I got a labeled sample pack from 3M months ago that has one sheet of DBEF-II (Vikuiti™ Dual Brightness Enhancement Film II 11 in. X 11 in., one sheet of DBEF-E 11 in. X 11 in. and two 14 in. X 14 in. sheets of DBEF-D400, one cut at 0 degrees and one at 45 degrees. I admit to being slightly confused at first when I got them, I expected two to be like mirrors and two to be diffuse but all four looked diffuse. But then I peeled the protective plastic off of both sides of one of them and boom, mirror surfaces. Duh .

The DBEF-E is slightly embossed and mirror-like on one side, and smooth and mirror-like on the other.
The DBEF-II is identical to the DBEF-E as far as I can tell, except the DBEF-E is slightly more transmissive.
I know that the information from 3M says that the DBEF-II has diffuse surfaces, but if so, the diffusion is extremely minimal, probably to cover their butts legally because it isn't perfectly specular.
I don't think that you guys have the diffusive models. The DBEF-D400 samples I have are unmistakeably diffuse. The 3M information says that it has diffusive layers, and boy oh boy they aren't kidding. I tried to shine my laser pointer through one, and couldn't even see any laser color on the wall at five feet. I had to get about a foot from the wall to see a diffuse blob of good color on the wall. And that's with a green laser pointer, very visible ordinarily.

Check out the plog link in my signature line. I used one for my PSOne projector.


I see what you mean. Hopefully the loss won't be any greater than using a small spherical reflector, and the cube retro-reflector will recycle the ordinarily lost mis-polarized light.

Tgreenwood

I have seen some retardation or birefringence from a fresnel. I’ll try finding the thread I posted some pics in.

DJ

Edit:
Here it is

In Sensibull's Birds Eye projector, he (accidentally) found out that 1/16th inch thick lexan rotated his polarization by around 90 degrees. The retardation is probably thickness-dependent.

Tgreenwood

Yeah, that pretty much confirms what we've been seeing. Glowies . That is going to get in the way some. It shouldn't keep it from working, though. We really don't want anything but linearly polarized light hitting the LCD polarizer. Elliptical and circular polarization will pass right through every sub-pixel = Bad. Too bad this stuff isn't glass.

Mark

It probably is.
I did try cellulose tape, each layer varied the color. Polycarbonate produced a slight yellow tint. By applying tape I could change the color to cyan, orange and all sorts of colors just not white, yet.

DJ

I thought everything leaving the light source was circular until reaching the polarizer adhesed on the lcd making it linear.

Also, it might be a question way to early in the game but if it is at all possible, how much gain can we predict with an enhancement?

I’ve never thought about the glowies it in terms of circular polarized light. If indeed it does pass through linear polarizes then perhaps a fix for glowies is some type of un-polarizing sheet placed between the fresnels and LCD, if there is such a sheet that isn’t diffusive.

DJ

I think you may be confusing circular polarize light with un-polarized light. Circular polarized light is a strange one to comprehend. The way I understand it is un-polarized light is random, multiple waves orientated at any angle but all traveling in the same direction. Linear polarized light has one angle of polarization. Circular or elliptical can be thought of as being linear polarized light that is twisting left of righhanded just like an out of control airplane spiraling before it crashes.
I’m not yet sure that circular polarized light does pass through linear polarizes. It could do, I think that is why cameras with auto focus use circular polarizes so it doesn’t interfere with the focusing part. Maybe Mark can enlighten us a bit more.

DJ

Theoretically 50% more but realistically I have no idea . Any gain's a good gain.

Ah right, un-polarized light, also called shear waves, right? And linear would be longitudinal waves?



Same here, unless the crystals within the lcd in those areas are not lining up correctly allowing a slight twist before it passes thru the other polar. I did like your internal reflection theory though.

Cicularly polarized light will pass through one linear polarizer regardless of its angle. After that it will be linearly polarized. I wasn't thinking right before about passing through the whole panel. My confusion came from the use of compensation film inside the panel. Completely different story.

