Optical device and method for switching polarizations, comprises a polarizations transformer containing two liquid-crystal cells in series in path between two separators/combiners

摘要

The optical device comprises at least one, in particular two inputs (1,2), at least one, in particular two outputs (3,4), the polarization transformer (7) which can modify the polarizations of optical signals in a controlled manner, at least one, in particular two separators/combiners (5,6) of input and output signals, respectively, and control modules (10,11). The polarizations converter (7) contains at least two liquid-crystal cells (8,9) placed in series and made of materials which allow an independent control of the directions of neutral axes of one cell and the birefringence of the other cell. The materials constituting the liquid-crystal cells (8,9) are chosen from the smectic surface-stabilized C asterisk liquid crystals, that is the surface stabilized ferroelectric liquid crystal (SSFLC), and/or nematic liquid crystals. The device combines two liquid-crystal cells (8,9) so that the fast axis of the first cell (8) is aligned with the slow axis of the second cell (9), or with the fast axis of the second cell (9). One cell (9) is controlled so to modulate the directions of neutral axes, and it is of type smectic surface-stabilized C asterisk liquid crystal. The other cell (8) is controlled so to modulate the birefringence, and it is of type nematic liquid crystal. In a variant of the device, which is folded and forms an interferometer, the optical signals are reflected back to the polarizations transformer and passed through the same separator/combiner. The device comprises supplementary reflecting elements which direct the optical signals from one arm to the other arm, and are placed so that the inputs coincide with the outputs, or so that the inputs are shifted with respect to the outputs. The polarization transformer is placed in two arms of the device, or only in one arm. The method for switching optical beams is claimed and is implemented by the device. One cell (8) switches the beam from one output to the other output, and the other cell (9) continually modulates the polarization states of the beams and diffuses the input beams to the outputs. One of the cells (9) compensates the difference in delays between the cells (8,9) relative to a delay corresponding to a nominal value of the wavelength. One of the cells (9) is controlled so to induce a phase-shift equal to 2(pi)(1-=l0/=l), where lambda 0 is the nominal wavelength of the other cell, and lambda is the wavelength of the transmitted beam. A set for switching optical channels comprises a demultiplexer which can spatially separate the channels of an optical beam, and a network of optical devices for switching polarizations which control different channels from inputs to outputs.