In the paper we present the results of investigating the effective birefringence of prototype photonic crystal fibre, partially infiltrated with "1550'' liquid crystal mixture. We use the modified Mueller matrix method with an additional depolarization matrix to calculate degree of polarization changes of the light propagating in the liquid-crystal infiltrated microstructured optical fibres. We conducted the research for red and infrared semiconductor laser diodes. The research may lead to construction of temperature controlled depolarizer.