The technology discussed below relates generally to spectrometers, and in particular to spectrometers for simultaneously capturing background or reference spectral density and sample spectral density.
Fourier Transform-Infrared (FT-IR) spectrometers measure a single-beam spectrum (power spectral density (PSD)), where the intensity of the single-beam spectrum is proportional to the power of the radiation reaching the detector. In order to measure the absorbance of a sample, the background spectrum (i.e., the single-beam spectrum in absence of a sample) should first be measured to compensate for the instrument transfer function. The single-beam spectrum of light transmitted or reflected from the sample may then be measured. The absorbance of the sample may be calculated from the transmittance or reflectance of the sample. For example, the absorbance of the sample may be calculated as the ratio of the spectrum of transmitted light or reflected light from the sample to the background spectrum.
For transmission measurements, the background spectrum may be obtained by measuring the spectrum of the beam at the input of the instrument without placing any material in the light path (e.g., an empty cuvette). For reflection measurements, the background spectrum may be obtained by placing a reference material with nearly flat spectral response across the spectral range of interest with greater than 95% reflectance instead of the sample. Background measurements should generally be performed under the same conditions at which the measurement of the sample is conducted.
To continue measuring accurate absorbance spectra, background measurements should be done frequently or even before each sample measurement, which consumes additional time. Spectroscopists have studied the frequency of background measurements and how the spectrum changes with temperature and time to attempt to derive models to simulate these effects and to determine how to compensate for them. Additional enhancements in spectrometer designs are desired to reduce the time in the measurement process, while maintaining an online reference/background measurement to compensate for any PSD drift effects.
The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.
Various aspects of the disclosure provide simultaneous measurement of a background or reference spectral density and a sample or other spectral density to maintain an online background/reference measurement, compensate for any PSD drift effects and minimize the time required to obtain the background/reference measurement and perform any PSD compensation. In an aspect of the disclosure, a self-referenced spectrometer includes an interferometer optically coupled to receive an input beam and to direct the input beam along a first optical path to produce a first interfering beam and a second optical path to produce a second interfering beam, where the first and second interfering beams are produced prior to an output of the interferometer. The spectrometer further includes a detector optically coupled to simultaneously detect a first interference signal produced from the first interfering beam and a second interference signal produced from the second interfering beam, and a processor coupled to the detector and configured to process the first interference signal and the second interference signal and to utilize the second interference signal as a reference signal in processing the first interference signal.
In an example, the interferometer may include a Michelson interferometer, a Mach-Zehnder interferometer, or a Fabry-Perot interferometer, which may be implemented within a Micro-Electro-Mechanical-Systems (MEMS) chip including a moveable mirror actuated by a MEMS actuator. In some examples, the interferometer may include retro-reflectors and two outputs, where one output passes through a sample arm forming the first optical path and another output passes through a reference arm forming the second optical path. In other examples, a coupler may be implemented near an input of a Michelson interferometer to direct the reflected second interfering beam onto an input port corresponding to the second optical path. In still other examples, a sample-under-test (SUT) and a diffuse reflectance reference material or other reflection surface may be simultaneously illuminated and the reflected light from the SUT and the reference may be directed to the interferometer. In further examples, the second optical path may include a reference material with reference absorption peaks or a narrowband optical filter for continuous wavelength correction of the first interference signal and/or online mirror positioning. In still further examples, each optical path may simultaneously measure a different spectral range or resolution.
These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.
The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
The interferometer 104 is optically coupled to receive the input beam 110 and to direct the input beam along one or more optical paths to produce two interfering beams 112a and 112b (e.g., interference patterns) at an output thereof. In some examples, the interfering beams 112a and 112b are produced within the interferometer 104 prior to the output thereof. One of the interfering beams 112a represents a sample or other spectrum, while the other interfering beam 112b represents a background or reference spectrum. Thus, each of the interfering beams 112a and 112b passes through a different respective medium (e.g., sample/other or background/reference) external to the interferometer 104. The interferometer 104 may include one or more Michelson interferometers, Mach-Zehnder (MZ) interferometers, and/or Fabry-Perot (FP) interferometers.
In addition, the interferometer 104 may be implemented on a Micro-Electro-Mechanical-Systems (MEMS) chip. As used herein, the term MEMS refers to the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through microfabrication technology. For example, the microelectronics are typically fabricated using an integrated circuit (IC) process, while the micromechanical components are fabricated using compatible micromachining processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical components. One example of a MEMS element is a micro-optical component having a dielectric or metallized surface working in a reflection or refraction mode. Other examples of MEMS elements include actuators, detector grooves and fiber grooves.
