First results with the bragg fiber

posted Jan 22, 2013, 7:38 PM by Sensorica Group   [ updated Jan 22, 2013, 7:41 PM by Tiberius Brastaviceanu ]
Hang, working from his lab at the Ecole Polytechnique de Montreal, obtained the first conclusive results for the intrinsic bend-sensitive optical fiber. This optical fiber has immediate applications in robotics (see Robot finger project).

Experimental setup used in this experiment

By Hang: A simple description of the experimental setup is given as follows: the light from supercontinuum (coming from the hole on the black box) goes through the beam splitter and is coupled to the Bragg fiber by a 20× objective. Then the light is reflected back by the silver mirror on the other end of the Bragg fiber, collimated by the same objective and projected to the beam splitter and detector. A nano-position stage is used to bend the silver-coating end of the Bragg fiber.  A black absorber is used to block the supercontinuum beam directly reflected by the input facet of the Bragg fiber. This reflection at the fiber input end could form a very bright, tiny spot due to the focusing by the objective and the reflection is insensitive to bending such that it will only constitute noise to the detector. With this setup, we are able to measure the intensity variations in response to the different bending of the Bragg fiber.







By Hang: The reflection of a 300-micron diameter 4-cm long Bragg fiber is measured in response to different bending radius. The bending of fiber is enabled by a nano-position stage which is used to bring the displacement to the fiber tip coated with a silver mirror [using Francois's technique for wet silver coating]. The reflection intensity is real time accompanied by the bending of the fiber. The displacement is noted in the figure below.


The input light is wight coherent light generated from a powerful fs laser, pumping a continuum generation crystal.



Results

By Hang: I found that with the 300 micron-diameter 4cm-long fiber, the minimal displacement that can be reliably detected is ~0.5mm


Further steps
We now need to find the wavelength at which this optical fiber is most sensitive, and filter it our of the input light, or before the detection. This will increase the sensitivity of the device.

Work must be done on signal conditioning.

Smaller fiber diameters will be tested next week, starting with 100 micron.

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