Patent Grant
11624707
This application claims the priority benefit of European Patent Application Number 20171655.2, filed Apr. 27, 2020, the disclosure of which is incorporated herein by reference in its entirety.
An optical spectrometer is an apparatus used to measure properties of light over a specific portion of an electromagnetic spectrum. An optical spectrometer can be used to perform spectroscopic analysis of investigated materials.
When a light beam hits material it does interact with material in a specific way, dependent on the interplay between the light waves and the atoms and molecules that make up the respective matter. Interaction can leave the energy of matter light unchanged (e.g. refraction, reflection or elastic scattering) or can lead to an energy exchange between both. Interaction between light and investigated matter can be used in spectroscopy to characterize the respective matter. Accordingly, spectroscopy is the study of interaction between matter and light. There are different types of spectroscopy which are typically named after either the used light source or the process of light matter interaction exploited.
For example, Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. Laser light generated by a laser light source interacts with molecular vibrations resulting in the energy of the laser photons being shifted up or down. The shift in energy provides information about the vibrational modes on the investigated matter. Typically, a sample is illuminated with a laser beam. An electromagnetic radiation from the illuminated spot can be collected. Elastic scattered radiation at the wavelength corresponding to the laser line (Rayleigh scattering) is filtered out by a filter where the rest of the collected light is dispersed onto a detector. However, Raman signals are inherently weak, especially when using visible light excitation and consequently only a low number of scattered photons are available for detection. A conventional method to amplify weak Raman signals is to employ Surface-Enhanced Raman Scattering (SERS). SERS uses nanoscale roughened metal surfaces that are typically made of gold (Au) or silver (Ag). Laser excitation of these roughened metal nanostructures resonantly drive the surface charges creating a highly localized (plasmonic) light field. When a molecule is absorbed or lies close to the enhanced field at the surface, a large enhancement in the Raman signal can be observed. Raman signals several orders of magnitude greater than normal Raman scattering are common, thereby making it possible to detect even low concentrations without the need for fluorescent labeling. A Raman signal can be amplified further when the roughened metal surface is used in combination with laser light that is matched to the absorption maxima of the molecule. This effect is also known as Surface-Enhanced Resonance Raman Scattering (SERRS).
SERS and other spectroscopic techniques can be used to detect various inorganic and organic substances, partially with high resolution and high sensitivity. Several of these conventional techniques have been implemented using fiber optic sensors. However, conventional spectroscopic apparatuses and methods rely on broadband spectrometers (fluorometers) and possibly broadband tunable excitation lasers to provide flexible measurement equipment. Accordingly, these conventional devices and methods are quite complex and they involve sophisticated hardware.
Accordingly there is a need to provide a method and apparatus which allow reliable spectrometric measurements of investigated materials which are easy to implement and which require a less complex hardware equipment.
The invention provides according to a first aspect an apparatus adapted to perform spectrometric measurements, said apparatus comprising:
a tunable laser light source adapted to generate a laser light with an excitation wavelength supplied to an optical sensor which produces a sample specific response light signal,
an optical reference filter adapted to measure laser light with the excitation wavelength fed back as a reference signal to provide wavelength calibration of the tunable laser light source,
at least one optical measurement filter adapted to measure the sample specific response light signal produced by the optical sensor,
wherein the optical reference filter and the at least one optical measurement filter are thermally coupled to maintain a constant wavelength relationship between the filter characteristics of the optical filters.
The apparatus according to the first aspect of the present invention does not form a broadband flexible spectrometer but uses a single or very few measurement filters instead. This is combined with certain limited excitation laser tunability sufficient to cover a few specific spectral peaks for being able to detect and discriminate different substances. Further, the apparatus according to the first aspect of the present invention comprises a temperature self-calibration.
In a possible embodiment of the apparatus according to the first aspect of the present invention, the optical reference filter and the at least one optical measurement filter are thermally coupled to provide a temperature drift self-calibration.