I need to leave for an Ultimate Frisbee tournament, but here are some awesome animations (at first glance anyway) that I just googled up:

http://www.ee.iastate.edu/~hsiu/descriptions/polar.html

They show that polarization axis is just an illusion based on how the electric and magnetic fields propogate. This visual makes it much easier to see why cicular polarization seems to have a memory as to how it should reset on the way back through a wave plate. I will try and come up with a potted explanation based on what I know when I get back. Basically it comes down to when you throw the electric and magnetic fields componets of light out of phase, you get varying effects on the amplitude of each component.

And the thickness of the birefringent material is critical to the phase shift. The birefringence and helical shape of the material being the other 2 that I can think of.

Be back in a couple days.

Mark

I think I do have the diffusive type. I tried the same laser test and got the same result as you.
I tried heating a corner today in the hope of separating the layers, no dice. Where and how did you get the sample pack?
DJ

I went on the 3M website and requested a sample pack. They emailed me back after a couple of days and asked what my application was. I told them that I was working on developing a children's LCD projector utilizing a fluorescent light source for heat safety, low power requirements and ease of bulb replacement (which I am). I got the sample pack about a week later.

Tgreenwood

I took some pictures of the DBEF samples I have.



Here's what DBEF-D400 looks like....
Click to view attachment
Very diffuse.



DBEF-E is slightly embossed with ridges on one side, but still nice and specular
Click to view attachment

Here's a close-up of the embossing
Click to view attachment
Keep in mind that the camera is focused on the sheet, not on what is in the reflection. The reflection IRL is sharp but wavy.



Here's the DBEF-E shown from the smooth side
Click to view attachment
No visible embossing, nice reflection.

Next is the DBEF-II

I can't help but think that they may have mislabeled this because it looks so much like the DBEF-E. There's just a very slight difference in transmissiveness (visually) between the two.


DBEF-II embossed side
Click to view attachment


DBEF-II embossed side close-up
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DBEF-II smooth side
Click to view attachment


DBEF-II smooth side focused on the reflection, not the sheet
Click to view attachment


Again, the reflections on the DBEF-E and DBEF-II sheets are sharp, not blurry. The reflections are wavy from the linear embossing on the embossed side.

Tgreenwood

(EDIT) Now that I look at it again, the embossing is heavier on the DBEF-E than it is on the DBEF-II.

50% is nice, what if we push it another 150% more? You probably have looked into it already, but what about Microlens array?

See this example. See the guy holding a sheet of it, well, I've been searching if these can or are fabricated in the acrylic way such as the fresnels and found this. Here are a few more demos here. This may be designed for a HTPS type LCD but it's an LCD nonetheless. I'm leaning on the idea of placing 2 of these facing each other next to the lcd and replacing the collimating fresnel alltogether

Great find SIM. Regarding the “Polarization changer element” in this link, it’s not that different than the diagram I drew, it may even be better to use a 1/2wave retarder like they have shown.
I’ve fiddled with a couple of these elements before and pondered on how to build one large enough for our use. Until now it hadn’t struck me that they were using a ½ wave retarder. With the element I played around with, I thought that the retardation was occurring inside the element and not realized that the strips of glass were the retarders. I’ve seen the light

I’ll have another think about if we could use DBEF in this design.

DJ

Oh, and they say 1.5 times gain which is 50% more but I don’t think they have realistically allowed for losses.

In the same link and some other sites I’ve seen they use red, green and blue as the colors used for the dichroic prism combiner. I have one here that uses cyan, magenta and yellow. And looking at others I’ve seen in the past, they have used the same secondary (primary?) colors. Maybe RGB are only used for describing the system and YMC are used for ease of manufacture.

Anyone have a dichroic prism that uses RGB?

DJ

As for the integrator lenses, you would still need to use them in the collimated light section of the projector. Meaning; in-between the front and rear fresnels.

DJ

Edit:
Some more info.
There is a problem with using an integrator lens array in our projectors. The arc image created will be too large to fit through the triplet. In a commercial projector they have the advantage of having a projection lens that is about the same size as the LCD.

Here’s a crude trace showing what would happen if we used an integrator in our projectors:
Click to view attachment
Each lens in the lens array takes a small portion of the initial beam and spreads it over the LCD. It is basically shuffling the light.

