Tellium, Inc.

Other

Jayantilal Patel

Janet L Jackel

W John Tomlinson

Jung-Chih Chiao

A liquid-crystal switching element relying upon a segmented liquid-crystal polarization modulator, at least one frequency-dispersive grating and one or more polarization-dispersive elements, such as Wollaston prisms, to switch separate wavelength-divided signals among four optical paths. The switching is done complementally between the fibers of each pair, and the same switching is done for the two pairs. According to the invention, all four beams can be processed by a single set of serial optics. The invention is particularly useful as an optical interconnect between two optical fiber communications rings in which each ring includes two counter-rotating fibers. The invention advantageously uses a dielectric thin-film beam splitter for one of the polarization-dispersive elements and a Wollaston prism for the other. The reflective embodiment in which a mirror replaces all the components on the output side can be improved by using two semitransparent electrode layers on the input side separated by a quarter-wavelength of dielectric.

Dual liquid-crystal wavelength-selective optical switch

A liquid crystal, cell having plates defining a gap between them which is filled with a liquid crystal, especially a twisted nematic. The plates are made non-parallel to a predetermined degree so that the liquid crystal assumes a wedge shape, producing different effective thicknesses of the liquid crystal depending on the lateral position within the cell. In use, a narrow beam irradiates a portion of the cell, and the cell is positioned along the wedge direction so as to optimize the cell performance. The invention is particularly useful with a liquid-crystal multi-wavelength switch, which requires extinction ratios between the two states of the cell.

Wedge-shaped liquid-crystal cell having nonlinear gap

A method and apparatus for compensating for temporally varying effects, such as temperature, in a liquid-crystal cell, particularly a wedge-shaped liquid-crystal cell. The temperature of the liquid crystal is measured, either directly with a thermocouple or the like, or by optical means which depend upon the temperature of the liquid crystal. For example, an intensity detector monitors the polarization rotation of a probe beam of light having a substantially different wavelength than that of the beam modulated by the liquid crystal, and a feedback circuit keeps the intensity at a predetermined value corresponding to the optimum path length in the liquid crystal of the modulated beam. The feedback signal from the temperature measurement is used to effectively change the gap filled with liquid crystal. For a wedge-shaped cell, the gap size is changed by moving the cell in the wedge direction. Other cell structures are available in which the gap size is physically changed by mechanical movement of the cell walls.

Temperature compensation of a wedge-shaped liquid-crystal cell

A liquid-crystal cell having plates defining a gap between them which is filled with a liquid crystal, especially a twisted nematic. The plates are made non-parallel to a predetermined degree so that the liquid crystal assumes a wedge shape, producing different effective thicknesses of the liquid crystal depending on the lateral position within the cell. In use, a narrow beam irradiates a portion of the cell, and the cell is positioned along the wedge direction so as to optimize the cell performance. The invention is particularly useful with a liquid-crystal multi-wavelength switch, which requires extinction ratios between the two states of the cell.

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State College, PA, United States of America

Jayantilal Patel