Method and system for analyzing a sample

Abstract

A method of analyzing a sample, comprises contacting the sample with a structure having a surface formed with a chiral pattern; directing to the structure two polarized incoming light beams from two different incoming directions, so as to induce two polaritonic modes propagating non-parallelly over the surface, and to diffract, for each propagation direction of the polaritonic modes, an outgoing light beam having a different polarization and / or a different phase; and analyzing a difference in the polarizations and / or phases of the outgoing light beams, thereby analyzing the sample.

Description

[0001] METHOD AND SYSTEM FOR ANALYZING A SAMPLE

[0002] TECHNICAL FIELD

[0003] The presently disclosed subject matter, in some embodiments thereof, relates to optics, and, more particularly, but not exclusively, to a method and a system for analyzing a sample, optionally and preferably a reciprocal sample.

[0004] BACKGROUND

[0005] Optical interferometry is based on the phenomenon of interference, for example constructive and destructive, between two coherent light waves. In some interferometer configurations, an initial light beam is projected from a light source and subsequently undergoes division via a beamsplitter into two separate beams. The measurement beam interacts with the analyte, the object under scrutiny, reflecting off it, while the reference beam remains unaffected thereby. These beams subsequently reunite so their waves project constructive and destructive interference. This interaction generates an interference pattern, the characteristics of which may be contingent upon the optical path difference (OPD) between the two beam trajectories. By analyzing this interference pattern, valuable insights into the properties of the test object can be extracted.

[0006] Sagnac interferometry, named after French physicist Georges Sagnac, is a powerful technique used for example in the field of analytical chemistry to study the properties of analytes, and in optical gyroscopes. This optical interferometric method relies on the interference of light beams traveling in opposite directions within a closed-loop interferometer, commonly known as a Sagnac interferometer. The interaction of these counter-propagating light waves provides valuable insights into various properties of analytes, such as refractive index, concentration, and molecular structure. In optical gyroscopes, the interferometer measures rotation. As opposed to other known types of interferometers, the Sagnac interferometer is sensitive to non-reciprocal phase-shifts in the two light beams that counter-prop agate in the circulatory path, and is insensitive to reciprocal phase-shifts in the circulatory path.

[0007] Sagnac interferometry is widely employed in analytical and biochemical research due to its high sensitivity and precision. It offers a non-destructive and label-free approach for probing analytes, making it a valuable tool in areas like spectroscopy, environmental monitoring, analytical chemistry and biotechnology.Plasmonic Resonance Interferometry, often referred to as PRI, is a cutting-edge analytical technique that leverages the principles of plasmonics and interferometry to study analytes at the nanoscale. Plasmonics involves the collective oscillations of electrons in metallic nanostructures when excited by incident light. This phenomenon results in enhanced light-matter interactions and is the foundation of plasmonic resonance. PRI may be used to probe light interactions with specific analytes, such as biomolecules, nanoparticles, and gases.

[0008] The interference between light waves reflected from the sensor surface and the reference beam allows for real-time, label-free, and highly sensitive analysis of analytes. Plasmonic Resonance Interferometry has found applications in various fields, including biosensing, environmental monitoring, and materials science.

[0009] Interferometry over the passing decades has become a highly popular non-destructive method of sensing and probing analytes and phenomena in general which would otherwise elude detection due to their low signal. In micro and nanoscience, interferometers have shown much promise in many sub-fields, such as; surface topography, thin film characterization, nanomedicine, and optical spectroscopy.

[0010] The easy to align Sagnac interferometer is a ubiquitous method for numerous measurements of these and other sensors. Surface Plasmon Polaritons (SPPs) were introduced to applications as a highly sensitive means of measurement, partially due to the sensitivity of the plasmonic response to the precise and local dielectric function of all materials in proximity to the metal supporting the plasmonic activity. Methods employing SPP interference include for example film transmission interferometry, heterodyne interferometry, fiber interferometry and free-space interferometry.

[0011] Free-space SPP interferometry systems may incorporate a prism for the excitation of the SPP, wherein a metal nano-film or grating may be applied to the back of a prism. Thereby, SPPs may be excited at the metal-dielectric interface behind it via total internal reflection. Thus, the internally reflected wave may be informative of the plasmonic interaction with the analyte, and this in turn may be interfered with another beam sharing coherence.

[0012] SUMMARY

[0013] According to an aspect of some embodiments of the presently disclosed subject matter, there is provided a method of analyzing a sample. The method comprises:

[0014] contacting the sample with a structure having a surface formed with a chiral pattern; directing two polarized incoming light beams from two different incoming directions to the structure, so as to induce two polaritonic modes propagating non-parallelly over the surface, and to diffract, for each propagation direction of the polaritonic modes, an outgoing light beam having a different polarization and / or a different phase; and

[0015] analyzing a difference in the polarizations and / or phases of the outgoing light beams, thereby analyzing the sample.

[0016] According to another aspect of the presently disclosed subject matter, there is provided a method of analyzing a sample, the method comprising:

[0017] contacting the sample with a structure having a surface formed with a chiral pattern; directing two polarized incoming light beams from two different incoming directions to the structure, so as to induce two polaritonic modes propagating over said surface along opposite directions, and to diffract, for each propagation direction of said polaritonic modes, an outgoing light beam having a different polarization; and

[0018] analyzing a difference in said polarizations of said outgoing light beams, thereby analyzing the sample.

[0019] The method according to each of the above aspects may be further characterized as described in one or more of the following paragraphs.

[0020] The sample and the incoming light beams may be at opposite sides of the structure.

[0021] Analyzing the difference may comprise generating an interference between the outgoing light beams.

[0022] Analyzing the difference may comprise applying a polarimeter and / or a polarizer to each outgoing light beam.

[0023] The structure may comprise a two-dimensional grating. The two-dimensional grating may be defined over two orthogonal axes and comprise a plurality of elongated grating elements, wherein an orientation of the grating elements varies cyclically and periodically along one of the axes and is constant along another one of the axes.

