Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-03-19
1988-05-03
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356332, G01J 350
Patent
active
047422220
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a selective optical detector apparatus which is adapted for the reception of optical signals, when the spatially extending light bundle is parallel or can be formed into parallel and, when it is also substantially monochromatic. The detector should receive only the light which falls on a narrow wavelength range, and it should be insensitive to light which lies outside of such a range.
Worldwide considerable research efforts have been made in order to widen the operating frequency of locators, communication transmission devices and similar special measuring arrangements, into the optical region.
In the case of opto-electrical devices and measuring arrangements which are intended for the reception of spatially extending (cosmic, atmospheric and underwater signals) direct or reflected signals of slight intensity, the sensitivity of the receiver will become considerably reduced by the background light and interference light which fall onto the sensor surface. The background light and the interference light which fall within the operating angle of the receiver will result in a greatly reduced use of the electronic circuit elements within the receiver by reducing the otherwise available possibilities of sensitivity.
For this reason in the above-mentioned devices frequently the operating difficulties affecting the operating capacities during day and night, are separately listed. The function of a receiver of such opto-electronic devices resides conventionally in the reception of optical signals having a narrow spectrum. The sensing element usually is a photon multiplier or some type of light sensitive semiconductor device, which is adapted for the reception of a relatively wide spectrum and does not possess its own selectivity. In the hitherto known opto-electrical devices the influence of the background light and of the interference light has been attempted to be reduced by a narrowing of the operating angle (the angle of the field of vision) of the receiver and by employing a selective or color filter.
Such a solution has the following disadvantages: the effective angle of the receiver is now limited considerably on one hand due to the technical-technological limitation (stability of the aiming or sighting and of the fixation), and on the other hand, due to the nonuniform character of the transmission medium, the wandering of the light bundle in opto-electronic devices, the selection of the spectrum to be received, and the reduction of the background lights and of the interference lights will necessarily be performed by the use of filters. A relatively good selection can be accomplished by means of an interference filter having a small BW, the spectrum range of which has a value of 5-20 mm. Such interference filters are used in the receiver of many well-known opto-electronic devices. Their common disadvantages resides in that their use will lead to an additional damping. For such an application a number of examples can be found in the corresponding technical literature.
In the publication by B. G. King, P. J. Fitzgerald, and H. A. Steint entitled "An experimental study of atmospheric optical transmission" (The Bell System Technical Journal Vol. 62, No. 3. 1983) a narrow band filter is used in an optical receiver constructed as a communication experiment which will lead to a loss of 3 dB.
In addition to the filters a score of other solutions are used to reduce the influences of the background light and of the interference light, and for example, shielding cassettes are built for the optics and the operating angle of the receiver is limited. In the optical receiver according to M. J. Green entitled "Application of an Optical Data Link in an Airborne Scanning System" (Review of Scientific Instruments, Vol. 53, No. 8, 1982, pages 1278-1280), an infrared filter is used for filtering out the visible light, which, however, will not lead to any special result.
In the optical system according to G. Michael Lauham entitled "Air Force Lasercom Space Measureme
REFERENCES:
patent: 3185021 (1965-05-01), Thompson
patent: 3563659 (1968-02-01), Thompson
patent: 4585349 (1986-04-01), Gross et al.
Retfalvy Gyorgy
Sugar Peter
Zorkoczy Zoltan
Nelms David C.
Ruoff Jessica L.
Tavkozlesi Kutato Intezet
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