They look very promising; I’ve got what looks like the D400, which does nasty things to the efficiency of the reflections.
I wonder if they’ll send me a sample pack?

DJ

After thinking about it some more, it does look like it would work It’s a pity that polycarbonate has retardation properties, it would be a simple matter of gluing the DBEF to the polycarb and then cutting it into strips and gluing them all together in the same fashion as the “Polarization changer element”.

DJ

Edit:
I just checked a piece of Acrylic fresnel off-cut and it doesn’t seem to affect things to much, there’s hope .

The beauty of this design is that no other special elements would need to be added to a projector, just place the polarization element before the LCD and you get instant gain.

DJ

There’s a problem. Look at this diagram where I’ve added the other light paths.
Click to view attachment
They must be using some polarization black magic to get it to work.

DJ

Edit:
This is a real mind squeeze for me, I might be understanding it from the wrong view point. I’m now thinking that the reflected light can pass. So it may in fact work. I’ll just shut up now until I can get it clear in my mind how it is working. I’ve just gone and confused myself.

DJ

OK last one I promise
I think they are alternating the direction of the reflective polarizer.

DJ

It seems as though one layer of cellulose tape acts as a 1/2 wave plate. Here are some pics to explain:

There is one layer of tape stuck to my monitor at varying angles.
Click to view attachment


Now with the polarizer turned 90°
Click to view attachment
It's not perfect but the best so far.
Horizontal and vertical are acting like ½ wave retarders. The pieces of tape at 45° don’t seem to affect things greatly. So it appears that the tape needs to be orientated 45° to the polarization axis of the LCD polarizes. I tried a piece on my DBEF jig and it does appear to work. I couldn’t place the tape on the mirror though, that causes two passes through the ½ wave retarder. So I placed it at the opening from the mirror. Like this:
Click to view attachment


The tape could be used for the “Polarization changer element” very easily.

Here area couple of shots with varying layers of tape.
Click to view attachment
Click to view attachment

Bizarre isn’t it?
DJ

I made polarization changer element:

Click to view attachment

And the results
Click to view attachment

Click to view attachment

It appears to be nearly working. For this to work better I think I would need un-diffuse reflective polarizer and a good ½ wave retarder. The cellulose tape isn’t rotating the polarization 90°.

Click to view attachment
If you look in this photo you can see that the colors are sort of repeating them selves, magenta for example has four instances, which suggests that the tape is rotating just not where I need it to be. So with one layer the white is yellow and the black is blue.

DJ

Just a ponder really, but would any of these materials provide advantages at the screen? Such as a layer over UPW instead of going with High Power or something? I admit, it is hard for me to follow some of the discussions in this thread.

There is no change in the polarization state of the reflection if the beam is incident normally on the mirrors, or if the plane of polarization lies in or normal to the plane of incidence. However, if the polarization direction makes some angle with the plane of incidence, then the reflection often makes a small phase shift between the parallel and perpendicular components.
From Newport Optics Technical reference.

It looks like cellophane tape is very wavelength-dependent, and the wavelength that has its polarization rotated depends on the number of layers, or combined thickness.

What does lexan look like in the place of the tape? Does it effect all colors the same?

Tgreenwood

The useable light exiting a perfect theoretical "Polarization changer element" is 200% (2X). So losses have been taken into account here.

The 3M vikuiti polarizers can pass up to a 192%. In other words, DBEF can give you 97% more light. This is accounting for losses in a backlight. What our losses would be is to be seen.

Mark

Click to view attachment

Click to view attachment



Your guess is as good as mine

There’s a reflection for Durachko in the top pic, just so he knows I really are building a retainer.

This is for rear projection. I'm not sure if they can be used for front.

DJ

nice, bet they're pricey

So confuse me to the point of insanity and explain the polycarbonate effect please.
Seriously, you gurus are enough to put me into a drooling, blabbering state.Thank you. But it looks nothing like the retainer my orthodontist made for me???

Well, it's nice to see that I'm not the only one out there who's head is spinning with confusion.


I gotta' do some reasearch now....

DAZZ, what about using 2 of the BEF's crossed at 90 with the grooves facing forward to replace the mirror. I just tried it and it reflected. Could this be the 45 degrees your looking for?....Or am I just as confused as the rest?