[0024] The two polarized incoming light beams may be directed to the structure in free space. The two polarized incoming light beams may be directed to the structure via one or more optical waveguides.

[0025] Directing the two polarized incoming light beams to the structure may be executed to ensure that the incoming directions are at opposite sides of a normal to the surface and at equal angles relative thereto.

[0026] The structure may have a thickness of less than 500 nm.The structure and the incoming light beams may be selected so as to generate the polaritonic modes as surface plasmon polaritons.

[0027] The structure and the incoming light beams may be selected so as to generate the polaritonic modes as exciton polaritons.

[0028] The structure and the incoming light beams may be selected so as to generate the polaritonic modes as phonon polaritons.

[0029] According to another aspect of some embodiments of the presently disclosed subject matter, there is provided a system for analyzing a sample. The system comprises:

[0030] a structure having a surface formed with a chiral pattern for receiving the sample; a light source and optics for directing to the structure two polarized incoming light beams from two different incoming directions, so as to induce two polaritonic modes propagating non-parallelly over the surface, and to diffract, for each propagation direction of the polaritonic modes, an outgoing light beam having a different polarization and / or a different phase; and

[0031] a measuring system configured for measuring a difference in the polarizations and / or phases of the outgoing light beams.

[0032] According to another aspect of the presently disclosed subject matter, there is provided a system for analyzing a sample, the system comprising:

[0033] a structure having a surface formed with a chiral pattern for receiving the sample; a light source and optics for directing to said structure two polarized incoming light beams from two different incoming directions, so as to induce two polaritonic modes propagating over said surface along opposite directions, and to diffract, for each propagation direction of said polaritonic modes, an outgoing light beam having a different polarization; and

[0034] a measuring system configured for measuring a difference in said polarizations of said outgoing light beams.

[0035] The system according to each of the above aspects may be further characterized as described in one or more of the following paragraphs.

[0036] The sample and the incoming light beams may be at opposite sides of the structure.

[0037] The optics may be configured for generating an interference between the outgoing light beams.

[0038] The measuring system may comprise an imager constituted to image an interference pattern between the outgoing light beams.The optics may be arranged to form a Sagnac interferometer.

[0039] The measuring system may comprise a polarimeter.

[0040] The structure may comprise a two-dimensional grating.

[0041] The two-dimensional grating may be defined over two orthogonal axes and comprises a plurality of elongated grating elements, wherein an orientation of the grating elements varies cyclically and periodically along one of the axes and is constant along another one of the axes.

[0042] The optics may be configured to direct the incoming light beams in free space.

[0043] The system may comprise one or more optical waveguides arranged to direct the incoming light beams to the structure.

[0044] The optics may be arranged such that the incoming directions are at opposite sides of a normal to the surface and at equal angles relative thereto.

[0045] The structure may have a thickness of less than 500 nm.

[0046] The structure and the incoming light beams may be selected so as to generate the polaritonic modes as surface plasmon polaritons.

[0047] The structure and the incoming light beams may be selected so as to generate the polaritonic modes as exciton polaritons.

[0048] The structure and the incoming light beams may be selected so as to generate the polaritonic modes as phonon polaritons.

[0049] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the presently disclosed subject matter pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the presently disclosed subject matter, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0050] BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Some embodiments of the presently disclosed subject matter are herein described, by way of example only, with reference to the accompanying drawings and formulae. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the presently disclosed subject matter. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the presently disclosed subject matter may be practiced. In the drawings:Fig. 1 is a flowchart diagram describing a method suitable for analyzing a sample according to some embodiments of the presently disclosed subject matter;

[0052] Fig- 2 is an exemplary illustration of system suitable for analyzing a sample according to some embodiments of the presently disclosed subject matter;

[0053] Fig- 3 is an exemplary illustration of an interferometer setups according to some embodiments of the presently disclosed subject matter;

[0054] Figs.4A through 4D show chiral patterns according to some embodiments of the presently disclosed subject matter;

[0055] Figs.5A and 5B are exemplary illustrations of beam-grating interactions according to some embodiments of the presently disclosed subject matter;

[0056] Figs. 6A through 6C show illumination of plain gold and beam offset, baseline interferograms according to some embodiments of the presently disclosed subject matter;

[0057] Figs. 7A through 7D show illumination between two left-handed structures according to some embodiments of the presently disclosed subject matter;

[0058] Figs. 8A through 8D show direct illumination of one left-handed structure; according to some embodiments of the presently disclosed subject matter;

[0059] Figs. 9A through 9D show illumination of RH structures with TM polarization according to some embodiments of the presently disclosed subject matter;

[0060] Fig. 10 is an exemplary illustration of coordinates and reference frames of rays according to some embodiments of the presently disclosed subject matter;

[0061] Fig. 11 is an exemplary illustration of a non-twisted fiber setup according to some embodiments of the presently disclosed subject matter;

[0062] Fig. 12 is an exemplary illustration of Sagnac interferometer setups according to some embodiments of the presently disclosed subject matter; and

[0063] Figs. 13A and 13B are exemplary illustrations of optical configurations for measuring differences in optical properties of outgoing light beams according to some embodiments of the presently disclosed subject matter.

[0064] DETAILED DESCRIPTION

[0065] The presently disclosed subject matter, in some embodiments thereof, relates to optics, and, more particularly, but not exclusively, to a method and a system for analyzing a sample, optionally and preferably a reciprocal sample.

[0066] It is to be understood that the presently disclosed subject matter is not limited in its application and / or scope to what is disclosed herein, including, but not limited to, details ofinstructions and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the examples. The presently disclosed subject matter is capable of other embodiments or of being practiced or carried out in various ways.

[0067] Referring now to the drawings, Fig. l is a flowchart diagram of a method 100 suitable for analyzing a sample, and Fig. 2 is an illustration of a system 200 suitable for analyzing a sample 208, both according to some embodiments of the presently disclosed subject matter. System 200 can be used for executing method 100. It is to be understood that, unless otherwise defined, the operations described hereinbelow can be executed either contemporaneously or sequentially in many combinations or orders of execution. Specifically, the ordering of the flowchart diagrams is not to be considered as limiting. For example, two or more operations, appearing in the following description or in the flowchart diagrams in a particular order, can be executed in a different order (e.g., a reverse order) or substantially contemporaneously. Additionally, several operations described below are optional and may not be executed.

