Apparatus and method for evanescent waveguide sensing
By designing waveguide spectroscopy on a silicon substrate and using optical elements to couple light into and out of the waveguide outside the container, combined with a polarizer and a ridge waveguide, the problems of insufficient sensitivity and complex optical coupling in the prior art are solved, and efficient spectral and concentration measurements are realized in a sealed container.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2017-10-19
- Publication Date
- 2026-03-24
AI Technical Summary
Existing technologies for measuring the concentration of chemical or biological complexes in solutions suffer from problems such as insufficient sensitivity, difficulty in correcting instrument deviations, complex optical coupling, particle precipitation affecting spectral measurements, and the inability to perform optical coupling within a closed container.
The waveguide spectroscopy method on silicon substrates is employed. A waveguide core with a permeable window is placed adjacent to the container. Optical elements couple light into and out of the waveguide from outside the container. A polarizer is used to adjust the light polarization. By combining a ridge waveguide and a multi-segment polarizer, the coupling and measurement of light on opposite sides can be achieved.
It achieves highly sensitive spectral measurements in a closed container, reduces the influence of particle precipitation, simplifies the optical coupling process, and enables accurate measurement of solution component concentrations under background-free spectral measurement conditions.
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Figure CN121720933A_ABST
Abstract
Description
[0001] Cross-reference to related applications This application claims priority and benefits to U.S. Provisional Application No. 62 / 409899, filed October 19, 2016, the disclosure of which is incorporated herein by reference in its entirety. Technical Field
[0002] The topics disclosed herein generally relate to devices and methods for evanescent waveguide sensing. Background Technology
[0003] Attenuated total reflectance spectroscopy is a technique used for the identification, measurement, and concentration of chemical / biological complexes. Several methods have been reported. In one reported method, by reducing the thickness of the ATR crystal until it becomes less than a few wavelengths in thickness (also known as a planar waveguide), the sensitivity of the technique is improved due to a significant increase in the number of reflections at the interface between the sample and the waveguide. Improvements of up to 10,000 have been reported.
[0004] It is often of interest to measure the spectra of chemical or biological complexes in infrared regions where different absorption lines exist, in order to determine, for example, the concentration of the complex in solution. However, in many cases, the absorption bands of the complex of interest are very weak. For example, the absorption coefficient of a 10 mMol complex concentration can be only 0.0002 to 0.0035 in the 2 to 2.4 μm wavelength band. Therefore, it is desirable to maximize the effect of the absorption coefficient of the solution on the waveguide properties. Furthermore, careful correction for instrumental bias is required to accurately measure the minute changes in waveguide transmittance associated with these absorption bands.
[0005] The report describes a method for coupling light into a waveguide via a substrate. However, a complex combination of two gratings and prisms is required to achieve broadband coupling.
[0006] Another reported technique uses a single prism located on the same side of the substrate as a waveguide to couple light into the waveguide. However, in this technique, because light is coupled into the waveguide from the same side as the sample, it cannot be easily coupled into a sealed container.
[0007] Waveguide spectroscopy, or attenuated total internal reflection spectroscopy, has been previously discussed as a method for performing spectroscopic measurements of solutions without requiring light to be transmitted through the solution. In the techniques reported in waveguide spectroscopy, light does not transmit through the solution. Instead, the solution is adjacent to the waveguide core and interacts only with the waveguide within the evanescent field of the waveguide mode in the solution, typically only on the order of wavelength. Therefore, the influence of scattering particles within the solution is reduced. Only particles attached to or nearly attached to the waveguide core can have some influence on the light propagating through the waveguide core.
[0008] However, particles, especially cells, can have a tendency to deposit onto the waveguide core over time or attach themselves to it. Although these particles only interact with the core to the extent that they are within the approximate wavelength of their location on the core surface, they can still affect the spectrum of light transmitted through the core by scattering light outside the core. Therefore, conventional waveguide spectroscopy can still be affected by particles in solution.
[0009] Generally, waveguide cores have a thickness that supports multiple TE and TM modes. Cores can also be specifically designed or configured to allow only one TE and one TM mode to be transmitted.
