WO2006061819A1

WO2006061819A1 - Complementary masks

Info

Publication number: WO2006061819A1
Application number: PCT/IL2005/001256
Authority: WO
Inventors: Ofer David
Original assignee: Elbit Systems Ltd.
Priority date: 2004-12-07
Filing date: 2005-11-24
Publication date: 2006-06-15
Also published as: IL165618A0

Abstract

Apparatus for detecting the direction of light, arriving essentially collimated, the apparatus including at least one pair of masks, at least one aperture, a respective pair of detectors for each pair of masks, and a respective summator for each respective pair of detectors, each pair of masks including a mask and a complementary mask, each detector, of the respective pair of detectors, including at least one sensor, the aperture being located in front of the pair of masks, one detector, of the respective pair of detectors, being optically coupled with the mask of the respective pair of masks, the other detector, of the respective pair of detectors, being optically coupled with the complementary mask of the respective pair of masks, the summator being electrically coupled with the respective pair of detectors, wherein the mask is optically encoded and the complementary mask is complementarily optically encoded with respect to the mask, the aperture distributing light differently on the pair of masks for light impinging on the apparatus from different directions, wherein the respective pair of detectors detects light received from the respective pair of masks, and wherein the summator subtracts a signal received from one detector, of the respective pair of detectors, from a signal received from the other detector, of the respective pair of detectors, thereby producing a respective subtraction result.

Description

COMPLEMENTARY MASKS

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to systems for detecting and determining the direction of laser radiation sources in general and to methods and systems for detecting and determining the direction of such sources independent of the intensity of the laser radiation, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE The use of laser guided weapons in combat has long been known to militaries around the world. Various forms of weapons ranging from handguns to missiles, found in a wide range of vehicles like tanks and fighter planes, use some form of laser radiation to pinpoint and hone in on targets. As research and techniques in this field have grown, so have research and techniques been developed in its complementary field, that of detecting and determining the direction of the laser sources

One such technique for detecting and determining the direction of a laser source associated with laser guided weapons involves using an encoded mask. The basic technique is illustrated in Figure 1A, which is a perspective schematic illustration of generalized system 20 utilizing the encoded mask technique. System 20 includes plate 24, encoded mask 28, detectors 34A, 34B, 34C, 34D and 34E, leads 38A, 38B, 38C₁ 38D and 38E and processor 40. Plate 24 includes small thin slit 26 which extends over the length or width of plate 24. Plate 24 is located above encoded mask 28. A space exists between plate 24 and encoded mask 28 to allow system 20 to function properly. Encoded mask 28 includes openings 32 and opaque sections 30. Leads 38A, 38B, 38C, 38D and 38E connect detectors 34A, 34B, 34C, 34D and 34E to processor 40. Leads 38A, 38B, 38C, 38D and 38E are generally connected to operational amplifiers (not shown) that amplify signals received from detectors 34A, 34B, 34C, 34D and 34E. The amplified signals are then provided to processor 40. Detectors 34A, 34B, 34C, 34D and 34E, leads 38A, 38B, 38C₁ 38D and 38E and processor 40 can all rest directly on top of one another.

System 20 works in the following generalized manner. Laser radiation 22 arrives from a source. The distance from the source of laser radiation 22 to the detector is usually large enough, compared to the size of thin slit 26, such than when laser radiation 22 reaches plate 24, laser radiation 22 is substantially collimated, which means that all the beams of laser radiation 22 arriving at plate 24 are parallel to one another. All of the beams arrive at plate 24 with same angle 25 with respect to plate 24. It is noted that all of the angles referred to in Figure 1A, are with respect to plate 24. Thin slit 26 allows only a thin strip of laser radiation 22 to fall incident 31 on encoded mask 28.

Encoded mask 28 is composed of openings 32 and opaque sections 30. Openings 32 allow laser radiation 22 incident 31 on encoded mask 28 to fall incident 36 on detectors 34A, 34B, 34C, 34D and 34E. Opaque sections 30 do not allow laser radiation 22 incident 31 on encoded mask 28 to fall incident 37 on detectors 34A, 34B, 34C, 34D and 34E. The openings and opaque sections of encoded mask 28 are arranged in such a way that different patterns of laser radiation 22 are produced on detectors 34A, 34B, 34C, 34D and 34E for different incident angles 25 of laser radiation 22 on plate 24. In this manner mask 28 is encoded, because different incident angles 25 of laser radiation 22 on plate 24 produce different detection patterns on detectors 34A, 34B, 34C, 34D and 34E according to a specified code. The precision to which incident angle 25 of laser radiation 22 on plate 24 can be determined depends on the encoding scheme used on encoding mask 28, the number of detectors used, the width of thin slit 26 and the distance between plate 24 and encoded mask 28. The range of detectable angles of incidence depends on the distance between plate 24 and encoded mask 28. The smaller the distance between plate 24 and encoded mask 28, the more limited the range of detectable angles of incidence, and the smaller the field of view of system 20. The larger the distance between plate 24 and encoded mask 28, the broader the range of detectable angles of incidence, and the larger the field of view of system 20. When laser radiation 22 falls on detectors 34A, 34B, 34C, 34D and 34E, each detector transmits a signal, via leads 38A, 38B, 38C, 38D and 38E, whereby the signals are amplified by operational amplifiers (not shown), to processor 40. The signal indicates whether the detector detected laser radiation 22 on its surface 36 or not 37. Processor 40 receives all the signals of detectors 34A, 34B, 34C, 34D and 34E and then converts the specified code of the detection pattern it received into a direction for the source of laser radiation 22. The direction can be for example incident angle 25. Processor 40 can transmit the direction of laser radiation 22 to a user via a monitor, a voice system and the like (all not shown). A common operational amplifier (not shown) used in system 20 is illustrated in Figure 1 B. Operational amplifier 60 includes two signal inputs, positive signal input 62 and negative signal input 64. Operational amplifier 60 also includes single signal output 68, positive supply voltage 66 and negative supply voltage 70. In general, negative signal input 64 is connected to a reference potential, for example V_REF, positive signal input 62 is connected to a detector, for example V_DETECTOR and signal output 68 is connected to a processor. Operational amplifier 60 works in the following generalized manner. When signals, for example voltages, are detected at signal inputs 62 and 64, operational amplifier 60 amplifies the difference in voltage between signal inputs 62 and 64. The amplified signal is then provided via signal output 68 to another location, for example a processor. The range of amplifiable voltages is related to the difference between positive supply voltage 66 and negative supply voltage 70. A large voltage difference between positive supply voltage 66 and negative supply voltage 70 will allow a broader range of voltage differences between signal inputs 62 and 64 to be amplified. A small voltage difference between positive supply voltage 66 and negative supply voltage 70 will allow a more limited range of voltage difference between signal inputs 62 and 64 to be amplified. The maximum amplified voltage is limited by the difference between positive supply voltage 66 and negative supply voltage 70. In other words, the voltage difference between signal inputs 62 and 64 cannot be amplified more than the voltage difference between positive supply voltage 66 and negative supply voltage 70. The voltage difference between positive supply voltage 66 and negative supply voltage 70 defines an amplifiable voltage window. Voltage differences between signal inputs 62 and 64 that fall inside the amplifiable voltage window, will be amplified properly. Voltage differences between signal inputs 62 and 64 that fall outside the amplifiable voltage window, usually voltage differences above the maximum amplifiable voltage difference, will not be amplified properly. Voltage differences above the maximum amplifiable voltage difference cannot be amplified fully because the amplified voltage difference falls outside the difference between positive supply voltage 66 and negative supply voltage 70. As such, a voltage difference above the maximum amplifiable voltage difference will only be amplified up to the difference between positive supply voltage 66 and negative supply voltage 70, thereby saturating operational amplifier 60. This phenomenon of not fully amplifying a voltage difference that falls outside the amplifiable voltage window is referred to in the art as clipping or saturation.

