Application Notes

Here Kingfisher's experienced engineers share their experience in best practices and procedures for fiber optic testing related mostly to installation and maintenance. We hope that by sharing our knowledge, we will help grow our industry. Please enjoy & pass on these notes. Alternatively, browse Standards related Test Procedures, Equipment & Reporting

How to choose an optical detector

Which fiber optic power meter detector do I need?

It is important to correctly match the power meter detector type to the application.
The correct detector for loss and power measurements on fiber optic communications systems will generally be as follows:

InGaAs (Indium Gallium Arsenide)

Precision measurement over 1300 - 1650 nm wavelength bands.
Reduced measurement accuracy over 850 nm band due to wavelength sensitivity.
Maximum fiber core size 100 u.

VE Visual Enhanced (InGaAs)

Precision measurement over 850 - 1650 nm wavelength bands.
3x better accuracy than InGaAs across the 850 nm band, due to improved wavelength responsivity stability.
May have lower maximum power level specification.
Maximum fiber core size 50 u.

H series / high power (attenuated InGaAs)

Used for high power measurements. Choose from H5, H3B and H6 attenuation levels.
These detectors are more expensive and have lower accuracy than normal InGaAs detectors, so only specify them if expecting to measure beyond the range of a non-attenuated detector.
The peak or pulsed signal power must be within the meter range.
High power meters have less AutoTest sensitivity, which is a consideration for loss testing.
The KI2600-H5 or H3B offers the best balance for most high-power users, with up to +24 dBm range & reasonable Autotest sensitivity.
The KI2600-H6 offers the highest power level of +33 dBm. For single mode fiber applications only.

XL series / large area

Use XL series detectors for multi-fiber connectors such as MPO, MMC, or POF and other fibers above 200u active fiber core diameter.
HCS is 200u core diameter, so a standard meter is just OK for HCS installers. A large area Si5 detector will ensure laboratory grade results.
Select from Si5, Ge5, Ge7 or InGaAs5 using the above guidelines.
A Silicon detector is ideal for visible, POF & 850nm.
MPO connectors with 16 and 32 fibers require the larger Ge7 detector, which also works with other MPO fiber counts.
XL series detectors typically work with many connector styles, including e.g. LC, SC, FC & MPO, so are very versatile.
Large area InGaAs detectors are very expensive and are typically used in laboratory applications. For fiber optic installation applications from e.g. 850 - 1550 nm, a Ge detector is typically adequate.

What power level is the system?

Maximum system power level expectations

Most Telco digital transmission systems have maximum power levels below +5 dBm.
Most LAN transmission systems have maximum power levels below 0 dBm.
Specialist systems, typically RF or analogue, without an optical amplifier, have maximum power levels below +15 dBm.
Long distance systems with an optical power amplifier have maximum (fault) power levels below +23 dBm.
On installed single mode systems with standard polished-fiber connectors (SC / LC / FC etc.), total long-term system (fault) power per fiber cannot go above +23 dBm per fiber, owing to connector power density limitations. In fact, for routine operations, +18 dBm is regarded as a maximum, above which special operational precautions are needed to avoid catastrophic connector / system failure.
For systems operating above +18 dBm, typically either no connector, or expanded beam connectors are used, due to the extreme power density. Anything above +23 dBm tends to be a "non-installed" R&D system. R&D bench customers report using up to +33 dBm temporarily, on single mode fiber systems.

Minimum system power level expectations

It's rare to encounter system power levels below -35 dBm.
Use of a fiber amplifier pre-amp can extend recover sensitivity down to between -40 to -45 dBm.
Use of a power meter on a cabling system below about -45 dBm is problematic, due to the possibility of stray sunlight leaking into exposed cabling.

Useful graphs

Power meter responsivity wavelength dependence

Ge vs InGaAs responsivity @ long wavelengths

Ge and InGaAs detector responsivity from 1500 - 1650 nm

The above graph shows the room temperature response of power meters with Ge & InGaAs detectors as the wavelength is changed beyond 1500 nm.
The Ge meter is unsuitable for work on CWDM and DWDM systems above 1550 nm, the InGaAs meter is obviously a much better choice, since it is very stable. This graph uses real measurement data.

Ge response drift at over temperature @ 1580 nm

Ge detector effect of temperature on responsivity at 1580 nm

The above graph shows how the 1580 nm thermal response of a power meter with a Ge detector changes with temperature.
This instability makes Ge power meters basically unsuitable for field work on CWDM and DWDM systems above 1550 nm.
The thermal stability below 1550 nm is much better, around 0.2 dB, however it's never as good as InGaAs. This graph uses real measurement data.