U.S. patent number 3,788,730 [Application Number 05/239,087] was granted by the patent office on 1974-01-29 for multielement window.
This patent grant is currently assigned to Itek Corporation. Invention is credited to Allen H. Greenleaf.
United States Patent |
3,788,730 |
Greenleaf |
January 29, 1974 |
MULTIELEMENT WINDOW
Abstract
A window for separating a protected environment wherein a lens
system is located from a high pressure environment, such as deep
sea water, without allowing the high pressure differential across
the window to change the optical power of the window and defocus
the lens system. The window is constructed in a laminar fashion
with a thick outer window, a thin inner window and a compensating
section located between said inner and outer window sections. The
compensationg section is filled with a fluid having the same index
of refraction as the fluid of the high pressure environment, and is
exposed to the pressure of the protected environment. This
arrangement results in the entire pressure differential between the
outer environment and the protected environment being placed across
the thick outer window section. The fluid in the compensating
section accommodates any deformation of the outer window section
caused by the high pressure differential. No pressure is exerted
across the inner window section which defines the water-air
interface between the outer and inner environments. It is this
water-air interface which affects the optical power of the window,
and accordingly the optical power of the window does not
change.
Inventors: |
Greenleaf; Allen H. (Lexington,
MA) |
Assignee: |
Itek Corporation (Lexington,
MA)
|
Family
ID: |
22900547 |
Appl.
No.: |
05/239,087 |
Filed: |
March 29, 1972 |
Current U.S.
Class: |
359/665; 359/894;
396/26 |
Current CPC
Class: |
G03B
17/08 (20130101); G02B 23/22 (20130101) |
Current International
Class: |
G02B
23/22 (20060101); G02B 23/16 (20060101); G03B
17/08 (20060101); G02b 003/12 () |
Field of
Search: |
;350/179,180,319 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Corbin; John K.
Attorney, Agent or Firm: Homer O. Blair et al.
Claims
I claim:
1. An optical window for separating the interior of a housing from
an environment and wherein a pressure differential exists between
the pressure in the interior of the housing and the pressure of the
environment and without changing the net optical power across the
window when the pressure differential is applied across the window,
and comprising:
a. a housing having an aperture therein and adapted to be
surrounded by an environment, there being a pressure differential
between the pressure in the interior of said housing and the
pressure of the environment, said environment having a given index
of refraction; and
b. a window fixedly and immovably mounted in said aperture in said
housing for allowing a view of the environment, said window
including an outer window section, means for fixedly and immovably
mounting said outer window section to said housing in said
aperture, an inner window section, means for fixedly and immovably
mounting said inner window section to said housing in said aperture
and a compensating section located between said outer and inner
window sections, said compensating section having a fluid located
therein and exposed to the pressure within said housing, said fluid
having an index of refraction approximately equal to said given
index of refraction, whereby only said outer window section will be
deformed by the pressure differential across said window, and the
interface between the environment and the interior of said housing
will not be deformed and result in a change in the net optical
power across the window.
2. Apparatus as set forth in claim 1 wherein said window is a plane
parallel window.
3. Apparatus as set forth in claim 1 wherein said window is a
concentric spherical window.
4. Apparatus as set forth in claim 1 wherein the environment is an
environment wherein water at a very high pressure exerts a large
pressure differential across said window, and said fluid in said
compensating section is water.
5. Apparatus as set forth in claim 1 and including an optical
system positioned inside said housing for viewing the
environment.
6. Apparatus as set forth in claim 5 wherein said optical system is
a lens system.
7. Apparatus as set forth in claim 6 wherein the environment is an
environment wherein water at a very high pressure exerts a large
pressure differential across said window, and said fluid in said
compensating section is water.
8. Apparatus as set forth in claim 7 wherein said window is a plane
parallel window.
9. Apparatus as set forth in claim 7 wherein said window is a
concentric spherical window.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to windows which are placed
in front of lens systems, and wherein the window protects the lens
system from a high pressure differential existing across the
window. More particularly the present invention relates to an
improved window with a unique laminar structure whereby a pressure
differential across the window does not distort the window in a
manner which would change the optical power of the window.
In the field of protective windows for optical systems wherein a
large pressure differential exists across the window, it has been
the general practice to employ simply a thick plane parallel window
or a thick concentric spherical window. the thickness of these
windows was designed to be sufficient to withstand the pressure
differential across the window. These prior art windows have been
unsatisfactory in that deformation of the window caused by the
pressure differential ordinarily caused defocus of the lens system.