Systems resembling generalized system 20 are known in the art. US Patent No. 5,604,695 issued to Cantin et ai. and entitled "Analog high resolution laser irradiation detector (HARLID)" is directed to a device for detecting the presence of a beam of radiation and determining its angle-of-arrival with respect to the device to a high degree of angular resolution. The device, which is opto-electronic in nature, is designed to minimize the effects of atmospheric scintillations. The device includes a linear array of radiation detectors, each including at least one pair of photodetector elements, located at a predetermined height directly below a shadow mask. The shadow mask includes a plurality of apertures separated by opaque areas having substantially the same width as a single photodetector element. The inner apertures are arranged such that they are centered along their width over the area between adjacent photodetector elements. The device has means for adding signals from corresponding photodetector elements in the radiation detectors into separate channels. With the use of two separate channels, the angle-of-arrival of the beam of radiation with respect to the device can be determined.

US Patent No. 4,857,721 issued to Dunavan et al. and entitled Optical direction sensor having gray code mask spaced from a plurality of interdigitated detectors" is directed to an apparatus for detecting and determining the direction of arrival of a beam of radiation. The device includes a mask having at least one elongated slit aperture located above a binary encoding mask. The binary encoding mask, using a gray encoding scheme, senses the angle of arrival of a beam of radiation and provides a plurality of sets of differential signals, via interdigitated detectors, responsive to the beam's angle of arrival. Processing electronics connected to the detectors provide a plurality of digital signals corresponding to the sets of differential signals. The digital signals form a digital angle of arrival word indicative of the angle of arrival of the incoming beam. US Patent No. 4,674,874 issued to Halldorsson et el. and entitled "Laser detection device" is directed to a device for detecting the presence and direction of pulsating or intensity-modulated laser radiation incident on the device. The device includes two detector elements, with the first detector element providing a start signal once laser radiation is incident on it and the second detector element providing a stop signal which is delayed in time in relation to the start signal. The second detector element is connected to a plurality of optical delay lines, all unequal in length to one another. The optical delay lines are connected to a plurality of optical collecting apertures each having a specific orientation and a limited field of sight. The individual limited fields of sight overlap one another.

The direction of laser radiation is determined by measuring the time length of the signal generated by the first detector element until it is stopped by the second detector element. The length of time corresponds to a unique optical delay line which in turn corresponds to a unique direction. The overlapping of fields of sight allows for a more accurate determination of the direction of laser radiation by interpolating the weighted average of the time length of the signals via a conventional computer.

US Patent No. 5,771 ,092 issued to Dubois et al., entitled "Wavelength agile receiver with noise neutralization and angular localization capabilities (WARNALOC)" is directed to an opto-electronic device capable of detecting the presence of a collimated beam of radiation and determining its angle of arrival and wavelength. The device includes a linearly variable optical filter which allows for the transmission of a spectrum of wavelengths over its surface, superimposed over an elongated detector having at least one radiation detector element in each quadrant of the elongated detector.

Radiation incident on the filter will project two separate images of two portions of the filter onto two adjacent detector elements in separate quadrants of the elongated detector. The position of the projected images can be used to determine the wavelength of the radiation. One image is projected onto one side of the elongated detector, while the second image is projected onto the other side of the elongated detector. Each projected image on the elongated detector generates a signal. The signal generated by the second image is subtracted from the signal generated by the first image to reduce background noise. Processing electronics use the two difference signals to determine the angle of arrival of the beam of radiation.

Devices for detecting the presence of a beam of laser radiation and determining the direction of its source exhibit a limited dynamic range phenomenon to intensities of laser radiation common in military equipment utilizing laser guided weapons. Limited dynamic range phenomenon occurs when the components of a device can process a limited dynamic range of input values. Values outside the dynamic range will be processed, but the result of the processing will be incorrect. Values inside the dynamic range however will be processed correctly to a high degree of sensitivity. Therefore in applications where sensitivity is required, limited dynamic range phenomenon is needed. The tradeoff of having a high degree of sensitivity is a limited range of input values which can be processed correctly. To achieve a broader range of input values which can be processed correctly, devices exhibiting a broad dynamic range phenomenon can be used. Broad dynamic range phenomenon occurs when the components of a device can process a broad dynamic range of input values. Values that fall inside the dynamic range will be processed correctly, but to a low degree of sensitivity. The tradeoff of having a broad range of input values which can be processed correctly is a low degree of sensitivity.

In devices for detecting the presence of a beam of laser radiation and determining the direction of its source, limited dynamic range phenomenon occurs because the detectors and operational amplifiers generally used in such devices need to be very sensitive to intensities of radiation. This sensitivity ensures that an accurate direction of a laser source can be produced by such a device. This sensitivity also allows devices exhibiting limited dynamic range phenomenon to become saturated with laser radiation. If this occurs in a device used to determine the direction of a laser source, then a case can arise where all the detectors used in such a device detect the presence of laser radiation simultaneously on their surfaces. The resultant angle of arrival or incident angle 25 determined in such a case by such a device is at best very imprecise, and at worst completely mistaken. A case can also arise where operational amplifiers used in such a device become saturated by receiving signals to be amplified outside their amplifiable voltage windows.

Saturation of operational amplifiers used to transmit signals from detectors to a processor to compute an angle of arrival can occur because operational amplifiers used to transmit signals from detectors to a processor usually have a signal input connected to a steady reference voltage. The voltage difference between the two signal inputs can vary greatly because the voltage provided by a detector to an operational amplifier is directly related to the intensity of laser radiation incident on a detector and because one signal input has a steady, unaltered voltage. During the course of detecting a beam of laser radiation and determining the direction of its source, a system will receive beams of laser radiation of varying intensities. The varying intensities received are due to the wide range of detectable laser sources and their physical locations from such a system. Some laser sources may use very intense laser radiation while other may use a weak intensity of laser radiation. Laser sources located near a system will register more intensity on detectors than laser sources located further away from a system. A problem with a greatly varying voltage difference is that such differences can sometimes fall outside the amplifiable voltage window of an operational amplifier used in such a system. If the voltage difference is greater than the amplifiable voltage window, then such an operational amplifier can become saturated. If the operational amplifier becomes saturated, then the amplification of the voltage difference will be deviant from its true value because it will be clipped. This deviation will cause a processor receiving an amplified signal to incorrectly identify the direction of a laser radiation source, for example computing an incorrect angle of arrival. SUMMARY OF THE DISCLOSED TECHNIQUE

It is an object of the disclosed technique to provide a novel method and system for laser direction determination, which overcomes the disadvantages of the prior art. In accordance with the disclosed technique, there is thus provided an apparatus for detecting the direction of light, the light arriving essentially collimated. The apparatus includes at least one pair of masks, at least one aperture, a respective pair of detectors for each pair of masks, and a respective summator for each respective pair of detectors. Each pair of masks includes a mask and a complementary mask, and each detector of the respective pair of detectors includes at least one sensor. The aperture is located in front of the pair of masks. One detector, of the respective pair of detectors, is optically coupled with the mask of the respective pair of masks. The other detector, of the respective pair of detectors, is optically coupled with the complementary mask of the respective pair of masks. The summator is electrically coupled with the respective pair of detectors.

