MMI structures covered by bromocresol purple for ammonia detection

In the paper examinations of a lightguide sensor on the base of gradient index multimode interference structures are presented. Investigated structures were fabricated in potassium-sodium ion exchange process. Multimode interference sensor was designed for ammonia detection. Bromocresol purple covering the multimode section was used as a sensing layer. Numerical calculations were performed with the use of modal analysis and beam propagation method to optimise sensor geometry and sensing layer thickness. Experimental results show the possibility of ammonia detection from the concentration of tens ppm.