RU2312372C2 - Arrangement for detection and diagnostics of the sources of optical radiation - Google Patents

Abstract

FIELD: the invention refers to optics-electron arrangements designed for detection the sources of optical radiation and diagnostics the optical characteristics of these sources.

SUBSTANCE: the proposed arrangements have a panoramic mirror objective with a numerical aperture more then 0,5, an angular field of vision 360⁰ along the horizon and no less then -5⁰ +25⁰ along the vertical line, negative distortion no less then 50%, a photo receiving arrangement, a signals analysis block which is fulfilled with possibility to execute measuring of amplitudes, duration and periods of signals radiated by sources of optical radiation. The technical result is in simplification of the optical tract, in increasing the working spectral range, in increasing sensitiveness, in providing possibility to gain information about optical sources of radiation in the angular field of vision 360⁰ along the horizon and no less(-5 +25)⁰ along the vertical line, in providing possibility of gaining temporary information from the channels.

EFFECT: provides diagnostics of spectral characteristics of the sources of optical radiation.

2 cl, 5 dwg

Description

The invention relates to optical electronic devices designed to detect sources of optical radiation and diagnose the optical characteristics of these sources. The primary field of application of the proposed devices is security systems for various purposes, direction finding, television and thermal imaging devices, robotics control systems, navigation systems.

Known optical-electronic direction finder based on the HARLID sensor (US, patent No. 5428215), which allows to determine the angles of arrival of radiation with an accuracy of ± 1 ° in a field of ± 90 ° horizontally, containing an optical system based on cylindrical lens elements or a slit diaphragm forming a light strip on a mask made in accordance with the Gray code, behind which are photosensitive elements.

Also known is the development of a sensor from Defense Research Establishment, Canada (A. Cantin, J. Dubois, P. Webb and MP Altman "Miniaturized digital High Angular Resolution Laser Irradiation Detectors (HARLID ™) for Laser Warning Receivers" SPIE Vol.3061, 1997) in which two photosensitive elements based on Si and InGaAs are located one below the other. This approach allows you to expand the range of the spectral sensitivity of the sensor from 0.4 ... 1.1 to 0.4 ... 2.1 μm and, in addition, to increase the stability of the system to the influence of artificial and natural optical noise.

These devices have several disadvantages, the most significant of which are:

- due to the use of an anamorphic optical system, it is fundamentally impossible to implement an optical path with high relative apertures and image quality;

- the optical system of the direction finder forms a field of view along the horizon of not more than 100 ° ... 120 °;

- the working spectral range of the direction finder is narrow and is determined by the spectral sensitivity of the Si, InGaAs based photodetectors, superconducting bolometers or Ge, and when using an anamorphic optical system it deteriorates due to absorption in its lens components.

A device is known, proposed to eliminate the first of the above disadvantages (US patent No. 5627675 from 05/06/1997, John E. Davis). In it, the image of the field of view is formed by a radially symmetric optical system. This technical solution can significantly increase the effective area of the entrance pupil. However, the relative aperture of the device described in the patent under discussion does not exceed ~ 1: 3.

Closest to the proposed devices is a device (US patent No. 5710661 from 01.20.1998, Int. CI ⁶ G02B 17/00) containing an optical system, a photodetector and an electronic signal processing unit. It has a number of advantages, the main of which are:

- the image of the viewing area is formed by a radially symmetric optical system, which allows to provide a significant area of the entrance pupil (6.25 mm ² );

- the relative aperture of the optical system is brought to 1: 2;

- the device’s design layout allows the use of a cryogenic photodetector (the authors, first of all, suggest using InSb-based photocouplers), which provides good sensitivity in the spectral range up to 5 μm.

However, the known device also has disadvantages:

- the achievement of a relatively high relative aperture and, as a result, a significant area of the entrance pupil, is achieved by a significant complication of the optical path - it contains, in addition to aspherical mirrors, seven more aspherical lenses; the presence of lenses is especially undesirable, because this inevitably limits the possible working spectral range of the device, as the authors themselves note;

- the use of a two-dimensional, fully filled matrix (the authors recommend an InSb-based matrix with a format of 480 × 480), the reading of signals with which is possible with a frame frequency of not more than hundreds of Hz, which severely limits the ability to extract time information from signals, and this is especially undesirable when working with pulsed sources, for example laser;

- the presence of FPU, operating in the spectral range up to 5 μm, makes it difficult to obtain information about the spectral characteristics of sources, which prevents their diagnosis;

The objective of the invention is to simplify the optical path, increase the working spectral range, increase sensitivity, provide the ability to extract information about optical radiation sources in the angular field of view 360 ° horizontally and at least -5 ° ... + 25 ° vertically, provide the ability to extract from signals of temporal information and diagnostics of spectral characteristics of sources.