[0010] Typically, the background spectrum of the solution is measured immediately before the sample solution is measured, without any dissolved complexes. This assumes, among other things, that the spectral intensities of the light source, detector, and instrument response remain unchanged during the interval between the sample solution and background measurements, allowing the background spectrum to be used to accurately normalize the sample spectrum. However, in some cases, it is not possible to measure the background spectrum immediately before the sample measurement. For example, when the solution must be monitored over several weeks without the opportunity to periodically measure the background spectrum. In such cases, if any instrumental deviations occur over time, such as changes in the spectral output of the light source, the background spectrum measured at the start of the sample measurement may not be suitable for accurately normalizing the sample spectrum. Summary of the Invention
[0011] This invention addresses the need to measure the concentrations of various components in a solution, which may also contain particles, including but not limited to light-scattering particles. For example, in bioreactors, it is often necessary to monitor the concentrations of glucose, lactic acid, glutamate, ammonia, and other biochemicals as cells grow within the bioreactor. Determining the concentrations of these biochemicals by performing transmission light spectroscopy measurements on the bioreactor solution is impractical because the cells within the solution scatter the light as it propagates through the solution. This not only significantly reduces the amount of light transmitted through a given solution thickness to an undetectable level but also alters the spectral dependence of the transmitted light.
[0012] This invention also addresses the need for simple components for coupling light into and out of a waveguide on a substrate, allowing light to pass through the substrate from opposite sides of the waveguide. When the waveguide is located inside a sealed container, while the light source and detector are located outside the container, there is a need for waveguide sensors. Components for coupling light into and out of the waveguide may include, for example, optical elements configured to couple light into and out of the waveguide. Optical elements may include prisms, gratings, or other similar optical elements known to those skilled in the art. One aspect of the invention provides apparatus and methods for waveguide spectroscopy using a silicon substrate, wherein the light source and detector are located on opposite sides of the substrate of the sample.
[0013] In one embodiment, an apparatus for waveguide spectroscopy of a sample within a container is provided. The apparatus includes: a substrate having a window that is transparent at a wavelength of interest and coupled to the container containing the sample; a waveguide core of a material transparent at the wavelength of interest located on the inner surface of the transparent window adjacent to the sample, the waveguide core having a refractive index greater than that of the sample; optical elements configured to couple light into and out of the waveguide; a light source located outside the container; and one or more detectors located outside the container.
[0014] In another embodiment, a ridge waveguide is provided for performing waveguide spectroscopy on a sample containing particles. The ridge waveguide includes two or more ridges with a gap between the tops of the ridges, such that the gap is approximately one wavelength or smaller than one wavelength and smaller than the minimum size of the particles.
[0015] The waveguide may include a cladding, and the waveguide core has a refractive index greater than that of the cladding deposited between the core and the substrate. In some other embodiments, the waveguide may include a cladding, and the cladding has a refractive index less than that of the substrate, and the cladding has a thickness of three or more wavelengths. In still other embodiments, the waveguide core may have a refractive index greater than that of the substrate.
[0016] The waveguide core may be a thin-film waveguide core. In some embodiments, the waveguide core may have a thickness configured to allow transmission of a single TE-polarized waveguide mode. In some other embodiments, the waveguide core may have a thickness configured to allow transmission of both a single TE-polarized waveguide mode and a single TM-polarized mode. The waveguide core and cladding layer in the waveguide may have a thickness configured to support single TE and TM modes or configured to be greater than a predetermined value for the propagation mode.
[0017] Waveguide cores can be made from Si3N4, Al2O3, Ta2O5, Si x O y N 1-x-y Waveguides are made from materials selected from the group consisting of Si, Ge, diamond, ZnS, and ZnSe. Waveguides can also have materials from SiO2, MgF2, CaF2, and Si... x O y N 1-x-y The cladding is made of materials selected from the group consisting of Si, glass, fused silica, Al2O3, ZnS, ZnSe, diamond, KBr, BaF2, and CaF2.
[0018] In some embodiments, the device may include means located outside the container and configured to perform spectral measurements. The means may include at least one of a filter and a spectrometer.
[0019] In yet another embodiment, a method is provided for measuring waveguide spectra using a system comprising polarized light, including a waveguide, a light source, a polarizer, and a detector in contact with a sample supporting both TE and TM waveguide modes. In some embodiments, the polarizer may be rotated at a specific frequency to rotate the polarization of the transmitted light.
