Realisation and characterisation of a ferroelectric liquid crystal bistable optical switch

A bistable optical switch using a ferroelectric liquid crystal (FLC) layer sandwiched between two glass optical waveguides is reported. Input light can be switched from one waveguide to another one by changing electro-optically the FLC refractive index. Optical waveguides were made by ion-exchange in BK7 glass. On top of them indium tin oxide was deposited and lithographically patterned. Mixture FELIX-M4851-025 fills a 1.8 mum gap between the two optical waveguides. Such a thin cell gap and teflon film as alignment layer provides the switch with optical bistability which is its unique feature among waveguided FLC optical switches. The prototype can be driven by square morlopolar pulses of 200 mus width and 20 V amplitude. It shows a maximum extinction ratio of 15 dB and becomes about 9 dB because of relaxation of FLC molecules after removing driving voltage. Switching time of the device is about 300 mus.