Optical filter, spectrometer including the optical filter, and electronic apparatus including the optical filter

An optical filter, a spectrometer including the optical filter, and an electronic apparatus including the optical filter are disclosed. The optical filter includes a first reflector including a plurality of first structures that are periodically two-dimensionally arranged, each of the first structures having a ring shape, and a second reflector spaced apart from the first reflector and including a plurality of second structures that are periodically two-dimensionally arranged.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2019-0141900, filed on Nov. 7, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND

Example embodiments consistent with the present disclosure relate to an optical filter, a spectrometer including the optical filter, and an electronic apparatus including the optical filter.

2. Description of Related Art

Optical elements that change the transmission, reflection, polarization, phase, intensity, or path properties of incident light are used in various optical fields. Recently, attempts have been made to implement optical elements that exhibit various optical characteristics and that are miniaturized by using sub-wavelength structures.

The sub-wavelength structures may be used for spectrometers. In general, a resonant structure having a specific resonant wavelength may be implemented by arranging two reflectors spaced apart by a certain distance from each other. Such a reflector employed for this purpose includes a distributed Bragg reflector in which material layers having different refractive indexes are repeatedly stacked to a thickness of ¼ wavelength of incident light. In this case, as an increase in the number of stacked layers is necessary to increase reflectivity and the resonant wavelength is set by adjusting the distance between the reflectors, it may be difficult to set a desired resonant wavelength in an ultra-compact size.

SUMMARY

Example embodiments provide an optical filter, a spectrometer including the optical filter, and an electronic apparatus including the optical filter.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of embodiments of the disclosure.

According to an aspect of an example embodiment, an optical filter includes: a first reflector including a plurality of first structures that are periodically two-dimensionally arranged, each first structure of the plurality of first structures having a ring shape; and a second reflector spaced apart from the first reflector, the second reflector including a plurality of second structures that are periodically two-dimensionally arranged.

Each second structure of the plurality of second structures may have the ring shape or a disc shape.

A first size and a first pitch of the plurality of first structures may be less than a wavelength of incident light that is incident on the optical filter, and a second size and a second pitch of the plurality of second structures may be less than the wavelength of the incident light.

A transmission wavelength of the incident light may be determined based on at least one of respective refractive indexes of the plurality of first structures and the plurality of second structures, the first size of the plurality of first structures, the second size of the plurality of second structures, the first pitch of the plurality of first structures, the second pitch of the plurality of second structures, and an interval between the first reflector and the second reflector.

The first sizes of the plurality of first structures may include at least one of a first inner radius, a first outer radius, a first ratio between the first inner radius and the first outer radius, and a first height, and the second sizes of the plurality of second structures may include at least one of a second inner radius, a second outer radius, a second ratio between the second inner radius and the second outer radius, and a second height.

The transmission wavelength of the incident light may be determined based on at least one of the first inner radius, the first outer radius, the first ratio between the first inner radius and the first outer radius, the second inner radius, the second outer radius, and the second ratio between the second inner radius and the second outer radius.

Each second structure of the plurality of second structures may entirely overlap a corresponding first structure of the plurality of first structures in a direction perpendicular to a plane of the optical filter.

The optical filter may further include a material layer surrounding the plurality of first structures and the plurality of second structures.

The plurality of first structures and the plurality of second structures may each include a dielectric material having a higher refractive index and a lower absorption coefficient than a refractive index and an absorption coefficient, respectively, of the material layer.

The plurality of first structures and the plurality of second structures may each include at least one from among crystalline silicon, amorphous silicon, titanium oxide, silicon nitride, titanium nitride, transparent conductive oxide, a group III-V semiconductor compound, and metal oxide.

The optical filter may further include a third reflector spaced apart from the second reflector, the third reflector including a plurality of third structures that are periodically two-dimensionally arranged.

Each third structure of the plurality of third structures may have the ring shape or the disc shape.

In accordance with an aspect of an example embodiment, an optical filter includes: a plurality of partial filters having different center wavelengths, wherein each partial filter from among the plurality of partial filters includes a first reflector including a plurality of first structures that are periodically two-dimensionally arranged, each first structure of the plurality of first structures having a ring shape; and a second reflector spaced apart from the first reflector, the second reflector including a plurality of second structures that are periodically two-dimensionally arranged.

Each second structure of the plurality of second structures may have the ring shape or a disc shape.

A transmission wavelength of incident light is determined based on at least one of respective refractive indexes of the plurality of first structures and the plurality of second structures, a first size of the plurality of first structures, a second size of the plurality of second structures, a first pitch of the plurality of first structures, a second pitch of the plurality of second structures, and an interval between the first reflector and the second reflector.

The optical filter may further include a material layer surrounding the plurality of first structures and the plurality of second structures.