The mask is optically encoded and the complementary mask is complementarily optically encoded with respect to the mask. The aperture distributes light differently on the pair of masks for light impinging on the apparatus from different directions. The respective pair of detectors detects light received from the respective pair of masks. The summator subtracts a signal received from one detector, of the respective pair of detectors, from a signal received from the other detector, of the respective pair of detectors, thereby producing a respective subtraction result. The apparatus further includes a processor, coupled with the respective summator. The processor detects and determines a direction from which the light arrived at the aperture, according to at least some of the respective subtraction result provided by the respective summator. According to another aspect of the disclosed technique, there is thus provided a method for detecting the direction of light, the light arriving essentially collimated. The method includes the procedures of receiving the light on at least one pair of masks through at least one aperture, each pair of masks including a mask and a complementary mask, and for each pair of masks, measuring the amount of light that passed through the respective mask and the respective complementary mask, thereby producing a pair of respective light measurements. The method further includes the procedures of executing an operation on the pair of respective light measurements, for each pair of masks, thereby producing a respective operation result, and determining the direction of the light from the operation result.

The aperture distributes light differently, on the pair of masks, for different directions of the light impinging on the aperture. The mask is optically encoded and the complementary mask is complementarily optically encoded with respect to the mask. The mask and the complementary mask each comprise a plurality of segments, wherein at least one of the segments is optically transmissive, thereby allowing incident light to pass there through, and the remaining segments are opaque. Each pair of masks is encoded differently in comparison with at least another pair of masks.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Figure 1 A is a perspective schematic illustration of the prior art.

Figure 1 B is a schematic illustration of an operational amplifier commonly used in the prior art.

Figure 2A is a schematic illustration of an encoded mask and its complementary mask, constructed and operative in accordance with an embodiment of the disclosed technique.

Figure 2B is a perspective schematic illustration of an encoded mask and its complementary mask, constructed and operative in accordance with an embodiment of the disclosed technique.

Figure 3 is a perspective schematic illustration of the optical components of the disclosed technique.

Figure 4A is a cross-sectional view of the plate of Figure 1 A.

Figure 4B is a cross-sectional view of an embodiment of the plate of Figure 3.

Figure 4C is a cross-sectional view of another embodiment of the plate of Figure 3.

Figure 5 is a perspective schematic illustration of an embodiment the electronic components of the disclosed technique.

Figure 6 is a perspective schematic illustration of another embodiment of the electronic components of the disclosed technique. Figure 7 is a schematic illustration of another embodiment of the disclosed technique.

Figure 8 is a block diagram describing a method operative in accordance with an embodiment of the disclosed technique. DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art by providing a novel laser direction determination architecture, which includes a plurality of mask pairs of masks. Each of the mask pairs includes an encoded mask and a respective complementary encoded mask. The complementary encoded mask is encoded using the same configuration as the encoded mask but in a complementary manner to the encoded mask. Optically, the masks of a selected mask pair, are placed adjacent to one another and at in the same orientation. Electrically, the masks of a selected mask pair are connected to a single operational amplifier in such a way that their signals are subtracted from one another.

This architecture establishes a floating dynamic range of input values which extends the range of input values that can be processed. The floating dynamic range allows a system using the architecture to process a broad dynamic range of input values with a high degree of sensitivity. The floating dynamic range establishes a limited, sensitive amplifiable voltage window which can be moved over a broad dynamic range of possible input voltage signals. The disclosed technique uses the limited dynamic range of operational amplifiers known in the art. With the use of complementary encoded masks, the limited dynamic range of operational amplifiers known in the art can be floated over of a broad range of input values. According to the disclosed technique, saturation of operational amplifiers used in such systems is unlikely to occur. Also, according to the disclosed technique, if operational amplifiers used in such systems do become saturated, such systems can still yield an angle of incidence for incoming laser radiation. The disclosed technique essentially disassociates the limited dynamic range of operational amplifiers known in the art from the intensity of incident laser radiation falling on a system. The disclosed technique thereby allows a detection and direction determination system to work under a substantially broad dynamic range of laser radiation intensity without saturating detectors and operational amplifiers, meaning, without getting mistaken angles of arrival. The disclosed technique also allows a detection and direction determination system, to work under conditions which cause operational amplifier saturation, and still provide an accurate reading of the angle of incidence. It is noted that the description of the disclosed technique relates to laser radiation by way of example. The disclosed technique is applicable in cases of determining the direction of essentially any directional electromagnetic radiation (e.g., from ultraviolet to far infrared), when such electromagnetic radiation arrives at a system, constructed and operative in according with an embodiment of the disclosed technique, substantially collimated.

Reference is now made to Figure 2A, which is a schematic illustration of an encoded mask 100 and its complementary encoded mask 110, constructed and operative in accordance with an embodiment of the disclosed technique. Encoded mask 100 and complementary encoded mask 110 both include a matrix of segments of openings and opaque sections. Encoded mask 100 includes for example openings 104₍₁,₁₎, 104(₂,₁), 104(3,₂) and 104(₂,₃), and opaque sections 102₍₃,i), 102₍i,₂), 102₍₂,2), 102_(1,3) and 102_(3,3). Complementary encoded mask 110 includes for example openings 112_(3,i₎, 112₍i,₂), 112₍₂,₂₎, ^"112(₁,₃) and 112(₃,₃), and opaque sections for example opaque section 114₍i_,i₎, 114_(2,i₎, 114₍₃,₂₎ and 114_(2,3). Openings allow laser radiation, falling incident on those sections, to pass through the mask. Opaque sections do not allow laser radiation, falling incident on those sections, to pass through the mask. Complementary encoded mask 110 is encoded in such a way as to be complementary to encoded mask 100. Complementary encoded mask 110 is complementary to encoded mask 100 in the following manner if the masks are placed side by side in the same orientation, as they are in Figure 2A. Wherever there is a opening on encoded mask 100, for example opening 104_(2,3), there is an opaque section, for example opaque section 114_(2,3), in the same location on complementary encoded mask 110. Wherever there is an opaque section on encoded mask 100, for example opaque section 102_(2,2), there is an opening, for example opening 112(₂,₂), in the same location on complementary encoded mask 110.

Reference is now made to Figure 2B, which is a perspective schematic illustration of an encoded mask 130 and its complementary encoded mask 140. Encoded mask 130 and complementary encoded mask 140 both include a matrix of segments of openings and opaque sections. Encoded mask 130 includes for example openings 134₍₂,i₎, 134(₁,₂), 134(_1|3), 134₍₂,₃₎, 134₍₂,₄₎ and 134₍₂,₅), and opaque sections 132₍₁,i), 132₍₂,₂₎, 132_(1j4) and 132_(1,5). Complementary encoded mask 140 includes for example openings 144_{(1 1)}, 144_(2,2), 144₍i,₄₎ and 144₍₁,₅₎, and opaque sections 142(₂,₁), 142₍₁,₂₎, 142₍₁ ^' _i3)> 142₍₂,₃), 142₍₂,₄) and 142₍₂,₅)- Figure 2B is similar to Figure 2A except that encoded mask 130 and complementary encoded mask 140 are now presented on top of one another in the same orientation instead of being placed adjacent to one another in the same orientation.