[0020] Polarizers may include multi-segment polarizers that rotate at a specific frequency, wherein adjacent polarizer segments are oriented perpendicularly to each other, and half of the segments are oriented to pass light through a TE waveguide mode and the other half are oriented to pass light through a TM waveguide mode.
[0021] In some embodiments, the polarizer does not rotate and is fixed in orientation to light passing through it at a 45° angle to the orientation of the excited TE or TM waveguide mode. In some embodiments, the polarizer does not rotate but is fixed in orientation at a 45° angle relative to the waveguide. Attached Figure Description
[0022] Figure 1 An example of a container having a window at a location with a waveguide on the inner surface of the container according to an embodiment of the present disclosure, and an example of a spectroscopic optical device located outside the container.
[0023] Figure 2 A conventional device is shown in which light from a broadband light source is focused from a prism Pr onto a grating G1 on the top surface of a substrate S, and then onto a second grating G2 on the bottom surface of the substrate S, so as to emit light into a waveguide extending along the bottom surface of the substrate S.
[0024] Figure 3 A conventional device is shown in which light from a broadband light source is focused from a prism Pr onto a waveguide on the same side of a substrate.
[0025] Figure 4 An embodiment of this disclosure is shown, in which a waveguide with a core (e.g., a SiN core) and a cladding (e.g., a SiO2 cladding) is deposited on a Si substrate. The cladding thickness is typically several wavelengths to ensure that light entering the core does not couple back into the substrate too quickly. The substrate is substantially transparent below its bandgap (i.e., for wavelengths >~1 μm). At a wavelength of 2 μm, the refractive index of water is 1.438, that of Si3N4 is 1.924, and that of SiO2 is 1.326. A planar waveguide mode is present in the film stack; this planar waveguide mode is a transversely polarized (TE) mode and has a mode index of 1.4806. At this wavelength, the refractive index of Si is 3.449. At this wavelength, a prism made of SF6 glass has a refractive index of 1.75. The angle of incidence at this wavelength is approximately 57.8°. The beam of light will vanishably couple energy into the waveguide. For those with , The SF6 prism has an incident angle of approximately 25.4° within the silicon. The critical angle between the silicon substrate and the water is 24.6°. Therefore, total internal reflection occurs within the silicon substrate, resulting in no light transmission into the water.
[0026] Figure 5 An embodiment of this disclosure is shown, in which a grating coupler is used instead of a prism. The diffraction grating is located in the core / cladding region of the waveguide. For vertical incidence ( ), n mode =1.4806, n prism =1.75 and The grating period is 1.35 μm, so the same grating period will be selected for externally coupling waveguide light.
[0027] Figure 6 It shows something similar to Figure 4 The embodiments of this disclosure include a second prism for coupling light leaving the waveguide to the detector.
[0028] Figure 7 It shows something similar to Figure 5 The embodiments of this disclosure include a second prism for coupling light leaving the waveguide to the detector.
[0029] Figure 8 A prism, located on the opposite side of the substrate to the waveguide according to an embodiment of the present disclosure, is used to couple light into the waveguide. The angle of incident light within the prism is... And in the air is .
[0030] Figure 9 An embodiment of this disclosure is shown, in which a ridged waveguide, including a plurality of ridges, is arranged on top of a substrate. As... Figure 9 As shown, the waveguide can be designed such that the top surface of each ridge is slightly wider than the rest of the ridge. The gap between the ridges on the top surface is narrower than the size of the particle. For example, if the particles are primarily cardiomyocytes in a bioreactor solution, having an elongated shape typically 100 μm long and 10 μm to 25 μm wide, the gap between the ridges on the top surface could be only 5 μm wide, thus preventing cells from entering the region between the ridges (where a strong electric field exists) while still allowing fluid in the bioreactor to fill the space between the ridges and interact with the field from the waveguide mode.
[0031] Figure 10 A waveguide spectroscopy system according to an embodiment of the present disclosure is shown, which uses a rotating polarizer as a component to adjust the intensity of light transmitted through the waveguide.
[0032] Figure 11(a) shows a plate polarizer or wire grid polarizer attached to a rotating bracket according to an embodiment of the present disclosure.
[0033] Figure 11 (b) illustrates a multi-zone rotating support according to an embodiment of the present disclosure. Each zone contains a plate polarizer or a wire grid polarizer such that the polarization directions in adjacent zones are perpendicular.
