Why is Blu-Ray called Blu-Ray?

[dnar]

Dry.....very dry. :undecided:

Smeee.

 

[IsaacT]

You'd make a fine spindoctor!

Why thank you! :eg:

Uhm ..... aren't them called acronyms ? ..... (sorry, just kidding )

:shhh: They are called acronyms aren't they? Lol, forgive me, I hadn't slept in a couple days due to a shitty work schedule. :beer:

 

[JaiNobeZ]

Rofl @ this thread!

I think it's a ploy to mislead people for the scientists' amusement. Few years ago back when BluRay was new and well before I was into lasers I was bored waiting for a bus and I saw an ad on the side of a shop saying something about this new thing called "BluRay" which i'd heard about a few times but knew nothing about. So I went in and asked a grunt "what is BluRay?" and he told me it's a new type of DVD player which gives better quality picture, I accepted that guy didn't know what he was talking about and instead went to the guy behind the counter and asked him "what is BluRay?" and he started giving me the same nonsense so I interrupted and said "I know that, but what is it? How does it work?" and he told me it has a blue laser. I fantacised about having a blue laser for a few moments then said "thank you" and walked out.

Now that i'm into lasers and have a "Jim-Beam" laser in my pocket, i can honestly say i've never looked back.
xD

 

[pullbangdead]

It's blue in the sense that it's in the blue end of the spectrum. Up until when these diodes were invented in the mid-1990s, the diodes available were all in the red end of the spectrum, ie IR, red, maybe orange-ish. these new diodes came out, and while they were violet, they are in the blue end of the spectrum, away from the red end of the spectrum. Heck, just look at the term "blue-shift": it's often still called a "blue shift", as the counter part to a "red shift", even when you're in the violet or UV wavelengths, even though blue and red are both in the same direction in such cases. So "blue" often is just juxtaposed against red, as in on the blue side of things, towards shorter wavelength.

Then you add in some language barriers since these things were made in Japan, and you end up with the term "blue laser" encompassing blue, indigo, and violet laser diodes.

So it's some combination of marketing, scientific language with the fact that it's the blue-end of the spectrum, and language barriers. Shuji Nakamura's book about the original science on the subject mentions ONLY violet diodes, the highest wavelength in the book is like 415nm, but the book is called "The Blue Laser Diode: The Complete Story". Anyone want to go tell him he's wrong?

 

[Crazy Jay]

When they were working on the diode perhaps it was blue at first but they realized that making it even deeper into the wavelength would allow them to store more space.

It's blue in the sense that it's in the blue end of the spectrum. Up until when these diodes were invented in the mid-1990s, the diodes available were all in the red end of the spectrum, ie IR, red, maybe orange-ish. these new diodes came out, and while they were violet, they are in the blue end of the spectrum, away from the red end of the spectrum. Heck, just look at the term "blue-shift": it's often still called a "blue shift", as the counter part to a "red shift", even when you're in the violet or UV wavelengths, even though blue and red are both in the same direction in such cases. So "blue" often is just juxtaposed against red, as in on the blue side of things, towards shorter wavelength.

Then you add in some language barriers since these things were made in Japan, and you end up with the term "blue laser" encompassing blue, indigo, and violet laser diodes.

So it's some combination of marketing, scientific language with the fact that it's the blue-end of the spectrum, and language barriers. Shuji Nakamura's book about the original science on the subject mentions ONLY violet diodes, the highest wavelength in the book is like 415nm, but the book is called "The Blue Laser Diode: The Complete Story". Anyone want to go tell him he's wrong?

 

[pullbangdead]

When they were working on the diode perhaps it was blue at first but they realized that making it even deeper into the wavelength would allow them to store more space.

Nope, sorry. Blue is harder to make than violet, but quite some margin. The first laser diodes that were actually blue weren't made until years after the first violet ones. And yet they were all called "blue", even when they were only violet.

 

[Crazy Jay]

Nope, sorry. Blue is harder to make than violet, but quite some margin. The first laser diodes that were actually blue weren't made until years after the first violet ones. And yet they were all called "blue", even when they were only violet.

Since it was harder to make they ended up scraping the idea of using blue and going for the violet instead

 

[BShanahan14rulz]

As I understand it, they used new materials and got blu-ray. They tweaked and experiemented until they could push the wavelength of this new material up a good 40nm. I wonder how they're gonna do green?

I propose InGaNAsSeSiC... Because it has just the right number of letters to be believable :crackup:

 

[pullbangdead]

As I understand it, they used new materials and got blu-ray. They tweaked and experiemented until they could push the wavelength of this new material up a good 40nm. I wonder how they're gonna do green?