In various aspects of the present disclosure, the MEMS interferometer 104 may include one or more micro-optical components (e.g., one or more reflectors or mirrors) that may be moveably controlled by a MEMS actuator. In some examples, the MEMS interferometer 104 may be fabricated using a Deep Reactive Ion Etching (DRIE) process on a Silicon On Insulator (SOI) wafer in order to produce the micro-optical components and other MEMS elements that are able to process free-space optical beams propagating parallel to the SOI substrate.
The detector 106 is optically coupled to receive the interfering beams 112a and 112b from the interferometer 104 and to simultaneously detect a first interference signal 114a produced from the first interfering beam 112a and a second interference signal 114b produced from the second interfering beam 112b. For example, each of the interference signals 114a and 114b may correspond to interferograms.
The processor 108 is configured to receive the first and second interference signals 114a and 114b and to use the second interference signal 114b as a reference signal in processing the first interference signal 114a. For example, the processor 108 may be configured to apply a Fourier Transform to each of the interference signals 114a and 114b to obtain the respective spectrums, and then to use the spectrum obtained from the second interference signal 114b in further processing of the spectrum obtained from the first interference signal 114a. In some examples, the processor 108 may calculate the absorbance of a sample-under-test (SUT) as a ratio of the spectrum obtained from the first interference signal 114a to the spectrum obtained from the second interference signal 114b.
The processor 108 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The processor 108 may have an associated memory and/or memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of the processor. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information.
The interferometer 204 is a Michelson interferometer fabricated on a MEMS chip that includes a beam splitter 212, a fixed reflector 214, a moveable reflector 216, and a MEMS actuator 218 coupled to the moveable reflector 216. The fixed reflector 214 and the moveable reflector 216 are each retro-reflectors. The beam splitter 212 may include, for example, an air-propagation based spatial splitter (e.g., a hollow waveguide splitter) or an air/silicon beam splitter (e.g., a beam splitter formed at an interface between silicon and air). The interferometer 204 includes two outputs 238 and 240, each optically coupled to one of two optical paths within the interferometer 204 and each further optically coupled to a respective detector 206a and 206b external to the interferometer 204. For example, a first optical path is formed between the beam splitter 212 and the first output 238, which then passes through a sample 220 (e.g., SUT) at the first output 238 towards the first detector 206a. A second optical path is formed between the beam splitter 212 and the second output 240, which then passes through a reference 222 at the second output 240 towards the second detector 206b.
In the example shown in
In one example, the MEMS actuator 218 is formed of a comb drive and spring. By applying a voltage to the comb drive, a potential difference results across the actuator 218, which induces a capacitance therein, causing a driving force to be generated as well as a restoring force from the spring, thereby causing a displacement of moveable retro-reflector 216 to the desired position for reflection of the incident beam 228. An OPD is then created between the reflected beams 230 and 232 that is substantially equal to twice the displacement of the moveable retro-reflector 216.
The reflected beams 230 and 232 interfere at the beam splitter 212, allowing the temporal coherence of the light to be measured at each different OPD produced by the moveable retro-reflector 216. The beam splitter 212 is further optically coupled to split the interference beam resulting from interference between the first reflected beam 230 and the second reflected beam 232 to produce a first interfering beam 234 and a second interfering beam 236. The beam splitter 212 is further optically coupled to direct the first interfering beam 234 along the first optical path (e.g., which may correspond to a sample arm of the interferometer 204) and the second interfering beam 236 along the second optical path (e.g., which may correspond to a reference arm of the interferometer 204).
The sample arm and the reference arm may each operate in either a transmission configuration or reflectance configuration (e.g., a diffuse reflectance configuration). In a transmission configuration, the interfering beam (e.g., beam 234 or 236) propagates through the sample 220 or reference 222 towards the respective detector 206a or 206b. In a reflectance configuration, the interfering beam (e.g., beam 234 or 236) is reflected from the sample 220 or reference 222 to the respective detector 206a or 206b. For the reference arm, in the case of a transmission configuration, the reference 222 may be an empty cuvette, while in the case of a reflectance configuration, the reference 222 may include Spectralon or polytetrafluoroethylene (PTFE) standard reflectors. For the sample arm, in the case of a transmission configuration, the interfering beam 234 may propagate through the sample 220, while in the case of a reflectance configuration, the interfering beam 234 may be reflected from the sample 220 towards the detector 206a.
Each detector 206a and 206b is optically coupled to receive the respective interfering beam 234 and 236 (e.g., after propagation through or reflection from the sample 220/reference 222) and to detect a respective interference signal 242 and 244. The electronics interface 210 is coupled to the detectors 206a and 206b to receive the interference signals 242 and 244 and is configured to process each of the interference signals 242 and 244 to extract the respective interferograms therefrom. The DSP 208 is coupled to the electronics interface 210 to receive the interferograms and is configured to calculate a sample absorbance As as follows:
where Id1 is the detected interferogram signal from detector 206a and Id2 is the detected interferogram signal from detector 206b. It should be understood that any differences between the two detectors 206a and 206b that may affect the accuracy of the sample absorbance may be calibrated and compensated in the final calculation.