[0034] Figure 12 A waveguide spectroscopy system for monitoring the intensity of light transmitted through a waveguide using a fixed polarizer and a polarization beam splitter, according to an embodiment of the present disclosure, is shown.
[0035] Figure 13 The graph shows the imaginary part of the modulus index of a 100M glucose solution in contact with a Si3N4 waveguide core deposited on a fused silica substrate for TE and TM waveguide modes.
[0036] Figure 14 The graph shows the imaginary part of the mode index (Im(K)) of a 100M glucose solution on a 550nm Si3N4 waveguide core deposited on a fused silica substrate for TEO and TMO waveguide modes.
[0037] Figure 15 The graph shows the spectral transmittance and the difference in spectral transmittance for both TE0 and TM0 modes in a 1cm waveguide. Detailed Implementation
[0038] This disclosure describes a substrate on which a waveguide core and cladding film are deposited, which are transparent at a wavelength of interest. The refractive index of the core may be greater than that of the substrate and / or the cladding. If the refractive index of the substrate is greater than that of the core, the cladding may be several wavelengths thick to partially isolate the core from the substrate and reduce light leakage from the core waveguide mode into the substrate. If the refractive index of the substrate is less than that of the core, there is no need for a cladding layer, as the substrate itself acts as the cladding.
[0039] Light passing through a substrate can be coupled into a waveguide using a prism, a diffraction grating, or a combination of both. The prism can be located on the outer surface of the substrate or on a window outside the container. In some embodiments, the grating can be located inside the waveguide or adjacent to a waveguide inside the container. In some embodiments, the waveguide can be located at the waveguide-substrate interface.
[0040] For a light beam incident from the back side of a substrate (e.g., a silicon substrate) to excite a waveguide mode in the core thin film, the component of the wave vector of the incident light beam must be equal to the component of the waveguide mode's wave vector. For example, as Figure 4As shown, the prism can be configured to achieve this wave vector matching. If the prism has n prism The refractive index, and the angle of incidence of the beam inside the prism is The necessary requirements for matching wave vector components are shown in equation (1) or equation (2) as follows: Equation (1); and Equation (2) The mode index n of a waveguide mode mode The calculation can be performed using equations known to those skilled in the art. Commercially available prisms that are transmissive in the infrared region can be used. If the coupling prism angle is... For example, Figure 8 As shown, the angle of incidence in the air Provided by equation (3): Equation (3) The incident angle of the light beam within the silicon substrate is provided by equation (4): Equation (4) The critical angle between the silicon substrate and water is determined by equation (5): Equation (5) Figure 5 Another embodiment of this disclosure is shown, in which the prism is replaced by a diffraction grating located in the core / cladding region of the waveguide. The grating replaces the prism. The angle of incidence for coupling light into the waveguide can be adjusted by adjusting the period p of the grating. The coupling efficiency can be adjusted by adjusting the depth of the grating. By chirping the grating (slightly altering the period of the grating from one end to the other), the grating can be configured to effectively couple light over a wider range of angles of incidence and / or wavelengths than that of conventional gratings.
[0041] The diffraction grating couples the light into the waveguide by adding or subtracting an integer multiple of the grating vector from the component of the incident light wave vector in the waveguide plane, and when the sum of the two equals the waveguide mode wave vector. Specifically, the coupling equation is shown in equation (6): Equation (6) Where m is an integer and p is the period of the grating. In some embodiments, m=1 may be selected.
[0042] In this disclosure, coupling prisms from a variety of sources, including Thorlabs, Edmund Scientific, and Karl Lambrecht, Inc., can be used. Broadband light sources available from a variety of sources, including Thorlabs, Newport Corp., and Edmund Scientific, can be used. Wafer substrates available from a variety of sources, including University Wafer and WRS Materials, can be used. Thin film coatings available from a variety of sources, including Hionix, Inc., and Lionix BV, can be used. Spectrometers available from a variety of sources, including Spectral Products, Newport, and Ocean Optics, can be used. Detectors available from a variety of sources, including Thorlabs, Newport Inc., CalSensors, and Agiltron, can be used.