This can be achieved by using filters that belong to one thermal group, i.e. they are subject to similar temperature and related drift. That is, the filters can have a set/known passband difference. Further, this difference does not change significantly over a reasonable temperature range.
In a possible embodiment of the apparatus according to the first aspect of the present invention, the apparatus comprises at least one photo detector adapted to convert the sample specific excited response light signal into an electrical sample specific response signal supplied by the photo detector to a controller of the apparatus adapted to analyze the received electrical sample specific response signal to provide analytical results.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the controller is further adapted to control a tuning unit provided for tuning the excitation wavelength of the tunable laser light source.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the tuning unit comprises a thermal electric cooler attached to the tunable laser light source.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the apparatus comprises an optical coupling and splitting unit adapted to supply the laser light with the excitation wavelength generated by the tunable laser light source to the optical sensor and to supply the sample specific excited response light signal produced by the optical sensor to the photo detector of said apparatus.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the optical sensor is adapted to provide a sample specific response signal with wavelength shifts or based on reflections.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, if the optical sensor is adapted to provide a sample specific response signal based on reflections, the controller of the apparatus is adapted to control the tuning unit to tune the laser light source in predefined wavelength increments.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the wavelength increment corresponds to a peak wavelength difference between the peak wavelength of the optical reference filter and the optical measurement filter or corresponds to a peak wavelength difference between peak wavelengths of two optical measurement filters with neighboring passband frequency bands.
In a possible embodiment of the apparatus according to the first aspect of the present invention, the optical filters are formed by liquid crystal filters.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the optical filters are formed by thin film filters.
In a still further possible embodiment of the apparatus according to the first aspect of the present invention, the optical filters are formed by Mach-Zehnder interferometers.
In a still further possible embodiment of the apparatus according to the first aspect of the present invention, the optical filters are formed by fiber Bragg gratings integrated in the optical sensor.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the optical sensor adapted to provide a sample specific excited response signal with wavelength shifts comprises a Surface-Enhanced Raman Spectroscopy, SERS, sensor.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the optical sensor adapted to produce a sample specific excited response signal with wavelength shifts comprises a Tip-Enhanced Raman Spectroscopy, TERS, sensor.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the optical sensor adapted to produce a sample specific excited response signal comprises an optrode which operates reflectively analytic specific (i.e. without wavelength shift).
In a still further possible embodiment of the apparatus according to the first aspect of the present invention, the optical sensor adapted to produce a sample specific excited response signal with wavelength shifts comprises an optrode sensor.
In a still further possible embodiment of the apparatus according to the first aspect of the present invention, the apparatus further comprises at least one monitoring photo diode adapted to generate a signal used by the controller of the apparatus to perform a power calibration of the tunable laser light source.
In a still further possible embodiment of the apparatus according to the first aspect of the present invention, the apparatus further comprises a user interface connected to the controller and comprising a display unit adapted to display analytical results calculated by the controller of the apparatus.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the apparatus is integrated in a handheld device.
In a further possible embodiment of the apparatus according to the first aspect of the present invention, the apparatus is adapted to perform SARS-CoV-2 detection.
The invention provides according to the second aspect a method for performing spectrometric measurements, comprising the steps of:
supplying a laser light generated by a tunable laser light source with an excitation wavelength to an optical sensor which produces a sample specific response light signal, measuring by an optical reference filter the laser light with the excitation wavelength and feeding it back as a reference signal to provide wavelength calibration of the tunable laser light source,
measuring by an optical measurement filter the sample specific response light signal produced by the optical sensor and coupling thermally the optical reference filter and the measurement filter to maintain a stable wavelength relationship between the filter characteristics of the optical filters.
In the following, possible embodiments of the different aspects of the present invention are described in more detail with reference to the enclosed figures.
As can be seen from the embodiment illustrated in
The photo detector 5 of the apparatus 1 is adapted to convert the sample specific excited response light signal received via the measurement filter 6 into an electrical sample specific response signal supplied by the photo detector 5 to a controller 8 of the apparatus 1. The controller 8 is adapted to analyze the received electrical sample specific response signal to provide analytical results. The controller 8 is further adapted to control a tuning unit 9 provided for tuning the excitation wavelength λTX of the tunable laser light source 3. In a possible implementation as illustrated in
The apparatus 1 can further comprise as illustrated in
In the embodiment illustrated in
As illustrated in the block diagram of
The optical filters 6, 7 implemented in the apparatus 1 shown in the block diagram of
The coupling and splitting unit 4 of the apparatus 1 can comprise a directional fused fiber coupler with or without an asymmetric power ratio. The coupling and splitting unit 4 can further be formed by a circulator. In a still further possible implementation, the coupling and splitting unit 4 comprises a wavelength selective fiber coupler. The measurement filters 6 and the reference filter 7 allow relative wavelength calibration. Consequently, the respective spectroscopic techniques do not rely on absolute wavelength knowledge. With the apparatus 1 as illustrated in the embodiment of
Accordingly, in a possible implementation, the apparatus 1 according to the first aspect of the present invention can be a handheld spectroscopic device to which a wide range of different optical sensors 2 can be coupled investigating different materials of samples. This handheld spectroscopic device or apparatus 1 can also be used for detection of a specific virus such as SARS-CoV-2.
The Raman shift is the energy difference between the incident laser light and the scattered detected light. This energy difference is connected to the energetic properties of the molecular vibrations of the investigated sample and hence independent of the laser light wavelength. The Raman shift can be expressed in wave numbers. The count rate comprises a number of events the photo detector 5 does register for the respective Raman shift per second of detector integration. It can be a proportion to the intensity of the light imaged to the photo detector 5.
The identification performed by the controller 8 using spectroscopy can be carried out by using a comparison algorithm and a spectral database. Analytical results can be output to a user via a display unit of the user interface 12 as shown in the block diagram of
The optical reference filter 7 and the at least one measurement filter 6 are formed in a preferred embodiment by narrow bandpass filters BPFs which are used to pass (transmit) a range of wavelengths and to block (reflect) other wavelengths on either side of the bandpass filter range. The region of high transmittance is known as the passband and the region of high reflectance is known as the reject band or reflect band.
The passband and the reflect bands are separated by the role off region. The complexity of the bandpass filters depends on the steepness of the role off region, the width of the passband and also on the ripple and insertion loss specifications in the passband. Different embodiments and different implementations for the optical filters 6, 7 can be used. The optical filters 6, 7 may comprise liquid crystal filters, thin film filters or Mach-Zehnder interferometers.
The optical sensor 2 of the apparatus 1 is adapted to produce a sample specific response signal with wavelength shifts, e.g. because of Raman scattering. In an alternative embodiment, the optical sensor 2 can also operate based on reflections. In case that the optical sensor 2 is adapted to produce a sample specific response signal based on reflections, the controller 8 controls the tuning unit 9 which tunes the laser light source 3 in predefined wavelength increments. Wavelength increments can correspond to a peak wavelength difference between the peak wavelength of the optical reference filter 7 and the optical measurement filter 6. Further, the wavelength increment can also correspond to a peak wavelength difference between peak wavelengths of two optical measurement filters 6 having neighboring passband frequency bands.
The apparatus 1 can use different kinds of optical sensors 2 adapted to produce a sample specific excited response signal. Besides the Surface-Enhanced Raman Spectroscopy, SERS, sensor illustrated in
A group of target spectroscopic techniques does rely on wavelength shifts. This holds e.g. for SERS/TERS sensors and for FOCS and optrodes, which make use of fluorescence effects. Another technique makes use of interferometry. Interferometry is a technique in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference which can be used to extract information about investigated material. Spectroscopic techniques which rely on wavelength shifts may use an optical sensor having a sensor area which is coated with an analyte specific coating and is illuminated with a certain excitation wavelength. Wavelength requirements are not high because the analyte specificity results from the coating of the sensor area. It is also possible that several coating areas can be illuminated with different wavelengths so that a rough knowledge of the laser wavelength provided by the reference filter 7 is required.
In order to detect other characteristic spectral peaks, e.g. to make the analytic detection more unambiguous, the laser light source 3 is tuned incrementally by Δλi as shown in
In case that the sections of the measurement filters 6 produce direct reflections, a specific signal can be detected via related measurement filters 6 integrated in the optical sensor 2. If the passband peak difference between the reference frequency of the optical reference filter 7 and the at least one measurement filter 6 is preset by design and stable against temperature, a specific response signal can be detected without absolute laser wavelength knowledge if the laser light source 3 is referenced to the reference frequency of the optical reference filter 7. Even if the measurement filter 6 requires an absolute wavelength, for the reference filter 7 and the laser light source 3 only a relative wavelength is required.
The optical reference filter 7 and the at least one optical measurement filters 6 are thermally coupled to maintain a constant wavelength relationship. The thermal expansion coefficient TEC is about 0.5×10−6° C.−1 and is smaller by a factor of about 20 compared to the thermo-optic coefficient TOC which changes the refractive index n. For optical fibers, TOC is about 10×10−6° C.−1.
When an optical fiber is (homogeneously) temperature-shifted, the Bragg wavelengths λB of the different fiber Bragg gratings are shifted by the same temperature-induced factor which is negligible for reasonable wavelength increments between different fiber Bragg gratings. Otherwise, it can be considered by simple temperature measurement and applying a correction factor for the incremental tuning.
The temperature-induced AWG wavelength shift is:
For silica, dn/dT is in the range of 7.5×10−6/° C. and for silicon, α=2.6 ppm/° C., respectively. Further, L is the path length in the array. Accordingly, a silica-on-silicon device hence has a wavelength drift (red shift) of dλ/dT of about 12 pm/° C. (at a wavelength of 1550 nm). The difference between two filter passbands is in the same order of magnitude as for the fiber Bragg gratings FBG.
In a first step SA, the laser light is generated by the tunable laser light source 3 with an excitation wavelength λTx supplied to an optical sensor 2 which produces a sample specific response light signal.
In a further step SB, the laser light with the excitation wavelength is measured by an optical reference filter 7 and fed back as a reference signal to provide wavelength calibration of the tunable laser light source 3.
In a further step SC, the sample specific response light signal produced by the optical sensor 2 is measured by at least one optical measurement filter 6.
During the measurements in step SB, SC, the optical reference filter 7 and the measurement filter 6 are thermally coupled to maintain a stable wavelength relationship between the filter characteristics of the optical filters 6, 7. This is illustrated as step SD in the simplified flowchart of
In a further step S1, the tunable laser light source 3 is tuned to the optical reference filter 7 using the feedback signal provided by the reference filter 7. The laser light with the excitation wavelength can be fed back as a reference signal to provide wavelength calibration of the tunable laser light source 3. The tuning can be performed beginning with a maximum wavelength λmax.
In a further step S2, it is checked whether it is required to tune to the peak frequency of the optical measurement filter 6 to get an analytical result. This depends on whether the optical sensor 2 is adapted to produce a sample specific response signal based on reflections or to produce a sample specific response signal with wavelength shifts such as caused by Raman scattering. In case that the optical sensor 2 is adapted to produce a sample specific response signal with wavelength shifts, no tuning is required as performed in step S3 as shown in
In a further step S5, an analytical result is produced within the bandwidth of the optical measurement filter 6.
