GB2421789A

GB2421789A - Intruder detector with two optical Fresnel lens systems

Info

Publication number: GB2421789A
Application number: GB0504999A
Authority: GB
Inventors: Juan Sebastian Herre Stromberg; Craig Leivers
Original assignee: Pyronix Ltd
Current assignee: Pyronix Ltd
Priority date: 2005-03-10
Filing date: 2005-03-11
Publication date: 2006-07-05
Anticipated expiration: 2025-03-11
Also published as: GB0504906D0; GB0504999D0; GB2421789B

Abstract

A combined active and passive intruder detector 100 comprises a pair of passive infrared (PIR) detectors 102 and 104 and a Doppler shift microwave detector 106. The PIR detectors generate outputs 108 and 110 in response to an intruder entering fields of view 112 and 114 of respective lenses 116 and 118 associated with the PIR detectors. Each lens 116 and 118 comprises a number of Fresnel facets each facet providing a respective field of view. Selected facets on each lens are masked to prevent transmission of infrared radiation onto a respective PIR detector such that the two sets of fields of view derived from the two lenses 116 and 118 are interdigitally arranged. The fields of view are also separate i.e. they do not overlap.

Description

DETECTOR AND OPTICAL SYSTEM

Field of the Invention

The invention relates to a detector and optical system for such a detector.

Background to the Invention

Detection apparatuses, for example, intrusion monitoring apparatuses, are well known within the art. Typically, they are used to detect unauthorised entry or intrusion into a protected volume.

Commercially available intrusion monitoring apparatuses can be either passive or active. Passive intrusion monitoring apparatuses can comprise a sensor which detects infrared radiation emitted by people. Typically, such passive apparatuses comprise a thermal detection apparatus consisting of one or more thermal sensors arranged to detect infrared radiation and an optical system for directing such infrared radiation towards the thermal sensors. The optical system comprises at least one lens formed from a plurality of Fresnel lenses or at least portions thereof. Each Fresnel lens of the plurality of lenses typically known as a facet. Conventionally, facets view or monitor respective regions or angular sectors of the protected volume. Such apparatuses are activated when a source of infrared radiation passes from one region or angular sector to the next, that is, infrared radiation is detected in a plurality of angular sectors. Typical prior art intrusion monitoring apparatuses are illustrated in, for example, US patent application numbers 3703718 and 3,958,118 and UK patent application number 1,335,410, the entire disclosures of which are incorporated herein by reference for all purposes.

Active intrusion monitoring apparatuses are also known which comprise a transmitter and a receiver. The transmitter emits radiation at a defined frequency and the receiver measures the Doppler shift in any reflected signal. Such active monitoring apparatuses can, for example, operate at microwave frequencies using a microwave detection apparatus to detect the, reflected signal.

The above active and passive detection apparatuses can be used alone or in conjunction with one another. Apparatuses that use two or more technologies, that is, a passive detection technology and an active detection technology, to identify intrusion into a protected volume or, more particularly, movement of an intruder within the field of view of the apparatus, are known within the art as combined detectors, combined technology apparatuses, dual technology or multi- technology devices. Examples of combined detectors that use a photoelectric sensor and a microwave sensor are disclosed in US patent application Numbers 3,725,888 and 4,401,976, the entire disclosures of which are incorporated herein for all purposes by reference. There exists a British standard relating to combined passive infrared and microwave detectors, which is "Alarm systems -. Intrusion systems Part 2-4: Requirements for combined passive infrared and microwave detectors", the content of which is incorporated herein by reference for all purposes.

However, the revised DD243-2004 standard, entitled "Installation and configuration of intruder alarm systems designed to generate confirmed alarm conditions - Code of practice", under section 5.4, entitled "Design and configuration of sequential confirmation lASs", provides that within a sequentially confirmed alarm the movement detectors are not allowed to overlap each other. Furthermore, section 5.4.2 states that "[therefore], movement detectors should be located some distance apart, generally with a minimum distance between detector housings of 2. 5m".

One skilled in the art clearly appreciates that the above is a costly solution to the problem of providing sequentially confirmed alarms since it requires twice the investment, that is, two detectors, twice the cabling etc. It is an object of embodiments to at least mitigate some of the problems of the prior art.