[0043] Now for reference Figure 9 This illustrates an embodiment of the present disclosure, in which a ridged waveguide, including a plurality of ridges, is arranged on top of a substrate. Figure 9 As shown, the waveguide can be configured such that the top surface of each ridge is slightly wider than the rest of the ridge. The gap between the ridges on the top surface is narrower than the size of the particle. For example, if the particles are primarily cardiomyocytes in a bioreactor solution, having an elongated shape typically about 100 μm long and 10 μm to 25 μm wide, the gap between the ridges on the top surface could be only about 5 μm wide, thus preventing cells from entering the region between the ridges (where a stronger electric field exists) while still allowing fluid from the bioreactor to fill the space between the ridges and interact with the field from the waveguide mode.
[0044] In some embodiments of this disclosure, a ridged waveguide is provided and configured to enable waveguide spectroscopy with fluid contact to the waveguide core, while simultaneously preventing particles of a certain size from entering the high-electric-field region of the waveguide within the fluid. In one embodiment, the waveguide is configured to have a plurality of ridges spaced approximately one wavelength or less, such that the gaps between the ridges are smaller than the size of particles in the surrounding fluid. The gaps between the ridges on the top surfaces of the ridges may be smaller than the size of the particles, which is necessary to prevent particles from entering the gaps.
[0045] The ridge waveguide can be configured such that the top surface of at least one ridge is wider than the remainder of the at least one ridge.
[0046] In some embodiments, the ridge waveguide may comprise silicon on a silicon substrate. The material of the ridge waveguide may be selected from the group consisting of Si3N, Al2O3, Ta2O5, SixOyN1-xy, Si, Ge, diamond, ZnS, and ZnSe.
[0047] The processes for fabricating ridge waveguides for a wide variety of configurations are known to those skilled in the art and can be performed at a variety of different manufacturing facilities.
[0048] Now for reference Figure 10 This illustrates an embodiment of the present disclosure, in which the light from the light source can be unpolarized, circularly polarized, or linearly polarized using a polarization orientation of 45°. The light source can be linearly polarized such that the orientation of the light source is 45° to the orientation used to excite the TE or TM waveguide mode. Figure 11 As further shown in (a) or 11(b), a rotating polarizer is also provided. Light is focused onto a waveguide having a waveguide core in contact with the sample and a waveguide cladding beneath the waveguide core. A substrate may be located beneath the cladding. Figure 10 In the diagram, a rotating polarizer is shown positioned between the light source and the sample. Other configurations of the rotating polarizer are also envisioned. For example, in some embodiments, the rotating polarizer may be positioned between the sample and the detector. Figure 10 This further illustrates that a spectrometer or monochromator can be positioned behind the sample. It will be understood that a spectrometer or monochromator can also be positioned between the light source and the sample. If the light source is a single-wavelength source (e.g., a laser) or a tunable source (e.g., a tunable laser), then a spectrometer or monochromator may not be required.
[0049] A rotating polarizer can be rotated at a first specific frequency. This causes the polarization of the transmitted light to be adjusted at a second specific frequency, which can be a multiple of the rotation frequency. If the polarizer includes, for example... Figure 11 In the partition shown in (b), in the illustrated embodiment, the light transmitted through the polarizer should be alternately polarized in the directions of the TM waveguide mode and the TE waveguide mode (which are at 90° and 0°, respectively). For Figure 11 The rotating plate polarizer shown in (a) continuously changes the polarization of transmitted light from 0° to 90° as the polarizer rotates. If the rotating polarizer is placed in front of the waveguide, the transmitted light focused on the waveguide excites both TE and TM modes with a 90° phase shift at its modulated intensity. If the rotating polarizer is placed behind the waveguide, it transmits light from both TE and TM waveguide modes with a 90° phase shift between them.
[0050] The light intensities of the transmitted TE and TM modes can be measured and subtracted or divided separately to obtain the final spectrum. In other embodiments, the combined light intensities of the transmitted TE and TM modes can be measured by a single detector with a lock-in amplifier or phase-sensitive synchronous detection electronics. If the light intensities transmitted through the waveguide for both modes are equal, there is no change in light intensity when the polarizer is rotated. The detected light intensity is only adjusted by the polarizer if there is a change in the transmitted light intensities of the two polarizations of the waveguide mode. If the transmitted light intensities of the two polarizations differ due to factors other than sample absorption (such as different efficiencies of the coupled light entering the two modes), the transmitted light intensities of the two modes can be compensated for, for example, by adjusting the input polarization of the light source to put more light into the weaker mode to make them equal at the detector. A lock-in amplifier can be used to synchronously detect the transmitted signals through the polarizer and the waveguide. Since the two modes have a 90° phase shift relative to each other in their modulated signals, the phase of the lock-in detection can also be adjusted relative to the phase of the polarizer to compensate for and adjust the signal levels of the two modes for the zero output signal from the lock-in.
