Spectrometer with adjustable sensitivity

Abstract

A spectrometer for analyzing an input optical signal, the input optical signal being input to the spectrometer, the spectrometer comprising: an optical aperture device and an optical element. The optical aperture device is configured to receive a first optical signal derived from an input optical signal, and is configured to select a portion of the first optical signal to generate a second optical signal exiting the optical aperture device. The optical element is configured to receive a second optical signal exiting the optical aperture device on a surface thereof. The optical aperture device is movable relative to the optical element to change a surface area of a second optical signal incident on the optical element.

Description

Technical Field

[0001] The present invention relates to a spectrometer having a movable optical aperture arrangement for adjusting spectral sensitivity. Background Art

[0002] Optical spectroscopy is a technique used to analyze light signals whose wavelengths may lie in the ultraviolet (UV), visible (VIS), near-infrared (NIR), and / or infrared (IR) ranges of the electromagnetic spectrum. Spectral measurements are used in many applications, such as color measurement, determination of chemical concentrations, or analysis of electromagnetic radiation.

[0003] In general, a spectrometer is an optical measurement device that includes, along the optical path from input to output, an input slit, a potential aperture, collimating optics, a dispersive element such as a grating, lenses / focusing optics, and finally a detector that delivers the spectral measurement. The input slit is typically used to control the amount of light entering the spectrometer, thereby affecting the spectrometer's (spectral) resolution and throughput. Typically, in such systems, the input slit is in a fixed position, and its width is selected based on the desired (spectral) resolution.

[0004] In an optical system, the throughput of the system is limited by the minimum throughput of any aperture in the system. In a spectrometer, this means that the throughput is usually limited by the input slit or the pixel size of the detector. To achieve optimized throughput in an optical system, the etendue of the light source, the collection optics, and the etendue of the light receiving optics, optical fiber, or monochromator need to be closely matched. The etendue of a light source is equal to the source emission area (S) multiplied by the solid angle (Ω) of the light collected for a specific application.

[0005] Spectral resolution, or resolution, refers to the maximum number of spectral peaks that a spectrometer can resolve. For example, if a spectrometer with a wavelength range of 200 nm has a spectral resolution of 1 nm, the system will be able to resolve a maximum of 200 individual wavelengths (peaks) across the spectrum. There are three main factors that determine the spectral resolution of a spectrometer: the slit, the diffraction grating, and the detector. The slit determines the minimum image size that can be formed by the spectrometer's optical bench at the detector plane. The diffraction grating determines the total wavelength range of the spectrometer. The detector determines the maximum number and size of discrete points that can be digitized in the spectrum.

[0006] Another important parameter when designing a spectrometer is the (light) sensitivity or photometric sensitivity, which is related to how much light is required to detect a signal. (Light) sensitivity can be measured in photon counts, for example, normalized to microwatts per millisecond of integration time (counts / μW per ms). Spectral sensitivity, in turn, can be defined by the photosensitivity response over a range of wavelengths.

[0007] Interchangeable slits are known in the prior art and are often used to modify resolution. In practice, such interchangeable slit elements of varying slit sizes (widths) must be physically swapped to achieve the desired resolution for a given spectrometer. When the slit width is altered to change the resolution, the resulting availability of light detectable by the detector, and therefore the flux and, therefore, the spectral sensitivity of the system, also changes. Therefore, independently adjusting either flux or spectral sensitivity is not addressed in the prior art.

[0008] To specifically modify the sensitivity, the use of filters is also known from the prior art. However, filters affect the sensitivity differently across the spectrum, so that solutions using filters do not allow for a homogeneous adjustment of the spectral sensitivity, i.e., a homogeneous adjustment of the sensitivity response across the entire wavelength range. Summary of the Invention

[0009] It is an object of the present invention (among other objects) to provide an improved spectrometer in which the spectral sensitivity can be easily adjusted. In particular, it is an object of the present invention to provide a spectrometer in which the sensitivity response can be tuned independently of the resolution and uniformly over the wavelength range of the spectrometer.

[0010] This object (among others) is achieved by an optical spectrometer according to claim 1 .

[0011] Specifically, this is achieved by an optical spectrometer for analyzing an input light signal, which is input to the spectrometer. The spectrometer includes: an optical aperture device configured to receive a first light signal derived from the input light signal and to select a portion of the first light signal to generate a second light signal that exits the optical aperture device; and an optical element configured to receive light exiting the optical aperture device on its surface. The optical aperture device is movable relative to the optical element along the propagation direction of the first light signal to change the surface area of ​​the second light signal incident on the optical element. Thus, by moving the optical aperture device relative to the optical device, the size of the illuminated surface on the optical element can be easily adjusted, thereby adjusting the sensitivity response of the spectrometer. It is worth noting that the optical spectrometer can be a reflective or transmissive spectrometer. However, the present invention is applicable to any suitable type of spectrometer. Depending on the embodiment, the optical element can include any of the following: a collimating element, a reflective element (e.g., a plane mirror), or a grating element (e.g., a concave grating).

[0012] The spectrometer further comprises a light inlet configured to receive an input light signal and to generate a first light signal, wherein the first light signal is a diverging light beam, preferably a conical diverging light beam. The (conical) diverging light beam of the first light signal can be defined by a solid angle, which is a half-angle of a cone formed by the (conical) diverging light beam.

[0013] According to a preferred embodiment, the optical inlet can be configured to select a portion of the input optical signal to generate the first optical signal. More specifically, the optical inlet can generate the first optical signal by optically attenuating the input optical signal. Generating the first optical signal as a diverging beam facilitates the optical aperture device to cut out or select light from the first optical signal. Preferably, the optical inlet can include a slit element, more preferably, the slit element defines an input plane, from which the first and second optical signals originate, and the distance from the input plane to the optical element is predetermined. In this way, the input optical signal can be prepared for further processing by selecting a desired resolution. In particular, in the case of a slit element, the input optical signal can be processed to generate a first optical signal propagating from the input plane after the slit, and the first optical signal is configured to be received on the optical element to form an image. Alternatively, the optical inlet can be configured to couple the input optical signal to an optical spectrometer to generate the first optical signal. More specifically, the optical inlet can be an optical coupler for coupling an optical fiber used to input the input optical signal to the optical spectrometer.

[0014] Preferably, the light inlet is arranged at a fixed predetermined distance d relative to the optical element. Furthermore, the optical element may include a light receiving area thereof. The light receiving area may be defined by a height h and a width w. Based on the minimum between the width w and the height h of the light receiving area (i.e., the minimum lateral dimension of the light receiving area) and the predetermined distance d, the maximum numerical aperture NA of the spectrometer can be derived.

[0015] According to a preferred embodiment, the optical aperture device may include an exit aperture element comprising a surface for blocking a portion of the incident light signal and an opening for allowing another portion of the incident light signal to pass. This allows for fine control over the amount of light exiting the optical aperture device, while also varying the distance between the exit aperture and the optical element, thereby changing the size of the illuminated surface on the optical element.

[0016] The optical aperture device may include a first end and a second end located opposite thereto. The first end is located upstream of the second end, as viewed in the direction of propagation of the optical signal. Preferably, the exit aperture element is disposed closer to the second end than to the first end of the optical aperture device. More preferably, the exit aperture element is disposed at the second end of the optical aperture device.

