Fourier transform spectrometer and Fourier transform spectroscopy method

Abstract

A Fourier transform spectrometer 100 includes an interferometer 10, which includes a fixed mirror 11, a movable mirror 12, and a detector 101, wherein: the mirrors 11 and 12 are positioned parallel to each other and form an optical cavity; the movable mirror 12 is operable to move relative to the fixed mirror 11 to change the size of the optical cavity; a first mirror in the mirrors is positioned such that light 14 received from a sample passes through the back of the first mirror into the optical cavity; the detector 101 is positioned and operable to detect light that has passed through the back of a second mirror in the mirrors and exits the optical cavity and outputs an interferogram; and the mirrors 11 and 12 are spaced apart from each other such that the movable mirror is positioned or can be moved to a position in which at least two paths 16, 31 of the received light 14 reflected within the interferometer toward the detector 101 have equal lengths.

Description

Technical Field

[0001] This invention relates to Fourier transform spectrometers and Fourier transform spectroscopy methods. Specifically, but not exclusively, this invention relates to infrared Fourier transform spectrometers and spectroscopy. Background Technology

[0002] Each molecule and / or substance has a unique absorption spectrum, absorbing different wavelengths of light to varying degrees. Figure 1 An exemplary absorption spectrum is shown, in this case, that of dichloromethane. Therefore, spectroscopy can be used to determine molecules and / or substances and their composition by obtaining their absorption spectra.

[0003] Given its ability to determine molecules and / or substances and their composition, spectroscopy has a wide range of applications, including:

[0004] ● Food quality monitoring (e.g., food contamination or date determination);

[0005] ● Environmental monitoring (e.g., air pollution or water quality);

[0006] ● Medical applications (e.g., blood analysis and drug testing); and

[0007] ●Materials control.

[0008] However, many currently available spectrometers are relatively bulky and / or expensive, limiting their use outside of laboratory environments and thus their availability. For use outside the laboratory, spectrometers need to be miniaturized while also being low-cost. Ideally, a spectrometer would be scaleable down to a few square millimeters and inexpensive enough to be integrated into mobile electronic devices.

[0009] There are three main types of spectrometers that can be miniaturized: gratings, Fabry-Perot interferometers, and Michelson interferometers.

[0010] Figure 2 A grating is shown. For the grating, light 1 incident on the sample is guided to grating 2 at an incident angle α. Light passing through different slits in the grating or reflected from different slits interferes, thus producing an interference pattern 3 related to the output angle β, which can be detected by a detector. A given wavelength determines the location of the maximum and minimum values ​​of light at each wavelength in the pattern, and the detector can detect multiple wavelengths and thus establish a spectrum.

[0011] A large number of detectors are needed to detect sufficient patterns 3 and obtain all the necessary information to form a full absorption spectrum. Furthermore, patterns 3 require sufficient space to be unfolded to achieve adequate resolution. Finally, the free spectral range of the grating is limited due to higher-order reflections. These problems mean that the extent to which spectrometers using gratings can be miniaturized is limited, and the resulting spectrometer has a limited optical frequency range.

[0012] Figure 3 The image shows a Fabry-Perot interferometer. Light 1, incident on the sample, passes through the first reflecting mirror 4 and is transmitted into a cavity formed between two parallel reflecting mirrors 4 and 5. Light 1 is reflected between mirrors 4 and 5, and only the wavelength of light 1 that resonates with the size of the cavity will be transmitted through the second reflecting mirror 5, and then light 6 continues to the detector. The distance between mirrors 4 and 5 can be varied, allowing the user to scan different wavelengths. In this way, the spectrometer can be moved through various wavelengths to establish an absorption spectrum.

[0013] Several issues exist with using Fabry-Perot interferometers. First, they require a uniform mirror spacing of approximately one wavelength, which is difficult to manufacture. Second, higher-order reflections limit the free spectral range of the interferometer. Third, Fabry-Perot interferometers require high-quality optical mirrors, typically layered Bragg mirrors. This means that spectrometers using Fabry-Perot interferometers are relatively expensive to manufacture and have a limited optical frequency range.