The interferometer 304 is a MZ interferometer fabricated on a MEMS chip that includes a first beam splitter 308, a moveable reflector 310, a MEMS actuator 312 coupled to the moveable reflector 310, a first flat mirror 314, a second flat mirror 316, a fixed reflector 318, and a second beam splitter 320. The fixed reflector 318 and the moveable reflector 310 are each retro-reflectors. The interferometer 304 includes two outputs, one passing through a sample 322 (e.g., a SUT) towards a detector 306a at a first output and another passing through a reference 324 towards a detector 306b at a second output. A first optical path is formed between the second beam splitter 320 and a first output of the interferometer 304 at the sample 322, whereas a second optical path is formed between the second beam splitter 320 and a second output of the interferometer 304 at the reference 324.
In the example shown in
The reflected beams 332 and 334 interfere at the second beam splitter 320, allowing the temporal coherence of the light to be measured at each different OPD produced by the moveable retro-reflector 310. The second beam splitter 320 is further optically coupled to split the interference beam resulting from interference between the first reflected beam 332 and the second reflected beam 334 to produce a first interfering beam 336 and a second interfering beam 338. The second beam splitter 320 is further optically coupled to direct the first interfering beam 336 along the first optical path and the second interfering beam 338 along the second optical path.
Each detector 306a and 306b is optically coupled to receive the respective interfering beam 336 and 338 (e.g., after propagation through or reflection from the sample 322/reference 324) and to detect a respective interference signal. A processor (not shown) may then utilize the interference signal detected by detector 306b as a reference signal in processing the interference signal detected by detector 306a, as described above.
The interferometer 404 is a Michelson interferometer fabricated on a MEMS chip that includes a beam splitter 408, a fixed reflector 410 (e.g., a fixed mirror), a moveable reflector 412 (e.g., a moveable mirror), a MEMS actuator 414 coupled to the moveable reflector 412, and a coupler 420. The fixed reflector 410 and the moveable reflector 412 are each flat mirrors. The coupler 420 is positioned at an input of the interferometer 404. The interferometer 404 includes two outputs, one passing through a sample 416 (e.g., a SUT) towards a detector 406a and another passing back through the coupler 420 through a reference 418 towards a detector 406b. A first optical path is formed between the beam splitter 408 and a first output of the interferometer 404 at the sample 416, whereas a second optical path is formed between the beam splitter 408 and a second output of the interferometer 404 at the coupler 420/reference 418.
In the example shown in
The reflected beams interfere at the beam splitter 408, allowing the temporal coherence of the light to be measured at each different OPD produced by the moveable mirror 412. The beam splitter 408 is further optically coupled to split the interference beam resulting from interference between the reflected beam to produce a two interfering beams, each directed along one of the first optical path or the second optical path. Each detector 406a and 406b is optically coupled to receive a respective one of the two interfering beams (e.g., after propagation through or reflection from the sample 416/reference 418) and to detect a respective interference signal. A processor (not shown) may then utilize the interference signal detected by detector 406b as a reference signal in processing the interference signal detected by detector 406a, as described above.
The interferometer 504 is a Michelson interferometer fabricated on a MEMS chip that includes a beam splitter 508, a fixed reflector 510 (e.g., a fixed mirror), a moveable reflector 512 (e.g., a moveable mirror), and a MEMS actuator 514 coupled to the moveable reflector 512. The fixed reflector 510 and the moveable reflector 512 are each flat mirrors. In the example shown in
The interferometer 604 is a FP interferometer fabricated on a MEMS chip that includes a tunable FP filter 608 coupled to a MEMS actuator 610. The tunable FP filter 608 includes two slabs, one of which is coupled to the MEMS actuator 610. In an exemplary operation, the input beam from the light source 602 is transmitted through the top slab of the FP tunable filter 608 and enters a FP air cavity between the slabs, where the input beam is reflected multiple times off each of the interior reflecting surfaces of the slabs. The MEMS actuator 610 causes a displacement of the bottom slab, thus varying the width of the cavity, resulting in multiple offset beams that interfere with one another inside the FP air cavity. Part of the reflected light (interfering beam) is transmitted through the bottom slab each time the light reaches the slab, and is output by the interferometer 604.
In the example shown in
The MEMS chip 700 may further include a diffuse reflection surface 714 forming the reference material for the MEMS interferometer and an integrated reflector 716, each fabricated monolithically within the MEMS chip. In the example shown in
Using, for example, any of the self-referenced spectrometer configurations shown in
The MEMS chip 800 may further include an integrated reflector 816 fabricated monolithically within the MEMS chip. In addition, a diffuse reflection surface 814 may be wafer-level bonded to the MEMS chip 700. In the example shown in
Using, for example, any of the self-referenced spectrometer configurations shown in
In some examples, the interference signal from the reference material or optical filter 916 with reference absorption peaks detected by the detector 906b may be utilized by a processor (not shown) for continuous wavelength correction of the interference signal detected by the detector 906a. In addition, in examples in which a narrowband optical filter 916 is incorporated into the spectrometer 900, the narrowband optical filter 916 may also be utilized for online mirror positioning of the moveable reflector 912. For example, the detected interferogram from the detector 906b may be in the form of a sinusoidal signal of a period corresponding to the central wavelength λo of the filter 916. More particularly, one cycle of the detected interferogram signal may correspond to an OPD (equal to λo) between the reflected beams reflected back to the splitter 908 from the fixed retro-reflector 910 and the moveable retro-reflector 912 resulting from the displacement of the moveable retro-reflector 912.
In this example, the interfering beam produced at the output of the interferometer includes a combined interfering beam including both a first interfering beam produced as a result of passing through the mirrors 1002 and 1004 and beam splitter 1008 (e.g., the first optical path) and a second interfering beam produced as a result of passing through the mirrors 1002/1004, beam splitter 1008, and reference material 1012 (e.g., the second optical path). Thus, a single detector may be utilized to detect a single interference signal that includes both the first interference signal (e.g., the sample or other signal) and the second interference signal (e.g., the reference signal). In the example in
The spectrometer 1100 further includes optical components designed to simultaneously illuminate a sample (e.g., a SUT) 1110 and a reference (e.g., a diffuse reflectance surface) 1112. In the example shown in
The interferometer 1104 is a Michelson interferometer that includes a beam splitter 1120, a fixed reflector 1122 (e.g., a fixed mirror), a moveable reflector 1124 (e.g., a moveable mirror), and a MEMS actuator 1126 coupled to the moveable reflector 1124. The fixed mirror 1122 and the moveable mirror 1124 are each flat mirrors. In the example shown in
The fixed mirror 1122 is optically coupled to reflect the received first and third incident beams 1140 and 1144, respectively back towards the beam splitter 1120 as first and third reflected beams 1148 and 1152, respectively. The moveable mirror 1124 is optically coupled to reflect the received second and fourth incident beams 1142 and 1146, respectively, back towards the beam splitter 1120 as second and fourth reflected beams 1150 and 1154, respectively. The moveable mirror 1124 is coupled to the MEMS actuator 1126 to produce a desired respective optical path difference (OPD) between the first and third reflected beams and the second and fourth reflected beams.
The first and second reflected beams 1148 and 1150, respectively, interfere at the beam splitter 1120 to produce a first interfering beam 1156, whereas the third and fourth reflected beams 1152 and 1154, respectively, interfere at the beam splitter 1120 to produce a second interfering beam 1158. The beam splitter 1120 is further optically coupled to direct the first interfering beam 1156 towards detector 1106a to detect a first interference signal and the second interfering beam 1158 towards detector 1106b to detect a second interference signal. A processor (not shown) may then utilize the interference signal detected by detector 1106b as a reference signal in processing the interference signal detected by detector 1106a, as described above. In this example, a first optical path is formed between a first input of the interferometer 1104 optically coupled to receive the first input beam 1136 reflected from the sample 1110 and a first output thereof directing the first interfering beam 1156 towards the first detector 1106a, whereas a second optical path is formed between a second input of the interferometer 1104 optically coupled to receive the second input beam 1138 reflected from the reference 1112 and a second output thereof directing the second interfering beam 1158 towards the second detector 1106b.
In some examples, the interferometer 1104, splitter, 1108, reflective surfaces 1114 and 1116 and additional optical components 1118 may be fabricated monolithically on a MEMS chip. In addition, it should be understood that other optical components may be utilized to direct the original input beam towards the sample 1110 and the reference 1112 and to direct the reflected input beams from the sample 1110 and the reference 1112 into the interferometer 1104.
The spectrometer 1200 is configured to simultaneously illuminate a sample (e.g., a SUT) 1210 and a reference (e.g., a diffuse reflectance surface) 1212. In the example shown in
The interferometer 1204 is a FP interferometer that includes a tunable FP filter 1220 coupled to a MEMS actuator 1222. The tunable FP filter 1220 includes two slabs, one of which is coupled to the MEMS actuator 1222. In an exemplary operation, the first and second input beams 1236 and 1238, respectively, reflected from the sample 1210 and the reference 1212 are transmitted through the top slab of the FP tunable filter 1220 and enter a FP air cavity between the slabs, where the input beams are reflected multiple times off each of the interior reflecting surfaces of the slabs. The MEMS actuator 1222 causes a displacement of the bottom slab, thus varying the width of the cavity, resulting in multiple offset beams that interfere with one another inside the FP air cavity. Part of the reflected light associated with each of a first interfering beam 1240 and a second interfering beam 1242 is transmitted through the bottom slab each time the light reaches the slab towards the respective detectors 1206a and 1206b.