[0017] According to a preferred embodiment, the optical aperture device may further comprise an entrance aperture element comprising a surface for blocking a portion of the incident light signal and an opening for letting another portion of the incident light signal pass. In this way, stray light in a region before the optical aperture device (e.g. between a light inlet such as a slit and the optical aperture device) may be prevented from travelling further down the light path. Stray light may be defined as radiation of an undesired wavelength that, if propagated, may activate a response of the spectrometer. Stray light sources may include ambient light, scattered light from imperfect optical components or reflections from non-optical components, and order overlap. Preferably, the entrance aperture element is arranged closer to the first end of the optical aperture device than to the second end, more preferably, the entrance aperture element is arranged at the first end of the optical aperture device.

[0018] According to a preferred embodiment, the optical aperture device may include a tubular housing for holding the entrance aperture element and / or the exit aperture element, so that the entrance aperture element and / or the exit aperture element can be easily displaced by manipulating the tubular housing.

[0019] According to a preferred embodiment, the tubular housing can define a passage between a first end and a second end. The tubular housing can be positioned on the spectrometer such that the first end is upstream of the second end in the direction of propagation of the optical signal. The direction of propagation of the optical signal can also be referred to as the direction of the optical path. In this way, the tubular housing can form a closed passage, trapping light (particularly stray light) therein.

[0020] According to a preferred embodiment, an exit aperture element can be positioned at the second end of the tubular housing. In this way, the tubular housing and the exit aperture element can form a closed channel with an output opening, allowing only a portion of the first light signal to pass through, while the remainder is trapped within the tubular housing. This prevents potential stray light from traveling further downward in the direction of propagation of the light signal, i.e., further down the optical path (particularly, toward the detector), thereby improving spectrometer performance. Alternatively, the exit aperture element can be positioned at the middle portion of the tubular housing.

[0021] According to a preferred embodiment, an entrance aperture element can be provided to the first end of the tubular housing. In this way, the tubular housing and the aperture element can form a closed channel with an input opening, so that only a portion of the first light signal can be allowed to pass through, while the remaining portion is prevented from entering the tubular housing and further traveling toward the detector. Potential stray light can then be prevented from traveling further in the propagation direction of the light signal, that is, further traveling downward along the optical path (in particular, toward the detector), thereby improving the performance of the spectrometer. Alternatively, the entrance aperture element can be provided to the middle portion of the tubular housing along the optical path upward from the exit aperture element. The entrance aperture element may be optional.

[0022] According to a preferred embodiment, the tubular housing can have an outer surface with a circular cross section. In this way, the outer portion of the tubular housing can be cylindrical, thereby enabling easy integration into a spectrometer. Other shapes of the outer surface are also conceivable.

[0023] According to a preferred embodiment, the tubular housing may include at least a portion of its inner surface configured to prevent light from passing through the exit aperture element after reflection from the inner surface portion. Thus, at least a portion of the inner surface may include facets. Such facets can be configured to prevent the propagation of stray light by deflecting light incident on the inner surface from the main propagation direction, that is, away from the optical path and optical axis of the optical aperture device. The optical axis of the optical aperture device may be the longitudinal axis of the tubular housing. This further reduces stray light, thereby further improving the performance of the spectrometer.

[0024] According to a preferred embodiment, the inner surface of the tubular housing can be any of the following, or combinations thereof: a cylindrical portion, a conical portion, a threaded portion, or a spirally ribbed portion. This allows stray light to be scattered in various directions on the reflective inner surface of the tubular housing, particularly in directions not parallel to the optical axis of the optical aperture device, preventing it from propagating along the optical path. This prevents stray light from reaching the surface of the optical element, further reaching the surface of subsequent elements, and ultimately reaching the detector, thereby reducing the impact of noise on the measurement.

[0025] According to a preferred embodiment, at least a portion of the inner surface of the tubular housing has a light-absorbing coating. This further prevents stray light from escaping the tubular housing and reaching the surface of the optical element. The coating can be applied to any type of inner surface as described above, whether cylindrical, conical, threaded, spirally ribbed, or other. Alternatively, the tubular housing can be made of a material that inherently has light-absorbing properties, eliminating the need for a separate coating.

[0026] According to a preferred embodiment, the optical aperture device can be moved translationally along the optical axis of the optical aperture device. In this way, the distance between the optical aperture device and the surface of the optical element can be adjusted by a simple translation.

[0027] According to a preferred embodiment, the tubular housing is capable of sliding relative to the optical element. Preferably, the tubular housing can slide without requiring any further intermediate movement means. This allows for easy displacement of the tubular housing relative to the optical element. Alternatively, the tubular housing can be translated relative to the optical element via a movement means, such as a linear motor or any other actuator suitable for this purpose.

[0028] According to a preferred embodiment, the optical aperture device is movable between a first position and a second position, wherein in the first position, the surface area of ​​the second optical signal incident on the optical element is set to a predetermined maximum area while still being smaller than the total surface of the optical element, and wherein, by moving the optical aperture device from the first position to the second position, the illuminated surface is reduced by at least 10%, preferably by at least 30%. The surface area of ​​the second optical signal incident on the optical element can be referred to as the illuminated surface. This facilitates calibration of the amount of light received by the optical element.

[0029] Preferably, the optical aperture device is configured such that, in a first position (i.e., the position of the optical aperture device furthest from the optical element), the second optical signal corresponds to 100% of the first optical signal. Furthermore, the optical element can be shaped such that, in the first position, the illuminated surface corresponds substantially entirely to the light-receiving area of ​​the optical element. In other words, in the first position, the second optical signal can diverge according to the same solid angle as that defining the diverging beam of the first optical signal, the solid angle of the second optical signal corresponding to the maximum NA of the spectrometer.

[0030] Preferably, the optical aperture device is configured such that, in the second position (i.e., the position of the optical aperture device closest to the optical element), the second optical signal corresponds to between 40% and 60% of the first optical signal. In other words, in the second position, the solid angle over which the second optical signal diverges can be smaller than the solid angle of the diverging beam defining the first optical signal, and smaller than the solid angle corresponding to the maximum NA of the spectrometer.

[0031] According to a preferred embodiment, the optical aperture device is movable between the first position and the second position such that the sensitivity is adjusted by at least 10%, more preferably by at least 30%, even more preferably by at least 60%. In this way, calibration of the spectrometer sensitivity, in particular calibration of the spectral sensitivity, can be easily performed.

[0032] According to a preferred embodiment, the optical aperture device is movable between a first position and a second position such that a final numerical aperture of the illuminated surface of the second light signal incident on the optical element can be adjusted from a maximum numerical aperture of the spectrometer associated with the first position.

[0033] Preferably, the first position corresponds to a position where the optical aperture device is farthest from the optical element. Additionally or alternatively, the second position corresponds to a position where the optical aperture device is closest to the optical element.

[0034] According to a preferred embodiment, the spectrometer may further comprise a housing for holding the optical element and the optical aperture means and optionally the light inlet, wherein the optical element may optionally be fixedly mounted to the housing together with the light inlet, while the optical aperture means is movable relative to the housing. In this way, the relative distance between the optical element and the optional light inlet, on the one hand, and the optical aperture means, on the other hand, may be varied by moving the optical aperture means relative to the housing (or in other words, within the housing).

