Abstract: A twisted nematic liquid crystal-based electro-optic modulator with a twist angle between 0° and 90°, and preferably between 50° and 80° is provided. The modulator provides a relatively rapid switching time such as less than about 50 milliseconds, and provides relatively large extinction ratios, such as greater than −25 dB. Preferably the liquid crystal entrance director differs from the polarization direction by a beta angle of about 15°.

Abstract: Switch arrays are provided with controllable polarization modifiers and polarization-dependent diverters, such as one or more polarization beam splitters, for configuring switch arrays which can reduce or eliminate the need for optical fibers in the switch arrays. In one embodiment, input positions configured in a first preferably planar (e.g., horizontal) configuration are routed to one or more of a corresponding plurality of output positions which are configured in a different arrangement such as in an orthogonal (e.g., vertical) planar arrangement. Preferably some or all of the polarization-related optical components, including components such as birefringent devices, liquid crystal polarization rotator arrays and/or polarization beam splitters are integrated so that one such device can be used in connection with a plurality of input and/or output beams.

Abstract: A method and apparatus for optical wavelength routing separates even and odd optical channels from an input WDM signal. The input beam is first converted to at least one pair of orthogonally-polarized beams. A split-mirror resonator has a front mirror with two regions having different reflectivities, and a reflective back mirror spaced a predetermined distance behind the front mirror. Each of the orthogonally-polarized beams is incident on a corresponding region of the front mirror of the split-mirror resonator. A portion of each beam is reflected by the front mirror, while the remainder of each beam enters the resonator cavity where it is reflected by the back mirror back through the front mirror. The group delay of each reflected beam is strongly dependent on wavelength. The two reflected beams from the resonator are combined and interfere in a birefringent element (e.g., a beam displacer or waveplates) to produce a beam having mixed polarization as a function of wavelength.

Abstract: An optical wavelength division multiplex (WDM) demultiplexer can be provided in substantially passive form. In one embodiment a wavelength filter separates alternate channels to provide a first output containing even-numbered channels and a second output containing odd-numbered channels, each output having channels separated by a bandwidth twice the channel separation bandwidth of the original WDM signal.

Abstract: A wavelength division demultiplexing device is presented utilizing a polarization-based filter or a multi-cavity etalon (e.g., a multi-cavity Fabry-Perot etalon) to obtain a flat-top filter response which can be utilized to create a flat-top slicer which separates out odd and even wavelengths, or upper and lower channels of an input WDM signal. The flat-top slicer can be used as the first stage of a cascaded network of wavelength demultiplexers in which following stages can be based on polarization-based filters, multi-cavity etalons, or other interferometric WDM devices, which are adequate due to the increased channel spacing obtained in the first stage of the network.

Abstract: A twisted nematic liquid crystal-based electro-optic modulator with a twist angle between 0° and 90°, and preferably between 50° and 80° is provided. The modulator provides a relatively rapid switching time such as less than about 50 milliseconds, and provides relatively large extinction ratios, such as greater than −25 dB. Preferably the liquid crystal entrance director differs from the polarization direction by a beta angle of about 15°.

Abstract: An optical cross-connect network provides wavelength routing of optical channels between two arrays of optical fibers carrying WDM signals using interconnected arrays of optical wavelength switches based on combinations of a 1×2 wavelength switch architecture. For example, a cross-connect network can be made by interconnecting two arrays of 1×4 wavelength switches, each of which is made by combining three 1×2 wavelength switches. Each 1×2 optical wavelength switch has polarization separation element (e.g., a first birefringent element) that decomposes and spatially separates the input WDM signal into two orthogonally-polarized beams. A first polarization rotator selectably rotates the polarization of one of the beams to match the polarization of other beam, based on an external control signal. A wavelength filter (e.g.

Abstract: An optical add/drop wavelength switch is controllably changed from a bridge state, in which output is identical to input, e.g. a Wavelength Division Multiplexed (WDM) input, and an add/drop state, In which a signal input to an add port is substituted for a particular wavelength subrange of the WDM input, other wavelengths of the WDM input being unchanged. In one embodiment, the wavelength subrange of the WDM signal is given a polarization different from other wavelengths of the WDM, such as by using a stacked waveplate or other optical filter or polarization discriminator. The differently-polarized wavelengths can the be spatially separated, e.g. by a birefringent element or a polarization beam splitter, preferably In a bit-controlled fashion, such as by using a liquid crystal or other polarization controller. Polarization controllers and discriminators can be used similarly to selectably align or combine the add signal with the portion of the WDM signal outside the subrange.