Summary of Invention

Accordingly, a first aspect of embodiments of the present invention provides a detector comprising an optical arrangement comprising a plurality of facets creating a plurality of

separate, interdigitated, fields of view.

Advantageously, a detector can be realised that uses optically separate fields of view.

A second aspect provides a detector comprising a first lens system having a plurality of facets bearing respective fields of view and a second lens system having a plurality of facets bearing respective fields of view; the two pluralities of fields of view being interdigitally arranged.

A further aspect provides a detector comprising a first optical arrangement comprising a number of fields of view and a second optical arrangement comprising a number of fields of view; the first and second optical arrangements being arranged so that the fields of view are alternately arranged.

An embodiment provides a detector in which the fields of view are alternately arranged such that at least one field of view of the first optical arrangement is disposed between at least a pair of

fields of view of the second optical arrangement.

An aspect provides an optical arrangement comprising a plurality of Fresnel lenses or Fresnel facets forming a plurality of non-overlapping, interleaved, fields of view.

A further aspect provides an optical system or lens comprising a plurality of lenses corresponding to a plurality of fields of view; the plurality of lenses having disposed therebetween a plurality of blanks to optically separate the plurality of fields of view. The blanks, which at least substantially reduce transmission of energy, in particular, IR, and, preferably, block such transmission, can be made from machined metal blanking pieces and incorporated into or form part of the lens at lens manufacture. Alternatively, the blanks can be merely placed appropriately relative to the lens facets.

A still further aspect provides an optical system comprising a lens having a number of facets; the facets being arranged to form a first set of a number of fields of view and a second set of a number of fields of view; the fields of view of the first set being interdigitated with the fields of view of the second set.

Yet another aspect provides an optical system or lens comprising a first plurality of fields of view interposed with a second plurality of fields of view in a non-overlapping manner.

Brief Description of the drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a combined detector according to an embodiment; Figure 2 illustrates a lens according to an embodiment; Figure 3 depicts a Fresnel master for the lens described with reference to figure 2; Figure 4 shows a front view of a lens comprising a plurality of Fresnel facets; Figure 5 illustrates a lens according to an embodiment; Figure 6 depicts a lens according to another embodiment; Figure 7 illustrates schematically the fields of view of the facets of a lens according to an embodiment; Figure 8 depicts schematically further fields of views of facets of a lens according to an embodiment; Figure 9 shows a flow chart of the processing performed according to an embodiment; Figures 10 and 11 illustrate a detector according to an embodiment.

Detailed Description of Embodiments

Referring to figure 1, there is schematically shown a first embodiment of a combined detector 100 comprising a pair of passive infrared (FIR) detectors 102 and 104 and a microwave detector 106 for use as part of an intrusion detection system (not shown). The combined detector 100 is arranged to detect a relatively broad spectrum of infrared radiation emitted by an intruder and, substantially simultaneously, to emit microwave radiation into a protected volume and to analyse any returned or reflected signals such that an intrusion signal or message is generated when both technologies provide an indication of the presence of an intruder.

The PIR detectors 102 and 104 generate outputs 108 and 110 in response to receiving infrared radiation emitted by an intruder, that is, in response to an intruder entering the fields of view 112 and 114 of respective lenses 116 and 118 associated with the PIR detectors. It will be appreciated that the fields of view 112 and 114 are merely schematically depicted. The outputs 108 and 110 from the pair of PIR detectors 102 and 104 are fed to respective inputs IP I and 1P2 of a processor or circuit board 120 for further processing.

The microwave detector 106 is a Doppler shift microwave detector that produces an output signal 122 in response to receiving, at a receiver 124, an appropriately Doppler- shifted version of a signal transmitted via a microwave transmitter 126. The output 122 of the microwave detector 106 is also fed to an input 1P3 of the processor board 120 for further processing.

The processor board 120 comprises a processor 128 that is arranged to execute software 130 stored in a memory 132. The memory 132 comprises a ROM. The processor 128 processes the signals 108, 110 and 122 received from the detectors 102, 104 and 106 to determine whether or not there is an intruder within a protected volume. The processing undertaken by the processor will be described with reference to figure 9.

