Patent Description:
Infrared spectroscopy provides characterization of the vibrational and rotational energy levels of molecules in different materials. When the material is exposed to infrared light, absorption of photons occurs at certain wavelengths due to transitions between vibrational levels. In general, there are two mechanisms for performing spectral measurements: transmission mode in which the infrared light passes through a sample under test or reflection mode in which the infrared light is reflected from the sample under test.

Attenuated total internal reflection (ATR) spectroscopy is a type of reflection coupling which depends on internal reflection of light inside a high refractive index material while placing a sample in intimate contact with the material. ATR spectroscopy enables spectral analysis of all types of samples with minimal sample preparation. ATR has been used as an effective way to analyze fluid and solid samples based on the phenomenon of total internal reflection of light at the boundary between two media. Typically, a high refractive index material such as zinc selenide, germanium, or silicon, referred to as an ATR crystal, ATR internal reflection element (IRE), or ATR element, is illuminated with an IR source, while the sample covers the ATR crystal and is in intimate contact therewith. If the angle of input light is higher than a critical angle at the boundary between the ATR crystal and the sample, light is totally internally reflected and a special type of electromagnetic wave, called an evanescent wave, is formed on the sample side. The sample absorbs some of the intensity of the evanescent wave due to molecular vibrations at certain wavelengths. Hence, the intensity of reflected light is attenuated relative to the incoming intensity. The output light of the crystal may then be coupled to a Fourier Transform Infrared (FTIR) system, as an example for spectroscopic techniques, which may be based on a Michelson interferometer, and then to a broadband IR detector to analyze the sample spectrum.

ATR techniques are divided according to the size of the IRE into macro-ATR and micro-ATR techniques. In macro-ATR, commercial ATR crystals of different large sizes are used according to the required field of view and spatial resolution. In addition, the macro-ATR technique has been implemented as an analytical tool for liquids in microfluidic chips where liquid flows inside micron-size channels. An example of a macro-ATR technique includes a microfluidic device built on top of a commercial polished ATR IRE using a polydimethylsiloxane (PDMS) device.

To avoid the large cost of the IREs and the need for mechanical polishing, micromachined elements fabricated on silicon wafers have started to take the place of the bulky crystals, which is referred to as micro-ATR. Anisotropic KOH-etching of silicon wafers is used to provide an inclined optical surface for light interaction. Then, glass wafers with micromachined channels are bonded on the top of the wafer or the fluid patterns are fabricated on this non-grooved surface. This enables combining ATR spectroscopy and microfluidics, which has various applications in biology and chemistry disciplines. However, additional complexity is added to the sample preparation and measurement steps as there are three separate systems that need to be aligned together: the microfluidic chip, the micro-ATR IREs, and the spectrometer optical coupling system. Configurations of integrated spectral sensing devices are disclosed in <CIT>; in publication <NPL>; and in publication <NPL>.

The present invention is directed to an integrated spectral sensing device as defined in appended independent claim <NUM>. Particular embodiments of the invention are defined by the dependent claims. The scope of the invention is solely defined by the appended claims.

Various aspects of the disclosure relate to an integrated and compact ATR spectral sensing device. The spectral sensing device includes a substrate, a spectrometer, and a detector. The substrate includes an ATR element, a microfluidic channel, and a channel interface at a boundary between the ATR element and the microfluidic channel formed therein. The ATR element is configured to receive input light and to direct the input light to the channel interface for total internal reflection of the input light at the channel interface. An evanescent wave can then be produced by a sample contained within the microfluidic channel based on the total internal reflection of the input light. The evanescent wave attenuates the light output from the ATR element and the resulting output light may be analyzed using the spectrometer and the detector.

The spectrometer core can be based on an FTIR spectroscopic technique, tunable filter, diffraction grating or other suitable spectroscopic technique for selectively measuring different wavelengths of the light spectrum. In some examples, an ATR IRE (also referred to herein as an ATR crystal or ATR element) can be integrated with an FTIR-based spectrometer, which may include, for example, a micro-electro-mechanical systems (MEMS) Michelson interferometer and reflecting micro-optical elements (light redirecting elements) for light coupling to and from the spectrometer core.

In the integrated spectral sensing device, light propagates inside the ATR element in-plane with respect to the spectrometer, either in a separate substrate or in the same substrate of the spectrometer. In such an in-plane configuration, the ATR IRE element may be micromachined, using for example, deep reactive ion etching (DRIE), such that light travels parallel to the substrate, allowing a high level of monolithic integration of all ATR and spectrometer elements in a single compact module. In addition, in-plane ATR allows forming IREs with the desired shape and dimensions depending on the measured sample. For example, the incidence angle and number of reflections may be adapted in the design.

In some examples, the integrated spectral sensing device includes three substrates, one for the spectrometer (e.g., MEMS interferometer), another for the light redirecting element(s) and a third for an ATR crystal (ATR element), where the three substrates are coupled together in a single module. In other examples, the ATR element and spectrometer (e.g., MEMS interferometer) are formed in the same substrate (e.g., a silicon substrate) and coupled to another substrate containing the light redirecting element(s). The substrate containing the monolithically integrated ATR element/MEMS interferometer can further include guiding structures in the silicon to guide light to/from the microfluidic channels in which liquid flows.

Unlike conventional ATR element designs, in various aspects of the disclosure, the sample fluid flows between input and output ports adjacent to the ATR IRE on the same substrate avoiding difficult bonding and alignment steps of two separate wafers together. Both designs presented herein can easily be used to measure the ATR signal and analyze materials in the mid-infrared (MIR) range making use of silicon transmission properties in the IR range and free space coupling to MEMS chip. In addition, the integration of microfluidic channels with a micro-spectrometer in a single module results in a cheap and simple device to analyze samples in an ATR sampling mode. Different particle separation and sorting techniques may further be added to the microfluidic devices to analyze micro particles and contaminants using the integrated spectral sensing device.

<FIG> is a diagram illustrating a spectrometer <NUM> not according to the present invention. The spectrometer <NUM> may be, for example, a Fourier Transform infrared (FTIR) spectrometer. In the example shown in <FIG>, the spectrometer <NUM> is a Michelson FTIR interferometer. In other examples, the spectrometer may include an FTIR Fabry-Perot interferometer.

FTIR spectrometers measure a single-beam spectrum (power spectral density (PSD)), where the intensity of the single-beam spectrum is proportional to the power of the radiation reaching the detector. In order to measure the absorbance of a sample, the background spectrum (i.e., the single-beam spectrum in absence of a sample) may first be measured to compensate for the instrument transfer function. The single-beam spectrum of light transmitted or reflected from the sample may then be measured. The absorbance of the sample may be calculated from the transmittance, reflectance, or trans-reflectance of the sample. For example, the absorbance of the sample may be calculated as the ratio of the spectrum of transmitted light, reflected light, or trans-reflected light from the sample to the background spectrum.

The interferometer <NUM> includes a fixed mirror <NUM>, a moveable mirror <NUM>, a beam splitter <NUM>, and a detector <NUM> (e.g., a photodetector). A light source <NUM> associated with the spectrometer <NUM> is configured to emit an input beam and to direct the input beam towards the beam splitter <NUM>. The light source <NUM> may include, for example, a laser source, one or more wideband thermal radiation sources, or a quantum source with an array of light emitting devices that cover the wavelength range of interest.

The beam splitter <NUM> is configured to split the input beam into two beams. One beam is reflected off of the fixed mirror <NUM> back towards the beam splitter <NUM>, while the other beam is reflected off of the moveable mirror <NUM> back towards the beam splitter <NUM>. The moveable mirror <NUM> may be coupled to an actuator <NUM> to displace the movable mirror <NUM> to the desired position for reflection of the beam. An optical path length difference (OPD) is then created between the reflected beams that is substantially equal to twice the mirror <NUM> displacement. In some examples, the actuator <NUM> may include a micro-electro-mechanical systems (MEMS) actuator, a thermal actuator, or other type of actuator.

The reflected beams interfere at the beam splitter <NUM> to produce an interference beam (e.g., an interference pattern), allowing the temporal coherence of the light to be measured at each different Optical Path Difference (OPD) offered by the moveable mirror <NUM>. In some examples, the signal corresponding to the interference beam may be directed to a sample (not shown) and the output light (scattered light) from the sample may be detected and measured by the detector <NUM> at many discrete positions of the moveable mirror <NUM> to produce an interferogram. In other examples, the input beam may be directed to the sample prior to input to the interferometer <NUM>. In some examples, the detector <NUM> may include a detector array or a single pixel detector. The interferogram data versus the OPD may then be input to a processor (not shown, for simplicity). The spectrum may then be retrieved, for example, using a Fourier transform carried out by the processor.

