Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2000-04-07
2002-08-27
Lester, Evelyn A (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S263000, C359S245000, C359S318000, C359S322000, C359S584000, C359S572000, C359S385000, C359S010000
Reexamination Certificate
active
06441947
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electro-optic device of the kind appropriate for optical beam steering applications.
BACKGROUND OF THE INVENTION
Agile optical beam steering is often required in applications ranging from laser radar ranging to free-space optical communications. In a free-space optical communication system, beam steering is required to maintain the lock between the transmitter and receiver when either or both may be moving or may be affected by vibrations. In laser radar ranging, beam steering provides the ability to track moving or maneuvering targets. These applications require the ability to quickly steer an optical beam to a new direction, that is, they require agile optical beam steering.
One way in which to achieve beam steering is to transmit an optical beam onto a device that will reflect the beam in a different, but controllable direction. The beam steerer provides control over the angle between the optical beam incident on the beam steerer and the optical beam reflected by the device. A high performance beam steering system should provide a minimum of loss between the incident beam and the reflected beam.
Optical beam steering can be implemented with electro-mechanical systems. Such systems generally consist of a mirror mounted on an electrical actuator. These systems provide relatively low losses for the strength of the reflected beam. However, such electro-mechanical systems are limited to low response frequencies up to the order of 1 KHz. The moving parts of an electro-mechanical system along with size and weight factors are considered to be major limitations of such a system.
Electro-optical devices for optical beam steering are also known. One such device is disclosed in U.S. Pat. No. 4,639,091, issued Jan. 27, 1987 to J.-P. Huignard et al. Huignard discloses an optical beam steerer comprising an electro-optical liquid crystal having an upper side upon which strip electrodes are disposed and a lower side upon which a common electrode, reflective at the optical beam wavelength, is disposed. A step voltage waveform is applied to the electrodes, which causes local variations in the index of refraction within the liquid crystal. These variations create a diffraction grating, which is used to provide steering of a beam incident on the device. One of the shortcomings of the invention disclosed by Huignard et al. is the poor response time of the liquid crystal molecules to the variation in voltage. Hence, the steering angle cannot be quickly changed.
Another optical beam shifter using a liquid crystal is disclosed in U.S. Pat. No. 5,018,835, issued May 28, 1991 to T. A. Dorschner. Dorschner also discloses a liquid crystal with electrodes on its upper side and lower side. Additional refractive means are interposed between the incident optical beam and the liquid crystal, which allows a thinner liquid crystal to be used. A thinner liquid crystal provides faster response time to voltage variations, and thus, faster beam steering. The invention disclosed by Dorschner is still limited by the response time of the liquid crystal material, which will only allow beam steering rates on the order of 1 to 10 KHz. An additional shortcoming is that the beam angle is only steered in one dimension, the dimension defined by the plane that is perpendicular to the orientation of the surface of the liquid crystal.
A faster electro-optical beam steering device is described by J. A. Trezza, et al. in “Large Format Smart Pixel Arrays and Their Applications,” IEIEE 19th Aerospace Conference, Aspen, Colo., p. 299. It comprises modulator-emitter-detector (MED) GaAs based devices grouped together and connected in parallel to custom SRAM CMOS driver chips. Each device comprises a pixel in the array, and current technology allows the pixels to be closely spaced. Each pixel consists of quantum wells, and the refractive index of each pixel can be varied by changing an electric field applied across the pixel. Phase modulating the pixels within the array provides the capability of steering an optical beam incident on the array. Current technology provides the beam steering rates in two dimensions on the order of 20 MHz. However, the transmit efficiency of the device is quite low, where the intensity of reflected light is less than 10% of the intensity of the incident light.
Optical beam steering may also be provided by directing light through a device in which the angle of the light is changed. One such device is disclosed in U.S. Pat. No. 5,082,342, issued Jan. 21, 1992 to D. R. Wight, et al. Wight discloses an electro-optic waveguide device containing an array of electrically biasable waveguides of electro-optically active material. The array of waveguides creates a farfield diffraction grating. An electric field applied to the waveguides alters the refractive index within the waveguides. Changes in the refractive index change the diffraction angle resulting in shifts in the main lobe of the diffraction pattern generated by light sent through the device. Shifting the main lobe essentially results in steering the angle of an optical beam transmitted into the device. Wight also discloses an arrangement of the waveguides that allows for beam steering in two dimensions.
The invention disclosed by Wight provides substantially faster beam steering rates than the inventions earlier described. Choice of the appropriate electro-optically active material could provide steering rates in excess of 1 GHz. However, the device still has some limitations. Transmission of light through the device and the creation of a diffraction pattern may result in significant losses to light intensity and thus limit the utility of the device. In addition, manufacture of the device described by Wight is complicated. Creation of the two-dimensional beam steering device would require a micro-manipulation apparatus. Finally, the device provides no mechanism for compensating for beam dispersion for the optical beam incident on the device.
There exists a need in the art for an optical beam steering device that can provide high rate beam steering without significant loss of intensity to the steered optical beam. The need also exists for a device that can provide those capabilities and steer an optical beam in two dimensions. The need also exists for an optical beam steerer that can provide some measure of optical wavefront correction.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method and apparatus for optical beam steering that can provide low loss, high rate beam steering. It is another object of the present invention to provide such beam steering in one and two dimensions. It is a further object of the present invention to provide for optical wavefront correction.
These and other objects of the present invention are accomplished by providing at least one layer of electro-optically active material within which is formed a chirped distributed Bragg reflector. The chirped distributed Bragg reflector is oriented in the electro-optically active material so that the direction of propagation of the chirped distributed Bragg reflector is parallel with light incident on the electro-optically active material. The chirped distributed Bragg reflector reflects optical beams at different wavelengths from the electro-optically active material after those beams have traveled different distances within the electro-optically active material. An electric field is applied across the electro-optically active material in a direction parallel to the direction of propagation of the chirped distributed Bragg reflector. The applied electric field causes changes in the local index of refraction within the electro-optically active material, where the local index of refraction will vary with the intensity of the electric field. Changes in the local index of refraction will vary the distance at which an optical beam at a specific wavelength will travel within the electro-optically active material. The varying distance will cause the wavefront of the incident optical beam t
HRL Laboratories LLC
Ladas & Parry
Lester Evelyn A
LandOfFree
Method and apparatus for optical beam steering based on a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for optical beam steering based on a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for optical beam steering based on a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2965834