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What could cause a laser source with fiber coupled laser diodes to have extreme loss of power? The laser diodes have a wavelength of 658nm and have an output rated at 60mW but it seems as though the optical channels actually output ranges between 58 to 70mW.

During some troubleshooting I noticed that one of my optical channels had a loss of -13dB (95%) so I cleaned the fibers to make sure there was no blockage but when I remeasured I was only given a small gain of maybe +30dB (0.1%). I decided to spot check other channels and noticed that they also had significantly dropped in power.

The sources had been on for awhile so I thought that perhaps the sources had been on for too long. I shutdown everything down and proceeded to do a power check the next day after they had cooled but unfortunately the output was still extremely low.

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  • \$\begingroup\$ You ought have measured the Tj by measuring Vf*NTC [-'C/mV], you may have damaged them 70'C max (BTW 0.1% power gain =.004dB) \$\endgroup\$ – Sunnyskyguy EE75 Nov 19 '16 at 22:41
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    \$\begingroup\$ 60mW is the ABSOLUTE MAX? \$\endgroup\$ – Sunnyskyguy EE75 Nov 19 '16 at 22:50
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What could cause a laser source with fiber coupled laser diodes to have extreme loss of power?

I would suggest the designer was not aware of the critical thermal characteristics in the datasheet.

Hint Do not exceed 50'C junction temp where efficacy takes a "nose-dive"

As a reference I have another 60mW 658nm Laser diode in a TO-18 can

From this I extracted the thermal characteristics and replotted so you can understand them easier. Keep in mind when they spec the performance at 25'C this always uses an infinite heatsink for any semiconductor, which would be the same as a pulse test with no thermal rise.

It is a lesson for you to learn to read datasheets and understand them perfectly before designing or testing.

enter image description here

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After some more troubleshooting, I saw that that the bulkhead connectors were becoming loose which I believe is causing a misalignment between the two fiber connectors.

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