In some examples, the interferometer <NUM> may be implemented as a MEMS interferometer 100a (e.g., a MEMS chip). The MEMS chip 100a may then be attached to a printed circuit board (PCB) <NUM> that may include, for example, one or more processors, memory devices, buses, and/or other components. As used herein, the term MEMS refers to the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through microfabrication technology. For example, the microelectronics are typically fabricated using an integrated circuit (IC) process, while the micromechanical components are fabricated using compatible micromachining processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical components. One example of a MEMS element is a micro-optical component having a dielectric or metallized surface working in a reflection or refraction mode. Other examples of MEMS elements include actuators, detector grooves and fiber grooves.

In the example shown in <FIG>, the MEMS interferometer 100a may include the fixed mirror <NUM>, moveable mirror <NUM>, beam splitter <NUM>, and MEMS actuator <NUM> for moveably controlling the moveable mirror <NUM>. In addition, the MEMS interferometer 100a may include fibers <NUM> for directing the input beam towards the beam splitter <NUM> and the output beam from the beam splitter <NUM> towards the detector (e.g., detector <NUM>). In some examples, the MEMS interferometer 100a may be fabricated using a Deep Reactive Ion Etching (DRIE) process on a Silicon On Insulator (SOI) wafer in order to produce the micro-optical components and other MEMS elements that are able to process free-space optical beams propagating parallel to the SOI substrate. For example, the electro-mechanical designs may be printed on masks and the masks may be used to pattern the design over the silicon or SOI wafer by photolithography. The patterns may then be etched (e.g., by DRIE) using batch processes, and the resulting chips (e.g., MEMS chip 100a) may be diced and packaged (e.g., attached to the PCB <NUM>).

For example, the beam splitter <NUM> may be a silicon/air interface beam splitter (e.g., a half-plane beam splitter) positioned at an angle (e.g., <NUM> degrees) from the input beam. The input beam may then be split into two beams L1 and L2, where L1 propagates in air towards the moveable mirror <NUM> and L2 propagates in silicon towards the fixed mirror <NUM>. Here, L1 originates from the partial reflection of the input beam from the half-plane beam splitter <NUM>, and thus has a reflection angle equal to the beam incidence angle. L2 originates from the partial transmission of the input beam through the half-plane beam splitter <NUM> and propagates in silicon at an angle determined by Snell's Law. In some examples, the fixed and moveable mirrors <NUM> and <NUM> are metallic mirrors, where selective metallization (e.g., using a shadow mask during a metallization step) is used to protect the beam splitter <NUM>. In other examples, the mirrors <NUM> and <NUM> are vertical Bragg mirrors that can be realized using, for example, DRIE.

In some examples, the MEMS actuator <NUM> may be an electrostatic actuator formed of a comb drive and spring. For example, by applying a voltage to the comb drive, a potential difference results across the actuator <NUM>, which induces a capacitance therein, causing a driving force to be generated as well as a restoring force from the spring, thereby causing a displacement of moveable mirror <NUM> to the desired position for reflection of the beam back towards the beam splitter <NUM>.

The spectrometer <NUM> shown in <FIG> or other suitable spectral sensing unit may be incorporated into an integrated evanescent wave spectral sensing device. <FIG> is a diagram illustrating an example of an integrated spectral sensing device <NUM> not according to the present invention. The integrated spectral sensing device <NUM> includes a substrate <NUM>, such as a silicon substrate or a SOI substrate, a spectrometer <NUM> (e.g., a MEMS interferometer, as shown in <FIG>), and a detector <NUM>. The substrate <NUM> includes an ATR element <NUM> and a microfluidic channel <NUM> formed in the substrate <NUM> using, for example, a DRIE process. The ATR element <NUM> may correspond to or include a waveguide for passing light therethrough. The microfluidic channel <NUM> includes a sample <NUM> (e.g., a fluid) that flows through the microfluidic channel <NUM> between input and output microfluidic ports <NUM>. The sample <NUM> flows adjacent to a boundary <NUM> between the microfluidic channel <NUM> and the ATR element <NUM>. The boundary <NUM> corresponds to a channel interface between the ATR element <NUM> and the microfluidic channel <NUM> and may be formed by a surface of the ATR element <NUM> against which the sample <NUM> is in contact. For example, the boundary or channel interface <NUM> may correspond to an inclined or vertical surface of the ATR element <NUM> that further serves as an internal surface of the microfluidic channel <NUM>. In examples in which the substrate <NUM> is a silicon or SOI substrate, the channel interface <NUM> may correspond to a silicon-air (Si-air) interface forming a silicon-sample (Si-sample) interface with the sample inserted.

A light source <NUM> (e.g., an external IR blackbody source) is configured to generate input light <NUM> (e.g., IR light or NIR light). The input light <NUM> is directed into the ATR element <NUM> in the substrate <NUM>. The ATR element <NUM> may be a singlereflection ATR element, as shown in <FIG>, or a multiple-reflections ATR element. The ATR element <NUM> is designed to produce total internal reflection of the input light <NUM> at the channel interface <NUM>. For example, the ATR element <NUM> may have a size (dimensions, thickness, etc.) and shape (e.g., V-shaped input and output interfaces <NUM> and <NUM>) configured to produce an angle of the input light <NUM> that is higher than a critical angle at the boundary <NUM> between the ATR element <NUM> and the sample <NUM>. The resulting evanescent wave produced in the sample <NUM> based on the total internal reflection of the input light <NUM> attenuates the input light <NUM> to produce output light <NUM> that may be input to the spectrometer <NUM>. In some examples, the integrated spectral sensing device may further include one or more optical elements, such as optical focusing elements (e.g., lens) and/or light redirecting elements (e.g., mirrors or other reflectors) to direct the light into the ATR element <NUM> and/or from the ATR element <NUM> to the spectrometer <NUM>. The spectrometer <NUM> is configured to produce an interference beam (interference pattern) <NUM> of the output light <NUM> and to provide the interference beam <NUM> to the detector <NUM> for spectral analysis.

In some examples, the spectrometer <NUM> may be positioned before the ATR element <NUM>. In this example, the spectrometer <NUM> may be configured to receive the input light <NUM> from the light source <NUM>, to produce the interference beam <NUM> from the input light <NUM>, and to direct the interference beam <NUM> to the ATR element <NUM>. The output light <NUM> from the ATR element <NUM> may then be directed to the detector <NUM>.

<FIG> is a top view of another example of an integrated spectral sensing device
<NUM> not according to the present invention.

The integrated spectral sensing device <NUM> includes a substrate <NUM>, a spectrometer <NUM> (e.g., a MEMS interferometer, as shown in <FIG>), and a detector <NUM>. The substrate <NUM> includes an ATR element <NUM> and a microfluidic channel <NUM> formed in the substrate <NUM>. The ATR element <NUM> may correspond to or include a waveguide. The microfluidic channel <NUM> includes a sample <NUM> (e.g., a fluid) that flows through the microfluidic channel <NUM> adjacent to a boundary <NUM> (e.g., a channel interface) between the microfluidic channel <NUM> and the ATR element <NUM>.

A light source <NUM> (e.g., an external IR blackbody source) is configured to generate input light <NUM> (e.g., IR light or NIR light) and direct the input light <NUM> to an optical component (e.g., a lens) <NUM> that couples the input light <NUM> into the ATR element <NUM>. In the example shown in <FIG>, the ATR element <NUM> is a multiple-reflections ATR element. The ATR element <NUM> is designed to produce total internal reflection of the input light <NUM> at the channel interface <NUM>. For example, the ATR element <NUM> may be designed to produce an angle θ of the input light <NUM> that is higher than a critical angle θc at the channel interface <NUM> between the ATR element <NUM> and the sample <NUM>. The total internal reflection of the input light <NUM> forms an evanescent wave <NUM> on the sample side of the boundary <NUM>. The sample <NUM> absorbs some of the intensity of the evanescent wave <NUM> due to molecular vibrations at certain wavelengths. Hence, the intensity of the reflected light (total internally reflected light) is attenuated relative to the incoming intensity. The output light <NUM> attenuated with respect to the input light <NUM> based on the total internal reflection of the input light <NUM> and the evanescent wave produced by the sample <NUM> is coupled into the spectrometer <NUM> via a light redirecting element (e.g., a mirror) <NUM>.

