Read an article the other day which blew me away, Researchers Create ” Intelligent interaction between light and meterial – New form of computing, which discussed the use of a hydrogel (like raspberry jell-o) that could be used both as a photonics switch for optical communications and as modifiable material to create photonics circuits. The research paper on the topic is also available on PNAS, Opto-chemical-mechanical transduction in photeresponsive gel elicits switchable self trapped beams with remote interactions.
Apparently researchers have created this gel (see B in the graphic above)which when exposed to laser light interacts to a) trap the beam within a narrow cylinder and or b) when exposed to parallel beams interact such that it boosts the intensity of one of the beams. They still have some work to show more interactions on laser beam(s) but the trapping of the laser beams is well documented in the PNAS paper.
Jell-o optical fibres
Most laser beams broaden as they travel through space, but when a laser beam ise sent through the new gel it becomes trapped in a narrow volume almost as if sent through a pipe.
The beam trading experiment using a hydrogel cube of ~4mm per side. They sent a focused laser beam with a ~20um diameter through an 4mm empty volume and measured the beam’s disbursement to be ~130um diameter. Then the did the same experiment only this time shining the laser beam through the hydrogel cube and over time (>50 seconds) the beam diameter narrows to becomes ~22um. In effect, the gel over time constructs (drills) a self-made optical fibre or cylindrical microscopic waveguide for the laser beam.
A similar process works with multiple laser beam going through the gel. More below on what happens with 2 parallel laser beams.
The PNAS article has a couple of movies showing the effect from the side of the hydrogel. with a single and multiple laser beams.
Apparently as the beam propagates through the hydrogel, it alters the optical-mechanical properties of the material such that the refractive index within the beam diameter is better than outside the beam diameter. Over time, as this material change takes place, the beam diameter narrows back down to almost the size of the incoming beam. They call any material like this that changes its refractive index as chromophores.
It appears that the self-trapping effectiveness is a function of the beam intensity. That is higher intensity incoming laser beams (6.0W in C above) cause the exit beam to narrow while lower (0.37W) intensity incoming laser beams don’t narrow as much.
This self-created optical wave-guide (fibre) through the gel can be reset or reversed (> 45 times) by turning off the laser and leaving the gel in darkness for a time (200 seconds or so). This allows the material to be re-used multiple times to create other optical channels or to create the same one over and over again.
Jell-o optical circuits
It turns out that by illuminating two laser beams in parallel their distances apart can change their interaction even though they don’t cross.
When the two beams are around 200um apart, the two beams self channel to about the size of ~40um (incoming beams at ~20um). But the intensity of the two beams are not the same at the exit as they were at the entrance to the gel. One beam intensity is boosted by a factor of 12 or so and the other is boosted by a factor of 9 providing an asymmetric intensity boost. Unclear how the higher intensity beam is selected but if I read the charts right the more intensely boosted beam is turned on after the the less intensely boosted beam (so 2nd one in gets the higher boost.
When one of the beams is disabled (turned off/blocked), the intensity of the remaining beam is boosted on the order of 20X. This boosting effect can be reversed by illuminating (turning back on/unblocking) the blocked laser. But, oddly the asymmetric boosting, is no longer present after this point. The process seemingly can revert back to the 20X intensity boost, just by disabling the other laser beam again. .
When the two beam are within 25 um of each other, the two beams emerge with the same (or close to similar) intensity (symmetric boosting), and as you block one beam the other increases in intensity but not as much as the farther apart beams (only 9X).
How to use this effect to create an optical circuit is beyond me but they haven’t documented any experiments where the beams collide or are close together but at 90-180 degrees from one another. And what happens when a 3rd beam is introduced? So there’s much room for more discovery.
Just in case you want to try this at home. Here is the description of how to make the gel from the PNAS article: “The polymerizable hydrogel matrix was prepared by dissolving acrylamide:acrylic acid or acrylamide:2-hydroxyethyl methacrylate (HEMA) in a mixture of dimethyl sulfoxide (DMSO):deionized water before addition of the cross-linker. Acrylated SP (for tethered samples) or hydroxyl-substituted SP was then added to the unpolymerized hydrogel matrix followed by an addition of a catalyst. Hydrogel samples were cured in a circular plastic mold (d = 10 mm, h = 4 mm thick).“
How long it will take to get the gel from the lab to your computer is anyones guess. It seems to me they have quite a ways to go to be able to simulate “nor” or “nand” universal logic gates widely used in to create electronic circuits today.
On the other hand, using the gel in optical communications may come earlier. Having a self trapping optical channel seems useful for a number of applications. And the intensity boosting effect would seem to provide an all optical amplifier.
I see two problems:
- The time it takes to get to a self trapping channel, 50sec is long and it will probably take longer as you increase the size of the material.
- The size of the material seems large for optical (or electronic) circuitry. 4mm may not be much but it’s astronomical compared to the nm used in electronic circuitry
The size may not be a real concern as the movies don’t seem to show that the beam once trapped changes across the material, so maybe it could be a 1mm, or 1um cube of material that’s used instead. The time is a more significant problem. But then again there may be another gel recipe that acts quicker. But from 50sec down to something like 50nsec is nine orders of magnitude. So there’s a lot of work here.
Photo Credit(s): all charts are from the PNAS article, Opto-chemo-mechanical transduction in photo responsive gel…