Old 12-05-2008, 08:19 PM #1
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Default Finally I think that I may have found the answer.

...to why 803t diodes are so powerful, and why a 4x BR burner diode isn't that much more powerful.

I have always wondered why a 2.4x reader diode from an X-BOX hd-dvd system would be so powerful compared to BR reader system from the competing PS3. We have theorized many possibilities, now I believe I have found the answer.

It is due to the way HD-DVD was designed. I have been reading technical articles describing the way the two systems were built to operate and a few differences in design really popped of the page.

Blu-ray: Has an NA (numerical aperature) of 0.85 which combined with the 405 nm wavelength allows an extremely high density of information on the disk (yes obvious)

HD-DVD: Has a NA of 0.65 which combined which combined with the 405 nm again allows for high density though not as high as BR.

The reason for this is the disc itself: while HD-DVD uses a similar disc to the DVD (0.6 mm disc with 0.6 mm protective coating), Blu-ray steps away from the DVD norm and uses a 1.1 mm disc with a protective layer of only 0.1 mm. The recording layer is therefore very close to the surface of the disc. The advantage is that the laser has less material to read through, which allows a higher NA, a lower track pitch, a smaller pit length and therefore more storage compared to HD-DVD.

Another advantage for Blu-ray resulting from the NA/Wavelength combination. (higher data density) Blu-ray requires a much lower rotation speed of the disc to reach the specified transfer rate. A constant rotation speed of 10.000 RPM, which is the current upper limit for optical drives, will result in 12x BD but only 9x HD-DVD. This means that a HD-DVD must rotate faster to reach the same transfer rates.


Judging from all this data it appears clear to me (maybe only in my brain), that one of the predominant reason for "strenght" of the 803t and relative "weakness" of the 4x BR burner, is primarily the way in which the two technologies were made. BR has much smaller pits and thus requires less power to "cut" them into the disk or read them due to the thin protective layer. While HD-DVD on the other hand had relatively large pits hidden behind a larger protective layer.

This mostly explains the relative "weakness" of the 4x even the 6x burner (please don't flame me for that one ), when compared to a f'in reader diode. Basically the "dot" in a BR focused more tightly and thus has a higher energy density (at the same power from the diode) adding to this the higher NA allows more light to be focused, thus requiring less power to operate. However, this does not explain why the 803t sled came with such a powerful diode as opposed to the 811, maybe only partly.

Now imagine that even due to its unfavorable specs HD-DVD won, imagine the power a 4 or 6x HD-DVD burner would have. Time to start looking for some HD-DVD burners. 8-)





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Old 12-05-2008, 08:34 PM #2
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Default Re: Finally I think that I may have found the answ

You know, you may be onto something. Check out the GGW-H20L specs, it'll read or write Blu-Ray at 6x speed, but will only read HD-DVD at 3x speed.

This could just be a software or encoding issue that it can burn Blu-Ray but not HD-DVD. But the 2x difference in read speed available, could that be a software/encoding difference as well? Seems there's wouldn't be THAT much difference in reading them on the software side of things, but maybe there is that big of a difference in the encoding? Or could that be because of how much power it takes to read?

Interesting thoughts.
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Old 12-05-2008, 08:34 PM #3
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Default Re: Finally I think that I may have found the answ

Interesting

What are your thoughts on TTL blanking between the two? I have hooked up a 803t and blown it with TTL, as low as 100ma. I understand the stresses on the diode regarding TTL operation, but do you think that a 4x diode would serve better? Considering the 4x is definately meant for pulsed type operation at higher currents, would this also make it a better candidate for TTL?

Im putting together a scanner, and am trying to decide which diode would survive the constant current and voltage changes..

My driver at its lowest provides 80ma, and I think that the 803t will have trouble, even at the lower current. Besides, the beam is much fuller on the 4x, so its already in favor for this use, but dont want to blow it, as I only have 1, 4x left :-/
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Old 12-05-2008, 09:03 PM #4
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Default Re: Finally I think that I may have found the answ

pullbangdead: I think that it may indeed be the software/encoding? The power of the 6X diode should be enough for the drive to read at higher than 3x? One thing is for sure though, in order to read HD-DVD at the same speed as BR, the drive must spin quite a bit faster.


wannaburn: I have not come across anything regarding differences in TTL modulation between the two systems (mostly skimmed through the insane amount of reading looking for the juicy stuff). Nor do I really have an opinion on the subject (luckily I have not yet been led to the part of the scanner, I need some $ to eat ya know :P) One thing that you mentioned yourself is that blanking is quite stressful for any diode running above its designated power.


On a side note I have just sent an e-mail to the Toshiba Europe GmbH, Storage Device Division asking what happened with the SD-H903A HD DVD 1X ( ;D) burner drives, that were being shipped towards the end of the war. IMO they are probably recycled or gathering dust in a warehouse somewhere. It might be possible that the 1X HD-DVD burner uses a 803t though. .
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Old 12-05-2008, 10:04 PM #5
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Default Re: Finally I think that I may have found the answ

brtaman--

The toughness of the PHRs is FAKE. All but one of the phr-803T's that Igort has run at >150ma's have died in <24 hours. You still have a good idea though.

--hydro15
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Old 12-06-2008, 12:36 PM #6
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Default Re: Finally I think that I may have found the answ

Quote:
Originally Posted by hydrogenman15
brtaman--

The toughness of the PHRs is FAKE. All but one of the phr-803T's that Igort has run at >150ma's have died in <24 hours. You still have a good idea though.

--hydro15

That is very true hydrogenman, what was previously accepted as safe for 803t's is slowly being debunked as a myth.

