An automobile identification system and a method for producing it are disclosed. The system utilizes a conventional license plate with alpha-numeric characters conveying identifying information perceptible by the unaided eye in combination with a hologram embodying encoded identifying information which cannot be decoded by the unaided eye.

An identity card is secured against forgery of the information thereupon and the appearance thereof by imparting coded information holographically to a photosensitive sheet of the card as coded, binary, optical bits in a pair of overlapping holograms, one hologram being readable only in coherent visible light and the other being readable only in coherent light outside the visible spectrum. The information is thereby made machine-readable.

A falsification-proof identity card comprises a first transparent layer on the underneath side of which conventional data is applied by printing technology. The card contains a holographic safeguard and additional safety measures such as metal structures, fluorescent structures, safety imprints and the like which are only visible in response to holographic reconstruction and/or other light applications, such as ultra-violet light. The holographic safeguard comprises a second transparent or non-transparent layer which carries on the entire surface which faces the first layer a phase hologram or an amplitude hologram which can be read out by light transmission or by light reflection, depending on the transparency of the layer, and which contains at least the visible data printed on the first layer in a direct recording.

Vehicle (4) are automatically identified using a specially constructed windshield (8) which carries identifying indicia (10). The window is a layered construction, similar to safety glass, and includes an intermediate layer (20) sandwiched between inner and outer glass layers (22, 24). The intermediate layer carries the identifying indicia, typically in a bar coded pattern. The indicia are invisible to the unaided human eye but are detectable when illuminated with a chosen electromagnetic radiation, typically infrared light from a CO.sub.2 laser. The bar coded indicia are preferably unique to the particular vehicle. Since the bar coded indicia can cover substantially an entire windshield, and since windshields are normally kept clean, sensing of the indicia is aided. The vehicle identification system thus permits the non-invasive identification of a vehicle even under adverse environmental condition.

A method and apparatus for holographically processing optical signals in a fiber-optic sensor system. In the present invention, holographic processors are utilized in various combinations with light sources, fiber-optic transmission means, sensors and detectors to provide low cost, compact, sensitive and accurate sensor systems. By means of the holographic processors of the present invention, the aforementioned sensor systems are used to monitor such physical parameters as temperature, pressure, flow-rate, and the like, and to provide output signal indications thereof that are compatible with digital receiving stations and immune to electro-magnetic interference, hazardous atmosphere, and the inimical effects of inadvertent intensity variation due to equipment vibration and the like. In one typical embodiment, a pair of holographic processors are employed in a color multiplex-demultiplex sensor system in which a first holographic processor is employed to color multiplex a sensor signal and a second holographic processor is employed to decode the color-multiplexed signal into a binary pattern that is then transmitted onto a set of photodetectors. In each of the embodiments of the invention disclosed, a unique geometrical orientation of a hologram is utilized to minimize spurious signal interference that would otherwise hamper or totally preclude the holographic processing.