If the processing determines that an intruder is within the protected volume, the processor generates an alarm signal 134 or causes such an alarm signal to be generated. The alarm signal 134 is made available at a terminal or pair of terminals of a connector block 138, where it is output for further processing by, for example, a control panel of an intrusion detection system (not shown) or to an alarm for generating an alarm.

The connector block is also used to provide 5V and ground power to the detector 100 to power the various components contained in it. Other signals such as, for example, a tamper signal or fault signal may also be output by the connector block according to the capabilities of the software executable by the processor.

Figure 2 illustrates a lens 200 that can be used as the lenses 116 and 118. The lens 200 comprises a number of facets. In the embodiment illustrated, the lens has 27 facets. Each facet is, or selected facets are, shaped or profiled according to respective parts of a Fresnel lens master, which is described later with respect to figure 3. Each facet provides or comprises a respective field of view. The facets focus infrared radiation onto the PIR detectors 102 and 104.

The lens 200 comprises first 202, second 204 and third 206 rows of facets. The facets in the first row 202 have a common height and respective widths. In a preferred embodiment, the first row facets have a height of 17mm. The facets in the second row 204 also have a common height. In a preferred embodiment, the height of the second row facets is 6.5mm. The facets of the third row 206 have a common height. The third row facets have a height of 5mm in a preferred embodiment. Table 1 below summarises the heights and widths of the facets of the lens 200. The facets are also known as segments within the art.

Segment/Facet No. X coordinate Y coordinate Width 1 0.07 3.59 5.45 2 -0.77 4.19 4.5 3 -0.85 4.55 3.95 4 -0.52 4.74 3.66 0 4.8 3.58 6 0.52 4.74 3.66 7 0.85 4.55 3.95 8 0.77 4.19 4.5 9 -0.07 3.59 5.45 0.07 4.78 5.45 11 -0.77 5.59 4.5 12 -0.85 6.07 3.95 13 -0.52 6.32 3.66 14 0 6.4 3.58 0.52 6.32 3.66 16 0.85 6.07 3.95 17 0.77 5.59 4.5 18 -0.07 4.78 5.45 19 0.07 1.87 5.45 -0.77 2.18 4.5 21 -0.85 2.37 3.95 22 -0.52 2.47 3.66 23 0 2.5 3.58 24 0.52 2.47 3.66 0.85 2.37 3.95 26 0.77 2.18 4.5 27 -0.07 1.87 5.45

TABLE 1

Also shown in table 1 are coordinate values. Each facet has a respective pair of coordinates.

Referring to figure 3, there is shown schematically a Fresnel master 300 which has a centre 302.

The coordinates of table I provide an indication of the position of the centre 302 of a respective copy of the Fresnel master relative to respective facets. The X coordinate describes the x- coordinate position of the centre of a respective Fresnel master 300 from a centre line (not shown) of a respective facet. The Y coordinate describes the y-coordinate position of the centre 302 of a respective Fresnel master 300 relative to the bottom edge of a respective facet. For example, figure 3 also shows the fifth facet. It can be appreciated that the x-coordinate of Fresnel master centre lies on the centre line 304 of the fifth facet. It can also be appreciated that the y-coordinate of the Fresnel master 300 is 4.8mm above the bottom edge 306 of the fifth facet.

It will be recalled that the combined detector 100 comprises two such lenses 200. Therefore, one lens such as, for example, lens 116, will bear a first set of fields of view via its facets and the other lens 118 will bear a second set of fields of view via its facets. Each facet has a

corresponding field of view.

Referring to figure 4, there is shown a lens 400, comprising a plurality of Fresnel facets, such as those described above in relation to and as shown in figure 1 and 2. It can be appreciated that each facet I to 27 comprises a respective portion of the Fresnel master 300 positioned according to the data contained in table 1 above. It will be appreciated that embodiments can be realised in - - - - which a number of Fresnel masters are used to create the facets of the lens 400. For example, two, three, or more, different, Fresnel masters could be used to create the facets of the lens 400.

