Optical fiber sensors have reached a high state of maturity. Besides the high number of sensor groups, multi-mode fiber evanescent field sensors can be found in a lot of applications. Here, the signal source commonly excites many optical modes under steady-state conditions. Perturbations of the fiber then produce leaky modes. Thus, a simple intensity detector measures the degree of perturbation. In some cases also restricted mode launching conditions have been applied. They resulted in higher sensitivity but showed a narrower measurement range. Considering the individual modes as carriers of information we adapted multiple-input multiple-output (MIMO) signal processing which is well studied in the telecommunications community, for improvements on both the sensor sensitivity and its measurement range. In this paper MIMO signal processing is investigated for fiber optic sensor applications. A (2x2) MIMO implementation is realized by using lower-order and higher-order mode groups of a gradient-index multi-mode fiber as separate transmission channels. A micro-bending pressure sensor changes these separate transmission characteristics and introduces additional crosstalk. By observing the layer specific weight-factors of the MIMO system the amount of load applied was determined. Experiments verified a good correlation between the change of the MIMO weight coefficients and the load applied to the sensor and thus verified that MIMO signal processing can beneficially be used for fiber optic sensor applications. The experimental results also verified the superior sensitivity and measurement range when MIMO signal processing is utilized.


MIMO; optical fiber sensors

Arik S., Kahn J.M., Ho K.P.: MIMO Signal Processing for Mode-Division Multiplexing. IEEE Signal Processing Magazine 25(2014).

Donlagic D.: Microbend sensor structure for use in distributed and quasidistributed Sensor Systems based on selective launching and filtering of the Modes in Graded Index Multimode Fiber. Journal of Lightwave Technology 17(10)/1999, 1856–1868.

Leung A., Shankar P., Mutharasan R.: A review of fiber-optic biosensors. Sensors and Actuators B 125/2007, 688–703.

Leung C.K.Y.: Optical Fiber Sensors for Civil Engineering Applications. Materials and Structures 48(4)/2015, 871–906.

Pankow J., Aust S., Lochmann S., Ahrens A.: Modulation-Mode Assignment in SVD-assisted Optical S. MIMO Multimode Fiber Links. 15th International Conference on Optical Network Design and Modeling (ONDM), Bologna 8–10 February 2011.

Richardson D.J., Fini J.M., Nelson L.E.: Space Division Multiplexing in Optical Fibres. Nature Photonics 7/2013, 354–362.

Sandmann A., Ahrens A., Lochmann S.: Experimental Description of Multimode MIMO Channels utilizing Optical Couplers. ITG- Fachbericht 248: Photonische Netze. Leipzig, VDE VERLAG GMBH, 05–06 May 2014, 125–130.

Su L., Chiang K.S., Lu C.: Microbend-induced mode coupling in a graded-index multimode fiber. Applied Optics 44(34)/2005, 7394–7402.

Zamarreno C.R., Hernaez M., Matias I., Arregui F.: Optical fiber sensors based on indium tin oxide surface plasmon resonance supporting coatings. Proc. OFS-20. Edinburgh, SPIE 75503, 2009.

Zhuang X., Li P., Yao J.: A Novel Approach to Evaluate the Sensitivities of the Optical Evanescent Field Sensors. Fiber Optic Sensors, Dr Moh. Yasin (Ed.) InTech, 2012.


Published : 2016-08-08

Ahrens, A., Sandmann, A., Bremer, K., Roth, B., & Lochmann, S. (2016). IMPROVING OPTICAL FIBER SENSING BY MIMO SIGNAL PROCESSING. Informatyka, Automatyka, Pomiary W Gospodarce I Ochronie Środowiska, 6(3), 51-55.

Andreas Ahrens
Hochschule Wismar, Philipp-Müller Straße 14, 23966 Wismar, Germany  Germany
André Sandmann 
Hochschule Wismar, Philipp-Müller Straße 14, 23966 Wismar, Germany  Germany
Kort Bremer 
Leibniz University Hannover, Nienburger Strasse 17, 30167 Hannover, Germany  Germany
Bernhard Roth 
Leibniz University Hannover, Nienburger Strasse 17, 30167 Hannover, Germany  Germany
Steffen Lochmann 
Hochschule Wismar, Philipp-Müller Straße 14, 23966 Wismar, Germany  Germany