The technical result in the first embodiment of the invention is achieved by the fact that the device for detecting and diagnosing optical radiation sources comprises a lens, a photodetector, a signal analysis unit and a dichroic beam splitter forming image planes in which there are photodetector multichannel devices pairwise paired in the space of objects, photodetector channels which are configured to provide different monotonic spectral characteristics, the lens consists of it consists of mirror components and has a numerical aperture of more than 0.5, an angular field of view of 360 ° horizontally and at least -5 ° ... + 25 ° vertically, negative distortion of at least 50%, the signal analysis unit measures amplitudes, durations and periods of signals emitted by optical radiation sources.

The technical result in the second embodiment of the invention is achieved by the fact that the device for detecting and diagnosing optical radiation sources comprises a lens, a photodetector and a signal analysis unit, wherein the lens consists of mirror components and has a numerical aperture of more than 0.5, an angular field of view of 360 ° horizon and at least -5 ° ... + 25 ° vertically, negative distortion of at least 50%, a multichannel photodetector is a multilayer photosensitive structure, each layer of which it has different spectral sensitivity, the signal analysis unit is configured to measure the amplitudes, durations and periods of the signals emitted by the optical radiation sources.

The invention is illustrated by drawings, where:

Figure 1 shows the scheme of separation of light beams, providing the ability to install multi-channel photodetectors (for the first embodiment of the device for detecting and diagnosing sources of optical radiation).

Figure 2 shows the optical circuit of the lens.

Figure 3 shows the block electronic signal analysis.

Figure 4 shows the configuration of the photosensitive element for determining the horizontal coordinate of the optical radiation source.

Figure 5 shows the configuration of the photosensitive element to determine the horizontal and vertical coordinates of the optical radiation source.

Appendix 1 - lens data with three spherical mirrors.

The device for detecting and diagnosing optical radiation sources according to the first embodiment comprises a lens 1, photodetectors 2 and 3, a dichroic beam splitter 4 (Fig. 1) and an electronic signal analysis unit (Fig. 3). In the example shown in FIG. 1, a dichroic beam splitter 4 forms two image planes, and multi-channel photodetectors 2 and 3 are associated with these planes.

The lens forming the image of the spherical belt contains a convex primary mirror, a convex secondary mirror and a concave tertiary mirror. In the particular case, the mirrors may have a spherical shape. A specific example of such a special case is given in Appendix 1, and the corresponding optical scheme of the lens is shown in (Fig. 2). As follows from Appendix 1, the relative aperture of such an optical system can be brought to such a high value as 1: 0.5966.

The achievement of such a significant relative aperture improves the overall characteristics of the proposed device for two reasons:

- an increase in the area of the entrance pupil;

- reducing the area of the photosensitive elements of the FPU and, as a result, improving the threshold sensitivity of the device.

The provision of requirements for maximizing the relative aperture of the optical system in the proposed device is especially important to ensure the required potential in the entire ultra-wide spectral range for the following reasons:

- taking into account that the spectral sensitivity of photonic photodetectors increases with increasing wavelength of the detected radiation;

- by virtue of providing the necessary energy potential for detecting radiation in a very wide spectral range of 0.4 ... 16 μm due to a drop in spectral sensitivity to the short-wavelength limit of the range.

The choice of a purely mirror version of the lens of the proposed device is explained by the absence of chromatism introduced by the lens optical elements, and therefore, the proposed lens, using the appropriate coatings, can form an image at almost the maximum relative aperture, in almost the entire optical range.

The dimensions of the aberration spots formed by the described optical system depend on its relative aperture, vertical angular field of view, the scale of the system, and also on the number and order of applied aspherical surfaces. It should be said that such a level of forcing of the optical characteristics of the system will be optimal that the sizes of aberration spots are comparable to the selected size of the photosensitive elements of the FPU. This is precisely the level of forcing achieved in the optical system, the data on which are given in Appendix 1.

Obtaining an image of a zone located in the space of objects for which the angular field of view exceeds 180 °, subject to a finite size of the photosensitive region of the FPU, is possible only in the presence of negative distortion. The magnitude of this distortion should have some optimal value, depending on the given tactical and technical characteristics: large enough to possibly reduce the size of the photosensitive region of the FPU, but not excessive, since otherwise the accuracy of determining the vertical angular coordinate of the detected sources will not be ensured. For this reason, it is difficult to clearly define the desirable boundaries of negative distortion, and the authors have accepted the value that seems to them a reasonable compromise.

