AN121

The Photonics Pioneer

Stability Measurement
Application for 500 Series Optical Power Meter / Sensor
Over view
How does one measure the power stability of a light source and what are common pitfalls?
This application note describes how to setup the measurement with the OP500 series power meter modules. Dataacquisition is controlled by a computer that runs OPL5 application software. The measurement results for the 980nm
laser source are displayed in real time.

Why is source stability of interest?
To measure insertion loss of optical components, two measurements are taken; a reference measurement and ameasurement that includes the device under test. Power fluctuations between the two measurements will add to thesystematic error of the measurement. For this reason the fiber optic sources that are used for insertion loss measurements
have to operate extremely stable. That way the fluctuations of the sources are relatively small compared to the actual loss
measured. The standards (IEC61300) recommend a stability of <0.05dB or 1% of the attenuation/loss to be measured.
Any data logging fiber optic power meter can be used to measure source stability as long as the following requirements
are met:•The wavelength range of the photodetector matches the wavelength of the source (SI detector for 500nm to 1100nm,•The output power level of the source cannot exceed the sensitivity range of the optical power meter•

InGaAs or Ge detector for 830nm to 1650nm)

The measurement accuracy and resolution of the optical power meter should exceed the expected source stability.
(Usually a 0.01dB resolution/accuracy is sufficient to quantify stability <0.05dB)

For long-term stability measurements special care needs to be given to the test setup in order to eliminate external
influences that impair and falsify the stability data.
•Use only fiber optic cables with high quality and clean connectors. Specifically when measuring narrow line-width•

Use the appropriate core size and type of cable•sources, for example DFB, reflections at connector interfaces can cause fabry-perot effects

Secure measurement cables. Movement of fibers can cause changes in power readings. Bending a cable more or lessinduces additional loss. Moving fiber loops can change the polarization of light. Cables are easily moved by people
walking by or forced air from air condition vents

Measurement Setup

OP508
The equipment required for a single channel stability test setup are: PC, USB cable, OP500 Series Power Meter Module (OP508shown), OPL5 application software, the appropriate fiber cable and the source to be tested.

1

SANTEC CORPORATION
5823 Ohkusa-Nenjozaka, Komaki,
4750 Calle Quetzal
Aichi 485-0802,
Camarillo,
CA Japan
93012

OptoTest Corp.

11/18 /14
+81-568-79-3536

Doc: AN-121 Rev. B

www.santec.com
The Photonics Pioneer

SANTEC USA CORPORATION
1.8 05.987.170 0USA Toll Free
+1-800-726-8321
sales@ optotest.com
engineering @ optotest.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

Stability Measurement
Application for 500 Series Optical Power Meter / Sensor

AN121

The Photonics Pioneer

To command the data logging, a PC based application
software is needed. Either OPL5 is run or a similar programis executed. If OPL5 is used it is setup in data logging mode.
The acquired data (absolute, relative power level as well as
ambient temperature) is directly written to an EXCEL data
file. The screen shot (right) shows the application with thegraphing enabled.
Other methods to capture power readings from an OptoTest
optical power meter are the National Instruments Labview
environment or custom VB6, VB.NET, C++, or Delphi windows
applications. OptoTest provides for a DLL interface to theOP500 series that allows any of the above.

Test Example

To capture this data the OPL5 application is configured toacquire a power meter reading and temperature reading every
60 seconds. The captured data is directly written cell by cell
into an XLS spreadsheet.

stability [dB]

For the purpose of illustration a 980nm FP laser is tested. Thissample laser happens to exhibit a temperature dependancy
that is nicely captured by this 500 minute test run.

temperature [ºC]

Stability of 980nm Laser

The resulting chart to the right illustrates the temperature stepof approximately 1ºC causing a power drop of 0.01 dB.
time [minutes]

Common Pitfalls

To measure source stability, or the stability of any device, some precaution has to be taken. For example, make sure that:•The power meter stability is better than the expected stability of the device under test, typically <0.01dB•

A high performance cable, such as an HPR reference cable, is used to ensure high quality connections•••

Optical power levels do not saturate the power meter

Special attention is taken to maintain the highest standard of cleanliness on the fiber endfaces

Organized routing of all optical fiber is maintained. Suggestions for fiber routing include keeping all bend radii greaterthan 2” radius (5cm) and gently taping the fiber in place so that there is no possible movement as a result of passers-by
or forced airflowProduct discussed in this application note
The OP500 series of fiber optic power meter modules offer a very cost-effective solution to measure the stability of lightsources. Specifically for long term measurements that occupy test equipment for an extensive period of time.

OP508 Fiber Optic Power Sensor

2OP510 Optical Power Meter withbargraph display

OPL5 Power Meter
application with datalogging

SANTEC CORPORATION
OptoTest
Corp.

5823 Ohkusa-Nenjozaka, Komaki,
4750 Calle Quetzal
Aichi 485-0802,Camarillo,
CA Japan
93012
Doc: AN-121 Rev. B 11/18 /14+81-568-79-3536

www.santec.com
The Photonics Pioneer

HPR High Performance
Reference Cable

SANTEC USA CORPORATION
1.8 05.987.170 0
USA Toll Free
+1-800-726-8321
sales@ optotest.com
engineering @ optotest.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550