Yep, that's pretty much exactly it. For green, it turns out that by doing many of the same things they did to go up >40nm from violet to blue, it turns out you can go even farther just by doing many of the same things: "tweaking" the materials and the device structure.

GaN is amazing stuff, because it has already been pushed SO far, from violet to green already. More optimizing and more science, more tweaking, and the science has already managed to get GaN to go up over 100nm higher in wavelength than the original InGaN/GaN lasers at ~410nm.

How much higher will it go? Probably not much higher, as there's no commercial incentive and the walls they're starting to run into are pretty high in some cases. It's likely possible to go a bit higher, but there's not much financial incentive to spend millions trying to go beyond green. Green had huge financial incentive, and still does; yellow not so much though.

 

[HIMNL9]

Offtopic, but ..... :thinking: i'm just wondering, why they have not started to research also about Gallium 3 Phosphide resonators, too, instead only Gallium Nitride ? ..... after all it already emits in the yellow range (where GaN actually reach 570nm emissions only, as far as i remember, and only for LEDs) ..... or is just that it cannot be built a crystal structure "pure" enough for be used as cavity for the resonator, with GaP ? :thinking:

 

[pullbangdead]

Offtopic, but ..... :thinking: i'm just wondering, why they have not started to research also about Gallium 3 Phosphide resonators, too, instead only Gallium Nitride ? ..... after all it already emits in the yellow range (where GaN actually reach 570nm emissions only, as far as i remember, and only for LEDs) ..... or is just that it cannot be built a crystal structure "pure" enough for be used as cavity for the resonator, with GaP ? :thinking:

First, it's an indirect bandgap. That isn't a killer by itself, but it's a strike against any material when you're trying to emit light. It can work, and many indirect bandgap materials are used for optical applications, but when the competition is GaN which has a direct bandgap, then it's already behind the eight-ball, so to speak.

Second, the LEDs it makes aren't even that good. And if you can't make an excellent LED, then you can't make a laser diode. You have to be able to make a good LED before you can make a laser diode out of the same materials.

From what I know, which is admittedly little in many ways since I'm a GaN person and that's where my knowledge is focused, GaP isn't used for bright green LEDs, it's used for cheap green LEDs. And if it can't make bright green LEDs, it's not going to make laser diodes any better than GaN.

I'm sure there's more to it than that, but that's my first guess off the top of my head. People have been working on LEDs on both materials since the 1960s, and GaN has clearly shown more in the way of results, even if it has all been in the last 15 years.

 

[HIMNL9]

So, it's mainly for efficency (indirect bandgap) and probably impurities (how can i call it better ? ..... structure opacity ?)

Then GaN is the only actual choice ..... do you know it's efficence curve against emission wavelenght ? ..... i mean, GaN was already used for make good LEDs til 570nm, but not lasers til this wavelenght ..... it's also, maybe, matter of efficence vs wavelenght ? (i mean, i'm not an expert, only remember that under a certain efficence degree, there's no way for obtain a decent laser cavity ..... and the same under a certain "purity" in the crystal structure, IIRC) ..... ?

Trying to understand if the choice of 520nm for green LDs is due to technical difficults, or just from the fact that human eye sensitivity is better around this wavelenght .....

 

[pullbangdead]

How about saying it has a lower "luminous efficacy", just a generic term that says it's not as good at emitting light as GaN is.

As far as efficiency of GaN vs. wavelength, I do have an older image showing the idea of the "green gap" (attached), which shows the external quantum efficiency (EQE) of LEDs vs. wavelength. The idea is the same with lasers. If you can't make a high EQE LED, then you can't make a laser diode either. This chart is a bit out of date, and the green end of the GaN curve is a bit higher nowadays, especially if you want to count the stuff coming out of research labs and not just stuff that's in production already.



520nm is the choice because of color gamut, although it is fortunate that going higher isn't required, because the higher you go the harder it gets. It is best illustrated with a CIE diagram:

The color gamut produced by 3 monochromatic light sources is the triangle formed by connected the 3 light sources together. With 445nm and 640nm light sources as your blue and red, it's clear with a short glance that 520nm is just about perfect as far as the widest possible gamut of colors.

It might also look at first glance that going to higher wavelengths for red and lower for blue would widen the gamut, but on those corners of the chart you very quickly run into a loss of eye-sensitivity, and you get diminishing returns in colors the farther you get into those corners.

Another area of importance for this stuff is the idea represented by the idea of the MacAdam ellipse(s), which is the idea that colors which are close enough together are often indistinguishable to human eyes, even if they are slightly different.

 

[HIMNL9]

Thanks, now the reason is a bit more clear to me :beer: