SPECTROMETER DEVICE AND SYSTEM

Abstract

Described herein are a spectrometer system and a spectrometer device, which are suited for investigation or monitoring purposes, in particular, in the infrared (IR) spectral region, and for a detection of heat, flames, fire, or smoke.

The spectrometer device allows capturing incident light from an object and transferring the incident light to a length variable filter with a particularly high concentration efficiency. Apart from the spectrometer device, the spectrometer system further includes an evaluation unit designated for determining information related to a spectrum of an object by evaluating the detector signals provided by the spectrometer device.

Claims

1. A spectrometer device (112), comprising: an optical element (122) designed for receiving incident light (114) from an object (116) and transferring the incident light (114) to a length variable filter (118), wherein the optical element (122), wherein the optical element (122) comprises an optical concentrator device (124), wherein the optical concentrator device (124) is operated in a reverse direction (126), wherein the optical concentrator device (124) has a single sidewall (128) which is adapted for reflecting incident light, wherein the single sidewall (128) is designed as a rounded sidewall; the length variable filter (118) which is designated for separating the incident light (114) into a spectrum of constituent wavelength signals; and a detector array (120) comprising a plurality of pixelated sensors (144), wherein each of the pixelated sensors (144) is adapted to receive at least a portion of one of the constituent wavelength signals, wherein each of the constituent wavelength signals is related to an intensity of each constituent wavelength.

2. The device (112) according to claim 1, wherein the optical concentrator device (124) operated in the reverse direction (126) comprises an entrance pupil (180) at an input (130) and an exit pupil (184) at an exit (134), wherein an optically guiding structure (132) is located between the input (130) and the output (132).

3. The device (112) according to claim 2, wherein the entrance pupil (180) comprises an input angle of less than 90°, and wherein the exit pupil (184) comprises an output angle of not more than 30°.

4. The device (112) according to claim 2, wherein the single rounded sidewall (128) constitutes a shell surface (176) which is adapted to connect an entrance aperture (178) at the entrance pupil (180) and an exit aperture (182) at the exit pupil (184) as the optically guiding structure (132).

5. The device (112) according to claim 2, wherein the optical concentrator device (124) operated in the reverse direction (126) has a round entrance aperture (178) at the entrance pupil (180) and an elongated and rounded exit aperture (182) at the exit pupil (184).

6. The device (112) according to claim 1, wherein the optical concentrator device (124) comprises one of a conical shape or a non-conical shape.

7. The device (112) according to claim 6, wherein the non-conical shape of the optical concentrator device (124) comprises a shape selected from a parabolic shape (168) or an elliptical shape (182).

8. The device (112) according to claim 1, wherein the optical concentrator device (124) is arranged in an asymmetric manner with respect to the length variable filter (118),

9. The device (112) according to claim 8, wherein the optical concentrator device (124) is tilted with respect to a plane which is perpendicular to a receiving surface (136) of the length variable filter (118).

10. The device (112) according to claim 1, wherein the detector array (120) is separated from the length variable filter (118) by a transparent gap (146).

11. The device (112) according to claim 1, further comprising an illumination source (154) adapted for illuminating the object (116).

12. The device (112) according to claim 11, wherein the illumination source (154) comprises an incandescent lamp (156).

13. A spectrometer system (110), comprising the spectrometer device (112) according to claim 1; and an evaluation unit (150) designated for determining information related to a spectrum of an object (116) by evaluating detector signals (204, 204′, 204″) provided by the spectrometer device (112).

14. The system (110) according to claim 13, further comprising an illumination source (154) adapted for illuminating the object (116).

15. A method of using the spectrometer device (112) according to claim 1, the method comprising using the spectrometer device (112) for a purpose selected from the group consisting of an infrared detection application; a heat-detection application; a thermometer application; a heat-seeking application; a flame-detection application; a fire-detection application; a smoke-detection application; a temperature sensing application; a spectroscopy application; an exhaust gas monitoring application; a combustion process monitoring application; a pollution monitoring application; an industrial process monitoring application; a chemical process monitoring application; a food processing process monitoring application; a water quality monitoring application; an air quality monitoring application; a quality control application; a temperature control application; a motion control application; an exhaust control application; a gas sensing application; a gas analytics application; a motion sensing application; and a chemical sensing application.