[0014] In addition to the above, constructing a Bragg mirror requires alternating layers of different materials. Standard microelectromechanical systems (MEMS) processing techniques (such as gaseous hydrofluoric acid) are incompatible with many materials, and therefore limit material choices when scaling down spectrometers using Fabry-Perot interferometers.

[0015] Figure 4 The diagram shows a Michelson interferometer. Light 1 is incident on beam splitter 7, where a portion of the beam is reflected to the top mirror 8, and another portion passes through the beam splitter and is transmitted to the side mirror 9. Both portions are reflected back to beam splitter 7, where they are recombined. The position of the side mirror 9 is adjustable, allowing the path length of one portion of the light to be changed, thus introducing optical path difference.

[0016] The Michelson interferometer is used as part of a Fourier transform infrared spectrometer. The side mirror 9 moves rapidly, recording as it moves. The side mirror 9 must be moved from zero optical path difference to the desired maximum resolution, although it is generally easier to move the mirror through a position where the optical path difference is zero. The resulting recorded output can be converted into an absorption spectrum via a Fourier transform.

[0017] Compared to gratings and Fabry-Perot spectrometers, Fourier transform infrared spectrometers offer a wide wavelength range, high spectral resolution, and a high signal-to-noise ratio (i.e., Fellgett's advantage). However, problems associated with miniaturizing Fourier transform infrared spectrometers remain. The 90-degree rotated beam path is difficult to manufacture on a scale-down basis, especially on a large scale, meaning it is difficult to provide scaled-down spectrometers at a sufficiently reduced cost.

[0018] Furthermore, designing MEMS presents challenges in providing two perfectly equal optical path lengths due to issues such as the pull-in effect and tuning range. Additionally, the requirement for light to couple into and out of such systems via optical fibers further complicates manufacturing the system (and increases associated costs).

[0019] In addition to the above, comb actuators are used to move movable mirrors in many miniaturized spectrometers. The need for comb actuators increases the size of the physical device and the associated costs because they are relatively complex to manufacture.

[0020] The purpose of this invention is to overcome some or all of the problems associated with the above-described spectrometers and spectroscopic methods. Summary of the Invention

[0021] According to a first aspect of the invention, a Fourier transform spectrometer is provided, comprising: an interferometer including a fixed mirror, a movable mirror, circuitry, electrodes, and a detector, wherein: the mirrors are positioned parallel to each other and form an optical cavity; the movable mirror is operable to move relative to the fixed mirror to change the length of the optical cavity; a first mirror of the mirrors is positioned such that received light passes through the back surface of the first mirror into the optical cavity; the detector is positioned and operable to detect light that has passed through the back surface of a second mirror of the mirrors and exits the optical cavity and outputs an interferogram; the mirrors are spaced apart such that the movable mirror is positioned or can be moved to a position in which at least two optical paths of the received light reflected within the interferometer toward the detector have equal lengths; the movable mirror and the electrodes are positioned spaced apart, and the circuitry is connected to the movable mirror and the electrodes and operable to apply an electric field between them to move the movable mirror relative to the fixed mirror; and the electrodes are positioned such that the movable mirror is located between the fixed mirror and the electrodes.

[0022] The Fourier transform spectrometer of the present invention can apply Fourier transforms to certain higher-order combinations of interferences of these multiple reflections, the interferences arising when at least two optical paths of the reflected light within the interferometer have equal lengths. This contrasts with Fourier transform spectrometers using a Michelson interferometer, in which only one reflection occurs at each mirror surface and Fourier transforms are applied only to the interference of two zero-order reflected beams. In a 'coaxial' arrangement of mirrors and detectors, it is impossible to measure the zero-order interference of two beams reflected from the front of the mirrors, because it occurs when the path difference between the reflected light and the light transmitted straight through the optical cavity is equal, and therefore when the distance between the mirrors is zero.

[0023] While still possessing the associated advantages of a Fourier transform spectrometer (wide wavelength range, high spectral resolution, and high signal-to-noise ratio), the spectrometer also incorporates the advantage of placing the mirror and detector coaxial with each other and with the light from the sample (making the spectrometer easier and correspondingly cheaper to miniaturize).

