BIG News: Green Laser Diodes

[pullbangdead]

An update for you, here is a popular-press release about a paper the group I'm in recently published. It covers a little bit of some different approaches available for future diode work.

Semiconductor Today

 

[seoguy]

Awesome news!

A few questions -

The Sumitomo press release claims that they can somehow "tune" the LD to different wavelengths, but that it is not subject to shifts due to temp changes?

How the heck do they do that? Can they actually electrically "vary" the color of the laser light? :wtf:

Or is this just marketing hype, and they are just talking about manufacturing changes to the active layer size or Indium %???

Second, has their paper been published or otherwise available to those of us NOT lucky enough to be hanging-out with the likes of Dr. Nakamura and a fancy tech library like you probably have at UCSB?

Next, is the full paper that YOUR group recently published likewise available at a link someplace that us mere mortals can read it?

Finally, I noticed in the story you linked to about your group, that your new "off-kilter" m-plane design had a significantly lower threshold current (153ma). Is this advantage maintained at longer wavelengths, and do you feel that this could give your approach an edge at better efficiencies than the Sumitomo design in the green part of the spectrum?

Thanks!

 

[pullbangdead]

Awesome news!

A few questions -

The Sumitomo press release claims that they can somehow "tune" the LD to different wavelengths, but that it is not subject to shifts due to temp changes?

How the heck do they do that? Can they actually electrically "vary" the color of the laser light? :wtf:

Or is this just marketing hype, and they are just talking about manufacturing changes to the active layer size or Indium %???

Naah, they're just talking about while making it, they're just referring to changing indium amount (among other things) to "tune" the wavelength to different colors while making the diode. Once the diode is made, there's not a lot you can do. There re things you can do with laser diode with things like external cavities and things like that to "tune" wavelength, but those are no more or less accessible with this diode or any other diode. They're just talking to people who would say "well they have 531nm, can I get 525nm?", and telling them "yes, we can tune it to any specific wavelength in a range while manufacturing it".

Second, has their paper been published or otherwise available to those of us NOT lucky enough to be hanging-out with the likes of Dr. Nakamura and a fancy tech library like you probably have at UCSB?

It is published, the forum doesn't allow pdf attachments that I can tell. If you have a subscription to Applied Physics Express, the reference is: Applied Physics Express 2 (2009) 082101. Or, if a couple people want it, I don't reckon I would mind e-mailing out a copy or 2

Next, is the full paper that YOUR group recently published likewise available at a link someplace that us mere mortals can read it?

Ummm, come to think of it, I'm not sure I even have a copy of that paper, but I can probably find a pdf of it some time today. I think this is the reference for the paper we put out last week, but it's in the article I previously linked either way: Applied Physics Express, vol.2, p.082102, 2009. I'll see if I can rustle up a pdf somewhere around here of that one.

Finally, I noticed in the story you linked to about your group, that your new "off-kilter" m-plane design had a significantly lower threshold current (153ma). Is this advantage maintained at longer wavelengths, and do you feel that this could give your approach an edge at better efficiencies than the Sumitomo design in the green part of the spectrum?

That's one that I'm not sure I'm at liberty to discuss, as it involves future plans based on possibly proprietary information. Anything in a paper is fair game, but I don't recall off-hand what details are in the published papers and what isn't.

One thing I will say is Sumitomo's device was on a semi-polar plane [2 0 -2 1], whereas or recent paper was talking about miscuts on the non-polar m-plane [1 0 -1 0]. Most any discussion like that hinges on what plane you're using, and since the papers were talking about 2 different planes for the devices, then at least some of that discussion doesn't carry over, at least not in any straight-forward fashion. ie, a miscut on m-place won't behave the same was as a miscut on [2 0 -2 1]. There's a lot of discussion going on now about the general semi-polar vs. non-polar for green, and for blue also, as to which one will be better for which colors, and nobody really knows yet. But of course, everybody has their own ideas. Miscuts of non-polar, like we discussed, certainly have some advantages, but really every approach seems to have its own advantages right now.

Thanks!

No problem.

 

[HIMNL9]

Just wondering ..... but, with the actual technology level, is easy to build piezoelectric positioners that works in the nanometers range ..... it must be possible to build a multichannel chip that emits contemporarily more than one wavelenght (as example, RGB ), then build a resonant cavity for it, that be changed in lenght (and consequently, in wavelenght resonance), with a piezo positioner.

Someone imagine what this can end in ? ..... :eg:

 

[seoguy]

Naah, they're just talking about while making it, they're just referring to changing indium amount (among other things)...while manufacturing it.

That's what I figured. After all, within the limitations of the maximum wavelength possible for a given design, ALL InGaN laser diodes (including the blue ones, and the ones you are working on) should be capable of adjusting the wavelength to some degree at the manufacturing stage, simply by adjusting the % of Indium, correct?