16. A method of using the spectrometer system (110) according to claim 13, the method comprising using the spectrometer system (110) for a purpose selected from the group consisting of an infrared detection application; a heat-detection application; a thermometer application; a heat-seeking application; a flame-detection application; a fire-detection application; a smoke-detection application; a temperature sensing application; a spectroscopy application; an exhaust gas monitoring application; a combustion process monitoring application; a pollution monitoring application; an industrial process monitoring application; a chemical process monitoring application; a food processing process monitoring application; a water quality monitoring application; an air quality monitoring application; a quality control application; a temperature control application; a motion control application; an exhaust control application; a gas sensing application; a gas analytics application; a motion sensing application; and a chemical sensing application.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0131] Further optional details and features of the invention are evident from the description of preferred exemplary embodiments which follows in conjunction with the dependent claims. In this context, the particular features may be implemented alone or with features in combination. The invention is not restricted to the exemplary embodiments. The exemplary embodiments are shown schematically in the figures. Identical reference numerals in the individual figures refer to identical elements or elements with identical function, or elements which correspond to one another with regard to their functions.

[0132] Specifically, in the figures:

[0133] FIG. 1 shows an exemplary embodiment of a spectrometer system comprising a spectrometer device according to the present invention;

[0134] FIGS. 2A and 2B show cross-sections through exemplary embodiments of preferred non-conical shapes of an optical concentrator device;

[0135] FIG. 3 shows a further cross-section through an exemplary embodiment of the optical concentrator device;

[0136] FIGS. 4A and 4B show a further exemplary embodiment of the spectrometer device using an optical concentrator device in an asymmetric arrangement; and

[0137] FIGS. 5A and 5B show a variation of the light transmission in a symmetric arrangement (FIG. 5A) and an asymmetric arrangement (FIG. 5B), respectively, of the optical concentrator device.

EXEMPLARY EMBODIMENTS

[0138] FIG. 1 illustrates, in a highly schematic fashion, an exemplary embodiment of a spectrometer system 110 which comprises a spectrometer device 112 according to the present invention. As generally used, the spectrometer device 112 is an apparatus which is capable of recording a signal intensity of incident light 114 with respect to a corresponding wavelength or a wavelength interval of the incident light 114 over a range of wavelength which is denoted as a spectrum or a partition thereof. According to the present invention, the spectrometer device 112 may, especially, be adapted for recording a spectrum in the infrared (IR) spectral region, preferably, in the near-infrared (NIR) and the mid-infrared (MidIR) spectral range, especially, wherein the incident light may have a wavelength of 1 μm to 5 μm, preferably of 1 μm to 3 μm, and can, thus, be applicable for a detection of heat, flames, fire, or smoke, wherein further applications may be feasible. Herein, the incident light 114 may be generated and/or reflected by an object 116, which may be a living object and a non-living object, such as comprising one or more articles and/or one or more parts of an article, wherein the at least one article or the at least one part thereof may comprise at least one component which can provide a spectrum which may be suitable for investigations in the IR, especially in the NIR spectral region.

[0139] The exemplary spectrometer device 112 as schematically depicted in FIG. 1 comprises a linearly variable filter 118 as a preferred example of a length variable filter. Herein, the linearly variable filter 118 is designated for separating the incident light 114 into a spectrum of constituent wavelength signals, a detector array 120 which is designed for determining respective intensities of received wavelength signals, and an optical element 122 which is designated for receiving incident light 114 from the object 116 and transferring the incident light 114 to the linearly variable filter 118.

