Fiber optics power meter

An optical power meter (OPM) is a device used to measure the power in an optical signal. The term usually refers to a device for testing average power in fiber optic systems. Power meters are part of the toolbox essentials for all technicians installing or maintaining any type of fiber networks. They are used to measure that the optical signal level is in right range (not too high or too low). Together with a known level optical signal source and optical power meter can be used to measure fiber signal attenuation.

When I was in need for a fiber optic power meter, I found this pretty cheap model AUA-70A Fiber Optic Optical Power Meter Cable Tester Networks FC/SC Connectors -70 – +10dBm.  It looks like a slim upgraded version of CommScope Tyco AUA-70A Power Meter.

http://www.banggood.com/AUA-70A-Fiber-Optic-Optical-Power-Meter-Cable-Tester-Networks-FCSC-Connectors-70-10dBm-p-1032244.html?p=27131452996820140438

Features

User self-calibration function

Linear (mW) and nonlinear index (dBm) displayed simultaneously

Unique FC / SC / ST generic interface, without complicated conversion

The optional automatic shutdown function

Optional on / off backlight display

Test range is -70dBm~+10dBm.

This optical power meter can measure power of the light at 7 wavelengths: 850/980/1300/1310/1490/1550/1625nm

Powered with two AA batteries

The display is time averaged power of signal on fiber. A typical OPM measures accurately under most conditions from about 0 dBm (1 milli Watt) to about -50 dBm (10 nano Watt), although the display range may be larger (with this meter 70dBm~+10dBm)

Here is one setup where I test the meter with cheap fiber visual fault locator as signal souce:

All the signal wavelenghts are measured with the same sensor, which I quess is InGaAs detector. Basically this meter consists of a photodiode, amplifier and display unit. This meter is traditional optical power meter that responds to a broad spectrum of light, however the calibration is wavelength dependent. Before making measurement, you need to set the meter to correct wavelength (test wavelength is usually known so not usually an issue) before you can get accurate results – if you select wrong wavelenght you will get wring results. For example with exactly same signal I get at 850 nm settings several times higher power reading than with 1310 nm setting.

The meter comes with small bag that provides some protection to the device:

Pros:

- Meter works well

- Cheap

Cons:

- The case plastic is feels cheap, does not feel high quality

- What is actual accuracy this provides?

 

 

More related material: Links to information on fiber Ethernet signal levels:

https://www.juniper.net/documentation/en_US/junos12.3/topics/reference/general/fe-ge-fiber-optic-specs.html

https://www.ccontrols.com/pdf/abc3.pdf

http://etherealmind.com/can-fibre-optic-ethernet-cables-be-longer-than-the-standard/

https://www.juniper.net/documentation/en_US/release-independent/junos/topics/reference/specifications/transceiver-m-mx-t-series-10-gigabit-optical-specifications.html

 

3 Comments

  1. Tomi Engdahl says:

    Here is an interesting article on DIY fiber power meter alternative (considering the cheap price of ready made it might not make sense trying to build your own):

    Hackaday Prize Entry: An Optical Power Meter
    https://hackaday.com/2017/09/14/hackaday-prize-entry-an-optical-power-meter/

    This is the type of crowd that’s famous for building their own test equipment. If you need a way to program a flash chip, don’t go out and buy one — you can just build one. Need a spectrum analyzer? You can build that out of copper clad board. For his Hackaday Prize entry, [oakkar7] is building an optical power meter, capable enough to do futzy fiber work, but still completely DIY.

    [oakkar]’s optical power meter uses these SPF transceivers, tied together with a fairly simple circuit consisting of an Arduino, a few tact switches, a Nokia LCD, and an FTDI UART.

    Optical Power Meter (with SFP and DDM protocol)
    https://hackaday.io/project/21599-optical-power-meter-with-sfp-and-ddm-protocol

    DIY Optical Power Meter with SFP (Small Form-factor Pluggable transceiver) and DDM (Digital diagnostics monitoring ) protocol

    To build DIY optical power meter with standard SFP module and Arduino
    - Can measure optical power in dbm and watt
    - Can Enable/Disable TX power output (laser source)
    - Can debug via UART

    And Arduino Library
    - a lib for SFP/DDM interfacing (not only optical sfp transceiver
    - to interface and interpret DDM (Digital Diagnostics Monitoring ) protocol (which used in most optical fiber communication) scheme and format
    - to debug, monitor, detect alarm and control SFP via DDM
    - to extend the capability of handling data TX/RX interface (Arduino data over optical fiber)

    Initial concept

    - Most optical fiber module in today communication used from factor called SFP (small form-factor pluggable) physical interfacing. SFP is widely used in many switches, routers and many telecom devices. SFP modules comes with various transceivers option from electrical to optical interfaces such as Ethernet, Giga-bit Ethernet, optical fiber , SONET, STM, etc.

    - Although transceivers are different, all SFP modules are controllable with a standard protocol named DDM (Digital Diagnostics Monitoring).

    - DDM is The operating and diagnostic information is monitored and reported by a microcontroller inside the transceiver, which is accessed via a 2-wire serial bus (also known as “I2C” or “I2C” protocol).

    - I2C bus interfacing is easily done by Arduino

    Reply
  2. Tomi Engdahl says:

    here are four special wavelengths that you can use for fiber optic transmission with low optical loss levels, which this table lists:
    Windows Wavelength Loss
    1st wavelength 850nm 3dB/km
    2nd wavelength 1310nm 0.4dB/km
    3rd wavelength 1550nm (C band) 0.2dB/km
    4th wavelength 1625nm (L band) 0.2dB/km

    Source: https://www.cisco.com/c/en/us/support/docs/optical/synchronous-digital-hierarchy-sdh/29000-db-29000.html

    Reply
  3. Tomi Engdahl says:

    Troubleshooting TechNotes
    Introduction to Optical Fibers, dB, Attenuation and Measurements
    https://www.cisco.com/c/en/us/support/docs/optical/synchronous-digital-hierarchy-sdh/29000-db-29000.html

    Reply

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