PATENT DOCUMENT

Publication Number: US-10690591-B2
Application Number: US-201615751454-A
Country: US
Kind Code: B2

Title: Measurement time distribution in referencing schemes

Abstract:
Methods and systems for measurement time distribution for referencing schemes are disclosed. The disclosed methods and systems can be capable of dynamically changing the measurement time distribution based on the sample signal, reference signal, noise levels, and SNR. The methods and systems can be configured with a plurality of measurement states, including a sample measurement state, reference measurement state, and dark measurement state. In some examples, the measurement time distribution scheme can be based on the operating wavelength, the measurement location at the sampling interface, and/or targeted SNR. Examples of the disclosure further include systems and methods for measuring the different measurement states concurrently. Moreover, the systems and methods can include a high-frequency detector to eliminate or reduce decorrelated noise fluctuations that can lower the SNR.

Claims:
What is claimed is: 
     
       1. A system for determining a concentration and a type of substance in a sample at a sampling interface, the system comprising:
 one or more detector pixels including a first detector pixel, wherein the one or more detector pixels are configured to operate in a plurality of cycles, each cycle including a plurality of measurement states, the plurality of measurement states including:
 a first measurement state configured to measure one or more optical properties of the type of substance in the sample during a first time period, 
 a second measurement state configured to measure one or more optical properties of a reference during a second time period, and 
 a third measurement state configured to measure noise during a third time period; and 
 
 logic capable of dynamically changing one or more aspects of the plurality of cycles, wherein the one or more aspects include a duration of a respective time period. 
 
     
     
       2. The system of  claim 1 , wherein the one or more detector pixels further includes a second detector pixel, the first detector pixel configured into the first measurement state, and the second detector pixel configured into the second measurement state at a same time. 
     
     
       3. The system of  claim 2 , wherein the one or more detector pixels further includes a third detector pixel, the third detector pixel configured into the third measurement state at the same time. 
     
     
       4. The system of  claim 2 , further comprising:
 a plurality of mirrors, each mirror associated with a detector pixel included in the one or more detector pixels and configured with an orientation such that a first light is reflected or blocked, and further configured to provide the associated detector pixel access to a second light, different from the first light. 
 
     
     
       5. The system of  claim 1 , further comprising:
 a detector pixel configured into the first measurement state, second measurement state, and third measurement state, wherein the first, second, and third measurement states are consecutive and determination of the concentration and the type of substance is based on the first, second, and third measurement states. 
 
     
     
       6. A method of determining a concentration and a type of substance in a sample at a sampling interface during a plurality of cycles, the plurality of cycles including a first cycle and a second cycle, the method comprising:
 during the first cycle:
 measuring one or more optical properties of the type of substance in the sampling interface during a first time period; 
 measuring one or more optical properties of a reference during a second time period; 
 measuring noise during a third time period; and 
 
 dynamically changing a duration of at least one of the first time period, second time period, and third time period during the second cycle. 
 
     
     
       7. The method of  claim 6 , wherein the duration of at least two of the first time period, second time period, and third time period within the first cycle are different. 
     
     
       8. The method of  claim 6 , wherein measuring one or more optical properties of the substance includes obtaining a first signal value and measuring one or more optical properties of the reference includes obtaining a second signal value, the method further comprising:
 comparing the first signal value to the second signal value; and 
 setting the first time period greater than the second time period when the first signal value is less than the second signal value. 
 
     
     
       9. The method of  claim 8 , wherein the duration of the first time period is set greater than 50% of a duration of the first cycle. 
     
     
       10. The method of  claim 6 , wherein measuring one or more optical properties of the substance includes obtaining a first signal value and measuring one or more optical properties of the reference includes obtaining a second signal value, the method further comprising:
 comparing the first signal value to the second signal value; and 
 setting the first time period less than the second time period when the first signal value is greater than the second signal value. 
 
     
     
       11. The method of  claim 10 , wherein the duration of the second time period is set greater than 50% of a duration of the first cycle. 
     
     
       12. The method of  claim 6 , wherein the first cycle includes a first operating wavelength and the second cycle includes a second operating wavelength, the first operating wavelength different from the second operating wavelength, and the first cycle having at least one of the first time period, second time period, and third time period different from the second cycle. 
     
     
       13. The method of  claim 6 , wherein the duration of the first time period is the same as the duration of the second time period within the first cycle. 
     
     
       14. The method of  claim 6 , wherein each cycle included in the plurality of cycles is associated with a detector pixel included in a plurality of detector pixels, the method further comprising:
 retrieving one or more entries from a look-up table, the one or more entries including an association between the first time period, second time period, and third time period and at least one of an operating wavelength and the detector pixel; and 
 setting at least one of the first time period, second time period, and third time period based on the one or more entries. 
 
     
     
       15. The method of  claim 14 , wherein at least one of the first time period, second time period, and third time period are different for at least two detector pixels included in the plurality of detector pixels. 
     
     
       16. The method of  claim 14 , further comprising:
 determining a property associated with the operating wavelength and the detector pixel, the property being at least one of a measurement time, measurement accuracy, and signal-to-noise ratio (SNR); 
 comparing the property to the one or more entries from the look-up table; and 
 updating the one or more entries from the look-up table based on the comparison. 
 
     
     
       17. The method of  claim 6 , wherein the plurality of cycles further includes a third cycle, and further wherein a duration of the first time period for the first cycle is same as a duration of second time period for the second cycle and a duration of the third time period for the third cycle. 
     
     
       18. A system for determining a concentration and type of substance in a sample site including a sampling interface, the system comprising:
 a light source configured to emit a first light and a second light, the first light incident on the sampling interface and the second light incident on a reference, wherein the first light and the second light include a noise component; 
 a first detector configured to measure incident light, the incident light being at least one of the first light and the second light, and configured to generate a first signal indicative of the incident light; 
 a second detector configured to measure the noise component included in a range of frequencies, and configured to generate a second signal indicative of the measured noise component; and 
 logic capable of scaling the second signal and compensating the first signal using the scaled second signal. 
 
     
     