A processor (not shown) may then utilize the interference signal detected by detector 1206b as a reference signal in processing the interference signal detected by detector 1206a, as described above. In this example, a first optical path is formed between a first input of the interferometer 1204 optically coupled to receive the input beam 1236 reflected from the sample 1210 and a first output of the interferometer 1204 coupled to provide the first interfering beam 1240 to the first detector 1206a, whereas a second optical path is formed between a second input of the interferometer 1204 optically coupled to receive the input beam 1238 reflected from the reference 1212 and a second output of the interferometer 1204 coupled to provide the second interfering beam 1242 to the second detector 1206b.
It should be understood that the optical components illustrated in
The spectrometer 1300 further includes optical components designed to simultaneously illuminate a sample (e.g., a SUT) 1310 and a reference (e.g., a diffuse reflectance surface) 1312. In the example shown in
In the example shown in
The first and second fixed mirrors 1322a and 1322b are each optically coupled to reflect the respective received first and third incident beams back towards the beam splitter 1320 as first and third reflected beams, respectively. The moveable mirror 1324 is optically coupled to reflect the received second and fourth incident beams back towards the beam splitter 1320 as second and fourth reflected beams. The moveable mirror 1324 is coupled to the MEMS actuator 1326 to produce a desired respective optical path difference (OPD) between the first and third reflected beams and the second and fourth reflected beams.
The first and second reflected beams interfere at the beam splitter 1320 to produce a first interfering beam 1340, whereas the third and fourth reflected beams interfere at the beam splitter 1320 to produce a second interfering beam 1342. The beam splitter 1320 is further optically coupled to direct the first and second interfering beams 1340 and 1342, respectively, towards the focusing reflector 1328 that focuses each of the first and second interfering beams 1340 and 1342, respectively, onto the single detector 1306 to detect a combined interference signal including both a first interfering signal produced from the first interfering beam and a second interference signal produced from the second interfering beam. In this example, a first optical path is formed between a first input of the interferometer 1304 optically coupled to receive the first input beam reflected from the sample 1310 and the single output of the interferometer 1304 at the focusing reflector 1328, whereas a second optical path is formed between a second input of the interferometer 1304 optically coupled to receive the second input beam reflected from the reference 1112 and the single output of the interferometer 1304 at the focusing reflector 1328.
To use a single detector 1306, a sample interferogram (as shown in
In this example, the sample absorbance As may be extracted from the measured combined interferogram Id as follows:
where WS and WR are the window functions to detect the sample interferogram and the reference interferogram, respectively. In some examples, WS and WR are shifted versions of the same window function W of mirror displacement x of the moveable mirror 1324:
It should be understood that in some examples, the interferometer 1304 may include a single fixed mirror and two moveable mirrors that are spatially offset from one another to produce the same combined interferogram that may be processed as described above.
In the example shown in
The spectrometer 1400 further includes optical components designed to simultaneously illuminate a sample (e.g., a SUT) 1410 and a reference (e.g., a diffuse reflectance surface) 1412. In the example shown in
In the example shown in
Thus, the first fixed slab 1426 is included within a first optical path (e.g., a sample arm) between a first input of the interferometer 1404 optically coupled to receive the reflected input beam from the sample 1410 and the focusing lens 1430, while the second fixed slab 1428 is included within a second optical path (e.g., a reference arm) between a second input of the interferometer 1404 optically coupled to receive the reflected input beam from the reference 1412 and the focusing lens 1430.
The MEMS actuator 1422 is configured to displace the moveable slab 1424 of the FP tunable filter 1420 to vary a sample gap gs between the moveable slab 1424 and the first fixed slab 1426 such that the sample gap is increased (e.g., gs+Δ). The MEMS actuator 1422 is further configured to displace the moveable slab 1424 to vary a reference gap gr between the moveable slab 1424 and the second fixed slab 1426 such that the reference gap is decreased (e.g., gr−Δ). The displacement of the moveable slab 1424 results in two different isolated spectral bands being coupled to the detector 1406 via focusing lens 1430, where a first band λs corresponds to a sample interference signal detected by the detector 1406 and a second band λr corresponds to a reference interference signal detected by the detector 1406. The spectral range may be scanned by varying the gap of the FP tunable filter 1420. When both gaps are equal, the sample interference signal and the reference interference signal may be overlapping. However, a processor (not shown) may be configured to predict the overlapped band in order to isolate each signal (sample and reference).