[0140] According to the present invention, the optical element 122 comprises an optical concentrator device 124, wherein the optical concentrator device is operated in reverse direction 126, wherein the inversely-operated optical concentrator device 124 comprises a single rounded sidewall 128. Herein, the inversely-operated optical concentrator device 124 comprises an input 130, an optically guiding structure 132 and an output 134. Consequently, the incident light 114 which may be emitted or reflected by the object 116 or may have passed through the object 116 enters the inversely-operated optical concentrator device 124 at the input 130 which is designed for receiving the incident light 114. Thereafter, the incident light 114 captured by the input 130 passes through the optically guiding structure 132 which is, preferably, designed for spreading out the incident light 114. Finally, the incident light 114 which has been spread out in this manner is emitted by the output 134 which is being designated for this purpose. Thus, an angular spread of light beams which are emitted at the output 134 can, simultaneously, be reduced compared to the angular spread of the incident light 114. As a result, the inversely-operated optical concentrator device 124 allows modifying the incident light 114 as provided by the object 116 in a manner that the light which is emitted at the output 134 of the inversely-operated optical concentrator device 124 exhibits a reduced angular spread.

[0141] Consequently, a predominant share of the light beams provided by the output 134 of the inversely-operated optical concentrator device 124 impinges the linearly variable filter 118 in a parallel manner, especially, normal to a receiving surface 136 of the linearly variable filter 118 in a perpendicular manner. As used in this exemplary embodiment, the linearly variable filter 118 is or comprises an optical filter having a plurality of interference filters which are, preferably, provided in a continuous arrangement of interference filters. Herein, each of the interference filters may form a bandpass with a variable center wavelength for each spatial position 138 on the receiving surface 136 of the linearly variable filter 118 in a manner that the variable center wavelength may be a linear function of the spatial position 138. As exemplary shown in FIG. 1, the linearly variable filter 118 may, thus, be arranged, preferably continuously, along a single dimension, usually as “length” of the linearly variable filter 118. By way of example, the linearly variable filter 118 may be a wedge filter that may carry at least one response coating 140 on a transparent substrate 142, wherein the response coating 140 may exhibit a spatially variable property, in particular, a spatially variable thickness (not depicted here). Herein, the transparent substrate 142 may comprise at least one material that may exhibit a high degree of optical transparency in the IR spectral range which can, preferably, be selected from the group consisting of calcium fluoride (CaF.sub.2), fused silica, germanium, magnesium fluoride (MgF), potassium bromide (KBr), sapphire, silicon, sodium chloride (NaCl), zinc selenide (ZnSe), zinc sulfide (ZnS), borosilicate-crown glasses, transparent conducting oxides (TOO), and transparent organic polymers, wherein CaF.sub.2, fused silica, MgF, KBr, sapphire, NaCl, ZnSe, ZnS, borosilicate-crown glasses, transparent conducting oxides, and selected transparent organic polymers may, especially, be applicable for the NIR spectral range. However, other embodiments of the linearly variable filter 118 may also be feasible. However, other kinds of length variable filters may also be feasible for the purposes of the present invention.

[0142] The linearly variable filter 118 is designated for separating the incident light 114 into a spectrum of constituent wavelength signals. For this purpose, the incident light 114 may, preferably, pass through the linearly variable filter 118 at the particular spatial position 138 which is related to the wavelength of the incident light 114. After the incident light 114 has passed through the linearly variable filter 118 at the particular spatial position 138 related to the wavelength of the incident light 114, it, subsequently, impinges the detector array 120, in particular one of a plurality of pixelated sensors 144 as comprised by the detector array 120. Thus, each of the pixelated sensors 144 receives at least a portion of one of the constituent wavelength signals as provided by the incident light 114 after having passed through the linearly variable filter 118 as described above. Moreover, each of the pixelated sensors 144 is adapted to provide a detector signal which is related to an intensity of each constituent wavelength. In other words: The spectrometer device 112 is, thus, designated to generate a plurality of detector signals based on the constituent wavelength signals, wherein each of the detector signals is related to the intensity of each constituent wavelength of the spectrum.

