Electrically controlled optical switch for multimode fiber applications

Integration of liquid crystal elements for creating an infrared Lyot filter

An infrared Lyot filter was fabricated by integrating a polarization beam splitter and two retarders into a single device. A liquid crystal layer was constructed between two silicon pentaprisms that were designed suitably so that light was incident on this layer at 28°. At this angle, the liquid crystal transmitted p-polarized light (Brewster's angle) and reflected s-polarized light (total internal reflection). The p- or s-polarized light was directed to another liquid crystal layer (retarder) between the prism and a mirror, which induced a wavelength-dependent retardation in the reflection process. Consequently, the light that returned to the beam splitter was transmitted or reflected depending on wavelength.

All-optical stage of an omega network

All-optical multistage interconnection networks are desirable for overcoming the limitations of optical signal regeneration in switching systems. We present a new implementation of the perfect-shuffle interconnection pattern that is coupled with an all-optical switching element, forming a complete stage of a multistage network. Switching is performed with birefringent calcite crystals and a ferroelectric liquid-crystal device, while interconnection is achieved with a space-semivariant imaging configuration. Cascading the layout allows this system to be used to construct an all-optical multistage interconnection network. An experimental demonstration of the stage is presented.

High-optical-isolation low-loss moderate-switching-speed nematic liquid-crystal optical switch

A bulk polarization-rotation-based 1 x 2 optical switch is demonstrated by use of a birefringent-mode parallel-rub nematic liquid-crystal cell and a calcite Thompson-prism polarizing beam splitter. With 633-nm linearly polarized light the switch output ports exhibit a >36-dB optical isolation with less than -0.75 dB of optical insertion loss. A >1.5-ms switching speed is demonstrated for a cascade cell optical arrangement by means of the transient nematic effect with >30 dB of optical isolation and -1.45 dB of optical loss.

TE and TM modes in a cylindrical liquid-crystal waveguide

We consider a cylindrical waveguide consisting of an inhomogeneous anisotropic liquid-crystal core embedded in an infinite homogeneous isotropic cladding. The wave equations for the pure modes are uncoupled but may have complex coefficients owing to the inhomogeneity and anisotropy of the liquid crystal. A simple numerical method is proposed for solving these equations. For the configuration considered, numerical results for the TE modes agree exactly with the analytical solution. For the TM modes, no analytical solution is available, and the unusual result obtained is that the phase of the fields inside the core depends on the distance from the cylinder axis.

Liquid crystal optical routing switch

The design and experimental results of a new 2 x 2 optical routing switch based on liquid crystal is reported. The switch uses nematic liquid crystal for polarization beamsplitting and ferroelectric liquid crystal for polarization rotation. The polarization insensitive, broadcast capable, full duplex switch has a signal-to crosstalk ratio of ~20 dB, a switching speed below 250 micros and a measured insertion loss of 1.4 dB. We show that the basic 2 x 2 switch can be extended to form a N x N rearrangeable permutation network.

Optical interconnection network using polarization-based ferroelectric liquid crystal gates

A polarization-based 4 x 4 optical interconnection network using surface stabilized ferroelectric liquid crystal (SSFLC) gates is demonstrated. The SSFLC gates are comprised of an SSFLC device sandwiched between two polarizing beam splitters. Optical crosstalk using these fast switching programmable devices can be limited to ~-20 dB/gate, which would allow 2-D interconnection networks to be fabricated with thirty-one input channels and 3-D interconnection networks with approximately 225 input channels.

Thermooptic coupler for multimode optical fibers

The detailed theory is presented together with design considerations and recent experimental results for an electronically controllable directional coupler for multimode optical fibers. The device, based on plastic-clad silica fiber, is of exceptionally simple construction and compact size and is highly reliable. A theoretical model of the coupler is described and compared with actual device performance. The coupling can be varied from -4 to -28 dB with an excess loss of <0.2 dB over the entire coupling range, in agreement with theory. Improvements in the present device design are also discussed.

Nonmechanical optical switch for single-mode fibers

This paper introduces a bistable nonmechanical optical switch for single-mode optical fibers. A l-input/2-output device for the l-microm wavelength range, the optical losses of the switch are independent of the polarization state in the input fiber. The insertion losses for the optical signal from the input fiber to the output fiber are 1.4 dB and the crosstalks are -28 dB at 1.3-microm wavelength. Switching is performed by a 20-microsec one-shot pulse with a maximum current of 500 mA. The voltage to switch the optical path is 5 V.

Bistable magnetooptic switch for multimode optical fiber

A bistable nonmechanical optical switch for multimode optical fiber is presented. It is a 2-input/2-output device for the 1-microm wavelength range. The optical characteristics are independent of the polarization state of incident light. The switch consists of Faraday rotators of thin plates of yttrium-iron-garnet single crystal, electromagnets whose cores are made of semihard magnetic material, halfwave plates of crystal quartz, polarizing prisms of rutile, and lenses. Switching is performed by one-shot 3-V 20-microsec pulses with a maximum current of 500 mA. The 1.5-dB insertion losses and -32-dB cross talk were obtained at a wavelength of 1.3 microm.

Electrooptic 4x4 matrix switch for multimode fiber-optic systems

A new fiber-optic switch for multimode fiber networks has been developed. This voltage-controlled device can switch light from any of four input fibers to any of four output fibers. Four input/output connections are made simultaneously, and the matrix has twenty-four such states. No moving parts are needed because the switching is accomplished with an electrooptic effect in nematic liquid crystals. Low levels of optical crosstalk, ~40 dB below the output signal level, are obtained with a unique two-stage architecture. The design, construction, and observed performance of this optical switch are described.

Calcite 2 x 2 optical bypass switch controlled by liquid-crystal cells

Three blocks of birefringent calcite and two 6-V twisted nematic liquid-crystal cells have been used to make a 2 x 2 optical bypass switch for series-type fiber-optic networks. Optical cross-talk levels of -32 dB have been obtained in both states. The insertion loss was 3 dB in a nonoptimized switch.

Polarization-independent liquid-crystal optical attenuator for fiber-optics applications

A compact low-power low-voltage polarization-independent electrooptic attenuator has been developed using planar calcite elements and a standard twisted nematic liquid-crystal cell. A dynamic range of 31.5 dB and an insertion loss of 0.87 dB have been demonstrated with the attenuator interposed between a GaAlAs laser and a 0.20-N.A. multimode optical fiber.

Alterable grating fiber-optic switch

This paper describes a solid state high speed fiber-optic switch based on dynamically alterable magnetic stripe domains that occur naturally in epitaxial films of rare-earth iron garnet. The array of stripe domains acts collectively as a Faraday effect phase diffraction grating that deflects visible and infrared radiation. Electrically derived magnetic fields in the plane of the film steer incident light from an input fiber to one of several output fibers. Reciprocity and wavelength sensitivity can be exploited for systems applications. Both theoretical and experimental results are presented.

Low-cross-talk 2 x 2 optical switch

An electro-optical 2 x 2 switch for fiber-optic applications has been developed. Optical cross talk is reduced significantly by inserting two 2 x 1 switches in each optical path. A compact structure is used to contain the four 2 x 1's that are required. We observed -27-dB cross talk and 2.5-dB insertion loss in both switching states. The device is controlled by a 5-V twisted-nematic liquid-crystal cell. Multimode, unpolarized light is switched.