Electro-optical birefringence device employing edge effect

• US 3,945,715 A
• Filed: 04/15/1974
• Issued: 03/23/1976
• Est. Priority Date: 04/15/1974
• Status: Expired due to Term

• Current Assignee: Harris-Intertype Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris-Intertype Corporation (L3Harris Technologies, Inc.)
• Inventors: Drake, Marvin D.
• Primary Examiner(s): Corbin, John K.
• Application Number:
  US05/460,741
• Time in Patent Office: 708 Days
• Field of Search: 350/150
• US Class Current: 365/121
• CPC Class Codes: G02F 1/055 the active material being a ceramic G02F1/035 takes precedence
• CPC Class Codes: G11C 13/047 using electro-optical elements G11C13/042 takes precedence

Abstract

An electro-optical transducer and data storage device is operated by electrically establishing different electric field levels in a retentive ferroelectric PLZT crystal. The crystal may have a plurality of areas that serve as data storage elements, each of which is defined by crossover areas of rows and columns of transparent electrodes that are on opposite sides of the crystal, each storage element being spaced away from other storage elements of the crystal by surrounding edge regions. When a data storage element is retentively polarized by the application and removal of a voltage pulse to opposite electrodes, the portion of the crystal between the electrodes contracts transversely, establishing a strain gradient in the edge regions surrounding the data storage element. This localized strain gradient, together with a fringing electric field in the edge regions, causes a high level of birefringence there, and permits the edge regions to serve as amplitude modulators of polarized light. When light is applied on a path through a polarizer, through the crystal, and through a cross-polarized analyzer, the output of the analyzer has light from edge regions of elements which have not been polarized. The apparatus can serve as an electro-optical transducer and memory for large blocks of data, for example.

Claims

1. An electro-optical system for storing and reading data comprising an electro-optical birefringence device for use on a light path including a crystal having two major surfaces adapted to be disposed transversely to the light path, first and second conductive electrodes configured on portions of the first and second major surfaces respectively, a first volumetric portion of said crystal defined by the configurations of said electrodes and having electrodes on both of said surfaces, a second volumetric portion of said crystal having electrodes on fewer than both of said surfaces and forming a boundary with said first portion, and edge region of said crystal at and near said boundary, electrical energizing means connected with said electrodes for momentarilly and selectively producing a relatively high and a relatively low electric field transverse to said surfaces and principally in said first portion such that said high field causes a strain at said edge region that cooperates with said electric field to render said edge region birefringent, said crystal comprises a type of material exhibiting ferro-electric remanence, and wherein said relatively high electric field is a remanent ferro-electric field remaining in said crystal after said electrical energizing means has ceased to energize said first portion, optical means for passing light along said path and sensitive to the level of birefringence of said edge region, said optical means including light source means for directing linearly polarized light to said crystal from the same side as said first surface while said crystal is strained only at said edge region by said remanent ferro-electric field, and light analyzer means on said light path for receiving output light that has passed through said crystal, the polarization vector of said analyzer being oriented to transmit an elliptical component of polarization of said output light from said edge regions, which is produced only when said electric field is high.

2. An electro-optical system as defined in claim 1 and further comprising focusing means on said light path for focusing an image of said crystal at an image plane, and light detector means at a plane displaced along the path from said image plane for detecting a defocused image.

3. A method for storing and reading data including producing birefringence in a crystal to convert electrical signals to optical signals employing a crystal of a ferroelectric remanent type having two major surfaces disposed transversely to a light path and having first and second conductive electrodes on portions of the first and second major surfaces respectively and comprising the steps of

configuring the electrodes to define a first volumetric portion of the crystal having electrodes on both of the surfaces and a second volumetric portion of the crystal having electrodes on fewer than both of the surfaces and thereby establishing a boundary between said first and second portions,

temporarily electrically energizing said electrodes with signals to selectively produce one of a relatively high and a relatively low electric field transverse to said surfaces and principally in said first portion so that said high field induces in an edge region at and near said boundary a transverse strain that cooperates with said electric field to render said edge region birefringent,

removing the energizing signal so that the high electric field changes to a remanence level upon said removing of said energizing signal,

passing light having a polarization characteristic along the light path while said crystal is strained only at said edge region by virtue of the remanent field, the polarization characteristic of said light after emergence from said crystal being responsive to the level of birefringence of said edge region and thereby differently responsive to a said strained edge region than to a non-strained region.

4. A method as set forth in claim 3 including the further step of focusing light passed through said crystal for focusing an image thereof at an image plane, and detecting said passed light at a plane displaced from said image plane so as to detect a defocused image.