loss in a fiber optic cable§

The first is at connections where two fibers may mate together§§

Mated connections, fusion splices or mechanical splices
At an interface light can be reflection (return loss), lost through the cladding, ortransmit down the fiber.
§Reflected light and light that escapes through the cladding contribute to insertion loss.
Light lostThrough cladding

Launch Fiber

Return Loss

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Light transmitted
through fiber

Where Does Insertion Loss Occur?
§ The second source of loss is the fiber itself§

Fiber has inherent attenuation due to absorption and scattering§

Attenuation is expressed in dB/km typicallywww.optotest.com

Connection (Mating) Insertion Loss
§ Connection loss comes in a few forms§

Lateral misalignment§

Light at the core/cladding overlap will escape through the cladding.

Light exits throughthe cladding

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Connection (Mating) Insertion Loss
§ Connection loss comes in a few forms§

Mode field diameter mismatch§ Mode field diameter describes the electric field intensity of the light exiting the fiber.
This typically relates to how much light a fiber can accept for single mode fibers§ Typically 9 to 12µm for a single mode fiber§ Large MFD to Small MFD leads to large loss
§ The area at the core/cladding overlap leads to light exiting the fiber.

Large MFD
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Small MFD

Connection (Mating) Insertion Loss
§ Connection loss comes in a few forms§

Mode field diameter mismatch§ Small MFD into Large MFD leads to low loss

Small MFD

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Large MFD

Connection (Mating) Insertion Loss
§ Connection loss comes in a few forms§

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Angular misalignment will induce loss in connections

10

Multimode Insertion Loss
§ Multimode links present a distinct problem when testing insertion loss
§With single mode fiber there is only one mode that can induce loss. In multimode fiber thereare many modes, and these modes can all affect the loss seen by a connection

Above is a perfectly aligned fully populated multimode fiber, which would result in negligible loss

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Multimode Insertion Loss
§ Multimode links present a distinct problem when testing insertion loss§

If light is propagating through the entire core small misalignments will induce loss§§

The fiber on the right is misaligned slightly.
Light is lost due to this small core alignment offset

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Multimode Insertion Loss
§ Multimode links present a distinct problem when testing insertion loss§

A core size mismatch will lead to losses similar to an MFD mismatch in single mode fiber§§

The fiber on the right is slightly smaller than the fiber on the left.
Light is lost at the core/cladding interface

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Multimode Insertion Loss
Multimode links present a distinct problem when testing insertion loss

! "#$%&Transmission 𝑅𝑎𝑡𝑖𝑜 = '( "#$%& = 80%

IL = 0.97 dB§

The loss of the connection isdependent on how filled thelaunch fiber is§

A more filled core on the launchfiber produces high loss§

A lower filled launch fiberproduces low loss

) "#$%&

Transmission 𝑅𝑎𝑡𝑖𝑜 = ! "#$%& = 87.5%

IL = 0.56 dB* "#$%&

Transmission 𝑅𝑎𝑡𝑖𝑜 = * "#$%& = 100%

IL = 0 dB

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Multimode Insertion Loss§

Due to insertion loss being highly dependent on launch fiber “fill,” standards weredeveloped to harmonize the launch conditions for multimode IL measurements§

Encircled Flux§§

In practice, loss only matters on installed cabling, so EF mimics a “worst-case” transceiver VCSEL source launch§
Guarantees operability in the field when installed.
Helps to make multimode losses more reproducible across suppliers and test equipment

Nearfield Profile

Overfilled
Compliant
Underfilled
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Encircled Flux GraphRecap§§

Insertion Loss represents the light lost through connections and through fiberLight at connections is lost due to§§§§Angular misalignments
MFD mismatchesLight is lost through fiber due to absorption and scattering§§

Lateral misalignments

Referred to as “attenuation:”

Insertion loss in multimode fibers is extremely dependent on the light filling of the fiber§

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Launch conditions were standardized to make insertion loss measurements on multimode fiber more
reproducible

Insertion Loss Measurement
ü Fully automated, single or dual

wavelength insertion loss Measurement

ü Control through USB

ü Wide Multimode source with controlled
launch condition available for underfill,
full fill or overfill

OP815
Single Channel

OP850
Multichannel (4 to 24 channels)

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Insertion Loss & Return Loss Measurement
ü Quickly measure IL, RL, &optical powerü Control through USB

RL measurements(single mode - 0 to -80db|multimode - 0 to -58db)

OP940

OP925

Single Channel

Single Channel

OP940-SW

OP940-CSW

Multichannel

Multichannel(up to 24 channels)

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ü Wide dynamic range forwww.OptoTest.com
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