Optical shutter device

Details Optical shutter device Optical shutter device

1997-05-30

2001-01-09

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S265000, C359S275000, C359S290000

Reexamination Certificate

active

06172795

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of thermochromic materials and to applications for thermochromic materials where the response time for the optical absorption change of the thermochromic material is required to be extremely fast, e.g., 1 nanosecond or less.
BACKGROUND OF THE INVENTION
With the increasing availability of lasers, including pulsed lasers which produce very high intensities of optical radiation in pulses of short duration such as 1 nanosecond or less, it has become possible to develop many different new optical applications which operate on a time scale ranging from less than 0.1 picoseconds or 0.0001 nanoseconds up to 1 nanosecond. Examples of these applications are high speed optical communication and computing, optical data recording, security devices, and high speed imaging. The very high intensities of the optical radiation in very short exposure times also creates a need for protective devices which can shield eyes and mechanical sensors from excessive optical radiation. U.S. Pat. No. 4,933,110 to Tucker describes an optical shield for protection from lasers.
In many of these laser-based applications, there is a need for optical devices which change their optical transmission or optical density properties depending on the presence or absence of the laser radiation. Optical density, as used herein, is defined as log
10
(1/transmittance) for transmitted radiation. For example, with the protective devices, the optical transmission needs to reduce to an extremely low level, e.g., less than 0.01% for protecting the eyes of humans, at the wavelength of the incident laser radiation in a very short time before the cumulative optical radiation exposure causes damage to the eye, e.g., more than 0.5 microjoules/cm
2
. For example, in optical communications, typically involving the use of optical fibers, optical devices are used to modulate the laser signals at response times on the order of 1 picosecond.
Because of the extremely fast nature of these laser-based applications with time scales of less than a picosecond to 1 nanosecond, a variety of materials with different types of optical properties have been used to change the transmission properties of the laser radiation when passing through the devices of these applications. Materials which change their optical transmission properties upon undergoing a chemical change have not been suitable for these applications because of the long time scale of chemical reactions, e.g., 1000 nanoseconds or 1 microsecond up to seconds and minutes. This includes photochromic and conventional thermochromic materials, which undergo an optical absorption change due to a change in chemical structure when exposed to photons and heat, respectively. U.S. Pat. No. 5,091,984 to Kobayashi et al. describes an example of photochromic materials. U.S. Pat. No. 5,426,143 to de Wit et al. describes an example of conventional thermochromic materials. Another disadvantage of optical materials that depend on a chemical reaction to produce a useful optical change is that it is difficult to make them reversible over many thousands and more of optical changes. This is well known to be true for photochromic and thermochromic materials. Most high speed optical applications require very efficient reversibility because, by the nature of many repeat optical operations in 1 nanosecond or less time periods, they require millions and more of repeat optical changes during their useful life.
These requirements for very fast optical response times and for repeated reversibility have combined to make materials with a variety of nonlinear optical properties evaluated for use in these applications. These nonlinear optical materials do not typically undergo any chemical change during the optical change and are reversible in their change in optical properties. The optical nature of the change allows it to occur in typically less than 1 picosecond. Examples of the nonlinear optical changes are changes in optical transmission or absorption, changes in frequency of the laser radiation, and changes in the index of refraction. U.S. Pat. No. 5,472,786 to Pannell et al. describes optical switching materials based on changes in the index of refraction. Although these materials have found use in various high speed laser applications, many of them are inorganic materials and are difficult to fabricate into optical devices such as in a coated layer on a flexible substrate or in a plastic molded material. U.S. Pat. No. 5,406,407 to Wolff describes an optical switching device based on an inorganic material. Some of the nonlinear optical materials are difficult to fabricate into devices because their performance requires many extremely thin layers, e.g. dozens of layers only one or two molecular diameters thick for each layer, in order to provide an adequate nonlinear optical effect. Also, the magnitude of the optical changes with these nonlinear optical materials is often small, particularly for changes in optical transmission so that applications that would benefit from a large change in optical transmission, e.g., an optical shutter or eye and sensor protection devices, can not be readily done.
Therefore it is an object of this invention to provide an optical shutter which has a large change in optical transmission when exposed to a high intensity of photons in a very short period of time, such as 1 nanosecond or less.
It is a further object of this invention to provide an optical shutter for laser applications which is reversible and can be used repeatedly without degradation.
It is another object of this invention to provide an optical shutter that requires only 1 to 5 layers of materials and that can be fabricated using economical coating, plastic molding, and other conventional processes.
These and other objects of this invention will become more apparent from the following description of the invention.
SUMMARY OF THE INVENTION
The present invention provides an optical shutter device comprising one or more photon absorbing materials that convert photons to heat in less than 1 nanosecond and one or more thermochromic materials that undergo an increase or decrease of greater than 5% in optical density at one or more wavelengths when the thermochromic material is heated from 25° C. to a temperature greater than 100° C. in less than 1 nanosecond.
In one embodiment, the thermochromic material is reversible. In one preferred embodiment, the reversible thermochromic material increases or decreases its optical density at one or more wavelengths without undergoing a chemical change. The change in its optical density is from a shift in the optical absorption spectrum of the thermochromic material at elevated temperatures. In a most preferred embodiment, the thermochromic material is selected from the group consisting of tris (p-dialkylaminophenyl) aminium salts and phthalocyanine compounds. In one preferred embodiment, the thermochromic material has a molar extinction coefficient of greater than 20,000 M
−1
cm
−1
at 25° C. at one or more wavelengths over the range of 300 to 1500 nm. In a most preferred embodiment, the thermochromic material has a molar extinction coefficient of greater than 50,000 M
−1
cm
−1
at 25° C. at one or more wavelengths over the range of 300 to 1500 nm.
In one embodiment, the increase or decrease of the optical density of the thermochromic material upon heating is greater than 50% at one or more wavelengths. In one preferred embodiment, the increase or decrease of the optical density of the thermochromic material upon heating is greater than 100%. In one preferred embodiment, the increase or decrease of the optical density of the thermochromic material upon heating is greater than 200%. In a most preferred embodiment, the increase or decrease of the optical density of the thermochromic material upon heating is greater than 400%, and particularly greater than 600%.
In one embodiment, the wavelengths of increase or decrease of the optical density of the thermochromic material are selected from the visible regio

Affiliated with

Also associated with

Rating

Optical shutter device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical shutter device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical shutter device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2550793