The spectrometer <NUM> shown in <FIG> is a MEMS interferometer that includes a beam splitter <NUM>, a moveable mirror <NUM>, and a fixed mirror <NUM>. The beam splitter <NUM> is configured to split the output light <NUM> into two beams. One beam is reflected off of the fixed mirror <NUM> back towards the beam splitter <NUM>, while the other beam is reflected off of the moveable mirror <NUM> back towards the beam splitter <NUM>. The moveable mirror <NUM> may be coupled to an actuator (not shown) to displace the movable mirror <NUM> to the desired position for reflection of the beam. An optical path length difference (OPD) is then created between the reflected beams that is substantially equal to twice the mirror <NUM> displacement. The reflected beams interfere at the beam splitter <NUM> to produce an interference beam (e.g., an interference pattern) <NUM>, allowing the temporal coherence of the output light <NUM> to be measured at each different Optical Path Difference (OPD) offered by the moveable mirror <NUM>. The interference beam (interference pattern) <NUM> may be detected and measured by the detector <NUM> at many discrete positions of the moveable mirror <NUM> to produce an interferogram that represents a spectrum of the sample <NUM>.

<FIG> is a diagram illustrating an example of a multi-substrate integrated spectral sensing device <NUM> according to some aspects. In the example shown in <FIG>, the integrated spectral sensing device <NUM> includes three substrates <NUM>, <NUM>, and <NUM>. A first substrate <NUM> is positioned in a first plane that is parallel to a second plane of a third substrate <NUM>. The integrated spectral sensing device <NUM> may further include a package substrate <NUM>. The third substrate <NUM> may be positioned on (e.g., bonded to) the package substrate <NUM>. In addition, a second substrate <NUM> may be positioned over the third substrate <NUM> and bonded to the package substrate <NUM> at respective ends of the second substrate <NUM>. A detector <NUM> may further be positioned on the package substrate <NUM>. Each of the substrates <NUM>, <NUM>, and <NUM> may be, for example, a silicon or SOI substrate. In some examples, the second substrate <NUM> may be a plastic or glass substrate formed using injection molded optics technology.

The first substrate <NUM> includes an ATR element <NUM> and two opposing microfluidic channels 312a and 312b. The ATR element <NUM> and microfluidic channels 312a and 312b are formed within the first substrate <NUM> via, for example, a DRIE process. The ATR element <NUM> may correspond to or include a waveguide. Each microfluidic channel 312a and 312b includes a sample (e.g., a fluid) that flows through the microfluidic channels 312a and 312b adjacent to a respective boundary 314a and 314b (e.g., a channel interface) between the respective microfluidic channel 312a and 312b and the ATR element <NUM>. Each channel interface 314a and 314b may correspond to a deeply etched vertical surface of the first substrate <NUM>. For example, each channel interface 312a and 312b may correspond to a silicon-air (Si-air) interface forming a silicon-sample (Si-sample) interface with the sample inserted. The ATR element <NUM>, the first microfluidic channel 312a and the second microfluidic channel 312b are configured such that total internal reflection of light occurs within the ATR element <NUM> between the first channel interface 314a and the second channel interface 314b.

The second substrate <NUM> includes one or more light redirecting elements <NUM> and <NUM> formed therein. For example, the light redirecting elements <NUM> and <NUM> may be curved reflectors (e.g., micro-reflectors or micromirrors). In some examples, the light redirecting elements <NUM> and <NUM> may be fabricated in molded parts of the second substrate <NUM> with an aluminum metallic coating to improve the reflectivity thereof.

The third substrate <NUM> includes a spectrometer <NUM> formed therein via, for example, a DRIE process. The spectrometer <NUM> may include a beam splitter <NUM>, a fixed mirror <NUM>, and a moveable mirror <NUM>. The moveable mirror <NUM> may be coupled to an actuator <NUM>, such as a MEMS electrostatic actuator.

In the example shown in <FIG>, input light <NUM> from a light source (not shown) is input into the ATR element <NUM> on the first substrate <NUM>. For example, the ATR element <NUM> may include a V-shaped input interface configured to produce an angle of the input light <NUM> on the channel interface 314b of the microfluidic channel 312b that is higher than a critical angle to produce total internal reflection of the input light <NUM> at the channel interface 314b. The input light <NUM> is then total internal reflected between the channel interfaces 314a and 314b, where the input light <NUM> is attenuated by respective evanescent waves formed within the sample contained within each of the microfluidic channels 312a and 312b. The attenuated input light is then output from the ATR element <NUM> as output light <NUM>. For example, the ATR element <NUM> may include a V-shaped output interface configured to facilitate transmission of the output light <NUM> reflected from the channel interface 314b of the microfluidic channel 312b.

The output light <NUM> may be redirected by an optical element <NUM> (e.g., an inclined reflector or curved reflector) from an in-plane direction with respect to the plane of the first substrate <NUM> to an out-of-plane direction out-of-plane with respect to the first plane of the first substrate <NUM>. Thus, the optical element <NUM> receives the output light propagating parallel to the plane of the first substrate <NUM> and reflects the output light <NUM> by <NUM> degrees to facilitate propagation of the output light <NUM> perpendicular to the plane of the first substrate <NUM> towards the light redirecting element <NUM>. The optical element <NUM> may be formed as part of the second substrate <NUM> or may be an external component (the latter being illustrated). The light redirecting element <NUM> receives the output light <NUM> propagating out-of-plane with respect to the plane of the first substrate <NUM> and reflects the output light by another <NUM> degrees towards the spectrometer <NUM> to facilitate propagation of the output light <NUM> in-plane with respect to the plane of the third substrate <NUM>.

The output light <NUM> is input to the beam splitter <NUM> in the spectrometer <NUM>. The beam splitter <NUM> is configured to split the output light <NUM> into two beams. One beam is reflected off of the fixed mirror <NUM> back towards the beam splitter <NUM>, while the other beam is reflected off of the moveable mirror <NUM> back towards the beam splitter <NUM>. The moveable mirror <NUM> may be displaced by the actuator <NUM> to the desired position for reflection of the beam. An optical path length difference (OPD) is then created between the reflected beams that is substantially equal to twice the moving mirror <NUM> displacement. The reflected beams interfere at the beam splitter <NUM> to produce an interference beam (e.g., an interference pattern) <NUM>, allowing the temporal coherence of the output light <NUM> to be measured at each different Optical Path Difference (OPD) offered by the moveable mirror <NUM>. The interference beam (interference pattern) <NUM> may then be output by the spectrometer <NUM> and redirected by the light redirection element <NUM> towards the detector <NUM> to obtain a spectrum of the sample within the microfluidic channels 312a and 312b. For example, the light redirection element <NUM> may be a curved reflector configured to focus the interference beam <NUM> to the active area of the detector <NUM>.

The integrated spectral sensing device design shown in <FIG> is a reflector-based design instead of a lens-based design, thus reducing chromatic aberration in the integrated spectral sensing device <NUM>. In addition, the transmission properties of silicon enable the integrated spectral sensing device <NUM> to operate within an ultra-wide spectral range, limited only by the silicon crystal and detector material. Moreover, the integrated spectral sensing device <NUM> is shown integrated into a single package (e.g., using the package substrate <NUM>) to produce an inexpensive and simple device. Moreover, the crystal length (e.g., the length of the first substrate <NUM> containing the ATR element <NUM>) is shown of the same order as the optical mold design dimensions of the second substrate <NUM> for ease of packaging. However, in other examples, longer crystal designs or shorter crystal designs may be used according to the target number of internal reflections.

<FIG> is a diagram illustrating another example of a multi-substrate integrated spectral sensing device <NUM> according to some aspects. In the example shown in <FIG>, the integrated spectral sensing device <NUM> includes three substrates <NUM>, <NUM>, and <NUM>. A first substrate <NUM> is positioned in a first plane that is parallel to a second plane of a third substrate <NUM>. The integrated spectral sensing device <NUM> may further include a package substrate <NUM>. The third substrate <NUM> may be positioned on (e.g., bonded to) the package substrate <NUM>. In addition, a second substrate <NUM> may be positioned over the third substrate <NUM> and bonded to the package substrate <NUM> at respective ends of the second substrate <NUM>. A detector <NUM> may further be positioned on the package substrate <NUM>. Each of the substrates <NUM>, <NUM>, and <NUM> may be, for example, a silicon or SOI substrate. In some examples, the second substrate <NUM> may be a plastic or glass substrate formed using injection molded optics technology.

The first substrate <NUM> includes an ATR element <NUM> and two opposing microfluidic channels 412a and 412b. The ATR element <NUM> and microfluidic channels 412a and 412b are formed within the first substrate <NUM> via, for example, a DRIE process. Each microfluidic channel 412a and 412b includes a sample (e.g., a fluid) that flows through the microfluidic channels 412a and 412b adjacent to a respective boundary (e.g., a channel interface, similar to the channel interfaces shown in <FIG>) between the respective microfluidic channel 412a and 412b and the ATR element <NUM>.