[0024] The mirrors can be spaced a certain distance from each other, such that the movable mirror can be moved to a position where at least two paths of light reflected in the interferometer have equal lengths.

[0025] An interferometer may include three or more reflective surfaces, which are arranged such that received light on the optical path to the detector is reflected from two or more of the reflective surfaces.

[0026] One or more mirrors in a reflector may include one or more reflecting surfaces. One or more mirrors in a reflector may include two or more reflecting surfaces. The front side or each front side of one or more mirrors in a reflector may be a reflecting surface. The back side or each back side of one or more mirrors in a reflector may be a reflecting surface. Each reflecting surface is operable to reflect received light from its front / back side. Reflecting surfaces may be arranged such that received light in two or more optical paths in an optical path can be reflected from one or more of the same reflecting surfaces.

[0027] Mirrors can be arranged such that light received in one or more optical paths is reflected within one or more mirrors. Mirrors can be arranged such that light received in one or more optical paths is reflected within an optical cavity. Mirrors can be arranged such that light received in one or more optical paths travels back and forth within one or more mirrors. Mirrors can be arranged such that light received in one or more optical paths travels back and forth within an optical cavity.

[0028] One or more of the reflectors may have a coating on their front and / or back sides. The coating may be an anti-reflective coating. Each of the coatings may comprise one or more reflective surfaces. The coatings may include an electrical insulator. A fixed reflector may have a coating on its front side. A fixed reflector may have a coating on its back side. A movable reflector may have an uncoated front side. A movable reflector may have an uncoated back side.

[0029] A Fourier transform spectrometer may include a light source positioned to guide light through the back of a first reflecting mirror to enter an optical cavity.

[0030] A Fourier transform spectrometer may include a sample holder operable to receive and hold a sample in place so that light from a light source passes through or is reflected from the sample and then enters the optical cavity.

[0031] Each mirror may contain silicon. Each mirror may be made of silicon.

[0032] The process of forming a Fourier transform spectrometer can be simplified by using only silicon to manufacture the mirror, because, for example, there is no need to manufacture a Bragg mirror.

[0033] Each reflector can be flat. Each reflector can be rectangular. The first reflector can be a fixed reflector. The second reflector can be a movable reflector.

[0034] The interferometer may include a housing. A reflector may be attached to the housing. A fixed reflector may be attached to the housing such that its position is fixed relative to the housing. The fixed reflector may be attached to the housing by being inherently formed with the housing. A movable reflector may be attached to the housing such that it is movable relative to the housing. The movement of the movable reflector may be elastic. The interferometer may include one or more elastic elements that connect the movable reflector to the housing, and the movable reflector may be movable on the elastic element or each elastic element. The elastic element or each elastic element may be a flexure. The flexure element or each flexure may be a helical flexure. The second reflector may be circular. The helical flexure element or each helical flexure may partially or completely surround the circular reflector. Four flexure elements may be present. When multiple flexure elements are present, the positions of each flexure element connected to the reflector and / or housing may be regularly spaced apart from each other. Before being connected to the housing, the flexure element or each flexure may surround the reflector 360 degrees. The flexure element or each flexure may contain silicon. The elastic element, or each elastic element, may be composed of silicon.

[0035] The Fourier transform spectrometer may include an analysis unit operable to receive interferograms and perform Fourier transforms on them to obtain the spectrum of the sample. The analysis unit is operable to perform Fourier transforms on certain higher-order combinations of multiple reflections, excluding the zeroth-order interferometry. The analysis unit is operable to perform Fourier transforms on first-order interferometry. The spectrum may cover a wavelength range of 1–2.6 μm. The spectrum may cover one or more or all of the following ranges: visible light, near-infrared light, short-wave infrared light, mid-wave infrared light, and / or long-wave infrared light.

[0036] A Fourier transform spectrometer includes circuitry and electrodes. The circuitry is connected to a movable mirror and the electrodes and is operable to apply an electric field between them, causing the movable mirror to move relative to a fixed mirror. The circuitry is also operable to apply a voltage difference between the movable mirror and the electrodes to apply an electric field. The electrodes are positioned such that the movable mirror is located between the fixed mirror and the electrodes. The circuitry is operable to apply a voltage difference between the movable mirror and the electrodes to apply an electric field.

