| T O P I C R E V I E W |
| Kale |
Posted - Feb 25 2005 : 5:11:27 PM
Well, I'm not dead yet. Glad to be back on the forum again; glad to see people are still trying to do stuff likely to cause fires and/or death. 
My latest research toy is a superluminescent diode. It's a diode with an optical amplification medium built into the design. Unlike a laser it doesn't have any feedback; no mirrors. A photon is generated, starts travelling through the semiconductor, gets amplified, then exits with all its new friends. Mine emits from 800-860nm so in really dim lighting I can see the beam. Since I'm trying to do precision aligning with this thing it means I spend a lot of time standing around in the dark waiting for my eyes to adjust enough that I can see what I'm doing. Yay!
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| 8 L A T E S T R E P L I E S (Newest First) |
| Kale |
Posted - Apr 12 2005 : 11:42:39 PM
Well the experiment is still progressing. I had to send back a beamsplitter plate (twice) because the coating on it was screwed up. It turns out the coatings on the whole line of this splitter are faulty and the company is going to redesign it from scratch. In the meantime for my trouble they sent me a rather more expensive beamsplitter cube and mount for free. The cube is very nice. 20mm of 20/10 scratch/dig cubey goodness with coatings that actually work right.
I find it funny that the coatings on the cube work wonderfully whereas the plate splitter's coatings were completely fubar.
Anyway, I've done preliminary alignment with a He:Ne and discovered that I'm getting significant vibration through the floor. I stuck four 2" hemispherical dampening feet under my breadboard after lifitng it up off the table (not easy -very heavy! (2'x4')) and that seemed to fix the problem. The setup is sensitive enough that if I talk the pressure waves from my voice are visible on the oscilliscope hooked up to the detector in my interferometer. I can whistle notes and see their frequencies as carriers on the lower frequency vibrational noise in my interferometer. Needless to say I'll be doing most of my experimentation after everyone else has gone home for the night.
Tomorrow I'll be swapping out the He:Ne for my SLD, so we'll see how that goes.
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| Kale |
Posted - Mar 09 2005 : 10:29:05 PM
Well I'm not going to be standing in the dark anymore.
I dug through the junk cabinet in my lab and found a CCD camera that's sensitive to the IR wavelength of my SLD. I hooked the camera up to an old monitor and now I can see the spot from the diode, even under normal room lighting. It's making aligning my system much easier.
I've also constructed my own optical isolator so back reflections don't destroy my diode. I had a very nerve-wracking time testing it. I gradually turned up the power and did a lot of praying. Luckily it seems to work extremely well. I built it using a polarizer and a 1/4 wave plate.
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| Kale |
Posted - Mar 04 2005 : 5:53:16 PM
Coherence and its effects are never really properly explained, even at college and university levels. It's kinda something you have to figure out for yourself.
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| cirvin |
Posted - Mar 03 2005 : 2:03:35 PM
Cool.
I've alwase wondered why my laser's point looked "different" like that.
http://daxter12.topcities.com <Its updated as of 12/9/04, check out the Punk Phone! |
| Kale |
Posted - Mar 02 2005 : 5:04:28 PM
Well you can use them in optical gyroscopes; basically you circulate the beam through a fiber optic ring. Rotation of the ring causes a phase displacement that can be picked up with a detector. The phase displacement tells you how much the ring has turned. Basically it's a movement-detecting gyro with no moving parts, making it super reliable. You can also build an extremely sensitive interferometer with them (which is what I'm doing). This lets you measure distance and thickness of objects to a resolution of 30 microns or less, depending on the source you use.
Also, SLDs are speckle-free sources. If you take a conventional laser and shine it at a wall, you'll see little tiny black dots randomly moving across the surface. This is speckle caused by the laser's wavefront interfering with itself when it is irregularly reflected off the wall. A superluminescent diode does not experience this problem due to its short coherence length. For machine vision applications and other sensitive measurements the speckle in a conventional laser can screw up your measurements, so again, an SLD is a better choice.
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| cirvin |
Posted - Mar 02 2005 : 4:52:30 PM
So, of what use would this device be?
http://daxter12.topcities.com <Its updated as of 12/9/04, check out the Punk Phone! |
| Kale |
Posted - Feb 25 2005 : 5:30:07 PM
Umm... it's a little tiny gold box about half the size of a matchbox, with a fiber optic coming out one end. Not much to see. It was specially made by a company called QPhotonics in the US. He seems to be the cheapest source for them. They are used in optical gyroscopes and various medical applications. Mine cost $680 USD and requires a $1800 USD control unit and mount which temperature stabilizes the diode so it doesn't fry itself, and keeps the output spectrum stable (spectrum is temperature dependent).
go check out www.qphotonics.com and click on "broadband sources->superluminescent diodes" for pictures and specifications.
One really cool thing is that there's a temperature sensor (thermistor) and a light sensor (photo diode) built inside the box with the diode, so you can read the device's optical output and temperature very easily, which is how the control box gets its inputs.
Edited by - kale on Feb 25 2005 5:33:37 PM |
| cirvin |
Posted - Feb 25 2005 : 5:24:26 PM
Wow, that sounds cool!
You wouldn't have any pictures would you?
EDIT:
Oh yea, welcome back! :p
Edited by - cirvin on Feb 25 2005 5:27:15 PM |
