Experiments on a multichannel holographic optical switch with the use of a liquid-crystal display

Switch multiplexer of fiber-optic channels Based on multibeam acousto-optic diffraction

The peculiarities of the multibeam acousto-optic Bragg diffraction of light by a multifrequency acoustic signal are investigated. The investigation is related to design of fiber-optic space division switch multiplexer 1xN. It is proved that a specialized two-dimensional acousto-optic deflector can perform high efficiency multifunctional light switching of fiber-optic channels. The device has advanced characteristics--the number of channels is up to a few hundred, the switching time is about a few microseconds, and the cross talk is limited to -45 dB.

Adaptive correction to the speckle correlation fringes by using a twisted-nematic liquid-crystal display

An innovative technique for reducing speckle noise and improving the intensity profile of the speckle correlation fringes is presented. The method is based on reducing the range of the modulation intensity values of the speckle interference pattern. After the fringe pattern is corrected adaptively at each pixel, a simple morphological filtering of the fringes is sufficient to obtain smoothed fringes. The concept is presented both analytically and by simulation by using computer-generated speckle patterns. The experimental verification is performed by using an amplitude-only spatial light modulator (SLM) in a conventional electronic speckle pattern interferometry setup. The optical arrangement for tuning a commercially available LCD array for amplitude-only behavior is described. The method of feedback to the LCD SLM to modulate the intensity of the reference beam in order to reduce the modulation intensity values is explained, and the resulting fringe pattern and increase in the signal-to-noise ratio are discussed.

Estimation of insertion loss of a holographic switch with an optically addressed spatial light modulator

We investigate the cause of the insertion loss of our holographic switch by determining the relation between the diffraction efficiency and the hologram patterns generated by the control beams. According to the calculation the theoretical insertion loss is 7.4 dB with loss distribution of 0.03 dB under the conditions of a previous experiment. We find that incomplete storage of the interference pattern on the optically addressed spatial light modulator is the strongest factor determining the insertion loss.

Beam steering with two ferroelectric liquid-crystal spatial light modulators

Ferroelectric liquid-crystal spatial light modulators (FLC SLM's) are binary modulating devices that can be used for flexible beam steering in the microsecond range. Because they are binary, at least 60% of the light power is lost to unwanted diffraction orders, however. We suggest the use of a second FLC SLM, synchronously operating in amplitude-modulating mode, to block the unwanted orders. The proposed beam-steering method is demonstrated in a simple scanner experiment. The efficiency of the suggested beam steerer is independent of the number of steering directions.

Reconfigurable time-steered array-antenna beam former

We present and analyze a hardware-optimized technique that provides true-time-delay steering for broadband two-dimensional array-antenna applications. The technique improves on previous approaches by the reduction of the two-dimensional beam-former architecture complexity, by the provision of flexibility in time-delay unit selection, and by the potential reduction of optical loss. The technique relies on a one-dimensional bank of time-delay units to form the required time-delay gradient for proper off-broadside angle steering. A reconfigurable optical interconnection fabric is used to reassign dynamically the connections between the time-delay units and individual array elements of a two-dimensional array to effect the proper steering angle along the off-broadside cone.

4 x 1204 holographic switching with an optically addressed spatial light modulator

We extended the scale of a previously reported holographic switch [Appl. Opt. 34, 8137 (1995)] in which each input is assigned to one of the control light sources to control a large-scale switch with low power. The average losses of the four inputs were 28, 33, 35, and 36 dB. The average cross-talk-to-signal ratio of one of the inputs was -16 dB.

Holographic switch with a ferroelectric liquid-crystal spatial light modulator for a large-scale switch

A holographic switch with a ferroelectric liquid-crystal spatial light modulator is proposed for large switching systems such as those used in subscriber networks. Preliminary experiments have achieved a one-input, 48-output switch. The relationship between the power of the control-light source and the number of outputs is calculated; the results agree well with the experiment. The calculation suggests that 10384-output switching can be obtained with a 25-mW control-light source. It should therefore be possible to control a large-scale switch with low-power control-light sources.

1 x 1104 holographic switching with a ferroelectric liquid-crystal spatial light modulator

We demonstrate 1 x 1104 holographic switching with a ferroelectric liquid-crystal spatial light modulator to test the feasible output size of a holographic switch. The demonstration proves that switching was achieved when the power of a laser diode used as the control light source was 6.3 mW. The average of the insertion loss was 31.6 dB.

Programmable optical logic systems using free-space optical interconnections

A free-space optical logic technique is presented that utilizes a two-dimensional array of diffractive optical elements. Each optical element focuses light to multiple, separate positions in the output focal plane. The focal spots from different optical elements are allowed to overlap spatially, resulting in interference. By changing the phase shift between the optical elements, one can create different optical logic operations in the focal plane. The technique is demonstrated by the use of two input beams incident onto a multiplexed optical element written onto a programmable spatial light modulator. The optical element simultaneously creates both AND and XOR logic functions in the output plane.

Estimation of the possible scale for holographic switches with liquid-crystal displays

Simulating the positions of output beams under the assumption that a liquid-crystal display acts as a binary phase modulator reveals that the number of the outputs increases almost linearly with the square root of the number of pixels assigned to an input. This result is confirmed by experiments, and it is estimated that 1016 outputs can be obtained when the number of pixels is 700 × 700. Holographic switches with liquid-crystal displays are therefore suitable for large-scale switches.