In accordance with an aspect of an example embodiment, a spectrometer includes: an optical filter including at least one partial filter; and a light detecting device configured to receive light transmitted through the optical filter, wherein each partial filter from among the at least one partial filter includes a first reflector including a plurality of first structures that are periodically two-dimensionally arranged, each first structure from among the plurality of first structures having a ring shape and a second reflector spaced apart from the first reflector, the second reflector including a plurality of second structures that are periodically two-dimensionally arranged.

Each second structure from among the plurality of second structures may have the ring shape or a disc shape.

The light detecting device may include an image sensor or a photodiode.

In accordance with an aspect of the disclosure, an electronic apparatus includes: a light source configured to radiate light toward an object; a spectrometer disposed on a light path of light reflected from the object; and a processor configured to analyze at least one from among physical properties, a shape, a location, and a motion of the object, by using light detected by the spectrometer, wherein the spectrometer includes an optical filter including at least one partial filter and a light detecting device configured to receive light transmitted through the optical filter; a first reflector including a plurality of first structures that are periodically two-dimensionally arranged, each first structure from among the plurality of first structures having a ring shape; and a second reflector spaced apart from the first reflector, the second reflector including a plurality of second structures that are periodically two-dimensionally arranged.

In accordance with an aspect of the disclosure, an optical filter includes: a first layer of first nanostructures, the first nanostructures having a ring shape or a disc shape; and a second layer of second nanostructures, the second nanostructures having the ring shape or the disc shape, wherein a dimension from among a plurality of dimensions of the first nanostructures and the second nanostructures is less than a wavelength of light incident upon the optical filter.

The first nanostructures may have the ring shape.

The plurality of dimensions may include an inner radius of the first nanostructures and the second nanostructures, an outer radius of the first nanostructures and the second nanostructures, a ratio between the inner radius and the outer radius, a height of the first nanostructures and the second nanostructures, and a distance between the first layer and the second layer.

The first nanostructures may be periodically arranged at a first interval in the first layer and the second nanostructures may be periodically arranged at a second interval in the second layer.

The plurality of dimensions may include an inner radius of the first nanostructures and the second nanostructures, an outer radius of the first nanostructures and the second nanostructures, a ratio between the inner radius and the outer radius, a height of the first nanostructures and the second nanostructures, a distance between the first layer and the second layer, the first interval, and the second interval.

A first dimension of the first nanostructures may be different from a corresponding second dimension of the second nanostructures.

A spectrometer may include a plurality of the optical filters in accordance with the above-noted aspect of the disclosure, wherein the plurality of the optical filters includes a first optical filter and a second optical filter, and wherein a first dimension from among the plurality of dimensions of the first optical filter is different from a corresponding second dimension of the second optical filter such that the first optical filter transmits light of a first wavelength and the second optical filter transmits light of a second wavelength different from the first wavelength.

DETAILED DESCRIPTION

Example embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, the expression, “at least one of a, b, and c,” should be understood as including only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

In the description below, when a constituent element is disposed “above” or “on” another constituent element, the constituent element may be directly on the other constituent element or may be above the other constituent elements in a non-contact manner. Terms such as “first” and “second” are used herein merely to describe a variety of constituent elements, but the constituent elements are not limited by the terms. Such terms are used only for the purpose of distinguishing one constituent element from another constituent element.

The expression of singularity in the present specification includes the expression of plurality unless clearly specified otherwise in context. When a part may “include” a certain constituent element, unless specified otherwise, it may not be construed to exclude another constituent element but may be construed to further include other constituent elements.

Terms such as “˜portion”, “˜unit”, “˜module”, and “˜block” stated in the specification may signify a unit to process at least one function or operation and the unit may be embodied by hardware, software, or a combination of hardware and software.

The connecting lines or connectors shown in the various figures presented are intended to represent functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device.

FIG. 1is a perspective view of an optical filter100according to an example embodiment.FIG. 2is a cross-sectional view of the optical filter100ofFIG. 1, andFIG. 3is a plan view of the optical filter100ofFIG. 1.FIG. 4is a conceptual diagram of a principle of transmitting light of a specific wavelength by first and second reflectors provided in the optical filter100ofFIG. 1.

Referring toFIGS. 1 to 4, the optical filter100may include first and second reflectors110and120(i.e., a first layer and a second layer) spaced apart from each other. The first and second reflectors110and120may be provided on a substrate105. The substrate105may include, for example, a transparent material. The substrate105may include a material having a refractive index smaller than those of first and second structures115and125, which are described later.

The first and second reflectors110and120may be arranged spaced apart from each other on or above the substrate105at a certain interval S as shown inFIG. 2. The first reflector110provided on an upper surface of the substrate105may include a plurality of first structures115(i.e., first nanostructures) arranged cyclically (i.e., periodically) in two dimensions. The second reflector120provided above the first reflector110may include a plurality of second structures125(i.e., second nanostructures) cyclically arranged in two dimensions.

The first and second structures115and125may include sub-wavelength structures. The sub-wavelength structures signify structures having sizes and pitches less than the wavelength of the incident light. Light incident on the optical filter100may include, for example, visible rays or infrared rays. However, the disclosure is not limited thereto.

