Polychromatic beams are separated into component colors or wavelength bands by wavelength selective filters combined with a beamsplitter. These filters are arranged on three sides of a cubic space, with a beamsplitter on the diagonal. The space may be air or a cube of transparent material, such as glass. If the beam is to be split into more than three colors, a second cube is used with additional beamsplitters. At least one filter which receives a beam split by the beamsplitter, either the filter which receives the transmitted beam or the reflected beam, must be a reflecting filter which reflects the wavelengths that are not transmitted. Preferably such filters are interference filters. Two or three reflecting filters give better energy utilization. The beamsplitters may be chromatic or achromatic. Phase retardation plates compensate to polarization effects. The invention is particularly useful with electrical signal detectors for readouts for coded marks using photoluminescent components forming the code.
CROSS-REFERENCES
This application is a continuation-in-part of application Ser. No. 810,476, Mar. 26, 1969 entitled "SEPARATION OF POLYCHROMATIC LIGHT BEAMS INTO THEIR CONSTITUENTS BY MEANS OF WAVELENGTH SELECTIVE MIRROR SYSTEM," now U.S. Pat. No. 3,527,523.
First and second dielectric multilayer film filters are disposed along a straight optical axis and inclined about 45.degree. with respect thereto. The second filter is rotated about the optical axis by a predetermined angle with respect to the first filter so as to divide a path of light incident upon or emitting from the first filter into a first path of light transmitting through the first and second filters, and a second path of light reflected by the first filter. The second path is orthogonal to the first path. The apparatus is used for separating or synthesizing light signals.
A method of real-time color masking is disclosed wherein pairs of color filters are inserted at specific locations in the optical paths of an electro-optical image multiplication system to thereby produce a modulated radiation pattern representative of the product of the reflectance of the positive of one color component and the negative of other color components of the original.
A wavelength-division multiplexing optical transmission system is disclosed which transmits light of wavelengths .lambda..sub.1, .lambda..sub.2 and .lambda..sub.3 (.lambda..sub.1 <.lambda..sub.2 <.lambda..sub.3) by way of a single optical fiber. An optical multiplexer/demultiplexer of the filter type is used which includes a parallelogram prism, a first filter formed on a side face of the parallelogram prism, and second and third filters formed on the opposite side face of the parallelogram. Bidirectional optical fiber communications between the central telephone exchange side and a subscriber side can be achieved using such optical multiplexer/demultiplexer of the filter type. With the arrangement of the invention, an optical multiplexer/demultiplexer of the filter type can be produced at a low cost without the necessity of using a filter having a wide stopping band as a filter to be formed on a parallelogram prism.
An optical modulator which is capable of passing the greatest intensity of light incident upon it when the light incident upon it is either unpolarized or has a partial or variable state of polarization, comprises a beam splitter (1) to resolve the light beam incident upon it into two plane polarized components having mutually perpendicular polarization states, one or more electro-optic cell or cells (2,18,19,22,23) which is or are arranged to receive both components of the light beam and, in use change the state of polarization of both of the components to a corresponding extent in dependence upon an electrical modulation signal applied to it or them. The optical modulator also includes analyzer means (1,17) arranged to receive the output from the electro-optic cell or cells (2,18,19,22,23) the arrangement being such that the intensity of the light output from the analyzer means (1,17) is a function of the change of the state of polarization generated in both components during their passage through the electro-optic cell or cells (2,18,19,22,23). The beam splitter and the analyzer means may be formed by the same piece of apparatus (1) and in this case the modulator preferably includes a half wave plate in the light path of both components to change their polarization states.
An illumination optical system for supplying polarized illumination light to an object to be illuminated. The light from a light source is separated by a polarizing beam splitter into a first polarized light component as the illumination light and a second polarized light component which is different in polarizing direction from the first polarized light component. A first reflecting optical member for returning the second polarized light component to the light source side and a converging optical system are arranged in such a manner that a light source image due to the backward light from the first reflecting optical member is formed at a position apart from the light source in a direction substantially perpendicular to the optical axis of the converging optical system. The backward light is converted by a polarizing element to a polarized light of the same polarizing direction as the first polarized light component and it is again emitted from the polarizing beam splitter at an optical axis position adjacent to the first polarized light component.
