Search

EP-3732534-B1 - WIDE FIELD OF VIEW ELECTRO-OPTIC MODULATOR AND METHODS AND SYSTEMS OF MANUFACTURING AND USING SAME

EP3732534B1EP 3732534 B1EP3732534 B1EP 3732534B1EP-3732534-B1

Inventors

  • SCHMIDT, BODO
  • BANKS, PAUL S.
  • TUVEY, Charles S.
  • EBBERS, Christopher Allen

Dates

Publication Date
20260506
Application Date
20181226

Claims (14)

  1. An electro-optic modulator (10, 50) having an optical axis (18), comprising: a first electro-optic material (12, 56) configured to receive light, the first electro-optic material having a first optic axis (22) indicating a direction through the first electro-optic material along which a ray of light passing through the first electro-optic material experiences no birefringence, the first electro-optic material being positioned within the modulator so that the first optic axis is not parallel to the optical axis of the modulator; first means (16, 60) for changing the polarization state of light output from the first electro-optic material to produce rotated light; a second electro-optic material (14, 58) configured so that the rotated light passes through the second electro-optic material, the second electro-optic material having a second optic axis (24) indicating a direction through the second electro-optic material along which a ray of light passing through the second electro-optic material experiences no birefringence, the second electro-optic material being positioned within the modulator so that the second optic axis is not parallel to the optical axis of the modulator, the second electro-optic material configured to compensate birefringence and/or other higher-order optic characteristics of the first electro-optic material so as to reduce optical transmission errors of the electro-optic modulator and thereby increase angle of acceptance for incoming light; a third electro-optic material configured to receive light output from the second electro-optic material, the third electro-optic material having a third optic axis indicating a direction through the third electro-optic material along which a ray of light passing through the third electrooptic material experiences no birefringence, the third electro-optic material being positioned within the modulator so that the third optic axis is not parallel to the optical axis of the modulator; second means for changing the polarization state of light output from the third electro-optic material to produce second rotated light; a fourth electro-optic material configured so that the second rotated light passes through the fourth electro-optic material, the fourth electro-optic material having a fourth optic axis indicating a direction through the fourth electro-optic material along which a ray of light passing through the fourth electro-optic material experiences no birefringence, the fourth electro-optic material being positioned within the modulator so that the fourth optic axis is not parallel to the optical axis of the modulator. and a plurality of electrodes (26, 28, 70, 72) configured to produce an electric field within the first electro-optic material and the second electro-optic material when a potential is applied between the electrodes, the electrodes being configured so that the electric field is generally transverse to the optical axis of the modulator.
  2. The electro-optic modulator (10, 50) of claim 1, wherein the first electro-optic material (12, 56) and the second electro-optic material (14, 58) are positioned in the modulator so that the first optic axis (22) and the second optic axis (24) are each directed outside the field of view of the modulator.
  3. The electro-optic modulator (10, 50) of claim 1, wherein the first optic axis (22) is orthogonal to the optical axis (18) of the modulator.
  4. The electro-optic modulator (10, 50) of claim 1, wherein the second optic axis (24) points in a direction opposite the first optic axis (22).
  5. The electro-optic modulator (10, 50) of claim 1, wherein the first electro-optic material (12, 56) and the second electro-optic material (14, 58) are each a birefringent crystal.
  6. The electro-optic modulator (10, 50) of claim 1, wherein at least one of the first electro-optic material (12, 56) and the second electro-optic material isKD*P.
  7. The electro-optic modulator (10, 50) of claim 1, wherein at least one of the first electro-optic material (12, 56) and the second electro-optic material (14, 58) includes a ferroelectric oxide.
  8. The electro-optic modulator of claim 1, wherein the means (16, 60) for changing the polarization state of light output includes a half-wave plate, a plurality of half-wave plates configured to provide a zero-order wave plate or an optical rotator, or a combination thereof.
  9. The electro-optic modulator (10, 50) of claim 1, wherein the means (16, 60) for changing the polarization state of light output includes the second electro-optic material (14, 58) rotated relative to the first electro-optic material (12, 56) so that the second electro-optic material functions as a half-wave plate.
  10. The electro-optic modulator of claim 1, wherein the first electro-optic material, the second electro-optic material, the third electro-optic material, and the fourth electro-optic material are positioned in the modulator so that the first optic axis, the second optic axis, the third optic axis, and the fourth optic axis are each directed outside the field of view of the modulator.
  11. The electro-optic modulator of claim 1, wherein the thicknesses of the first electro-optic material, the second electro-optic material, the third electro-optic material, and the fourth electro-optic material are about equal.
  12. The electro-optic modulator of claim 1, wherein the first electro-optic material, the second electro-optic material, the third electro-optic material, and the fourth electro-optic material are each selected from the group consisting of lithium niobate (LiNbO 3 ) and lithium tantalate (LiTaO 3 ).
  13. The electro-optic modulator of claim 1, wherein at least one of the first electro-optic material, the second electro-optic material, the third electro-optic material, and the fourth electro-optic material is selected from the group consisting of lithium niobate (LiNbO 3 ) and lithium tantalate (LiTaO 3 ).
  14. The electro-optic modulator of claim 1, at least one of the first electro-optic material, the second electro-optic material, the third electro-optic material, and the fourth electro-optic material is selected from a solid solution of lithium tantalate niobate LiNb x Ta (1-x) O 3 , where 0≤x≤1.