The first and second structures115and125each may have a ring shape. In this state, the first structure115may have an outer radius R1out, an inner radius R1in, and a height t1, and the second structures125may have an outer radius R2out, an inner radius R2in, and a height t2as shown inFIG. 2.

The first structures115may be cyclically arranged in a direction with a first pitch P1(i.e., a first interval). The first structures115may be arranged in two dimensions, for example, in an equilateral triangular or regular hexagonal pattern, as illustrated inFIG. 3. In this case, three neighboring first structures115may be arranged at the respective vertexes of an equilateral triangle pattern. However, this is an example, and the first structures115may be arranged in other various patterns.

The second structures125may be cyclically arranged in a direction with a second pitch P2(i.e., a second interval). The second structures125, like the first structures115, may be arranged in two dimensions, for example, in the form of an equilateral triangle or a regular hexagon. However, this is an example, and the second structures125may be arranged in other various patterns.

FIG. 1illustrates an example in which the second structures125are symmetrically arranged with respect to the first structures115. In other words, each second structure125may entirely overlap a corresponding first structure115in a direction perpendicular to a plane of the optical filter100. In this case, the second structures125may have the same material, size, shape, and pitch as those of the first structures115, respectively. In other words, the first and second structures115and125may be cyclically arranged in a direction, with the same pitch, in the form of an equilateral triangle or a regular hexagon. As illustrated inFIG. 3, when viewed from a plan view that is perpendicular to a z-axis direction in which the first and second reflectors110and120are spaced apart from each other, the first structures115and the second structures125may be arranged to be overlapped with each other.

The second structures125may be asymmetrically arranged with respect to the first structures115. In this case, at least one of a material, a size, a shape, a pitch, or an arrangement pattern of the second structures125may be different from those of the first structures115, respectively.

The substrate105may further include a material layer150to fill around (i.e., surround) the first and second structures115and125. In this state, the first and second structures115and125may include a dielectric material having a refractive index higher than, and an absorption coefficient lower than, those of the material layer150formed around them. Furthermore, as described above, the first and second structures115and125may have a refractive index higher than that of the substrate105.

The first and second structures115and125may include, for example, at least one of crystalline silicon, amorphous silicon, titanium oxide, silicon nitride, titanium nitride, transparent conductive oxide (ITO), a group III-V semiconductor compound, or metal oxide. However, the disclosure is not limited thereto. The material layer150filling around the first and second structures115and125may include, for example, silicon oxide, polymer-based material (SU-8, PMMA), or hydrogen silsesquioxane (HSQ), but the disclosure is not limited thereto.

As illustrated inFIG. 4, the first reflector110and the second reflector120form a Fabry-Perot resonator. The Fabry-Perot resonator includes a cavity in a space between the two separated reflectors110and120each having high reflectivity. Light input between the two reflectors110and120reciprocates between the reflectors110and120facing each other, causing constructive interference and destructive interference. In this state, light having a wavelength corresponding to the resonant wavelength λcmay satisfy a constructive interference condition, thereby being transmitted through the Fabry-Perot resonator. Light λanhaving a different wavelength band may not be transmitted through the Fabry-Perot resonator. The Fabry-Perot resonator has excellent performance as a transmission spectrum has a narrower bandwidth with respect to the resonant wavelength λccorresponding thereto. The performance of the Fabry-Perot resonator may be defined by a quality factor (Q factor) or a full width at half maximum (FWHM).

As the optical filter100according to the present example embodiment employs the first and second structures115and125, each having a ring shape, which are a sub-wavelength structure having a high refractive index, as reflectors constituting the Fabry-Perot resonator, the optical filter100may exhibit a high reflectivity and may reduce the device volume. Furthermore, no polarization dependency may occur in the transmission of light of a specific wavelength due to the shape symmetry of the first and second structures115and125.

The resonant wavelength λcthat is transmitted through the optical filter100(i.e., the transmission wavelength) is determined by design variables such as an optical material or a geometrical structure of the first reflector110and the second reflector120. In detail, the resonant wavelength λcthat is transmitted through the optical filter100may be determined by at least one of an interval S (i.e., a distance) between the first and second reflectors110and120, refractive indexes of the first and second structures115and125, sizes of the first and second structures115and125, and pitches P1and P2of the first and second structures115and125. The sizes of the first and second structures115and125may include at least one of the inner radii R1inand R2in, the outer radii R1outand R2out, a ratio between the inner radius and the corresponding outer radius, and the heights t1and t2. Furthermore, when the optical filter100further includes the material layer150that fills around the substrate105and the first and second structures115and125, the resonant wavelength λcthat is transmitted through the optical filter100may be determined further by the refractive index of the substrate105and the refractive index of the material layer150.

In the optical filter100, the resonant wavelength λcbetween the first and second reflectors110and120may be finely adjusted by changing design variables of the first and second reflectors110and120, and further the resonant wavelength within each of the first and second structures115and125, each having a ring shape, may be adjusted.