I'm a little bit lost here. I've been reading these experiments and don't quite know what direction they are going in.

From my understanding the BEF is simply a microprism sheet. It may be useful for our applications if we want to use two or more light sources off at about 45 degrees from center. However, it does not collimate light enough to make it worth implementing.

The DBEF, however, may be of help. It is a reflective polarizer. Half the light is polarized and transmitted. The other half is polarized at 90 degrees from the first half and reflected. Now, maybe I'm wrong, but if you simply put this behind the collimating fresnel and rotate it to align with the lcd polarizer, then the reflected half should transmit back through the collimating fresnel, reflect off the reflector and come back at a polarization angle different from what it was reflected at. The process should repeat itself ad infinitum until the light is transmitted or absorbed.

Now, the system will take an initial hit (brightness wise) because of two polarizers being used in parallel. However, there should be a net increase from some of the reflected light being utilized.

Has anyone tried this? I tried to determine if anyone has tried this but could not make sense of these experiments. I think it is vital that the DBEF is rotated to ensure it is aligned with the lcd polarizer. As a matter of fact, theoretically, you should be able to replace the rear lcd polarizer with the DBEF altogether.

Did I get the gist of it or did I miss something.

OK. It was only $5 for the DBEF shipped from ebay. I bought a sheet. Maybe this will work with the led projector I'm working on.

I'm trying to make heads or tails out of this too.

See my sketch of how I found light will go through at the BEF when the films where crossed and their grooves faced the opposite way of the light source. Light had to be at an angle of 45 degrees towards center but only from the corners in order to penetrate. When shined from top, bottom or sides even at 45 degrees or head on directly towards the center there was no penetration. But when shining the light on the opposite side of the films and towards the grooves sides there was a reflection in either way the light source was pointed at it. So this is my question, if light is only going through at 45 from the back of the BEF films and from it's corners, would a reflection from the front be twisted at 45? If so, would this replace the tape that DAZZ is using in his setup?

From here on I'm not sure of what recycling may occur (if any) in this setup.

I believe that Dazzzla is trying to do something like this.

Found this page a while back. It describes how to maximize light for LCD's.

You are right, BEF isn't much use with a point source light projector.


You have it exactly right. The reflector has to be made of a corner cube retro-reflector to rotate the polarization 90 degrees. A spherical reflector won't rotate the polarization correctly.



You got it.

The latest experiments are a search for a material or film that will rotate the polarization of the reflected light 90 degrees by passing through it. I don't really know for sure why, when a corner cube retro-reflector will rotate all of the wavelengths' polarization by 90 degrees.

It is vital to align the polarization of the DBEF with the LCD polarizer, that's right. Since DBEF, as it is now, is designed to work with the LCD's polarizer, it would probably be best to keep them both.

From what I understand so far, if you could get a sheet of DBEF (the specular, mirror-like, kind) align it with your LCD polarizer, and replace your current reflector with a corner-cube retro-reflector, you should see a big boost in brightness. The system should be recycling the incorrectly polarized light.

I can't test this, because I use diffuse fluorescent light and no fresnels in my projector. I'm currently looking for retroreflective sheeting that is made from corner-cubes, not spheres, for use in my projector. No luck yet.

Tgreenwood

They sell DBEF sheets for just $5 on ebay. Here is the site. These look like the clear reflective polarizers, perfect for our systems.

I don't see why we need a corner cube retroreflector or why we have to rotate the reflected light 90 degrees. I know these would be optimal, but any rotation would net a significant increase in lumens. If the reflected light is rotated ...let's say 45 degrees... then it would simply require several passes. This would definitely reduce overall efficiency due to absorption and off reflections, but it should still work. The spherical reflector should also work just as well. who knows, that may induce some rotation in polarization. We can always coat it with some type of clear coat or high temp paint that will induce a rotation or even just diffuse the light.

So, we use lexan as our rotating medium (or simply the stainless steel reflector). Put the DBEF just behind the collimating fresnel. The reflected light should go through the collimating fresnel and be focused at the point light source. It will hit the reflector and be reflected back towards the collimating fresnel like any light.

