Patent Description:
A spectrometer may measure an optical spectrum of incoming light. A scanning-type spectrometer may use one or more tunable bandpass filters to select different spectral components of the incoming light. A scanning-type spectrometer operates by scanning the center wavelength of the tunable bandpass filter while measuring optical power levels of light transmitted through the tunable bandpass filter, so as to obtain the optical spectrum. Alternatively, a polychromator-type spectrometer uses a wavelength-dispersing element optically coupled to a photodetector array for parallel detection of the optical.

<CIT> discloses a multi-spectral imager with two stacked filter arrays. <CIT> discloses a flow spectrometer using a linear variable bandpass filter.

<CIT> discloses inter alia a cuvette with at least a cylindrical inner portion for the photometric measurement of liquids.

Conventional optical filters and spectrometers are bulky, which limits their usefulness in portable light-sensing devices and applications. Linearly variable filters have been used in spectrometers to provide a wavelength separating function. Referring to <FIG>, a conventional linearly variable filter <NUM> may be illuminated with white light, which includes top <NUM>, middle <NUM>, and bottom <NUM> multi-wavelength light beams. The top <NUM>, middle <NUM>, and bottom <NUM> multi wavelength light beams may strike the linearly variable filter <NUM> at respective top 11A, middle 12A, and bottom 13A locations. The linearly variable filter <NUM> may have a center wavelength of a passband varying linearly along an x-axis <NUM>. For instance, the filter <NUM> may transmit a short wavelength peak 11B at the top location 11A; a middle wavelength peak 12B at the middle location 12A; and a long wavelength peak 13B at the bottom location 13A.

Referring to <FIG>, a conventional spectrometer <NUM> may include the linearly variable filter <NUM> of <FIG>, a tapered light pipe <NUM> disposed upstream of the linearly variable filter <NUM>, and a linear array <NUM> of photodetectors disposed downstream of the linearly variable filter <NUM>. In operation, non-collimated incoming light <NUM> may be conditioned by the light pipe <NUM> to produce a partially collimated light beam <NUM>. The linearly variable filter <NUM> may transmit light at different wavelengths as explained above with reference to <FIG>. The tapered light pipe <NUM> may reduce a solid angle of the incoming light <NUM>, thereby improving spectral selectivity of the linearly variable filter <NUM>. The linear array <NUM> of photodetectors may detect optical power levels of light at different wavelengths, thereby obtaining an optical spectrum, not shown, of the incoming light <NUM>.

The tapered light pipe <NUM> may often be the largest element of the spectrometer <NUM>. A collimating element, such as tapered light pipe <NUM>, may be needed because without it, the spectral selectivity of the linearly variable filter is degraded. This may happen because the linearly variable filter <NUM> includes a stack of thin dielectric films. The wavelength-selective properties of thin film filters are generally dependent on the angle of incidence of incoming light, which may deteriorate spectral selectivity and wavelength accuracy of thin film filters.

According to the present invention, there is provided a flow spectrometer optical assembly with the features of claim <NUM>. Favourable modifications are defined in the dependent claims.

According to an aspect of the present disclosure, there is provided an optical spectrometer assembly comprising:.

Optionally, the cavity comprises a slab extending parallel to the first direction.

Optionally, at least one of the first and second laterally variable bandpass optical filters comprises a plurality of bandpass optical filter segments arranged side by side, wherein each bandpass optical filter segment has a laterally invariable transmission center wavelength different from a laterally invariable transmission center wavelength of an immediate neighboring bandpass optical filter segment.

Optionally, each of the first and second laterally variable bandpass optical filters comprises an array of bandpass optical filter segments arranged side by side,.

Optionally, the optical assembly further comprises a black grid between neighboring bandpass optical filter segments of at least one of the first and second laterally variable bandpass optical filters.

Optionally, the optical assembly further comprises a photodetector array optically coupled to the second laterally variable bandpass optical filter and comprising photodetectors separated by boundaries therebetween, for wavelength selective detection of the signal light propagated through the second laterally variable bandpass optical filter; wherein the black grid is disposed between neighboring bandpass optical filter segments of the second laterally variable bandpass optical filter and along the boundaries between the photodetectors.

Optionally, the optical assembly further comprises a circular polarizer disposed in the optical path between the first and second laterally variable bandpass optical filters, for suppressing light reflected from the second laterally variable bandpass optical filter in a direction towards the first laterally variable bandpass optical filter.

Optionally, the arrays of the bandpass optical filter segments of each one of the first and second laterally variable bandpass optical filters each comprise a two-dimensional array of the bandpass optical filter segments; and
the transmission center wavelengths of the bandpass optical filter segments of the first and second laterally variable bandpass optical filters are mutually coordinated along the first direction and along a second direction perpendicular to the first direction and transversal to the optical path.

Optionally, the optical assembly further comprises a two-dimensional photodetector array optically coupled to the second laterally variable bandpass optical filter and comprising photodetectors disposed along the first direction and the second direction, for wavelength selective detection of the signal light propagated through the second laterally variable bandpass optical filter.

Optionally, the optical assembly further comprises a plurality of photodetector arrays extending along the first direction and spaced apart along the second direction, wherein each photodetector array is optically coupled to the second laterally variable bandpass optical filter and comprises photodetectors disposed along the first direction, wherein each photodetector array has a corresponding operational wavelength range and a corresponding plurality of the bandpass optical filter segments optically coupled thereto; and
the transmission center wavelengths of the pluralities of the bandpass optical filter segments are within the operational wavelength ranges of the corresponding photodetector arrays.