[0143] As further indicated in FIG. 1, the detector array 120 may, preferably, be separated from the linearly variable filter 118 by a transparent gap 146, wherein the transparent gap 146 may, by way of example, be obtained by using the transparent substrate 142. As a result, by selecting a suitable width for the transparent gap 146 a more precise adjustment of the detector array 120 with regard to the linearly variable filter 118 can be achieved. As indicated below in more detail, adjusting the transparent gap 146 may allow further increasing the efficiency of the spectrometer device 112.

[0144] The plurality of detector signals may, as schematically depicted in FIG. 1, via a signal lead 148 be transmitted to an evaluation unit 150, which may be comprised by the spectrometer system 110 in addition to the spectrometer device 110. Herein, the evaluation unit 150 is, generally, designated for determining information related to a spectrum of the object 116 by evaluating the plurality of detector signals as provided by the detector array 120 of the spectrometer device 112. For this purpose, the evaluation unit 150 may comprise one or more electronic devices and/or one or more software components, in order to evaluate the plurality of the detector signals, which are symbolically denoted by a signal evaluation unit 152. Herein, the evaluation unit 150 may be adapted to determine the at least one item of information related to a spectrum of the object 116 by comparing more than one of the detector signals.

[0145] The incident light 114 which is received by the optical element 122 of the spectrometer device 112 may be generated by a light-emitting object 116. Alternatively or in addition, the incident light 114 may be generated by a separate illumination source 154, which may include an ambient light source and/or an artificial light source, in particular an incandescent lamp 156, which may be designated for illuminating the object 116 in a manner that at least a part of the light generated by the illumination source 154 may be able to pass through the object 116 (not depicted here) and/or in a manner that the object 116 may be able to reflect at least a part of the light generated by the illumination source 154 such that the incident light 114 may be configured to be received by the optical element 122. Herein, the illumination source 154 may be or comprise a continuously emitting light source and/or a modulated light source. As further depicted in FIG. 1, the illumination source 154 may be controlled by at least one illumination control unit 158 which may be adapted, if required, for providing modulated light. Herein, the illumination control unit 158 may, additionally, provide information about the illumination to the signal evaluation unit 152 and/or be controlled by the signal evaluation unit 152, which is symbolically indicated by a connection between the illumination control unit 158 and the signal evaluation unit 152 in FIG. 1. Alternatively or in addition, controlling the illumination of the object 116 may be effected in a beam path between the illumination source 154 and the object 116 and/or between the object 116 and the optical element 122. Further possibilities may be conceivable.

[0146] Generally, the evaluation unit 150 may be part of a data processing device 160 and/or may comprise one or more data processing devices 160. The evaluation unit 150 may be fully or partially integrated into a housing 162 which at least comprises the spectrometer device 112 and/or may fully or partially be embodied as a separate device which may electrically be connected in a wireless or wire-bound fashion to the spectrometer device 112. The evaluation unit 150 may further comprise one or more additional components, such as one or more electronic hardware components and/or one or more software components, such as one or more measurement units and/or one or more evaluation units and/or one or more controlling units (not depicted here).

[0147] As further illustrated in the exemplary embodiment of FIG. 1, the spectrometer device 112 comprises the optical element 122, the linearly variable filter 118, and the detector array 120, which are, in this particular embodiment, arranged along an optical axis 164 of the spectrometer device 112. Specifically, the optical axis 164 may be an axis of symmetry and/or rotation of the setup of at least one of the optical element 122, the linearly variable filter 118, and the detector array 120. Especially, the optical axis 164 may, thus, be parallel to a plane which is perpendicular to the receiving surface 136 of the linearly variable filter 118. Further, the optical element 122, the linearly variable filter 118, and the detector array 120 may, preferably, be located inside the housing 162 comprising at least the spectrometer device 112.

[0148] In a further embodiment, at least one transfer device (not depicted here), in particular, a refractive lens, may, additionally, be placed between the optical element 122 and the linearly variable filter 118. However, since the optical element 122 is implemented in the particular embodiment of FIG. 1 in form of the inversely-operated optical concentrator device 124 comprising the conical shape 128, the use of a transfer device, in particular, a refractive lens, appears to be dispensable because this implementation of the optical element 122 is capable of, concurrently, taking over the function of the transfer device, in particular, a refractive lens, especially with regard to providing a predominant share of parallel light beams which may impinge on the linearly variable filter 118 normal to the receiving surface 136 of the linearly variable filter 118 in a perpendicular manner.