The second substrate <NUM> includes one or more light redirecting elements <NUM> and <NUM> formed therein. For example, the light redirecting elements <NUM> and <NUM> may be curved reflectors (e.g., micro-reflectors or micromirrors). In some examples, the light redirecting elements <NUM> and <NUM> may be fabricated in molded parts of the second substrate <NUM> with an aluminum metallic coating to improve the reflectivity thereof. The third substrate <NUM> includes a spectrometer <NUM> formed therein via, for example, a DRIE process.

In the example shown in <FIG>, input light <NUM> from a light source (not shown) is input into the ATR element <NUM> on the first substrate <NUM>. For example, the ATR element <NUM> may include a V-shaped input interface configured to produce an angle of the input light <NUM> that is higher than a critical angle to produce total internal reflection of the input light <NUM> through the ATR element <NUM> between the microfluidic channels 412a and 412b. The input light <NUM> is attenuated by respective evanescent waves formed within the sample contained within each of the microfluidic channels 412a and 412b. The attenuated input light is then output from the ATR element <NUM> as output light <NUM>.

In the example shown in <FIG>, the ATR element <NUM> includes an angled surface <NUM> for out-of-plane coupling of the output light <NUM> towards the light redirecting element <NUM>. For example, the angled surface <NUM> may couple the output light <NUM> in an out-of-plane direction with respect to the plane of the ATR element <NUM> (e.g., the plane of the first substrate <NUM>) to the light redirecting element <NUM>. In some examples, the angled surface <NUM> may be anisotropically etched in the first substrate <NUM> using, for example, KOH etching. The light redirecting element <NUM> receives the output light <NUM> propagating out-of-plane with respect to the plane of the first substrate <NUM> and redirects the output light <NUM> (e.g., reflects the output light by <NUM> degrees) towards the spectrometer <NUM> in the third substrate <NUM> to facilitate propagation of the output light <NUM> in-plane with respect to the plane of the third substrate <NUM>.

The spectrometer <NUM> produces an interference beam (interference pattern) <NUM> based on the output light <NUM>, which is redirected by the light redirection element <NUM> towards the detector <NUM> to obtain a spectrum of the sample within the microfluidic channels 412a and 412b. For example, the light redirection element <NUM> may be a curved reflector configured to focus the interference beam <NUM> to the active area of the detector <NUM>.

The first substrate <NUM> includes an ATR element <NUM> and two opposing microfluidic channels 512a and 512b. The ATR element <NUM> and microfluidic channels 512a and 512b are formed within the first substrate <NUM> via, for example, a DRIE process. Each microfluidic channel 512a and 512b includes a sample (e.g., a fluid) that flows through the microfluidic channels 512a and 512b adjacent to a respective boundary (e.g., a channel interface, similar to the channel interfaces shown in <FIG>) between the respective microfluidic channel 512a and 512b and the ATR element <NUM>.

The second substrate <NUM> includes one or more light redirecting elements <NUM>, <NUM>, and <NUM> formed therein. For example, the light redirecting elements <NUM>, <NUM> and <NUM> may be curved reflectors (e.g., micro-reflectors or micromirrors). In some examples, the light redirecting elements <NUM>, <NUM>, and <NUM> may be fabricated in molded parts of the second substrate <NUM> with an aluminum metallic coating to improve the reflectivity thereof. The third substrate <NUM> includes a spectrometer <NUM> formed therein via, for example, a DRIE process.

In the example shown in <FIG>, input light <NUM> from a light source (not shown) is input into the ATR element <NUM> on the first substrate <NUM>. For example, the ATR element <NUM> may include a V-shaped input interface configured to produce an angle of the input light <NUM> that is higher than a critical angle to produce total internal reflection of the input light <NUM> through the ATR element <NUM> between the microfluidic channels 512a and 512b. The input light <NUM> is attenuated by respective evanescent waves formed within the sample contained within each of the microfluidic channels 512a and 512b. The attenuated input light is then output from the ATR element <NUM> as output light <NUM>.

In the example shown in <FIG>, the output light <NUM> is directed towards the light redirecting element <NUM> for out-of-plane coupling to the light redirecting element <NUM>. For example, the light redirecting element <NUM> is configured to receive the output light <NUM> in a first plane of the ATR element <NUM> (e.g., the first substate <NUM>) and to reflect (redirect) the output light <NUM> in an out-of-plane direction with respect to the first plane towards the light redirecting element <NUM>. The light redirecting element <NUM> receives the output light <NUM> propagating out-of-plane with respect to the plane of the first substrate <NUM> and redirects the output light <NUM> (e.g., reflects the output light by <NUM> degrees) from the out-of-plane direction to an in-plane direction with respect to a second plane of the third substrate <NUM> towards the spectrometer <NUM>.

The spectrometer <NUM> produces an interference beam (interference pattern) <NUM> based on the output light <NUM>, which is redirected by the light redirection element <NUM> towards the detector <NUM> to obtain a spectrum of the sample within the microfluidic channels 512a and 512b. For example, the light redirection element <NUM> may be a curved reflector configured to focus the interference beam <NUM> to the active area of the detector <NUM>.

<FIG> is a diagram illustrating another example of a multi-substrate integrated spectral sensing device <NUM> according to some aspects. In the example shown in <FIG>, the integrated spectral sensing device <NUM> again includes three substrates (e.g., a first substrate <NUM>, second substrate <NUM>, and third substrate <NUM>). However, the first substrate <NUM> and the third substrate <NUM> are positioned in a same plane. The integrated spectral sensing device <NUM> may further include a package substrate <NUM>. The first substrate <NUM> and the third substrate <NUM> may be positioned on (e.g., bonded to) the package substrate <NUM>. In addition, the second substrate <NUM> may be positioned over the first substrate <NUM> and the third substrate <NUM> and bonded to the package substrate <NUM> at respective ends of the second substrate <NUM>. A detector <NUM> may further be positioned on the package substrate <NUM>. Each of the substrates <NUM>, <NUM>, and <NUM> may be, for example, a silicon or SOI substrate. In some examples, the second substrate <NUM> may be a plastic or glass substrate formed using injection molded optics technology.

The first substrate <NUM> includes an ATR element <NUM> and two opposing microfluidic channels 612a and 612b. The ATR element <NUM> and microfluidic channels 612a and 612b are formed within the first substrate <NUM> via, for example, a DRIE process. Each microfluidic channel 612a and 612b includes a sample (e.g., a fluid) that flows through the microfluidic channels 612a and 612b adjacent to a respective boundary (e.g., a channel interface, similar to the channel interfaces shown in <FIG>) between the respective microfluidic channel 612a and 612b and the ATR element <NUM>.

In the example shown in <FIG>, input light <NUM> from a light source (not shown) is input to the integrated spectral sensing device <NUM> in an out-of-plane direction with respect to a plane of the first substrate <NUM> and the third substrate <NUM> towards the light redirecting element <NUM>. The light redirecting element <NUM> is configured to receive the input light <NUM> in the out-of-plane direction and to direct the input light <NUM> towards the first substrate <NUM> (e.g., redirect/reflect the input light <NUM> by <NUM> degrees towards the first substrate <NUM>). The input light <NUM> may impinge on the ATR element <NUM> at an angle of incidence that is higher than a critical angle to produce total internal reflection of the input light <NUM> through the ATR element <NUM> between the microfluidic channels 612a and 612b. The input light <NUM> is attenuated by respective evanescent waves formed within the sample contained within each of the microfluidic channels 612a and 612b. The attenuated input light is then output from the ATR element <NUM> as output light <NUM> towards the spectrometer <NUM> in the third substrate <NUM>.

The spectrometer <NUM> produces an interference beam (interference pattern) <NUM> based on the output light <NUM>, which is redirected by the light redirection element <NUM> towards the detector <NUM> to obtain a spectrum of the sample within the microfluidic channels 612a and 612b. For example, the light redirection element <NUM> may be a curved reflector configured to focus the interference beam <NUM> to the active area of the detector <NUM>.