[0037] By positioning the electrodes such that the movable mirror is located between the electrodes and the fixed mirror, the means of actuating the movable mirror (applying an electric field between the movable mirror and the electrodes) is disengaged from the optical cavity. If the electric field is applied across the optical cavity (i.e., between the fixed and movable mirrors), the range of movement of the movable mirror and the minimum size of the optical cavity will be limited to approximately one-third of the original distance between the mirrors. If the movable mirror moves closer, the required electric field will cause attraction to occur.

[0038] The engagement via the positioning electrodes does not limit the minimum size of the optical cavity or the range through which the movable mirror can move, because when the electric field is zero, the movable mirror approaches the fixed mirror as desired, and as the electric field increases, the movable mirror moves away from the fixed mirror.

[0039] An electrode can be positioned between a movable reflector and a detector. The electrode may have an aperture through it. The detector may be positioned below the aperture. The detector may be positioned inside the aperture. The electrode may be positioned next to the detector. The electrode and detector may be placed together on a base.

[0040] The electrode may contain 2D materials. The thickness of the 2D material is less than 10 nanometers. The 2D material may be conductive. The 2D material may be transparent. The electrode may contain graphene. Graphene may be conductive. Graphene may be transparent. The electrode may contain graphene on a quartz substrate. The electrode may be constructed from graphene on a quartz substrate. The graphene may have a thickness of less than 10 nanometers.

[0041] By forming electrodes from graphene, the electrodes can be transparent and ultimately thin, thus not affecting the interferometer's optics, even when the electrodes are positioned between a movable mirror and a detector.

[0042] The electrodes can be parallel to each mirror. The electrodes can form the base of the housing. Wall portions can extend from the movable mirrors to the electrodes, thus positioning them a certain distance apart from each other.

[0043] The mirrors can be spaced a certain distance from each other, allowing the movable mirror to be positioned or movable to a location where the optical cavity length is between 20-45 μm. Alternatively, the mirrors can be spaced a certain distance from each other, allowing the movable mirror to be positioned or movable to a location where the optical cavity length is between 25-40 μm. Finally, the mirrors can be spaced a certain distance from each other, allowing the movable mirror to be positioned or movable to a location where the optical cavity length is between 30-35 μm.

[0044] The movable mirror may be able to move along a line. The line may be a straight line. The movable mirror may only be able to move along a line. The line may extend perpendicularly from the movable mirror. The line may extend perpendicularly from the back of the movable mirror. The line may begin at the back of the movable mirror.

[0045] A Fourier transform spectrometer can be an infrared Fourier transform spectrometer.

[0046] According to a second aspect of the present invention, a mobile electronic device is provided, which includes the Fourier transform spectrometer of the first aspect.

[0047] By providing Fourier transform spectrometers in mobile electronic devices, the public can use spectroscopy in everyday life, thus greatly expanding its uses and availability.

[0048] Mobile electronic devices can be mobile phones, tablets, or laptops.

[0049] According to a third aspect of the invention, an interferometer for a Fourier transform spectrometer is provided, the interferometer comprising: a fixed mirror and a movable mirror forming an optical cavity, the movable mirror being operable to move relative to the fixed mirror to change the size of the optical cavity; and circuitry and electrodes connected to the movable mirror and the electrodes and operable to generate an electric field between them to move the movable mirror relative to the fixed mirror, the movable mirror being positioned between the fixed mirror and the electrodes.

[0050] By positioning the electrodes such that a movable mirror lies between the electrodes and a fixed mirror, the means of actuating the movable mirror (applying an electric field between the movable mirror and the electrodes) is disengaged from the optical cavity. Therefore, attraction does not limit the minimum size of the optical cavity or the range through which the movable mirror can move, because when the electric field is zero, the movable mirror approaches the fixed mirror as desired, and as the electric field increases, the movable mirror moves away from the fixed mirror. The electrodes can be positioned between the movable mirror and the detector.