[0035] According to a preferred embodiment, the housing may include a guide for guiding the movement of the optical aperture device relative to the optical element. More preferably, the guide is a groove in the housing configured as a tubular groove for mating with the tubular housing. This allows for simple translational, preferably sliding, guidance. Alternatively, an additional tubular component fixedly mounted to the housing may serve as the guide. Preferably, the tubular housing may also include a groove at a first end of its outer surface for inserting the tubular housing into the groove. The groove allows for easy insertion of the tubular housing into the tubular groove.

[0036] According to a preferred embodiment, the housing may comprise an interface for moving the optical aperture device, wherein the interface may preferably comprise an elongated opening allowing an external object to come into contact with the optical aperture device to displace the optical aperture device along the elongated opening. Alternatively, an interface for controlling a (linear) motor or a mechanical actuator may be envisaged to forcibly displace the optical aperture device based on user input.

[0037] According to a preferred embodiment, the housing may include a fastening mechanism for fastening the optical aperture device to the housing, wherein the fastening mechanism may preferably include a threaded hole and a screw extending through the hole to contact a groove on the outer surface of the optical aperture device. In this way, the user can easily fix the position of the optical aperture device after calibrating the spectrometer. Although screws have been disclosed, it is worth noting that alternative solutions using known fixing means (glue, clips, bolts) can be envisioned for fastening the optical aperture device to the housing without requiring an inventive step.

[0038] According to a preferred embodiment, the optical element can be a collimating optical element, more particularly a reflector, even more particularly a spherical mirror. According to a preferred embodiment, the opening of the exit aperture element can have a square shape. In this way, the shape of the opening of the exit aperture element can match the shape of the optical element. Alternatively, the opening of the exit aperture element can have a circular shape. According to a preferred embodiment, the opening of the entrance aperture element can have a circular shape. The circular shape of the entrance aperture element avoids the need to align with the exit aperture element. Alternatively, the entrance aperture element can have a square-shaped opening to optionally align with the optical element and / or the exit aperture element. Preferably, the entrance aperture element has an opening that has the same shape as the opening of the exit aperture element. This option still requires precise alignment of the two openings.

[0039] According to a preferred embodiment, the spectrometer may further comprise a dispersive element, a lens optical element and a detector.

[0040] According to another aspect of the present invention, there is provided a method for calibrating a spectrometer, comprising the following steps in the following order:

[0041] a) measuring the spectral response of the spectrometer (100), preferably measuring the sensitivity, more preferably measuring the spectral sensitivity,

[0042] b) moving the optical aperture device (10) relative to the optical element (20) to adjust the spectral response towards a reference spectral response.

[0043] In this way, the sensitivity can be controlled simply by adjusting the position of the optical aperture device relative to the optical device (without changing any components of the spectrometer, such as the slit). This method allows for increased unit-to-unit reproducibility and versatility of use of the spectrometer, thereby reducing costs.

[0044] Those skilled in the art will understand that the reference spectral response can correspond to a desired curve using a given optical bench and at specific settings of the optical spectrometer (integration time, sensor sensitivity, etc.), and optionally includes data processing (e.g., averaging) of the data output by the optical spectrometer. The step of moving the optical aperture device is intended to reproduce or match the reference spectral response using the same specific settings, optical bench, and optionally the same data processing. In practice, the reference spectral response can be obtained from a "mother" reference system with a viable / proven sensitivity.

[0045] According to a preferred embodiment, the method further comprises iteratively performing a) and b) until the measured spectral response is substantially similar to the reference spectral response. In this way, the calibration process can be specifically performed for multiple devices, and similar sensitivity settings can be easily set for the multiple devices.

[0046] According to a preferred embodiment, the method further comprises, when the measured spectral response is substantially similar to the reference spectral response, fixedly securing the optical aperture arrangement relative to the optical element. In this way, the setting can be fixed for later use.

[0047] Although the optical aperture device is configured for a spectrometer, it can generally be configured for other optical systems. Therefore, the principles of the device described herein are not limited to spectrometers, as the scope of the concept of a movable optical aperture device disclosed herein can also be applied to other types of optical devices accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] This and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings which show a currently preferred embodiment of the invention, in which:

[0049] Figure 1 illustrates a schematic perspective view of the interior of a spectrometer according to an embodiment of the present invention;

[0050] Figure 2 The diagram shows Figure 1 a schematic perspective cut-away view of a portion of a spectrometer cut away to show a perspective view of an optical aperture arrangement according to an embodiment of the present invention;

[0051] Figure 3 The diagram shows Figure 1 The cross section of the spectrometer along the optical axis A;

[0052] Figure 4A and Figure 4B Illustrated are two perspective views of an optical aperture device according to an embodiment of the present invention;

[0053] Figures 5 to 7 illustrates cross-sections of optical aperture devices according to various embodiments of the present invention;

[0054] Figure 8A and Figure 8B A through-view perspective view and a transverse cross-section of an optical aperture device according to yet another embodiment of the present invention are respectively shown;

[0055] Figure 9a and Figure 9b illustrates a schematic representation of a spectrometer of the present invention for two different positions of an optical aperture arrangement according to an embodiment;

[0056] Figure 10a and Figure 10b illustrates a schematic representation of a spectrometer of the present invention for two different positions of the optical aperture arrangement according to another embodiment;

[0057] Figure 11 The diagram shows Figure 9a 、 Figure 9b 、 Figure 10a 、 Figure 10b Schematic sensitivity diagrams within spectra obtained for two different positions according to any one of the embodiments of FIG.

[0058] Figure 12 A flow chart showing the steps of a calibration method according to an embodiment of the present invention is illustrated. DETAILED DESCRIPTION

[0059] Notably, like reference numerals are used throughout the description and drawings to describe like elements. Figure 1 A schematic perspective view of a spectrometer according to an embodiment is shown. The spectrometer 100 may have a housing 30 with a cover (not shown) for closing the housing 30. As in prior art systems, the connector 2 may protrude outside the housing 30 of the spectrometer 100. The connector 2 may be configured to receive a fiber optic cable (not shown). An input optical signal (in other words, an input light consisting of a beam of light) may enter the optical spectrometer 100 through the connector 2 and proceed through the slit 4 (at Figure 2 1 and 2. The slit 4 is a slit having a diameter of 100 nm and a diameter of 100 nm ...

[0060] The optical aperture device 10 is configured to receive a first optical signal and select a portion of it as a second optical signal. In other words, the optical aperture device can control the amount of light at its exit by cutting out a portion of the incident light. The second optical signal can include only a portion of the light present in the first optical signal. Thus, the optical aperture device 10 can act as a physical filter, allowing only a portion of the light output from the slit 4 to pass through. The second optical signal exiting the optical aperture device 10 can then be incident on the next optical element 20 in the optical path.