Abstract: A wavelength division multiplexing/demultiplexing device is presented utilizing a polarization-based filter to obtain a flat-top filter response which can be utilized to create a flat-top slicer which separates out odd and even wavelengths, or upper and lower channels of an input signal. The polarization-based filter provides superior peak flatness and isolation for narrow channel spacings over what can be obtained in traditional interferometric devices. The flat-top slicer can be used as the first stage of a cascade of WDM devices in which following stages can be based on polarization-based filters or traditional interferometric WDM devices, which are adequate due to the increased channel spacing obtained in the first stage of the cascade.

Abstract: A system, method and apparatus for performing optical beamsplitting are disclosed. In a preferred embodiment, a high extinction ratio polarization beamsplitter comprises at least two polarized beamsplitting surfaces that are aligned parallel to each other. The beamsplitter receives a first input light beam that is incident on a first polarized beamsplitting surface. The beamsplitter receives a second input light beam that is also incident on the first polarized beamsplitting surface. In a preferred embodiment, the first and second input light beams have a cross point that is not incident on such first polarized beamsplitting surface. Further, in a preferred embodiment, each of the first and second input light beams are incident on such first polarized beamsplitting surface at a point that is not its center point. Cross talk noise is reduced in a preferred embodiment by directing resulting noise to a point that is not co-linear with an output signal.

Abstract: A hybrid analog/binary electro-optic modulator using a twisted ferroelectric liquid crystal structure is provided. Ferroelectric liquid crystals with a tilt angle of between about 20.degree. and about 25.degree., preferably about 22.5.degree. are used. Rubbing directions for the two cell walls (relative to one another) can be varied from about 45.degree. to about 90.degree.. In one embodiment, a weak buffing force is used resulting in a relatively weak anchoring energy at the surface, aligning the liquid crystal molecules without locking the molecules into the buffing directions and a high pre-tilt structure for the molecules close to the surface boundaries. In one embodiment, strong buffing is used with buffing directions offset about 45.degree.. Use of this invention provides relatively fast response time, low required driving voltage, high contrast, and/or the ability to achieve both analog and binary operations.

Abstract: A programmable wavelength router having a plurality of cascaded stages where each stage receives one or more optical signals comprising a plurality of wavelength division multiplexed (WDM) channels. Each stage divides the received optical signals into divided optical signals comprising a subset of the channels and spatially positions the divided optical signals in response to a control signal applied to each stage. Preferably each stage divides a received WDM signal into two subsets that are either single channel or WDM signals. A final stage outputs optical signals at desired locations. In this manner, 2.sup.N optical signals in a WDM signal can be spatially separated and permuted using N control signals.

Abstract: Switch arrays are provided with controllable polarization modifiers and polarization-dependent diverters, such as one or more polarization beam splitters, for configuring switch arrays which can reduce or eliminate the need for optical fibers in the switch arrays. In one embodiment, input positions configured in a first preferably planar (e.g., horizontal) configuration are routed to one or more of a corresponding plurality of output positions which are configured in a different arrangement such as in an orthogonal (e.g., vertical) planar arrangement. Preferably some or all of the polarization-related optical components, including components such as birefringent devices, liquid crystal polarization rotator arrays and/or polarization beam splitters are integrated so that one such device can be used in connection with a plurality of input and/or output beams.

Abstract: An apparatus for holding and tuning a thin film optical assembly is presented in which a housing receives a cylindrical thin film optical assembly which can be rotated to adjust the wavelength at which it passes or reflects an optical signal. The thin film optical assembly is composed of a thin film optical filter mounted on a cylindrical unit having a flat mounting face and an aperture for the transmission of light. The housing has a light path machined through it which permits light to pass to each thin film optical assembly, where one wavelength is separated by transmission and the remaining wavelengths are reflected to a subsequent filter. Each thin film optical assembly can be rotated within the housing to permit wavelength tuning. Once the thin film optical assembly is tuned it can be held in place using solder applied between the thin film optical assembly and the housing. Optical fibers are coupled to the housing using ferrules and graded rod index lenses.