The fact is, the reflected light will pass through an acrylic layer, a heat shield, several layers of tempered glass, the plasma light source, a reflector, the plasma light source, several layers of glass, the heat shield, and the acrylic layer before being incident back onto the DBEF. It is hard for me to believe that it won't have some type of rotation or randomness in polarization after all of this.

Usually, non-ideal material properties work against us. In this case they may work for us by slightly randomizing the polarization through each pass.

Also note that even a non-ideal quarter wave plate may work. The cellophane tape may rotate certain wavelengths more, but it don't quite matter. This is because all wavelengths will recycle back and forth until they pass through the DBEF. Again, the only real issue is the losses per cycle. This may throw the color slightly off, but that can be addressed with the lcd color filters.

OK then
This is taken from tgreenwood’s link: just re-worded
A zero order wave plate is one that only rotates or retards polarized light the desired angle and no more. Meaning, if it is a ½ wave zero order retarder then it only rotates the wave 90°. The problem with zero order retarders is that they need to be very thin. Multiple order retarders will do a similar job but instead of changing a wave’s angle by 90°, it may rotate it 450°, 540°, 630° and so on. As the order increases. its ability to retard off axis waves does as well so a multiple order retarder should be used in a collimated beam. What I think is happening with the polycarb is that it is a multiple order retarder and by using the very diffuse back light of my monitor, off axis waves are being retarded more than the normal waves so they are seen as different colors. It kind of makes sense, when I placed the tape in varying layers on the monitor, each layer would retard a bit more and change the color. And it can be seen that the colors were repeating as the order increased. The tape didn’t show the rainbow of colors like the polycarb because it is thinner, a lower order, and less affected by the off axis waves. I presume though that if I laid enough layers of tape that eventually the rainbow would be seen.
What this all means is that the wave plate should be as thin as possible and kept in a collimated beam

Something a bit off track that I found interesting while reading was in the “Polarization cleanup” section. There have been a few members that have used a polarizer in the triplet and used a mirror in between that have had problems with colors, focus and glowies. This section describes what could be the cause or part of it.

DJ

That’s the stuff we want .
DBEF-P2 isn’t available from 3M only OEM. I’m fairly certain that it isn’t diffuse or dimpled so it would be perfect for this experiment.
Unfortunately they don’t ship international so who ever buys some, get a couple of extra sheets for me, please .

DJ

I’ve discussed this before with Mark. The biggest problem is that the rays passing back though the fresnel won’t travel the same path as they did to get to the fresnel. A fresnel being a asymmetrical lens means that it refracts light differently depending on the surface facing the lamp. It is also spherically corrected so this will make it even more asymmetrical.
The polarization changer that I’ve been suggesting would be used in the collimated part of the system and do all the retardation there without sending it elsewhere.

DJ

Edit:
Another note. I think that it will be very important to retard the wave very close to 90°. The tests I’ve done tend to suggest this as well. Apart from the inefficiency of improper angles, the color of the light is going to impact the final outcome.
I also tend to dislike diffusion of any type in the light path, it just plain sucks the efficiency out.


Edit2:
One more note. Don’t underestimate the amount of light that is going to be lost from several passes. The reflector is going to loose a%, each surface of the fresnel is going to loose some more and the DBEF reflection will eat into it as well. Multiply this a few times and not a lot is going to be left.

That 13x8 size on the film is not a great fit for a 15" 4:3 though. It will be interesting to see someone put this to use in a pj though. Do you really think it will bump up light?

Don't understand what you mean. the fresnel would be facing the lamp. the reflected light would be incident on the opposite side of the fresnel as collimated parallel rays. They should be copndensed along the exact same path they originated from. Obviousely, non-idealities in positioning would change the rays slightly. But how much is important to know.

I agree that your setup would be ideal. However, in the absence of the right materials I think that simply putting the DBEF behind the fresnel should work. We know a mirror will rotate the polarization slightly. No reason to think that all the layers the light will pass through won't do the same.

According to the title that is the DBEF-P2. who knows, they may have gotten it from an OEM as surplus or something.

Is this the order you are talking about?

Not by itself but used as part of a system, theoretically yes.