Complementary encoded mask 140 is complementary to encoded mask 130 in the following manner if the masks are placed on top of one another in the same orientation as they are in Figure 2B. Wherever there is an opening on encoded mask 130, for example opening 134_(2,i₎, there is an opaque section, for example opaque section 142_(2,i₎, located directly below the opening of encoded mask 130 on complementary encoded mask 140. For example, opaque section 142₍₂,i₎ on complementary encoded mask 130 is delineated by phantom line (dash-dot-dot-dash) 138. Projection lines (dash-dot-dash) 136 have been placed between the masks to clearly show the complementary nature of complementary encoded mask 140 with regard to encoded mask 130 if the masks were placed one on top of the other. This complementary nature is shown by connecting openings of encoded mask 130, for example sections 134₍i_,2) and 134_(1i3), to opaque sections of complementary encoded mask 140, for example sections 142₍i_,2) and 142₍i_,3). Wherever there is an opaque section on encoded mask 130, for example opaque section 132_(1]4), there is an opening, for example opening 144_(1|4), located directly below the opaque section of encoded mask 130 on complementary encoded mask 140. Reference is now made to Figure 3, which is a schematic illustration of the optical components of a system, generally referenced 170, constructed and operative in accordance with an embodiment of the disclosed technique. System 170 includes, in terms of its optical components, plate 176, mask pairs 183A, 183B and 183N, detectors 184_A; 184_B and 184₂N and plate 186. Plate 176 includes small, thin slit 178. Mask pairs 183A, 183B and 183N include encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N. Plate 186 houses mask pairs 183A, 183B and 183N, which include encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N. Detectors 184_A, 184_B and 184_2N are located directly below encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N. Detectors 184_A, 184_B and 184₂N may include multiple sensors (not shown).

Encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N are arranged on plate 186 such that each encoded mask has its complementary encoded mask located immediately adjacent to it in the same orientation. For example, encoded mask 180A has its complementary encoded mask 182A located adjacent to it in the same orientation. Due to the nature of air in the atmosphere not being homogenous, the intensity of incoming radiation 172 falling incident on an encoded mask and its respective complementary mask will be different. In this arrangement, of an encoded mask and its respective complementary encoded mask being located immediately adjacent to one another, the difference in intensity of the incident radiation falling on an encoded mask and its respective complementary encoded mask is reduced. This reduction in intensity reduces the probability that operational amplifiers 210A, 210B and 210N used in system 170 (Figure 5) become saturated. Encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N are encoded using any suitable coding configuration known in the art. It is noted that mask pairs 183A, 183B and 183N are each encoded differently according the coding configuration used to encode the masks. It is also noted that thin slit 178 can be replaced by any form of aperture that distributes laser radiation 172, impinging on encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N, differently, for different incoming directions of laser radiation 172. In another embodiment of the disclosed technique, plate 176 includes a plurality of small, thin slits, each thin slit being substantially similar to thin slit 178. In this embodiment of the disclosed technique, above each mask pair, there is a respective thin slit located in plate 176. In a further embodiment of the disclosed technique, each encoded mask as well as each complementary encoded mask has a respective thin slit located above it in plate 176.

The optical components of system 170 work in the following generalized manner. Laser radiation 172 arrives at system 170 from a distant radiation source. Since the distance between system 170 and the radiation source is usually quite large, compared to the size of thin slit 178, laser radiation 172 arrives at plate 176 substantially collimated. All the substantially collimated beams arrive at plate 176 with angle 174 with respect to plate 176. It is noted that all of the angles referred to in Figures 3, 4A, 4B and 5, are with respect to plate 176. Thin slit 178 allows only a thin strip of laser radiation 172 to fall incident 188 on plate 186 which falls incident on encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N. Laser radiation 188 incident on plate 186 will pass through openings (not shown) of encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N onto detectors 184_A, 184_B and 184₂N- The detection patterns generated on detectors 184_A, 184_B and 184_2N by complementary encoded masks 182A, 182B and 182N will be the complement of the patterns generated on detectors 184_A, 184_B and 184₂N by encoded masks 180A, 180B and 180N. Detectors 184_A, 184_B and 184₂N may include multiple sensors, provided that the laser radiation detected by the sensors of a detector located directly below an encoded mask, can be distinguished from the laser radiation detected by the sensors of a detector located directly below a complementary encoded mask.

Reference is now made to Figure 4A, which is a cross-sectional view of plate 24 of Figure 1A, which is commonly used in the prior art. Components common to Figures 1A and 4A have been labeled using identical numbers. In Figure 4A, the size of angle 25 determines the field of view of system 20 (not shown) and the range of angles of incidence which can pass through thin slit 26, onto encoded mask 28 (not shown). Due to the thickness of plate 24, only a limited range of angles of incidence of incoming radiation 22 will pass through thin slit 26, unless the distance between plate 24 and encoded mask 28 is increased.

Reference is now made to Figure 4B, which is a cross-sectional view of plate 176 of Figure 3, constructed and operative in accordance with an embodiment of the disclosed technique. Components common to Figures 3 and 4B have been labeled using identical numbers. In Figure 4B, the size of angle 174 determines the field of view of system 170 (not shown) and the range of angles of incidence which can pass through thin slit 178, onto plate 186 (not shown). In an embodiment of the disclosed technique, the edges of plate 176 adjacent to thin slit 178, are etched. It is noted that the sizes of thin slit 26 (Figure 4A) and plate 24 (Figure 4A) are the same as thin slit 178 and plate 176, although the size of angle 25 (Figure 4A) is substantially larger than the size of angle 174. Angle 174 is substantially smaller than angle 25 due to the etching of the edges of plate 176 adjacent to thin slit 178. The etching increases the field of view of system 170 and allows a substantially larger range of angles of incidence of incident radiation 172 to pass through thin slit 178, without having to increase the distance between plate 176 and plate 186.

Reference is now made to Figure 4C, which is a cross-sectional view of a plate 194, constructed and operative in accordance with an embodiment of the disclosed technique. Plate 176 of Figure 3 can be replaced by plate 194. In Figure 4C, the size of angle 192 determines the field of view of system 170 (not shown, Figure 3) and the range of angles of incidence which can pass through thin slit 196, onto plate 186 (not shown, Figure 3). The edges of plate 194 adjacent to thin slit 196, are slanted. In a further embodiment of the disclosed technique, the edges of the plate adjacent to the thin slit are slanted in the opposite direction to the direction of the slanted edges illustrated in Figure 4C. It is noted that the sizes of thin slit 26 (Figure 4A) and plate 24 (Figure 4A) are the same as thin slit 196and plate 194, although the size of angle 25 (Figure 4A) is substantially larger than the size of angle 192. Angle 192 is substantially smaller than angle 25 due to the slanting of the edges of plate 194 adjacent to thin slit 196. The slanting increases the field of view of system 170 and allows a substantially larger range of angles of incidence of incident radiation 190 to pass through thin slit 196, without having to increase the distance between plate 194 and plate 186.