[0061] The optical element 20 is configured to receive the second light signal leaving the optical aperture device 10 on its surface. According to an embodiment, the optical element 20 may include any one of the following: a collimating element, a reflecting element (e.g., a plane mirror), a grating element (e.g., a concave grating). Figure 1In the embodiment of FIG, the optical element 20 can act as a collimating optical element and can typically be a spherical mirror. The second optical signal, collimated by the optical element 20, can then reach a dispersive element 3 such as a grating, and continue to a lens / focusing optical element 7 (e.g., a spherical mirror), and finally be incident on the detector 1. The detector 1 can be one of a charge-coupled device (CCD) array or a complementary metal-oxide-semiconductor (CMOS) array. Several detectors suitable for this purpose are known in the art and can be selected based on the desired wavelength range, measurement speed, and accuracy.

[0062] In contrast to the prior art, the optical aperture device 10 is movable relative to the optical element 20 to change the surface area of ​​light incident on the optical element 20. Accordingly, the size of this surface area can affect the illumination (meaning the amount of light) at the detector 1, thereby affecting the sensitivity of the spectrometer in terms of photon counting, for example, normalized per μW per millisecond integration time. The optical aperture 10 can be a movable part of the spectrometer 100, while the connector 2, slit 4, mirrors 20 and 7, grating 3, and detector 1 can be fixedly mounted to the spectrometer housing 30. For calibration purposes, the optical aperture device 10 can be moved relative to the spectrometer housing 30 to adjust the spectrometer's spectral sensitivity by changing the relative distance between the optical aperture device 10 and the optical element 20. Once the adjustment is performed, the optical aperture device 10 can be fixed to the housing 30, concluding the spectrometer calibration protocol. The spectrometer can then be used to analyze samples. It is worth noting that adjusting the spectrometer's spectral sensitivity can be important for calibration so that data from different spectrometers can be compared. Therefore, this sensitivity adjustment can be performed as a calibration step between a group of spectrometers planned to be used together.The range of movement of the optical aperture device can be such that the sensitivity can be adjusted within a margin of plus or minus 5%, preferably plus or minus 15%, more preferably plus or minus 30%.

[0063] Figure 2 The diagram shows Figure 1Schematic see-through perspective view of a portion of a spectrometer 100, wherein a portion shows a perspective view of an optical aperture device 10 according to an embodiment of the present invention. A connector 2 for connecting to an external optical fiber (not shown) can accommodate a slit 4 serving as a light entrance. The distance between the slit 4 and the optical element 20 can be fixed and predetermined to obtain a focused image on the surface of the optical element. Optionally, a glass filter 5 can be inserted along the light path between the slit 4 and the optical aperture device 10. The glass filter 5 can be used to filter out second-order spectral effects. Alternatively, an order separation coating can be provided on a window in front of the detector. The filter 5 can confine the light to a spectral region where order overlap is undesirable.

[0064] The optical aperture device 10 may include a tubular housing 13 that holds an exit aperture element 11 and, optionally, an entrance aperture element 12. The exit aperture element 11 may preferably be mounted at one end of the tubular housing 13, while the entrance aperture element 12 may preferably be mounted at the other end. Alternatively, the exit aperture element 11 may be mounted within the tubular housing 13 at a predetermined distance from either end, preferably within the last 50%, more preferably within the last 20%, and even more preferably within the last 10% of the tubular housing's longitudinal direction relative to the ends. It is worth noting that the tubular housing 13 may have a cylindrical outer shape, i.e., an annular outer cross-section. Other outer cross-sections, such as rectangular or star-shaped outer cross-sections, may also be envisioned by those skilled in the art without inventive step. The housing 30 includes a recess 31 for receiving the optical aperture device 10. Obviously, the recess 31 in the housing 30 must therefore be configured to conform to the outer shape of the tubular housing 13. The groove 31 may also serve as a guide for guiding the movement of the optical aperture device 10 relative to the optical element 20. Alternatively, a separate tubular housing or component fixedly mounted to the housing may serve as the guide.

[0065] like Figure 1As explained above, the optical aperture device 10 is movable relative to the optical element 20. The size and position of the exit aperture element 11 relative to the optical element 20 can determine the surface area of ​​light incident on the optical element 20 (i.e., the illuminated surface), and thus the illumination intensity of the detector 1. It is worth noting that the position of the slit 4 relative to the optical element 20 is predetermined to obtain a focused image on the optical element 20. In this sense, the size and position of the exit aperture element 11 relative to the slit 4 also affect the surface area of ​​light incident on the optical element 20 (i.e., the illuminated surface), and thus the illumination intensity of the detector 1. In fact, because the first light signal propagates through the slit, only light rays in the first light signal that travel in a straight line from the slit to the aperture of the exit aperture element 11 can be incident on the optical element 20. Therefore, the optical aperture device 10 can be considered to be movable relative to the assembly comprising the slit 4 and the optical element 20.

[0066] As previously described, the optical aperture device 10 can be inserted into the interior of the housing 30 of the spectrometer 100 and can generally be mounted within the housing 30. Specifically, the tubular housing 13 can be movably mounted within the tubular recess 31 in the housing 30 of the spectrometer 100. Thus, the tubular housing 13 can be guided by the tubular recess 31 to slide within the housing 30 along the optical axis A, which is also the longitudinal axis of the tubular housing 23 and the longitudinal axis of the tubular recess 31. Specifically, the outer dimension (e.g., diameter) of the tubular housing 13 can be smaller than the inner dimension (e.g., diameter) of the tubular recess 31 to allow relative displacement between these elements 13 and 31.

[0067] In order to move the optical aperture device 20, there may be interfaces on the outer surface of the housing 30 and on the outer surface of the optical aperture device 10. In one embodiment, there may be grooves 16 on the outer surface of the optical aperture device 10, more specifically on the outer surface of the tubular housing 13. The tool 50 (on Figure 2 A pin (shown in FIG. 1 ) can be inserted through a groove in housing 30 to engage groove 16, thereby moving optical aperture device 10 in a direction parallel to the optical path. Alternatively, an interface including a motor or mechanical actuator can be envisioned to force displacement of the optical aperture device based on user input.

[0068] Figure 3 The diagram shows Figure 1A cross-section of the spectrometer along the optical axis A can be defined along this optical axis. The optical axis A can be defined by the direct optical path through the optical aperture device 10 and the optional slit 4 toward the optical element 20. The optical axis A can intersect the optical element 20 at the center of the surface of the optical element 20. The movement of the optical aperture device 10 can be a translation along the optical axis A. The range of movement can be such that the size of the illuminated surface on the optical element 20, and therefore the sensitivity, can be adjusted within a margin of plus or minus 5%, preferably plus or minus 15%, and more preferably plus or minus 30%.