[0051] The mirrors can be parallel to each other.

[0052] Depending on the expectation and / or the circumstances, the third aspect of the invention may include any of the optional features of the first aspect.

[0053] According to a fourth aspect of the invention, a Fourier transform spectrometer is provided, which includes the interferometer of the third aspect.

[0054] According to a fifth aspect of the invention, an interferometer for a Fourier transform spectrometer is provided, the interferometer comprising a housing, a movable mirror, one or more flexures, circuitry, and electrodes, the movable mirror being connected to the housing via the flexures or each flexure and being movable relative to the housing by means of the flexures or each flexure, the circuitry being connected to the movable mirror and the electrodes and operable to apply an electric field between them to move the movable mirror.

[0055] The required setup is much simpler to build than that of a comb actuator. Therefore, the interferometer is easier and cheaper to manufacture.

[0056] The interferometer may include a fixed mirror and a movable mirror positioned to form an optical cavity, and the movable mirror may be movable relative to the fixed mirror. The mirrors may be parallel.

[0057] Depending on the expectation and / or the circumstances, the fifth aspect of the invention may include any of the optional features of the first aspect.

[0058] According to a sixth aspect of the present invention, a Fourier transform spectrometer is provided, which includes the interferometer of the fifth aspect.

[0059] According to a seventh aspect of the invention, a Fourier transform spectroscopy method is provided, comprising the steps of: moving or moving a movable mirror of an interferometer from or through a position in which at least two paths of light reflected within the interferometer have equal lengths, and detecting light at a detector of the interferometer to obtain an interferogram of a sample; and applying a Fourier transform to an interferogram of one order of interference other than the zeroth order interference to obtain a spectrum.

[0060] Interferometers that can provide interferograms of higher-order interferences but not zero-order interferences, by applying a Fourier transform to an interference of a certain order other than zero-order interference, can be used with the method described above. Such interferometers do not require a 90-degree beam rotation, thus making it easier and cheaper to build miniaturized spectrometers.

[0061] Fourier transform spectroscopy can be used to apply Fourier transform to first-order interference.

[0062] The Fourier transform spectroscopy method can be performed using a Fourier transform spectrometer of the first aspect to perform the steps.

[0063] Fourier transform spectroscopy can be performed using infrared Fourier transform spectroscopy. The spectrum can cover a wavelength range of 1-2.6 μm. Detailed Implementation

[0064] To provide a clearer understanding of the invention, one or more embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0065] Figure 1 This is the absorption spectrum of dichloromethane;

[0066] Figure 2 It's a raster setting;

[0067] Figure 3 It is a Fabry-Perot interferometer;

[0068] Figure 4 It is a Michelson interferometer;

[0069] Figure 5 It is the interferometer of an infrared Fourier transform spectrometer;

[0070] Figure 6 It is a simulated interferogram from an infrared Fourier transform spectrometer;

[0071] Figure 7 It is an interferogram of a first-order side burst.

[0072] Figure 8 It is the spectrum of white light captured by an infrared Fourier transform spectrometer;

[0073] Figure 9 yes Figure 5 The second movable mirror of the interferometer;

[0074] Figure 10 It is an interferometer for an infrared Fourier transform spectrometer, including the electrodes and voltage source necessary for moving the second reflecting mirror;

[0075] Figure 11The step-by-step process of forming the first reflecting mirror of the infrared Fourier transform spectrometer is shown;

[0076] Figure 12 The step-by-step process of forming the second mirror of the infrared Fourier transform spectrometer is shown;

[0077] Figure 13 An infrared Fourier transform spectrometer is shown; and

[0078] Figure 14 The images show spectra obtained for acrylates using an infrared Fourier transform spectrometer and a conventional spectrometer; and

[0079] Figure 15 It is a spectrum obtained for milk with various fat contents.

