OPTICAL DEVICE

Abstract: The optical device includes a pair of interfaces (14, 16) spaced one generally behind the other. The rear interface (16) is arranged to deflect incident parallel radiation of radio frequency, while the other (14) is positioned to intersect the parallel radiation of radio frequency but is arranged substantially not to disturb that radiation while deflecting parallel radiation of optical frequency.

Description: "OPTICAL DEVICE' FIELD OF THE INVENTION This invention relates to an optical device which has particular utility as a telescope but may also be employed for simultaneous tracking and transmission purposes. SUMMARY OF THE INVENTION More particularly, the invention provides an optical device comprising a pair of interfaces, spaced one generally behind the other, wherein said one interface is arranged to deflect incident parallel radiation of radio frequency, and the other interface is positioned to intersect said parallel radiation of radio frequency but is arranged substantially not to disturb that radiation while deflecting parallel radiation of optical frequency. It is to be understood that, as employed herein and in accordance with accepted practice, the term "radio" embraces the microwave band and the term "optical", when applied to radiation, frequency or wavelength, embraces the ultraviolet and infrared bands. Preferably, said interfaces are arranged to separately converge coincident radio and optical radiation to differently located foci. In a preferred configuration said one interface and said other interface are respectively reflective to the radio and optical radiation, but said other interface is transparent to the radio radiation. The device may further comprise a surface positioned to receive and reflect said convergent optical radiation, whereby to define a Cassegrain path. There may also be a detector for the deflected radio radiation, which may conveniently be in the plane of the aforementioned Cassegrain reflection surface. In one application, applicable in a dual frequency telescope of conventional optical configuration, the pair of interfaces comprise respective concave reflective surfaces of different focal lengths. In an alternative application, the device may further comprise a source of radiation positioned to transmit radiation along the convergent path of said optical radiation but in the direction towards said other interface. The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a highly schematic representation of an embodiment of optical apparatus comprising a dual optical/radio telescope in accordance with the invention; and Figure 2 is a diagram of the optics of an alternative embodiment of optical apparatus in accordance with the invention, incorporating an optical telescope configured as a celliostat and a radio telescope configured as an off-axis parabaloid. BEST MODES FOR PRACTISING THE INVENTION The dual telescope 10 schematically illustrated in Figure 1 includes an optical assembly 12 which defines a pair of interfaces comprising respective front and rear concave surfaces 14, 16 of different focal lengths. Surface 14 is figured and coated as an optical mirror arranged to converge parallel radiation of optical frequencies while surface 16 is figured as a radio antenna arranged to converge parallel radiation of radio frequencies. In use of the apparatus the optical and radio radiation are co-incident, as indicated by ray lines 8, and both are intersected by surface 14.. However, the material of this surface is chosen so that it substantially does not disturb, and indeed is transparent to, radio radiation. Surface 16 may be clad in polished metal, or other material highly reflective at the radio frequency desired. Assembly 12 is typically not solid but is provided with means to cool surfaces 14, 16, for example by being hollow inside to permit internal circulation of a liquid or gaseous coolant. Convergent optical radiation reflected by surface 14 is further reflected from a secondary, convex, mirror 18 so as to follow a Cassegrain path indicated by ray lines 20, to a Cassegrain focus 22 behind and perhaps to the side of assembly 12. A suitable detector (not shown) may typically be disposed at or near focus 22. • The radio signal reflected from antenna surface 16 is focussed to a radio detector 24 at the centre of secondary mirror 18. It will be appreciated that the configuration depicted in Figure 1 allows the telescope principle axis to be the same for the radio telescope component 16, 24 and for the optical telescope conponent 14, 18, 22. Tracking data from both telescopes may thus be merged with complete confidence. This is to be con¬ trasted with conventional arrangements utilizing side- by-side radio and optical telescopes, in which there may be many microradians of error in translating from one system to the other. An important application of the invention is as a directed energy device utilizing tracking radar and transmission of a beam of optical energy, e.g. a laser beam. With such devices, less than ' one microradian of error is allowable. For example, the configuration of Figure 1 may be utilized to axially lock a microwave radar system, employing ^ the radio telescope component 16, 24, with sub-microradian accuracy to a laser transmitter which utilizes the optical telescope component 14, 18, 22 to transmit the laser beam to precisely the point, perhaps in space, where the radio telescope is "looking". In the latter case, a source of radiation, in the exemplary case a laser resonator, is disposed to transmit radiation along the convergent path of the optical radiation but in the direction towards surface 14. In general, the illustrated device may be employed to simultaneously receive and/or transmit in both radio and optical bands. Another application (not illustrated) is in a purely RADAR/LIDAR mode, where a target is tracked optically or by RADAR, or both simultaneously. The invention has applications to counter stealth anti-radar technology in this mode. Also, the optical tracking is capable of overcoming radar chaff and electronic counter- measures against radar When telescopes of the kind illustrated in Figure 1 are operated jointly, in pairs or arrays containing several or many, the separate radio (e.g. microwave) telescopes can be combined using phased array or synthetic aperture techniques to produce an effective single large telescope. The optical telescopes, which are spatially well defined, can be used for transmitting and receiving, in coherent and incoherent modes. That is, the optical telescopes could transmit as independent directed energy devices or coherently, in phase, to achieve greater effect. Conversely, they can be used as an optical interferometer to detect and map targets. The essential advantage of this inventive device is that capabilities at two widely disbursed frequencies can be axially locked together at a precision for each single instrument which is limited by the diffraction limit of the aperture chosen at the longer wavelength. A further embodiment is shown in Figure 2, where the optical telescope is a celiostat, and the radio telescope is an off-axis parabaloid with prime focus. The focus of the radio telescope moves with both axes of the optical telescope, but this need not always be so. The effective area of the radio and optical telescopes need not always be the same.

Claims: CLAIMS 1. An optical device comprising a pair of interfaces spaced one generally behind the other, wherein said one interface is arranged to deflect incident parallel radiation of radio frequency, and the other interface is positioned to intersect said parallel radiation of radio frequency but is arranged substantially not to disturb that radiation while deflecting parallel radiation of optical frequency. 2. An optical device according to claim 1 wherein said interfaces are arranged to separately converge coincident radio and optical radiation to differently located foci. 3. An optical device according to claim 1 or 2 wherein said one interface and said other interface are respectively reflective to the radio and optical radiation, but said other interface is transparent to the radio radiation. 4. An optical device according to claim 2 further comprising a surface positioned to receive and reflect said convergent optical radiation, whereby to define a Cassegrain path therefor. 5. An optical device according to any preceding claim further comprising a detector for said deflected radio radiation. 6. An optical device according to claims 4 and 5 wherein said detector at the centre of said surface. 7. .An optical device according to any preceding claim wherein said pair of interfaces comprise respective concave reflective surfaces of different focal lengths. 8. An optical device according to claim 2 further comprising a source of radiation positioned to transmit radiation along the convergent path of said optical radiation but in the direction towards said other interface. 9. An optical device according to any preceding claim wherein said interfaces comprise respective spaced surfaces on a common assembly. 10. An optical device according to claim 9 wherein said assembly is provided with means to cool said interfaces.

Inventors: COCHRAN COLIN STEWART, GREENE BENNY ALLAN, COCHRAN, COLIN, STEWART, GREENE, BENNY, ALLAN
Applicants: COCHRAN COLIN STEWART, GREENE BENNY ALLAN, COCHRAN, COLIN, STEWART, GREENE, BENNY, ALLAN
Application year: 1986
Main classification: H01Q15
IPC codes: G02B13, G02B23, H01Q5, H01Q15, H01Q19