The spectrometer 1500 may further include a housing 1512 containing the light sources 1502a and 1502b and including a window 1506 on which a sample (e.g., SUT) 1510 may be placed. The housing 1512 further includes an opening 1514 forming an input or coupling aperture into the interferometer 1504. In some examples, the interferometer may include a Michelson interferometer, a MZ interferometer or a FP interferometer. In some examples, the interferometer 1504 may be implemented on a MEMS chip and the housing 1512 may be bonded to the MEMS chip.
In the example shown in
The wavelength range reflected from the window 1506 may be used to estimate the entire background signal, as illustrated in the graph of
In some examples, the remaining portion of the background signal may be estimated using both the measured BG spectrum and a calibration reading of the background signal taken when a reference diffuse-reflectance standard is placed on the window 1506. The calibration reading may be updated periodically to compensate for any changes in the spectrometer. In addition, readings from a temperature sensor (not shown) may also be utilized to compensate for any changes in the detector response due to temperature changes. In other examples, instead of providing an anti-reflection coating 1508 on the window 1506, the back-reflection from the window 1506 (e.g., without a SUT or reference diffuse-reflectance standard present) may be utilized as the background signal. However, in this example, the background signal is not measured simultaneously with the sample signal.
The spectrometer 1600 may further include a housing 1616 containing the light emitters 1602a-1602d and including a window 1606 on which a sample (e.g., SUT) 1610 may be placed. The housing 1616 further includes an opening 1618 forming an input or coupling aperture into the interferometer 1604. In some examples, the interferometer may include a Michelson interferometer, a MZ interferometer or a FP interferometer. In some examples, the interferometer 1604 may be implemented on a MEMS chip and the housing 1616 may be bonded to the MEMS chip.
In the example shown in
To extract the sample spectrum and the background spectrum, the light emitters 1602a-1602d may be coupled to a switch 1614 configured to alternately turn on the first set of light emitters 1602a and 1602b and the second set of light emitters 1602c and 1602d. For example, the switch 1614 may turn on the first set of light emitters 1602a and 1602b and turn off the second set of light emitters 1602c and 1602d at a first time (t1) to enable the interferometer 1604 to measure a first combined interference signal S1. Then, at a second time (t2), the switch 1614 may turn off the first set of light emitters 1602a and 1602b and turn on the second set of light emitters 1602c and 1602d to enable the interferometer to measure a second combined interference signal S2. The combined interference signals S1 and S2 may be expressed as:
S1=aSS+bSR (Equation 4)
S2=cSs+dSR (Equation 5)
where SS is the contribution of the sample interference signal, SR is the contribution of the background interference signal, and a, b, c, and d are constants representing ratios of adding the sample interference signal to the background interference signal. As a result, the signals S1 and S2 may be considered as originating from different light sources, and therefore the processor (not shown) may utilize a blind source separation (BSS) algorithm to extract Ss and SR. In some examples, the switch 1614 may further be controlled by the processor.
In some examples, the window 1606 may include an optional blocking material 1608 extending along a top surface of the window 1606 and further extending below the window 1606 surrounding the sample 1610. The blocking material 1608 may be designed to prevent light emitted from the second set of light emitters 1602c and 1602d from reaching the sample 1610 and to further prevent light emitted from the first set of light emitters 1602a and 1602b from reaching the window 1606 surrounding the sample 1610. In this example, S1=SS and S2=SR. However, in this example, the sample interference signal SS and background interference signal SR are measured separately (e.g., at time t1 and t2, respectively).
In the example shown in
In some examples, the blocking material 1608 may further be included along a top surface of the reference diffuse reflectance material 1612 and surrounding the window 1606 such that light emitted from the second set of light emitters 1602c and 1602d is reflected by the reference diffuse reflectance material 1612 and coupled to the interferometer 1604 to produce the background interference signal, while light emitted from the first set of light emitters 1602a and 1602b is reflected by the sample 1610 and coupled to the interferometer to produce the sample interference signal. Thus, the light emitted from the first set of light emitters 1602a and 1602b contributes only to Ss, while light emitted from the second set of light emitters 1602c and 1602c contributes only to SR. However, in this example, the sample interference signal Ss and background interference signal SR are measured separately (e.g., at time t1 and t2, respectively).
The interferometer 1704 is a Michelson interferometer that includes a beam splitter 1708, a fixed reflector 1710 (e.g., a fixed mirror), a moveable reflector 1712 (e.g., a moveable mirror), and a MEMS actuator 1714 coupled to the moveable reflector 1712. The fixed mirror 1710 and the moveable mirror 1712 are each flat mirrors. In the example shown in
The fixed mirror 1710 is optically coupled to reflect the received first and third incident beams 1720 and 1724, respectively back towards the beam splitter 1708 as first and third reflected beams 1728 and 1732, respectively. The moveable mirror 1712 is optically coupled to reflect the received second and fourth incident beams 1722 and 1726, respectively, back towards the beam splitter 1708 as second and fourth reflected beams 1730 and 1734, respectively. The moveable mirror 1712 is coupled to the MEMS actuator 1714 to produce a desired respective optical path difference (OPD) between the first and third reflected beams and the second and fourth reflected beams.