Description

TECHNICAL FIELD This disclosure relates generally to electro-optic modulators, more particularly, to electro-optic modulators suitable for processing incoming light having a relatively large angle of incidence. BACKGROUND Kerr cells and Pockels cells are particular types of electro-optic modulators (EOMs) that can modulate the polarization of light incident on them. In an EOM, an electric field is applied to a material that changes properties under the influence of the electric field. The EOM's change in properties modifies the phase of light transmitted therethrough. Pockels cells are based on the Pockels effect, in which a material's refractive index changes linearly with applied electric field. Kerr cells are based on the Kerr effect, in which a material's refractive index varies quadratically with the applied electric field. For certain materials and certain orientations of the applied electric field, the Pockels effect creates an anisotropy in the refractive index of the material. Such materials and fields may be used to create a Pockels cell, in which the induced anisotropy changes the polarization state of light transmitted therethrough linearly as a function of applied voltage. EOMs such as Pockels cells may be placed between crossed polarizers to modulate the intensity of light. The temporal response of a Pockels cell may in some circumstances be less than 1 nanosecond, enabling its use as a fast optical shutter. Although widely used for laser applications, Pockels cells traditionally have been viewed as having significant limitations, rendering such devices unsuitable for optical processing in other types of applications. Pockels cell materials have birefringence (different values of the refractive index for light polarized along different axes of the crystal structure), which restricts the angular acceptance of incoming light to the cell. Some known Pockels cells may only effectively modulate incident light deviating by less than few degrees from the surface normal of the Pockels cell, significantly limiting their use in such applications. For example, the paper "Extending the field of view of KD*P electrooptic modulators," by Edward West, Applied Optics, Vol. 17 No. 18, pp. 3010-3013, September 1978 ("West paper"), discusses using compensation techniques to achieve larger acceptance angles for Pockels cells. However, the paper also describes how the compensation techniques have a small impact on the acceptance angle when voltage is applied to the Pockels cell during operation. Thus, the compensation techniques of the West paper are not entirely useful for wide acceptance angle applications, such as imaging, where incident light may hit a Pockets cell at larger range of incident angles. US5659411 discloses an optical device having an optically transparent birefringent medium that selectively shifts the optical axis. US5381253A·discloses optical modulators which comprise aligned chiral smectic liquid crystal cells within an optical resonance cavity. The cavity configurations include symmetric and asymmetric Fabry-Perot etalons. The liquid crystal cells can be planar- or homeotropically-aligned and can be discrete state or analog cells. HUBAND S. ET AL: "Crystallographic and optical study of LiNb(1-x)TaxO3", ACTA CRYSTALLOGRAPHICA. SECTION B, STRUCTURAL SCIENCE, vol. 73, no. 3, 1 June 2017 (2017-06-01), pages 498-506, ISSN: 0108-7681 discloses a crystallographic and optical study of LiNb(1-x)TaxO3 materials. CN101216616A discloses an electrooptic modulator with high thermal stability relates to the field of an optical fiber communication device. The electrooptic modulator is characterized in that two electrooptic crystals identical in characteristics and size but reverse in optical axis direction are arranged between two orthogonal polarizers, and a halfwave plate is inserted between the two electrooptic crystals. An ordinary light and an extraordinary light in the first electrooptic crystal enter the second electrooptic crystal through the halfwave plate and change into an extraordinary light and a ordinary light. Accordingly, natural birefringence is eliminated completely and the phase differences produced by electric birefringence are added. The modulator can be ensured to work in a linear region by applying a DC bias on the electrooptic crystals or by inserting a quarter wave plate at a certain position between the two polarizers. The modulator with such structure eliminates the influence of natural birefringence, thus achieving better temperature stability. US3304428A discloses a transmission line light modulator. US20090219378-A1 discloses an electrooptic device having a simple structure that can efficiently increase deflection of a beam is provided. US20130094084-A1 discloses an exemplary patternable reflective film having an absorption characteristic suitable to, upon exposure to a radiant beam, absorptively heat a portion of the film by an amount sufficient to change a first reflective cha