As such, the optical filter100according to the present example embodiment may transmit a desired wavelength band by using the design variables of the first and second reflectors110and120. A degree of freedom with respect to wavelength selection is high, and the filtering characteristics with no polarization dependency and incident angle dependency may be obtained due to the shape symmetry of the first and second structures115and125. Accordingly, the optical filter100may be employed as a narrow band pass filter or employed in a spectrometer having excellent spectral characteristics in a wide wavelength band. Furthermore, as the optical filter100may be monolithically integrated in a light detecting device such as an image sensor by using a semiconductor process, an ultra-compact portable spectrometer may be implemented.

FIG. 5illustrates that the incident light is perpendicularly incident on an optical filter according to a comparative example. InFIG. 5, a k direction is an incident direction of the incident light and is parallel to the z-axis direction, and transverse electric (TE) polarized light of the incident light is parallel to a y-axis direction.FIG. 6Ais a graph of the spectral characteristics of the optical filter ofFIG. 5with respect to the TE polarized light.FIG. 6Bis a graph of the spectral characteristics of the optical filter ofFIG. 5with respect to transverse magnetic (TM) polarized light.

Referring toFIG. 5, the optical filter10according to a comparative example may include a substrate11, a first reflector13, and a second reflector15, and each of the first and second reflectors13and15may include a plurality of gratings each having a lengthwise direction in the y-axis direction. In the above structure, only the TE polarized portion of the light incident in the k direction exhibits resonant wavelength characteristics, that is, polarized light parallel to the y-axis direction inFIG. 5, but differently polarized light does not exhibit designed resonance characteristics.

In detail, as illustrated inFIG. 6A, the optical filter10according to a comparative example exhibits high transmittance at a certain center wavelength with respect to the TE polarized light and a spectrum having a good Q value, but exhibits, as illustrated inFIG. 6B, a different type of a spectrum with respect to the TM polarized light. As shown, the optical filter10does not perform a spectroscopic function with respect to the light of a designed wavelength. Certain polarized light is formed by a combination of TE and TM polarized light, that is, non-polarized light is in the form in which the TE and TM polarized light are evenly distributed, and thus the optical filter10has a light loss of 50% in the spectroscopy of the incident light. However, the optical filter100according to an example embodiment may have no light loss according to polarization as described below.

FIG. 7illustrates an example in which the incident light is perpendicularly incident on the optical filter100ofFIG. 1. The materials, shapes, sizes, and pitches of the first and second structures115and125are the same as those ofFIG. 1. In this state, the pitches of the first and second structures115and125are set to be about 400 nm. Referring toFIG. 7, the k direction is the incident direction of the incident light and is parallel to the z-axis direction, and the TE polarized light of the incident light is parallel to the y-axis direction.

FIG. 8Ais a graph of the spectral characteristics of the optical filter100ofFIG. 7with respect to TE polarized light.FIG. 8Bis a graph of the spectral characteristics of the optical filter100ofFIG. 7with respect to the TM polarized light. As illustrated inFIGS. 8A and 8B, it may be seen that, in the optical filter100according to an example embodiment, spectral characteristics of the TE polarized light and the TM polarized light have almost no difference in the wavelength band and the waveform. In general, as certain polarized light is generated by a combination of the two orthogonal polarizations, even when light of a certain polarization component is incident on the optical filter100according to an example embodiment, the above transmission spectrum may be obtained.

FIG. 9illustrates an example in which the incident light is perpendicularly incident on the optical filter100ofFIG. 1. The materials, shapes, sizes, and pitches of the first and second structures115and125are the same as those ofFIG. 1. In this state, the pitches of the first and second structures115and125are set to be about 400 nm. Referring toFIG. 9, the k direction that is the incident direction of the incident light is parallel to the z-axis direction, and the TE polarized light of the incident light forms a certain angle ϕ with respect to the y-axis direction.

FIG. 10is a graph of the spectral characteristics of the incident light according to a change in the angle ϕ of the TE polarized light with respect to the y-axis direction as shown inFIG. 9. As illustrated inFIG. 10, even when the angle ϕ of the TE polarized light changes, there is almost no difference in the spectral characteristics, and thus it may be seen that the optical filter100according to an example embodiment has characteristics that function independently of TE polarization angle.

FIG. 11illustrates an example in which the incident light is obliquely incident on the optical filter100ofFIG. 1. The materials, shapes, sizes, and pitches of the first and second structures115and125are the same as those ofFIG. 1. In this state, the outer radius and the inner radius of each of the first and second structures115and125are set to be about 126 nm and about 26.25 nm, respectively. Referring toFIG. 11, the k direction is the incident direction of the incident light and forms a certain angle θ with respect to the z-axis direction, and the TE polarized light of the incident light forms a certain angle with respect to the y-axis direction.

FIGS. 12A and 12Bare graphs of the spectral characteristics of the incident light according to a change of the incident angle θ of the incident light with respect to the z-axis direction inFIG. 11. As illustrated inFIGS. 12A and 12B, in the optical filter100according to an example embodiment, it may be seen that there is almost no difference in the spectral characteristics even when the incident angle θ of the incident light varies from about 0° to about 30°.