An undistorted plane parallel window has no optical power of its
own. However, deformation of the window caused by a large pressure
differential causes a change in optical power across the window
when the different optical media on the two sides of the window
have different indices of refraction.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment, an improved window with
a unique laminar structure is disclosed whereby a pressure
differential across the window does not change the optical power of
the window. The preferred embodiment provides a window including an
outer window section, an inner window section, and a compensating
section located between the outer and inner window sections. The
compensating section is filled with a fluid exposed to the pressure
within the window and having an index of refraction which is
approximately equal to the index of refraction of the environment
outside the window. Exposing this fluid to the pressure inside the
window results in the entire pressure differential across the
window being placed across the outer window section. In this
manner, the inner window section, which defines the optical power
of the window, is not distorted to change the optical power of the
window. Further, the preferred embodiment provides such a window
for use at great depths under water, and wherein the fluid in the
compensating section is also water.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a first embodiment of the invention wherein the
window is a plane parallel window.
FIG. 2 shows a second embodiment of the invention wherein the
window is a concentric spherical window.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 illustrates a plane parallel window built according to the
teachings of this invention. A housing 10 contains a lens system
12. The lens system forms an image upon image plane 14 of objects
located in an outer environment 16. A window 18 enables the lens
system 12 to view objects in environment 16. Window 18 is formed in
a laminer structure and has a thick outer section 20, a thin inner
section 22, and a compensating section 24. Compensating section 24
is filled with a fluid which has approximately the same index of
refraction as the outer environment 16. The fluid within
compensating section 24 is maintained at the pressure within the
housing by a pressure equalizer system 26. The embodiment
illustrated in FIG. 1 was built to operate at deep sea depths, and
the fluid within compensating section 24 is water.
When the housing 10 is not lowered to a great depth in water, the
pressure inside housing 10 is approximately the same as the
pressure outside the housing 10, and window 18 does not have a
pressure differential across it. With no pressure differential
across it, the outer window section 20 forms the shape of a plane
parallel plate of glass. When the housing 10 is lowered under
water, a pressure differential exists across mirror 18 between the
water at high pressure in the environment 16 and the air in the
housing 10. Since the fluid in compensating section 24 is at the
same pressure as the air in air housing 10, all of the pressure
differential will be across outer window section 20. This causes
outer window section 20 to deform as shown by exaggerated dashed
lines 28. A section 30 previously occupied by glass will now be
occupied by water. Likewise a section 32 previously occupied by
water will now be occupied by glass. Inner window 22, not having a
pressure differential across it, will retain its undeformed
shape.
The operation of this invention may be explained as follows. If a
window is used to separate an object space media from an image
space media and the indices of refraction for the two media are
different, then the shape of the interface between the two media as
defined by the window affects the net optical power across the
window. If the interface shape is changed by a bending of the
window, then the net optical power across the system will change.
However, if the indices of refraction of the two media are the
same, then the net optical power across the window is not changed
by a bending of the window. This invention utilizes this concept by
placing the pressure carrying element between two media having the
same index of refraction.
The glass window 18 may be considered as simply a means for
separating the existing water-air interface. The difference in
indices of refraction between water and air causes a change of
optical power in the system if the pressure differential is allowed
to distort this water-air interface. This invention effectively
operates to prevent a distortion of the water-air interface. If
inner window section 22 and compensating section 24 were not
provided, then window 20 would have its optical power changed by
the deformation of the water-air interface defined by outer window
section 20. This change in optical power is prevented by inner
window section 22 and compensating section 24, as now the water-air
interface is defined by inner window section 22. Glass previously
present in section 30 when the outer window section 20 was
undeformed is effectively transferred to section 32 in the deformed
condition of window section 20. Likewise water previously present
in section 32 is now effectively transferred to section 30. This
effective transfer of water is the reason the fluid in compensating
section 24 should have approximately the same index of refraction
as the fluid in environment 16. As seen in FIG. 1, inner window
section 22, which now defines the water-air interface, remains a
plane parallel plate, and thus the window 18 does not change its
optical power and defocus lens system 12.
FIG. 2 illustrates a second embodiment of this invention wherein
the window is a concentric spherical window. The window has an
outer window section 42, and inner section 44, and a compensating
section 46. The operation of the embodiment illustrated in FIG. 2
is substantially the same as the operation of the embodiment
illustrated in FIG. 1, and accordingly will not be gone into in
detail. Although the windows illustrated in FIGS. 1 and 2 were
designed to have zero optical power, the teachings of this
invention extend to embodiments having negative or positive optical
power. For instance, some embodiments might be designed having
nonconcentric spherical surfaces, and other embodiments might be
designed with aspherical surfaces. Also, in some embodiments the
lens system might not be required.
While several embodiments have been described, the teachings of
this invention will suggest many other embodiments to those skilled
in the art.
* * * * *