[0080] like Figure 5 As shown, the interferometer 10 of the infrared Fourier transform spectrometer includes two mirrors 11 and 12. Mirrors 11 and 12 are parallel to each other and face each other to form a cavity 13. The first mirror 11 (fixed mirror) is positioned above the second mirror 12 (movable mirror). The second mirror 12 is movable relative to the first mirror 11 toward and away from it to change the size of the cavity and the distance between the mirrors 11 and 12. Mirrors 11 and 12 are held within a housing formed by two walls 30, the first mirror 11 being inherently formed with the walls 30, and the second mirror 12 being connected to the walls 30 such that the second mirror is movable relative to the walls.

[0081] Light 14, already incident on the sample of interest, is transmitted through the back of the first reflecting mirror 11. Multiple paths then pass through reflecting mirrors 11 and 12 and the optical cavity 13. The first path 15 of the light is a straight path through the second reflecting mirror 12, exiting the cavity 13, and most of the light 14 takes this first path 15. However, a portion of the light 14 takes other paths within and through the first and second reflecting mirrors 11 and 12, and through the cavity 13. For example, as... Figure 5 As shown, the second path 16 of light is reflected back and forth between the front surfaces of the mirrors 11 and 12 forming the cavity, then transmitted through the back surface of the second mirror 12 and exits the cavity 13. Another path 31 of light 14 is reflected from both the front and back surfaces within the second mirror 12, then exits from the back surface of the second mirror 12. Another example would be a path in which light is reflected from both the front and back surfaces within the first mirror 11, then enters the cavity 13 and is transmitted straight through the second mirror 12.

[0082] The position of the second reflecting mirror 12 is adjustable so that path 31 (and other paths through which light is reflected within the interferometer) can have the same length as the second path 16 and / or other paths through which light is reflected within the interferometer, thereby producing interference. This interference is a higher-order interference than the 0th-order interference and is referred to as "edge peaks" on the interferogram. Figure 6 As shown, the signal strength of edge peaks 17 and 18 is less than that of the 0th-order interference 19 between the light on the first path 15 and the second path 16. However, the first-order edge peak 17 is large enough to be converted into a spectral signal, and because it appears when the mirrors are a certain distance apart, a complete measurement of the edge peak necessary to obtain the spectrum can be obtained. Conversely, the 0th-order interference occurs when the gap distance is zero, which is impossible to measure.

[0083] In use, the position of the second reflector 12 will be moved through a gap distance of equal length between the second path 16 and the third path 31 (or through a gap distance of equal length between two paths other than the first path 15), which, for the setup described herein, is approximately 35 μm. Detector 101 (in Figure 13 (As shown in the image) Measurements are taken as the second mirror 12 moves in order to capture the first-order edge peak 17, as... Figure 7 As shown in the image.

[0084] The displacement of the second reflector 12 is measured using a non-contact distance sensor such as a laser interferometer, a capacitive sensor, or the like.

[0085] Then the analysis unit 102 of the Fourier transform infrared spectrometer 100 (also in Figure 13 (As shown in the figure) A Fourier transform can be performed on the captured interferogram to produce an absorption spectrum. Figure 8 The constructed spectrum of white light produced in the absence of a sample is shown.

[0086] The first reflector 11 and the second reflector 12 are made of silicon. Figure 9 A second reflector 12 used in the setup is shown. The reflector 12 is circular and partially cut from the silicon wafer 20. The reflector 12 is connected to the remainder of the wafer 20 by a silicon strip 21 that spirals from the reflector 12 to the rest of the wafer 20. The remainder of the wafer 20 thus forms part of the wall 30 of the interferometer 10. Four flexures 21 are present, each spirally extending around the entire circumference of the reflector 12, such that the position of the flexure 21 connected to the reflector 12 around the circumference is the same as the position of the flexure 21 connected to the remainder of the wafer 20 relative to the circumference. The four flexures 21 are regularly positioned around the circumference.

[0087] The flexure 21 allows the second reflector 12 to move up and down relative to the rest of the sheet 20 (i.e., to move perpendicular to the plane of the sheet 20). This allows the reflector to move relative to the first reflector 11, and thus changes the gap distance and the size of the cavity 13.