       19. The system of  claim 18 , wherein a gain of the first detector is different from a gain of the second detector. 
     
     
       20. The system of  claim 19 , wherein an intensity of the first light is different from an intensity of the second light.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/220,887, filed Sep. 18, 2015, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     This relates generally to methods and systems for improving signal-to-noise ratio for referencing schemes, and more particularly, methods and systems for dynamically changing the measurement time distribution and removing high-frequency noise. 
     BACKGROUND 
     Absorption spectroscopy is an analytical technique that can be used to determine the concentration and type of one or more substances in a sample at a sampling interface. Conventional systems and methods for absorption spectroscopy can include emitting light at the sampling interface. As light is transmitted through the sample, a portion of the light energy can be absorbed at one or more wavelengths. This absorption can cause a change in the properties of the light exiting the sample. The properties of the light exiting at the sampling interface can be compared to the properties of the light exiting a reference, and the concentration and type of one or more substances in the sample at the sampling interface can be determined based on this comparison. 
     Although the comparison can determine the concentration and type of one or more substances in the sample at the sampling interface, the measurements can include a fixed measurement time distribution scheme. In some examples, the fixed measurement time distribution scheme can include an equal distribution of a cycle time to three measurement states: measuring the sample, measuring the reference, and measuring dark. However, the sample signal, reference signal, dark signal, and their corresponding noise levels can differ with operating wavelength, the surrounding environment, and/or measurement location of the substance in the sample. As a result, a fixed measurement time distribution scheme may not be optimal for all operating wavelengths and measurement locations in the sample. Additionally, the fixed measurement time distribution scheme can lead to long measurement times with unimportant information, erroneous measurement data, low signal-to-noise ratio (SNR), or a combination thereof. Thus, methods and systems for dynamically changing the measurement time distribution may be desired. Moreover, high-frequency noise in the system can lead to unacceptable SNR, so methods and systems for removing high-frequency noise may be desired. 
     SUMMARY 
     This relates to measurement time distribution for referencing schemes. The disclosed methods and systems can be capable of dynamically changing the measurement time distribution based on the sample signal, reference signal, noise levels, and SNR. The methods and systems can be configured with a plurality of measurement states, including a sample measurement state, reference measurement state, and dark measurement state. In some examples, less time can be allocated to the dark measurement state when the noise levels in the system are low. In some examples, the sample signal can be weak, and the system can allocate a greater amount of time to the sample measurement state than the other measurement states. In some examples, the sample signal can be strong, and the system can allocate a greater amount of time to the reference measurement state than the other measurement states. In some examples, the measurement time distribution scheme can be based on the operating wavelength, the measurement location in the sample, and/or targeted SNR. Examples of the disclosure further include systems and methods for measuring the different measurement states concurrently. Moreover, the systems and methods can include a high-frequency detector to eliminate or reduce decorrelated noise fluctuations that can lower the SNR. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary system comprising multiple detectors for measuring the concentration and type of one or more substances in a sample according to examples of the disclosure. 
         FIG. 2  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising multiple detectors according to examples of the disclosure. 
         FIG. 3  illustrates an exemplary system comprising a shared detector for measuring the concentration and type of one or more substances in a sample according to examples of the disclosure. 
         FIG. 4  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising a shared detector according to examples of the disclosure. 
         FIG. 5  illustrates an exemplary plot of absorbance measurements for determining the concentration and type of one or more substances according to examples of the disclosure. 
         FIG. 6  illustrates an exemplary system comprising a modulator located between the light source and the sample for measuring the concentration and type of one or more substances in a sample according to examples of the disclosure. 
         FIG. 7  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. 
         FIG. 8  illustrates an exemplary system comprising a modulator located between the light source and the sample for measuring the concentration and type of one or more substances in a sample according to examples of the disclosure. 
         FIG. 9  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. 
         FIG. 10  illustrates an exemplary plot of absorbance measurements used for determining the concentration and type of one or more substances according to examples of the disclosure. 
         FIG. 11  illustrates an exemplary plot of the absorbance measurements including three measurement states with an equal measurement time distribution according examples of the disclosure. 
         FIG. 12  illustrates an exemplary plot of absorbance measurements including three measurement states with unequal measurement time distribution according to examples of the disclosure. 
         FIG. 13  illustrates an exemplary process flow for dynamically changing the measurement time distribution according to examples of the disclosure. 
         FIG. 14  illustrates a portion of an exemplary system for measuring the concentration and type of one or more substances in a sample and capable of measuring different measurement states concurrently according to examples of the disclosure. 
         FIG. 15  illustrates an exemplary plot of measurement states for a system capable of measuring different measurement states concurrently according to examples of the disclosure. 
         FIG. 16  illustrates a cross-sectional view of a portion of an exemplary system including a plurality of MEMS components and capable of measuring different measurement states concurrently according to examples of the disclosure. 
         FIG. 17  illustrates an exemplary plot of absorbance measurements with noise fluctuations according to examples of the disclosure. 
         FIG. 18  illustrates an exemplary system for measuring the concentration and type of one or more substances in a sample including a high-frequency detector according to examples of the disclosure. 
         FIG. 19  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system including a high-frequency detector according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. 
     Representative applications of methods and apparatus according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting. 
     Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     Further, although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred. 
     This disclosure relates to measurement time distribution for referencing schemes. The disclosed methods and systems can be capable of dynamically changing the measurement time distribution based on the sample signal, reference signal, dark signal, noise levels, SNR, or a combination thereof. The methods and systems can be configured with a plurality of measurement states, including a sample measurement state, reference measurement state, and dark measurement state. In some examples, less time can be allocated to the dark measurement state when the noise levels in the system are low. In some examples, the sample signal can be weak, and the system can allocate a greater amount of time to the sample measurement state than the other measurement states. In some examples, the sample signal can be strong, and the system can allocate a greater amount of time to the reference measurement state than the other measurement states. In some examples, the amount of time allocated to the sample measurement state and reference measurement state can be based on the noise level. In some examples, the noise level can depend on the intensity of the sample signal, reference signal, or both. In some examples, the measurement time distribution scheme can be based on the operating wavelength, the measurement location in the sample, the surrounding environmental conditions, and/or targeted SNR. Examples of the disclosure can further include systems and methods for measuring the different measurement states concurrently. Moreover, the systems and methods can include a high-frequency detector to eliminate or reduce time-decorrelated noise fluctuations that can lower SNR in particular referencing schemes. 
     For substances in a sample, each substance can have a signature in a certain wavelength regime, indicated by the pattern as a function of wavelength formed by one or more absorbance peaks. One exemplary wavelength regime can be short-wavelength infrared (SWIR). A substance can absorb higher amounts of energy at one or more wavelengths and can absorb lower amounts of energy at other wavelengths, forming a spectral fingerprint unique to the substance. Determination of the type of one or more substances in the sample can be performed by matching the measured spectrum to the contents of a spectral library including fingerprints of relevant substances. Additionally, the concentration of the substance can be based on the amount of absorption. 
     The sample can comprise multiple substances that can modify incident light. Of the multiple substances, one or more substances can be a substance of interest and other substances may not be of interest. In some examples, the substances not of interest can absorb more incident light than the substance of interest. Additionally, spectral artifacts can “mask” the absorbance peaks of the one or more substances of interest. Both the spectral artifacts and the absorption of substances not of interest can make detection of the substance of interest difficult. Furthermore, the concentration of the one or more substances can be distributed in an inhomogeneous manner in the sample, which can produce variations in the optical properties (e.g., linear birefringence, optical activity, diattenuation) of the sample. Variations of the optical properties in the sample can lead to different signal values based on the measurement location in the sample. Additionally, the absorbance of the substances not of interest or the noise levels at different locations within the sample can differ. Furthermore, the components in the system can have differing drift with time, which can change the signal values and/or noise levels. Different signals values and/or different noise levels can lead to an SNR that varies based on several factors, such as wavelength, measurement location in the sample, or both. 
     Absorption spectroscopy is an analytical technique that can be used to determine the concentration and type of one or more substances in a sample. Light can have an initial intensity or energy when emitted from a light source and incident on a sample. As the light is transmitted through the sample, a portion of the energy can be absorbed at one or more wavelengths. This absorption can cause a change (e.g., loss) in the intensity of the light exiting the sample. As the concentration of the substance in the sample increases, a higher amount of energy can be absorbed, and this can be represented by the Beer-Lambert Law as: 
                   A   =       ɛ   ⁢           ⁢   lc     =       -       log   10     ⁡     (   T   )         =     -       log   10     ⁡     (       I   sample       I   reference       )                     (   1   )               
where ε can be the absorptivity of the substance in the sample at the measurement wavelength, l can be the path length of light through the sample, c can be the concentration of the substance of interest, T can be the transmittance of the light exiting the sample, I sample  can be the intensity along the sample path measured at the measurement wavelength, and I reference  can be the intensity along the reference path measured at the measurement wavelength.
 
     As shown in Equation 1, the amount of light exiting the sample can be an exponential function of concentration. Given the relationship between absorbance and transmittance measurement stated in Equation 1, a linear relationship can exist between absorbance and the concentration of the substance in the sample. In some examples, the concentration of a substance can be determined based on the absorbance measurement. In some examples, the reference path can include a reference “sample” with a known concentration of the one or more substances of interest. In some examples, the concentration of the substance in the sample can be calculated using a reference and a proportional equation, defined as: 
                       A   sample       A   reference       =       C   sample       C   reference               (   2   )               
where A sample  and A reference  are the sample absorbance and reference absorbance, respectively, and C sample  and C reference  are the concentrations of the substance in the sample and in the reference, respectively. In some examples, the substance can include one or more chemical constituents, and the measurement can be used to determine the concentration of each chemical constituent present in the sample.
 