[0149] FIGS. 2A and 2B illustrate cross-sections through two exemplary embodiments of preferred shapes of the single rounded sidewall 128 of the inversely-operated optical concentrator device 124. FIG. 2A schematically depicts a compound parabolic concentrator 166 in which the rounded shape of the single sidewall 128 of the optical concentrator device 124 comprises a parabolic shape 168 while FIG. 2B schematically depicts a compound elliptical concentrator 170 in which the rounded shape of the single sidewall 128 of the optical concentrator device 124 comprises an elliptical shape 172. However, the single sidewall 128 of the inversely-operated optical concentrator device 124 may also assume a further shape which may be a single rounded shape.

[0150] Herein, the inversely-operated optical concentrator device 124 may be provided in form of a full body (not depicted here) of a transparent optical material having a high optical transmittance in the IR spectral range in order to enhance a reflectivity of the optical concentrator device 124. In particular, the inversely-operated optical concentrator device 124 may be provided in form of the full body of an at least partially optically transparent material having a high degree of optical transparency in the IR spectral range which can, preferably, be selected from the group consisting of calcium fluoride (CaF.sub.2), fused silica, germanium, magnesium fluoride (MgF), potassium bromide (KBr), sapphire, silicon, sodium chloride (NaCl), zinc selenide (ZnSe), zinc sulfide (ZnS), borosilicate-crown glasses, transparent conducting oxides (TOO), and transparent organic polymers, wherein CaF.sub.2, fused silica, MgF, KBr, sapphire, NaCl, ZnSe, ZnS, borosilicate-crown glasses, transparent conducting oxides, and selected transparent organic polymers may, especially, be applicable for the NIR spectral range, wherein silicon and germanium having high refractive indices are particularly preferred since they are capable of supporting total reflection which may occur on sidewalls of the full body.

[0151] However, as further illustrated in FIGS. 2A and 2B, the inversely-operated optical concentrator device 124 may, as an alternative, be provided in form of a hollow body 174 having the single sidewall 128 which may be arranged in a manner that it constitutes the desired shape, in particular, the parabolic shape 168 of FIG. 2A or the elliptical shape 172 of FIG. 2B. Again, the single sidewall 128 of the inversely-operated optical concentrator device 124 may assume a different shape 165 as long as this different shape generates the desired single sidewall 128. For this purpose, the hollow body 174 having the single sidewall 128 may comprise a vacuum or may, preferably fully and/or uniformly, be filled with a gaseous and/or fluid optically transparent material, especially selected from ambient air, nitrogen gas, carbon dioxide, immersion oil, or Canada balsam, in order to be applicable as the optical concentrator device 124 operated in the reverse direction 126.

[0152] In known optical concentrator devices the sidewalls of the hollow body 174 which constitutes the inversely-operated optical concentrator device 124 may be designed as sidewalls which are adapted to absorb such wavelengths of the incident light 114 which may deviate to a high degree from a path which can, eventually, guide the incident light to impinge the linearly variable filter 118 in a predominantly parallel manner. However, such kinds of sidewalls of the hollow body 174 may, as indicated above, diminish the efficiency of the spectrometer device 112 since an absorptive share of the incident light 114 is deterred from passing the linearly variable filter 118 and, eventually, reaching the detector array 120 and can, thus, not contribute to the detector signal.