[0069] Figures 4a and 4b illustrate two perspective views of an optical aperture device according to an embodiment of the present invention. In this embodiment, a tubular housing 13 may be cylindrical, holding an entrance aperture element 12 at one end and an exit aperture element 11 at the other end. Exit aperture element 11 may include a surface 11b for blocking light from exiting optical aperture device 10 and a rectangular opening 11a for allowing light to exit the optical aperture device. Exit aperture element 11 can select only a portion of the first light signal from slit 4. Exit aperture element 11 can also trap stray light within tubular housing 13. Entrance aperture element 12 may include a surface 12b for blocking light from entering optical aperture device 10 and an annular opening 12a for allowing light to pass into the interior of the optical aperture device. Other shapes for opening 12a are contemplated without requiring an inventive step. By adding an entrance aperture element, the first selection of light can be achieved while simultaneously trapping stray light outside tubular housing 13. Stray light can be defined as radiation of undesirable wavelengths that, if propagated, could potentially activate the signal at detector 1. Stray light sources in the detector 1 can include ambient light, scattered light from imperfect optical components, reflections from non-optical components, and order overlap. To reduce stray light propagation, a light-absorbing coating can be applied to at least a portion of the inner surface 13d of the tubular housing 13. In this way, unwanted reflections from this portion of the inner surface 13d can be reduced. The coating should have low reflectivity within the desired wavelength range. Preferably, a stray light-absorbing coating is selected whose average reflectivity across the entire wavelength range is less than at least 30%, more preferably less than 15%, and even more preferably greater than 10%. A black anodized coating can serve as a default solution.

[0070] A fastening mechanism 40 for fastening the optical aperture device 10 to the housing 30 may be provided on the outer surface 13b of the tubular housing 13. The fastening mechanism 40 may include a hole extending from the outer surface of the housing 30 to the outer surface 13b, a screw, and a groove 15 on the outer surface 13b of the tubular housing 13. The groove 15 may be an elongated groove to receive a fastening element at multiple positions along the elongated direction of the groove. After adjusting its position using a tool 50 engaged in the groove 16, the screw may engage with the groove 15 to secure the optical aperture device 10 in a fixed position. This allows for easy adjustment and securing of the optical aperture device 10 without opening the housing. An interface for moving the optical aperture device may further be provided.

[0071] A groove 13c may be provided on the outer surface 13b of the tubular housing at the end of the tubular housing 13 away from the exit aperture element 11 (i.e., at the end of the tubular housing holding the entrance aperture element 12) to facilitate insertion of the optical aperture device 10 into the groove 31 of the housing 30. In addition, a hole 14 may be provided at the end of the tubular housing 13 holding the exit aperture element 11 to clamp the optical aperture device 10 and insert it into the groove 31.

[0072] Figures 5 to 7 The diagrams illustrate cross sections of optical aperture devices according to various embodiments of the present invention.

[0073] Figure 5 A cross section of an optical aperture device according to a first embodiment is shown, wherein the inner surface 13d of the tubular housing 13 may have a cylindrical shape. This embodiment may serve as a reference for comparison with other embodiments regarding the amount of stray light at the exit of the optical aperture device.

[0074] Figure 6 1 shows a cross section of an optical aperture device according to a second embodiment, wherein a portion of the inner surface of the tubular housing 13 may be a conical portion 13d, and another portion of the inner surface of the tubular housing 13 may be a cylindrical portion 13e, with the axis of the cone being the optical axis A. Figure 5 Compared with the reference example, Figure 6 Embodiments can show 4 or 5 times less stray light. The inner surface 13d can be exposed at the end of the optical aperture device 10 where the exit aperture element 11 is configured. In this way, stray light can be reflected on the tapered inner surface portion 13d away from the opening 11a of the exit aperture element 11, thereby being trapped within the optical aperture device 10. The conical portion can extend over at least 10% of the inner surface 13d, more preferably at least 25% of the inner surface 13d, and even more preferably at least 40% of the inner surface 13d. The conical portion 13d can have a cross-section that increases along the optical path toward the exit aperture element 11.

[0075] Figure 7 FIG shows a cross section of an optical aperture device according to a third embodiment, wherein the inner surface 13d of the tubular housing 13 may have a threaded portion. Figure 5 Compared with the reference example, Figure 7 The embodiment can show 5 times less stray light. In other words, the threaded inner surface can help further reduce stray light outside the optical path.

[0076] Figure 8A A through-view perspective view of an optical aperture device according to yet another embodiment of the present invention and a transverse cross-section thereof are shown. The inner surface 13d may then be spirally ribbed along the entire length of the tubular housing 13. Alternatively, only a portion of the inner surface of the tubular housing may be spirally ribbed. The spirally ribbed inner surface (portion) 13d may include ribs 14 extending in a spiral / helical pattern along the optical path. The ribs may have a substantially triangular cross-section. The ribs 14 may extend toward the interior of the tubular housing and twist along the optical path. A helical angle may be defined between the ribs and the optical axis A. The cross-section of the spirally ribbed inner surface (portion) 13d may be as follows: Figure 8B As shown, and can be characterized by an eight-star shape, its inner diameter d1, corresponding to the top of the ribs 14 extending toward the optical axis A at the center of the tubular housing 13, is smaller than the diameter d2 corresponding to the valley of the ribs 14. The multiple orientations of the surfaces on the spiral rib portion can reflect stray light in so many directions that it can be trapped within the optical aperture device 10. The additional spread of the reflected angles directs the light away from the optical axis A. In this way, stray light can be further reduced. Figure 5 Compared to the reference embodiment, the embodiment of FIG8 shows 15 times less stray light.

[0077] Figure 9a The diagram shows a schematic side view representation of the spectrometer of the present invention for two different positions P1 and P2 of the optical aperture device 10. For ease of explanation, Figure 9b In the embodiment of the present invention, optical element 20 may have a square shape and exit aperture element 11 may have a circular opening 11a. However, the present invention is not limited thereto and other shapes of optical elements and exit aperture element openings are contemplated.

[0078] The light inlet 4 (usually a slit) can receive an input light signal I (usually from an optical fiber (not shown) with a given numerical aperture). The light inlet 4 can then derive a first light signal (not shown) downward along the optical path (i.e., along the optical axis A) from the input light signal I. Passing through the light inlet 4, light can be scattered outward in the shape of a free-form light cone, preferably in a pattern such as Figure 9a and Figure 9bIn other words, the light beam (ie the first light signal) generated by the light inlet 4 is a diverging light beam defined by a solid angle (also called a cone half angle).

[0079] A plane perpendicular to the optical axis A at the light inlet 4 can define an input plane B from which the first light signal propagates. In other words, the light inlet 4 can be seen as a light source from which the first light signal originates, as seen from an element further down the light path. It follows that the distance d between the optical element 20 and the input plane B can be predetermined to achieve the desired operation of the spectrometer, in particular to obtain an image on the optical element 20. Further, the optical element 20 can include a light receiving area thereof. The light receiving area can be defined by a height h and a width w. Based on the minimum value between the width w and the height h of the light receiving area (i.e., the minimum lateral dimension of the light receiving area) and the predetermined distance d, the maximum numerical aperture NA of the spectrometer can be derived.

[0080] exist Figure 9a In FIG, only some of the light rays exiting the optical aperture device 10 are shown to illustrate the present invention in a schematic manner. When the optical aperture device 10 can be located at a position P1 along the optical axis A, the light exiting the optical aperture device 10 can be the portion of the first light signal that is cut out by the optical aperture device 10. The exit aperture element 11 and the optional entrance aperture element 12 and / or tubular housing 13 (if present) can help select the portion of the first light signal. This portion of the first light signal can be contained in a light cone originating from the input plane B and having a cone half-angle α1 (also referred to herein as the first solid angle). When this light is incident on the optical element 20, it can form an illuminated surface having a surface area of ​​diameter S1.