       FIG. 1  illustrates an exemplary system and  FIG. 2  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising multiple detectors according to examples of the disclosure. System  100  can include light source  102  controlled by controller  140  through signal  104 . Light source  102  can emit multi-band or multi-wavelength light  150  towards monochromator  106  (step  202  of process  200 ). A monochromator is a component that can select one or more discrete wavelengths from multi-wavelength light  150 . In some examples, one or more discrete wavelengths can include a finite range of wavelengths. In some examples, monochromator  106  can comprise an entrance slit configured to select a spectral resolution and/or exclude unwanted or stray light. The monochromator can be coupled with one or more interference or absorption filters, prisms, or diffraction gratings for wavelength selection. Monochromator  106  can separate light  150  into one or more discrete wavelengths forming light  152  (step  204  of process  200 ). Light  152  can be incident on beamsplitter  110 . A beamsplitter is an optical component that can split a beam of light into multiple beams of light. Beamsplitter  110  can split light  152  into two light beams: light  154  and light  164  (step  206  of process  200 ). 
     Light  154  can be incident on sample  120 . A portion of light can be absorbed by the substance in sample  120 , and a portion of light can be transmitted through sample  120  (step  208  of process  200 ). In some examples, a portion of the light can scatter. Scattering can lead to light loss and can alter the path length of the light transmitted through sample  120 . The portion of light that is transmitted through sample  120  can be represented as light  156 . Light  156  can comprise a set of photons that can impinge upon the active area of detector  130 . Detector  130  can respond to or measure light or photons impinging on the active area (step  210  of process  200 ) and can generate electrical signal  158 , which can be indicative of the properties of light  156  (step  212  of process  200 ). Electrical signal  158  can be input into controller  140 . 
     Light  164  can be directed towards mirror  112  (step  214  of process  200 ). Mirror  112  can be any type of optics capable of directing or redirecting light towards reference  122 . In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. In some examples, system  100  can include other types of optics such as light guides, diffraction gratings, or a reflectance plate. Light  164  can be incident on reference  122 . A portion of light  164  can be absorbed by the substance in reference  122 , and a portion of light  164  can be transmitted through reference  122  as light  166  (step  216  of process  200 ). Light  166  can comprise a set of photons that can be incident on detector  132 . In some examples, detector  130  and detector  132  can be matched detectors. That is, detector  130  and detector  132  can have similar characteristics including, but not limited to, the type of detector, operating conditions, responsivity, and performance. Detector  132  can respond to or measure light or photons impinging on the active area (step  218  of process  200 ) and can generate electrical signal  168  indicative of the properties of light  166  (step  220  of process  200 ). Electrical signal  168  can be input into controller  140 . 
     Controller  140  can receive both signal  158  and signal  168 . In some examples, signal  158  can include the sample signal, and signal  168  can include the reference signal. Controller  140  can divide, subtract, or scale the sample signal by the reference signal to obtain a ratio, for example. The ratio can be converted to absorbance by using Equation 1, and an algorithm can be applied to the absorbance spectrum to determine the concentration of the substance. 
     One advantage to determining the composition of the substance in the sample using system  100  (illustrated in  FIG. 1 ) can be that fluctuations, drift, and/or variations originating from the light source, and not originating from changes in the composition of the substance, can be compensated. For example, if the properties of light  152  emitted from light source  102  unexpectedly change, both light  154  and light  164  can be equally affected by this unexpected change. As a result, both light  156  and light  166  can also be equally affected such that the change in light can be canceled or ratioed out when controller  140  divides, scales, or subtracts signal  158  by signal  168 . However, since system  100  includes two different detectors (e.g., detector  130  and detector  132 ) for absorbance measurements, fluctuations, drift, and/or variations originating from the detectors themselves may not be compensated. Although detector  130  and detector  132  can be matched (i.e., have the same characteristics), the rate or effect that various factors unrelated to the substance, such as environmental conditions, can have on the different detectors may not be the same. One skilled in the art would appreciate that the same characteristics can include tolerances that result in a 15% deviation. With differing effects to the different detectors, only one signal, and not both signals, can be perturbed. Instead of controller  140  realizing that there is a factor unrelated to the substance that has perturbed only one signal, controller  140  can erroneously calculate this perturbation as a difference in the concentration of sample  120  compared to the reference  122 . Alternatively or additionally, controller  140  can mistake the type of substance if the perturbation leads to change in the spectral fingerprint. 
     There can be many sources of fluctuations, drift, and variations. One exemplary drift can be an initialization drift due to “warming up” the components. While the user can wait a certain time until such initialization drift has stabilized, this may not be a suitable solution in certain applications. For example, in systems where low power consumption is desired, certain components can be turned off when not in use to conserve power and then switched on when in use. Waiting for the components to warm up may become frustrating for the user depending on how long it would take for stabilization. Furthermore, the power consumed while waiting may negate the benefit of turning off the components. 
     Another exemplary drift can be due to noise. For example, 1/f noise can be present due to randomly changing non-ohmic contacts of the electrodes and/or influences from surface measurement state traps within a component. With random changes, not only are the changes unpredictable, but also may affect the different detectors in a different manner. Another exemplary drift can be thermal drift due to variations in temperature and/or humidity of the ambient environment, which may also affect the different detectors in a different manner. 
     Regardless of the source of the fluctuations, drift, and variations, the effect of having a detector measure the sample and a different detector measure the reference can lead to an unwanted change in the sensitivity, detectivity, and/or absorbance spectrum. Since the light path traveling through the sample can be different from the light path traveling through the reference and there can be many non-shared components or unmapped correlations between the two paths, any change in signal due to mismatch between the light paths may not be differentiated from a change in signal due to the substance of interest. 
     Since light source  102  in system  100  can be shared, drift and instabilities originating from light source  102  can be compensated for. However, drift or instabilities originating from components that are not shared (i.e., not common) along both light paths may not be compensated for. Moreover, the measurement capabilities of the system can be limited in situations where the detectors are shot noise limited. Shot noise is the noise or current generated from random generation and flow of mobile charge carriers. With shot noise limited detectors, the different detectors can have random and/or different noise floors. As a result, system  100  (illustrated in  FIG. 1 ) may not be suitable for high sensitivity or low signal measurements. 
       FIG. 3  illustrates an exemplary system and  FIG. 4  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising a shared detector according to examples of the disclosure. System  300  can include light source  302  controlled by controller  340  through signal  304 . Light source  302  can emit multi-wavelength light  350  towards monochromator  306  (step  402  of process  400 ). Monochromator  306  can separate multi-wavelength light  350  into one or more discrete wavelengths of light comprising light  352  (step  404  of process  400 ). Light  352  can be directed towards beamsplitter  310 , which can then split light into two light beams: light  354  and light  364  (step  406  of process  400 ). 
     Light  354  can be incident on sample  320 . A portion of light can be absorbed by the substance in sample  320 , and a portion of light can be transmitted through sample  320  (step  408  of process  400 ). The portion of light that is transmitted through the sample can be referred to as light  356 . Light  356  can be directed towards mirror  314 . Mirror  314  can direct or change the direction of propagation of light  356  toward selector  324  (step  410  of process  400 ). 
     Light  364  can be incident on mirror  312 . Mirror  312  can change the direction of propagation of light towards reference  322  (step  412  of process  400 ). A portion of light  364  can be absorbed by the chemical substance in reference  322 , and a portion of light  364  can be transmitted through reference  322  (step  414  of process  400 ). The portion of light that is transmitted through reference  322  can be referred to as light  366 . 
     Both light  356  and  366  can be incident on selector  324 . Selector  324  can be any optical component capable of moving or selecting the light beam to direct towards chopper  334 . Chopper  334  can be a component that periodically interrupts the light beam. System  300  can alternate in time between chopper  334  modulating light  356  and modulating light  366 . Light is transmitted through chopper  334  can be incident on the active area of detector  330 . Both light  356  and light  366  can each comprise a set of photons incident on detector  330 . Detector  330  can respond to or measure incident light or photons and can generate an electrical signal indicative of the properties of light. 
     In a first time, chopper  334  can modulate light  356  (step  416  of process  400 ). Detector  330  can measure light  356  that has been transmitted through the sample  320  (step  418  of process  400 ) and can generate an electrical signal  358  indicative of the properties of light  356  (step  420  of process  400 ). In a second time, chopper  334  can modulate light  366  (step  422  of process  400 ). Detector  330  can measure light  366  that has been transmitted through reference  322  (step  424  of process  400 ) and can generate an electrical signal  368  indicative of the properties of light  366  (step  426  of process  400 ). 
     Controller  340  can receive both signal  358  and signal  368  at different times. Signal  358  can include the sample signal, and signal  368  can include the reference signal. Controller  340  can divide, subtract, or scale the sample signal by the reference signal (step  428  of process  400 ) to obtain a ratio, for example. The ratio can be converted to absorbance by using Equation 1, and an algorithm can be applied to the absorbance spectrum to determine the concentration of the substance. 
     Although system  300  (illustrated in  FIG. 3 ) can compensate for minor fluctuations, drifts, and/or variations in the detector due to the shared detector, it may be difficult for system  300  to discern between different types of drift. There can be multiple types of drift, such as zero drift and gain drift. Zero drift can refer to a change in the zero level over time, thereby preventing a constant (i.e., horizontal) relationship with time. Gain drift can refer to a change in the average number of electronic carriers per generated electron-hole pair. That is, gain drift can refer to a change in the efficiency or ratio of generated electron-hole pairs to the current response of the detector. In order to discern between zero drift and gain drift, the system can be capable of stabilizing one type of drift and measuring the other. For example, to determine the gain drift from the light source, the system can be DC stabilized (i.e., a stable zero drift). However, due to lack of capability for stabilizing one type of drift in system  300 , zero drift and gain drift may not be discerned. 
     In some instances, the presence of stray light can be measured by the detector, which can lead to an erroneous signal and an erroneous determination of the concentration and type of one or more substances. In system  300 , the placement of chopper  334  after light has transmitted through sample  320  or reference  322  can lead to the stray light reaching sample  320  or reference  322 . The stray light may not contribute to the spectroscopic signal, so by allowing the stray light to reach sample  320  or reference  322 , detector  330  can detect the photons included in the stray light. Detecting the photons included in the stray light can lead to erroneous changes in either signal  358  or signal  368 . With a change in signal  358  or signal  368 , controller  340  may not be able to determine whether or how much this change is due to stray light or due to variations in light source  302 . Therefore, system  300  may not be suitable for situations where there can be non-negligible amounts of stray light present. 