<FIG> are diagrams illustrating examples of a compact ATR spectrometer <NUM> of an integrated spectral sensing device according to some aspects. In the examples shown in <FIG>, the compact ATR spectrometer <NUM> includes a spectrometer <NUM>, an ATR element <NUM>, and a microfluidic channel <NUM> integrated on a same substrate <NUM>. The substrate <NUM> may be, for example, a silicon or SOI substrate. The ATR element <NUM> may correspond to or include a waveguide for passing light therethrough. The microfluidic channel <NUM> includes a sample <NUM> (e.g., a fluid) that flows through the microfluidic channel <NUM> between input and output microfluidic ports <NUM>. The sample <NUM> flows adjacent to a boundary <NUM> between the microfluidic channel <NUM> and the ATR element <NUM>. The boundary <NUM> corresponds to a channel interface between the ATR element <NUM> and the microfluidic channel <NUM> and may be formed by a surface of the ATR element <NUM> against which the sample <NUM> is in contact. For example, the boundary or channel interface <NUM> may correspond to a vertical surface of the ATR element <NUM> etched in the substrate <NUM> (e.g., via a DRIE process) that further serves as an internal surface of the microfluidic channel <NUM>. Thus, the channel interface <NUM> corresponds to a Si-air/Si-sample interface.

The spectrometer <NUM> shown in <FIG> is a deeply etched micromachined MEMS interferometer. The MEMS interferometer includes a beam splitter <NUM>, a fixed mirror <NUM>, a moving mirror <NUM>, and an actuator <NUM> (e.g., an electrostatic MEMS actuator) coupled to the moving mirror <NUM>. In addition, one or more guiding structures <NUM> and <NUM> may be etched in the substrate <NUM> (e.g., via a DRIE process) to couple the MEMS interferometer <NUM> to the ATR element <NUM> and microfluidic channel <NUM>. Each guiding structure <NUM> and <NUM> may be a Si-air interface.

In the examples shown in <FIG>, input light <NUM> may be coupled into the compact ATR spectrometer <NUM>. In some examples, the integrated spectral sensing device may include a second substrate (not shown) containing one or more light redirecting elements (e.g., molded free-space reflectors), as shown in <FIG>, coupled to the substrate <NUM>. The input light <NUM> may be directed from the molded free-space reflector(s) to the MEMS interferometer <NUM>, where the optical path difference is varied between the two paths of the fixed mirror <NUM> and the moving mirror <NUM> using the actuator <NUM> to produce an interference beam <NUM>. The interference beam <NUM> may then be directed to the channel interface <NUM> between the ATR element <NUM> and the microfluidic channel <NUM> via the guiding structure <NUM>. The guiding structure <NUM> is designed to produce an incident angle of the interference beam <NUM> on the channel interface <NUM> greater than the critical angle of Si-sample channel interface <NUM> to produce total internal reflection of the interference beam <NUM> at the channel interface <NUM>.

In the example shown in <FIG>, the interference beam <NUM> is subjected to a single total internal reflection and the resulting evanescent wave in the sample <NUM> attenuates the interference beam <NUM> to produce output light <NUM> that may be directed to a detector (not shown) via an output of the compact ATR spectrometer <NUM>. In some examples, the reflected output light <NUM> carrying the information from the sample <NUM> may be collected by an output light redirecting element (e.g., molded in a second substrate coupled to the substrate <NUM>) after refraction at the output of the compact ATR spectrometer <NUM>. The output light redirecting element may redirect the output light <NUM> to the detector, as shown in <FIG>. In the example shown in <FIG>, multiple total internal reflections of the interference beam <NUM> are achieved by using the additional guiding structure <NUM>. The guiding structure <NUM> is designed to produce an incidence angle of the interference beam <NUM> above the internal reflection critical angle at each reflection.

<FIG> is a diagram illustrating another example of a compact ATR spectrometer <NUM> of an integrated spectral sensing device according to some aspects. The compact ATR spectrometer <NUM> includes a spectrometer <NUM>, an ATR element <NUM>, and two opposing microfluidic channels 808a and 808b integrated on a same substrate <NUM>. The substrate <NUM> may be, for example, a silicon or SOI substrate. The microfluidic channels 808a and 808b each include a sample <NUM> (e.g., a fluid) that flows through the microfluidic channels 808a and 808b between respective input and output microfluidic ports <NUM> thereof.

Typically, the sample <NUM> is measured from one side of the ATR crystal in either macro-ATR or micro-ATR. However, the in-plane design of the multi-substrate integrated spectral sensing device shown in <FIG> or the compact ATR spectrometer shown in <FIG> and <FIG> allows inserting the sample on both sides of the ATR element <NUM> by trapping the light between the two microfluidic channels 808a and 808b while preserving the incident angle higher than the critical angle. This design increases the ATR sensitivity due to the higher number of reflections that may be achieved.

The sample <NUM> flows adjacent to a respective boundary 830a and 830b between the corresponding microfluidic channels 808a and 808b and the ATR element <NUM>. Each of the boundaries 830a and 830b corresponds to a respective channel interface between the ATR element <NUM> and the respective microfluidic channels 808a and 808b and may be formed by a respective surface of the ATR element <NUM> against which the sample <NUM> is in contact. For example, the channel interfaces 830a and 830b may each correspond to a Si-air/Si-sample interface.

The spectrometer <NUM> is a deeply etched micromachined MEMS interferometer. The MEMS interferometer includes a beam splitter <NUM>, a fixed mirror <NUM>, a moving mirror <NUM>, and an actuator <NUM> (e.g., an electrostatic MEMS actuator) coupled to the moving mirror <NUM>. In addition, a guiding structure <NUM> may be etched in the substrate <NUM> to couple the MEMS interferometer <NUM> to the ATR element <NUM> and microfluidic channels 808a and 808b. The guiding structure <NUM> may be a Si-air interface.

In the example shown in <FIG>, input light <NUM> may be coupled into the compact ATR spectrometer <NUM>. In some examples, the integrated spectral sensing device may include a second substrate (not shown) containing one or more light redirecting elements (e.g., molded free-space reflectors), as shown in <FIG>, coupled to the substrate <NUM>. The input light <NUM> may be directed from the molded free-space reflector(s) to the MEMS interferometer <NUM>, where the optical path difference is varied between the two paths of the fixed mirror <NUM> and the moving mirror <NUM> using the actuator <NUM> to produce an interference beam <NUM>. The interference beam <NUM> may then be directed to the ATR element <NUM> and the microfluidic channels 808a and 808b via the guiding structure <NUM>. The guiding structure <NUM> is designed to produce an incident angle of the interference beam <NUM> on the channel interface 830a greater than the critical angle of Si-sample channel interface 830a to produce multiple total internal reflections of the interference beam <NUM> within the ATR element <NUM> between the channel interfaces 830a and 830b.

The multiple total internal reflections of the interference beam <NUM> produces an evanescent wave in the sample <NUM> that attenuates the interference beam <NUM> to produce output light <NUM> that may be directed to a detector (not shown) via an output of the compact ATR spectrometer <NUM>. In some examples, the resulting output light <NUM> carrying the information from the sample <NUM> may be collected by an output light redirecting element (e.g., molded in a second substrate coupled to the substrate <NUM>) after refraction at the output of the compact ATR spectrometer <NUM>. The output light redirecting element may redirect the output light <NUM> to the detector, as shown in <FIG>.

<FIG> is a diagram illustrating an example of an integrated spectral sensing device <NUM> including a compact ATR spectrometer <NUM> according to some aspects. The spectral sensing device <NUM> includes a first substrate <NUM> and a second substrate <NUM>. The first substrate <NUM> includes the compact ATR spectrometer <NUM>. The second substrate <NUM> may include one or more light redirecting elements <NUM> and <NUM> formed therein. For example, the light redirecting elements <NUM> and <NUM> may be curved reflectors (e.g., micro-reflectors or micromirrors). In some examples, the light redirecting elements <NUM> and <NUM> may be fabricated in molded parts of the second substrate <NUM> with an aluminum metallic coating to improve the reflectivity thereof.

The integrated spectral sensing device <NUM> may further include a package substrate <NUM>. The first substrate <NUM> may be positioned on (e.g., bonded to) the package substrate <NUM>. In addition, the second substrate <NUM> may be positioned over the first substrate <NUM> and bonded to the package substrate <NUM> at respective ends of the second substrate <NUM>. A detector <NUM> may further be positioned on the package substrate <NUM>. Each of the substrates <NUM> and <NUM> may be, for example, a silicon or SOI substrate. In some examples, the second substrate <NUM> may be a plastic or glass substrate formed using injection molded optics technology.

The compact ATR spectrometer <NUM> includes a spectrometer <NUM>, an ATR element <NUM>, and two opposing microfluidic channels 920a and 920b integrated on the first substrate <NUM>. The microfluidic channels 920a and 920b each include a sample <NUM> (e.g., a fluid) that flows through the microfluidic channels 920a and 920b between respective input and output microfluidic ports <NUM> thereof. The sample <NUM> flows adjacent to a respective boundary 922a and 922b between the corresponding microfluidic channels 920a and 920b and the ATR element <NUM>. Each of the boundaries 922a and 922b corresponds to a respective channel interface between the ATR element <NUM> and the respective microfluidic channels 920a and 920b. For example, the channel interfaces 922a and 922b may each correspond to a Si-air/Si-sample interface.

