Reflection elimination system

• US 4,007,979 A
• Filed: 04/18/1975
• Issued: 02/15/1977
• Est. Priority Date: 04/18/1975
• Status: Expired due to Term

• Current Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Coblitz, David B.
• Primary Examiner(s): Bauer, Edward S.
• Assistant Examiner(s): Rusenberger, Richard A.
• Application Number:
  US05/569,480
• Time in Patent Office: 669 Days
• Field of Search: 350/156, 350/157, 350/158, 350/159
• US Class Current: 359/488.01
• CPC Class Codes: G02B 27/0018 with means for preventing ghost images anti-reflection coatings G02B1/11
• CPC Class Codes: G02B 27/144 using partially transparent surfaces without spectral selectivity G02B27/147 takes precedence
• CPC Class Codes: G02B 27/28 for polarising used in stereoscopes G02B30/25

Abstract

A device which eliminates unwanted light rays and permits passage of desired light rays. For the purposes of this specification, the desired light rays are those which originate on a first side of a material capable of effecting light passage, and which pass through the material to a second side. Undesirable light rays are those originating on the second side of the material, which pass through the material to the second side of the material. The material, in the embodiment illustrated, is a beam splitter intended to present a desired scene to an observer. The preferred embodiment includes a linear polarizer and a quarter wave retarder which impart an elliptical polarization to the undesired light rays. The polarizer and the retarder are arranged with respect to one another and to the beam splitter so that undesired light passing through the polarizer, retarder, and the beam splitter, and which is reflected back through the beam splitter to the polarizer will return, after reflection, with the same ellipticity but with orthogonal orientation. A method for determining the ratio components of light polarization when light is transmitted through a material, reflected and returned through the same material.

Claims

1. In a device including a material which partially polarizes radiation passing through it, said material having a P axis and an S axis, the improvement which comprises a retarder and a linear polarizer for imparting an elliptical polarization to radiation passing through the retarder and the linear polarizer, said retarder having a fast axis and a slow axis, said fast axis being aligned parallel to one of said P and S axes of said material, the retardance of the combination of said retarder and said material being approximately a quarter wave, said linear polarizer having a pass axis, said pass axis being placed at an angle φ

with respect to the P axis of said material, where φ

is determined from the formula tan² φ

= |t_p² /t_s² |, in which t_p is the amplitude transmittance of the material for light polarized in the P direction, and t_s is the amplitude transmittance of the material for light polarized in the S direction.

2. The improvement of claim 1 wherein the device comprises an optical system for a portion of an aircraft simulator, said simulator further including a mirror, said material comprising a beam splitter for said optical system, a cathode ray tube display adapted to be reflected by said beam splitter to said mirror for observation through said beam splitter in said aircraft simulator, said retarder and said linear polarizer comprising a window of said aircraft simulator.

3. The improvement of claim 2 wherein said fast axis of said retarder is aligned with the P axis of said beam splitter.

4. In a device having a material which partially polarizes radiation passing through it, said material having a P polarization axis and an S polarization axis, the improvement comprising means for preventing the observation of radiation passing through said material in two directions by elliptically polarizing the radiation upon its initial pass through the observation preventing means in the first direction so that the radiation returns to the observation preventing means in the second direction after passage through the partially polarizing material with the same ellipticity but with orthogonal orientation, said radiation observation preventing means including a retardation means having a fast axis, the retardance of the combination of said retarder and said partially polarizing material being a predetermined value, the fast axis of said retarder being arranged parallel to one of said P and said S axes directions, and a polarizer having a pass axis, said pass axis being positioned at an angle φ

with respect to the P axis of said material, where φ

is determined from the formula tan² φ

= t_p² /t_s², t_p being the amplitude transmittance of the material for light linearly polarized in the P axis direction and t_s being the amplitude transmittance of the material for light linearly polarized in the S axis direction of the material.

5. The improvement of claim 4 wherein the fast axis of said retarder is parallel to the P axis of said material.

6. The improvement of claim 5 wherein the retardance of the combination of said retarder and said material is equal to 90°

.