But they seemed to be claiming they had created something "unique", that while all of the other LDs were fixed-frequency, theirs were "tunable"! -

...we have succeeded in covering the entire range of the lasing spectrum in the green region. While the lasing wavelengths of the conventional frequency-converted lasers are locked at a specific wavelength, our device can be tuned to any wavelength in the green region.

There re things you can do with laser diode with things like external cavities and things like that to "tune" wavelength, but those are no more or less accessible with this diode or any other diode.

Was the laser described in the paper an open-cavity design? (And if so, do they actually intend to manufacture them that way?)

It is published, the forum doesn't allow pdf attachments that I can tell.

That is one of the issues w/the new forum, it places limits on the types (and sizes) of attachments. c0ld can easily adjust that if you ask him (If so, have him set the max size for PDFs at something like 10mb, as they can get pretty big w/pics in them!)

Or, if a couple people want it, I don't reckon I would mind e-mailing out a copy or 2.

Definitely, thanks! (PM sent).

I can probably find a pdf of it some time today. I think this is the reference for the paper we put out last week...I'll see if I can rustle up a pdf somewhere around here of that one.

Ditto!

That's one that I'm not sure I'm at liberty to discuss, as it involves future plans based on possibly proprietary information. Anything in a paper is fair game, but I don't recall off-hand what details are in the published papers and what isn't...

Understood. Once I have had a chance to review the respective papers, I will be in a better position to discuss this within the bounds of what is publicly available.

One thing I will say is Sumitomo's device was on a semi-polar plane [2 0 -2 1], whereas or recent paper was talking about miscuts on the non-polar m-plane [1 0 -1 0]. Most any discussion like that hinges on what plane you're using, and since the papers were talking about 2 different planes for the devices, then at least some of that discussion doesn't carry over, at least not in any straight-forward fashion. ie, a miscut on m-place won't behave the same was as a miscut on [2 0 -2 1]. There's a lot of discussion going on now about the general semi-polar vs. non-polar for green, and for blue also, as to which one will be better for which colors, and nobody really knows yet. But of course, everybody has their own ideas. Miscuts of non-polar, like we discussed, certainly have some advantages, but really every approach seems to have its own advantages right now.

As I recall, in the SciAm article I referenced earlier this year on this topic, your group and Rohm also appeared to have gone in different directions based on crystal alignment, with Rohm pursuing the non-polar m-plane approach, while UCSB was pursuing the at-the-time more successful semi-polar direction.

But your latest research seems to have switched back from semi-polar to a slightly skewed version of an m-plane design - while the company that achieved this took the semi-polar approach you were pursuing previously - Things seem to have gone full circle!

BTW, why the shift back to non-polar?

 

[pullbangdead]

That's what I figured. After all, within the limitations of the maximum wavelength possible for a given design, ALL InGaN laser diodes (including the blue ones, and the ones you are working on) should be capable of adjusting the wavelength to some degree at the manufacturing stage, simply by adjusting the % of Indium, correct?

But they seemed to be claiming they had created something "unique", that while all of the other LDs were fixed-frequency, theirs were "tunable"! -

Yep, the indium content and some other things. For instance, changing the wavelength changes refractive index of the material, so you have to adjust how you guide light within the laser, as well. And so on for other design factors in the diode.



Was the laser described in the paper an open-cavity design? (And if so, do they actually intend to manufacture them that way?)

Naah, it was a fairly standard diode, just imprecise wording. Press releases can do that. If you've never seen it, this comic sums it up nicely: PHD Comics: Science News Cycle



Understood. Once I have had a chance to review the respective papers, I will be in a better position to discuss this within the bounds of what is publicly available.

Sounds good.



As I recall, in the SciAm article I referenced earlier this year on this topic, your group and Rohm also appeared to have gone in different directions based on crystal alignment, with Rohm pursuing the non-polar m-plane approach, while UCSB was pursuing the at-the-time more successful semi-polar direction.

But your latest research seems to have switched back from semi-polar to a slightly skewed version of an m-plane design - while the company that achieved this took the semi-polar approach you were pursuing previously - Things seem to have gone full circle!

BTW, why the shift back to non-polar?

A luxury of being in academia vs. being in industry. Industry must work on ideas until something works, and then focus their efforts in order to get a product out the door. They needed a prototype, a working sample, so they focus their energy into the best-available-guess at an approach, and then their energy is more focused into certain related areas.

In academia, we have the freedom to not have to worry about being tied to a certain approach. You don't have to go back very far at all to find papers from our group on both non-polar and semi-polar devices. They may have slightly different author lists (maybe names in a different order), but still the same group.

And you have an e-mail, as well.

 

[pullbangdead]

A slightly self-serving bump here, but if anyone is interested, there are a couple of new developments that I don't remember reporting on here.

Osram has reported some more green laser diodes, in addition to Sumitomo. And the piece de resistance, there has now been reported a working, CW green laser diode. The stats on some of the newer reporting are a LOT better, and of course, having CW is another great step in the process. Maybe I'll have some news with my very own name on it someday soon. If anyone is interested, I can get links and such.