The spectrometer <NUM> is a deeply etched micromachined MEMS interferometer. The MEMS interferometer includes a beam splitter <NUM>, a fixed mirror <NUM>, a moving mirror <NUM>, and an actuator <NUM> (e.g., an electrostatic MEMS actuator) coupled to the moving mirror <NUM>. In addition, a guiding structure <NUM> may be etched in the substrate <NUM> to couple the MEMS interferometer <NUM> to the ATR element <NUM> and microfluidic channels 920a and 920b. The guiding structure <NUM> may be a Si-air interface.

In the example shown in <FIG>, input light <NUM> may be coupled into the compact ATR spectrometer <NUM> via the light redirecting element <NUM>. For example, the light redirecting element <NUM> may receive the input light <NUM> in an out-of-plane direction with respect to a plane of the first substrate <NUM> and to direct the input light <NUM> towards the first substrate <NUM> (e.g., redirect/reflect the input light <NUM> by <NUM> degrees towards the first substrate <NUM>). The input light <NUM> may be refracted at an input to the compact ATR spectrometer <NUM> to impinge on the channel interface 922b between the microfluidic channel 920b and the ATR element <NUM> at an angle of incidence that is higher than a critical angle (e.g., the critical angle of the Si-sample interface of channel interface 922b) to produce multiple total internal reflections of the input light <NUM> through the ATR element <NUM> between the microfluidic channels 920a and 920b. The input light <NUM> is attenuated by respective evanescent waves formed within the sample <NUM> contained within each of the microfluidic channels 920a and 920b. The attenuated input light is then output from the ATR element <NUM> as output light <NUM> and is refracted towards an input of the MEMS interferometer <NUM> via the guiding structure <NUM>.

Within the MEMS interferometer <NUM>, the optical path difference is varied between the two paths of the fixed mirror <NUM> and the moving mirror <NUM> using the actuator <NUM> to produce an interference beam (interference pattern) <NUM> based on the output light <NUM>. The interference beam <NUM> output by the MEMS interferometer <NUM> is redirected by the light redirection element <NUM> towards the detector <NUM> to obtain a spectrum of the sample <NUM> within the microfluidic channels 920a and 920b. For example, the light redirection element <NUM> may be a curved reflector configured to focus the interference beam <NUM> to the active area of the detector <NUM>.

In ATR spectroscopy, the light penetration depth inside the sample for a single reflection is given in Equation (Equation <NUM>), where dp, λ, θ, n<NUM> and n<NUM> are the penetration depth, wavelength of radiation, incident angle, ATR crystal refractive index and sample refractive index. Hence, the light incidence angle and number of reflections inside the crystal may be selected based on the application and measured absorption peaks.

In some applications, a small ATR penetration depth is preferable to reduce strong water infrared absorption that may totally block light. However, in other applications, an enhanced effective interaction length between the infrared light and the sample may enhance absorption of weak infrared (IR) signals above the noise level of the spectrometer. Examples of such applications include, but are not limited to, oil analysis and biological samples sensing where samples are commonly dried before measuring them using IR spectroscopy. While increasing the number of reflections by increasing the ATR crystal length or reducing the ATR thickness may enhance IR absorption, there may be limitations on the length, due to limited design area and fabrication difficulties, and on the thickness, due to beam truncation at the input and output interfaces that affects optical throughput of the device.

The in-plane ATR element designs shown in <FIG> above allow forming ATR IREs with the desired shape and dimensions depending on the measured sample. Hence, the incidence angle and number of reflections may be adapted in the design. In addition, ATR crystals may be designed to enhance the effective path length by increasing the number of reflections without changing the crystal dimensions. These designs may allow for different implementations of the ATR substrate or compact ATR spectrometer using different optical designs for the molded light redirecting element(s).

<FIG> is a diagram illustrating an example of an ATR element design according to some aspects. The ATR element design shown in <FIG> is a multi-path ATR element design that enables a longer path length to be obtained in the same area. Increasing the effective path length may further increase the absorbance of the sample without any loss in power and signal to noise ratio. However, there may be bending losses (of the light) that cause power loss and affect the spectrometer's detection limits. Hence, the ATR element design shown in <FIG> may be optimized to minimize the bending losses, while enhancing the absorption due to a higher number of reflections.

The ATR element design includes a substrate <NUM> having an ATR element <NUM> and microfluidic channels 1006a and 1006b formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

The microfluidic channels 1006a and 1006b each include a sample (e.g., a fluid) that flows through the microfluidic channels 1006a and 1006b between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to a respective channel interface 1008a and 1008b between the corresponding microfluidic channels 1006a and 1006b and the ATR element <NUM>. For example, the channel interfaces 1008a and 1008b may each correspond to a Si-air/Si-sample interface.

In the example shown in <FIG>, the ATR element <NUM> has a waveguide pattern formed by the channel interfaces 1008a and 1008b. The waveguide pattern includes an array of parallel waveguides <NUM> optically coupled at respective ends <NUM> thereof. As such, input light <NUM> incident on the channel interface 1008b at an angle greater than the critical angle of the Si-sample channel interface 1008b is reflected via total internal reflection through the waveguide pattern of parallel waveguides <NUM> to produce output light <NUM>. The output light <NUM> is attenuated by an evanescent wave formed in the sample based on the total internal reflected input light <NUM>.

<FIG> is a diagram illustrating another example of an ATR element design according to some aspects. The ATR element design includes a substrate <NUM> having an ATR element <NUM> and microfluidic channels 1106a and 1106b formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

The microfluidic channels 1106a and 1106b each include a sample (e.g., a fluid) that flows through the microfluidic channels 1106a and 1106b between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to a respective channel interface 1108a and 1108b between the corresponding microfluidic channels 1106a and 1106b and the ATR element <NUM>. For example, the channel interfaces 1108a and 1108b may each correspond to a Si-air/Si-sample interface.

The ATR element design shown in <FIG> is based on inputting two IR beams 1112a and 1112b to the ATR element <NUM> using V-shaped input and output interfaces <NUM> and <NUM>, respectively. The two input beams 1112a and 1112b may originate from two IR sources or a single light source with a beam splitter and coupling optics (e.g., onchip or external optical reflectors) that reflect the input beams 1112a and 1112b to the V-shaped input interface <NUM>. For example, the V-shaped input interface <NUM> is configured to receive a first input beam 1112a and direct the first input beam 1112a towards a first channel interface 1108a at an angle higher than the critical angle to produce total internal reflection of the first input beam 1112a through the ATR element <NUM> between the channel interfaces 1108a and 1108b. The V-shaped interface <NUM> is further configured to receive a second input beam 1112b and direct the second input beam 1112b towards a second channel interface 1108b at an angle higher than the critical angle to produce total internal reflection of the first input beam 1112a through the ATR element between the channel interfaces 1108a and 1108b.

Each input light beam 1112a and 1112b is attenuated by respective evanescent waves formed within the sample contained within each of the microfluidic channels 1106a and 1106b. The attenuated input light beams are then output from the ATR element <NUM> as output light beams 1114a and 1114b via the V-shaped output interface <NUM>. For example, a first output beam 1114a produced from total internal reflection of the first input beam 1112a may be output from the second channel interface 1108b via the V-shaped output interface <NUM>. In addition, a second output beam 1114b produced from total internal reflection of the second input beam 1112b may be output from the first channel interface 1108a via the V-shaped output interface <NUM>. The output beams 1114a and 1114b may be focused by reflectors 1116a and 1116b onto the spectrometer. For example, the V-shaped output interface <NUM> may be configured to direct the first output beam 1114a to a first reflector 1116a and the second output beam 1114b to a second reflector 1116b for combination of the first and second output light beams 1114a and 1114b to produce output light <NUM> that is focused onto the spectrometer input.

In the ATR element design shown in <FIG>, the number of internal reflections is doubled inside the ATR element <NUM>. In some examples, the IR beam spot size may be smaller than input interface <NUM>, i.e., no truncation at the input.

<FIG> are diagrams illustrating another example of an ATR element design according to some aspects. The ATR element design shown in <FIG> includes a substrate <NUM> having an ATR element <NUM> and microfluidic channels 1206a and 1206b formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

The microfluidic channels 1206a and 1206b each include a sample (e.g., a fluid) that flows through the microfluidic channels 1206a and 1206b between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to a respective channel interface 1208a and 1208b between the corresponding microfluidic channels 1206a and 1206b and the ATR element <NUM>. For example, the channel interfaces 1208a and 1208b may each correspond to a Si-air/Si-sample interface.

