US4055838A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ferroelectric information optical storage device with self biasing
Assignee: Thales SA
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Filing: 1976-05-07
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Granted: 1977-10-25
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Expires: 1996-05-07
Abstract
Abstract For amplifying the photosensitivity of a ferroelectric crystal in which information is to be stored, an external field applied to the crystal is created by means of a heavily doped, reduced photocell crystal illuminated uniformly by radiation within the absorption band of the crystal. The photocell crystal connected to the terminals of the lightly doped, non-reduced ferroelectric crystal, of which the resistivity is very much higher than that of the photocell crystal, develops a very high voltage which relaxes with a high time constant. Such a voltage increases the variations in the birefraction of the ferroelectric crystal.
Inventors
- 👤 Jean Pierre Huignard
- 👤 Francois Micheron
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 16:32
CPC Classifications
G; G11; G11C; G11C13/00; G11C13/04; G11C13/042; G11C13/044; G02; G02F; G02F1/00; G02F1/01; G02F1/03; G02F1/05; G02F1/0541; G11C13/047
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
105 words
An information optical storage device comprising a lightly doped non-reduced ferroelectric cyrstal for holographic storage of information, a heavily doped reduced photocell crystal, having an absorption frequency band, adapted for being photoexcited by means of a uniform luminuous radiation having a frequency band within said absorption band, said photocell crystal thus producing an electrical field, and direct connecting means for applying said electrical field to said ferroelectric crystal, being formed by the common edge between the two crystals and by a conductor wire connecting the two faces opposite the said common edge, said ferroelectric crystal having a very much higher resistivity than said photocell crystal.
Claim 2
Dependent Claim
105 words
An information optical storage device comprising a lightly doped non-reduced ferroelectric cyrstal for holographic storage of information, a heavily doped reduced photocell crystal, having an absorption frequency band, adapted for being photoexcited by means of a uniform luminuous radiation having a frequency band within said absorption band, said photocell crystal thus producing an electrical field, and direct connecting means for applying said electrical field to said ferroelectric crystal, being formed by the common edge between the two crystals and by a conductor wire connecting the two faces opposite the said common edge, said ferroelectric crystal having a very much higher resistivity than said photocell crystal.
Claim 3
Dependent Claim
33 words
An information optical storage device as claimed in claim 1, wherein, said ferroelectric crystal having a crystallographic axis, said electrical field is applied parallel to said crystallographic axis, maximum photosensitivity thus being obtained.
Claim 4
Dependent Claim
28 words
An information optical storage device as claimed in claim 2, wherein said connecting means are formed by two direct connections between the photocell crystal and said ferroelectric crystal.
Claim 5
Dependent Claim
34 words
An information optical storage device as claimed in claim 2, wherein said electrical field created by photoexcitation of the photocell crystal relaxes with a high time constant after the radiation has been switched off.
Claim 6
Dependent Claim
81 words
An information optical storage device as claimed in claim 4, wherein said ferroelectric crystal and said photocell crystal are two joined coplanar parts of one and the same rectangular plate of photosensitive ferroelectric material, said parts being limited by a common edge orthogonal to said crystallographic axis, one of said parts being lightly doped and non-reduced and the other of said parts being heavily doped and reduced, the lateral edges of said rectangular plate which are perpendicular to said crystallographic axis.
Claim 7
Dependent Claim
62 words
An information optical storage device as claimed in claim 5, wherein said ferroelectric crystal is lithium niobate lightly doped with iron and having a remanent polarisation at ambient temperature, inducing an internal field, the photosensitivity of said ferroelectric crystal being maximal when the sum of said internal field and of said electrical field applied by means of said photocell crystal is maximal.
References Cited (Backward Citations)
US3932025A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-10-24 | 1981-04-25 | 1981-10-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-10-24 | 1985-04-25 | 1985-10-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-10-24 | 1989-04-25 | 1989-10-25 | $7700.00 | Window Closed / Lapsed |