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NEW LOC Laser diode review.

Mike, do you have an accurate spectrometer? When the diode gets hot, It MAY be going through a wavelength shift. This would make the diode far less efficient as it is not lasing at its DESIGNED wavelength. Is this a possibility to consider? Even a shift of 3-4nm could make a big difference in the efficiency of the diode. Have you tried cooling the diode while it runs?
 





Tyler ---

I've been running the current up quickly and the effect appears before the heatsink even warms. My spectrometer isnt good enough to see 3nM shift.

PS -- I went to see The Moody Blues yesterday and I didn't get back until late.

HMike

I'm sending a mounted LD to Benm to comnfirm my readings! It's to "dangerous" to press out a working LOC diode.
 
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Thanks all for the great advice -

MIKE !! Thank you for your EXTREMELY thorough testing ! :)

These diodes were presented to me as being THE REPLACEMENT for the LPC-815c diodes. Exidently (according to my distributor) they will soon be replacing the 815's with these, so the 815's MIGHT be coming to the end of their life cycle. That would be a bummer, since they are definitely more powerful - although this diode does seem to be a lot sturdier. I'm interested to find out what Bemn comes up with for info - I know Mike's testing methods are beyond reproach (whether YOU folks know that or not is immaterial ! I know !) and he is more than thorough in testing out diodes. *sigh* I was hoping that he would be rewarded with a nice fat, 1/2 Watt of power for all his troubles out of these diodes, but I guess it is not meant to be !

The WORST news about these diodes is this : They cost 50% MORE than the LPC-815c's do.....which means eventually we will see the pricing go UP instead of down on red diodes for FUN STUFF. Damnit, that sucks !

Thanks again to Mike for doing all this work - I'll try to find SOME way to compensate you, I'm sure of it !!!!

-Greg
 
Greg ---

I actually couldn't believe what I got for readings after all these years. A "foldback" ???? I posted the data knowing there would be questions and Benm jumped in with questions. Questions of scientific basis - SO -- at great personal expense ($2.28), I sent him diode 1 in the Aixiz housing to confirm or negate my data. That is what science is about.
Understand that Ben's data may differ on PO than mine since in this hobby - power meters are not correlated and we have different lenses. We are looking for 1. The similar foldback curve at about 400 mA. --- 2. Is temperature a factor? --- 3. How and Why this foldback exists. Might it be to limit hobby power? Will we see this built into future diodes?

HMike
 
Hemlock_Mike said:
Greg ---

I actually couldn't believe what I got for readings after all these years. A "foldback" ???? I posted the data knowing there would be questions and Benm jumped in with questions. Questions of scientific basis - SO -- at great personal expense ($2.28), I sent him diode 1 in the Aixiz housing to confirm or negate my data. That is what science is about.
Understand that Ben's data may differ on PO than mine since in this hobby - power meters are not correlated and we have different lenses. We are looking for 1. The similar foldback curve at about 400 mA. --- 2. Is temperature a factor? --- 3. How and Why this foldback exists. Might it be to limit hobby power? Will we see this built into future diodes?

HMike
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Mike - I cannot deal with the fact that it cost you money to continue this review ! Send me your Pay-Pal address so I can reimburse you that outlandish amount you spent ! :-)

In all seriousness - if ANYONE ever needs an assist with a review, make sure to add Mike to your list of testers ! If I had more diodes of this variety, I would have spread the wealth a little bit and sent some to the other great testers as well ! (no offense meant for any ommisions, I assure you !) I look forward to Benm's data.

Too bad these diodes cost about 50% more than the LPC-815's do ! I was hoping they would blast on outta there *sigh* I'll find a decent 1/2 Watt or full Watt red diode sometime soon for Mike (and others) to test - if they are out there, I'll find them !

*Greg
 
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I'm definitely interested in 1/2 or full watt reds! :D
Red has always been good to me, and I shall always love it for nostalgic reasons ;)
 
SenKat_Stonetek said:
Mike - I cannot deal with the fact that it cost you money to continue this review ! Send me your Pay-Pal address so I can reimburse you that outlandish amount you spent ! :-)

In all seriousness - if ANYONE ever needs an assist with a review, make sure to add Mike to your list of testers ! If I had more diodes of this variety, I would have spread the wealth a little bit and sent some to the other great testers as well ! (no offense meant for any ommisions, I assure you !) I look forward to Benm's data.

Too bad these diodes cost about 50% more than the LPC-815's do ! I was hoping they would blast on outta there *sigh* I'll find a decent 1/2 Watt or full Watt red diode sometime soon for Mike (and others) to test - if they are out there, I'll find them !

*Greg
Click to expand...

I was looking for that too! I have the lenses for them if you find them...