Reference is now made to Figure 5, which is a schematic illustration of an embodiment of the electronic components of the same system illustrated in Figure 3, generally referenced 170, constructed and operative in accordance with an embodiment of the disclosed technique. Components common to Figures 3 and 5 have been labeled using identical numbers. System 170 includes, in terms of its electronic components, signal input leads 208_A, 208_B and 208_2N, operational amplifiers 210A, 210B and 210N, signal output leads 214A, 214B and 214N and processor 212. Each of operational amplifiers 210A, 210B and 210N can be replaced by any suitable summator for subtracting two signals from one another. Signal input leads 208_A, 208_B and 208₂N connect detectors 184_A, 184_B and 184₂N to operational amplifiers 210A, 210B and 210N. Signal output leads 214A₁ 214B and 214N connect operational amplifiers 210A, 210B and 210N to processor 212. A detector located directly under an encoded mask and a detector located directly under its complementary encoded mask are connected to a single operational amplifier. For example, detector 184A, located directly below encoded mask 180A, is connected to operational amplifier 210A via lead 208_A and detector 184_B, located directly below complementary encoded mask 182A, which is the complementary encoded mask of encoded mask 180A, is also connected to operational amplifier 210A via lead 208_B. In one embodiment of the disclosed technique, detectors located under encoded masks are all connected to the positive signal input of operational amplifiers 210A, 210B and 210N and detectors located under complementary encoded masks are all connected to the negative signal input of operational amplifiers 210A, 210B and 210N. In another embodiment of the disclosed technique, the connections are reversed, whereby detectors located under encoded masks are all connected to the negative signal input of operational amplifiers 210A, 210B and 210N and detectors located under complementary encoded masks are all connected to the positive signal input of operational amplifiers 210A, 210B and 210N. In a further embodiment of the disclosed technique, a detector located directly under an encoded mask and a detector located directly under its complementary encoded mask are connected to a single signal input of a single operational amplifier. The other signal input is connected to a reference signal.

The electronic components of system 170 work in the following generalized manner. As described in Figure 3, laser radiation 172 falling incident 188 on plate 186, falls incident on encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N. The openings (not shown) of encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N allow laser radiation 172 falling incident 188 on their respective surfaces to fall incident on detectors 184_A) 184_B and 184₂N- The amount of laser radiation 172 falling incident on detectors 184_A, 184_B and 184₂N generates a particular signal, for example a specific voltage, which is provided via leads 208_A, 208_B and 208_2N to operational amplifiers 210A, 210B and 210N. The difference of the two values received by the signal inputs, from the detectors located under an encoded mask and its complementary encoded mask is amplified in each operational amplifier and then provided to processor 212 via leads 214A, 214B and 214N. Processor 212 computes a direction for the source of laser radiation 172, for example an angle of arrival or incident angle 174 (Figure 3), by converting the specific detection pattern it received from detectors 184_A, 184_B and 184_2N into such a direction. The conversion depends on the type of coding configuration used in encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N.

In another embodiment of the disclosed technique, in which a detector located directly under an encoded mask and a detector located directly under its complementary encoded mask are connected to a single signal input of a single operational amplifier, the electronic components of system 170 work in the following generalized manner. As described in Figure 3, laser radiation 172 falling incident 188 on plate 186, falls incident on encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N. The openings (not shown) of encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N allow laser radiation 172 falling incident 188 on their respective surfaces to fall incident on detectors 184_A, 184_B and 184_2N. The amount of laser radiation 172 falling incident on detectors 184_A, 184_B and 184_2N generates a particular signal, for example a specific voltage, which is provided via leads 208_A, 208_B and 208_2N to operational amplifiers 210A, 210B and 210N. The rise time of a signal depends in part on the intensity of laser radiation falling incident on the detectors. Since the detectors located under an encoded masks and its complementary encoded mask are both connected to a single signal input of a single operational amplifier, the signal, provided from the detector with the higher rise time, will rise before the other signal and will reach the signal input of the operational amplifier first. In one embodiment of the disclosed, when the signal provided by a detector, located under an encoded mask, reaches the amplifier it is connected to first, the amplifier assigns a positive value to the difference of that signal and the signal provided by a detector located under a complementary encoded mask. When the signal provided by a detector, located under a complementary encoded mask, reaches the amplifier it is connected to first, the amplifier assigns a negative value to the difference of that signal and the signal provided by a detector located under an encoded mask. In another embodiment of the disclosed technique, when the signal provided by a detector, located under an encoded mask, reaches the amplifier it is connected to first, the amplifier assigns a negative value to the difference of that signal and the signal provided by a detector located under a complementary encoded mask. When the signal provided by a detector, located under a complementary encoded mask, reaches the amplifier it is connected to first, the amplifier assigns a positive value to the difference of that signal and the signal provided by a detector located under an encoded mask.

The difference of the two values received by the signal inputs, one from the detectors located under an encoded mask and its complementary encoded mask, the other from the reference signal, is amplified in each operational amplifier. The difference will either yield a positive or negative value, depending on the embodiment of the disclosed technique. The amplified difference is then provided to processor 212 via leads 214A, 214B and 214N. Processor 212 computes a direction for the source of laser radiation 172, for example an angle of arrival or incident angle 174 (Figure 3), by converting the specific detection pattern it received from detectors 184_A, 184_B and 184₂N into such a direction. The conversion depends on the type of coding configuration used in encoded masks 18OA, 18OB and 18ON and complementary encoded masks 182A, 182B and 182N.

System 170 can work in two modes, an unsaturated mode and a saturated mode. System 170 works in an unsaturated mode when the signals received by operational amplifiers 210A, 210B and 210N are within the amplifiable voltage window determined by the supply voltage differences of the operational amplifiers. System 170 works in a saturated mode when the signals received by operational amplifiers 210A, 210B and 210N are greater than the amplifiable voltage window determined by the supply voltage differences of the operational amplifiers.

As mentioned in the background, operational amplifiers used in the prior art exhibit a limited dynamic range phenomenon. This phenomenon can cause operational amplifiers used in the prior art to saturate when varying laser radiation intensities provide varying signals to operational amplifiers which have one signal input connected to a steady reference signal, for example a reference voltage. Using the disclosed technique, with the system operating in an unsaturated mode, operational amplifier saturation is unlikely to occur because the two signal inputs of an operational amplifier used in the disclosed technique are connected to two separate detectors. Since the detectors are located beneath an encoded mask and its complementary encoded mask, the amount of laser radiation detected on the detectors will be somewhat similar due to the relationship between an encoded mask and its complementary encoded mask. The signals provided by the detectors to an operational amplifier are subtracted from one another. Since the signals will, in general, be similar to one another, for example on the same order of magnitude, the result of the subtraction will essentially be a relatively small number. For example, if strong laser radiation falls incident on an encoded mask and generates a large signal on a detector, strong laser radiation will also fall incident on the encoded mask's complementary encoded mask, which will also generate a large signal on a detector. When the signals are subtracted from one another, the result will be a small value in comparison to the individual signals generated by the detectors. This small value will essentially always fall within the amplifiable voltage window determined by an operational amplifier's supply voltage difference. Since the result of the subtraction will essentially always fall within the voltage range determined by the amplifiable voltage window, operational amplifiers used in the disclosed technique will essentially not become saturated.