[0153] Therefore, according to the present invention, the single sidewall 128 of the hollow body 174 constituting the inversely-operated optical concentrator device 124 may, as depicted in FIGS. 1, 2A and 2B, be designated as a single reflective sidewall 128 which may be adapted for reflecting incident light 114. As a result, the single reflective sidewall 128 may, thus, be capable of increasing the efficiency of the spectrometer device 112 by allowing additional light beams 186 to be guided, by reflection on the single reflective sidewall 128, to the linearly variable filter 118 and, subsequently, to the detector array 120 where they, may, in addition, contribute to the detector signal. Consequently, providing the single reflective sidewall 128 which may define the hollow body 174 which implements the inversely-operated optical concentrator device 124 can, thus, further increase the efficiency of the spectrometer device 112, in particular, by reducing the signal-to-noise ratio.

[0154] Further, FIG. 3 shows a cross-section through an exemplary embodiment of a preferred inversely-operated optical concentrator device 124 according to the present invention. Herein, the single reflective sidewall 128 is generated by the hollow body 174 which may, as indicated above, comprise a vacuum or may, preferably fully and/or uniformly, be filled with a gaseous and/or fluid optically transparent material, especially selected from ambient air, nitrogen gas, carbon dioxide, immersion oil, or Canada balsam. Herein, the single reflective sidewall 128 forms a boundary which may be adapted to limit the inversely-operated optical concentrator device 124 and constitute a surface thereof. In particular, the single rounded sidewall 128 may constitute a shell surface 176 which may, specifically, be adapted to connect an entrance aperture 178 at an entrance pupil 180 and an exit aperture 182 at an exit pupil 184. More particular, the single rounded sidewall 128 may, preferably, comprise a non-conical profile, specifically, selected from a parabolic profile or an elliptical profile. Thus, the shell surface 176 of the single rounded sidewall 128 as exemplarily illustrated in FIG. 3 assumes a shape in three-dimensional space in a manner that the shape of the single rounded sidewall 128 is devoid of any corners.

[0155] In the particularly preferred embodiment as schematically depicted in FIG. 3, the entrance aperture 178 at the entrance pupil 180 the inversely-operated optical concentrator device 124 may, in order to be capable of catching as much light as possible, preferably comprise a small round opening having dimensions d.sub.x, d.sub.y, wherein a quotient d.sub.y/d.sub.x may assume a value of 0.75 to 1.25, preferably of 0.9 to 1.1, in particular of 0.95 to 1.05. On the other hand, the exit aperture 182 at the entrance pupil 184 the inversely-operated optical concentrator device 124 may, in order to allow guiding as much light as possible via the length variable filter 118 onto the detector array 120 which exhibits a rectangular form in this embodiment, may comprise an elongated and rounded opening, in particular an elliptical opening having dimensions D.sub.x, D.sub.y, wherein a quotient D.sub.y/D.sub.x may assume a value of 1.5 to 20, preferably of 2 to 10, in particular of 2.5 to 6. However, especially depending on the form of the detector array 120, other shapes of the entrance aperture 178 and/or of the exit aperture 182 of the optical concentrator device 124 being operated in reverse direction may also be feasible.

[0156] Further, FIG. 4 schematically illustrates a further exemplary embodiment of the spectrometer device 112 according to the present invention. In contrast to the exemplary embodiment of the spectrometer device 112 of FIG. 1 which assumes a symmetric arrangement of the optical element 122, the linearly variable filter 118, and the detector array 120 along the optical axis 164 of the spectrometer device 112, the optical element 122 of the spectrometer device 112 as depicted in FIG. 4A assumes an asymmetric arrangement 200.

[0157] In addition, a transfer device (not depicted here) which may, in particular, be an optical lens, a curved mirror, a grating, or a diffractive optical element, may be arranged between the inversely-operated optical concentrator device 124 and the length linearly variable filter 118. Preferably, the optical lens may, especially, be selected from a group consisting of a biconvex lens, a plano-convex lens, a biconcave lens, a plano-concave lens, an aspherical lens, a cylindrical lens and a meniscus lens. However, other kinds of transfer devices may also be feasible.