But all I could find is multimode diodes in that power...
 
Jay - They're coming - I do NOT have any yet (had to make sure that is clear...I have received 25 emails since I posted - asking me where the 1 Watt red diodes are listed !!), but when they are out there, rest assured I will have OOOODLES in stock !

*Greg
 
Mike kindly sent me one of these diodes for further analysis.

I just received it today, but was curious enough to mount it in a big heatsink, and do some power vs current tests. These are on an uncalibrated thermal meter, but the relative power level readings are valid (the absolute ones may be off up to 10% or so).

This series of test was done CW, with the diode in an aixiz (provided by Mike), with an aixiz glass lens i still had here.

Current - Power Benm - Power HMike

200 - 127 - 134
300 - 196 - 210
350 - 214 - 226
400 - 233 - 240
450 - 234 - 240
500 - 242 - 237
600 - 227 - 192
650 - 206 - 163

As you can see my results match Mikes pretty well, certainly for trend, putting the optimum optical power in the 400 - 500 mA range. The differnce in absolute values can easily be explained by a different lens and/or miscalibration on my end, but is not significant for the results.

Since i want to do pulsed testing with this diode i havent pushed it any further, the down trend is clearly visible when exceeding 500 mA, resulting in about the same power output for 300 and 650 mA - amazing!

While adjusting current i noticed the drop in optical output seemed to lag the adjustment up in current a bit. This might be due to jittering in the potmeter or even the current source adjusting, or it could be something caused by this laser diode itself.

I will try to do some 50% duty cycle measurements tomorrow, at various frequencies. That should shed some coherent light on whats going on.
 
For those interested, a spot-shot with the lpc822 diode (bottom left) compared to the DX dilda (top right). Both have the 'wings' in the output pattern, they are a little more pronouned on the lpc822. Its running at 350 mA in this picture.
 

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Benm -- Looking similar so far. Did you also notice the power come back up as
you reduced the current? That's what amazed me. Something seems to actively limit the power.

HMike
 
Seems so - when you look at the optical output instead of the current reading on the meter, you think you're turning the pot the wrong way. I'm sure its not a thermal effect, i ran in for several minutes arond the 600-650 range, then turned the current down to 450, and it was at full power again right away.

I'm gonna test the cw/pulsed performance later today, i was thinking to start with 200 cw / 400 @ 50% and working upwards from there, using a couple of frequencies.
 
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Some pulsed test results, at ca 1 kHz and exactly 50% duty cycle. I have re-taken the measurements for the CW values during this experiment, so they may differ a few mW from the ones above.

300@50 - 106mW | 150CW - 075mW | 300CW - 210mW
400@50 - 127mW | 200CW - 120mW | 400CW - 237mW
500@50 - 150mW | 250CW - 158mW | 500CW - 239mW
600@50 - 147mW | 300CW - 191mW | 600CW - 192mW
700@50 - 144mW | 350CW - 214mW

These results are a bit puzzling: I'm sure the effect is not thermal, or it must me something that warms up and cools down as fast as in 1 milisecond. In pulsed operation the plateau seems so be at a little bit of a higher current comparing peak-to-CW... the optimum at CW seems to be about 400 mA, the optimum at 1 kHz 50% is closer to 500mA (250 average).

For now, i can only conclude that pulsed operation at 1 kHz offers no benefit in achievable output power. I stopped at 700mA@50% because it was clear the power curve was on its way down already. As for an overal conclusion for this diode: Its by no means a LOC or LCC buster, but it does give you 240-ish mW and seems very resilient to overdriving.

I'll try a couple of different frequencies and duty cycles to see if that yields any result.

@HMike: is this the diode you already tested at 1 amp, or a different one?
 
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I don't claim to know anything about these electron holes and quantum tunnels and whatnots, but could it be that when these fill up too quickly, the electrons might have nowhere else to go and just add heat to the system? I dunno, maybe that will give someone who actually has a brain an idea.

I don't think they'd add more components like temp sensors and such to a LD chip, so it has to be something that they tweaked in the chip itself that causes it to act this way, where after a certain point, efficiency drops like a brick.
 
I dont think there is some circuitry that controls this behaviour, but there must be some mechanism. One option i consider is an absorber, that absorbes the excess light above a certain treshold, dumping it as heat onto the chip base.

I've done some tests with 50% duty at 600 mA peak using various frequencies:

10Hz -124
100Hz - 137
1kHz - 140
10kHz - 142
50kHz -143

Aproaching 100 kHz the current got distorted - i'll have to find out if this is the driver at fault or something the diode is doing (capacitive load etc). Also, i'll try some other duty cycles as a final part of analysis.
 
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