Using the disclosed technique, with the system operating in a saturated mode, operational amplifiers which become saturated provide a saturated signal to processor 212 that can be computed to yield a direction for the source of laser radiation 172. When operational amplifiers 210A, 210B and 210N receive signals from detectors 184_A) 184_B and 184₂N that are greater than the amplifiable voltage window, determined by the supply voltage differences of operational amplifiers 210A, 210B and 210N (all not shown), operational amplifiers 210A, 210B and 210N each go into saturation. When operational amplifiers 210A, 210B and 210N go into saturation, each of operational amplifiers 210A, 210B and 210N is operative to provide one of two distinct saturated signals to processor 212. The two distinct saturated signals are indicative of which of the detectors located directly below a mask pair caused the operational amplifier the detectors are connected to, to go into saturation. If the detector located directly below an encoded mask of a mask pair, receives more incident radiation of its surface than the detector located directly below a complementary encoded mask of the same mask pair, and the operational amplifier the detectors are connected to becomes saturated, the operational amplifier the detectors are connected to provides a positive saturated signal to processor 212, for example a signal of +1. If the detector located directly below a complementary encoded mask of a mask pair, receives more incident radiation of its surface than the detector located directly below an encoded mask of the same mask pair, and the operational amplifier the detectors are connected to becomes saturated, the operational amplifier the detectors are connected to provides a negative saturated signal to processor 212, for example a signal of -1.

Due to the relationship between an encoded mask and its complementary encoded mask, the amount of incident radiation falling on a detector located directly below an encoded mask of a mask pair, will always be distinct from the amount of incident radiation falling on a detector located directly below a complementary encoded mask of a mask pair. Therefore, even in a case of saturation, operational amplifiers 210A, 210B and 210N will provide processor 212 with a set of saturated signals indicative of which one of the respective pair of detectors (i.e., located directly below an encoded mask and a complementary encoded mask of the respective mask pair), caused the operational amplifier the detectors are connected to, to become saturated. The specific detection pattern of positive and negative saturated signals provided to processor 212 via leads 214A, 214B and 214N received from detectors 184_A, 184_B and 184_2N can be used for detecting and determining the direction from which laser radiation 172 was received. The conversion of the specific detection pattern of positive and negative saturated signals into a direction from which laser radiation 172 was received, when system 172 operate in a saturated mode, depends on the type of coding configuration used in encoded masks 180A, 180B and 180N and complementary encoded masks 182A, 182B and 182N.

Using the disclosed technique, the intensity of laser radiation incident on detectors has essentially no connection to the saturation of operational amplifiers. The disclosed technique allows laser detection and direction determination systems to work in a broad dynamic range of laser intensities without getting mistaken directions for laser radiation sources due to operational amplifier saturation. This in essence means that the disclosed technique works independently of the intensity of laser radiation it detects.

Reference is now made to Figure 6, which is a perspective schematic illustration of another embodiment of the electronic components of a system, generally referenced 230, constructed and operative in accordance with another embodiment of the disclosed technique. System 230 is similar in construction and operation to system 170 (Figures 3 and 5). System 230 includes, in terms of its electronic components, detectors 232_A, 232_B and 232_2N, leads 234_A, 234_B and 234_2N, comparators 236_A, 236_B and 236₂N (labeled with a ¹C in Figure 6), signal input leads 238_A, 238_B and 238₂N, leads 242_A; 242_B and 242_2N, operational amplifiers 240A, 240B and 240N, signal output leads 244A, 244B and 244N and processor 246. Each of detectors 232_A, 232_B and 232_2N is located behind a respective mask (i.e., which can either be encoded or complementary encoded) (not shown). Each of operational amplifiers 240A, 240B and 240N can be replaced by any suitable summator for subtracting two signals from one another. Each of comparators 236_A, 236_B and 236₂N can be replaced by any suitable threshold detector. Leads 234_A, 234_B and 234_2N connect detectors 232_A, 232_B and 232_2N to comparators 236_A; 236_B and 236_2N- Signal input leads 238_A, 238_B and 238_2N connect comparators 236_A, 236_B and 236_2N to operational amplifiers 214A, 240B and 240N. Leads 242_A, 242_B and 242_2N connect comparators 236_A, 236_B and 236_2N to processor 246. Signal output leads 244A, 244B and 244N connect operational amplifiers 240A, 240B and 240N to processor 246. Each detector is connected to a comparator. A detector located directly under an encoded mask (not shown) and a detector located directly under its complementary encoded mask (not shown) are connected, each via a respective comparator, to a single operational amplifier. For example, detector 232_A, which is located directly below an encoded mask (not shown), is connected to operational amplifier 240A via comparator 236_A and detector 232_B, located directly below a complementary encoded mask (not shown), which is the complementary encoded mask of an encoded mask, is also connected to operational amplifier 240A via comparator 236_B. In one embodiment of the disclosed technique, detectors located under encoded masks are all connected, via respective comparators, to the positive signal input of operational amplifiers 240A, 240B and 240N and detectors located under complementary encoded masks are all connected, via respective comparators, to the negative signal input of operational amplifiers 240A, 240B and 240N. In another embodiment of the disclosed technique, the connections are reversed, whereby detectors located under encoded masks are all connected, via comparators, to the negative signal input of operational amplifiers 240A, 240B and 240N and detectors located under complementary encoded masks are all connected, via comparators, to the positive signal input of operational amplifiers 240A, 240B and 240N. In a further embodiment of the disclosed technique, a detector located directly under an encoded mask and a detector located directly under its complementary encoded mask are connected to a single signal input of a single operational amplifier via a single comparator. The other signal input is connected to a reference signal. As described in Figure 3, laser radiation (not shown) falling incident on a plate (not shown), falls incident on encoded masks (all not shown) and complementary encoded masks (all not shown). The openings (not shown) of the encoded masks and complementary encoded masks allow the laser radiation falling incident on their respective surfaces to fall incident on detectors 232_A, 232_B and 232_2N- The amount of the laser radiation falling incident on detectors 232_A, 232_B and 232₂N generates a particular signal, for example a specific voltage, which is provided via leads 234_A, 234_B and 234₂N to comparators 263_A, 236_B and 236_2N. Comparators 236_A, 236_B and 236₂N each determine if the strength of the respective signal received is above or below a predetermined threshold level. The predetermined threshold level can be, for example, the level of a noise signal. If the respective signal is determined to be above the threshold level, then comparators 236_A, 236_B and 236_2N each provide the respective signal to operational amplifiers 240A, 240B and 240N via signal input leads 238_Al 238_B and 238₂N- The difference of the two values received by the signal inputs, from the detectors located under an encoded mask and its complementary encoded mask, is amplified in each operational amplifier. The amplified difference is then provided to processor 246 via leads 244A, 244B and 244N. Processor 246 computes a direction for the source of the laser radiation, for example an angle of arrival or an incident angle 174, by converting the specific detection pattern it received from detectors 232_A, 232_B and 232₂N into such a direction. The conversion depends on the type of coding configuration used in the encoded masks and complementary encoded masks.

