Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1995-03-02
1998-05-26
Dzierzynski, Paul M.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 3, 359569, G02B 532, G02B 518, G03H 102
Patent
active
057575231
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB93/01591 filed on Jul. 28, 1993.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device, particularly an antenna device, for emitting a beam of optical radiation to irradiate a remote target area. The invention also concerns an optical free space communication system where an antenna device is transmitting a signal over distances ranging from around half a meter up to several kilometers and where the remote target area is at least 0.5 m.sup.2.
2. Related Art
It is well known that a laser can be used to produce a sharply defined and intense beam of infra-red radiation, and that a conventional lens can spread this beam out over a target area. Other point sources, such as infra-red light emitting diodes, can also produce sharply defined directional beams and are used, for example, to illuminate target areas in remote television and video control apparatus.
In general, however, when irradiating a remote target area with optical radiation, much of the radiation from the original source inevitably falls outside the target area and is wasted. Moreover, although the angle of divergence of a beam can be controlled, there is little or no control over the intensity distribution within the beam or he shape of the beam envelope. It is particularly difficult to illuminate a square, rectangular or other non-circular target area with a uniform intensity beam. In an optical free space communication system where the radiation is carrying a telecommunication signal, the spillage of energy can also result in inadvertent detection of the signal by a detector outside the target area.
With intensely bright optical sources, such as lasers, there is also a risk that the infra-red radiation could be inadvertently focused by a lens, for example a binocular lens, on to the skin, or worse still, the retina, and cause permanent damage. This latter problem is particularly acute at high power levels i.e. levels exceeding a few milliwatts and restricts the possible use of high power sources, including both light emitting diode (LED) and laser emitters, in an optical free space communication system, or in any application where optical radiation is emitted into a populated area.
A paper entitled "Transforming a circular laser beam into a square or trapezoid-almost" (Optical Engineering Vol. 31, No. 2, February 1992 pp. 245-250) discusses how a computer-generated hologram positioned in the path of a laser beam can be arranged to transform the shape of the beam from, say, a round beam into a square beam with rounded corners. The transformation is based on the phenomenon that an aberrated laser beam will change shape as it propagates.
A further pacer entitled "Efficient optical elements to generate intensity weighted spot arrays: design and fabrication" (Applied Optics Vol. 30, No. 19, pp. 2685-2691), discusses the design and fabrication of holographic beam splitters for producing multiple beams from a single coherent beam. The computer-generated patterns are made into surface relief diffraction elements or phase gratings by electron-beam lithography followed by plasma etching into quartz glass. Such elements are therefore expensive to produce and are for use in laboratory and in optical parallel computing systems where the multiple beams provide the optical power supply to arrays of modulators or logic devices.
SUMMARY OF THE INVENTION
According to the present invention such elements are designed so that when the beam splitter hologram pattern is positioned in the path of a beam originating from a coherent optical source emitting radiation predominately in a wavelength band having an upper limit less than twice the lower limit, the pattern scatters the incident wavefront into a multiplicity of beams at different angles and out of phase with one another such that the beams cannot be refocused by a lens to reproduce an image of the source.
In addition, when the element is used in an optical free space communication system, the optical radiation is modulated with a teleco
REFERENCES:
patent: 3882207 (1975-05-01), Hannan et al.
patent: 4214807 (1980-07-01), Gefeller et al.
patent: 4504122 (1985-03-01), Bartholomew
patent: 4626069 (1986-12-01), Dammann et al.
patent: 4960314 (1990-10-01), Smith et al.
patent: 5056880 (1991-10-01), Barbanell
patent: 5289299 (1994-02-01), Paek et al.
patent: 5412506 (1995-05-01), Feldblum et al.
Smyth et al, "Optical Wireless: New Enabling Transmitter Technologies", IEEE International Conference on Communications '93, May 23-26, 1993, Geneva, Switzerland, vol. 1, 26 May 1993, pp. 562-566.
Sweatt, "Transformimg a Circular Laser Beam Into a Square or Trapezoid-Almost", Optical Engineering, vol. 31, No. 2, Feb. 1992, Bellingham US, pp. 245-250 XC257531.
Dames et al, "Efficient Optical Elements to Generate Intensity Weighted Spot Arrays: Design and Fabrication", Applied Optics, vol. 30, No. 19, 1 Jul. 1991, New York US, pp. 2685-2691.
Smyth Peter Paul
Wood David Charles
British Telecommunications public limited company
Chang Andrew
Dzierzynski Paul M.
LandOfFree
Optical radiation devices 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 radiation devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical radiation devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1969045