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Optical Source Power

  1. Oct 7, 2016 #1
    I have multiple sources that have a max power output of 60mW, I am using a power meter that can read up to 200mW but when I connect directly to the source channel I get approximately 15mW or less. I have tried a different meter and I have tried different sources only to end up with the same results.

    I thought perhaps that I had received the wrong power meters and was using one that could only read up to 20mW but when I lowered the power to 10 I got an output of 2mW. I've made sure that everything is clean but that has made little difference.

    Hoping maybe someone might a solution that I might try

    Thank you
  2. jcsd
  3. Oct 7, 2016 #2

    Simon Bridge

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    Describe the problem - so far the answer "the sources are not outputting at maximum" fits the description. There can be any number of reasons for this, including "the source is not set up to output at maximum".

    Do I understand that you have an optical source that has a dial labelled "output power" and you set it to it's "60mW" mark, but only get 15mW from a detector placed directly in the path of the source?
    The geometry of the source, and the geometry of the detector, can affect the reading... have you checked?
    ie. if the source is a hole 1cm square, and the detector has an aperture of 0.25cm square, then it would be reasonable to expect the meter to read 15mW for a total 60mW output evenly across the hole. The reading may be less if the detector is not exactly square to the source, or if the source intensity varies across the hole.

    You may want to calibrate the detector against a source you trust ... but it may be that the detector is inefficient for the type of source you are using. A visible light detector will underreport UV for instance.

    You have reported 0.2 to 0.25 of the expected value depending on the set output ... but I cannot tell how reliable this report is since you also say "or less" for one of them. This means I cannot attach any significance to the consistency or inconsistency of the discrepancy.

    But you have not actually said how the measurement was carried out - just "plugged into the channel" ... so is this more of a digital ammeter that sits between the source and it's power supply? You should not assume that everyone will be familiar with the setup of your equipment - besides, the discipline of describing what you are doing in enough detail that someone unfamiliar with the setup or even the field will understand what you have done can yield unexpected solutions.
  4. Oct 8, 2016 #3
    Thanks Simon,

    I am using laser sources that each have 32 channels, each channel has a single mode FC terminated fiber that is coupled to a 658nm laser diode with a 60mW max output. The FC connected fiber is then mated to a FC to ST bulkhead adapter.

    I've connected an optical power meter that falls within the 658nm wavelength range and that is suppose to go up to 200mW. The power meter was connected to the laser source either directly to the laser diode using the FC connector or by connecting it to the ST bulkhead adapter using a ST jumper cable.

    When connected to the source my output power was approximately 15mW with some loss when connecting through the adapter. The manufacturer of the handheld laser source say that the high output should be 2.5mW but could be more and the low output should be 1mW but could be less.

    Using a photodiode and a photodiode amplifier I was able to get a power reading that was close to what I was looking for but only if the the power was set below 10mW.
  5. Oct 8, 2016 #4

    Simon Bridge

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    Manufacturer says to expect "high output" 2.5mW, maybe more... that would be the "high output channel" diode right? The 32 diodes provide a range of powers...
    You measure 15mW off something somehow. That is more than 2.5mW. Alarmingly more so probably not directly off the high output channel.
    The max output rating of the diodes is irrelevant... the output depends on the input, and I don't see how you are adjusting the equipment to set what the output power should be. So far it sounds like the manufacturer has set the output power for each channel.

    Your description of the problem remains unclear:
    You only get some undisclosed desired value of "power reading" when you somehow set the power of something undisclosed to less than 10mW.

    So far there is nothing in your description to indicate anything other than normal, correct, operation of the equipment. Tell me what you expect the equipment to do and why.
    Last edited: Oct 8, 2016
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