If the respective signal is determined to be below the threshold level, then comparators 236_A, 236_B and 236₂N each provide a respective noise indication signal to processor 246. The respective noise indication signal indicates that the strength of the incident radiation received by detectors 232_A, 232_B and 232₂N is too weak to accurately determine the angle of arrival of the incident radiation. This type of weak strength incident radiation is known as scatter in the art.

Referring back to Figure 3, due to the complementary nature of encoded mask 180A and complementary encoded mask 182A, the code of the detection pattern formed by incoming radiation 172 on detector 184_A, located behind encoded mask 180A, should be the complement of the respective code formed by incoming radiation 172 on detector 184_B, located behind complementary encoded mask 182A. For example, referring back to Figure 2A, if incoming radiation falls on an opening, then a value of 1 may be assigned to the opening, and if incoming radiation falls on an opaque section, then a value of 0 may be assigned to the opaque section. Since the openings and opaque sections of an encoded mask and its complementary encoded mask are arranged in horizontal and vertical rows, a code for each row, or column, of a mask can be formed by reading the binary number formed by a horizontal or vertical sequence of openings and opaque sections. It is noted that if mask 100 and complementary mask 110 in Figure 2A were used in system 170, then each row of openings and opaque sections of mask 100 and complementary mask 110 would have a detector located behind it. Therefore mask 100 would have a detector behind opening 104_(1,1), and opaque sections 102_{(1 ,2)} and 102_(1j3), a detector behind openings 104_(2]1) and 104_(2,3), and opaque section 102₍₂,₂), and a detector behind opening 104_(3,2), and opaque sections 102_(3,i₎ and 102₍₃₃₎. A similar arrangement of detectors would be used for complementary mask 110. If incoming radiation (not shown) were to fall on the left side of encoded mask 100 and complementary encoded mask 110, such that the incoming radiation fell incident on openings 104₍U₎ and 104_(2,i₎, and opaque section 102^₁) of encoded mask 100, and opaque sections 114₍i_,i₎ and 114_(2ii₎, and opening 112_(3,1) of complementary encoded mask 110, then a code of '1' would be formed on the first detector (not shown), a code of '1' would be formed on the second detector (not shown), and a code ¹O¹ would be formed on the third detector (not shown) located behind encoded mask 100, giving the encoded mask a complete code of '1 ,1 ,0.' A code of '0' would be formed on the first detector (not shown), a code of ¹O' would be formed on the second detector (not shown), and a code of '1' would be formed on the third detector (not shown) located behind complementary encoded mask 110, giving the complementary encoded mask a complete code of '0,0,1.' It is noted that the complete code '1 ,1 ,0' of encoded mask 100 is complementary to the complete code '0,0,1 ' of complementary encoded mask 110, because each '1 ' in the complete code of encoded mask 100 becomes a '0' in the complete code of complementary encoded mask 110, and each '0' in the complete code of encoded mask 100 becomes a '1 ' in the complete code of complementary encoded mask 110. In another embodiment of the disclosed technique, processor 246 performs an error check and compensation of the codes formed on the detectors of each mask pair (not shown).

If the respective signal provided to comparators 236_A, 236_B and 236₂N is determined to be above the threshold level, then comparators 236_A, 236_B and 236₂N each provide a signal to processor 246 which is indicative of the respective code formed on the detectors located behind each encoded mask and its complementary encoded mask. In general, each detector indicates whether a code of '1' or '0' is formed. For example, the code formed on detector 232_A, provided by comparator 236_A to processor 246, is checked for errors in processor 246 with the code formed on detector 232_B, provided by comparator 236_B to processor 246, by comparing the digit of the respective codes formed on detectors 232_A and 232_B. If the codes are perfectly complementary, then processor 246 computes a direction for the source of the laser radiation, for example, an angle of arrival or an incident angle, by converting the specific detection pattern and complete code it received from detectors 232_A, 232_B and 232₂N into such a direction.

The respective codes of an encoded mask and its complementary encoded mask will not be complementary if the digit of both codes is the same. For example, if the code formed on detector 232_A is '1 ' and the code formed on detector 232_B is also '1 ' then the codes are not complementary, because the digit of both codes is the same, and therefore not complementary. If processor 246 determines that the codes of a respective mask pair are not complementary, then processor 246 compensates for the error in the codes by sequentially altering all of the erroneous digits in each of the codes to make the codes of the respective mask pair complementary. For each alteration, processor 246 computes a direction for the source of the incoming radiation, thereby providing a number of choices to a user as to which direction the incoming radiation is coming from. In the example, processor 246 would alter the code '1 ' formed on detector 232_A to '0' and determine the direction for the source of the incoming radiation according to the codes ¹O¹ for detector 232_A and '1 ' for detector 232_B. Processor 246 would then alter the code '1' formed on detector 232_B to '0' and determine the direction for the source of the incoming radiation according to the codes '1' for detector 232A and '0' for detector 232_B. Processor 246 would finally give a user two possible choices for the direction of the source of the incoming radiation.

Reference is now made to Figure 7, which is a schematic illustration of a system, generally referenced 260, constructed and operative in accordance with an embodiment of the disclosed technique. System 260 includes central processor 262 and laser direction determination systems 264^ 264₂, 264₃ and 264₄. Each of laser direction determination systems 264_{1 ;} 264₂, 264₃ and 264₄ are similar in construction and operation to system 170 (Figures 3 and 5). Central processor 262 is coupled (i.e., either wired or wireless) with laser direction determination systems 264-,, 264₂, 264₃ and 264₄. System 260 may be mounted on a vehicle, or a stationary structure, with each of laser direction determination systems 264-ι, 264₂, 264₃ and 264₄ located at a different corner of the vehicle, or the stationary structure. Incident radiation 266 impinges on system 260. Incident radiation 266 impinging on system 260 may arrive at each of laser direction determination systems 264_{1 ;} 264₂,

264₃ and 264₄ from a different incoming direction because of internal reflections of incident radiation 266 between the different laser direction determination systems. In such a case, each of laser direction determination systems 264-ι, 264₂, 264₃ and 264₄ may determine a different incoming direction for incident radiation 266.

In order to determine the actual direction of incident radiation 266, each of laser direction determination systems 264^ 264₂, 264₃ and

