Patent Application
20090231677
The invention was made in part by employees of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
1. Field of the Invention
This invention relates to variable focal point optical assemblies. More specifically, the invention is an optical assembly having a variable focal point where the assembly includes a zone plate and electro-optical material.
2. Description of the Related Art
As illustrated in a plan view in
Accordingly, it is an object of the present invention to provide a variable-focal-point optical assembly using a zone plate.
Another object of the present invention is to provide a variable-focal-point optical assembly based on a zone plate that does not require the use of any moving parts or assemblies.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an optical assembly includes a zone plate having concentric spaced-apart rings of opaque material. Between the opaque rings, light is transmitted through the zone plate. Electro-optic material is disposed on one side of the zone plate. Coupled to the electro-optic material is the means to control an index of refraction thereof.
Referring again to the drawings and more particularly to
Optical assembly 20 includes a zone plate 30 that is defined by a planar arrangement of concentric and spaced-apart opaque rings as is known in the art. In the illustrated embodiment, zone plate 30 has a circular and opaque central region 31 and four concentric and spaced-apart rings 33, 35, 37 and 39 to thereby define four concentric and spaced-apart transparent ring regions 32, 34, 36, and 38. It is to be understood that this pattern (i.e., starting with opaque central region 31) could be reversed (i.e., starting with a transparent central region) without departing from the scope of the present invention. In addition, the number of opaque rings/transparent ring regions is not a limitation of the present invention. Still further, the size and spacing used for zone plate 30 can be tailored for a particular application without departing from the scope of the present invention.
Disposed adjacent to one face of zone plate 30 is an optically transparent electrode 40 (e.g., made from a material such as indium tin oxide or zinc oxide). Adjacent and coupled to electrode 40 is a planar face of one or more layers/types of an electro-optic material 42. Electro-optic material 42 is any of a variety of materials that can experience a change in refractive index or absorption coefficient by one or multiples in the presence of an applied electric field, current, or magnetic field. Choices for electro-optic material 42 include, but are not limited to, non-linear optical crystals, ferroelectric materials, piezoelectric materials, electro-active polymers, and liquid crystals.
Adjacent and coupled to the opposing planar face of electro-optic material 42 is another optically transparent electrode 44. The combination of electrode 40, material 42 and electrode 44 span an area that, at a minimum, covers the area defined by transparent ring regions 32, 34, 36, and 38. In the illustrated embodiment, the combination of electrode 40, material 42 and electrode 44 span the entire area defined by zone plate 30. Although not shown, the above-described assembly can be fabricated on a rigid and transparent substrate such as glass, quartz or sapphire.
A controllable voltage source 50 is electrically coupled to electrodes 40 and 44. When a voltage is applied to electrodes 40 an 44, an electric field is developed across electro-optic material 42. The electric field causes a circular gradient refractive index zone to be formed inside electro-optic material 42. This gradient refractive index changes the phase of photons of light 100 passing therethrough thereby changing the focal point 102 of light 100 passing through optical assembly 20. The focal distance F is controlled by the electric field in electro-optic material 42.
By itself, a zone plate is known to have a strong dispersion relation with the wavelength of light passing therethrough. Therefore, conventional zone plates can only serve as a focusing element with a specific monochromatic wavelength. However, in the optical assembly of the present invention, the circular gradient refractive index caused by the applied electric field also changes the properties (i.e., focal point at a specific wavelength, distribution of intensity of passing photons, and phase of passing photons) of the zone plate such that the zone plate can be optimized for a new wavelength. Thus, the present invention can also be used to control the designated wavelength of operation by controlling the electric field in the electro-optic material.
The present invention is not limited to the optical assembly construction illustrated in
Still another embodiment of the present invention is illustrated in
As mentioned briefly above, electro-optic material 42 can be realized by a single homogeneous layer of electro-optic material or multiple distinct layers of electro-optic material with each of such layers having unique electro-optic properties. For example, as shown in
The advantages of the present invention are numerous. The optical assembly can be adjusted in terms of focal point location without the use of any moving parts. The assembly can be used in a neutral state (i.e., no voltage applied) to provide a fixed focal point for a specific wavelength of operation. However, the assembly can also be used in an active state (i.e., voltage applied) to adjust the wavelength of operation and/or the location of the assembly's focal point. The optical assembly can function as a programmable micro-lens whose focal distance changes with the applied voltage. The optical assembly can also form part of a micro-spectrometer that transmits a specific wavelength of light to a photo-detector where the specific wavelength is controlled by the applied voltage.
Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. For example, the controllable voltage source could be replaced with a controllable current or magnetic field source without departing from the scope of the present invention It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.