However, based on klimbak's early findings, the diodes last for thousands of hours at around 100ma, which still gives around very decent power levels. (though with no lens and therefore no back reflection and smaller final output with lens). This is still an insanely high power any way you look at it for just a reader. Igors work has also proven that 6X in order to survive must be run at less or around 200ma providing around generally less than or around 200mw. We have no definitively proven a "safe" power level for either. However, this still brings about the question/absurdity as to how a 2.4X reader diode could compare in such a way to a 6X burner diode (emphasis on reader and burner). Lets, for the sake of argument, say that an accepted power level for quite a long life for a 803t is around 70mw post lens and compare that to 150-200mw for 6X. The 803t still provides from 1/2 to 1/3 the power of a 6X. An absurd situation given that DVD readers generally contained diodes of 5-10mw (assumption, anyone who has worker with them please chime in) while the power of the burners is obviously much higher. That is what I was getting to with the above post. That the fundamental differences in the burning/reading process between HD-DVD and blu-ray are one of the if not the main reason behind that apparent weakness of a 4X blu-ray burner diode compared to a simple reader diode of a now obsolete technology.
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Old 12-06-2008, 03:25 PM #7
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Default Re: Finally I think that I may have found the answ

Quote:
Originally Posted by brtaman
[quote author=hydrogenman15 link=1228511980/0#4 date=1228518263]brtaman--

The toughness of the PHRs is FAKE. All but one of the phr-803T's that Igort has run at >150ma's have died in <24 hours. You still have a good idea though.

--hydro15

That is very true hydrogenman, what was previously accepted as safe for 803t's is slowly being debunked as a myth.

However, based on klimbak's early findings, the diodes last for thousands of hours at around 100ma, which still gives around very decent power levels. (though with no lens and therefore no back reflection and smaller final output with lens). This is still an insanely high power any way you look at it for just a reader. Igors work has also proven that 6X in order to survive must be run at less or around 200ma providing around generally less than or around 200mw. We have no definitively proven a "safe" power level for either. However, this still brings about the question/absurdity as to how a 2.4X reader diode could compare in such a way to a 6X burner diode (emphasis on reader and burner). Lets, for the sake of argument, say that an accepted power level for quite a long life for a 803t is around 70mw post lens and compare that to 150-200mw for 6X. The 803t still provides from 1/2 to 1/3 the power of a 6X. An absurd situation given that DVD readers generally contained diodes of 5-10mw (assumption, anyone who has worker with them please chime in) while the power of the burners is obviously much higher. That is what I was getting to with the above post. That the fundamental differences in the burning/reading process between HD-DVD and blu-ray are one of the if not the main reason behind that apparent weakness of a 4X blu-ray burner diode compared to a simple reader diode of a now obsolete technology.[/quote]


Yes, its quite amazing that something meant to READ at 2.4x is a 60-70mW diode. Its also quite strange that its got a "fake toughness" in the first place. Your explanation is good and HD dvd was made around 2 months before blu-ray so might not have to consistent compared to blu-ray.

--hydro15
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Old 12-06-2008, 04:56 PM #8
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Default Re: Finally I think that I may have found the answ

interesting thread! i don't really understand much but we all learn new things every day.
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Old 12-07-2008, 11:21 PM #9
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Default Re: Finally I think that I may have found the answ

Well, 4x diodes are not weak. They are definitelly much more powerful, than PHRs. It's our expectations, that are too high, fueled by the deceiving short-lived fake toughness of the PHRs. (i think it's this fake toughness that 4x's lack, but at a power they can survive, they would outlive a PHR set to the same power).

The PHR is not even nearly as powerful as everyone thinks. It's a 40-60mW diode at best. The 4x diode on the other hand is probably an 80-100mW diode. The consistency of it's wavelength also shows it's a more powerful writer diode.


I had big plans for testing of 4x's. I prepared different setups for torturing, but when i thought i could get 6x's, i changed my mind, cos i thought it'd be a waste of money. But now... I have some 4x's left over, and i'll hook them up to my diode terminators. Do some diode vs. diode competitions under different conditions..


But back on topic, yeah, it is possible, that HD-DVD needs a higher power, in order to read at the same speed.

But there are also numerous other things involved here:
1. Losses in the optics:
- The PHR sled has a joint BRIR optical path = more optics to pass, with broadband coatings, with higher reflective losses
- 4x and 6x writer has a separate optimised 405nm optical path with wavelength specific coatings on the optics, and less optics to pass

2. Diode output shape:
- PHRs have a BAD aspect ratio, much of the power we measure is in the edges of the fast axis. The power that is usefull to us is not all usefull in a sled. PHR sled optics clip the fast axis of the beam, there is even an LCD in the path, to shape the beam further - lossy shaping
- 4x & 6x writer diodes have a better aspect ratio and circularise the better output directly after the diode. This way, they make the use of most of it


Basically, a 4x and a 6x sled makes MUCH better use of the diode's power, than a PHR sled. Even if they were the same format, and both had the same power diode inside, a 4x sled would be capable of much more than the PHR sled design.


PHR is a strange little diode. Inconsistent efficiency, inconsistent wavelength, inconsistent reliability. It's no miracle it ended up in a reader sled. It would not do well as a writer. If nothing else, because of the wavelength inconsistency.



BTW, in the last batch i found a diode, that didn't seem too good at first glance, but i marked it as a freak. I use this filter to compare the wavelengths. If i shine two diodes through it side by side, onto a white paper, the brighter one has a higher wavelength (regardless of the power difference). This one barelly came through! I've NEVER seen such a short wavelength. It won't be much to look at, but it had good efficiency after a plastic lens! Imagine how much more there has to be behind the lens, with such a short wavelength!
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