The first and second reflected beams 1728 and 1730, respectively, interfere at the beam splitter 1708 to produce a first interfering beam 1736, whereas the third and fourth reflected beams 1732 and 1734, respectively, interfere at the beam splitter 1708 to produce a second interfering beam 1738. The beam splitter 1708 is further optically coupled to direct the first interfering beam 1736 towards detector 1706a to detect a first interference signal and the second interfering beam 1738 towards detector 1706b to detect a second interference signal. A processor (not shown) may then utilize the interference signal detected by detector 1706b as a reference signal in processing the interference signal detected by detector 1706a. For example, the interference signal corresponding to the second spectral range detected by detector 1706b may be used to compensate or calibrate any errors in the interference signal corresponding to the first spectral range detected by detector 1706a. In this example, a first optical path is formed between a first input of the interferometer 1704 optically coupled to receive the first input beam 1716 and a first output thereof directing the first interfering beam 1736 towards the first detector 1706a, whereas a second optical path is formed between a second input of the interferometer 1704 optically coupled to receive the second input beam 1718 and a second output thereof directing the second interfering beam 1738 towards the second detector 1706b. In some examples, a sample and reference may be present at the respective outputs of the interferometer, as in
The interferometer 1804 is a Michelson interferometer that includes two beam splitters 1808a and 1808b, two fixed reflectors 1810a and 1810b (e.g., fixed mirrors), two moveable reflectors 1812a and 1812b (e.g., moveable mirrors), and a MEMS actuator 1814 coupled to the moveable reflectors 1812a and 1812b. In some examples, each beam splitter 1808a and 1808b is optimized for the particular wavelength range produced by the corresponding light source 1802a and 1802b. For example, one of the beam splitters 1808a may be an air/silicon beam splitter, while the other beam splitter 1808b may be a hollow waveguide splitter, thus enabling the wavelength range to be extended into the UV/visible spectrum, where propagation inside of silicon may be lossy. Each of the beam splitters 1808a and 1808b may be monolithically integrated with the same MEMS actuator 1814, as shown in
In the example shown in
The first fixed mirror 1810a is optically coupled to reflect the received first incident beam back towards the first beam splitter 1808a as a first reflected beam. The first moveable mirror 1812a is optically coupled to reflect the received second incident beam back towards the first beam splitter 1808a as a second reflected beam. In addition, the second fixed mirror 1810b is optically coupled to reflect the received third incident beam back towards the second beam splitter 1808b as a third reflected beam. The second moveable mirror 1812b is further optically coupled to reflect the received fourth incident beam back towards the second beam splitter 1808b as a second reflected beam. Each moveable mirror 1812a and 1812b is coupled to the MEMS actuator 1814 to produce a desired respective optical path difference (OPD) between the first and third reflected beams and the second and fourth reflected beams.
The first and second reflected beams interfere at the first beam splitter 1808a to produce a first interfering beam towards the first detector 1806a, whereas the third and fourth reflected beams interfere at the second beam splitter 1808b to produce a second interfering beam towards the second detector 1806b. A processor (not shown) may then utilize the interference signal detected by detector 1806b as a reference signal in processing the interference signal detected by detector 1806a, as described above. In this example, a first optical path is formed between a first input of the interferometer 1804 optically coupled to receive the first input beam and a first output thereof directing the first interfering beam towards the first detector 1806a, whereas a second optical path is formed between a second input of the interferometer 1804 optically coupled to receive the second input beam and a second output thereof directing the second interfering beam towards the second detector 1806b. In some examples, a sample and reference may be present at the respective outputs of the interferometer, as in
The interferometer 1904 is a Michelson interferometer that includes a beam splitter 1908, a fixed reflector 1910 (e.g., a fixed mirror), two moveable reflectors 1912a and 1912b, and a MEMS actuator 1914 coupled to the moveable reflectors 1912a and 1912b. A first moveable reflector 1912a is an optical path difference (OPD) multiplier corner mirror, while a second moveable reflector 1912b is a flat mirror. The two different moveable reflectors 1912a and 1912b enable measuring the PSD of an input beam from the light source 1902 at two different resolutions simultaneously.