[0068] The sample to be analyzed may be a fluid sample (liquid or gas), but may in some embodiments of the presently disclosed subject matter be a solid sample. The sample can include a biological sample, such as, but not limited to, blood, serum, plasma, saliva, mucus, breath, urine, CSF, sputum, sweat, stool, seminal fluid, soft tissue, hard tissue, cytological sample, platelets, reticulocytes, leukocytes, and epithelial cells. Other types of samples include, without limitation, flammable gas, noxious gas, air, any type of biological fluid or other type of fluid, and polluting substances.

[0069] Method 100 begins at 110 at which a sample 208 is contacted with a structure 202 having a surface 204 formed with a chiral pattern 206. Fig. 2 shows sample 208 and pattern 206 at opposite sides of substrate 202 but, this need not necessarily be the case, since, for some applications, it may be desired to contact sample 208 with surface 204 of structure 202 at the side that is formed with pattern 206.

[0070] When the sample and the chiral pattern are at opposite sides of structure 202, the sample interacts with evanescent waves created when light beams impinge on surface 204. When the sample and the chiral pattern are both on surface 204, the sample interacts with the light beams before then impinge on surface 204.

[0071] As used herein, the term “chiral,” in relation to a pattern, refers to a pattern which is non-superimposable on its mirror image.

[0072] Preferably, the chiral pattern 206 of the present embodiments is designed and configured to interact with an electromagnetic wave in a manner that causes diffraction of the electromagneticwave, wherein at least one property of the diffracted electromagnetic wave depends on the propagation direction of the electromagnetic wave relative to the chiral pattern. The property preferably comprises at least one of polarization and phase of the diffracted electromagnetic wave. The property depends on the propagation direction in the sense that diffracted electromagnetic waves originating from electromagnetic waves propagating at different directions relative to the chiral pattern have different property.

[0073] Representative examples of types of patterns 206 suitable for the present embodiments include, without limitation, grating, cavities, bumps, areas of materials with different electromagnetic conductance and / or the like. Some examples such as, but not limited to, as a structure comprises a two-dimensional grating are provided below, however other methods of creating chiral patterns are also contemplated.

[0074] A representative example of a pattern 206 suitable for the present embodiments is provided in Figs. 4A through 4D. In these embodiments, pattern 206 is in the form of a two-dimensional grating. The two-dimensional grating 206 of this example is defined over two orthogonal axes x and y, and comprises a plurality of elongated grating elements 206-1, 206-2, etc., wherein an orientation of grating elements 206-1, 206-2, etc., vary cyclically and periodically along one of the axes (the x-axis in this example) and is constant along another one of the axes (the y-axis in this example).

[0075] The elements of pattern 206 can be of any type having an axis of anisotropy such as, but not limited to, rectangles, ellipsoids, triangles, or any elongated polygon. Also contemplated are vortex structures such as structures spiraling inwards to a common center. The diameter of each element in grating 206 can be from about 0.5 to about 5 wavelengths of the incoming light beams. The elements can be in the form of slots or be formed as relief structures. Also contemplated is the use of nano-antennas on the order of 0.1-1 wavelength of the incoming beams.

[0076] The surface of the structure is preferably planar, but some implementations may feature a curved surface. The thickness of structure 202 is optionally and preferably less than 500 nm.

[0077] The method continues to 120 at which two or more polarized incoming light beams 210, 212 are directed to the structure, from two different incoming directions. The light beams 210, 212 are preferably monochromatic and may be generated by a light source, such as, but not limited to, a laser. The light beams 210, 212 are preferably coherent light beams. For example, they can be formed by a single light source and pass through a wave splitting mechanism such as, but not limited to, a beamsplitter or two or more optical waveguides.The light beams 210, 212 can be directed to the substrate 202 is in free space, or via one or more optical waveguides, such as, but not limited to, optical fibers. In some embodiments of the presently disclosed subject matter beams 210 and 212 are directed in a manner that the respective incoming directions are at opposite sides of a normal 226 to surface 204, and at equal angles 228, 230 relative thereto.

[0078] In some embodiments of the presently disclosed subject matter, structure 202 and incoming light beams 210, 212 are selected so as to generate in structure 202 respective polaritonic modes 214, 216 in the form of surface plasmon polaritons; in some embodiments of the presently disclosed subject matter, structure 202 and incoming light beams 210, 212 are selected so as to generate in structure 202 respective polaritonic modes 214, 216 in the form of exciton polaritons; and in some embodiments of the presently disclosed subject matter, structure 202 and incoming light beams 210, 212 are selected so as to generate in structure 202 respective polaritonic modes 214, 216 in the form of phonon polaritons. Polaritonic modes 214, 216 propagate non-parallelly over surface 204.

[0079] In various exemplary embodiments of the presently disclosed subject matter, for each propagation direction of the polaritonic modes 214, 216, an outgoing light beam 218, 220 is diffracted out of surface 204. The diffraction occurs due to the interaction of the incoming light beam and / or the generated polaritonic modes with pattern 206. Since pattern 206 is chiral, outgoing light beam 218, 220 differ in at least one of their optical properties, preferably in their polarization and / or phase. The incoming light beams 210, 212 are preferably polarized by a polarizer (not shown, see Fig. 3) before they strike the chiral structure.

[0080] The propagation directions of polaritonic modes 214, 216 may be opposite to each other as illustrated in Fig. 2, but some implementations may use different non-parallel propagation directions such directions forming an acute or obtuse angle therebetween.

