MCU for optical fibers - Page 1
Forum section: electronics / projects

author: victus
author_rank: Newbie
timestamp: January 25, 2016, 05:26:34 pm
content: I am working on a project where I would like use optical fibers as sensors for measuring strain, perturbance and shape sensing. The required hardware and measurement devices are usually very expensive and thus inappropriate in my case, so I was wondering if there are any solutions available with commercial microcontrollers, which would consequently drastically lower the expenses? Are there perhaps any demo projects or articles out there about designing of low-budget optical fiber systems? I am aware that optical emitters represent a major cost as well, so I was wondering where may I find any comparisons on price/performance ratio?I know that a company named Darma has managed to build a similar system according to the photos here:https://www.dropbox.com/sh/sncu1b7c2lknc0u/AABfOkkTa3hHn6IlD_gg1fqZa?dl=0, so I am really curious what components did they use.

author: Yansi
author_rank: Super Contributor
timestamp: January 25, 2016, 06:22:40 pm
content: I think when talking about optical fiber pressure transducers, MCUs will really be the last thing to be concerned about.

author: nfmax
author_rank: Super Contributor
timestamp: January 27, 2016, 01:40:16 pm
content: For the sort of mechanical strain, displacement sensing you mention the most common type of fibre sensor is an FBG (Fibre Bragg Grating). These have a more-or-less strong reflection of light at a narrow peak of wavelengths, and transmit light at all other wavelengths. As the strain on the grating (and/or its temperature) change, the wavelength of peak reflection also changes. The strain sensitivity is around 1.2pm/?? and the temperature sensitivity is around 12pm/°C, for centre wavelengths in the 1550nm band.For low speed measurements, there are two basic techniques to measure peak wavelength:Use a broadband detector and a swept-frequency source, record the wavelength of the source when the response from the detector reaches its maximumUse a broadband source and a wavelength-sensitive detector (or detector array). This might be a multi-channel array, or a tuneable filter followed by a broadband detectorCommercial 'Bragg Meters' use one of these techniques, but they aren't cheap. You don't give a budget, or a timescale, or quantities for your requirement, so it's difficult to be specific.Assuming you are breadboarding something experimental, for low cost, low accuracy designs the broadband source is probably the way to go. This might be an LED or SLED source, and maybe an integrated diffraction grating & diode array detector. Still not cheap. You can make a very cheap tuneable filter by using a second FBG in reflection and a 50% coupler, and applying strain or temperature to the FBG to tune it. Another idea is to use a commercial WDM chosen so that the sensing grating peak lies right on the 50% wavelength. Alternatively you might look out for a second hand fibre Fabry-Perot filter.The microcontroller is the least of your worries. Except maybe for deciding what colour to paint the box

author: dmills
author_rank: Super Contributor
timestamp: January 27, 2016, 05:10:42 pm
content: There was a talk at the CCC congress this year on a university rocket project that flew a FBG based accelerometer, might be worth tracking it down (Some EU group doing balloon and sounding rocket launches of student science payloads as I recall) and contacting the team who built the payload package.Regards, Dan.