Eye and sensor laser protection

Large-aperture direct-view high-speed electro-optic shutter

Materials Electronics

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Positive and ground conducting buses are connected in parallel within the eyeglass frame, terminating in one of the earpieces of the frame. An insulated wire pair connects the frame to a compact circuit box.

Conventional optical switches can be classified as either a passive or active optical switch. A passive optical switch receives incoming light and changes state based upon the received light. In this regard, some passive optical switches are semiconductors that employ two-photon absorption to activate, while others employ all-optical components and organic dyes. In contrast, active optical switches receive incoming light and are activated or deactivated by a power signal.

Optical switches are deployed in telecommunications and fiber optic technologies and may employ semiconductors or organic polymers. Typically, active optical switches are not used to propagate images in a whole, un-encoded state, as this can easily be accomplished with a passive device. However, passive devices tend to suffer from several problems. Although they are inherently fast, their dynamic range is generally very limited, as there are only so many available molecules to respond. Thus, passive devices can saturate quickly. In addition, the fluence or irradiance threshold to turn a conventional passive device on may be intolerably high, effectively preventing the device from performing its intended function.

Electro-optic (EO) shutters have a quick response time and good attenuation, but conventional active and passive shutters are generally unable to extinguish light evenly over the extent of the EO element. Further, conventional devices are generally passive in nature, in that they use part of the incoming light to drive the device to a blocking state. This type of conventional construction has been found to be deficient in speed and effectiveness in blocking optical transients that would be harmful to a human eye or sensor.

In response to the above, scientists at the Army Research Laboratory have developed a Pockels cell-based electro-optic shutter device capable of blocking optical transients to such an extent that damage to eyes and sensors does not occur.

The Pockels effect is exhibited in chromophore-doped polymers where changes in birefringence in an optical medium are induced by an electric field. In the Pockels effect, also known as the linear electro-optic effect, the birefringence is proportional to the electric field.

The Pockels cell device operates with very fast electrical pulses (sub-nanosecond) and provides a significant advantage in speed over conventional mechanical shutters. Further, the device provides for a higher attenuation than conventional passive chemical dye-based shutters. The device may be incorporated in a thin, flexible electro-optic shutter device composed entirely of a solid-state polymer.

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