[0081] The method continues to 130 at which the difference in the optical properties (e.g., polarizations and / or phases) of outgoing light beams 218, 220 is analyzed. This difference depends on the optical properties of the sample and therefore serves as a proxy to the optical properties of the sample. In some embodiments of the presently disclosed subject matter, the difference is measured and analyzed so as to determine the refractive index and / or other optical properties of the sample. Such analysis can include, for example, measuring the output state (polarization difference and / or phase difference) and compare this state to a library that maps between the state and the sample. Such analysis can alternatively or additionally include matching the output state to a simulation model. Such analysis can alternatively or additionally include applying sinusoidalRF modulation of the incoming beams, and then measuring the RF amplitude and phase of the output of detectors that measure the light power, for example, as disclosed in U.S. Patent Nos.

[0082] 11,686,621, and / or 10,009,114, the contents of which are hereby incorporated by reference.

[0083] The difference in the optical property can be measured in more than one way. In some embodiments of the presently disclosed subject matter, a polarimeter 222, 224, is applied to each of the outgoing beams 218, 220. A polarimeter can provide information pertaining to the phase and / or polarization difference between the beam. Preferably, the polarimeter comprises a rotating polarizer.

[0084] One example of a polarimeter suitable for the present embodiment is a polarimeter incorporating thin-film polarizers. For example, the beam can pass through a series of apertures, a neutral-density filter, and then split into object and reference beams. These beams are optionally and preferably modulated by a rotating polarizer, and the phase difference is determined by analyzing the modulated beams. This method may optionally and preferably utilize photodiodes and a microcontroller. The phase difference can then be calculated from the difference in the angle of rotation of the beams, with and without the sample. These techniques are advantageous since they allow for the non-interferometric phase difference measurement between optical beams.

[0085] In some embodiments of the presently disclosed subject matter, an interference is generated between outgoing light beams 218, 220. Such interference creates an interference pattern which can then be detected and analyzed in order to determine the polarization and / or phase difference between the outgoing light beams. A description of a representative example of an interferometer that can be used according to some embodiments of the presently disclosed subject matter to generate and measure such an interference is provided in Fig. 3. The interferometer comprises a laser source. The light from the laser source may be reflected using mirrors (M) or directed by media such as finer optics through a half-wave plate (HWP) to ensure TM polarization. A beamsplitter (BS) may be used to split the beam to two different beams, some implementations may feature more than two beams. The light may be followingly directed to the structure having a surface formed with a chiral pattern and continue through the interferometer to a detector.

[0086] Other optical configurations for measuring the difference in optical property are illustrated in Figs. 13 A and 13B. In the configuration shown in Fig. 13 A, beams 210 and 212 are directed to the same region on pattern 206, and outgoing beams 220 and 218 follow the optical paths of beams 210 and 212, respectively, in the opposite direction, beamsplitters 230, 232 are positioned in the optical paths of outgoing beams 218 and 220, to redirect outgoing beams 218 and 220 to polarimeter 222, 224.The configuration shown in Fig. 13B is similar to the configuration shown in Fig. 13 A, with the addition of beamsplitters 234, 236 that are arranged to form a Sagnac loop 238 and to cause interference between the outgoing beams 220 and 218 at an additional beamsplitter 240.

[0087] Beamsplitter 240 redirects a combined light beam that constitutes the interference into a detector 242. Detector 242 can, in some embodiments of the presently disclosed subject matter, be an imager, such as, but not limited to, a CCD or a CMOS imager.

[0088] As used herein the term “about” refers to ± 10%

[0089] The terms “comprises,” “comprising,” “includes,” “including,” “having” and their conjugates mean “including but not limited to.”

[0090] The term “consisting of’ means “including and limited to.”

[0091] The term “consisting essentially of’ means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0092] As used herein, the singular form “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof.

[0093] Throughout this description, various embodiments of the presently disclosed subject matter may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as limiting the scope of the presently disclosed subject matter. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0094] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0095] It is appreciated that certain features of the presently disclosed subject matter, which, for clarity, are described in the context of separate embodiments, may also be provided in combinationin a single embodiment. Conversely, various features of the presently disclosed subject matter, which, for brevity, are described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the presently disclosed subject matter. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0096] Various embodiments and aspects of the present presently disclosed subject matter as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

[0097] Examples

[0098] Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the presently disclosed subject matter in a nonlimiting fashion.

[0099] Some embodiments of the presently disclosed subject matter comprise a series of optical elements which at first split an incoming laser beam into two coherent laser beams propagating with different momenta, subsequently routing these beams so that they complete some circuit in space during which they are constantly interfering with each other, where there may be a section of this circuit which comprises a sensing area. An element which recombines the beams following their transversion of the circuit such that they share momentum once more, and the recombined beam may be measured by some sensor.

[0100] Some implementations apply Sagnac interferometry to reciprocal analytes via a chiral structure. Using chiral structures and their resonances may improve the Sagnac interferometer sensing, particularly of reciprocal analytes.

[0101] Some implementations relate to the similar field of plasmonic resonance interferometry, where the reciprocal plasmon-polaritonic response is implemented, however the reciprocity renders known Sagnac interferometry methods inapt.

[0102] In some embodiments of the presently disclosed subject matter, the Sagnac interferometer is in free space, which is shown in the document below. Fiber interferometer are also ubiquitous implementations. The disclosure comprises a chiral structure for sensing, imbuing a Sagnac interferometer with the ability to sense reciprocal analytes, which are ordinarily inaccessible to Sagnac interferometers. The non-reciprocity of the structure, combined with the highly sensitive polaritonic nature of the material comprising the structure, enable highly sensitive polaritonic response of certain materials on a non-reciprocal substrate, such that the combination may bereliably implemented in the Sagnac method. The polaritonic response may further offer finer detail than known contemporary interferometric or spectroscopic technologies.

[0103] Some embodiments of the presently disclosed subject matter may be used for optical spectrometer with improved resolution. Some other embodiments of the presently disclosed subject matter may be used for IR spectrometer with improved resolution. Some other embodiments of the presently disclosed subject matter may be used for measurement accessory for existing products.

[0104] The highly sensitive polaritonic response of certain materials may be realized on a nonreciprocal substrate, such that the combination could be reliably implemented in the Sagnac method. This method is in itself highly sensitive, and when combined with the polaritonic response should offer finer detail than contemporary interferometric / spectroscopic technologies.

