I want to share an amazing invention that I daresay will soon become common-place in the guitar world, Dagmar Guitars has been working with Dr Hans-Peter Loock of Queen’s University in Canada developing a new type of pickup using Fiber Optics. I recently had an email conversation with Dr. Loock where he gave me this great explanation:

The sound of many acoustic instruments (mostly acoustic guitars) is frequently recorded using piezo-electric pickups. Piezos record the vibration of the soundboard of the guitar and convert the vibration amplitude into a voltage. Piezos work quite well, but – as I understand – have some disadvantages: they measure acceleration as well as amplitude and therefore cannot have a completely flat frequency response. They are sometimes susceptible to radio frequency noise (the 60 Hz hum) and it is difficult to use more than a few of these pickups on one instrument.

Instead of piezo electric pickups we use strain sensitive fiber optic cables. Our fibers have a strain sensor, called a 'œFiber Bragg Grating' near their end, which reflects light of only one particular wavelength. When the grating is strained a different wavelength is reflected. The FBG is fixed to the guitar body and we send laser light at the 'œunstrained reflection wavelength' along the fiber and record the intensity of the reflected light. When the guitar body vibrates, the FBG is strained, laser light of the same wavelength is no longer reflected (but is transmitted) and the reflected light intensity is reduced. The photodetector can therefore monitor the amplitude of vibration. We feed its output directly into an audio amplifier for recording and reproduction.

The advantage is that this pickup is still the size and weight of a fiber optic cable (micrograms and dimensions of about 100 micrometers diameter and 2 mm length). In Pete's [Pete Swanson - Dagmar Guitars] guitar seven pickups were embedded into the wood of the soundplate before varnishing and therefore become a part of the body. Also the frequency response is flat up to 20 kHz and we have not observed any interference form electromagnetic fields (or room light!). We do have issues with laser intensity noise and with intensity noise form the fiber optic cables though. Our current research project (was funded only last week!) will focus on eliminating these last sources of noise to get as close as possible to the true sound of the instrument.

I realize this is a lot of optics, but in essence the technology is not that different from what is already used in the fiber-optic vibration monitoring of airplane wings, wind turbine blades, generators, buildings and bridges. We focus on musical instruments, but hope that eventually all other applications will also benefit from our research.

We have commissioned a guitar from Dagmar Guitars (luthier: Pete Swanson) that has 7 fiber optic pickups permanently built in. The guitar is called 'œVicky' (pictured above).

This all sounds very exciting to me, totally eliminating external, and hopefully with their latest round of funding, internal noise from a pickup will mean a totally true representation of the guitar’s tone which will be very popular with Acoustic and Archtop jazz guitars.

For more info keep an eye on http://www.dagmarcustomguitars.com/ for more info.

Update: khas evets posted a comment asking about how you capture the sound of the string as well as the body with this pickup system. Dr Loock’s has responded to this comment with a little more info:

“The question is an interesting one: of course the fiber optic sensors – just like good piezos – record faithfully the vibration of the guitar body but not necessarily that of the strings. To get more of the sound of the strings one can put either pickup right at the bridge. In fact, Pete’s guitar has two fiber optic pickups on either side of the “floating” bridge, in addition to five more pickups at other places on the body. We also experimented with putting fiber optics on the headstock (works well for solid body guitars!), but decided against that for Pete’s guitar.”