[0081] When the optical aperture device 10 is positioned at position P2 along the optical axis A (where position P2 is closer to the optical element 20 than position P1), light exiting the optical aperture device 10 can be contained within a light cone that also originates from the input plane B and has a cone half-angle α2 (also referred to as a second solid angle) that is smaller than the cone half-angle α1 (i.e., the first solid angle). Then, when the light is incident on the optical element 20, it can form an illuminated surface having a surface area of ​​diameter S2, which is smaller than the surface area of ​​diameter S1 obtained for the illuminated surface at position P1. Therefore, the solid angle of the second light signal at position P1 is greater than the solid angle of the second light signal at position P2.

[0082] Figure 9b Schematically illustrates Figure 9a The light is incident on the surface of the optical element 20 at the two positions shown in FIG. The surface of the optical element 20 may be located at Figure 9a, which is perpendicular to the optical axis A. When the optical aperture device 10 can be located at position P1, the illuminated surface can be a disk with a diameter of S1, and when the optical aperture device 10 can be located at position P2, the illuminated surface can be a smaller disk with a diameter of S2. The shape of the opening 11a of the exit aperture element 11 can determine the shape of the illuminated surface on the optical element 20. The distance between the exit aperture element 11 and the input plane B can determine the surface area of ​​the illuminated surface on the optical element 20. It should be noted that these figures are only schematic and the dimensions may not be inferred from these figures. The range of motion between P1 and P2, and the degree of difference between S1 and S2 shown should not be considered representative, but are merely used to explain the principles behind the present invention.

[0083] As can be seen from these figures, by moving the optical aperture device 10 toward and away from the optical element 20, the surface of light incident on the optical element (which surface may also be referred to as the illuminated surface or image in the present invention) can be changed, thereby adjusting the illumination intensity and, in turn, the sensitivity of the detector 1. When the optical aperture device 10 is displaced between its most extreme positions, the size of the illuminated surface / image on the optical element 20 can typically be changed from 10*10 mm to 7*7 mm for a spectrometer in the range of 200 nm to 1100 nm.

[0084] It is noteworthy that when the optical aperture device 10 is moved, the intensity received per unit surface area of ​​the optical element 20 can remain constant. Moving the optical aperture device 10 can only modify the half-angle α of the light cone that reaches the surface of the optical element 20 (in other words, it does not expand the amount of light received). By moving the optical aperture 10, the amount of light received at the optical element 20 can be changed, thereby tunable The sensitivity of the spectrometer.

[0085] Figure 10a and Figure 10b Another embodiment of the present invention is shown. Figure 9a and Figure 9b The embodiment shown differs only in that there may be no slit. The light inlet 4 may be a fiber coupler located directly in plane B' and receive the input light signal I via an optical fiber with a numerical aperture (not shown). In this case, the input plane from which the light incident on the optical element 20 originates will be outside the drawing, along the optical axis A. However, in contrast to the embodiment shown in FIG. Figure 9a and Figure 9b The same principles as explained will apply, ie by moving the optical aperture arrangement 10 the size of the illuminated surface on the optical element 20 can be changed and thus the sensitivity can be tuned.

[0086] Go to Figure 11 and Figure 12, further explains the method for calibrating a spectrometer according to the invention. As explained, the invention is based on the idea of ​​tuning the sensitivity independently of the resolution and in a uniform manner over the entire spectral range. Figure 11 Schematically illustrates the spectrometer according to the present invention for Figure 9a and Figure 9b (or Figure 10a 、 Figure 10b spectral response plots for two positions P1 and P2 (because P1 and P2 represent only the most extreme displacement positions of the optical aperture device according to any embodiment of the present invention). Spectral response can be defined by measuring the sensitivity of the spectrometer by photon counts (e.g., normalized per microwatt per millisecond of integration time (counts / μW per ms)) within the wavelength range of the spectrometer. It can be seen that movement between P1 and P2 can cause the spectral response to shift in sensitivity. Therefore, movement of the optical aperture device 10 can result in a uniform adaptation of the spectral response.

[0087] Figure 11 Also shown is a reference spectral response Ref, which can be used as a calibration reference. The reference spectral response can be obtained using a standard input source. Those skilled in the art will understand that the reference spectral response can correspond to the expected curve using a given optical bench, under specific settings of the optical spectrometer (integration time, sensor sensitivity, etc.), and optionally includes data processing (e.g., averaging) of the data output by the optical spectrometer. The step of moving the optical aperture device is made in order to reproduce or match the reference spectral response using the same specific settings, optical bench, and optionally the same data processing. In practice, the reference spectral response can be obtained from a "mother" reference system with a feasible / proven sensitivity.

[0088] To be able to compare the measured spectral response of a spectrometer (which requires calibration) with a reference spectral response, the same standard source should be coupled to the calibrated spectrometer. For example, the measured spectral response can be plotted on the same graph as the reference spectral response and presented to an operator. At position P1, the spectral response can be higher than the desired reference spectral response, while at position P2, the spectral response can be lower than the desired reference spectral response. To achieve the reference, such that the measured spectral response is substantially similar to the reference spectral response, the optical aperture device 10 can then be moved in one direction or the other, depending on whether the measured response is higher or lower than the reference. The arrows in the figure indicate the direction used to meet the reference when adjusting from P1 or P2. Moving from P1 to P2 is equivalent to displacing the optical aperture device in the direction of propagation of the optical signal (i.e., downward along the optical path); while moving from P2 to P1 is equivalent to displacing the optical aperture device against the direction of propagation of the optical signal (i.e., upward along the optical path). Positions P1 and P2 can be selected to achieve the desired tuning range around the reference.

[0089] Figure 12 A flow chart illustrating the steps of a calibration method according to an embodiment of the present invention is illustrated. At step S101, the spectral response of the spectrometer can be measured, preferably using the same standard source as used to obtain the reference response. At step S102, the measured spectral response can be compared with the reference spectral response. In the event of a difference, the optical aperture device can be moved at step S103. As long as the measured spectral response is different from the reference spectral response, steps S101, S102 and S103 can be iterated. Once a spectral response that is substantially similar to the desired reference spectral response is measured, the calibration can be terminated. The operator can intuitively complete the iterations as the operator moves the optical aperture device 10 in a stepless manner during the measurement. Optionally, at S104, the optical aperture device can be fixed.

[0090] It should also be noted that step S103 may include establishing a movement direction based on whether the spectral response is above or below a reference spectral response. Although the principles of the present invention have been described above with reference to specific embodiments, it should be understood that this description is made only as an example and does not limit the scope of protection determined by the appended claims.

[0091] The following clauses describe further embodiments:

[0092] Clause 1. A spectrometer (100) for analyzing an input optical signal, the input optical signal being input to the spectrometer, the spectrometer comprising:

[0093] - an optical aperture device (10) configured to receive a first optical signal derived from an input optical signal and configured to select a portion of said first optical signal to generate a second optical signal exiting the optical aperture device, and

[0094] - an optical element (20) configured to receive on its surface a second optical signal exiting the optical aperture means,

[0095] The optical aperture device (10) is characterized in that the optical aperture device (10) is movable relative to the optical element (20) to change the surface area of ​​the second optical signal incident on the optical element (20).

