mixed optical and electronic circuit? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: October 05, 2021, 02:04:41 am
content: I was thinking about instrumentation PCBs and I was wondering where we are on a time line for having optical to THz power distribution systems on circuit boards.I know right now the hot issue is to use electronic control systems to control photonics, but are there any systems that work backwards, and use optical power and high watt density photoelectric generators to break paths but power electronics with many rails?If a fiber line was copper clad, it would be possible to solder it over a exposed PCB area to mate it with a board, making a mixed optical electrical wiring board in a similar form factor to conventional electronics.Are there any parts like this available that are made in mind with PCBs? So instead of a barrel DC connector it would have a high power fiber line. Ground planes totally split instead of joined and without any power transformer. I know the bandwidth of power transformers to specific measurement problems is a limiting factor of equipment related to isolation.I know the application is off beat but keep in mind we use mechanically disciplined electrical systems and vise versa all the time, with either loads of electronics being used to reduce mechanics or vise versa.. neither is obsolete. I know you have optical power over fiber but thats a systems level concept, I am looking for component PCB level.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 05, 2021, 09:37:33 am
content: Power-over-fiber is generally a lot lossier than transferring the same power over copper wires. This is especially true for shorter distances, as most of the losses come from the electrical-optical and optical-electrical conversion. Laser diodes can typically be 50 % efficient, and apparently photovoltaic junctions optimized for monocromatic light can reach efficiencies of 70 %, giving a total conversion efficiency of 35 %. Cost would also be significantly higher than the wired solution.Under what circumstances would these disadvantages be justified? One of the few I can think of is in cases where the high isolation voltage that fiber can provide is needed, such as when powering instrumentation or control systems floating at high voltage potential. Curiously, both temperature and voltage can be sensed directly by optical fibers, without any electronics. Voltage- or current-induced changes in the optical properties of fibers are monitored via interferometry or polarimetry. They also make directly optically triggered thyristors for assembling into high voltage stacks, where a common laser can fire a long series chain of thyristors without the usual challenge of having to isolate the gate drive signal across the potential over the whole stack.

author: coppercone2
author_rank: Super Contributor
timestamp: October 05, 2021, 04:25:14 pm
content: Watch the EEVBlog video about the isolated differential probe in the trade show, they had problems with hf coupling over the transformer and it took a year to design, its a example of a problem that is not related so much to safety as telemetry. When there is lt3045 and 1028 I don’t think many people would care about 35 percent being a problemI am imagining circuits that run on 8 dollar + op amps, ADC’s with a lot of bits, it’s a instrumentation supply

author: richard.cs
author_rank: Super Contributor
timestamp: October 05, 2021, 05:00:57 pm
content: I was involved in this project:https://www.ashwireless.com/pages/43-energy-and-data-via-one-optical-fibreRemote uC powered over optical fibre, but in that case the use of an optical approach was driven by ATEX requirements.

author: mawyatt
author_rank: Super Contributor
timestamp: October 05, 2021, 05:04:37 pm
content: On 9/11/15 DARPA had a conference in St Louis called "Wait What?" I saw a demonstration by Northrop Grumman of a THz communication system based upon NG's custom InP IC process and custom designed THz RF Type amplifiers, mixers, modulators and demodulator chips. They used custom developed "wired" interfaces with custom connectors.This was quite an impressive demonstration, almost as much as the Boston Dynamics Roboticshttps://defensesystems.com/articles/2010/06/01/darpa-northrop-terahertz-chip.aspx?m=1https://www.nextbigfuture.com/2014/10/darpa-terahertz-chip-for-high.htmlhttps://www.militaryaerospace.com/computers/article/16718804/terahertz-chip-offers-new-applications-in-sensors-communications-and-collision-avoidancehttps://investor.northropgrumman.com/news-releases/news-release-details/northrop-grumman-sets-world-record-one-terahertz-circuitAnyway, suspect we'll begin to see THz chips and circuits soon.Best,