     When the substance of interest in the sample has a low concentration, a system with increased accuracy and sensitivity, compared to system  100  (illustrated in  FIG. 1 ) and system  300  (illustrated in  FIG. 3 ), may be desired. To measure the concentration and type of one or more substances, system  100  (illustrated in  FIG. 1 ) and system  300  (illustrated in  FIG. 3 ) can measure the sample and reference multiple times.  FIG. 5  illustrates an exemplary plot of the absorbance measurements for determining the concentration and type of one or more substances according to examples of the disclosure. The system can begin with dark phase  570 , where one or more components in the system can be optimized, calibrated, and/or synchronized to minimize errors. Dark phase  570  can include, for example, measuring the reference absorbance. In some examples, dark phase  570  can include measuring the dark current and noise of the system. A sample with a known, stable concentration of the substance can be placed in the light path where the sample is located. The system can be either on or off. The controller can determine the absorbance and set the “zero level” equal to this absorbance. If the signal has saturated or clipped due to a significant drift, the controller can adjust the light source emission properties until the signal is no longer saturated. 
     Once dark phase  570  is complete and the zero level has been determined, the system can proceed to measurement phase  572 . In measurement phase  572 , the concentration of the substance in the sample can be measured by sampling several times to generate a plurality of sample points  574 . In some examples, the system can measure tens to hundreds of sample points  574 . Once a certain number of sample points  574  have been measured, the controller can average the values of the sample points  574  to determine the absorbance. Measuring multiple sample points and determining the average may be needed because, as illustrated in the figure, the absorbance measurements can include minor perturbations that, if not accounted for, can lead to errors in the determination of the concentration of the substance. In some examples, dark phase  570  can be repeated to re-zero the zero level when the light source changes emission wavelength, after a pre-determined time has elapsed between consecutive dark phases, or after a pre-determined number of sample points have been measured. 
     In some instances, the measurement procedure illustrated in  FIG. 5  can have long times between consecutive dark phases, such that an inaccurate average signal measurement can result due to the set zero level drifting from the actual zero level. The figure illustrates the zero drift or gain drift, where the absorbance signal can start to deviate from a constant (i.e., horizontal) relationship with time due to the zero level or gain value drifting away from the actual zero level or actual gain value, respectively. While the time between consecutive dark phases can be shortened, there can be a limit on the minimum time period between dark phases due to the minimum number of sample points that may be needed for an accurate measurement. This can be particularly true in situations where the SNR is low, which can require tens to hundreds of repeated measurements in order to achieve an average absorbance value that is somewhat accurate. 
       FIG. 6  illustrates an exemplary system and  FIG. 7  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. System  600  can include light source  602  coupled to controller  640 . Controller  640  can send signal  604  to light source  602 . In some examples, signal  604  can include a current or voltage waveform. Light source  602  can be directed towards filter  606 , and signal  604  can cause light source  602  to emit light  650  towards filter  606  (step  702  of process  700 ). Light source  602  can be any source capable of generating light including, but not limited to, a lamp, a laser, a light emitting diode (LED), an organic LED (OLED), an electroluminescent (EL) source, a super-luminescent diode, any super-continuum source including a fiber-based source, or a combination of one or more of these sources. In some examples, light source  602  can be capable of emitting a single wavelength of light. In some examples, light source  602  can be capable of emitting a plurality of wavelengths of light. In some examples, the plurality of wavelengths can be adjacent to one another, providing a continuous output band. In some examples, light source  602  can be a super-continuum source capable of emitting light in at least a portion of both the SWIR and MWIR ranges. A super-continuum source can be any broadband light source that outputs a plurality of wavelengths. In some examples, light source  602  can be any tunable source capable of generating a SWIR signature. 
     Filter  606  can be any type of filter capable of tuning or selecting a single wavelength or multiple discrete wavelengths by tuning the drive frequency. In some examples, filter  606  can be an acousto-optic tunable filter (AOTF). In some examples, filter  606  can be an angle tunable narrow bandpass filter. Although not illustrated in the figure, filter  606  can be coupled to controller  640 , and controller  640  can tune the drive frequency of filter  606 . In some examples, filter  606  can be a passband filter configured to selectively allow one or more continuous bands (i.e., wavelength ranges) of light to transmit through. Light  650  can comprise multiple wavelengths (step  702  of process  700 ) and after transmitting through filter  606 , can form light  652  comprising one or more discrete wavelengths (step  704  of process  700 ). In some examples, light  652  can comprise fewer wavelengths of light than light  650 . Light  652  can be directed towards beamsplitter  610 . Beamsplitter  610  can be any type of optic capable of splitting incoming light into multiple light beams. In some examples, each light beam split by the beamsplitter  610  can have the same optical properties. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. Beamsplitter  610  can split light  652  into two light beams (step  706  of process  700 ): light  654  and light  664 , as illustrated in the figure. 
     Light  654  can be transmitted through chopper  634 , where chopper  634  can modulate the intensity of light  654  (step  708  of process  700 ). Chopper  634  can be any component capable of modulating the incoming light beam. In some examples, chopper  634  can be an optical chopper. In some examples, chopper  634  can be a mechanical shutter. In some examples, chopper  634  can be a modulator or a switch. Light  654  can be transmitted through optics  616  (step  710  of process  700 ). Optics  616  can include one or more components configured to change the behavior and properties, such as the beam spot size and/or angle of propagation, of light  654 . Optics  616  can include, but are not limited to, a lens or lens arrangement, beam directing element, collimating or focusing element, diffractive optic, prism, filter, diffuser, and light guide. Optics  616  can be placed in any arrangement, such as a resolved path sampling (RPS) system, confocal system, or any optical system suitable for measuring a concentration and type of one or more substances in sample  620  at a sampling interface. The optics can be an optical system capable of resolving multiple angles of incidence on the sample interface and different path lengths included in a plurality of optical paths. In some examples, the optical system can be configured to accept one or more incident light rays with a path length within a range of path lengths and an angle of incidence within a range of angles, and rejecting optical paths with a path length outside the range of path lengths and with an angle of incidence outside the range of angles. 
     Light  654  can be transmitted through sample  620 . Energy can be absorbed at one or more wavelengths by the substance in the sample  620 , causing a change in the properties of light  656  exiting the sample (step  712  of process  700 ). In some examples, light  656  can be formed by reflection or scattering of the substance located in the sample. Light  656  can be incident on mirror  614 , which can direct or redirect light  656  towards selector  624  (step  714  of process  700 ). Mirror  614  can be any type of optics capable of changing the direction or angle of propagation of light. For example, mirror  614  can be a concave mirror configured to change the direction of light propagation by 90°. In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. 
     Light  664  can be incident on mirror  612  (step  716  of process  700 ). Mirror  612  can redirect light  664  towards detector  630 . Mirror  612  can be any mirror capable of changing the direction or angle of propagation of light. In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. In some examples, mirror  612  can have the same optical properties as mirror  614 . Light  664  can be transmitted through chopper  636 , which can modulate the intensity of light  664  (step  718  of process  700 ). In some examples, chopper  634  and chopper  636  can have the same chopper characteristics, such as chopping frequency and disc configuration. One skilled in the art would appreciate that the same chopper characteristics can include tolerances that result in a 15% deviation. In some examples, chopper  636  can be a shutter, such as a microelectromechanical system (MEMS) shutter. In some examples, chopper  636  can be a modulator or a switch. The modulated light can be transmitted through filter  608  to generate light  666  (step  720  of process  700 ). Filter  608  can be any type of filter capable of selectively transmitting light. In some examples, filter  608  can be a neutral density filter, blank attenuator, or filter configured to attenuate or reduce the intensity of all wavelengths of light. In some examples, filter  608  can attenuate light by a pre-determined or known constant value or attenuation factor. 
     Both light  656  and light  666  can be incident on selector  624 . Selector  624  can be any optical component capable of moving or selecting the light beam to be directed towards detector  630 . System  600  can alternate in time between allowing light  656  to be incident on detector  630  at one time and allowing light  666  to be incident on detector  630  at another time. In both situations, light  656  and light  666  can each include a set of photons. The photons can be incident on detector  630 , and detector  630  can generate an electrical signal indicative of the properties of the incident light or number of impinging photons. Detector  630  can measure the set of photons from light  656  (step  722  of process  700 ) and can generate an electrical signal  658  (step  724  of process  700 ). Signal  658  can be indicative of the properties of light  656 , which can represent the energy from light  654  returned by the substance of interest in sample  620 . Detector  630  can measure the set of incident photons from light  666  (step  726  of process  700 ) and can generate an electrical signal  668  (step  728  of process  700 ). Signal  668  can be indicative of the properties of light  664  that was not absorbed by filter  608  and can act as a reference signal. 
     Detector  630  can be any type of detector capable of measuring or responding to light or photons, such as photodiodes, photoconductors, bolometers, pyroelectric detectors, charge coupled devices (CCDs), thermocouples, thermistors, photovoltaics, and photomultiplier tubes. Detector  630  can include a single detector pixel or a detector array, such as a multi-band detector or a focal plane array (FPA). A detector array can include one or more detector pixels disposed on a substrate. A detector pixel can include one or more detector elements with a common footprint. A detector element can be an element designed to detect the presence of light and can individually generate a signal representative of the detected light. In some examples, detector  630  can be any type of detector capable of detecting light in the SWIR. Exemplary SWIR detectors can include, but are not limited to, Mercury Cadmium Telluride (HgCdTe), Indium Antimonide (InSb), and Indium Gallium Arsenide (InGaAs). In some examples, detector  630  can be a SWIR detector capable of operating in the extended wavelength range (up to 2.7 μm). 
