3rd meeting of young researchers at UP 1 - IJUP - Universidade do ...

High-Birefringent Fibre Loop Mirror for Sensor Applications
R. M. André 1,2 , O. Frazão 1,2 , and M. B. Marques 1,2
1 Department of Physics, Faculty of Science, University of Porto, Portugal.
2 INESC Porto, Rua do Campo Alegre 687, Porto, Portugal.
The Fibre Loop Mirror (FLM) is a very attractive optical device for use in fibre
communications or fiber sensors [1]. The loop mirror is easily obtained by a splice between the
output ports of a directional optical coupler. In this case, the two waves travel with identical
optical paths in opposite directions and a constructive interference is assured when the waves
reenter the coupler. All the light is then reflected back into the input port, with the reflectivity
limited only by the losses of the splice, fibre and coupler, while no light is transmitted to the
output port. Another type of fibre loop mirror containing a section of highly birefringent (Hi-
Bi) fibre present several advantages compared with a more traditional interferometer. One of
them is the input polarization independence. Another one is the periodicity of the formed
spectral filter, which depends only on the length of the Hi-Bi fibre and not on the total length
of the fiber loop mirror [1]. In this work is presented a Hi-Bi fibre loop mirror sensor using a
section of Hi-Bi Photonic Crystal Fibre (PCF).
We have analyzed the sensitivity of a fiber loop mirror sensor with an 18.5 cm section of Hi-Bi
PCF to variations of temperature and applied
strain. The filter obtained has a mean
wavelength spacing of 6.5 nm which can be
easily controlled by varying solely the length of
the Hi-Bi fiber. See Figure 1. Investigating the
spectral response we obtained different
sensitivities for both physical parameters. Being
so, we have demonstrated its application as a
simple sensor for the simultaneous measurement
of temperature and strain.
References:
Fig. 3. Spectral response of the FLM sensors.
[1] O. Frazão, J.M. Baptista, J.L. Santos, (2007) Recent advances in high-birefringence fiber loop
mirror sensors, Sensors 7, 2970-2983
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