For a device that registers information from a significant part of the space surrounding it, a spherical coordinate system is the only system providing isotropy of the direction-finding characteristic. The projection of the spherical coordinate system of the space of objects into the space of images leads to the natural polar configuration of the photosensitive zone of the FPU. In the simplest case, such a configuration may take the form of a photosensitive ring, broken into trapezoidal "petals" (figure 4). The need to determine the vertical coordinate of the sources leads to a multi-ring structure (figure 5). The fundamental possibility of determining the angular coordinates of the source of optical radiation is a necessary but not sufficient condition for its detection and, especially, diagnosis. A complete solution to the problem is provided by obtaining additional information about the temporal parameters of the radiation and its optical spectrum. Determining the temporal parameters of radiation is a complex problem. To solve it, the FPU must have sufficient sensitivity and a sufficiently wide bandwidth of electrical frequencies. Typical sources of interest can emit pulses of optical radiation with durations from a few nanoseconds to hundreds of milliseconds, as well as modulated continuous radiation at frequencies from hundreds of Hz to tens of kHz. An additional complicating factor is the necessary very wide range of spectral sensitivity of the FPU, from about 0.4 to 16 microns. At the current level of development of photoelectronics, the CdHgTe-based FPUs at various cooling levels largely satisfy these requirements.

The electronic signal analysis unit has the following structure (see figure 3). N inputs correspond to the number of photosensitive FPU channels. Each of the N inputs translates the signal into two subunits of analysis. The first subunit contains a parallel comb of M filters, consistent with the pulse durations emitted by the sources of interest. Behind each of the filters there is a pulse amplitude meter. Thus, the first subunit provides optimal detection of pulsed optical radiation, measuring the duration, amplitude and period of the pulses. The second subunit is intended for the analysis of continuous signals. It measures their frequency and amplitude.

The inventors do not specify methods for measuring amplitudes, durations, and periods of electrical signals that can be used in a signal analysis unit, because these methods are developed in detail in the framework of classical radio engineering and, by themselves, do not have elements of significant novelty.

The optical spectral characteristics of the sources are determined as follows: in the first embodiment of the proposed device, in each of the two image planes (the example shown in Fig. 1) there are congruent photosensitive structures having different, but necessarily monotonic spectral sensitivity characteristics. The implementation of such a solution has long been known: by installing optical filters with different spectral sensitivity in front of each FPU or by choosing materials differing in spectral sensitivity of each FPU and in other ways. In the space of objects, the angular position of each of the photosensitive channels located in one of the planes coincides with the conjugate channel located in the second plane. Under this condition, the ratio of the amplitudes from these pairwise conjugate channels will carry information about the spectrum of the optical radiation source.

In the second embodiment, the device for detecting and diagnosing optical radiation sources comprises a lens, a multichannel photodetector and an electronic signal analysis unit (Fig. 3). The design of the lens and the signal analysis unit for the second embodiment of the device is similar to their design for the first embodiment of the device.

The photodetector is a multilayer photosensitive structure, each layer of which has a different spectral sensitivity.

The multilayer photosensitive structure necessary for the second variant of the proposed device, the layers of which have different spectral characteristics, can be realized by varying the stoichiometric composition of the CdHgTe compound, as well as creating a multilayer photosensitive element from various semiconductor materials and other known methods.

As follows from the above, the proposed device allows to obtain the following information about the source of optical radiation: angular coordinates, optical spectral characteristics, the amplitude of the signal generated on the entrance pupil of the device and, thus, the irradiation on the entrance pupil, the duration of the emitted pulses, period, in the case of continuous radiation mode. It is proposed to include all these values as components in the target feature vector, which, according to the authors, will provide a significantly higher probability of detecting sources of optical radiation compared to the prototype, as well as sufficient resistance of the device to natural optical interference.

Claims (2)

1. Device for detecting and diagnosing optical radiation sources, comprising a lens, a photodetector multichannel device and a signal analysis unit, characterized in that a second photodetector multichannel device and a dichroic beam splitter are introduced, forming two image planes, each of which contains photodetector multichannel devices, in pairs space-conjugated objects whose photodetector channels are configured to provide different monotonous specs directional characteristics, the lens consists of mirror components and has a numerical aperture of more than 0.5, an angular field of view of 360 ° horizontally and at least -5 ° ... + 25 ° vertically, negative distortion of at least 50%, the signal analysis unit with the possibility of measuring the amplitudes, durations and periods of the signals emitted by the sources of optical radiation. 2. A device for detecting and diagnosing optical radiation sources, comprising a lens, a photodetector multichannel device and a signal analysis unit, characterized in that the lens consists of mirror components and has a numerical aperture of more than 0.5, an angular field of view of 360 ° horizontally and not less than -5 ° ... + 25 ° vertically, negative distortion of at least 50%, the multichannel photodetector is a multilayer photosensitive structure, each layer of which has a different spectral sensitivity In fact, the signal analysis unit is configured to measure the amplitudes, durations, and periods of the signals emitted by the optical radiation sources.

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