Abstract: A system for dealing with faults in wavelength division multiplexed (WDM) optical communications between two terminals connected by at least two optical fibers monitors the status of communications over both optical fibers. If both optical fibers are operating normally, a first set of channels is routed over the first optical fiber and a second set of channels (which is mutually exclusive of the first set of channels) is routed over the second optical fiber. However, if a fault is detected in either optical fiber, the first terminal combines the first and second sets of channels and routes the combined channels over the remaining optical fiber to the second terminal. The second terminal separates the combined channels to recreate the first and second sets of channels. Wavelength slicers can be used to multiplex and demultiplex the channels at both terminals. This architecture allows the first and second sets of channels to be interdigitally spaced.

Abstract: A switchable wavelength router switches wavelength division multiplexed (WDM) optical signals between N input ports and M output ports. Each WDM signal is spatially decomposed into N pairs of orthogonally polarized beams by a polarization-dependent routing element, such as a birefringent element. A polarization rotator array rotates the polarization of each beam pair so that both beams in each pair have the same polarization. A wavelength filter then demultiplexes each beam pair to create N sets of four beams, such that the first beam in each pair decomposes into third and fourth orthogonally-polarized beams, and the second beam in each pair decomposes into fifth and sixth orthogonally-polarized beams. The third and fifth beams carry a first spectral band at a first polarization, and the fourth and sixth beams carry a second complementary spectral band at an orthogonal polarization.

Abstract: A programmable wavelength router having a plurality of cascaded stages where each stage receives one or more optical signals comprising a plurality of wavelength division multiplexed (WDM) channels. Each stage divides the received optical signals into divided optical signals comprising a subset of the channels and spatially positions the divided optical signals in response to a control signal applied to each stage. Preferably each stage divides a received WDM signal into two subsets that are either single channel or WDM signals. A final stage outputs optical signals at desired locations. In this manner, 2.sup.N optical signals in a WDM signal can be spatially separated and permuted using N control signals.

Abstract: An optical power regulator employs a variable optical attenuator having a first birefringent element that spatially separates the input optical beam into two orthogonally-polarized beams. Both beams pass through a polarization modulator (e.g., a liquid crystal material) that rotates their polarizations to an extent determined by the control voltage applied across the polarization modulator. A final birefringent element spatially separates both beams exiting the polarization modulator into two pairs of orthogonally-polarized beams (i.e., two horizontally-polarized and two vertically-polarized components). The thicknesses and optical properties of the birefringent elements are selected so that two of the four beams are combined by the final birefringent element to exit at the output port of the regulator, while the remaining two beams are blocked.

Abstract: A switchable wavelength router has a first polarization-dependent routing element (e.g., a birefringent element, polarized beamsplitter, or angled polarization separator) that decomposes and spatially separates an incoming WDM optical signal into two orthogonally-polarized beams. A first polarization rotator selectably rotates the polarization of one of the beams to match the polarization of other beam, based on an external control signal. A wavelength filter (e.g., stacked waveplates) provides a polarization-dependent optical transmission function such that the first beam decomposes into third and fourth orthogonal beams, and the second beam decomposes into fifth and sixth orthogonal beams. The third and fifth beams carry a first spectral band at a first polarization and the fourth and sixth beams carry a second spectral band at an orthogonal polarization. A second polarization-dependent routing element spatially separates these four beams into four horizontally polarized and vertically polarized components.

Abstract: In all-optical networks, optical switching and routing become the most important issues for interconnecting the transport network layers. This invention describes a novel tunable optical add/drop filter for the all-optical wavelength-division-multiplexing (WDM) network applications. This filter can add or drop part of the high transmission capacity signals of a WDM link. It can be used to decentralized access point in the access network or as small core network node to realizing branching points in the network topology. It works in both wavelength and space domains. It has the advantages of: 1) High throughput and low voltage operation; 2) Wide tuning range and therefore, high channel capacity; 3) High isolation and high directivity between input and output ports; 4) Compact device packaging is possible as compares to the conventional grating and mechanical switching type of add/drop filter; 5) Multiple ports add/drop tunable filters can be realized with this invention to interconnect multiple WDM networks.