Figure 5 depicts a lens 500 according to an embodiment. The lens 500 is identical to that shown in and described with reference to figure 4 but for selected facets or regions having been rendered ineffective or omitted ie not formed. In the embodiment shown, it can be seen that the even numbered facets of the top 502 and bottom rows 504 of figure 4 have been omitted or rendered ineffective in the lens 500. Similarly, the odd numbered facets of the middle row 506 of the lens shown in figure 4 have been omitted or rendered ineffective in the lens 500 according to the embodiment. This arrangement results in five columns 508 to 516 of Fresnel facets with each column comprising three such Fresnel facets.

Figure 6 depicts a lens 600 according to an embodiment. The lens 600 is identical to that shown in and described with reference to figure 4 but for selected facets or regions having been rendered ineffective or omitted ie not formed. In the embodiment shown, it can be seen that the odd numbered facets of the top 602 and bottom 604 rows of figure 4 have been omitted or rendered ineffective in the lens 600. Similarly, the even numbered facets of the middle row 606 of the lens shown in figure 4 have been omitted or rendered ineffective in the lens 600 according to the embodiment. This arrangement results in four columns 608 to 614 of Fresnel facets with each column comprising three such Fresnel facets.

Therefore, it will be appreciated that not all of the facets of the lens 400 are used in forming or using the lenses 116 and 118, that is, some of the facets are masked to prevent transmission, and subsequent focusing, of infrared radiation onto a respective PIR detector or detectors. The masking is achieved by placing an infrared attenuating or absorbing material on the inwardly directed faces of the lenses 116 and 118 in registry with facets that are to be rendered ineffective.

Furthermore, the masking of the lenses 116 and 118 is such that the fields of view of one lens do not overlap with the fields of view of the other lens. Alternatively, embodiments can be realised in which the facets or regions of the lenses 116 and 118 that are intended to be masked or rendered ineffective are fabricated from or contain a material that prevents or at least substantially reduces transmission of infrared radiation.

Referring to figure 7, there is shown a perspective view 700 of two sets of fields of view derived from two lenses such as lenses 116 and 118 when realised according to figures 5 and 6 respectively. The upper set of fields of view 702 has three rows with three pairs of fields of view or fingers visible of the five columns. It will be appreciated that the fields of view are arranged in pair due to the construction of PIRs used by those skilled in the art since current PIRs have both positive and negative elements. The lower set of fields of view 704 also comprises three rows but with two pairs of fields of view or fingers of the four columns being visible. The fields of view of the second set 704 are disposed in between the fields of view of the first set, that is, they are interdigitated. However, the fields of view of the first set 702 do not overlap with or intersect the fields of view of the second set 704. It can be appreciated that the focuses 706 and 708 of the first 702 and second 704 sets of fields of view are offset. In preferred embodiments, the first 702 and second 702 fields of view are vertically offset. In preferred embodiments, the foci are offset by between 2 and 10 cm.

Figure 8 illustrates a second perspective 800 of the first 702 and second 704 fields of views shown in figure 7. It can be seen that all of the five columns of the fields of view of the lens according to figure 5 are visible and that the first set 702 of fields of view comprises three rows of five pairs of fields of view or fingers interposed with three rows of four pairs of fields of view of the second set 704 produced by a lens according to figure 6.

It will be appreciated from figures 7 and 8 that the fields of view are arranged in pairs with, for example, a pair of fields of view associated with one lens being disposed between two pairs of fields of view or a pair of single fields of view of another lens. However, embodiments can be realised in which a single field of view of one lens is disposed between a pair of single fields of view of another lens. Alternatively, a pair of fields of view of one lens may be disposed between two pairs of fields of view of the other lens. Embodiments can be realised in which a predetermineable number of fields of view of one lens are disposed between, or interdigitated with, a predetermineable number of fields of view of the other lens.

It will be appreciated that the fields of view are separate, that is, they do not overlap.

Referring to figure 9, there is illustrated a flow chart 900 of the processing undertaken by the processor when executing the software in processing the signals received from the microwave and PIR detectors. The processor 128, executing the software 130, is arranged to be "idle" until the detection of the signal or trigger from at least one of the microwave detector 106 and the passive infrared detectors 102 and 104 or from all of the detectors 102 to 106. The idle state of the processor 128 is achieved, for example, using a processing loop such as that shown at step 902 in figure 9. Alternatively, the "idle" state of the processor 128 can be left if the signals from at least one of the microwave detector 106 and the passive infrared detectors 102 and 104, or from all of the detectors 102 to 106, is or are used as an interrupt or interrupts that is or are serviced by the processor 128 according to the software 130.