[0105] Extending the capabilities of interferometry, such as Sagnac interferometry via chiral structure and their resonances, may allow the Sagnac method to sense reciprocal analytes, i.e., analytes which otherwise would produce identical optical responses from both interferometer media or arms.

[0106] Some embodiments of the presently disclosed subject matter comprise prism-based, SPP enhanced Sagnac interferometers. These embodiments feature high sensitivities attainable by implementing the Sagnac configuration with a chiral structure. However, isolating the inherent non-reciprocities of the measurement system itself may require further design improvements for similar sensitivities in measurement of reciprocal phenomena as well. Some methods of implementing plasmonic resonance may be used to heighten the sensitivity of measuring both reciprocal and non-reciprocal analytes in a Sagnac interferometer, via topological bi-grating induced non-reciprocity. Other embodiments implemented for example in a fiber-optic setup may be analogous and may show similar fundamental behavior.

[0107] Alternatively to surface plasmon polaritons other examples of polaritonic surface providing polaritonic interface structure include for example Optical Phonon Polaritons and Dielectric-Hyperbolic Material Interfaces. Semiconductor-Dielectric Interfaces, and surface exciton polaritons such as UV-VIS-NIR in semiconductors may also be used. Surface phonon polaritons, which may be preferred with wavelength ranging from 3 to 20 microns, in ceramics, as an additional alternative.

[0108] While the disclosure is most useful for reciprocal analytes, non-reciprocal analytes may also be probed, as long as their response differs from the opposite to the response of the polaritonic interface structure.Reference is now made to Figs. 4A through 4D which is an exemplary illustration of nonreciprocal, topological plasmonic gratings according to some embodiments of the presently disclosed subject matter.

[0109] This example shows two-dimensional grating defined over two orthogonal axes and comprises a plurality of elongated grating elements, wherein an orientation of said grating elements vary cyclically and periodically along one of said axes and is constant along another one of said axes.

[0110] In this example, the film is characterized by topological bi-grating for induced nonreciprocity. Some exemplary non-reciprocal, topological plasmonic gratings used as a chiral structure for receiving a set of projections, are hereby shown: Fig. 4A is a SEM image of the LH structure with a grating constant of 575 nm and a rotation rate of 71 / 6 radians per site; Fig. 4C shows calculated k-space of the LH structure, Fig. 4B is a SEM image of the RH structure with a grating constant of 950 nm and a rotation rate of 7t / 6 radians per site; and Fig. 4D shows calculated k-space of the RH structure. In Figs. 4C and 4D, the “x” symbol in the middle of each circle denotes the location of the ordinary grating diffractions, the small circles at the right and left of each dotted circle correspond, respectively, to right and left circularly polarized light topologically diffracted from the structures. The dotted lines represent the numerical apertures, and the solid lines denote the plasmonic circles. The k-space dimensions are normalized to the surface plasmon momentum k' = ki / ksp.

[0111] In order to generate a reference interferogram, the different arms of the interferometer may be offset by a small angle a, for example ~ 10-1 milliradians, as can be seen in Fig. 6C from the optical axis. In this way, horizontal fringes corresponding to the resulting interference may represent the system at baseline. Any non-reciprocal phase shift in the fields would then appear as variations in the baseline interferogram. Two such baseline interferograms are measured, one for plain gold and TM polarization, where the plasmonic absorption line appears, and one for plain gold with non-TM polarization where there is no plasmonic response. The film under examination may be comprised of two sets of three repeating, non-reciprocal, topological plasmonic structures as shown in Figs. 4A through 4D. The 88 nm gold film may be evaporated on to a 160 pm cover slip, and the gratings were milled via FIB. The two sets may be separated by 630 pm to prevent cross-talk, while the structures in a set were separated by 60 pm to allow plasmons to propagate from the beam to the two adjacent structures. The structures may be designed such that an incident SPP, excited on the gold, would couple in the grating to a different CP mode depending on the direction of the SPP incidence. In one structure (right-handed), a SPP incident from the right wouldcouple to outgoing RCP, while a SPP from the left would couple tq,LCP light. In the other structure (left-handed), these relationships are reversed. In Figs. 4C and 4D, the k-space of the respective structures can be seen. Note the intersection of the modes with the plasmonic circle at k'y= 0. Just as light impinging on the grating, which may match these momenta, couples to plasmons in the film, so do incoming plasmons couple to such light upon impingement from within the film.

[0112] Reference is now made to Figs. 5A and 5B, which are exemplary illustrations of beamgrating interactions according to some embodiments of the presently disclosed subject matter.

[0113] As illustrated in Fig. 5A, incoming transmitted beam kt and incoming reflected beam kreach scatter a surface plasmon ksp,t into identical gratings from opposite ends. The gratings couple the incoming plasmons to oppositely polarized leakage radiation which can then be interfered. As illustrated in Fig. 5B, incoming beams diffract multiple modes with differing polarization, which may or may not include SPPs.

[0114] In the experiment part shown in Fig. 5 A, the laser illuminates the plain gold film in between two structures from the same set, sending SPPs both to the right and the left. Each SPP is then incident upon an identical grating, however, one SPP may be incident from the left of the grating, and the other from the right. In this way, each arm of the interferometer may cause some diffraction of oppositely polarized grating photons. Due to this clear non-reciprocity, these photons should then interfere in some detectable way, changing the interferogram. In another experiment the experiment part shown in Fig. 5B, the laser directly illuminates one structure from a set, creating a more complex diffraction pattern, possibly including SPPs. Due to the inbuilt non-reciprocity, these diffractions should be, at least partially, differently polarized. It may be predicted that only non-reciprocal gratings will produce variations in the baseline interferogram, and in the case the experiment part shown in Fig. 5A, only for incident beam polarizations which couple to plasmons in the film. Additionally, the right and left-handed sets should display mirrored interferograms.