264₄ measures general radiation properties (e.g., intensity, pulse width, time of arrival, and the like) of incident radiation 266 arriving thereto, in addition to determining a respective direction for incident radiation 266. Each of laser direction determination systems 264i, 264₂, 264₃ and 264₄ provides these measurements and determinations to central processor 262. Central processor 262 determines the actual direction of incident radiation 266 by executing a weighted calculation on the measured general radiation properties of incident radiation 266. Each measured radiation property is given a weight in the calculation. For example, in the weighted calculation, the time of arrival of incident radiation 266 may be given the most significance, whereas the intensity of incident radiation 266 may be given the least significance. The result of the weighted calculation is used to determine the actual direction of incident radiation 266. Reference is now made to Figure 8, which is a schematic illustration of a method operative in accordance with an embodiment of the disclosed technique. In procedure 280, light is received through an aperture towards a plurality of mask pairs. In another embodiment of the disclosed technique, light is received through a plurality of apertures towards a plurality of mask pairs. Each mask pair includes an encoded mask and a complementary encoded mask. Each encoded mask and its complementary encoded mask are placed adjacent to one another in the same orientation. The masks are encoded differently using any suitable coding configuration known in the art. Since the distance between the aperture and the source of the light is usually quite large, compared to the size of the aperture, the light passing through the aperture is substantially collimated. The aperture distributes light differently, on the plurality of mask pairs, for different directions of light impinging on the aperture. In procedure 282, for each mask pair, the amount of light passing through an encoded mask and its complementary encoded mask is measured. In procedure 284, for each mask pair, an operation is executed on the amount of light measured that passed through an encoded mask and the amount of light measured that passed through its complementary encoded mask. In an embodiment of the disclosed technique, the operation includes subtracting, for each mask pair, the amount of light measured that passed through an encoded mask from the amount of light measured that passed through its complementary encoded mask. In another embodiment of the disclosed technique, the operation includes assigning, for each mask pair, a positive or negative value depending on the amount of light measured that passed through an encoded mask and its complementary encoded mask. If more light passed through an encoded mask, then a positive value is assigned for that mask pair. If more light passed through a complementary encoded mask, then a negative value is assigned for that mask pair. The positive and negative value assignments can be reversed. In procedure 286, the result of the operation executed for each mask pair is used to determine a direction for the incoming light.

It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.

Claims

1. Apparatus for detecting the direction of light, arriving essentially collimated, the apparatus comprising: at least one pair of masks, each said at least one pair of masks including a mask and a complementary mask, wherein said mask is optically encoded and said complementary mask is complementarily optically encoded with respect to said mask, at least one aperture, located in front of said at least one pair of masks, said at least one aperture distributing light differently on said at least one pair of masks for light impinging on said apparatus from different directions, for each said at least one pair of masks, a respective pair of detectors, each detector of said at least one respective pair of detectors comprising at least one sensor, one detector of said at least one respective pair of detectors being optically coupled with the mask of said respective one of said pair of masks, the other detector of said at least one respective pair of detectors being optically coupled with the complementary mask of said respective pair of masks, wherein said respective pair of detectors detects light received from said respective pair of masks, for each of said respective pair of detectors, a respective summator, electrically coupled with said respective pair of detectors, wherein said respective summator subtracts a signal received from said one detector of said respective pair of detectors from a signal received from said other detector of said respective pair of detectors, thereby producing a respective subtraction result.

2. The apparatus according to claim 1 , wherein said mask and said complementary mask each comprise a plurality of segments, wherein at least one of said segments is optically transmissive, thereby allowing incident light to pass there through, and wherein the remaining of said segments are opaque.

3. The apparatus according to claim 2, wherein said encoding of each of said at least one pair of masks comprises a segment configuration of

5 said optically transmissive segments and said opaque segments on each of said at least one pair of masks.

4. The apparatus according to claim 3, wherein said segment configuration produces different light configurations on said o respective pair of detectors, for different directions of said light impinging on said aperture.

5. The apparatus according to claim 1 , wherein said mask and said complementary mask are placed adjacent to one another in the same 5 orientation.

6. The apparatus according to claim 1 , wherein said mask defines a plurality of segments and said complementary mask defines a plurality of complementary segments, each said segments being 0 associated with a respective one of said complementary segments, wherein at least one of said segments is optically transmissive and the rest of said segments are opaque, wherein said complementary mask is complementarily encoded, such that the respective complementary segments of each of said 5 optically transmissive segments are opaque, and wherein the respective complementary segments of each of said opaque segments, are optically transmissive.

7. The apparatus according to claim 1 , wherein each of said at least one o pair of masks is encoded differently in comparison with at least another of said at least one pair of masks.

8. The apparatus according to claim 1 , further comprising a processor, coupled with said at least one respective summator, for detecting and determining a direction from which said light arrived at said aperture,

5 according to at least some of said respective subtraction result provided by said at least one respective summator.

9. The apparatus according to claim 1 , wherein the edges of said at least one aperture that allow said light to pass there through, are o etched.

10. The apparatus according to claim 1 , wherein the edges of said at least one aperture that allow said light to pass there through, are slanted. 5

11. The apparatus according to claim 1 , wherein said apparatus comprises at least two apertures for said at least one pair of masks, wherein one of said at least two apertures is located above a mask of said at least one pair of masks, and wherein the other of said at least 0 two apertures is located above a complementary mask of said at least one pair of masks.

12. The apparatus according to claim 8, wherein said respective summator assigns a particular value to the signals received from said 5 respective pair of detectors, said particular value being indicative of which signal received from said respective pair of detectors was stronger, thereby producing a respective assignment result.

13. The apparatus according to claim 12, wherein said processor detects o and determines a direction from which said light arrived at said aperture, according to at least some of said respective assignment result provided by said at least one respective summator.

14. The apparatus according to claim 1 , further comprising a threshold 5 detector, coupled with said at least one respective pair of detectors and said at least one respective summator, for determining an intensity level of said light.

15. The apparatus according to claim 8, wherein said processor verifies o the codes, formed by said optically encoded mask and said complementarily optically encoded complementary mask, for errors.

16. The apparatus according to claim 15, wherein said processor compensates for errors found in said codes. 5

17. A method for detecting the direction of light, arriving essentially collimated, comprising the procedures of: receiving said light on at least one pair of masks through at least one aperture, wherein said at least one aperture distributes light o differently on said at least one pair of masks, for different directions of said light impinging on said aperture, each said at least one pair of masks including a mask and a complementary mask, wherein said mask is optically encoded and said complementary mask is complementarily optically encoded with respect to said mask, wherein 5 said mask and said complementary mask each comprise a plurality of segments, wherein at least one of said segments is optically transmissive, thereby allowing incident light to pass there through, and the remaining of said segments are opaque, and wherein each of said at least one pair of masks is encoded differently in comparison o with at least another of said at least one pair of masks, for each said at least one pair of masks, measuring the amount of said light that passed through said respective mask and said respective complementary mask, thereby producing a pair of respective light measurements, for each said at least one pair of masks, executing an operation on said pair of respective light measurements, thereby producing a respective operation result, and determining the direction of said light from the at least one operation result.

18. The method according to claim 17, wherein said encoding of each of said at least one pair of masks, comprises a segment configuration of said optically transmissive segments and said opaque segments on each of said at least one pair of masks.

19. The method according to claim 18, wherein said segment configuration produces different light configurations for different directions of said light impinging on said aperture.

20. The method according to claim 17, wherein said procedure of executing an operation comprises subtracting between said pair of respective light measurements.

21. The method according to claim 17, wherein said procedure of executing an operation comprises assigning a particular value to said pair of respective light measurements, said particular value being indicative of which light measurement of said respective pair of light measurements was stronger.

22. The method according to claim 17, further comprising the procedure of determining an intensity level of said light.

23. The method according to claim 17, further comprising the procedure of verifying the codes, formed by said optically encoded mask and said complementarily optically encoded complementary mask, for errors.

24. The method according to claim 23, further comprising the procedure of compensating for errors found in said codes.

25. The apparatus according to any of the claims 1-16 substantially as described hereinabove or as illustrated in any of the drawings.

26. The apparatus according to any of the claims 17-24 substantially as described hereinabove or as illustrated in any of the drawings.