[0088] like Figure 10 As shown, the electrode is positioned at a certain distance from the back of the second reflector 12, such that the first reflector 11 and the second reflector 12 are in three parallel planes with the electrode 22, and the second reflector 12 is located between the first reflector 11 and the electrode 22. The second reflector 12 and the electrode 22 are connected such that a voltage can be applied between them, thereby forming an electric field. The second reflector 12 is a circular reflector held in place by a helically extended flexure 21, meaning that the presence of the electric field will cause the second reflector 12 to shift away from the first reflector 11 and toward the electrode 22, the distance of which depends on the strength of the electric field. The second reflector 12 can be shifted by tens of μm. In use, an electric field is applied through the electrode and its strength is controlled and changed to move the second reflector 12 through a first-order edge crest.

[0089] Electrode 22 is made of quartz-based graphene, which makes it transparent and therefore has minimal effect on the optical cavity 13 formed between the first mirror 11 and the second mirror 12.

[0090] like Figure 11 As shown, the first reflector 11 is formed from a block 23 comprising two silicon layers 24 and 25. The first layer 24 is approximately 500 μm thick, and the second layer 25 is approximately 30-50 μm thick. A thin insulating layer 26 is sandwiched between the first layer 24 and the second layer 25. Two thin silicon nitride layers 27 sandwich the first layer 24, the second layer 25, and the insulating layer 26.

[0091] In order to form the first reflecting mirror 11, such as Figure 11 As shown, a portion of the second silicon layer 25 and the silicon nitride layer 27 covering it is removed using photolithography (reactive ion etching is used for the silicon nitride layer 27, and potassium hydroxide is used for etching the silicon 25) to expose the insulating layer 26. The second layer 26 and the covering silicon nitride layer 27 are etched such that the cut portion has a square cross-section and slopes downwards to the silicon 24.

[0092] The resulting cap-shaped structure 28 forms part of the first reflector 11, cavity 13, and wall 30. The first reflector 11 is in the middle of the first silicon layer 24, the cut portion forms the cavity 13, and the rest of the block 23 forms part of the wall 30.

[0093] like Figure 12As shown, the second reflector 12 is formed from a block 32 comprising two silicon layers 33 and 34. The first layer 33 is approximately 10 μm thick, and the second layer 34 is approximately several hundred micrometers thick, for example, approximately 500 μm thick. A thin insulating layer 35 is sandwiched between the first layer 33 and the second layer 34. Two thin silicon nitride layers 36 sandwich the first layer 33, the second layer 34, and the insulating layer 35.

[0094] For the second reflecting mirror 12, as Figure 12 As shown, a cap-like structure 28 is formed in the same manner as for the first reflector 11. Once this is complete, photolithography, particularly deep reactive ion etching, is used to cut spirally extending flexures into the first layer 33. Figure 12 (Not shown in the image). When doing so, the silicon nitride layer 36 on top of the first layer 33 is also removed from the top of the spirally extended flexure 21.

[0095] The next step is to remove the insulator 35 and the spirally extended flexure 21 from the mirror 12 using fumed hydrofluoric acid. To complete this process, the remaining silicon nitride layer 36 is laid from the top of the first layer 33 to form a microelectromechanical system (MEMS) 29. The portion of the MEMS 29, excluding the second mirror 12 and the spirally extended flexure 21, together with a portion of the cap 28, forms the wall 30 of the interferometer.

[0096] To form the interferometer 10, the MEMS 29 is placed on top of the electrode 22, with the cutout portion of the MEMS 29 positioned between the second mirror 12 and the electrode 22. Then, a cap 28 is placed on top of the MEMS 29, with the MEMS 29 positioned between the cap 28 and the electrode 22, and the cutout portion of the MEMS 29 positioned between the second mirror 12 and the electrode 22. All three components are then secured in place, and the detector is positioned behind the electrode 22 and the second mirror 12. A light source can be integrated behind the front mirror 11 in the system. Alternatively, the system can be configured to use an external light source.

[0097] The infrared Fourier transform spectrometer 10 has a wide spectral range of approximately 1–2.6 μm and a spectral resolution as low as approximately 10 nm, while the interferometer is only a few tens of cubic millimeters in size (approximately 4 × 4 × 1.5 mm in dimensions, and therefore has a 24 mm diameter). 3 (volume). Therefore, the infrared Fourier transform spectrometer 10 can be integrated into mobile electronic devices such as mobile phones and tablets, thereby providing the mobile electronic devices with the functions of a spectrometer.