[0115] Reference is now made to Figs. 6A through 6C, which is a set of exemplary illustrations of illumination of plain gold and beam offset, baseline interferograms according to some embodiments of the presently disclosed subject matter.

[0116] The illumination of plain gold and beam offset generated during the experiment comprise, baseline interferograms. Fig. 6A is an interferogram 500, TM incidence, Fig. 6B is an interferogram 510, non-TM incidence (A^ ~ 90 mrad), and Fig. 6C illustrates the vertical beam angle offset a, which is -10"1mrad. In Figs. 6A the characteristic plasmonic absorption line can be seen as a vertical, dark line at the center of the beam. Additionally, fainter, temperature dependent vertical lines are scattered throughout the beam cross section. In Fig. 6B the plasmonicline disappears as the polarization is non-TM and plasmonic modes are not allowed, as do the temperature dependent lines. The horizontal lines in both are interference fringes resulting from the beam propagation angles being vertically offset from the central axis by an order of 10-1 milliradians. Figs. 6A and 6B show the baseline interferograms for, respectively, TM incidence on plain gold 500 and non-TM incidence 510, while a slight offset in beam angle is introduced for reference horizontal interference lines. For TM polarization the SPPs are excited, and absorb light corresponding the tip of the cone of incident angles from the lenses, for an incident primary ray angle of 44.7°. This absorption may be seen as the central vertical dark line in Fig. 6A. For non-TM illumination, the entire cone is reflected and no absorption is seen. Additionally, the multitude of nearly vertical dark lines which appear across the TM image should be noted. These lines appear to be thermally dependent, as their position may fluctuate when the laser intensity or air-conditioning are changed, and may stabilize at an equilibrium position after a few minutes. The effect was observed under TM illumination and with the LP filter.

[0117] Reference is now made to Figs. 7A through 7D, which is a set of exemplary illustrations of illumination between two left-handed structures according to some embodiments of the presently disclosed subject matter.

[0118] The illumination between two left-handed structures is shown as follows: Fig. 7 A is an interferogram 610, illumination of plain gold with TM; Fig. 7B is an interferogram 620, illumination between two LH structures, TM; Fig. 7C is an interferogram 630, illumination between two LH structures, non-TM; Fig. 7D is a microscope image 640 of illuminated structures. Lines numbered 1-3 denote the reference interference lines. The white arrows in Fig. 7B denote forking locations.

[0119] Figures 7A through 7C are examples of receiving a wave interference pattern from the set of interferometer media on a chiral structure and measuring the wave interference pattern on the chiral structure using a detector such as a camera.

[0120] When comparing Fig. 7B to Figs. 7A and 7C, one can see a possible forking of the reference lines, suggesting some interference phenomenon which is only apparent for TM polarization and presence of structure. Red circle in Fig. 7D denotes the location of the impinging beams, and the two grating structures appear to the right and left of the beam, two diffractions can be seen adjacent to the structures.

[0121] Figs. 7A through 7D show the interferogram and microscope images of illumination between two left-handed structures. In this figure one can see possible weak forking of lines 1 and 2, when compared to Figs. 6A and 6B. This possible forking is apparent only for TM polarization.Reference is now made to Figs. 8A and 8B, which is a set of exemplary illustrations of direct illumination of one left-handed structure, according to some embodiments of the presently disclosed subject matter.

[0122] Direct illumination of one left-handed structure is shown as follows: Fig. 8A is an interferogram 710, illumination of plain gold with TM; Fig. 8B is an interferogram 720, direct illumination of a single LH structure, TM; Fig. 8C is an interferogram 730, illumination of a single LH structure, non-TM; and Fig. 8D is a microscope image 740 of illuminated structure. Lines numbered 1-3 denote the reference interference lines, and white arrows in Fig. 8B denote forking locations. When comparing Fig. 8B to Figs. 8A and 8C, one can see a clear forking of the reference lines, suggesting some interference phenomenon which is only apparent for TM polarization and presence of structure. Bright square in Fig. 8D is the grating structure, and the adjacent structure appears faintly to the left. A bright diffraction can be seen in proximity to the illuminated structure.

[0123] Figs. 8A through 8D show the interferogram and microscope images corresponding to direct illumination of a single left-handed structure. For TM illumination the forking is seen more clearly, and the resulting interferogram is significantly varied from baseline. When the incident polarization is changed to non-TM, the baseline interferogram returns, thereby strengthening the hypothesized predictions.

[0124] Reference is now made to Figs. 9A through 9D, which is a set of exemplary illustrations of illumination of RH structures with TM polarization according to some embodiments of the presently disclosed subject matter

[0125] Illumination of RH structures with TM polarization are shown as follows: Fig. 9A is an interferogram 810, illumination of plain gold 100 pm away from RH structure; Fig. 9B is an interferogram 820, direct illumination of a single RH structure, TM; Fig. 9C is an interferogram 830, characteristic of remaining two RH structures and their vicinities, and Fig. 9D is a microscope image 840 of illuminated structure. The images of Figs. 9A and 9A do not resemble LH counterparts in form, and are unique only to the lead RH structure. This may be due to dust in the vicinity of the structure. The invariant nature of the image of Fig. 9C as characteristic of the rest of the RH structures suggests that the effect is not exemplified here, possibly due to poor structure coupling as apparent by the darker image in Fig. 9D as compared to LH structures.

[0126] Figs. 9A through 9D shows the interferogram of RH structures illuminated with TM polarization. Fig. 9A shows the illumination of the gold film 100 pm away from the leading RH structure in the set; Fig. 9B shows the illumination of the leading structure; and Fig. 9C shows a characteristic image of the illumination of the rest of the row — the image does not changesignificantly after the first structure, regardless of the position of the beam. Fig. 9D shows a microscope image corresponding to direct illumination of the leading RH structure. These images do not match the hypothesis, as only the lead structure shows any meaningful interference phenomenon, and the pattern does not change during the rest of the structure scan. This may be due to dust in the vicinity of the lead structure in addition to poor coupling of light to the structure itself, the latter of which fits the microscope image of the structure which is significantly darker than its LH counterparts. More discussion on this matter in the conclusions. Note that the experiment is provided for proof of plausibility and to help clarify some application, and other settings and implementations are apparent to the person skilled in the art.