FIG. 13illustrates an example in which the incident light is obliquely incident on the optical filter100ofFIG. 1. The materials, shapes, sizes, and pitches of the first and second structures115and125are the same as those ofFIG. 1. In this state, the outer radius and the inner radius of each of the first and second structures115and125are set to be about 126 nm and about 26.25 nm, respectively. Referring toFIG. 13, the k direction is the incident direction of the incident light and forms a certain angle ψ with respect to the z-axis direction, and the TE polarized light of the incident light is parallel to the y-axis direction.

FIGS. 14A and 14Bare graphs of the spectral characteristics of the incident light according to a change in an incident angle ψ of the incident light with respect to the z-axis direction inFIG. 13. As illustrated inFIGS. 14A and 14B, in the optical filter100according to an example embodiment, it may be seen that there is almost no difference in the spectral characteristics even when the incident angle ψ of the incident light varies from about 0° to about 30°.

As illustrated inFIGS. 11 to 14B, in the optical filter100according to an example embodiment, it may be seen that the spectral characteristics of the incident light do not change much even when the incident angle of the incident light varies. As described above, the optical filter100according to an example embodiment may have excellent spectral characteristics without polarization dependency and incident angle dependency.

FIGS. 15A to 15Care graphs of the spectral characteristics according to a ratio of the outer radius to the inner radius of the first and second structures115and125, in the optical filter100ofFIG. 1.FIGS. 15A to 15Cillustrate a case in which the incident light is perpendicularly incident on the optical filter100ofFIG. 1. The materials, shapes, sizes, and pitches of the first and second structures115and125are the same as those ofFIG. 1. The pitches of the first and second structures115and125are set to be about 400 nm, the heights of the first and second structures115and125are set to be about 370 nm, and the interval between the first and second reflectors110and120is set to be about 350 nm.FIGS. 15A to 15Crespectively illustrate the spectral characteristics of the incident light when the outer radius of the first and second structures115and125varies from about 120 nm to about 130 nm.

FIG. 15Aillustrates the spectral characteristics when a ratio Rout/Rinof the outer radius to the inner radius of the first and second structures115and125is about 4.0.FIG. 15Billustrates the spectral characteristics when a ratio Rout/Rinof the outer radius to the inner radius of the first and second structures115and125is about 4.3.FIG. 15Cillustrates the spectral characteristics when a ratio Rout/Rinof the outer radius to the inner radius of the first and second structures115and125is about 4.8.

Referring toFIGS. 15A to 15C, in the optical filter100according to an example embodiment, it may be seen that various spectral characteristics may be obtained by changing the ratio Rout/Rinof the outer radius to the inner radius of the first and second structures115and125, and sharp and uniform spectral characteristics having a FWHM of about 2 nm to about 6 nm may be obtained.

In the optical filter100ofFIGS. 15A to 15Caccording to an example embodiment, various spectral characteristics may be obtained by changing the ratio of the outer radius to the inner radius among the design variables of the first reflector110and the second reflector120. However, the disclosure is not limited thereto, and various spectral characteristics may be obtained by changing at least one of the other design variables of the first reflector110and the second reflector120.

FIG. 16is a cross-sectional view of an optical filter200according to an example embodiment.FIG. 17is a plan view of the optical filter200ofFIG. 16.

Referring toFIG. 16, the optical filter200may include first and second reflectors210and220arranged spaced apart from each other at the certain interval S. The first reflector210may include a plurality of first structures215, each having a ring shape, and the second reflector220may include a plurality of second structures225, each having a ring shape.

In the optical filter200according to the present example embodiment, the first and second structures215and225are asymmetrically arranged with each other. In this state, the first and second structures215and225may be different from each other in terms of at least one of a material, a shape, a size, a cycle, or an arrangement pattern.

For example, the first structures215are arranged in two dimensions with the first pitch P1in a direction, and each of the first structures215may have the outer radius R1out, the inner radius R1in, and the height t1. The second structures225are arranged in two dimensions with the second pitch P2in a direction, and each of the second structures225may have an outer radius R2out, an inner radius R2in, and a height t2.FIG. 16illustrates an example in which the outer radius R1outof the first structures215is greater than the outer radius R2outof the second structures225and the height t1of the first structures215is less than the height t2of the second structures225.

As illustrated inFIG. 17, when viewed from a plan view that is perpendicular to the z-axis direction in which the first and second reflectors210and220are spaced apart from each other, the first structures215and the second structures225may be arranged to be overlapped with each other. However, the disclosure is not limited thereto. Furthermore, although each of the first structures215and the second structure225may be arranged, for example, in the form of a regular hexagon or an equilateral triangle, the disclosure is not limited thereto.

