Optical: systems and elements – Polarization without modulation – By relatively adjustable superimposed or in series polarizers
Reexamination Certificate
1999-08-27
2001-03-06
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Polarization without modulation
By relatively adjustable superimposed or in series polarizers
C359S485050, C359S494010, C359S833000, C359S834000, C359S835000, C359S857000
Reexamination Certificate
active
06198574
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is related to commonly owned, copending U.S. patent application No. 09/384,855 (Attorney Docket No. 0202/US) filed on even date herewith in the name of Henry Allen Hill and Peter J. de Groot and entitled INTERFEROMETERS UTILIZING POLARIZATION PRESERVING OPTICAL SYSTEMS.
BACKGROUND OF THE INVENTION
This invention relates to polarization preserving optical systems and their use in displacement measurement interferometers (DMIs).
Non-polarization preserving retroreflectors are well-known and operate to deflect light through 180 degrees such that an incoming beam is exactly reversed in direction traveling as an outgoing beam parallel to the direction of propagation of the incoming direction and spatially offset with respect to it. The classical retroreflector essentially contains the intersection corner of three mutually perpendicular plane surfaces and is known as the cube corner retroreflector or sometimes the tetrahedron. Here, a ray generally undergoes 3 reflections, one from each 120° sector in the process of entering and exiting the retroreflector. Ideally, the direction of the reflected ray is opposite that of the incident ray but displaced due to a reflection through the retroreflector intersection corner. From the standpoint of polarization affects, the primary problem with the classical retroreflector is that the angles the rays make with the mirror surfaces are skew. Detailed calculations using the Jones matrix formalism along with the Fresnel reflection formulas can be used to predict the resultant polarization for different initial polarizations and retroreflector types. From the standpoint of their use in DMI applications where small, linearly polarized beams interact with only small sub-apertures of the retroreflector, the net effect is to rotate the plane of polarization by several degrees (typically 6°). This phenomenon is called Retro Induced Polarization Rotation (RIPR) and misaligns the beam polarization directions with respect to the polarization beam splitter of the interferometer which can cause large periodic errors in the measured interferometric phase. A particularly troublesome periodic or “cyclic” error which occurs in High Stability Plane Mirror Interferometers (HSPMI) produces an error with a frequency at ½ the Doppler shift (as well as other frequencies). It has been shown that this error, which is due to the polarization rotation properties of the retroreflector, can be extremely large and will occur regardless of the beamsplitter quality.
Consequently, it is a primary object of the present invention to provide polarization preserving optical systems that provide beam deflection properties for a variety of applications without introducing deleterious polarization effects.
It is another object of the present invention to provide polarization preserving optical systems for use in displacement measurement interferometers in place of traditional cube corner retroreflectors.
It is yet another object of the present invention to provide polarization preserving optical systems for deflecting plane polarized beams through arbitrary angles without introducing polarization mixing between orthogonally plane polarized beams passing through the system.
Yet another object of the present invention is to provide polarization preserving optical systems for use at multiple wavelengths.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter when the following detailed description is read in connection with the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention relates to polarization preserving optical systems for use in deviating plane polarized beams through preselected angles without changing their linear state of polarization. The inventive optical systems have a variety of applications and are particularly suitable for use in the field of distance measuring interferometry (DMI) to enhance measurement accuracy by reducing undesirable polarization effects that can introduce errors associated with an otherwise present undesirable polarization rotation found in classical retroreflectors.
The polarization preserving optical systems of the invention comprise a plurality of reflecting surfaces arranged such that a change in the direction of propagation of an input beam, normal to both the input beam and an output beam, causes a change in the direction of propagation of the output beam in a direction opposite to the direction of the change in the input beam, and a change in the direction of propagation of the input beam, normal to the input beam and in a plane orthogonal to a normal to both the input beam and the output beam, causes a rotation in the output beam in the plane that is the same as a corresponding rotation of the input beam caused by the change in the direction of propagation of the input beam and wherein the plane of incidence at each of the reflecting surfaces is either orthogonal or parallel to the plane of polarization of an incident beam thereto.
The polarization preserving optical systems are preferably fabricated of a plurality of prismatic optical elements wherein the plurality of reflecting surfaces comprise selected surfaces of the prismatic optical element and preferably operate by total internal reflection.
The plurality of prismatic optical elements are preferably arranged as an integral assembly in which at least one surface of each prismatic optical element contacts at least one surface of another prismatic optical element and in which at least one polarizing beam splitter may be included.
The prismatic optical elements are selected from the group consisting of Porro, right angle, Dove, penta, and “K” prisms, one embodiment comprises a sequential combination of a right angle prism, a Porro prism, and a pentaprism.
At least one of the plurality of reflecting surfaces may have formed thereon a multilayer polarizing beam splitter coating arrangement to enhance the extinction ratio between orthogonally polarized beams entering the polarization preserving optical system and originating upstream of it, and such coatings may be structured to operate at multiple wavelengths. Birefringent materials may also be used to construct the various prismatic optical elements for similar purposes.
A variety of input to output beam relationships is demonstrated and depend on the particular design geometry of a system.
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Caufield Francis J.
Jr. John Juba
Spyrou Cassandra
Zygo Corporation
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