[0051] In one embodiment, the polarizer is not rotated but fixed in orientation to the light passing through it at a 45° angle to the orientation of the excited TE or TM waveguide mode. Figure 12 In another embodiment shown, the polarizer is fixed at a 45° orientation relative to the waveguide instead of rotating. If unpolarized light from the light source is transmitted through the polarizer, half of the light will excite the TE waveguide mode and the other half will excite the TM waveguide mode. At the system output, a polarized beam splitter is provided, which reflects light from one of these modes onto a detector, while the transmitted light enters a second detector. As shown, two lock-in amplifiers can be used to separately detect the TE and TM mode transmitted signals. If the output signal amplitudes of the two modes are not equal, the gain of the detector electronics can be adjusted to make the amplitudes of the detected output signals equal for both lock-in amplifiers.
[0052] TE and TM modes interact differently with the fluid in contact with the waveguide core. Electric field penetration through the fluid depends on the specific mode type, core / cladding thickness, and refractive index. Figure 13In this calculation, the imaginary part of the waveguide mode index (which measures how quickly light propagating in the waveguide is attenuated) is plotted as a function of the core thickness of the Si3N4 core on a glucose solution and a fused silica substrate. The calculation can be based on standard waveguide formulas known to those skilled in the art. In this calculation, neither the core nor the cladding absorbs light. Only the glucose solution absorbs light, so the imaginary part of the mode index is due to the absorption of light in the glucose solution. Depending on the core thickness, different numbers of TE and TM modes can exist in the waveguide. If the core is too thin, no propagation mode of either polarization exists. As the core thickness increases from zero, it first reaches a thickness at which the TE0 mode can propagate (as indicated by the value of the imaginary mode index for a core thickness greater than 320 nm). The large imaginary part of the mode index at this core thickness indicates that the TE0 waveguide mode is highly attenuated. Generally, this is desirable because it indicates that the mode is interacting strongly with the sample solution (such as glucose solution). As the core thickness increases further, the attenuation of the TE0 mode decreases rapidly. Once the core thickness reaches approximately 540 nm, the first TM mode (TM0) begins to propagate. For a core thickness of approximately 540 nm, it also exhibits a very large imaginary mode exponent, indicating high attenuation. However, the imaginary part of the mode exponent of the TE0 mode at this core thickness is much smaller. Therefore, at this core thickness, the TM0 mode interacts more strongly with the glucose solution than the TE0 mode.
[0053] For both TE0 and TM0 modules with a fixed core thickness of 550nm, Figure 14 The imaginary part of the mode exponent as a function of wavelength is plotted. The non-zero value of the imaginary part of the mode exponent is entirely due to the absorption of glucose in the model calculations. It is clearly shown that there is a significant difference in absorption between the two modes due to glucose, with the TM0 mode exhibiting greater attenuation than the TE0 mode across the entire wavelength range.
[0054] like Figure 12 As shown in one embodiment, the transmittance signals of the TE and TM modes can be detected separately by different lock-in amplifiers. These signals can be digitally subtracted or divided by a control computer. Figure 15 The calculated transmittance for the TE0 and TM0 modes along a 1 cm waveguide through a 10 mMol glucose solution is presented, along with the transmittance difference spectrum. The transmittance difference spectrum clearly reveals the absorption characteristics of the glucose solution and can therefore be used to determine the glucose concentration. By subtracting the signal from the TE and TM modes, common variations in source light intensity, waveguide coupling efficiency, or any other factor similarly affecting the signal intensity of both modes can be substantially removed from the difference / division spectrum, thus providing the ability to perform long-term measurements of the spectral absorption of glucose solutions without requiring periodic supply of a pure solution (e.g., a particle-free sample) to the waveguide sensor for background spectral measurements.