7. A method for determining the ratio of intensity transmittance for a partially polarizing material having a P axis and an S axis, comprising the steps:

positioning said partially polarizing material before a mirror at a predetermined angle with respect to said material;

positioning a retarder means before said material, said retarder means having a fast axis, said fast axis being aligned with one of said P and said S axes of said material;

positioning a polarizer of light before said retarder means;

directing a radiation beam through said polarizer, retarder, and material for reflection by said mirror and returning through said material retarder and polarizer;

rotating said polarizer until the amount of reflected radiation passing through said polarizer is extinguished; and

measuring the angle between the pass axis of said polarizer and the fast axis of said wave retarder.

8. The method of claim 7 wherein the angle between the fast axis of said retarder means is positioned parallelwise with one of the P and S axes of said material.

9. A method of extinguishing an electromagnetic radiation comprising the steps of:

passing said electromagnetic radiation through an elliptically polarizing means, said elliptically polarizing means imparting an original desired elliptical polarization to said electromagnetic radiation, said polarizing means blocking electromagnetic radiation having an opposite polarization from said desired elliptical polarization;

passing said electromagnetic radiation through a partially polarizing material in a first direction;

reflecting said electromagnetic radiation back through said partially polarizing material in a second direction so that said radiation returns to said elliptically polarizing means with opposite polarization from said original desired elliptical polarization.

10. The method of claim 9 wherein said elliptical polarizing means comprises a linear polarizer having a pass axis, and a quarter wave retarder having a fast axis.

11. The method of claim 10 wherein the angle between the pass axis of said linear polarizer and the fast axis of said quarter wave retarder is adjusted to achieve extinction of said electromagnetic radiation.

12. The method of claim 10 wherein said partially polarizing material has a P axis and an S axis, the fast axis of said retarder being aligned with one of said P axis and said S axis of said partially polarizing material, the pass axis of said polarizer being positioned at an angle φ

with respect to said P axis, φ

being obtained from the formula, tan² φ

= |t_p² /t_s² |, where t_p is the amplitude transmittance of the partially polarizing material in the P axis direction and t_s is the amplitude transmittance of the partially polarizing material in the S axis direction.

13. The method of claim 9 wherein said partially polarizing material has a P axis and an S axis, said elliptically polarizing means includes a linear polarizer having a pass axis, and a retarder having a fast axis, the pass axis of said polarizer being aligned with one of said P and S axes, the fast axis of said retarder being oriented at an odd multiple of 45°

with respect to the pass axis of said polarizer, including the further step of varying the retardance of said retarder until the radiation returning to said polarizer has the opposite polarization from said original desired elliptical polarization.

14. The method of claim 9 wherein said partially polarizing material has a P axis and an S axis, said elliptical polarizing means includes a linear polarizer, said linear polarizer having a pass axis, and a retarder, said retarder having a fast axis, the fast axis of said retarder being oriented at 45°

with respect to the pass axis of said polarizer, including the further step of varying the position of said partially polarizing material until the radiation returning to said polarizer has the opposite polarization from said original desired elliptical polarization.

15. A device for eliminating reflections of undesired electromagnetic radiations from a system, comprising:

reflecting means;

partially polarizing means, said partially polarizing means being aligned with said reflecting means, said partially polarizing means having a property wherein a greater amount of a first linearly polarized component of electromagnetic radiation incident upon it is transmitted as compared to a second linearly polarized component of electromagnetic radiation incident upon it, said partially polarizing means maintaining the relative phase relation of said first and said second polarized components; and

elliptically polarizing means disposed on a side of said partially polarizing means opposite said reflecting means, said polarizing means being arranged so that all undesired electromagnetic radiation passes through it, said polarizing means further having a property enabling it to block electromagnetic radiation having an opposite polarization from that originally imparted by said polarizing means, said polarizing means being adapted and arranged to impart an original polarization to said undesired electromagnetic radiation such that an opposite polarization is present at said polarizing means after passage through said partially polarizing means, reflection from said reflecting means, and passage again through said partially polarizing means.