[0096] Clause 2. The optical spectrometer according to clause 1, further comprising a light inlet (4) configured to receive an input light signal and to select a portion of the input light signal to generate the first light signal,

[0097] Wherein, preferably, the light inlet (4) includes a slit element, and more preferably, the slit element defines an input plane (B), the first light signal and the second light signal originate from the input plane (B), and the distance from the input plane (B) to the optical element (20) is predetermined.

[0098] Item 3. An optical spectrometer according to Item 1 or Item 2, wherein the optical aperture device (10) comprises an exit aperture element (11), wherein the exit aperture element (12) comprises a surface (11b) for blocking a portion of the incident light signal and an opening (11a) for allowing another portion of the incident light signal to pass through.

[0099] Item 4. An optical spectrometer according to any one of the above items, wherein the optical aperture device (10) includes an entrance aperture element (12), the entrance aperture element (12) including a surface (12b) for blocking a portion of the incident light signal and an opening (12a) for allowing another portion of the incident light signal to pass.

[0100] Clause 5. An optical spectrometer according to clause 3 and / or clause 4, wherein the optical aperture arrangement (10) comprises a tubular housing (13) for holding the entrance aperture element (12) and / or the exit aperture element (11).

[0101] Item 6. An optical spectrometer according to the preceding item, wherein the tubular housing (13) defines a passage between a first end and a second end, the second end being opposite to the first end, wherein the tubular housing (13) is arranged to the spectrometer so that the first end is upstream of the second end in the direction of propagation of the optical signal.

[0102] Clause 7. The optical spectrometer according to the preceding clause, wherein the exit aperture element (12) is provided to the second end of the tubular housing (13).

[0103] Clause 8. The optical spectrometer according to clause 6 or clause 7, wherein the entrance aperture element (11) is provided to the first end of the tubular housing (13).

[0104] Clause 9. The optical spectrometer according to any one of clauses 5 to 8, wherein the tubular housing (13) has an outer surface with a circular cross section.

[0105] Item 10. An optical spectrometer according to any one of Items 7 to 9, wherein the tubular housing (13) has at least a portion of an inner surface (13d) configured to prevent light from passing through the exit aperture element after being reflected on the at least a portion of the inner surface (13d).

[0106] Clause 11. The optical spectrometer according to any one of clauses 5 to 10, wherein at least a portion of the inner surface (13d) of the tubular housing (13) is any one of the following and combinations thereof: a cylindrical portion, a conical portion, a threaded portion, a spiral rib portion.

[0107] Clause 12. The optical spectrometer according to any one of clauses 5 to 11, wherein at least a portion of the inner surface (13d) of the tubular housing (13) has a light-absorbing coating.

[0108] Clause 13. The optical spectrometer according to any of the preceding clauses, wherein the optical aperture device is configured to be translationally movable along an optical axis (A) of the optical aperture device (10).

[0109] Clause 14. The optical spectrometer according to any one of the preceding clauses, wherein the tubular housing (13) is slidable relative to the optical element (20).

[0110] Clause 15. An optical spectrometer according to any of the above clauses, wherein the optical aperture device (10) is capable of moving between a first position and a second position, wherein, in the first position, the surface area of ​​the second light signal incident on the optical element (20) is set to a predetermined maximum size, and wherein, by moving the optical aperture device from the first position to the second position, the illuminated surface is reduced by at least 10%, preferably by at least 30%.

[0111] Clause 16. An optical spectrometer according to any of the preceding clauses, wherein the optical aperture device is movable between a first position and a second position such that the sensitivity is adjusted by at least 10%, more preferably at least 30%, even more preferably at least 60% between the first position and the second position.

[0112] Item 17. An optical spectrometer according to any of the above items and optionally according to item 2, further comprising a housing (30) for holding the optical element (20) and the optical aperture device (10) and optionally the light inlet (4), wherein the optical element (20) is optionally fixedly mounted to the housing (30) together with the light inlet (4), and the optical aperture device (10) is capable of moving relative to the housing (30).

[0113] Clause 18. An optical spectrometer according to the preceding clause and optionally according to any one of clauses 5 to 12, wherein the housing (30) includes a guide for guiding the movement of the optical aperture device (10) relative to the optical element (20), preferably, the guide is a groove (31) in the housing (30), the groove (31) being configured as a tubular groove for cooperating with the tubular housing (13), wherein more preferably, the tubular housing (13) further includes a groove (13c) at a first end of its outer surface, the groove (13c) being used to insert the tubular housing (13) into the groove (31).

[0114] Item 19. A spectrometer according to any of the above items, wherein the housing (30) includes an interface for moving the optical aperture device (10), wherein the interface preferably includes a first elongated opening that allows an external object to contact the optical aperture device and displace the optical aperture device along the elongated opening.

[0115] Clause 20. An optical spectrometer according to the preceding clause, wherein the housing (30) comprises a fastening mechanism (40) for fastening the optical aperture device to the housing (30), wherein preferably the fastening mechanism comprises a hole and a screw extending through the hole to contact the optical aperture device (10).

[0116] Clause 21. An optical spectrometer according to any of the preceding clauses, wherein the optical aperture device (10) comprises a groove (15) for receiving a fastening device configured to fasten the position of the optical aperture device (10) ... relative to the optical element (20).

[0117] Clause 22. The optical spectrometer according to any of the preceding clauses, wherein the optical element (20) is a collimating optical element, more particularly a mirror, even more particularly a spherical mirror.

[0118] Clause 23. The optical spectrometer according to any of the preceding clauses, wherein the opening (11a) of the exit aperture element (11) has a square shape.

[0119] Clause 24. The optical spectrometer according to any one of the preceding clauses, wherein the opening (12a) of the entrance aperture element (12) has a circular shape.

[0120] Clause 25. An optical spectrometer according to any one of the preceding clauses, further comprising a dispersive element (3), a lens optical element (7) and a detector (1).

[0121] Clause 26. A method for calibrating a spectrometer according to any one of the preceding clauses, comprising the following steps in the following order:

[0122] a) measuring (S101) the spectral response of the spectrometer (100), preferably measuring the sensitivity, more preferably measuring the spectral sensitivity,

[0123] b) moving (S103) the optical aperture device (10) relative to the optical element (20) to adjust the spectral response toward a reference spectral response.

[0124] Clause 27. The calibration method according to the preceding clause, further comprising iteratively performing a) and b) until a reference spectral response is measured.

[0125] Clause 28. The calibration method of the preceding clause, wherein the optical aperture device (10) is fixedly secured relative to the optical element (20) when the reference spectral response is measured.

Claims

1. An optical spectrometer (100) for analyzing an input optical signal, wherein the input optical signal is input to the spectrometer, the spectrometer comprising: - an optical inlet (4) configured to receive the input optical signal and to generate a first optical signal, the first optical signal being a diverging optical beam, - an optical aperture device (10) configured to receive the first optical signal derived from the input optical signal and configured to select a portion of the first optical signal to generate a second optical signal exiting the optical aperture device, and - an optical element (20) configured to receive on its surface said second optical signal exiting said optical aperture means, - wherein the optical aperture device (10) is movable relative to the optical element (20) along the propagation direction of the first optical signal to change the surface area of ​​the second optical signal incident on the optical element (20).