[0127] Reference is now made to Fig. 10 which is an exemplary illustration of Coordinates and reference frames of rays according to some embodiments of the presently disclosed subject matter.

[0128] Fig. 10 illustrates the solid angle in the beam frame of reference (0,

[0129]

[0130] and the angle of incidence of the primary ray upon the film in 900. The Coordinates and reference frame are as follows. The primary ray 901, incident on the film at angle a, focal cone half-angle given by Beam frame of reference given by coordinates (x, y, z) with the optical axis on z, where the polar coordinates for the beam cross section 902 are given by (r, ff). The dashed lines correspond to the marginal rays as they would propagate in air, with the solid lines denoting the actual marginal rays as they converge more strongly in the glass. The dash-dotted line is the plane of symmetry in the prism 903. In this example the chiral structure comprises a prism and a film.

[0131] Note some transformation corresponding to the film T?(r, 0), which may transport the field polarization to any point on the Poincare sphere, shift any phases by some amount and reduce field component amplitudes. Additionally, the values of this transformation are dependent on the polar coordinates r = fL • sin(^) and Q of the beam cross section. As the beam strikes M2 it is reflected to the non-polarizing beamsplitter where it recombines with the clockwise propagating reflected beam, which has completed the exact opposite route (experiencing

[0132]

[0133] at the film). For thoroughness we assume two transformations Mi and M2 for the mirrors Mi and M2, respectively, which account for any reciprocal changes in polarization. In some implementations the lenses do not affect polarization, and that they are fully reciprocal. Upon recombination, the beam propagating towards the primary CCD may first pass through a LP where filtration of TM light is carried out for contrast improvement. In order to help understand the embodiment, exemplary formulation of the measured field before the LP is presented, however it is obvious to the person skilled in the art that some other embodiments may follow a different formulation and are within the scope of the claims. First:

[0134]

[0135] The above can be simplified by defining the interferometer transfer functions:

[0136] U = / 2• M2• / / • Mi, and

[0137] Tr = r2• Ml • ' • M2

[0138] such that:

[0139] Eout(r, 0) = (Ti(r, 0) + Tr(r, 0)) • E,„ (1.2)

[0140] and hence the power distribution may be:

[0141] Iout = ^r, 0) - Iin(1.3) where = (17 + Tr) • (Tz + T,-)* is the interference factor which takes values between [0, 1] and corresponds to the absorption and interference pattern before the LP.

[0142] Under the assumption that the absorption is reciprocal, we get that:

[0143] Iout = A(r, 0) • 2 cos[^(r, 0)] • lin (1.4) where A(r, 0) is the absorption map on the beam cross section, which takes values between [0, 1], and ^(r, e) is the non-reciprocal phase which also varies across the section. In the weakly polarizing case, i.e., when the polarization due to the film does not vary strongly over the cross section, the LP introduces a uniform factor T] which does not change the interference pattern:

[0144] Iout = A(r, 0) • 2 cos[^(r, 0)] • lin • / / (1.5) Reference is now made to Fig. 11 which is an exemplary illustration of a non-twisted fiber setup according to some embodiments of the presently disclosed subject matter.

[0145] In some implementations the light may be directed to the structure having a surface formed with a chiral pattern using an optical fiber or similar closed media, where r and t represent two different incoming directions the light comes from. Some implementations may direct additional light in additional direction. While many implementations use wavelengths ranging from 5 pm to 20 pm, some implementations may also use waveguides, and / or the likes.

[0146] Reference is now made to Fig. 12, which is an exemplary illustration of Sagnac interferometer setups according to some embodiments of the presently disclosed subject matter.

[0147] Fig. 12 features an exemplary Sagnac interferometer setup. A fiber laser at the bottom right of 1150 is collimated with an objective, then passed through a half-wave plate (HWP) to ensure TM polarization. Followingly beamsplitter may be used on the light from the light source. Once collimated and polarized the beam enters the interferometer through the beamsplitter (BS) where each arm includes a mirror (M) and a lens (L), where the lens focuses the beam into a prism and onto a gold film in a cone of angles which increase the probability of matching momentum to aplasmon. Any radiation which does not undergo total internal reflection at the film is collected by the microscope, while the reflected light is recoupled at the non-polarizing beamsplitter and read by the interferometer camera.

[0148] This structure may be used for guiding the light using through a set of interferometer media, at least one medium from the set of interferometer media, guiding the light from the light source to a sample, each of the set of interferometer media receiving a reflected light from the sample, and each interferometer media comprising a lens which generate a set of projections which constitute a wave interference pattern. In this example the beamsplitter and set of interferometer media constitute a Segnac interferometer. The sample may be characterized by reciprocity.

[0149] The results of the experiment shown in Figs. 6A through 9D were generated using a firee-space Sagnac interferometer as shown in Fig. 12. The diode laser was expanded and collimated via an objective (lOx, 0.25NA), then passed through a HWP to achieve the required TM polarization J = (1, 0). The laser may be a source polarized light.

[0150] As the precise polarization of the laser before the HWP may be unknown, a polarimeter may be to measure the polarization leaving the HWP, which may be subsequently removed to allow the full construction of the setup. Once polarized, the beam may pass through the nonpolarizing beamsplitter. The transmitted field may be referred to as E / =

[0151]

[0152] and the reflected field may be referred to as E,- = rE;w, where E;wis the incoming field, and t and r are the field transmittivity and reflectivity of the non-polarizing beamsplitter, respectively. The transmitted beam may proceed counter-clockwise to strike Mi, subsequently arriving at LI where it is focused into a cone defined by the focal length, fL = 100 mm in this example, the solid angle in the beam frame of reference £2(0,

[0153]

[0154] and the angle of incidence of the primary ray upon the film a as described in Fig. 10. Upon impingement, the beam may undergo scattering or diffractive processes.