FIGS. 18A to 18Cillustrate examples of different optical filters300a,300b, and300ceach manufactured with a different outer radius of a first structure, according to an example embodiment. In other words, the outer radius of the first structure315aare changed to R1a, R1b, and R1cwhen other values remain fixed, including the inner radius R1inand the height t1of a first structure315a, the first pitch P1of the first structures315a, the outer radius R2out, the inner radius R2in, and the height t2of a second structure325, the second pitch P2of the second structures325, and the interval S between the first and second reflectors310and320.

FIG. 18Aillustrates an example in which, assuming that the outer radius of the first structure315ais R1a, light L1of a first wavelength of incident light L transmits through an optical filter300a.FIG. 18Billustrates an example in which, assuming that the outer radius of the first structure315bis R1b(>R1a), light L2of a second wavelength of the incident light L transmits through an optical filter300b. Furthermore,FIG. 18Cillustrates an example in which, assuming that the outer radius of the first structure315cis R1c(>R1b), light L3of a third wavelength of the incident light L transmits through an optical filter300c. As such, transmission wavelength may be selectively adjusted by changing only the outer radius of the first structure315a,315b, and315c.

FIGS. 19A to 19Cillustrate examples of different optical filters400a,400b, and400ceach manufactured with a different outer radius of the second structure, according to an example embodiment. In other words, the outer radius of a second structure425aare changed to R2a, R2b, and R2cwhen other values remain fixed, including the outer radius R1out, the inner radius R1in, and the height t1of a first structure415, the first pitch P1of the first structures415, the inner radius R2inand the height t2of the second structure425a, the second pitch P2of a second structures425, and the interval S between first and second reflectors410and420.

FIG. 19Aillustrates an example in which, assuming that the outer radius of the second structure425ais R2a, the light L1of a first wavelength of the incident light L transmits through an optical filter400a.FIG. 19Billustrates an example in which, assuming that the outer radius of the second structure425bis R2b(>R2a), the light L2of a second wavelength of the incident light L transmits through an optical filter400b. Furthermore,FIG. 19Cillustrates an example in which, assuming that the outer radius of the second structure425cis R2c(>R2b), the light L3of a third wavelength of the incident light L transmits through an optical filter400c. As such, the transmission wavelength may be selectively adjusted by changing only the outer radius of the second structure425a,425b, and425c.

In the above description, a case of selectively adjusting the transmission wavelength by changing the outer radius of the first or second structure is described as an example. However, the disclosure is not limited thereto, and the transmission wavelength may be selectively adjusted by changing the inner radius or the ratio of the outer radius to the inner radius of the first or second structure. In addition, the transmission wavelength may be selectively adjusted by changing other design variables of the first and second structures.

FIG. 20is a perspective view of an optical filter500according to an example embodiment. The optical filter500ofFIG. 20is the same as the optical filter100ofFIG. 1, except for the arrangement pattern of first and second structures515and525.

Referring toFIG. 20, the optical filter500may include first and second reflectors510and520arranged spaced apart from each other. In this state, the first reflector510may include a plurality of first structures515, each having a ring shape, and the second reflector520may include a plurality of second structures525, each having a ring shape. In this state, each of the first structures515and the second structures525may be arranged in a square pattern.

FIG. 21is a perspective view of an optical filter600according to an example embodiment. The optical filter600ofFIG. 21is the same as the optical filter100ofFIG. 1, except that a first structure615has a disc shape, not a ring shape.

Referring toFIG. 21, the optical filter600may include first and second reflectors610and620arranged spaced apart from each other. In this state, the first reflector610may include a plurality of first structures615cyclically arranged in two dimensions, and the second reflector620may include a plurality of second structures625cyclically arranged in two dimensions. In this state, the first and second structures615and625may be sub-wavelength structures. Each of the first structures615and the second structures625may be arranged, for example, in the form of an equilateral triangle, a square, or a regular hexagon.

The first structures615each may have a disc shape. The first structures615each may have a radius and a height, and the first structures615may be cyclically arranged with a first pitch in a direction. The second structures625each may have a ring shape. The second structures625each may have an outer radius, an inner radius, and a height, and the second structures625may be cyclically arranged with a second pitch in a direction.

The substrate105may be provided and a material layer150may be provided to fill around the first and second structures615and625. The first and second structures615and625may include a dielectric material having a higher refractive index and a lower absorption coefficient than corresponding values of the material layer150.

The first reflector610including the first structures615, each having a disc shape, and the second reflector620including the second structures625, each having a ring shape, may constitute the Fabry-Perot resonator. A resonant wavelength of light that is transmitted through the optical filter600may be determined by at least one of the design variables such as an optical material or a geometrical structure of the first reflector610and the second reflector620.

AlthoughFIG. 21illustrates an example in which the first structures615each has a disc shape of a cylindrical form, the disclosure is not limited thereto, and the first structures615each may have a disc shape of a rectangular column or other polygonal column. Furthermore, although, in the above description, each of the first structures615has a disc shape and each of the second structures625has a ring shape, the first structures615may have a ring shape and the second structures625may have a disc shape.