The ATR element design shown in <FIG> is based on having two light paths back and forth inside the ATR element <NUM>, while the input and output are on a single side of the ATR element <NUM>. For example, the ATR element <NUM> may include an input-output interface <NUM> on a first side thereof and a rear interface <NUM> on a second side thereof opposite the first side. The ATR element <NUM> is configured to receive input light <NUM> via the input-output interface <NUM>. The input light <NUM> may impinge a channel interface (e.g., channel interface 1208b) at an angle greater than the critical angle to produce total internal reflection of the input light <NUM> through the ATR element <NUM> between the channel interfaces 1208a and 1208b towards the rear interface <NUM>. The rear interface <NUM> may further be configured to reflect the input light via total internal reflection back through the ATR element <NUM> between the channel interfaces 1208a and 1208b to produce output light <NUM> that may be output via the input-output interface <NUM>. The output light <NUM> is attenuated by an evanescent wave formed in the sample based on the total internal reflected input light <NUM>.

The ATR element design shown in <FIG> increases the number of reflections within the same ATR element length. As further illustrated in <FIG>, the two light paths (back and forth) in the ATR element <NUM> may be achieved using two different face angles (θ, ϕ), one on either side of the ATR element. For example, the input-output interface <NUM> may have a first face angle θ, and the rear interface <NUM> may have a second face angle ϕ. The first face angle θ may be configured to produce the total internal reflection of the input light <NUM> at a channel interface (e.g., channel interface 1208b) of the ATR element <NUM> when the input light is incident normal to the input-output interface <NUM>. The second face angle may be configured to produce total internal reflection of the input light <NUM> at the rear interface <NUM> and the other channel interface (e.g., channel interface 1208a) of the ATR element. In addition, the second face angle may be configured to produce refraction of the output light <NUM> at the input-output interface <NUM>.

Thus, the first face angle (input-output face angle (θ)) is higher than the critical angle of the channel interface 1208b (e.g., the interface between the ATR element <NUM> and the sample) as follows: <MAT> where n<NUM> and n<NUM> are the ATR element refractive index and sample refractive index, respectively. In addition, the second face angle (rear face angle (ϕ)) is configured to ensure total internal reflection of light on the rear interface <NUM> as follows: <MAT> where nair is the air refractive index.

Furthermore, the rear face angle (ϕ) is further configured to ensure total internal reflection of light on the channel interfaces 1208a and 120b while light is reflecting back through the ATR element <NUM> as follows: <MAT>.

Moreover, the rear face angle (ϕ) is further configured to ensure refraction of the light on the input-output interface <NUM> as follows: <MAT>.

Thus, the output light <NUM> can be deflected from the direction of the input light <NUM> with an angle that depends on the rear face angle as follows: <MAT>.

<FIG> is a diagram illustrating another example of an ATR element design according to some aspects. The ATR element design shown in <FIG> is based on total internal reflection and interaction between light and the measured sample on four faces of the ATR element. In this ATR element design, the ATR element is fabricated using a geometry that has face angles on both side walls in addition to the input and output interfaces.

The ATR element design includes a substrate <NUM> having an ATR element <NUM> and microfluidic channels 1306a and 1306b formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

The microfluidic channels 1306a and 1306b each include a sample (e.g., a fluid) that flows through the microfluidic channels 1306a and 1306b between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to a respective channel interface 1308a and 1308b between the corresponding microfluidic channels 1306a and 1306b and the ATR element <NUM>. For example, the channel interfaces 1308a and 1308b may each correspond to a Si-air/Si-sample interface. In the example shown in <FIG>, the channel interfaces 1308a and 1308b are inclined sidewalls of the substrate <NUM>. For example, an additional etching step may be added to the DRIE process used in the MEMS spectrometer's fabrication procedure, such as anisotropic KOH etching, to create the inclined sidewalls.

The inclined sidewalls forming the channel interfaces 1308a and 1308b produce a light path <NUM> having a helical shape in the ATR element <NUM> in three dimensions instead of multiple reflections in a conventional single 2D plane. For example, the ATR element <NUM> may be configured to receive input light <NUM> at an incidence angle higher than the critical angle of one of the inclined sidewalls (e.g., channel interface 1308b) and to reflect the input light <NUM> via total internal reflection through the ATR element <NUM> in a helical manner such that the input light <NUM> is reflected off both of the inclined sidewalls (e.g., channel interfaces 1308a and 1308b) and the top and bottom surfaces of the ATR element <NUM> to produce output light <NUM> attenuated by the evanescent wave formed in the sample.

In some examples, an additional microfluidic channel <NUM> including the sample may be inserted above the substrate <NUM> (e.g., on a top surface <NUM> of the substrate <NUM>) to take advantage of added reflections. For example, a microfluidic PDMS device <NUM> may be bonded on the top surface <NUM> of substrate <NUM>. In this ATR element design, the input light <NUM> propagates not only parallel to the substrate <NUM>, but also reflects back from the upper silicon interface with the PDMS device <NUM>.

<FIG> is a diagram illustrating another example of an ATR element design according to some aspects. The ATR element design shown in <FIG> provides a variable number of internal reflections to support different target applications. The ATR element design includes a substrate <NUM> having an ATR element <NUM> and a plurality of sets of opposing microfluidic channels (e.g., a first set of opposing microfluidic channels 1406a and 1406b, a second set of opposing microfluidic channels 1406c and 1406d, and a third set of opposing microfluidic channels 1406e and 1406f) formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

One or more of the sets of microfluidic channels 1406a/1406b, 1406c/1406d, and/or 1406e/1406f may include a sample (e.g., a fluid) that flows through the microfluidic channels between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to respective channel interfaces 1408a/1408b, 1408c/1408d, and/or 1408e/1408f between the corresponding microfluidic channels 1406a/1406b, 1406c/1406d, and/or 1406e/1406f and the ATR element <NUM>. For example, the channel interfaces 1408a-1408f may each correspond to a Si-air/Si-sample interface.

Since the optimum ATR effective penetration depth depends directly on the target application and measured sample IR absorption level, the ATR element <NUM> may be configured as a stepped waveguide having different respective widths 1416a, 1416b, and 1416c between the opposing microfluidic channels of each of the sets of opposing microfluidic channels 1406a/1406b, 1406c/1406d, and 1406e/1406f. The number of reflections is a function of the width 1416a, 1416b, and 1416c as follows: <MAT> where N is the number of internal reflections, θ is the incident angle, and L and W are the ATR element length and width. Wide ATR elements may be used for strongly absorbing materials, while narrow ATR elements may be used for weakly absorbing materials.

Thus, the ATR element stepped waveguide design shown in <FIG> may be used to measure different types of samples. For example, a strongly absorbing sample may be inserted into the microfluidic channels 1406a and 1406b that have a larger ATR width 1416a therebetween. Input light <NUM> incident on the channel interface 1408b at an angle greater than the critical angle of the Si-sample channel interface 1408b is reflected via total internal reflection through the ATR element <NUM> between channel interfaces 1408a and 1408b and between Si-air channel interfaces 1408c/1408d and 1408e/1408f to produce output light <NUM>. The output light <NUM> is attenuated by an evanescent wave formed in the sample within microfluidic channels 1406a and 1406b based on the total internal reflected input light <NUM>. Samples having weaker absorption properties may similarly be measured using the second set of microfluidic channels 1406c/1406d or the third set of microfluidic channels 1406e/1406f.

<FIG> is a diagram illustrating another example of an ATR element design according to some aspects. The ATR element design shown in <FIG> also provides a variable number of internal reflections to support different target applications. The ATR element design includes a substrate <NUM> having an ATR element <NUM> and a plurality of sets of opposing microfluidic channels (e.g., a first set of opposing microfluidic channels 1506a and 1506b and a second set of opposing microfluidic channels 1506c and 1506d) formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

One or more of the sets of microfluidic channels 1506a/1506b and/or 1506c/1506d may include a sample (e.g., a fluid) that flows through the microfluidic channels between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to respective channel interfaces 1508a/1508b and/or 1508c/1508d between the corresponding microfluidic channels 1506a/1506b and/or 1506c/1506d and the ATR element <NUM>. For example, the channel interfaces 1508a-1508d may each correspond to a Si-air/Si-sample interface.