[0155] However, only those fields which propagate within the light collection cone of the identical lens L2 given by (£2, -a), will be recollimated. Other wave-vectors which scatter within some number of wavelengths may not reach the detector, and therefore the reflected beam forms a field which varies only in-plane, with all components maintaining spatial and temporal coherence. It should be noted that a Sagnac interferometer may be built in other methods such as fiber optics and different interferometer structures may be used.

[0156] It is appreciated that there are other methods of realizing non-reciprocal structure-based polaritonic interferometry, and that these methods are also contemplated according to some embodiments of the presently disclosed subject matter. It is appreciated that polaritons mayinclude, but are not limited to: plasmon polaritons, exciton polaritons, and phonon polaritons. The present embodiments contemplate free space Sagnac interferometry, fiber optic based Sagnac interferometry, and / or any other type of interferometer that is sensitive to non-reciprocal phaseshifts.

[0157] The present embodiments contemplate other structures such as, but not limited to, metasurfaces, bulk metamaterials, twisting or inverting optical fibers, and / or any other medium of optical propagation which supports both polaritonic activity and non-reciprocity of counterpropagating optical signals within the medium.

[0158] Additionally, while the Sagnac interferometer may provide better discemibility, interferometer examples such as Michelson Interferometers, Mach-Zehnder Interferometer, Fabry-Perot Interferometers, White-Light Interferometers and Fizeau Interferometers and the like may be used in some embodiments of the presently disclosed subject matter.

[0159] It is expected that during the life of a patent maturing from this application many relevant interferometers and optical devices will be developed and the scopes of the terms such as interferometer are intended to include all such new technologies a priori.

[0160] Although the presently disclosed subject matter has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0161] It is the intent of the applicant(s) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the presently disclosed subject matter. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

CLAIMS1. A method of analyzing a sample, the method comprising:contacting the sample with a structure having a surface formed with a chiral pattern; directing two polarized incoming light beams from two different incoming directions to said structure, so as to induce two polaritonic modes propagating non- parallelly over said surface, and to diffract, for each propagation direction of said polaritonic modes, an outgoing light beam having a different polarization and / or a different phase; andanalyzing a difference in said polarizations and / or phases of said outgoing light beams, thereby analyzing the sample.

2. The method according to claim 1, wherein said sample and said incoming light beams are at opposite sides of said structure.

3. The method according to any one of the preceding claims, wherein said analyzing said difference comprises generating an interference between said outgoing light beams.

4. The method according to any one of claims 1 and 2, wherein said analyzing said difference comprises applying a polarimeter to each outgoing light beam.

5. The method according to any one of the preceding claims, wherein said structure comprises a two-dimensional grating.

6. The method according to claim 5, wherein said two-dimensional grating is defined over two orthogonal axes and comprises a plurality of elongated grating elements, wherein an orientation of said grating elements varies cyclically and periodically along one of said axes and is constant along another one of said axes.

7. The method according to any one of the preceding claims, wherein said directing is in free space.

8. The method according to any one of claims 1 through 6, wherein said directing is via one or more optical waveguides.

9. The method according to any one of the preceding claims, wherein said directing is executed to ensure that said incoming directions are at opposite sides of a normal to said surface and at equal angles relative thereto.

10. The method according to any one of the preceding claims, wherein said structure has a thickness of less than 500 nm.

11. The method according to any one of the preceding claims, wherein said structure and said incoming light beams are selected so as to generate said polaritonic modes as surface plasmon polaritons.

12. The method according to any one of claims 1 through 11, wherein said structure and said incoming light beams are selected so as to generate said polaritonic modes as exciton polaritons.

13. The method according to any one of claims 1 through 11, wherein said structure and said incoming light beams are selected so as to generate said polaritonic modes as phonon polaritons.

14. A system for analyzing a sample, the system comprising:a structure having a surface formed with a chiral pattern for receiving the sample; a light source and optics for directing to said structure two polarized incoming light beams from two different incoming directions, so as to induce two polaritonic modes propagating non-parallelly over said surface, and to diffract, for each propagation direction of said polaritonic modes, an outgoing light beam having a different polarization and / or a different phase; anda measuring system configured for measuring a difference in said polarizations and / or phases of said outgoing light beams.

15. The system according to claim 14, wherein said sample and said incoming light beams are at opposite sides of said structure.

16. The system according to any one of claims 14 and 15, wherein said optics are configured for generating an interference between said outgoing light beams.

17. The system according to claim 16, wherein said measuring system comprises an imager constituted to image an interference pattern between said outgoing light beams.

18. The system according to any one of claims 16 and 17 wherein said optics are arranged to form a Sagnac interferometer.

19. The system according to any one of claims 14 through 18, wherein said measuring system comprises a polarimeter.

20. The system according to any one of claims 14 through 19, wherein said structure comprises a two-dimensional grating.

21. The system according to claim 20, wherein said two-dimensional grating is defined over two orthogonal axes and comprises a plurality of elongated grating elements, wherein an orientation of said grating elements varies cyclically and periodically along one of said axes and is constant along another one of said axes.

22. The system according to any one of claims 14 through 21 , wherein the optics are configured to direct said incoming light beams in free space.

23. The system according to any one of claims 14 through 21, comprising one or more optical waveguides arranged to direct said incoming light beams to said structure.

24. The system according to any one of claims 14 through 23, wherein said optics are arranged such that said incoming directions are at opposite sides of a normal to said surface and at equal angles relative thereto.

25. The system according to any one of claims 14 through 24, wherein said structure has a thickness of less than 500 nm.

26. The method or system according to any one of claims 14 through 25, wherein said structure and said incoming light beams are selected so as to generate said polaritonic modes as surface plasmon polaritons.

27. The method or system according to any one of claims 14 through 25, wherein said structure and said incoming light beams are selected so as to generate said polaritonic modes as exciton polaritons.

28. The method or system according to any one of claims 14 through 25, wherein said structure and said incoming light beams are selected so as to generate said polaritonic modes as phonon polaritons.

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