FIG. 22is a cross-sectional view of an optical filter700according to an example embodiment. The optical filter700ofFIG. 22is the same as the optical filter100ofFIG. 1, except that three reflectors are provided.

Referring toFIG. 22, the optical filter700may include first, second, and third reflectors710,720, and730arranged spaced apart from each other. In this state, the first and second reflectors710and720may be arranged spaced apart from each other with a first interval S1, and the second and third reflectors720and730may be arranged spaced apart from each other with a second interval S2.

The first reflector710provided on the substrate105may include a plurality of first structures715cyclically arranged in two dimensions, the second reflector720may include a plurality of second structures725cyclically arranged in two dimensions, and the third reflector730may include a plurality of third structures735cyclically arranged in two dimensions. Each of the first, second, and third structures715,725, and735may have a ring shape as a sub-wavelength structure.

Each of the first, second, and third structures715,725, and735may have an outer radius, an inner radius, and a height. The first structures715may be cyclically arranged in a direction with the first pitch P1, the second structures725may be cyclically arranged in a direction with the second pitch P2, and the third structures735may be cyclically arranged in a direction with a third pitch P3. Each of the first, second, and third structures715,725, and735may be arranged, for example, in the form of an equilateral triangle, a square, or a regular hexagon, but the disclosure is not limited thereto.

The first, second, and third structures715,725, and735all may have the same material, size, shape, pitch, and arrangement pattern. Alternatively, the first, second, and third structures715,725, and735may be different from each other in terms of at least one of a material, a size, a shape, a pitch, or an arrangement pattern. The substrate105may be provided and the material layer150may be provided to fill around the first, second, and third structures715,725, and735.

A resonant wavelength of light that is transmitted through the optical filter700may be determined by at least one of the design variables such as an optical material or a geometrical structure of the first, second, and third reflectors710,720, and730.

In the above description, an example in which the first, second, and third structures715,725, and735all have a ring shape is described. However, the disclosure is not limited thereto, and at least one of the first, second, or third structures715,725, or735may have a ring shape, and the other structure(s) may have a disc shape. Furthermore, although in the above description, the optical filter700is described as having three reflectors710,720, and730, the disclosure is not limited thereto, and the optical filter700may include four or more reflectors arranged spaced apart from each other.

FIG. 23is a perspective view of a spectrometer1000according to an example embodiment.

Referring toFIG. 23, the spectrometer1000may include a light detecting device1500and an optical filter1100provided above the light detecting device1500. In this state, the optical filter1100may include a plurality of partial filters1110arranged in two dimensions above the light detecting device1500. However, this is an example, and the partial filters1110may be arranged in one-dimension. The partial filters1110may be monolithically integrated on the light detecting device1500by using a semiconductor process.

Each of the partial filters1110may be any one or more of the optical filters described in the above-described example embodiments. Accordingly, a detailed description about the partial filters1110is omitted. In the above-described example embodiments, the wavelength of light transmitted through the optical filter may be selectively adjusted by changing at least one of the design variables of the structures constituting the optical filter. Accordingly, in the present example embodiment, by changing at least one of the design variables of the structure constituting each of the partial filters1110, the partial filters1110may be provided to transmit light of different wavelength bands of the incident light.

The light detecting device1500may receive the light transmitted through the optical filter1100and convert the received light to electrical signals. In detail, the light incident on the optical filter1100is transmitted through the partial filters1110, and the light of a different wavelength band that is transmitted through the partial filters1110arrives at pixels of the light detecting device1500. The light detecting device1500converts the light incident on the pixels to electrical signals, thereby performing spectroscopy on the light incident on the optical filter1100.

The light detecting device1500may include, for example, an image sensor or a photodiode such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) image sensor. However, the disclosure is not limited thereto.

An additional optical filter for transmitting light of a different wavelength band may be further provided considering a wavelength band included in the light that is subject to spectroscopy, according to a specific use of the spectrometer1000. Furthermore, other additional optical filters may be further provided to block light of a wavelength band that is not subject to spectroscopy.

The spectrometer1000may be used for various optical apparatuses or sensors. For example, the spectrometer1000may be used for gas sensors, chemical sensors, skin sensors, or food sensors. Such sensors may identify the types of and/or detect the concentrations of various molecules existing in the atmosphere by using the spectrometer1000. The sensors may rely on the properties of the measured components, such that transmittance varies with respect to the wavelength according to the types and concentrations of components. Furthermore, the spectrometer1000may be used as a testing apparatus with respect to an object. For example, the spectrometer1000may be used as an apparatus for analyzing the location or shape of an object, or analyzing the components and physical properties of an object or freshness of foods according to the Raman spectroscopy.

FIG. 24is a schematic block diagram of an electronic apparatus2000according to an example embodiment.