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 05, 2021, 05:23:03 pm
content: Quote from: coppercone2 on October 05, 2021, 04:25:14 pmYet they ended up using a transformer. I'm sure they didn't spend an entire man-year developing that one transformer, even if it was a significant part of the challenge. And once the transformer is designed, it costs cents to make.Looking at what you can actually buy in terms of power-over-fiber systems, I found this:https://www.fiberopticlink.com/product/fiber-optic-isolation-systems/power-solutions-for-fiber-optic-isolation-systems/power-over-fiber-system-pof/#specs75 W input to transmit 1 W, 2250 dollars for the transmitter and 2075 for the receiver. I'm sure better and cheaper systems can be developed in the future, but this is where we are today as far as commercially available systems go. There might be cheaper, more efficient and more powerful systems on the market that I didn't find, but it's still far from competing with a piece of wire unless you need hundreds of kilovolts of galvanic isolation.Precision systems where you need very low charge injection like you mentioned could also be an application, but if you don't need to pipe the power over more than a few centimeters, then a focused LED and a solar cell would be a lot cheaper.

author: coppercone2
author_rank: Super Contributor
timestamp: October 05, 2021, 08:28:21 pm
content: Yeah it does not need to be a laser, I call it the PPDS (photon power delivery system) experiment nowI was thinking about using a microscope fiber light source to do some experiments with chip sized things to see what can be made with the device sizes I am imagining (i.e. dip, dc/dc converter blocks soldered to the board, etc). I am wondering if panels that small got past the graphing calculator efficiency stage yet, or what is a better more efficient electrooptical power converter for single frequency from LED or laser light. The most cheap system would be to put a lens, a calculator solar panel and a fiber optic connector inside of a small box that has leads that can be board mounted.. I wonder how much power you can get out of that setup.I think for PCB scale, a standard match box size should be the upper size limit.

author: ajb
author_rank: Super Contributor
timestamp: October 05, 2021, 08:55:40 pm
content: The problem with an idea like copper-coated optical fibers you can just solder to the board (or any other situation where the person putting the board together has to deal with raw fiber) is that the optical interface between the fiber and whatever it's connecting to is critical to the effectiveness of that interface. That's why fiber splicing/termination is a specialty job.It's not designed to convey power or as an intra-board system, but Samtec's Firefly Optical products are a reasonable example of what a practical way to integrate photonics into PCBs might look like.https://www.samtec.com/optics/optical-cable/mid-board/fireflyLike the rest of their 'Flyover' offerings, the selling point is to move high throughput data links off of the board which can directly and significantly reduce the cost/complexity of the board design in some situations. But as with the case for optical power transmission, there isn't much advantage over data copper connections for most scenarios, so you'd only go for the optical solution where you need an optical connection to go out of the box anyway, which doesn't happen with power connections. Otherwise, for intra-board links you can just use one of their copper flyover systems.The main impediment to progress in tighter integration of photonics and electronics at the PCB level is: what problem would it solve that can't be solved more easily/at a lower cost some other way? If you just need to break a galvanic connection we already have transformers, optocouplers, and digital isolators, and there just aren't that many scenarios where those solutions aren't adequate. That isolated scope is probably a prime example of where the standard solutions might not be up to it, but they ended up with a (admittedly very specialized) transformer anyway. And most of the time when you need electrical isolation you don't also 100dB CMRR @50MHz. The other primary benefit is larger isolation distances that you can get with fiber, but there are already niche solutions for that.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 05, 2021, 09:12:21 pm
content: I think the Art of Electronics or something had a story about using lights + solar cell for power transmission... to power some sensor at the target of a particle accelerator with millions of voltage isolation. I could imagine something similar for high side sensors on HVDC power converters although I don't actually know if that happens. Its reasonably common to need signals with very high CMMR at high frequency but that is achieved with ordinary optical isolation or even fiber optics. Its pretty rare that you need to transmit power across that gap as well.