[0158] Accordingly, a symmetry axis 202 of the optical element 122 which is provided in accordance with the present invention in form of the optical concentrator device 124 arranged in reverse direction 126 and having the single rounded reflective sidewall 128 is tilted by an angle α with respect to the optical axis 164 of the spectrometer device 112 which is, as indicated above, parallel to the plane which is perpendicular to the receiving surface 136 of the linearly variable filter 118. Herein, the angle α is chosen in view of the incident light 114 which is transferred to the linearly variable filter 118 not only impinging the linearly variable filter 118 perpendicular to the receiving surface 136 of the linearly variable filter 118 on a spatial position 138 of the linearly variable filter 118 which is designed for receiving a wavelength of the incident light 118 but, in addition, also impinging a further spatial position 138′ on the linearly variable filter 118 which is designed for receiving a further wavelength which exceeds the wavelength of the incident light 114.

[0159] Therefore, the light beam 186 may pass the linearly variable filter 118 at a longer wavelength compared to its inherent wavelength but due to the relative arrangement between the linearly variable filter 118 and the detector array 120, which is separated here by the transparent gap 146 as described elsewhere in this document in more detail, the light beam 186 may, still, impinge the particular pixelated sensor 144 which is provided for determining the intensity of the incident light at the particular wavelength of the incident light beam 114. Consequently, not only light beams 186 which impinge the linearly variable filter 118 normal to the receiving surface 136 of the linearly variable filter 118 at the spatial position 138 on the linearly variable filter 118 which is designated for this purpose but also light beams 186′ which impinge the linearly variable filter 118 on the further spatial position 138′ which is designated for receiving the longer wavelength compared to the wavelength of the incident light 144, still, impinge the same particular pixelated sensor 144 which is designed for receiving the particular wavelength of the incident light 114. As a result, also the light beams 186′ may, thus, contribute to the electrical signals as generated by the particular individual pixelated sensor 144, whereby the efficiency of the spectrometer device 112 can further be increased.

[0160] As schematically shown in FIG. 4B, the asymmetric arrangement 200 of the optical element 122 within the spectrometer device 112 as depicted in FIG. 4A may provide additional advantages. As illustrated herein, each of three different light beams 186, 186′, 186″ having three different wavelengths may generate a detector signal 204, 204′, 204″ in the corresponding pixelated sensor 144 of the detector array 120 having, within a defined tolerance level, the same intensity irrespective of their wavelength. This advantage may even be achieved when using an incandescent lamp 156 as the illumination source 158 which can be considered as a thermal emitter within the IR spectral range and, therefore exhibits an emission power which decreases with increasing wavelength. However, this effect may be outweighed by the asymmetric arrangement 200 of the optical element 122, wherein a longer path for the light beam 186 having the shorter wavelength compared to a light beam 186″ having the longer wavelength may be provided.

[0161] In addition, further effects which may influence the intensity of the light beam 186, 186′, 186″ at the pixelated sensor 144 may be outweighed in this manner. Especially, known IR absorption materials exhibit a tendency of increased absorption with increasing wavelength. Further, since a bandpass width of the linearly variable filter 118 typically, assumes a constant value, such as 1%, over the spectral range of the linearly variable filter 118, the resolution of the linearly variable filter 118 being inversely proportional to the bandpass width, also decreases with increasing wavelength. Further, the resolution of the linearly variable filter 118, in general, depends on the center wavelength of the linearly variable filter. However, the asymmetric arrangement 200 of the optical element 122 may facilitate the spectrometer device 112 to be more receptive for longer wavelengths while the higher emission power of the incandescent lamp 158 and the lower bandpass width at shorter wavelengths may result in an efficiency of the spectrometer device 112 being more equally distributed over its wavelength range.

[0162] The efficiency of the spectrometer device 112 can even further be increased since the single rounded sidewall 128 of the inversely-operated optical concentrator device is designed as a single reflective sidewall. As schematically shown in FIG. 4B, the single reflective sidewall 128 may allow additional light beams 186* to be guided, by reflection on the single reflective sidewall, to the linearly variable filter 118 and, subsequently, to the detector array 120 where they, may, in addition, contribute to the detector signal.