Referring toFIG. 24, the electronic apparatus2000may include a light source2200for radiating light Li toward an object OBJ, a spectrometer2500disposed on an optical path of light Lr reflected from the object OBJ, the light Li being radiated by the light source2200, and a processor2700for analyzing at least one of physical properties, shape, location, or motion of the object OBJ by analyzing the light detected by the spectrometer2500. In this state, the spectrometer2500may include a light detecting device2530and an optical filter2510provided on the light detecting device2530, which may be the spectrometer ofFIG. 23.

The operation of the electronic apparatus2000is described below with an example of the Raman spectroscopy.

The Raman spectroscopy uses a phenomenon that an energy state is shifted when light of a single wavelength scatters through the interaction with the molecular vibrations of a material forming the object OBJ.

Light Li radiated by the light source2200may act as exciting light to the object OBJ. The light source2200may provide light of a single wavelength that is suitable for detecting a wavelength shift. For example, a pulse-type laser light of a single wavelength may be provided. In other words, light is scattered by the molecular structure of the object OBJ. Light Lr reflected from the object OBJ may be scattered light having a wavelength converted by the molecular structure of the object OBJ, and the scattered light may include various spectrums having a different degree of wavelength conversion according to the molecular state of the object OBJ. This is referred to as a Raman signal.

When the Raman signal is input to the spectrometer2500, each partial filter constituting the optical filter2510transmits light of a corresponding wavelength, the transmitted light is input to pixels of the light detecting device2530, and the quantity of the light is detected.

The detected Raman signal is analyzed by the processor2700. The Raman signal may include a wavelength shift of the incident light, which, as energy shift, may include information related to molecular vibration of a material, for example, information about a molecular structure or a bond form, or information about a functional group included in the object OBJ. Depending on the molecular composition forming the object OBJ, Raman peaks appear differently on the Raman spectrum, for example, glucose, urea, ceramide, keratin or collagen contained in the intercellular fluid or blood of the object OBJ may be analyzed. As such, the processor2700may analyze a material distribution amount in the object OBJ from the light from the object OBJ, that is, the Raman signal.

The electronic apparatus2000may be used as a three-dimensional optical sensor, that is, an apparatus for sensing the shape or motion of the object OBJ, an example of which is described below.

The light source2200may radiate the light Li including a plurality of wavelength bands toward the object OBJ. The light Li may be radiated to scan the object OBJ, and to this end, an optical element such as a beam steering component may be further disposed between the light source2200and the object OBJ.

The light Lr reflected from the object OBJ is received by the spectrometer2500. In the spectrometer2500, the optical filter2510may be configured to transmit light of a corresponding wavelength to detect the light of the wavelength bands radiated by the light source2200.

The processor2700may analyze information about the object OBJ from the signal about the light of the wavelengths detected by the spectrometer2500. For example, the determination of a three-dimensional shape of the object OBJ may be performed by performing an operation for measuring a time of flight from the detected light signal. In addition, the shape of the object OBJ may be determined through a direct time measurement method or an operation using correlation.

When the light source2200radiates light of different wavelengths and the spectrometer2500detects the light Lr reflected from the object OBJ for each wavelength, for example, a speed of scanning the object OBJ may be increased, and information about the location or shape of the object OBJ may be obtained at a relatively fast speed.

Although, in the above description, the physical properties of the object OBJ are analyzed by the Raman spectroscopy in which the electronic apparatus2000detects a change in the wavelength caused by the object OBJ, or the location or shape of the object OBJ is analyzed by analyzing the light Lr reflected from the object OBJ, the disclosure is not limited thereto.

Furthermore, the processor2700may control an overall operation of the electronic apparatus2000. For example, the processor2700may control power supply control or pulse wave (PW) or continuous wave (CW) generation control with respect to the light source2200. The electronic apparatus2000may include a memory for storing programs needed for an operation of the processor2700and other data.

A result of the operation in the processor2700, that is, information about the shape, location, or physical properties of the object OBJ may be transmitted to another unit. For example, the information may be transmitted to autonomous driving equipment that needs information about the three-dimensional shape, motion, or location of the object OBJ, or to a medical apparatus using the physical properties of the object OBJ information, for example, biometric information. Alternatively, the unit to which the result is transmitted may include a display apparatus or a printer that outputs the result. In addition, the unit to which the result is transmitted may include smartphones, cell phones, personal digital assistants (PDAs), laptops, PCs, and other mobile or non-mobile computing devices, but the disclosure is not limited thereto.

According to the above-described example embodiments, as the optical filter includes a reflector having ring-shaped structures, a desired wavelength band may be selectively transmitted. Accordingly, an optical filter may be implemented, which has a high degree of freedom with respect to the wavelength selection and has no polarization dependency or incident angle dependency due to the shape symmetry of the structures. Accordingly, the optical filter according to the disclosure may be employed as a narrow band pass filter, or applied to spectrometers having excellent spectral characteristics in a wide wavelength band. Furthermore, as the optical filter may be monolithically integrated in the light detecting device such as an image sensor by using a semiconductor process, an ultra-compact portable spectrometer may be implemented.

Although the above optical filter, spectrometer, and optical apparatuses are described with reference to the example embodiments illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the following claims.