In a further step S6, it is checked whether it is necessary to tune to a next spectral event. If this is not the case, the process stops in step S11. Otherwise, the tunable laser light source 3 is tuned by an increment which corresponds to the peak wavelength difference between two peak wavelengths of two optical measurement filters 6 having neighboring passband frequency bands in step S7.
In step S8, it is checked whether to use the measurement signal of measurement filter 6 for analysis. If the optical sensor 2 is adapted to produce a sample specific response signal based on reflections, the process continues with step S9, whereas if the optical sensor 2 is adapted to produce a sample specific response signal with wavelength shifts, the process continues with step S10. In step S9, the results produced within the bandwidth of the next measurement filter 6 are analyzed. Accordingly, the process loop including steps S6, S7, S8, S9 is adapted to interrogate further spectral events based on reflection.
In contrast, in step S10, results produced within the bandwidth of the measurement filter 6 are analyzed. Consequently, the process loop comprising steps S6, S7, S8, S10 analyzes spectral events wherein a sample specific response signal is produced with wavelength shifts caused e.g. by Raman scattering.
As can be seen from the flowchart in
The method and apparatus 1 according to the present invention can use fiber optical sensors 2 which detect a single or very few specific spectral peaks only. The apparatus 1 according to the present invention does not comprise a broadband flexible spectrometer but uses a single or a very few narrow band optical filters 6, 7 instead. This is combined with a certain limited excitation laser tunability sufficient to cover a few specific spectral peaks for being able to detect and discriminate for instance two different substances. Because of few components required for the hardware equipment of the apparatus 1 according to the present invention, this allows for cheap mass production of the apparatus 1. In a possible use case, the apparatus 1 can comprise a handheld device used for detection of a specific virus such as SARS-CoV-2 detection. Accordingly, in a possible implementation, the apparatus 1 can be implemented as a handheld spectroscopic virus scanning device which can be used in the field. The handheld spectroscopic apparatus 1 can comprise a connector 13 which allows to replace the used optical sensor 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20171655 | Apr 2020 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5386295 | Switalski | Jan 1995 | A |
| 6455854 | Richman | Sep 2002 | B1 |
| 8111392 | Deck | Feb 2012 | B1 |
| 20070023661 | Wagner | Feb 2007 | A1 |
| 20070195320 | Sriram | Aug 2007 | A1 |
| 20100182607 | Chau | Jul 2010 | A1 |
| 20170245796 | Zalevsky | Aug 2017 | A1 |
| 20210298604 | Kurki | Sep 2021 | A1 |
| 20220018840 | Akhtari | Jan 2022 | A1 |
| Number | Date | Country |
|---|---|---|
| 108291443 | Jul 2018 | CN |
| 2135060 | Sep 2015 | EP |
| WO-2012003046 | Jan 2012 | WO |
| Entry |
|---|
| Kukushkin et al., “Highly sensitive detecdtion of influenza virus with SERS aptasensor,” PLoS ONE, vol. 14, No. 4, pp. 1-14 (2019). |
| Wu et al., “A Simple SERS-Based Trace Sensing Platform Enabled by AuNPs-Analyte/AuNPs Double-Decker Structure on Wax-Coated Hydrophobic Surface,” Frontiers in Chemistry, vol. 6, Article 482, pp. 1-9 (Oct. 2018). |
| Staudinger et al., “A versatile optode system for oxygen, carbon dioxide, and pH measurements in seawater with integrated battery and logger,” Limnology and Oceaongraphy: Methods, pp. 459-473 (2018). |
| Durmanov et al., “Non-labeled selective virus detection with novel SERS-active porous silver nonofilms fabricated by Electron Beam Physical Vapor Deposition,” Sensors and Actuators B, pp. 1-26 (2017). |
| Gu et al., “Recent advance in fiber SERS sensors,” Proceedings of SPIE—The international Society for Optical Engineering, pp. 1-13 (Aug. 2008). |
| Number | Date | Country | |
|---|---|---|---|
| 20210333205 A1 | Oct 2021 | US |
