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Thread: A Statistical Analysis of A130 vs A140

  1. #1
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    Default A Statistical Analysis of A130 vs A140, Power and Wavelength

    I have been working on testing a large number of diodes to determine if A140 really is better than A130, and in general characterize these projectors.

    Test Setup:
    Mechanical
    The test setup consists of TEC cooler, upon which complete XJ-A130/A140 arrays are mounted to. The internal thermistor is used for temperature feedback, and the stock lenses are used for collimation. The temperature is kept at 25.0C, +/-1C, over the entire array.

    A typical IV plot is shown below:
    Click image for larger version. 

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    Power (electrical)
    The diodes are powered by a HP6633a power supply, in constant current mode, in a stairstep current sweep from 0.001 to 1.500A. Each current is kept for 0.5s, to allow the diode to come into thermal equilibrium with the mounting block and allow the power meter to settle. For reference, it was found that decreasing the pulse length to 0.1s changed the power reading less than 5%.

    Power (optical)
    A Coherent FieldMaster GS and LM-2 probe w/1000x attenuator is used to measure the power. The calibration on the meter is out of date and I suspect it may be as much as 10% off comparing to other meters, but for relative measurements I have found it is very repeatable (retesting an array over a period of several weeks gave results within 1% of each other). A simple robot is used to move the power meter to each of the diodes in the array, such that large number of diodes can be tested 'easily'

    Wavelength
    A piece of optical fiber was mounted in the LM-2 power meter probe, such that some of the back power is sent to an Ocean Optics USB650 (aka, Red Tide) grating based spectrometer. Due to the fact that some of these diodes have very broad spectra (some over 2nm wide) I do a Gaussian fit to the data, and take the center value. This seems to be fairly reliable, however I have not had a chance to do a rigorous calibration of the system, so I would only trust the wavelength readings to +/-5nm absolute and +-2nm relative to each other. The std dev of the fit is checked, and it below 1.1 the data point is ignored in the plots.

    Findings - A130 vs A140
    These plots were generated in late 2010 with 96 A140 diodes, and 1656 A130 diodes (thanks guys!), so while the A140 sample size is a little on the small size I believe I have enough information to draw statistically significant conclusions.
    A130 vs A140
    Below find a histogram of the A130 vs A140 power distribution.
    Click image for larger version. 

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    For the skeptics, here are some numbers:
    Code:
    	A130	A140
    Mean	1.09	1.03
    Std Dev	0.16	0.08
    So-
    The A130 diodes are more spread out than the 140 diodes, that is to say that there are many more bad diodes (approximately 3% of the A130 diodes put out less than 0.5w, where as I have yet to see a single dud diode from an A140), however I have also seen a much higher percentage of the <1.2w output diodes form A130s.


    Findings - Wavelength
    I was able to test 888 A130 and 360 A140 diodes for wavelength, and have attached a histogram of the results below:
    Click image for larger version. 

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    As you can see, the wavelength spread is quite broad, with significant numbers of diodes from 435 to 455nm. Furthermore, on average the A140 diodes have a shorter wavelength than the A130 diodes, which is quite unexpected (one would expect that the A140 would use longer wavelength diodes, because longer wavelengths have a higher luminosity)

    Additionally, I plotted the wavelength vs power for each of the diodes to generate the following scatter plot:
    Click image for larger version. 

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    From this you can see that there is almost no correlation between wavelength and power, however you can also see that the corner we are after (high wavelength, high power) is pretty sparse. Again, this shows that while the A140 did have a slightly higher power on average, it has a significantly lower average wavelength.
    Last edited by krazer; 03-16-2011 at 15:12. Reason: added wavelength info

  2. #2
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    Default

    Interesting findings. Thanks for sharing.

    You tested over 1700 diodes? You need to get out more lol!

    Do you plan to test A150 diodes also?
    This space for rent.

  3. #3
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    Default

    Thank you for sharing your results, it's valuable information.

  4. #4
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    Default A130vsA140

    Any look at a temperature effect on the power output of either diode?

  5. #5
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    Hi guys-

    I apologize for the long delay in updating this thread, school has really been busy this quarter. I have tested about 800 diodes for wavelength, and have found that the wavelength is fairly random from 435-455nm, for A130 projectors.

    I have updated the first post with info on my findings, and am investigating the temperature dependence now.
    Last edited by krazer; 02-12-2011 at 13:02. Reason: updated first post

  6. #6
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    I just wanted to bump this thread now that I have added a comparison between the wavelength of the A140 vs A130. Curiously enough, the A140 arrays I tested had slightly shorter wavelength diodes on average, quite the opposite of what I would have expected.

    I would really like to get my hands on an A150 projector to see if the theories about longer wavelengths are true.

  7. #7
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    Some time ago you mentioned that you were looking into the temperature effect on output wavelength. Any progress?

  8. #8
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    I started looking at the effect due to temperature, however the wavelength shift was too small for my current setup to measure reliably, so I am working on building a better test rig.

    The initial results show that you get significantly higher wavelength with more current (~5nm shift from 500ma to 1500ma), but very little change with temperature (well under 1nm for a 10C temp shift). There is a marked power decrease with higher temps, so keeping them cool seems to be the best bet from what I can tell.

  9. #9
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    Curiously enough, the A140 arrays I tested had slightly shorter wavelength diodes on average, quite the opposite of what I would have expected.
    Maybe a shorter wavelength yields a better efficiency in the phosphor wheel.

  10. #10
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    Quote Originally Posted by -bart- View Post
    Maybe a shorter wavelength yields a better efficiency in the phosphor wheel.
    Maybe this, or maybe the diodes closest to the design wavelength go in the 'A' bin, so go to the higher end projectors by default?
    http://img62.imageshack.us/img62/3985/laser.gif

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