One skilled in the art appreciates that the processing loop or "idle" state are actually used to perform other tasks within the movement detector such as, for example, temperature measurements, self-testing, compensation measurements/actions etc. Therefore, it is not strictly correct to describe the processing ioop or processor as idle.

In an embodiment, a determination is made, at step 904, as to whether or not the signal 122 received from the microwave detector 106 is indicative of detection of an event, that is, can be properly classified as a valid trigger signal. If the signal 122 is determined at step 904 to be indicative of detection of an event such as, for example, detection of movement by the microwave detector 106, a timer corresponding to or associated with the microwave detector 106 is started at step 906. If the determination at step 904 is that the signal 122 is not indicative of detection of an event, a determination is made at step 908 as to whether or not the processing ioop 902 or "idle" state was interrupted by a signal 108 from the first passive infrared detector 102. If the determination at step 908 is positive, a timer associated with the first passive infrared detector 102 is started at step 910. However, if the determination at step 908 is negative, processing proceeds to step 912. A determination is made at step 912 as to whether or not the timer associated with the microwave detector 106 and the timer associated with the first passive infrared detector 102 are both running. If the determination is positive, an alarm signal 134 is generated for a predetermined period of time at step 914. If the determination at step 912 is negative, a determination is made, at step 916, as to whether not the signal that interrupted the processing at step 902 or the "idle" state was signal 110 from the second passive infrared detector 104. If the determination at step 916 is negative, the processing loop 902 is re-entered or the "idle" state is re-entered. However, if the determination at step 916 is positive, an output signal or alarm signal 135 is output, at step 918, via the second output terminal 0P2 for a predetermined period of time. Thereafter, processing returns to step 902 or the "idle" state is re- entered.

Referring to figure 10, there is shown a front view 1000 of a combined detector according to an embodiment. It can be appreciated that the combined detector comprises a front cover 1002 having to apertures or windows 1004 and 1006 and bearing lenses such as those shown in figures and 6. The front cover 102 optionally comprises a further pair of apertures 1008 and 1010 bearing optical guides 1012 and 1014 for outputting light from LEDs to provide an indication that - the combined detector is operating correctly.

Figure 11 shows a further view 1100 of the combined detector illustrated in figure 10 with the front cover 1002 removed. It can be appreciated that the pair of lenses 500 and 600 are curved.

Also more clearly illustrated are the optical guides 1012 and 1014. The curved nature of the lenses may contribute, at least in part, to maintaining the separation of the fields of view.

It will be appreciated that the processing undertaken in figure 9, insofar as concerns the processing of the output signals from the PIR detectors, is arranged to realise a detector providing a sequentially confirmed alarm.

Although the embodiments have been described with reference to the combined detector generating an intrusion signal in response to detecting an intruder, embodiments can be realised in which an intrusion message is generated as well as, or as an alternative to, such an intrusion signal.

Furthermore, embodiments have been described with reference to combined detectors. However, embodiments can be realised in which single technology sensors or detectors are used.

The embodiments described above have been realised using a common master for all facets.

However, embodiments are not limited thereto. Embodiments can be realised in which a number of Fresnel masters can be used to form the facets.

Although the above embodiments have been described with reference to a combined detector comprising dual technology sensors or detectors, embodiment are not limited thereto.

Embodiments can be realised in which the detector merely comprises, for example, a pair or multiple PIR detectors. Such embodiment will still have the capability of providing a sequentially confirmed alarm. It will be appreciated that the use of a second technology such as, for example, microwave or ultrasound technology, assists in providing greater immunity to false alarms.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) and/or all of the steps of any method or process so disclosed, may be combined in - - any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A detector comprising an optical arrangement comprising a plurality of facets creating a plurality of separate, interdigitated, fields of view.

2. A detector as claimed in any preceding claim in which the plurality of fields of view is

arranged as a number of sets of fields of view.