For example, a first optical path may be formed through the moveable flat mirror 1912b, whereas a second optical path may be formed through the moveable OPD multiplier corner reflector. The second optical path through the flat moveable mirror 1912b provides a resolution Ro, while the second optical path through the OPD multiplier corner reflector 1912a provides a resolution Ro/n, with n=2 for the OPD multiplier corner reflector 1912a shown in
The interferometer 2004 is a Michelson interferometer that includes a beam splitter 2008, a fixed reflector 2010 (e.g., a fixed mirror), two moveable reflectors 2012a and 2012b, and a MEMS actuator 2014 coupled to the moveable reflectors 2012a and 2012b. A first moveable reflector 2012a is an optical path difference (OPD) multiplier corner mirror, while a second moveable reflector 2012b is a flat mirror. Similar to the example shown in
The interferometer 2104 is a Michelson interferometer that includes a beam splitter 2108, a fixed reflector 2110 (e.g., a fixed mirror), a moveable reflector 2112 (e.g., a moveable mirror), and a MEMS actuator 2114 coupled to the moveable reflector 2112. The fixed mirror 2110 and the moveable mirror 2112 are both flat mirrors. The interferometer 2104 further includes a tap splitter or coupler 2116 at an input of the interferometer 2104 optically coupled to receive the input beam from the light source 2102 and to redirect a portion of the input beam to the second detector 2106b to sample the light source power upon entering the interferometer. The tap splitter or coupler 2116 may further direct the remaining portion of the input beam to the interferometer 2104 for coupling an output thereof to the first detector 2106a. The PSD measured at the second detector 2106b may be utilized to compensate for source power variations or source noise in the interference signal measured at the first detector 2106a.
Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another—even if they do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly physically in contact with the second object. The terms “circuit” and “circuitry” are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure.
One or more of the components, steps, features and/or functions illustrated in
It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
This application claims priority to and the benefit of Provisional Application No. 62/651,016, filed in the U.S. Patent and Trademark Office on Mar. 30, 2018, the entire content of which is incorporated herein by reference as if fully set forth below in its entirety and for all applicable purposes.
Number | Name | Date | Kind |
---|---|---|---|
3915573 | Knoll et al. | Oct 1975 | A |
4444501 | Schwiesow | Apr 1984 | A |
4538910 | Doyle | Sep 1985 | A |
6025913 | Curbelo | Feb 2000 | A |
7079252 | Debreczeny et al. | Jul 2006 | B1 |
7796267 | Saadany et al. | Sep 2010 | B2 |
8154731 | Arnvidarson et al. | Apr 2012 | B2 |
8736843 | Medhat et al. | May 2014 | B2 |
8922787 | Mortada et al. | Dec 2014 | B2 |
10151633 | O'Rourke | Dec 2018 | B2 |
20020154379 | Tonar et al. | Oct 2002 | A1 |
20070291255 | Larsen | Dec 2007 | A1 |
20080228033 | Tumlinson et al. | Sep 2008 | A1 |
20080290279 | Juhl | Nov 2008 | A1 |
20110082353 | Kiesel et al. | Apr 2011 | A1 |
20120002212 | Chandler et al. | Jan 2012 | A1 |
20140098371 | Sabry et al. | Apr 2014 | A1 |
20140192365 | Mortada et al. | Jul 2014 | A1 |
20150062586 | Zhu et al. | Mar 2015 | A1 |
20150260573 | Ishimaru | Sep 2015 | A1 |
20150276588 | Marshall et al. | Oct 2015 | A1 |
20150323383 | Pastore | Nov 2015 | A1 |
20170363469 | Sabry et al. | Dec 2017 | A1 |
20200037883 | Islam | Feb 2020 | A1 |
Number | Date | Country |
---|---|---|
413241 | Dec 2005 | AT |
1058110 | Dec 2000 | EP |
1931939 | Jun 2008 | EP |
2419770 | Mar 2013 | EP |
2017138390 | Aug 2017 | JP |
9838475 | Sep 1998 | WO |
Entry |
---|
Invitation to Pay Additional Fees and Partial Search Report for PCT/US2019/025021, 18 pages, dated Jul. 29, 2019. |
Hans Villemoes Andersen, Anders Friderichsen, Sønnik Clausen, and Jimmy Bak, “Comparison of noise sources in dual- and single-beam Fourier-transform near-infrared spectrometry”, vol. 44, No. 29 Applied Optics 6, Oct. 10, 2005. |
International Patent Application No. PCT/US2019/025021, International Search Report and Written Opinion, 37 pages (dated Nov. 4, 2019). |
Elsayed, Ahmed A. et al. “Optical diffuse reflectance of Back Silicon and its isotropicity”, 2016 URSI Asia-Pacific Radio Conference, IEEE, pp. 1944-1946 (Aug. 21, 2016). |
International Patent Application No. PCT/US2019/025021, Written Opinion, 9 pages (dated Jul. 24, 2020). |
Number | Date | Country | |
---|---|---|---|
20190301939 A1 | Oct 2019 | US |
Number | Date | Country | |
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62651016 | Mar 2018 | US |