2. The optical spectrometer according to claim 1, wherein: The optical inlet (4) is further configured to select a portion of the input optical signal to generate the first optical signal, or to couple the input optical signal to the optical spectrometer to generate the first optical signal. Wherein, preferably, the light inlet (4) includes a slit element or an optical coupler, and more preferably, the slit element defines an input plane (B), the first light signal and the second light signal originate from the input plane (B), and the distance from the input plane (B) to the optical element (20) is predetermined.

3. The optical spectrometer according to claim 1 or 2, wherein: The optical aperture device includes a first end and a second end opposite thereto, wherein the first end is located upstream of the second end as viewed along the propagation direction of the first optical signal; wherein the optical aperture device (10) comprises an exit aperture element (11), the exit aperture element (11) is preferably arranged closer to the second end than the first end, the exit aperture element (12) comprises a surface (11b) for blocking a portion of the incident light signal and an opening (11a) for allowing another portion of the incident light signal to pass through; and / or wherein the optical aperture device (10) comprises an entrance aperture element (12), the entrance aperture element (12) is preferably arranged closer to the first end than the second end, the entrance aperture element (12) comprises a surface (12b) for blocking a portion of the incident light signal and an opening (12a) for allowing another portion of the incident light signal to pass through.

4. The optical spectrometer according to claim 3, wherein: The optical aperture device (10) comprises a tubular housing (13) for holding the entrance aperture element (12) and / or the exit aperture element (11).

5. An optical spectrometer according to the preceding claim, wherein The tubular housing (13) defines a passage between the first end and the second end, wherein the tubular housing (13) is arranged to the spectrometer such that the first end is upstream of the second end as viewed in the propagation direction of the optical signal.

6. The optical spectrometer according to any one of claims 4 or 5, wherein: The outlet aperture element (12) is provided to the second end of the tubular housing (13).

7. The optical spectrometer according to any one of claims 4 to 6, wherein: The inlet aperture element (11) is provided to the first end of the tubular housing (13).

8. The spectrometer according to any one of claims 4 to 7, wherein: The tubular housing (13) has an outer surface with a circular cross-section.

9. The optical spectrometer according to any one of claims 4 to 8, wherein: The tubular housing (13) has at least a portion of an inner surface (13d) configured to prevent light from passing through the exit aperture element after being reflected on the at least a portion of the inner surface (13d).

10. The optical spectrometer according to any one of claims 4 to 9, wherein: At least a portion of the inner surface (13d) of the tubular housing (13) is any one of the following and combinations thereof: a cylindrical portion, a conical portion, a threaded portion, a spiral ribbed portion.

11. The optical spectrometer according to any one of claims 4 to 10, wherein: At least a portion of the inner surface (13d) of the tubular housing (13) has a light-absorbing coating.

12. An optical spectrometer according to any one of the preceding claims, wherein: The optical aperture device is configured to be capable of translational movement along an optical axis (A) of the optical aperture device (10).

13. An optical spectrometer according to any one of claims 4 to 11, optionally in combination with claim 12, wherein: The tubular housing (13) is slidable relative to the optical element (20).

14. An optical spectrometer according to any one of the preceding claims, wherein: The optical aperture device (10) is movable between a first position and a second position, wherein, in the first position, a first illuminated surface of the second light signal incident on the optical element (20) is set to a predetermined maximum size corresponding to a maximum numerical aperture NA of the spectrometer, and wherein, by moving the optical aperture device from the first position to the second position, the first illuminated surface is reduced by at least 10%, preferably by at least 30%.

15. An optical spectrometer according to any one of the preceding claims, wherein: The optical aperture arrangement is movable between a first position and a second position such that sensitivity is adjusted by at least 10%, more preferably at least 30%, even more preferably at least 60% between the first position and the second position.

16. An optical spectrometer according to any one of the preceding claims, wherein: The optical aperture device is movable between a first position and a second position so that a final numerical aperture of an illuminated surface of the second light signal incident on the optical element (20) can be adjusted from a maximum numerical aperture of the spectrometer associated with the first position.

17. The optical spectrometer according to any one of claims 14 to 16, wherein: The first position corresponds to a position where the optical aperture device (10) is farthest from the optical element (20), and / or the second position corresponds to a position where the optical aperture device (10) is closest to the optical element (20).

18. An optical spectrometer according to any one of the preceding claims and optionally according to claim 2, further comprising a housing (30) for holding the optical element (20) and the optical aperture arrangement (10) and optionally the light inlet (4), wherein The optical element (20) is optionally fixedly mounted to the housing (30) together with the light inlet (4), while the optical aperture device (10) is movable relative to the housing (30).

19. An optical spectrometer according to any one of the preceding claims and optionally claims 4 to 11 or 13, wherein The housing (30) includes a guide for guiding the optical aperture device (10) to move relative to the optical element (20), preferably, the guide is a groove (31) in the housing (30), and the groove (31) is configured as a tubular groove for cooperating with the tubular shell (13), wherein more preferably, the tubular shell (13) also includes a groove (13c) at the first end on its outer surface, and the groove (13c) is used to insert the tubular shell (13) into the groove (31).

20. An optical spectrometer according to any one of the preceding claims, wherein: The housing (30) comprises an interface for moving the optical aperture device (10), wherein the interface preferably comprises a first elongated opening, the first elongated opening allowing an external object to contact the optical aperture device and displace the optical aperture device along the elongated opening.

21. An optical spectrometer according to the preceding claim, wherein The housing (30) comprises a fastening mechanism (40) for fastening the optical aperture device (10) to the housing (30), wherein preferably, the fastening mechanism comprises a hole and a screw extending through the hole to contact the optical aperture device (10).

22. An optical spectrometer according to any one of the preceding claims, wherein: The optical aperture device (10) comprises a groove (15) for receiving a fastening device, the fastening device being configured to secure the position of the optical aperture device (10) relative to the optical element (20).

23. An optical spectrometer according to any one of the preceding claims, wherein: The optical element (20) is a collimating optical element, more particularly a reflecting mirror, even more particularly a spherical mirror.

24. An optical spectrometer according to claim 3 and optionally in combination with any one of claims 4 to 23, wherein The opening (11a) of the exit aperture element (11) has a square shape.

25. An optical spectrometer according to claim 3 and optionally in combination with any one of claims 4 to 24, wherein The opening (12a) of the entrance aperture element (12) has a circular shape.

26. The optical spectrometer according to any one of the preceding claims, further comprising a dispersive element (3), a lens optical element (7) and a detector (1).

27. A method for calibrating a spectrometer according to any one of the preceding claims, comprising the following steps in the following order: a) measuring (S101) the spectral response of the spectrometer (100), preferably measuring the sensitivity, more preferably measuring the spectral sensitivity, b) moving (S103) the optical aperture device (10) relative to the optical element (20) to adjust the spectral response towards a reference spectral response.

28. The calibration method of the preceding claim, further comprising iteratively performing a) and b) until the measured spectral response is substantially similar to the reference spectral response.

29. The calibration method according to the preceding claim, further comprising the steps of: When the measured spectral response is substantially similar to the reference spectral response, the optical aperture device (10) is fixedly secured relative to the optical element (20).

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