[0163] FIGS. 5A and 5B each schematically show a variation of a transmission rate, which can be defined by a relative intensity I/I.sub.0 of transmission peaks 206, as a function of a wavelength A [nm] of the corresponding transmission peak 206 after transmission of the incident light 114 through the linearly variable filter 118 of the spectrometer device 112 as determined by a respective simulation. Herein, a symmetric arrangement 208 of the optical concentrator device 124 with respect to the optical axis 164 of the spectrometer device 112 as, for example, depicted in FIGS. 1, 2A and 2B, has been chosen for determining the transmission peaks 206 of FIG. 5A whereas the asymmetric arrangement 200 of the optical concentrator device 124 as shown in FIGS. 4A and 4B has been used for obtaining the transmission peaks 206 as displayed in FIG. 5B.

[0164] As a result of the asymmetric arrangement 200 of the optical concentrator device 124, a shift of the maximum of the relative intensity I/I.sub.0 of the transmission peaks 206 and of the focus of their angle α towards longer wavelengths can be observed. In addition, the transmission peaks 206 appear to have a smaller peak width 210, in particular, a smaller peak width 210 at half-height, in the asymmetric arrangement 200 of FIG. 5B compared to the peak width 210′ at half-height in the symmetric arrangement 208 of FIG. 5A, thus, resulting in a reduction of the bandpass width in the asymmetric arrangement 200. By way of example, the peak width 210 at half-height and, therefore, the bandpass width can be reduced by approx. 5% for the transmission peak 212 having the longest wavelength. Further, the spectrum which can completely be acquired with the respective spectrometer device 112 can, thus, be estimated to slightly increase from a first spectral range 214 of 1270 nm to 2340 nm in the symmetric arrangement 208 as used for FIG. 5A to a second range 216 of 1230 nm to 2390 nm in the asymmetric arrangement 200 as used for FIG. 5B.

[0165] Summarizing, the transmission rate stronger increases towards longer wavelengths and, also, stronger decreases towards smaller wavelengths in the asymmetric arrangement 208 compared to the asymmetric arrangement 200 of the optical concentrator device 124, thus, facilitating the spectrometer device 112 to exhibit a higher reception for longer wavelengths. However, as indicated above, this effect can easily be outweighed by using an incandescent lamp 158 having a higher emission power whereby, eventually, a spectrometer device 112 having an efficiency which may be more equally distributed over its wavelength range may be provided in this manner.

LIST OF REFERENCE NUMBERS

[0166] 110 spectrometer system [0167] 112 spectrometer device [0168] 114 incident light [0169] 116 object [0170] 118 linearly variable filter as a preferred example of a length variable filter [0171] 120 detector array [0172] 122 optical element [0173] 124 inversely-operated optical concentrator device [0174] 126 reverse direction [0175] 128 single rounded sidewall [0176] 130 input [0177] 132 guiding structure [0178] 134 output [0179] 136 receiving surface [0180] 138, 138′ spatial position [0181] 140 response coating [0182] 142 transparent substrate [0183] 144 pixelated sensor [0184] 146 transparent gap [0185] 148 signal lead [0186] 150 evaluation unit [0187] 152 signal evaluation unit [0188] 154 illumination source [0189] 156 incandescent lamp [0190] 158 illumination control unit [0191] 160 data processing device [0192] 162 housing [0193] 164 optical axis [0194] 166 compound parabolic concentrator [0195] 168 parabolic shape [0196] 170 compound elliptical concentrator [0197] 172 elliptical shape [0198] 174 hollow body [0199] 176 shell surface [0200] 178 entrance aperture [0201] 180 entrance pupil [0202] 182 exit aperture [0203] 184 exit pupil [0204] 186, 186′, 186″, 186* light beam [0205] 200 asymmetric arrangement [0206] 202 symmetry axis [0207] 204, 204, 204″ detector signal [0208] 206 transmission peak [0209] 208 symmetric arrangement [0210] 210, 210′ peak width (at half-height) [0211] 212 transmission peak having the longest wavelength [0212] 214 first spectral range [0213] 216 second spectral range