[0098] like Figure 14As shown, by comparing the spectrum of acrylate obtained by infrared Fourier transform spectrometer 100 with the spectrum of the same material obtained by a conventional spectrometer side by side, the obtained spectrum can be compared with that of a conventional spectrometer and can be used to identify substances with known spectra.

[0099] like Figure 15 As shown, the infrared Fourier transform spectrometer 100 is accurate enough to distinguish substances with similar spectra—in the case of milk with different fat contents, as shown in the attached figure.

[0100] The above description of one or more embodiments is by way of example only. Many variations are possible without departing from the scope of protection provided by the appended claims.

Claims

1. A Fourier transform spectrometer, comprising: Interferometer The interferometer includes a fixed mirror, a movable mirror, circuitry, electrodes, and a detector, wherein: the mirrors are positioned parallel to each other and form an optical cavity; the movable mirror is operable to move relative to the fixed mirror to change the length of the optical cavity; a first mirror is positioned such that received light passes through the back of the first mirror into the optical cavity; the detector is positioned and operable to detect light that has passed through the back of a second mirror and exited the optical cavity and output an interferogram; the mirrors are spaced apart such that the movable mirror is positioned or can be moved to a position where at least two optical paths of the received light reflected within the interferometer toward the detector have equal lengths; the movable mirror and the electrodes are positioned spaced apart, and the circuitry is connected to the movable mirror and the electrodes and operable to apply an electric field between them to move the movable mirror relative to the fixed mirror; and the electrodes are positioned such that the movable mirror is located between the fixed mirror and the electrodes.

2. The Fourier transform spectrometer according to claim 1, wherein the mirror comprises silicon.

3. The Fourier transform spectrometer according to any one of claims 1 or 2, wherein the interferometer includes a housing.

4. The Fourier transform spectrometer of claim 3, wherein the interferometer comprises one or more elastic elements that connect the movable mirror to the housing, the movable mirror being movable on the elastic elements or on each elastic element.

5. The Fourier transform spectrometer according to claim 4, wherein the elastic element or each elastic element is a flexural element.

6. The Fourier transform spectrometer according to claim 1, wherein the electrode comprises graphene.

7. The Fourier transform spectrometer according to claim 6, wherein the electrode comprises a quartz-based graphene.

8. The Fourier transform spectrometer according to claim 1, wherein the mirrors are spaced apart from each other such that the movable mirror is located or can be moved to a position where the optical cavity is between 20-45 μm.

9. The Fourier transform spectrometer according to claim 8, wherein the mirrors are spaced apart from each other such that the movable mirror is located or can be moved to a position where the optical cavity is between 25-40 μm.

10. The Fourier transform spectrometer according to claim 9, wherein the mirrors are spaced apart from each other such that the movable mirror is located or can be moved to a position where the optical cavity is between 30-35 μm.

11. The Fourier transform spectrometer according to claim 1, comprising: An analysis unit is operable to receive the interferogram and perform a Fourier transform on it to obtain the spectrum of the sample.

12. The Fourier transform spectrometer of claim 11, wherein the analysis unit is operable to perform the Fourier transform on an interference of a certain order other than the zeroth order interference.

13. The Fourier transform spectrometer of claim 12, wherein the analysis unit is operable to perform the Fourier transform on a first-order interferometer.

14. A Fourier transform spectroscopy method, comprising the following steps: Provided a Fourier transform spectrometer according to any one of claims 1 to 13; moving or moving through the position of the movable mirror of the interferometer from or through the position where at least two paths of light reflected within the interferometer have equal lengths, and detecting the light at the detector of the interferometer to obtain an interferogram of a sample; and applying a Fourier transform to an interference of a certain order other than the zeroth order interference of the interferogram to obtain a spectrum.

15. The Fourier transform spectroscopy method according to claim 14, comprising: The Fourier transform is applied to the first-order interference.

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