Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2002-08-14
2003-11-25
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S629000
Reexamination Certificate
active
06654178
ABSTRACT:
REFERENCE TO COMPUTER PROGRAM LISTING
This patent document includes a computer program listing appendix that was submitted on a compact disc containing the following files: NPBS1, created Aug. 14, 2002, having an on-disk size of 16.0 kbits; NPBS2, created Aug. 14, 2002, having an on-disk size of 16.0 kbits; NPBS3, created Aug. 14, 2002, having an on-disk size of 16.0 kbits; NPBS4, created Aug. 14, 2002, having an on-disk size of 16.0 kbits; NPBS5, created Aug. 14, 2002, having an on-disk size of 16.0 kbits; NPBS6, created Aug. 14, 2002, having an on-disk size of 16.0 kbits; and NPBS7, created Aug. 14, 2002, having an on-disk size of 16.0 kbits. The material on the compact disc is hereby incorporated by reference herein in its entirety.
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND
Conventional non-polarizing beamsplitters that are constructed from reflective thin film coatings split an incident beam into a reflected beam and a transmitted beam that have the same polarization as the incident beam. Constructing a non-polarizing beamsplitter can be complicated because for most non-absorbing thin films, the reflectance for the P-polarized beam component (i.e., the component having an electric field in a plane defined by the incident and reflected beams) differs from the reflectance for the S-polarized beam component (i.e., the component having an electric field perpendicular to the plane defined by the incident and reflected beams). The difficulty of constructing a non-polarizing beamsplitter increases in an immersed system where thin film coatings are sandwiched between optical elements.
FIG. 1A
illustrates an immersed non-polarizing beamsplitter
100
. Beamsplitter
100
includes a beamsplitter coating
120
between optical elements
110
and
130
. Optical elements
110
and
130
can be prisms, plates, or other elements made of a material such as an optical quality glass.
FIG. 1A
specifically shows a configuration where optical elements
110
and
130
are right angle prisms, and an incident monochromatic beam
140
is along a path perpendicular to an input surface of optical element
110
and at an angle of 45° with beamsplitter coating
120
. As a result, a reflected beam
150
exits perpendicular to an output face of optical element
110
, and a transmitted beam
160
exists perpendicular to an output face of optical element
130
.
To make beamsplitter
100
non-polarizing, beamsplitter coating
120
is such that for the selected wavelength, S-polarized light and P-polarized light in beam
140
have the same reflectance from beamsplitter coating
120
and the same transmittance through beamsplitter coating
120
.
FIG. 1B
shows the structure of beamsplitter coating
120
, which includes
4
Q thin films
120
-
1
to
120
-
4
Q formed of materials having different refractive indices. The choices of materials and thicknesses of thin films
120
-
1
to
120
-
4
Q provide beamsplitter
100
with the desired reflectance and transmittance of incident beam
140
. Incident beam
140
, which arrives through optical element
110
, partially reflects at the interface between optical element
110
and thin film
120
-
1
, each interface between adjacent pairs of thin filns [
120
-
1
,
120
-
2
] to [
120
-(N−1),
120
-
4
Q], and the interface between thin
120
-
4
Q and optical element
130
. The partial reflections combine and interfere to form reflected beam
150
, while the portion of incident beam
140
not reflected (and not absorbed) becomes a transmitted beam
160
.
Equations 1 are formulas for the reflection coefficients rs and rp respectively for S-polarized and P-polarized light in beamsplitter
100
when each of thin films
120
-
1
to
120
-N has an optical thickness that is one quarter of the wavelength of incident beam
140
. In Equations 1, values N
0
, N
1
to N
4Q
, and N
4Q+1
are the respective refractive indices of element
110
, thin films
120
-
1
to
120
-
4
Q, and element
130
; and values &thgr;
0
, &thgr;
1
to &thgr;
4Q
, and &thgr;
4Q+1
are the respective propagation angles of the transmitted beams in element
110
, thin films
120
-
1
to
120
-
4
Q, and element
130
.
Equations 1:
rs
=
1
-
U
*
W
1
+
U
*
W
rp
=
1
-
U
/
W
1
+
U
/
W
U
=
N
0
*
N
2
*
N
4
*
…
N
4
Q
N
1
*
N
3
*
…
N
4
Q
-
1
*
N
4
Q
+
1
W
=
cos
θ
0
*
cos
θ
2
*
…
cos
θ
4
Q
cos
θ
1
*
cos
θ
3
*
…
cos
θ
4
Q
+
1
A non-polarizing bearnsplitter is equally efficient at reflecting S-polarized and P-polarized light. The reflection coefficient rs of non-polarizing beamsplitter
100
thus must be non-zero and equal in magnitude to the reflection coefficient rp of the non-polarizing beamsplitter
100
.
FIG. 1B
illustrates a combination of thin films
120
-
1
to
120
-
4
Q for which reflection coefficients rs and rp are non-zero and equal because one of factor W or U of Equations 1 is equal to 1 and the other factor U or W is not equal to 1. Non-polarizing beamsplitter
100
uses three materials H, M, and L for thin film layers
120
-
1
to
120
-
4
Q and organizes thin film layers
120
-
1
to
120
-
4
Q into Q groups of four layers each. Each group of four thin film layers includes a first layer of material M having an intermediate refractive index N
M
, a second layer of material H having a higher refractive index N
H
, a third layer of material M, and a fourth layer of material L having a low refractive index N
L
. The three materials are selected so that refractive indices N
H
, N
M
, and N
L
make one factor W or U equal to 1.
Factor W of Equations 1 depends on the propagation angles &thgr;
1
to &thgr;
4Q
for light passing through thin films
120
-
1
to
120
-
4
Q, and the propagation angles depend on the refractive indices N
0
, N
1
to N
4Q
, and N
4Q+1
. Snell's Law as applied in Equation
2
indicates that the product of the refractive index and the sine of the propagation angle is a constant L for all of the thin films
120
-
1
to
120
-
4
Q. Accordingly, any two of thin films
120
-
1
to
120
-
4
Q that have the same refractive index will have the same propagation angle.
Equation 2
N
0
*sin &thgr;
0
=N
1
*sin &thgr;
1
=N
2
*sin &thgr;
2
. . . =N
4Q+1
*sin &thgr;
4Q+1
=L
In beamsplitter
100
, thin films having refractive indices N
M
, N
H
, and N
L
respectively have propagation angles &thgr;
M
, &thgr;
H
, and &thgr;
L
. When the elements
110
and
130
have the same refractive index, cos&thgr;
0
is equal to cos&thgr;
4Q+1
, and use of propagation angles &thgr;
M
, &thgr;
H
, and &thgr;
L
simplifies the formula for factor W as illustrated in Equation
3
. If incident angle &thgr;
0
(e.g., 45°) and refractive indices N
M
, N
H
, and N
L
make angles &thgr;
M
, &thgr;
H
, and &thgr;
L
satisfy Equation 4, factor W is equal to 1, and beamsplitter
100
is non-polarizing.
Equation 3:
W
=
cos
θ
0
*
cos
θ
2
*
…
cos
θ
4
Q
cos
θ
1
*
cos
θ
3
*
…
cos
θ
4
Q
+
1
=
(
cos
θ
H
*
cos
θ
L
cos
θ
M
*
cos
θ
M
)
Q
Equation 4:
cos
θ
H
*
cos
θ
L
cos
θ
M
*
cos
θ
M
=
1
The materials suitable for optical-quality thin
Agilent Technologie,s Inc.
Schwartz Jordan M.
Stultz Jessica
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