[0055] Polarizers or polarizer partitions can be made from one or both of sheet polarizers and wire-grating polarizers. Sheet polarizers and wire-grating polarizers are available from a wide range of sources, including Thorlabs, Edmund Scientific, and Knight Optical, for various wavelength ranges. These can be cut to suitable shapes and polarization angles and attached to a rotating “splitter” support. Rotating “splitters” are available from various sources, including Thorlabs, Edmund Scientific, and Newport Corp. In some embodiments, the polarizer can be a polarization beam splitter cube, a Glan-Thomson prism, a Wollaston prism, a Glan-Taylor prism, or any combination thereof.
Claims
1. An apparatus for waveguide spectroscopy of samples within a container, the apparatus comprising: A substrate having a window that is transparent at the wavelength of interest and coupled to the container holding the sample; The waveguide core is a transparent material at the wavelength of interest, located on the inner surface of a transparent window adjacent to the sample. The waveguide core has a refractive index greater than that of the sample. Optical elements, the optical elements being configured to couple light into and out of the waveguide, A light source, located outside the container; as well as One or more detectors, the one or more detectors being located outside the container.
2. The device of claim 1, wherein the waveguide includes a cladding and the waveguide core has a refractive index greater than the refractive index of the cladding deposited between the core and the substrate.
3. The device of claim 1, wherein the waveguide includes a cladding having a refractive index less than that of the substrate, and wherein the cladding has a thickness of three or more wavelengths.
4. The device of claim 1, wherein the waveguide core has a refractive index greater than that of the substrate.
5. The device of claim 1, wherein the optical element comprises one of a prism and a grating.
6. The device of claim 5, wherein the prism is positioned on the window outside the container.
7. The device of claim 5, wherein the grating is located inside the container adjacent to or within the waveguide.
8. The device of claim 1, wherein the waveguide core has a thickness configured to allow a single TE-polarized waveguide mode to be transmitted.
9. The device of claim 1, wherein the waveguide core has a thickness configured to transmit a single TE polarized waveguide mode and a single TM polarized mode.
10. The device of claim 1, wherein the core is composed of Si3N4, Al2O3, Ta2O5, Si x O y N 1-x-y It is made from materials selected from the group consisting of Si, Ge, diamond, ZnS and ZnSe.
11. The device of claim 1, wherein the waveguide has a structure composed of SiO2, MgF2, CaF2, and Si x O y N 1-x-y The cladding is made of materials selected from the group.
12. The device of claim 1, wherein the substrate is made of a material selected from the group consisting of Si, glass, fused silica, Al2O3, ZnS, ZnSe, diamond, KBr, BaF2 and CaF2.
13. The device of claim 1, further comprising means located outside the container and configured to perform spectral measurements.
14. The apparatus of claim 13, wherein the apparatus comprises at least one of a filter and a spectrometer.
15. A method for measuring waveguide spectra using a system comprising polarized light, including a waveguide, a light source, a polarizer, and a detector that are in contact with a sample and support both TE and TM waveguide modes.
16. The method of claim 15, wherein the polarizer rotates at a specific frequency, causing the polarization of the transmitted light to rotate.
17. The method of claim 15, wherein the polarizer comprises a multi-segment polarizer rotating at a specific frequency, wherein adjacent polarizer segments are oriented perpendicularly to each other, and half of the segments are oriented for light passing through a TE waveguide mode and half are oriented for light passing through a TM waveguide mode.
18. The method of claim 15, wherein the polarizer does not rotate and is fixed in the orientation of light passing through it at 45° to the orientation of the excited TE or TM waveguide mode.
19. The method of claim 15, wherein the light source is unpolarized or circularly polarized.
20. The method of claim 15, wherein the light source is linearly polarized such that the orientation of the light source is at 45° to the orientation used to excite the TE or TM waveguide mode.
21. The method of claim 20, wherein the light intensities of the transmitted TE and TM modes are measured separately and subtracted or divided to obtain the final spectrum.
22. The method of claim 15, wherein the intensity of the combined transmitted TE and TM modes of light is measured by a single detector with a lock-in amplifier or phase-sensitive synchronous detection electronics.
23. The method of claim 15, wherein the polarizer or polarizer partition is made of one or both of a plate polarizer and a wire grid polarizer.
24. The method of claim 15, wherein the polarizer is a polarization beam splitter cube, a Glan-Thomson prism, a Wollaston prism, a Glan-Taylor prism, or any combination thereof.
25. The method of claim 15, wherein the core and cladding in the waveguide have thicknesses selected to support a single TE and TM mode or selected to have a cutoff only slightly greater than that of a propagation mode.