     Controller  640  can receive both signal  658  and signal  668 , where each signal can be received at a different time. Signal  658  can include the sample signal, and signal  668  can include the reference signal. Controller  640  can divide, subtract, or scale the sample signal by the reference signal (step  730  of process  700 ) to obtain a ratio, for example. The ratio can be converted to absorbance by using Equation 1, and an algorithm can be applied to the absorbance spectrum to determine the concentration of the substance. In some examples, controller  640  can compare the reference absorbance to one or more absorbance values stored in a lookup table or in memory to determine the concentration and type of one or more substances in the sample. Although Equation 2 and the above discussion is provided the context of absorbance, examples of the disclosure include, but are not limited to, any optical property such as reflectivity, refractive index, density, concentration, scattering coefficient, and scattering anisotropy. 
     System  600  can be an alternative to system  100  (illustrated in  FIG. 1 ) and system  300  (illustrated in  FIG. 3 ). System  600  can have a shared detector (e.g., detector  630 ) to measure light through sample  620  and (an optional) filter  608 . Utilizing a shared detector can eliminate or alleviate unpredictable changes in sensitivity, detectivity, and/or absorbance due to differing (or random) fluctuations, drifts, and/or variations. As discussed above, the fluctuations, drifts, and/or variations can be due to initialization, 1/f noise, and/or environmental changes that can affect the two detectors in a different manner. Additionally, system  600  can tolerate and discern non-negligible amounts of stray light due to the placement of chopper  634  and chopper  636  in the light path prior to being incident on sample  620  and filter  608 , respectively. Furthermore, unlike system  100  and system  300 , system  600  can account for any fluctuations, drifts, and/or variations originating from both light source  602  and detector  630 . 
     In some examples, attenuation of incoming light by filter  608  by a pre-determined or known constant value can lead to a mismatch between light  656  (i.e., light that is transmitted through sample  620 ) and light  666  (i.e., light that is transmitted through filter  608 ). This mismatch can be due to differing absorbance at different wavelengths. At one or more wavelengths, the substance in sample  620  can absorb a large percentage of light, and therefore, a low attenuation factor for filter  608  would be suitable at those one or more wavelengths. At other wavelengths, the same substance and same concentration of that substance in sample  620  can absorb very little light, and therefore, a high attenuation factor for filter  608  would be suitable. Since filter  608  can attenuate by a constant value for all wavelengths of interest, accurate measurements of system  600  can be limited to only one or a small number of wavelengths. Furthermore, a blank attenuator or neutral density filter may not be effective when detecting a low concentration of the substance of interest in the sample if the attenuation factor is not optimal. Therefore, a system that can account for the variations in absorbance with wavelength in sample  620  and can be capable of detecting a low concentration of the substance in the sample may be desired. 
       FIG. 8  illustrates an exemplary system and  FIG. 9  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample at a sampling interface using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. System  800  can include light source  802  coupled to controller  840 . Controller  840  can send signal  804  to light source  802 . In some examples, signal  804  can include a current or voltage waveform. Light source  802  can be directed towards filter  806 , and signal  804  can cause light source  802  to emit light  850  (step  902  of process  900 ). Light source  802  can be any source capable of emitting light  850 . In some examples, light source  802  can be capable of emitting a single wavelength of light. In some examples, light source  802  can be capable of emitting a plurality of wavelengths of light. An exemplary light source can include, but is not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, the plurality of wavelengths can be close to or adjacent to one another providing a continuous output band. In some examples, light source  802  can be any tunable source capable of generating a SWIR signature. In some examples, light source  802  can be a super-continuum capable of emitting light at least in a portion of both the SWIR and MWIR. 
     Filter  806  can be any filter capable of tuning and selecting a single wavelength or multiple discrete wavelengths by tuning the drive frequency. In some examples, filter  806  can be an AOTF. In some examples, filter  606  can be an angle tunable narrow bandpass filter. Although not illustrated in the figure, filter  806  can be coupled to controller  840 , and controller  840  can tune the drive frequency of filter  806 . In some examples, filter  806  can be a transmit band filter configured to selectively allow one or more continuous bands (i.e., wavelength ranges) of light to be transmitted through. Light  850  can comprise multiple wavelengths and, after being transmitted through filter  806 , can form light  852  comprising one or more discrete wavelengths (step  904  of process  900 ). In some examples, light  852  comprises fewer wavelengths of light than light  850 . Light  852  can be directed towards beamsplitter  810 . Beamsplitter  810  can be any type of optic capable of splitting incoming light into multiple light beams. In some examples, each light beam split by beamsplitter  810  can have the same optical properties. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. As illustrated in the figure, beamsplitter  810  can split light  852  into two light beams: light  854  and light  864  (step  906  of process  900 ). 
     Light  854  can be transmitted through chopper  834 , where chopper  834  can modulate the intensity of light  854  (step  908  of process  900 ). Chopper  834  can be any component capable of modulating or periodically interrupting the incoming light beam. In some examples, chopper  834  can be an optical chopper. In some examples, chopper  834  can be a mechanical shutter, such as a MEMS shutter. In some examples, chopper  834  can be a modulator or a switch. Light  854  can be transmitted through optics  816  (step  910  of process  900 ). Optics  816  can include one or more components configured to change the behavior and properties of the light, such as the beam spot size and/or angle of propagation, of light  854 . Optics  816  can include, but are not limited to, a lens or lens arrangement, beam directing element, collimating or focusing element, diffractive optic, prism, filter, diffuser, and light guide. Optics  816  can include any type of optical system, such as a RPS system, confocal system, or any optical system suitable for measuring a concentration and type of one or more substances in sample  820 . 
     Light  854  can be directed towards sample  820 . Sample  820  can absorb a portion of light  854  and a portion of light  854  can be transmitted at one or more wavelengths (step  912  of process  900 ). A portion of light  854  can be absorbed by the substance in sample  820 , and a portion of light  854  can be transmitted through the sample  820 . The portion of light  854  that is transmitted through the sample  820  can be referred to as light  856 . In some examples, light  856  can be formed by reflection or scattering of the substance located in sample  820 . Light  856  can be directed towards mirror  814 , and mirror  814  can redirect light  856  towards mirror  814  (step  914  of process  900 ). Mirror  814  can be any type of optics capable of changing the direction of light propagation. In some examples, mirror  814  can be a concave mirror configured to change the direction of light propagation by 90°. In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. 
     The second light path formed by the beamsplitter  810  splitting light  852  can be referred to as light  864 . Light  864  can be directed towards mirror  812 . Mirror  812  can be any type of optics capable of changing the direction of the propagation of light  864 . Mirror  812  can direct or redirect light  864  towards selector  824  (step  916  of process  900 ). Light  864  can be transmitted through chopper  836 , and chopper  836  can modulate light  864  (step  918  of process  900 ). Chopper  836  can be any component capable of modulating the intensity of the incoming light beam. In some examples, chopper  834  and chopper  836  can have the same chopping characteristics, such as chopping frequency and disc configuration. One skilled in the art would appreciate that the same chopping characteristics can include tolerances that result in a 15% deviation. In some examples, chopper  836  can be a mechanical shutter, such as a MEMS shutter. In some examples, chopper  834  can be an optical modulator or a switch. Light  864  can be transmitted through optics  818  (step  920  of process  900 ). Optics  818  can include one or more lenses, beam directing elements, collimating or focusing elements, diffractive optics, prisms, filters, diffusers, light guides, or a combination of one or more these optical elements and can be arranged in any arrangement (e.g., RPS system or confocal system) suitable for measuring a concentration and type of one or more substances in sample  820  or reference  822 . In some examples, optics  818  can have the same components, arrangement, and/or characteristics as optics  816 . 
     Light exiting optics  818  can be incident on reference  822  (step  922  of process  900 ). Reference  822  can have the same spectroscopic properties (e.g., scattering characteristics, reflection characteristics, or both) as sample  820 . One skilled in the art would appreciate that the same spectroscopic properties can include tolerances that result in a 15% deviation. In some examples, reference  822  can be a copy or a “phantom” replica of sample  820 . In some examples, the absorption spectra of reference  822  can be the same as the absorption spectra of sample  820 . One skilled in the art would appreciate that the same absorption spectra can include tolerances that result in a 15% deviation. A portion of light can be absorbed by reference  822 , and a portion of light can be transmitted through reference  822 , forming light  866 . After transmitting through reference  822 , light  866  can be directed towards selector  824 . 
     Selector  824  can be any optical component capable of moving or selecting the light beam to be directed towards detector  830 . In some examples, selector  824  can be coupled to controller  840 , and controller  840  can send a signal (not shown) to control the movement of selector  824 . In one time period, selector  824  can allow light  856  to be incident on the active area of detector  830 . Light  856  can comprise a set of photons, and detector  830  can measure the number of photons in light  856  (step  924  of process  900 ). Detector  830  can generate an electrical signal  858  indicative of the properties (or the number of photons) of light  856  (step  926  of process  900 ). Signal  858  can be sent to controller  840 , which can store and/or process the signal. In another time period, selector  824  can allow light  866  to be incident on the active area of detector  830 . Light  866  can also comprise a set of photons, and detector  830  can measure the number of photons in light  866  (step  928  of process  900 ). Detector  830  can generate an electrical signal  868  indicative of the properties (or the number of photons) of light  866  (step  930  of process  900 ). Signal  868  can be sent to controller  840 , which can store and/or process the measured signal. 
     Detector  830  can include single detector pixel or a detector array. In some examples, detector  830  can be any type of detector capable of detecting light in the SWIR. In some examples, detector  830  can be a HgCdTe, InSb, or InGaAs single detector or a FPA. In some examples, detector  830  can be a SWIR detector capable of operating in the extended wavelength range of up to 2.7 μm. 
     Controller  840  can receive both signal  858  and signal  868  at different times. Signal  858  can include the sample signal, and signal  868  can include the reference signal. In some examples, controller  840  can divide, subtract, or scale the sample signal by the reference signal to obtain a ratio. The ratio can be converted to absorbance by using Equation 1, and an algorithm can be applied to the absorbance spectrum to determine the concentration of the substance of interest in sample  820  (step  932  of process  900 ). In some examples, controller  840  can compare the reference absorbance to one or more absorbance values stored in a lookup table (LUT) or in memory to determine the concentration and type of one or more substances in sample  820 . In some examples, signal  858  can differ from signal  868  by the amount of drift from light source  802 , detector  830 , or both. Controller  840  can divide, subtract, or scale signal  858  by signal  868  to determine the amount of drift. Although Equation 2 and the above discussion are provided in the context of absorbance, examples of the disclosure can include, but are not limited to, any optical property, such as reflectivity, refractive index, density, concentration, scattering coefficient, and scattering anisotropy. 