The ATR element <NUM> shown in <FIG> is configured as a tapered waveguide with a linearly varying ATR width <NUM> between the microfluidic channels 1506a/1506b and 1506c/1506d. In this example, the incident angle may change through the ATR element <NUM> due to tapering; however, the ATR element design can preserve the incident angle above the critical angle of the Si-air (or Si-sample) interface. As in the example shown in <FIG>, wider ATR widths may be used for strongly absorbing samples, while narrower widths may be used for weakly absorbing samples. For example, a weakly absorbing sample may be inserted into the second set of microfluidic channels 1506c and 1506d. Input light <NUM> incident on the channel interface 1508b at an angle greater than the critical angle of the Si-air channel interface 1508b is reflected via total internal reflection through the ATR element <NUM> between the Si-air channel interfaces 1508a and 1508b and between the Si-sample channel interfaces 1508c and 1508d to produce output light <NUM>. The output light <NUM> is attenuated by an evanescent wave formed in the sample within microfluidic channels 1506c and 1506d based on the total internal reflected input light <NUM>.

<FIG> is a diagram illustrating another example of an ATR element design according to some aspects. The ATR element design shown in <FIG> also provides a variable number of internal reflections to support different target applications. The ATR element design includes a substrate <NUM> having an ATR element including a plurality of waveguides 1604a, 1604b, and 1604c and a plurality of sets of opposing microfluidic channels (e.g., a first set of opposing microfluidic channels 1606a and 1606b, a second set of opposing microfluidic channels 1606c and 1606d, and a third set of opposing microfluidic channels 1606e and 1606f) formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

One or more of the sets of microfluidic channels 1606a/1606b, 1606c/1606d, and/or 1606e/1606f may include a sample (e.g., a fluid) that flows through the microfluidic channels between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to respective channel interfaces 1608a/1608b, 1608c/1608d, and/or 1608e/1608f between the corresponding microfluidic channels 1606a/1606b, 1606c/1606d, and/or 1606e/1606f and the corresponding waveguide 1604a, 1604b, and/or 1604c. For example, the channel interfaces 1608a-1608f may each correspond to a Si-air/Si-sample interface.

Each of the ATR waveguides 1604a, 1604b, and 1604c may have different respective widths 1620a, 1620b, and 1620c configured to produce a different number of internal reflections. In addition, the ATR element design may further include moveable mirrors <NUM> and <NUM> formed in the substrate <NUM> (e.g., via a DRIE process with a metallization step). Each moveable mirror (e.g., input mirror <NUM> and output mirror <NUM>) may be coupled, for example, to a respective actuator (e.g., a MEMS actuator, such as an electrostatic comb drive actuator). In the example shown in <FIG>, two different actuators may be used since the input and output mirrors <NUM> and <NUM> are translated in two perpendicular directions due to the <NUM>-degree light deflection in the trapezoidal shaped ATR element design. If a parallelogram-shaped ATR element design is used, in which the light path may be translated without deflection, a single actuator may be used for both mirrors <NUM> and <NUM>.

According to the position of the moveable mirrors <NUM> and <NUM>, input light <NUM> may be reflected by the input mirror <NUM> towards a selected one of the ATR waveguides 1604a, 1604b, or 1604c with a desired number of reflections for the particular application (sample). The output light <NUM> produced based on the number of total internal reflections within the selected waveguide 1604a, 1604b, or 1604c may then be received by the output mirror <NUM> and reflected towards an output interface.

ATR analysis of micron-sized particles in liquids, such as microplastics in water, is typically challenged by the random distribution of particles across the liquid, which may be outside the vicinity of ATR effective penetration depth, accompanied by strong IR absorption in water. In various aspects of the disclosure, particle accumulation on the sidewalls of the ATR elements may be performed, by means of separating and sorting particles in microfluidic channels, to enter the evanescent field region of the guided modes outside the ATR crystal.

In some examples, Field Flow Fractionation (FFF) may be used for particle separation. In FFF, an external field of actuation is applied to force particles to move towards the sidewall in the direction of the applied field. Generally, the applied field could be electrically, thermally, gravitationally, or cross flow induced. Various other active separation mechanisms may also be used with the ATR design. For example, dielectrophoresis (DEP) can be used to electrically control translation of particles that are suspended in a fluid. In DEP, a suspended dielectric particle is exposed to a non-uniform electric field to polarize the particle, thereby causing the particle to move towards or away from regions of high electric field intensity. The strength and direction of the DEP force depends on the medium and the particle's electrical properties, the shape and size of the particle, and on the frequency and phase of the applied electric field.

<FIG> is a diagram illustrating another example of an ATR element design based on FFF according to some aspects. The ATR element design includes a substrate <NUM> having an ATR element <NUM> (e.g., a waveguide) and microfluidic channels 1706a and 1706b formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

The microfluidic channels 1706a and 1706b each include a sample (e.g., a fluid) that flows through the microfluidic channels 1706a and 1706b between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to a respective channel interface 1708a and 1708b between the corresponding microfluidic channels 1706a and 1706b and the ATR element <NUM>. For example, the channel interfaces 1708a and 1708b may each correspond to vertical sidewalls of the ATR element <NUM> forming a Si-air/Si-sample interface.

In the FFF ATR element design shown in <FIG>, an actuation field generator <NUM> formed of electrodes may further be positioned on the top surface of the substrate <NUM> adjacent to the microfluidic channels 1706a and 1706b to electrically induce an external actuation field <NUM>. The applied actuation field <NUM> is configured to cause microparticles <NUM> in the sample to move to the sidewalls (e.g., the channel interfaces 1708a and 1708b) of the ATR element <NUM>. The microparticles <NUM> accumulated on the sidewalls interact with an evanescent wave produced based on total internal reflection of input light <NUM> through the ATR element <NUM> to produce output light <NUM> attenuated by the evanescent wave.

<FIG> is a diagram illustrating another example of an ATR element design based on DEP according to some aspects. The ATR element design includes a substrate <NUM> having an ATR element <NUM> (e.g., a waveguide) and microfluidic channels 1806a and 1806b formed therein (e.g., via a DRIE process). The substrate may be, for example, a silicon or SOI substrate. In some examples, the spectrometer may be formed on the same substrate <NUM> as the ATR element <NUM>, as shown in <FIG>, or on a different, separate substrate, as shown in <FIG>.

The microfluidic channels 1806a and 1806b each include a sample (e.g., a fluid) that flows through the microfluidic channels 1806a and 1806b between respective input and output microfluidic ports <NUM> thereof. The sample flows adjacent to a respective channel interface 1808a and 1808b between the corresponding microfluidic channels 1806a and 1806b and the ATR element <NUM>. For example, the channel interfaces 1808a and 1808b may each correspond to vertical sidewalls of the ATR element <NUM> forming a Si-air/Si-sample interface.

In the DEP ATR element design shown in <FIG>, an actuation field generator <NUM> formed of an interdigitated electrode system may further be over the substrate <NUM> to electrically induce a non-uniform electric field. The interdigitated electrode system <NUM> produces a large value of an electric field gradient using modest values of applied voltage. In the example shown in <FIG>, the interdigitated electrodes <NUM> may be applied to a backside of a glass substrate <NUM> using, for example, lithography techniques. The glass substrate <NUM> may then be bonded to the top of silicon substrate <NUM> that includes the ATR element <NUM>. The electrodes <NUM> with applied AC voltage provide the DEP force to trap microparticles below the center of the electrodes <NUM>. The electrodes <NUM> may be positioned with respect to the microfluidic channels 1806a and 1806b such that the microparticles in the sample are aggregated towards the sidewalls (e.g., channel interfaces 1808a and 1808b) in the vicinity of the light interaction region.

Thus, the applied actuation field is configured to cause microparticles in the sample to move to the sidewalls (e.g., the channel interfaces 1808a and 1808b) of the ATR element <NUM>. The microparticles accumulated on the sidewalls interact with an evanescent wave produced based on total internal reflection of input light <NUM> through the ATR element <NUM> to produce output light <NUM> attenuated by the evanescent wave.

Claim 1:
An integrated spectral sensing device, comprising:
a first substrate (<NUM>) comprising an attenuated total internal reflection ATR, element (<NUM>), a microfluidic channel (<NUM>), and a channel interface (<NUM>) corresponding to a boundary between the ATR element (<NUM>) and the microfluidic channel (<NUM>) formed therein, the ATR element (<NUM>) configured to receive input light (<NUM>) and to produce output light (<NUM>) based on total internal reflection of the input light at the channel interface (<NUM>), the output light (<NUM>) being attenuated by an evanescent wave produced by a sample (<NUM>) contained within the microfluidic channel (<NUM>) based on the total internal reflection of the input light;
a spectrometer (<NUM>) configured to produce an interference beam (<NUM>), the interference beam (<NUM>) corresponding to the input light or being produced based on the output light; and
a detector (<NUM>) configured to detect a spectrum of the interference beam (<NUM>) or the output light (<NUM>);
characterized in that the channel interface (<NUM>) is formed at sidewalls (1708a, 1708b) of the ATR element (<NUM>).