Is this possible?

bobhaha · Mar 16, 2012

Is this idea possible? I would like to combine 3 (or more) laser beams of the same wavelength, but would like to know if this is possible.

If you have any suggestions or thoughts I would be interested to hear them!

-Adrian

BShanahan14rulz · Mar 16, 2012

If I see correctly, you have 3 polarizing beam splitter cubes in your drawing.

The one above laser B seems kinda useless, it's just reflecting both beams.

Also, the top-left cube will split the A+B beam since the A beam is polarized one way and the B beam is polarized the other way. The B beam would end up dumping out the left side of the cube I think.

You'll have to use prisms or knife edging, or cut down the lasers to 2. What kind of lasers are these? Sometimes knife edging can actually help form a better-shaped beam out of multi-mode diodes.

rhd · Mar 16, 2012

Conceptually, it's a flawed.

You have two polarities, and three lasers. It really doesn't make any difference how you arrange the mirrors and cubes, at some point, you're going to be attempting to mix two beams that contain the same polarity, and it won't work.

Cyparagon · Mar 16, 2012

Specifically, when the "B" component of the "A+B" beam goes into the "A+B+C" cube. It will be directed left, not up.

bobhaha · Mar 17, 2012

Oh you're right!

So basically if beam B was the same polarization as A when it goes into PBS ABC then this set up will work?

rhd · Mar 17, 2012

bobhaha said:
Oh you're right!

So basically if beam B was the same polarization as A when it goes into PBS ABC then this set up will work?

No, the problem then, is that beam B will be directed left as soon as it enters A+B cube.

Again, there are two possible polarizations, and three beams. You just can't do it.

bobhaha · Mar 17, 2012

You can.. you have to polarize the B beam after it combines with the A beam to have the same polarization before it enters PBS ABC. This will involve more optics and changing the lengths of the beam A and B.

rhd · Mar 17, 2012

bobhaha said:
You can.. you have to polarize the B beam after it combines with the A beam to have the same polarization before it enters PBS ABC. This will involve more optics and changing the lengths of the beam A and B.

- So beam A and B have different polarization, lets call it vertical and horizontal polarization.
- They combine in a PBS to form one single beam, lets say "Beam X"
- Beam X thus contains two polarizations of light, vertical and horizontal, originally from beam A and B.

Now, with beam X, how do you selectively change the portion of the beam that is vertically polarized, into horizontally polarized light, without splitting the beam into two again (and thus defeating the purpose of combining them in the first place)?

PS - You might be completely correct. I don't have a lot of experience with this. But based on my conceptual understanding of how this all works, I don't think you can do what you're proposing. But, I could be completely wrong.

BShanahan14rulz · Mar 19, 2012

Yes, there are optics that will rotate your polarization by 90. Alas, I don't think it will work.

general article: Polarization rotator - Wikipedia, the free encyclopedia
most common method w/ lasers: Wave plate - Wikipedia, the free encyclopedia

You can't throw beam A+B through a waveplate and expect it only to rotate one component's polarity, though.

What lasers are you working with, and what is your end goal? If you are using multimode emitters, your beam cross-section will benefit from knife-edging, in that you can stack several | shapes to approximate a square, which is a decent approximation of a circle (at least, a better approximation than a line

).

bobhaha · Mar 20, 2012

I know you can't selectively change the polarity of one component of the beam. But if you split it then recombine it, it would have worked... but that's not very efficient and way too many variables.

I was thinking... What about something like this?

Component count is down

Also this isn't for a specific diode or colour, it's just thinking out loud.

-Adrian

rhd · Mar 20, 2012

The middle beam exits left through the first PBS.

BShanahan14rulz · Mar 20, 2012

bobhaha said:
But if you split it then recombine it, it would have worked...

You could split a two-component beam where the two components are orthagonally polarized by using a polarizing beam splitter cube. Then you could rotate the polarization of one of the beams. But then you couldn't recombine them with the PBS because they'd be the same polarization.

In your newest example, beam B (assuming [A][C]) will transmit through the first cube and exit to the left side. If you changed B's polarization before it entered the cube, it would be added to beam A, but then it would reflect in the second cube and exit to the left side. Beam C, being the same polarization as beam B, will also reflect in the second cube and exit out the top side.

Bionic-Badger · Mar 20, 2012

Basically, you've gotta have two different polarizations to combine in a PBS. Therefore the bottom cube would either all-pass or all-reflect the light entering because both beams have the same polarity.

rhd · Mar 20, 2012

I feel like I'm invisible here

Bluefan · Mar 21, 2012

You're probably just a different polarization, you're passing straight through without interaction

bobhaha · Mar 21, 2012

Why would it pass through the first PBS? Is the reflection dependent on the second incoming beam? ie can not use a beam splitter with only one beam?

I thought the coating inside the PBS reflects in one direction but passes in the other (given the beam polarization has not changed).

Is this possible?

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