     System  800  can include all of the advantages of system  600  while also accounting for variations in the absorbance of sample  820  with wavelength. Although the systems disclosed above illustrate one or more components, such as choppers, optics, mirrors, sample, light source, filters, and detector, one of ordinary skill in the art would appreciate that the system is not limited to only the components illustrated in the exemplary figures. Furthermore, one of ordinary skill in the art would appreciate that the location and arrangement of such components are not limited solely to the location and arrangement illustrated in the exemplary figures. 
     While an ideal layout or arrangement of the system would have all components shared between the light path traveling through the sample and the light path traveling the reference, such an arrangement might not be physically possible or feasible. Examples of the disclosure can include locating one or more components susceptible to drifting such that these components are common or shared among the two (or multiple) light paths, and locating components not susceptible to drifting (i.e., stable components) to be non-common or not shared among the two (or multiple light paths). For example, components susceptible to drifting can include any electronics or optoelectronic components. Additionally, components not susceptible to drifting can include optics. As illustrated in both system  600  of  FIG. 6  and system  800  of  FIG. 8 , the light source (e.g., light source  602  and light source  802 ) and the detector (e.g., detector  630  and detector  830 ) can be susceptible to drifting, and therefore can be shared between the two light paths (e.g., light  656  and light  666 ; light  856  and light  866 ). On the other hand, choppers (e.g., chopper  634 , chopper  636 , chopper  834 , and chopper  836 ) and optics (e.g., optics  616 , optics  816 , and optics  818 ) can be stable and not susceptible to drifting, and therefore can be individual to each light path. 
       FIG. 10  illustrates an exemplary plot of absorbance measurements used for determining the concentration and type of one or more substances according to examples of the disclosure. The absorbance measurement can comprise a plurality of cycles  1076 . Each cycle  1076  can include one or more dark phases  1070  and one or more measurement phases  1072 . Each dark phase  1070  can include one or more steps to measure the zero level, noise floor, stray light leakage, or a combination thereof. For example, the light source in the system can be off or deactivated such that emitted light is not incident on the sampling interface or reference. The detector can take a measurement to determine the amount of dark current and stray light leakage. In some examples, this measurement can be used to determine the zero level. The detector can send this measurement to the controller, and the controller can store the measurement and/or the relevant information in memory. The controller can use this information to determine the actual absorbance of the substance in the sample or reference, or can use this information to set the zero level. 
     Measurement phases  1072  can be interspersed in between the dark phases  1070 . Measurement phases  1072  can include measuring the absorbance spectrum of the sample during one time and measuring the absorbance spectrum of the reference during another time. In some examples, any optical property (e.g., reflectivity, refractive index, density, concentration, scattering coefficient, and scattering anisotropy) can be measured instead of, or in addition to, the absorbance. The controller can divide, subtract, or scale the absorbance spectrum of the sample by the absorbance spectrum of the reference. In some examples, the controller can compare the reference absorbance to one or more absorbance values stored in a LUT or memory to determine the concentration of the substance in the sample. The measurement can be repeated multiple times within each measurement phase  1072  to generate a plurality of sample points  1074 , and the average of the sample points  1074  can be used. In some examples, the controller can compile sample points  1074  from multiple cycles  1076  when determining the average signal value. In some examples, the duration of at least one measurement phase  1072  can be based on a pre-determined or fixed number of sample points  1074 . In some examples, the number of sample points  1074  within at least one measurement phase  1072  can be less than 10. In some examples, the number of sample points  1074  within at least one measurement phase  1072  can be less than 100. In some examples, the duration of at least one measurement phase  1072  can be based on the stability (e.g., time before drifting by more than 10%) of the reference. For example, if the reference remains chemically stable for 60 seconds, the duration of measurement phase  1072  can also be 60 seconds. In some examples, the duration of measurement phase  1072  can be based on the stability of the shared components (e.g., light source and detector). Once a measurement phase  1072  is complete, the controller can proceed to the next cycle  1076 . 
     By calibrating more frequently, both the zero drift and gain drift can be accounted for. Additionally, unlike the procedure illustrated in  FIG. 5 , the drift can be corrected at every cycle (or after a multiple number of cycles), which can prevent any significant deviation from the zero level. Furthermore, any fluctuations and/or variations can be compensated for prior to, during, or shortly after the signal begins to deviate. By compensating for the fluctuations, drift, and/or variations and re-zeroing the zero level early on, instead of after tens or hundreds of sample points  1074  are measured, the accuracy of the averaged signal value can be improved. In some examples, the number of sample points  1074  taken during measurement phase  1072  can be less than the number of sample points  574  taken during measurement phase  572  (illustrated in  FIG. 5 ). In some examples, measurement phase  1072  can be shorter than measurement phase  572 . 
     In some examples, each cycle can include three measurement “measurement states.”  FIG. 11  illustrates an exemplary plot of the absorbance measurements including three measurement states with equal measurement time distribution according examples of the disclosure. The absorbance measurements can include a plurality of cycles  1176 . Each cycle  1176  can include three measurement states: sample measurement state  1182 , reference measurement state  1184 , and dark measurement state  1186 . Sample measurement state  1182  can be configured to measure the absorbance (or any other optical property) of the sample (e.g., sample  620  illustrated in  FIG. 6  or sample  820  illustrated in  FIG. 8 ). Reference measurement state  1184  can be configured to measure the absorbance (or any other optical property) of the reference (e.g., filter  608  illustrated in  FIG. 6  or reference  822  illustrated in  FIG. 8 ). Dark measurement state  1186  can be configured to measure the dark current, stray light leakage, and/or noise. In some examples, the system can be configured to process, assess, and/or allocate the time distribution during dark measurement state  1186 . The system can be configured to repeat the sample measurement state  1182 , reference measurement state  1184 , and dark measurement state  1186 , where none of the measurement states is shared in time. The measurement states can be configured with a time duration t. In some examples, time duration t of each measurement state can be the same. One skilled in the art would appreciate that the same time duration can include tolerances that result in a 15% deviation. In this manner, the time allocated to sample measurement state  1182  can be 33% (or ⅓ rd ) of the time for cycle  1176 . Similarly, the time allocated to reference measurement state  1184  and dark measurement state  1186  can each be 33% (or ⅓ rd ) of time for cycle  1176 . 
     Although the cycle time can be equally distributed among each of the three measurement states, the signal value, noise levels, and SNR for one measurement state (or measurement type) can be different from another measurement state in the same cycle. Therefore, the measurement time distribution of the three measurement states may be optimal for one measurement state, but may not be optimal for the other measurement states in the cycle. Additionally, the signal value, noise levels, and SNR may differ with wavelength, surrounding environment, and/or measurement location of the substance in the sample. As a result, the optimal measurement time distribution can be different for different wavelengths and different locations in the sample. Additionally, configuring the measurements to include three measurement states with equal measurement time distributions can lead to long measurement times with unimportant information, erroneous measurement data, low SNR, or a combination thereof. 
       FIG. 12  illustrates an exemplary plot of absorbance measurements including three measurement states with unequal measurement time distribution according to examples of the disclosure. The absorbance measurements can include a plurality of cycles, such as cycle  1276 , cycle  1277 , and cycle  1278 . In some examples, cycle  1276  can be configured with the same time duration t 4  as cycle  1277 . Each cycle can include three measurement states: sample measurement state  1282 , reference measurement state  1284 , and dark measurement state  1286 . Sample measurement state  1282  can be configured to measure the absorbance of the sample for a time t 1 , reference measurement state  1284  can be configured to measure the absorbance of the reference for a time t 2 , and dark measurement state  1286  can be configured to measure the absorbance of the noise (e.g., dark current and stray light) for a time t 3 . In some examples, the sample signal can be weak or can have a low intensity (e.g., less than 20% of the intensity of the reference signal), such as illustrated in cycle  1276 . The system can allocate the time for sample measurement state  1282  in cycle  1276  to be greater than the time for the other measurement states. For example, the intensity of the sample signal can be 4.3% of the intensity of the reference signal, and time t 4  can be distributed with times t 1 , t 2 , and t 3  comprising 65%, 30%, and 5%, respectively. In some examples, time t 1  can be greater than or equal to 50% of the time for cycle  1276 . 
     In some examples, the sample signal can be strong or can have a high intensity relative to the reference signal, such as illustrated in cycle  1277 . Sample measurement state  1282  can be configured with time t 11 , reference measurement state  1284  can be configured with time t 12 , and dark measurement state  1286  can be configured with a time t 13 . The system can allocate the time for reference measurement state  1284  in cycle  1277  to be greater than the time for the other measurement states. For example, the intensity of the sample signal can be 85% of the intensity of the reference signal, and time t 4  can be distributed with times t 11 , t 12 , and t 13  comprising 20%, 60%, and 5%, respectively. In some examples, time t 12  can be greater than or equal to 50% of the time for cycle  1277 . 
     As illustrated in the figure, the measurement time per cycle can be distributed based on the signal values and noise levels, and this distribution can change dynamically. For example, if the noise levels are low, the system can be configured to spend less time in the dark measurement state. In some examples, each cycle time can be different and/or can be dynamically changed. In some examples, the measurement time distribution can be based on the operating wavelength. For example, the operating wavelengths can include one or more wavelengths of lower importance (e.g., due to a lower probability of absorbance by the substance of interest), and therefore, the system can be configured to spend less time measuring the one or more wavelengths of lower importance. In this manner, the overall measurement time can be reduced, long measurement times with unimportant information can be avoided, and measurement accuracy can be improved. 
     In some examples, the measurement time distribution can be based on a pre-determined or targeted SNR. For example, if the signal values are weak, the system can be configured to spend more time in the sample measurement state or the reference measurement state, so that an accurate signal value can be measured and unimportant measurement information can be avoided. In some examples, the time spent measuring the noise can be dynamically changed based on the SNR, and the remaining time can be distributed such that half of the remaining time is spent measuring the sample and the other half of the remaining time is spent measuring the reference. 
     In some examples, the measurement time distribution can be based on the measured location in the sample or the associated detector pixel. Each detector pixel can be associated with a location or a corresponding optical path within the sample. In some examples, different optical paths can be incident on different locations in the sample. In some examples, the sample signal value of the detector pixels can be different. Different sample signal values can be due to any number of sources, such as differing absorbance at one location in the sample from another, drift from the system components (e.g., light source, waveguides, modulators, optics, detectors), or changes in operating conditions (e.g., operating temperature of the components or environmental changes). Therefore, the system can be configured with at least two detector pixels with different measurement time distribution values. 
