Before all are safety! - Laser safety

What this device is for? 

This is in-field test device which can test & measure:

  1. Identify working wavelength;
  2. Measure optical power;
  3. Determine the connection link speed;
  4. Identify the existence of a CATV RF signal;
  5. Works as calibrated laser source.

test link (if other side connected to SFP or media converter (MC)) 100/1000Mbps for one or two fibers link,

This test device have 2 optical ports. First port is for standart using, then we need to determine: working wavelength, optical power, identify the existence of a CATV RF signal, and link connection speed. Second optical port needed if we will measure PON (passive optical network). ;

But now about everything in details...

First Optical port for optical power, wavelength and link tester

Connected optical power goes through two opto-mechanical switch (next OMswitch) to the first Sp1 PLC splitter (Planar Lightwave Circuit) 1/2 with 50/50% insertion loss (what is approximately ≤4.0dB) with one output directly to the first photodiode D1 for optical power measuring.

Second output of the first splitter connected to Sp2, which needed for making "passthrough" channel for PON testing, to the Sp3 - which collects two line signals to one output (this splitter also needed also needed due to PON network measurements). After all optical line connects to the first FM1 FWDM (Filter Wavelength Division Multiplexer)Pass line of this filter with filtered 1490nm connected to the second photodiode D2 for optical power detection/measurement of 1490nm, Reflected line with filtered 1310 and 1550nm connected to the second FM2 filter. Second filter Pass and Reflected lines connected to photodiodes D3 and D4 for 1550nm and 1310nm optical power detection/measurement respectively.

Each photodiode is InGaAs photodiode. 

Because each photodiodes requires an operational amplifier with a programmable gain factor (since the power range is too wide 76dB), a solution was found using only one programmable operation amplifier for all four photodiodes. But I'll describe this step a little later.

So when microcontroller detects signal from one of photodiodes and if this signal will not be higher as -2dBm, microcontroller will switch OMswitch to defined SFP 1310, 1550 or 1490nm (if detected signal will be from 1550nm photodiode - will be switched to 1550 SFP, if detected from 1310nm - will be switched first to the 1310 and so on).

Next step is detecting link speed (if other side connected to SFP or to MC-media converter). This stage are realized through integrated into SFP DDM (Digital Diagnostic Monitoring). DDM can show us not only transceiver temperature, supply voltage, laser bias current, transmitted average optical power, received optical modulation amplitude (OMA) or Average Optical Power, but also by received code detect link speed and identify SFP or MC connected at the other end of the fiber.

Second port for PON testing

Optional* - Third port, visual laser source

Very often need to determinate/identify correct fiber port in ODF (optical distribution frame). The laser source can work in 850nm and can be switched to CW or as modulated with different modulation frequency.

This device can replace multiple test devices used at the same time with fiber optic to determine and analyzing line work parametrs and faults.

Ideas and comments are welcome ;)