Birefrigent array consists of two plates with retardation properties nearly independent of direction of incident light over unlimited range of wavelengths. Array can be used as birefrigent color filter. Optical properties of plates may also be changed electro-optically rather than thermally

Miller, A.

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June 1975	 B75-10105 
NASA TECH BRIEF 
Lyndon B. Johnson Space -Center 	
A A 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Wide-Field Birefringent Elements 
.
Birefringent elements are employed in different 
optical systems, for example as biasing elements in 
electro-optical modulators and as wavelength-deter-
mining elements in special color filters and more 
complex optical networks. For best performance, 
especially if the system is to be fast, the birefringent 
retardation in these elements should be independent 
of the direction of incident light at each point on the 
elements. 
A newly-proposed birefringent array consists of two 
plates with the retardation properties nearly inde-
pendent of the direction of incident light over an 
unlimited range of wavelengths. The two plates shown 
in the illustration are made from the same material; 
the thickness of the plate with its optic axis in the 
plane of the plate is twice that of the other. 
Optic Axis Normal to
Plane of Plate
The birefringent retardation 1 is a function of the 
angles e and 0 that specify the direction of the 
incident light. A general expression for such a 
function is 
1 = 10 + 0f1(cD) + e2f(0) + e3f3(0) + e4f4(0) +..., 
where F0 is a constant and f 1((D), f2(4)), f3(4)), etc., are 
functions of 0 only. For this array, it can be shown 
that when 0 is any integral multiple of 45°, the 
functions f1((P), f2(0), and f3(0) vanish. The net effect 
is that the optical behavior of this array is more 
independent of the direction of the incident light than 
is a simple retarder regardless of the wavelength. 
The array can be used as a birefringent color filter. 
The wavelength response of a birefringent color filter 
is changed by altering the retardation of each 
element. This is done by changing the temperature of 
the entire array. If both plates in the element are 
made of the same material, their optical properties 
vary in precisely the same way, and the thickness ratio 
remains very nearly 2:1 at all temperatures. The result 
is an element with a thermally-adjustable birefringent 
retardation that is independent of the direction of the 
incident light. 
The optical properties of the plates may also be 
changed electro-optically rather than thermally. 
Electrical signals should be applied to both plates in 
order to change their optical properties synchro-
nously. However, in some cases it may be practical to 
vary only the optical properties of the plate with its 
optic axis in the plane. The thickness of the other 
plate then must be selected to produce angular 
compensation when the optical properties of the first 
plate are midway between their extreme values. In this 
way a fair degree of angular independence can be 
obtained for all values of the resultant retardation. 
Birefringent Array
(continued overleaf) 
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https://ntrs.nasa.gov/search.jsp?R=19750000105 2020-03-19T20:06:16+00:00Z
Note: 
No further documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Johnson Space Center 
Code AT3 
Houston, Texas 77058 
Reference: B75-10105
Patent status: 
NASA has decided not to apply for a patent. 
Source: A. Miller of
RCA Corp.
under contract to
Johnson Space Center
(MSC-12677)
. 
S 
B75-10105	 Category: 03 (Physical Sciences)


Wide-field birefringent elements

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