     Because the optimal measurement time distribution can vary based on signal values, noise levels, wavelength, and measurement location in the sample, the system can be configured to dynamically change the actual measurement time distribution, which can lead to reduced overall measurement time without compromising measurement accuracy with improved SNR. In some examples, the system can include a LUT that can include the actual measurement time distribution values and associations to the operating wavelength and detector pixel. In some examples, a LUT can store various configurations from which a configuration can be selected based on calibration-phase measurements. The system can be optimized and tuned based on the operation conditions for the measurement and/or application of the system. 
       FIG. 13  illustrates an exemplary process flow for dynamically changing the measurement time distribution according to examples of the disclosure. Process  1300  can include measuring the signal value for a detector pixel, noise levels, or both at a given wavelength (step  1302 ). In some examples, the measurement can be a coarse measurement performed for a pre-determined time. The measurement can be repeated for other detector pixels included in the system (step  1304  and step  1306 ). Based on the measured signal value and noise levels, a controller or processor included in the system can determine the times and percentages for each of the plurality of measurement states using the LUT (step  1308 ). In some examples, the LUT can include targeted or pre-determined SNR, which can be used for determining the times and percentages for the measurement states. Using the determined times and percentages, the system can dynamically change the measurement time distribution (step  1310 ). In some examples, the system can include logic that provides feedback regarding the overall measurement time, measurement accuracy, and actual SNR, and based on any deviation from the targeted values, the system can rewrite or update the LUT. The measurement can be repeated for other wavelengths of interest (step  1312  and step  1314 ). When all detector pixels of interest and wavelengths of interest are measured, the system can repeat the measurements (step  1316 ). 
     In some examples, different measurement states can be measured concurrently.  FIG. 14  illustrates a portion of an exemplary system for measuring the concentration and type of one or more substances in a sample and capable of measuring different measurement states concurrently according to examples of the disclosure. System  1400  can include several components, such as light source  1402 , controller  1440 , filter  1406 , filter  1407 , beamsplitter  1410 , mirror  1412 , chopper  1434 , chopper  1436 , optics  1416 , optics  1417 , and optics  1418 , that have one or more of the properties as discussed above in the context of system  100  (illustrated in  FIG. 1 ), system  300  (illustrated in  FIG. 3 ), system  600  (illustrated in  FIG. 6 ), and system  800  (illustrated in  FIG. 8 ). System  1400  can further include a plurality of detectors, such as detector  1430 , detector  1431 , and detector  1432 . Detector  1430  can be configured to measure the reference signal during the reference measurement state (e.g., reference measurement state  1184  or reference measurement state  1284 ) and can generate signal  1468  indicative of the properties of light  1466  through reference  1422 . Detector  1431  can be configured to measure noise (e.g., dark current) during the dark measurement state (e.g., dark measurement state  1186  or dark measurement state  1286 ) and can generate signal  1478  indicative of the properties of dark current  1476 . Detector  1432  can be configured to measure the sample signal during the sample measurement state (e.g., sample measurement state  1182  or sample measurement state  1282 ) and can generate signal  1458  indicative of the properties of light  1456  through sample  1420 . In this manner, the plurality of detectors can be used to measure the sample signal, reference signal, and noise signal concurrently. During one cycle, the system can generate a plurality of reference measurements values, and at least one detector pixel can be measuring a signal (e.g., sample signal, reference signal, or noise signal) at all times. 
       FIG. 15  illustrates an exemplary plot of measurement states for a system capable of measuring different measurement states concurrently according to examples of the disclosure. The system can include three detectors: detector  1 , detector  2 , and detector  3 , and can be configured with three measurement states: sample measurement state  1582 , reference measurement state  1584 , and dark measurement state  1586 . During time t 1 , detector  1  can be configured to measure the noise signal in dark measurement state  1586 . At the same time, detector  2  can be configured to measure the reference signal in reference measurement state  1584 , and detector  3  can be configured to measure the sample signal in sample measurement state  1582 . At another time t 2 , the measurement states for each detector can change. Detector  1  can be configured to measure the sample signal in sample measurement state  1582 , detector  2  can be configured to measure noise signal in dark measurement state  1586 , and detector  3  can be configured to measure the reference signal in reference measurement state  1584 . As illustrated in the figures, each detector (e.g., detector  1 , detector  2 , and detector  3 ) can measure one of the three signal values at all times. That is, the measurement states can be measured concurrently across different detectors, and consecutively at each detector. In some examples, the system can include a tunable mirror configured to direct or redirect the light to different detectors. In some examples, the tunable mirror can include a plurality of data light processing (DLP) mirrors. In some examples, light can be redirected using one or more beamsplitters. 
     In some examples, the system can include a plurality of microelectromechanical systems (MEMS) components.  FIG. 16  illustrates a cross-sectional view of a portion of an exemplary system including a plurality of MEMS components and capable of measuring different measurement states concurrently according to examples of the disclosure. System  1600  can include a plurality of detector pixels, such as detector pixel  1633  and detector pixel  1635 , included in detector array  1630  and a plurality of MEMS components, such as MEMS component  1623  and MEMS component  1625 . Each detector pixel can be coupled to a MEMS component. For example, detector pixel  1633  can be coupled to MEMS component  1623 , and detector pixel  1635  can be coupled to MEMS component  1625 . Light  1656  can be light reflected off the sample, and MEMS component  1623  can be angled or oriented such that light  1656  is incident on detector pixel  1633 . Additionally, light  1666 , which can be light reflected off the reference, can be blocked by MEMS component  1623 . MEMS component  1625  can be angled or oriented such that light  1666  is incident on detector pixel  1637 , and light  1656  (i.e., light reflected off the sample) can be blocked and prevented from reaching detector pixel  1635 . In some examples, the MEMS component can change orientations during different times to measure light from the sample at one time and then measure light from the reference at another time. In some examples, one or more adjacent detector pixels or adjacent sets of detector pixels in the detector array  1630  can have MEMS components with different orientations. 
     In some examples, the noise levels can lead to fluctuations that can be decorrelated in time.  FIG. 17  illustrates an exemplary plot of absorbance measurements with noise fluctuations according to examples of the disclosure. The measurement can include a plurality of sample points, such as sample point  1774  and sample point  1775 . Sample point  1774  can be included in sample measurement state  1782 , and sample point  1775  can be included in reference measurement state  1784 . Noise included in sample point  1774  can be different from noise included in sample point  1775 , which can lead to time decorrelated noise in the sample signal and the reference signal. Decorrelated noise in the sample signal and the reference signal can lead to erroneous measurements. 
     Noise common to both the sample signal and reference signal can be referred to as common mode noise. In some examples, common mode noise can originate from the light sources included in the system, as well as other components in the system that can be used to route, attenuate, and/or shape the light beam emitted from the light sources. The light sources can include multiple types of noise, such as long-term drift and short-term noise. The decorrelated noise referred to earlier can be short-term noise, which can be high frequency noise. 
       FIG. 18  illustrates an exemplary system and  FIG. 19  illustrates an exemplary process flow for measuring the concentration and type of one or more substances in a sample including a high-frequency detector according to examples of the disclosure. System  1800  can include several components, such as light source  1802 , controller  1840 , filter  1806 , beamsplitter  1810 , mirror  1812 , chopper  1834 , chopper  1836 , optics  1816 , optics  1818 , detector  1830 , and detector  1832 , that have one or more of the properties discussed above in the context of system  100  (illustrated in  FIG. 1 ), system  300  (illustrated in  FIG. 3 ), system  600  (illustrated in  FIG. 5 ), system  800  (illustrated in  FIG. 8 ), and system  1400  (illustrated in  FIG. 14 ). System  1800  can further include beamsplitter  1811  and detector  1833 . Beamsplitter  1811  can be an optical component configured to split incident light into multiple light beams. One or more of these hardware components can operate under the software control of controller  1840  to change the measurement cycles and states described herein. One or more of these hardware components and the controller can be referred to herein as logic. 
     Light source  1802  can be directed towards filter  1806 , and signal  1804  can cause light source  1802  to emit light  1850  (step  1902  of process  1900 ). Light  1850  can comprise multiple wavelengths, can be transmitted through filter  1806 , and can form light  1852  comprising one or more discrete wavelengths (step  1904  of process  1900 ). Light  1852  can be directed towards beamsplitter  1811 , and beamsplitter  1811  can split light  1852  into two light paths: light  1853  and light  1855  (step  1906  of process  1900 ). 
     Light  1853  can be directed towards beamsplitter  1810 , and beamsplitter  1811  can split light  1853  into two light beams: light  1854  and light  1864  (step  1908  of process  1900 ). Light  1854  can be transmitted through chopper  1834  and optics  1816 . Light  1854  can be incident on sample  1820  and one or more substances in sample  1820  can absorb at least a portion of light  1854 . Light that is transmitted through or reflects off sample  1820  can be referred to as light  1856 . Detector  1832  can detect light  1856  and can generate signal  1858  indicative of the properties of light  1856  (step  1910  of process  1900 ). Additionally, light  1864  can be directed or redirected by mirror  1812  and can be transmitted through chopper  1836  and optics  1818 . Light  1864  can be incident on reference  1822  and a portion can be transmitted through or reflect off reference  1822  as light  1866 . Detector  1830  can detect light  1866  and can generate signal  1868  indicative of the properties of light  1866  (step  1912  of process  1900 ). In some examples, detector  1830  and detector  1832  can measure the reference signal and the sample signal, respectively, at the same time or concurrently. In some examples, detector  1830  and detector  1832  can measure the reference signal and sample signal at different times. In some examples, system  1800  can be configured such that a single detector measures both the sample signal and the reference signal. 
     Detector  1833  can be configured to measure light  1853  and can generate signal  1888  indicative of the properties of light  1855  (step  1914  of process  1900 ). In some examples, detector  1833  can be a high-frequency detector that can be AC coupled to measure high-frequency noise. Controller  1840  can receive signal  1888  and can calculate the common mode noise for each of the signals (e.g., sample signal and reference signal) in time (step  1916  of process  1900 ). Based on the calculated common mode noise, controller  1840  can generate one or more normalizing factors for each of the signals (step  1918  of process  1900 ). In some examples, the normalizing factors can be generated based on matching the noise intensity of signal  1888  with signal  1858  and/or signal  1868 . In some examples, matching the noise intensity of signal  1888  with signal  1858  and/or signal  1868  can include reducing differences in intensity values of the signals. The sample signal and reference signal can be corrected or scaled based on the normalizing factors or a scaling scheme (step  1920  of process  1900 ). In some examples, the normalizing factors or scaling scheme can be based on a standard deviation. The corrected or scaled signals are then used to determine the concentration and type of the one or more substances in the sample (step  1922  of process  1900 ). 
