Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2002-05-13
2003-12-16
Spector, David N. (Department: 2874)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S321000, C372S011000, C372S026000
Reexamination Certificate
active
06665111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This present invention relates to a laser beam steering system operable with no moving parts and functional at room temperature.
2. Background Art
The advantages of deflecting and steering optical signals is well known. There are numerous products and industries employing reflected, deflected and steered laser beams for applications such as scanners, laser printer, and laser etching, and in general to the telecommunications and medical industry. Routing laser signals is also useful for a variety of military applications such as counter-measures, range finding, multi-target designation and guidance.
Devices for directing an optical beam or the spatial patterns of illumination produced by lasers have generally been restricted to mechanical methods, such as galvanic mirrors and various mirro/gimbal combinations. The prior art includes many mechanical mirror scanning, acousto-optic and electro-optic methods and apparatus for steering of laser beams, and, the disadvantages of the mechanical methods being bulky, slow, expensive, and relatively inaccurate, and highly susceptible to vibrations and misalignment.
Spatial light modulators are devices having optical properties of the material that are spatially controlled. These light modulator are typically very large compared to the wavelength of light, and have therefore been impractical for obtaining diffraction patterns. Advances in semiconductor technology allow the use of quantum well devices to make smaller spatial light modulators where diffraction effects dominate. These quantum well devices have fast response times, and can be made lithographically using standard fabrication equipment. There has been on-going efforts to create beam steering devices using modulators to eliminate the mechanical devices of the prior art. The optical modulators devices can work in transmission mode, where the light passes directly through the quantum well region, or in reflection mode, where external or integrated mirrors are used to enhance reflectivity changes and contrast.
The prior art has addressed the aspects of light altering the complex refractive index of a semiconductor material, wherein the intensity of an optical wave changes the complex refractive index of Si, GaAs, InGaAsP and other semiconductors in the microwave range (1 mm-1 cm) and infrared (IR) range (1.0 .mu.-100 .mu.). Light induced modulation of both the real and imaginary parts of the refractive index occurs, wherein the real part controls phase and the imaginary part controls amplitude of the modulated electromagnetic field. The real part is primarily responsible for changes in IR waves and the imaginary part for changes in millimeter waves (MMW). This effect is described by Drude theory and involves carrier induced changes in the complex permittivity of metals and semiconductors when illuminated by light.
Under this principle, devices that alter the phase of lightwaves by illumination of semiconductors with a second control lightwave have been developed. In particular, various forms of optical phase modulators have been developed. For example, optically controlled spatial light modulators based on semiconductor materials have been demonstrated. In such an spatial light modulators, optically induced changes in the semiconductor material affect an adjacent layer of electromaterial which in turn affects an EM wave propagating through the electro-optic material.
While spatial light modulators devices transmit some two-dimensional patterns through an optical wave, phased array antennas transmit EM waves in a particular direction in the microwave region without moving parts. A phased array is a network of radiating elements, each of which is usually non-directive but whose cooperative radiation pattern is a highly directed beam because constructive interference occurs between radiating elements. Whereas previous radar antennas had to be mechanically steered for beampointing, the phased array antenna achieves the same effect electronically by individually changing the phases of the signals radiating from each element. Narrow angular band beams can be formed by simply driving each element of the array with an appropriately phased signal. Moreover, electronic steering is much faster and more agile than mechanical beam steering and can form several beam lobes and nulls to facilitate multiple target tracking or other functions such as anti-jamming. The flexibility of electronic steering afforded by phased array radars comes at the cost of individual control of each element. The N elements of the antenna are driven with the same signal but each with a different phase. In practice, a single signal is equally split into N signals to feed the elements, and a phase shifting network, such as those using ferrites or diodes, is provided for individual phase control of each element. For large arrays (i.e., N>100), the complexity of the power splitting network and the cost of providing N phase shifters can become quite high, not to mention the bulkiness of the necessary waveguide plumbing. Moreover, for very large arrays, the computation required to calculate the array phase distribution for a desired radiation pattern is a serious burden.
Phased array antenna theory is based on Fourier optics in general and the theory of diffraction gratings in particular. It is well known from Fourier optics that the optical beam is diffracted in a particular direction if the phase difference between the particular optical rays is a multiple of the wavelength of the optical beam.
With respect to phased array radars, photonic architectures are typically characterized as either optically coherent or non-coherent. Optically coherent architectures are considered impractical because of the thousands of optical signals that must be phase locked.
Military Applications include targeting/guidance and countermeasures systems. The countermeasures system seeks to protect military personnel and property from hostile threats such as missiles, aircraft and helicopters that employ laser tracking systems such as precision guided munitions and other electro-optical guided munitions. For example, a missile with a sensor uses acquisition electronics to home in on a target, such as F22 or F16 aircraft. The aircraft usually has sensors for countermeasures and knows of the missile tracking the aircraft. Thus, missile sees aircraft and aircraft sees missile. The primary function of the aircraft countermeasures system is to blind or distort the missile sensor.
The missile sensor typically operates in the 3-5 micron wavelength range, and the countermeasures systems tries to blind the missile by scanning a pattern with a signal intended to overload or saturate the missile electronics. The aircraft uses a countermeasures laser that operates in the 3-5 micron range and this laser shoots a laser beam at the missile in an attempt to blind the tracking sensor. It is not enough to have a static laser beam that strikes only a portion of the missile, and the countermeasures laser must be scanning or rastering all around the missile threat.
Prior art systems use a camera or other sensor to track the in-coming target and the countermeasure laser mechanically illuminates and tracks the missile using a mirror and gimbal technique. The camera and gimbal are computer controlled in an attempt to focus the laser on the missile by continuously adjusting the mirror by the gimbal. This mirror and gimbal combination is not highly reliable and subject to numerous errors and malfunctions. The stabilization and maintenance of a line of sight on the threat is exceedingly difficult with such a system especially in conditions of excessive vibrations and air turbulence. There are considerable alignment problems with the mirror and gimbal system that make the system inoperable if out of alignment. The gimbal is typically a hydraulic system and the system relies upon the gimbal being able to quickly respond to commands to track the movement of the incoming missile threat.
In addition to being unre
Maine & Asmus
Spector David N.
Teraconnect Inc.
LandOfFree
Laser beam steering system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser beam steering system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser beam steering system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3133772