3. A detector as claimed in claim 2 in which the fields of view of a first set are linearly arranged.

4. A detector as claimed in either of claims 2 and 3 in which the fields of a second set are linearly arranged.

5. A detector as claimed in any preceding claim in which the first set of fields of view has a common first focus.

6. A detector as claimed in any preceding claim in which the second set of fields of view has a common second focus.

7. A detector as claimed in which the first and second common focuses are vertically disposed relative to one another.

8. A detector as claimed in any preceding claim in which the at least one field of view is, and preferably all of the fields of view are, divergent.

9. A detector as claimed in any preceding claim in which the fields of view of the first set have a common first focal point.

10. A detector as claimed in any preceding claim in which the fields of view of the second set have a common focal point.

11. A detector substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

12. A detector comprising a first lens system having a plurality of facets bearing respective fields of view and a second lens system having a plurality of facets bearing respective fields of view; the two pluralities of fields of view being interdigitally arranged.

13. A detector comprising a first optical arrangement comprising a number of fields of view and a second optical arrangement comprising a number of fields of view; the first and second optical arrangements being arranged so that the fields of view are alternately arranged.

14. An optical arrangement or lens substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

14. A detector as claimed in claim 13, in which the fields of view are alternately arranged such that at least one field of view of the first optical arrangement is disposed between at least a pair of fields of view of the second optical arrangement.

15. A detector as claimed in either of claims 13 and 14, in which the fields of view are alternately arranged such that one or more than one field of view of the first optical arrangement is disposed between two or more than two fields of view of the second optical arrangement, preferably, a pair of fields of view of the first optical arrangement or a second set of facets is interposed between two pairs of fields of view of the second optical arrangement or a second set of facets.

16. An optical arrangement comprising a plurality of Fresnel lenses or Fresnel facets forming a plurality of non-overlapping, interleaved fields of view.

17. A lens substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

18. An optical arrangement or system for a detector as claimed in any preceding claim.

19. An optical system or lens comprising a plurality of lenses corresponding to a plurality of fields of view; the plurality of lenses having disposed therebetween a plurality of blanks to optically separate the plurality of fields of view.

20. An optical system or lens as claimed in claim 19 in which the plurality of lenses are arranged in at least first and second groups such that the plurality of fields of views of the groups are iriterdigitated.

21. An optical system or lens comprising a first plurality of fields of view interposed with a second plurality of fields of view in a nonoverlapping manner.

22. An optical system or lens substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

23. An optical system comprising a lens having a number of facets; the facets being arranged to form a first set of a number of fields of view and a second set of a number of fields of view; the fields of view of the first set being interdigitated with the fields of view of the second set.

24. A detector comprising a housing having a pair of apertures bearing a first lens and a second lens; the first and second lenses having respective pluralities of facets wherein the respective pluralities of facets are complementary such that the fields of view of the facets do not overlap.

Amendments to the claims have been filed as follows 1. A detector comprising first and second lenses for use with respective PIR sensors; each lens comprising a plurality of Fresnel facets having respective fields of view adapted such that the fields of view of the first lens are alternately arranged with the fields of view of the second lens such that the fields of view of the first lens are adjacent only to, but do not overlap with, the fields of view of the second lens in a single direction.

arranged as a number of sets of fields of view.

6. A detector as claimed in any preceding claim in which the second set of fields of view has a common second focus. * S. * . S I.. S

* . 7. A detector as claimed in which the first and second common focuses are vertically disposed relative to one another. * S. * S *

:. 8. A detector as claimed in any preceding claim in which the at least one field of view is, and preferably all of the fields of view are, divergent. * *

9. A detector as claimed in claim 8 in which all of the fields of view are divergent.

10. A detector substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

11. An optical arrangement comprising a plurality of Fresnel lenses or Fresnel facets forming first and second sets of fields of view; the first set of fields of view being alternately disposed relative to the second set of fields of view such that the fields of view of the first set are adjacent only to, but do not overlap with, the fields of view of the second set in a first direction. jL.

12. An optical arrangement as claimed in claim 11 in which the plurality of lenses or facets have disposed there between a plurality of blanks to optically separate the first and second sets of

fields of view.

13. An optical arrangement or system for a detector as claimed in any of claims ito 10.