     By detecting the high-frequency noise included in light  1852  with detector  1833 , the sample signal noise can be reduced and SNR can be improved. In some examples, detector  1833  can be configured with a different gain than detector  1830 , detector  1832 , or both. In some examples, beamsplitter  1811  can split light  1852  such that light  1853  and light  1855  have different intensities. 
     One or more of the functions described above can be performed, for example, by firmware stored in memory and executed by a processor or controller. The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding a signal) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such as a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks and the like. In the context of this document, a “transport medium” can be any medium that can communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation medium. 
     As discussed above, examples of the disclosure can include measuring a concentration of a substance in a sample at a sampling interface. In some examples, the sample can include at a least a portion of a user, where additional information can be used to improve the delivery of measured information, analysis, or any other content that may be of interest to the users. In some examples, the measured information, analysis, or other content may include personal information such as information that can uniquely identify the user (e.g., can be used to contact or locate the user). In some examples, personal information can include geographic information, demographic information, telephone numbers, email addresses, mailing addresses, home addresses, or other identifying information. Use of such personal information can be used to the benefit of the user. For example, the personal information can be used to deliver the measured information, analysis, or other content to the user. Use of personal information can include, but is not limited to, enabling timely and controlled delivery of the measured information. 
     The disclosure also contemplates that an entity that may be measuring, collecting, analyzing, disclosing, transferring, and/or storing the personal information will comply with well-established privacy policies and/or practices. These privacy policies and/or practices can be generally recognized as meeting (or exceeding) industry or governmental requirements for private and secure personal information and should be implemented and consistently used. For example, personal information should be collected for legitimate and reasonable purposes (e.g., to deliver the measured information to the user) and should not be shared (e.g., sold) outside of those purposes. Furthermore, collected personal information should occur only after receiving the informed consent of the user(s). To adhere to privacy policies and/or practices, entities should take any steps necessary for safeguarding and securing outside access to the personal information. In some examples, entities can subject themselves to third party evaluation(s) to certify that the entities are adhering to the well-established, generally recognized privacy policies and/or practices. 
     In some examples, the user(s) can selectively block or restrict access to and/or use of the personal information. The measurement system can include one or more hardware components and/or one or more software applications to allow the user(s) to selective block or restrict access to and/or use of the personal information. For example, the measuring system can be configured to allow users to “opt in” or “opt out” of advertisement delivery services when collecting personal information during registration. In some examples, a user can select which information (e.g., geographical location) to provide and which information (e.g., phone number) to exclude. 
     Although examples of the disclosure can include systems and method for measuring a concentration of a substance with the use of the user&#39;s personal information, examples of the disclosure can also be capable of one or more functionalities and operation without the user&#39;s personal information. Lack of all or a portion of the personal information may not render the systems and methods inoperable. In some examples, content can be selected and/or delivered to the user based on non-user specific personal (e.g., publicly available) information. 
     A system for determining a concentration and type of substance in a sample at a sampling interface is disclosed. In some examples, the system comprises: one or more detector pixels including a first detector pixel, wherein the one or more detector pixels are configured to operate in a plurality of cycles, each cycle including a plurality of measurement states, the plurality of measurement states including: a first measurement state configured to measure one or more optical properties of the substance during a first time period, a second measurement state configured to measure one or more optical properties of a reference during a second time period, and a third measurement state configured to measure noise during a third time period; and logic capable of dynamically changing one or more aspects of the plurality of cycles, wherein the one or more aspects include a duration of a respective time period. Additionally or alternatively, in some examples, the one or more detector pixels further includes a second detector pixel, the first detector pixel configured into the first measurement state, and the second detector pixel configured into the second measurement state at a same time. Additionally or alternatively, in some examples, the one or more detector pixels further includes a third detector pixel, the third detector pixel configured into the third measurement state at the same time. Additionally or alternatively, in some examples, the system further comprises: a plurality of mirrors, each mirror associated with a detector pixel included in the plurality of detector pixels and configured with an orientation such that a first light is reflected or blocked, and further configured to provide the associated detector pixel access to a second light, different from the first light. Additionally or alternatively, in some examples, the system further comprises: a detector pixel configured into the first measurement state, second measurement state, and third measurement state, wherein the first, second, and third measurement states are consecutive and determination of the concentration and type of substance is based on the first, second, and third measurement states. 
     A method of determining a concentration and type of substance in a sample at a sampling interface during a plurality of cycles, the plurality of cycles including a first cycle and a second cycle, is disclosed. In some examples, the method comprises: during the first cycle: measuring one or more optical properties of the substance during a first time period; measuring one or more optical properties of a reference z: a second time period; measuring noise during a third time period; and dynamically changing a duration of at least one of the first time period, second time period, and third time period during the second cycle. Additionally or alternatively, in some examples, the duration of at least two of the first time period, second time period, and third time period within the first cycle are different. Additionally or alternatively, in some examples, measuring one or more optical properties of the substance includes obtaining a first signal value and measuring one or more optical properties of the reference includes obtaining a second signal value, the method further comprising: comparing the first signal value to the second signal value; and setting the first time period greater than the second time period when the first signal value is less than the second signal value. Additionally or alternatively, in some examples, the first time period is set greater than 50% of a time period for the first cycle. Additionally or alternatively, in some examples, measuring one or more optical properties of the substance includes obtaining a first signal value and measuring one or more optical properties of the reference includes obtaining a second signal value, the method further comprising: comparing the first signal value to the second signal value; and setting the first time period less than the second time period when the first signal value is greater than the second signal value. Additionally or alternatively, in some examples, the second time period is set greater than 50% of a time period for the first cycle. Additionally or alternatively, in some examples, the first cycle includes a first operating wavelength and the second cycle includes a second operating wavelength, the first operating wavelength different from the second operating wavelength, and the first cycle having at least one of the first time period, second time period, and third time period different from the second cycle. Additionally or alternatively, in some examples, the first time period is the same as the second time period within the first cycle. Additionally or alternatively, in some examples, each cycle included in the plurality of cycles is associated with a detector pixel included in a plurality of detector pixels, the method further comprising: retrieving one or more entries from a look-up table, the one or more entries including an association between the first time period, second time period, and third time period and at least one of an operating wavelength and the detector pixel; and setting at least one of the first time period, second time period, and third time period based on the one or more entries. Additionally or alternatively, in some examples, at least one of the first time period, second time period, and third time period are different for at least two detector pixels included in the plurality of detector pixels. Additionally or alternatively, in some examples, the method further comprises: determining a property associated with the operating wavelength and the detector pixel, the property being at least one of a measurement time, measurement accuracy, and signal-to-noise ratio (SNR); comparing the property to the one or more entries from the look-up table; and updating the one or more entries from the look-up table based on the comparison. Additionally or alternatively, in some examples, the plurality of cycles further includes a third cycle, and further wherein the first time period for the first cycle is same as the second time period for the second cycle and the third time period for the third cycle. 
     A system for determining a concentration and type of substance in sample at a sampling interface is disclosed. In some examples, the system comprises: a light source configured to emit a first light and a second light, the first light incident on the sampling interface and the second light incident on a reference, wherein the first light and the second light include a noise component; a first detector configured to measure incident light, the incident light being at least one of the first light and the second light, and configured to generate a first signal indicative of the incident light; a second detector configured to measure the noise component included in a range of frequencies, and configured to generate a second signal indicative of the measured noise component; and logic capable of scaling the second signal and compensating the first signal using the scaled second signal. Additionally or alternatively, in some examples, a gain of the first detector is different from a gain of the second detector. Additionally or alternatively, in some examples, an intensity of the first light is different from an intensity of the second light. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.

Metadata:
Filing Date: 20160829
Publication Date: 20200623
Grant Date: 20200623
Priority Date: 20150918
Inventors: CHEN, ROBERT
RIDDER, TRENT D.
KANGAS, Miikka M.
SIMON, DAVID I.
TERREL, MATTHEW A.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01N2201/12776", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/12723", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/124", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/274", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01N2201/12776", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/12723", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/31", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01N2201/12723", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/12776", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/274", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01N2201/124", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/274", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01N2201/124", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/31", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01N2201/124", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/12776", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/12723", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/274", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 56889226