Extreme Fiber Coupled Laser Diode Power Loss

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Discussion Overview

The discussion revolves around the causes of extreme power loss in fiber coupled laser diodes, specifically those with a wavelength of 658nm and a rated output of 60mW. Participants explore troubleshooting methods, measurements, and potential factors affecting performance, including thermal effects and connector issues.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant notes a significant power loss of -13dB (95%) in one optical channel and questions the accuracy of their dB to percentage conversions.
  • Another participant challenges the interpretation of the dB measurements, suggesting that a +30dB gain represents a substantial increase in power, contradicting the claim of a small gain.
  • Concerns are raised about the output power dropping below expected levels, with one participant reporting a decrease from 54mW to 4mW in a specific channel.
  • Questions are posed regarding the impact of prolonged operation on diode performance and whether noise could contribute to the observed issues.
  • Suggestions are made to monitor the temperature of the module and check the matching of the fiber to the power meter as potential factors in the power loss.
  • Participants inquire about the specifications of the laser diode module and the power meter being used to better diagnose the problem.
  • A later reply indicates that the issue may be related to the bulkhead connector.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of measurement data and the causes of power loss. There is no consensus on the root cause of the issue, and multiple competing explanations are presented.

Contextual Notes

Limitations include potential misunderstandings in the conversion of dB to percentage, the need for more information about the specific equipment used, and unresolved questions about the effects of temperature and noise on diode performance.

daniel1211
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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.

I thought that perhaps the sources had been on for too long and that perhaps the diodes where being affected by heat, I shut everything down and proceeded to check the systems the next day after they had cooled but unfortunately the output was still extremely low.
 
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daniel1211 said:
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.
They appear to be close to the specified output. What output do you expect from a 60mW diode?

daniel1211 said:
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 do not understand your dB to % conversions. What do the % represent?
How can +30dB be a small gain when it represents 1000 times as much power?
 
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daniel1211 said:
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.
I'm going to agree with Baluncore

your misunderstanding / misinterpretation of the figures is leading you to believe there is a problem when one doesn't existDave
 
I was using a guide that was helping me convert dB to percentage, I must of made a mistake.

Either way I still don't understand why my source channels are outputting less then 10mW when after considering loss they should be outputting around 50mW and are rated at 60mW.

For example when I first measured one channels output power I was given 54mW yet when I recently did a spot check on the same channel I measured 4mW.

Would a source that has been powered on for a day cause the diode to lose power?

Could noise cause this problem?
 
Powering off for a time should not make a difference. If it does then that is an important clue. Monitor the temperature of the module.

It might be matching of the fibre to your power meter that is a problem. How is the connection made ?

Some laser diodes have an optical power monitor built onto the back of the diode. Are you able to use that sensor output to independently monitor the laser diode output before the fibre ?

I believe we can identify the problem if we are given a little more information. It would help if we knew the make and model of the fibre coupled laser diode module, and the make and model of the power meter you are using.
 
This is the link to the laser diode spec sheet
http://www.blueskyresearch.com/fileupload/FiberTec_II_02-05-2015.pdf

The fiber coupled laser diode uses a FC connector
The fiber jumper used to connect to the power meter is ST to FC

The source that we are using is a recent custom build and the sensor is supposed to be part of the next build

I am using a Thorlab PM200 power meter
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5386
[PLAIN]https://www.thorlabs.com/dra...3-5056-0103-79616E9683171250/PM200-Manual.pdf[/PLAIN]
as well as a Thorlab Photodiode Amplifier
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1003
 
Last edited by a moderator:
It seems that the issue was due to the bulkhead connector.
 

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