Optionally, the bandpass optical filter segments of each one of the first and second laterally variable bandpass optical filters are grouped into compound pixels, each compound pixel comprising a pre-defined set of the bandpass optical filter segments having a pre-defined set of transmission center wavelengths common to each compound pixel,
the optical assembly further comprising:.

Optionally, the optical assembly further comprises a photodetector array optically coupled to the second laterally variable bandpass optical filter and comprising photodetectors disposed along the first direction for wavelength selective detection of the signal light propagated through the second laterally variable bandpass optical filter.

The following detailed description refers to the accompanying drawings.

<FIG> are diagrams of an optical assembly <NUM> (<FIG>) for spectral filtering of light according to an example implementation described below. For example, the optical assembly <NUM> may include sequentially disposed first 21A and second 21B laterally variable bandpass optical filters separated by a distance L in an optical path <NUM> of signal light <NUM>. The second laterally variable bandpass optical filter 21B may be fixed relative to the first laterally variable bandpass optical filter 21A in the optical path <NUM> downstream of the first laterally variable bandpass optical filter 21A. In other words, the second laterally variable bandpass optical filter 21B may be disposed and fixed so that it may not be moved laterally with respect to the first laterally variable bandpass optical filter 21A. As shown in <FIG>, the first 21A and second 21B laterally variable bandpass optical filters each may have a bandpass center wavelength λT varying in a mutually coordinated fashion, that is, varying with distance along a common first direction <NUM> represented by x-axis. The first direction <NUM> is transversal to the optical path <NUM>. The term "laterally variable" as used herein is defined to mean that the bandpass center wavelength λT varies in any direction transversal to the optical path <NUM> such as, for example, the first direction <NUM>. By way of a non-limiting example, the bandpass center wavelength λT of both the first 21A and second 21B laterally variable bandpass optical filters of <FIG> may have respective monotonic, e.g. linear dependences 24A, 24B, as shown in <FIG>. The center wavelength dependences λ<NUM> T (x) and λ <NUM> T (x) of the first 21A and second 21B laterally variable bandpass optical filters, respectively, on the distance along the first direction <NUM>, represented by the x-coordinate, may be identical, or may be shifted with respect to each other. For example, the center wavelength dependences λ<NUM> T (x) and λ <NUM> T (x) may be such that λ2T(x) = λ<NUM> T (x+x<NUM>), where x<NUM> is a constant; or scaled e.g. λ <NUM> r (x) =c λ<NUM> T (x), where c is a constant e.g. <NUM>< c <<NUM>. The term "coordinated fashion" or "mutually coordinated" as used herein with respect to the bandpass center wavelength λT is defined to mean a pre-determined functional relationship between the center wavelength dependences λ1T(x) and λ2T(x) of the first 21A and second 21B laterally variable bandpass optical filters, respectively.

The configuration of the optical assembly <NUM> may enable a dependence of spectral selectivity of the optical assembly <NUM> on a degree of collimation of the signal light <NUM> to be lessened as compared to a corresponding dependence of spectral selectivity of the second laterally variable bandpass optical filter 21B on the degree of collimation of the signal light <NUM>. This performance improvement of the optical assembly <NUM> may result from a spatial filtering effect illustrated in <FIG>. In monochromatic light at a wavelength λ <NUM>, the first 21A and second 21B laterally variable bandpass optical filters may be approximately represented by slits having "openings" <NUM> corresponding to locations along the x-axes where the center wavelength λ T = λ <NUM>. Outside of the "openings" <NUM>, the first 21A and second 21B laterally variable bandpass optical filters may be essentially opaque for the monochromatic light at the wavelength λ <NUM>. The "openings" <NUM> define an acceptance cone, or solid angle <NUM> (<NUM>θ), which depends on the interfilter distance L. Any rays outside of the solid angle <NUM> may be blocked, thus improving the spectral selectivity of the second laterally variable bandpass optical filter 21B.

The operation of the optical assembly <NUM> of <FIG> may be further explained by referring to <FIG> showing the optical assembly <NUM> in a side cross-sectional view. As shown in <FIG>, the center wavelength λT may increase from left to right along the first direction <NUM>, shown as the x-coordinate, for both the first 21A and second 21B laterally variable bandpass optical filters. In <FIG>, the bandpass center wavelengths λT of the first 21A and second 21B laterally variable bandpass optical filters may be linearly dependent on the x-coordinate: <MAT> where λ <NUM> represents a reference bandpass center wavelength at a reference point x <NUM>, D represents the proportionality coefficient, herein termed a "slope" of a laterally variable filter, and Δx represents an offset from the reference point x <NUM>. The slope D may correspond to the slopes of the linear dependences 24A and 24B in <FIG>, which may, but does not have to, be identical to each other. Deviations from identical slopes of the linear dependences 24A and 24B may be advantageous in some applications.

In the example implementation of <FIG>, the first 21A and second 21B laterally variable bandpass optical filters may be aligned with each other, so that the reference point x <NUM> corresponding to the reference bandpass center wavelength λ<NUM> of the second laterally variable bandpass optical filter 21B is disposed directly under the reference point x <NUM> corresponding to the reference bandpass center wavelength λ<NUM> of the first laterally variable bandpass optical filter 21A. The first laterally variable bandpass optical filter 21A may function as a spatial filter for the second laterally variable bandpass optical filter 21B, defining an angle of acceptance <NUM> for the second laterally variable bandpass optical filter 21B. The angle of acceptance <NUM> may be limited by left <NUM> and right 31R marginal rays at the reference wavelength λ<NUM>, each propagating at the angle θ to a normal <NUM> to the first 21A and second 21B laterally variable bandpass optical filters and striking second laterally variable bandpass optical filter 21B at the same reference point x <NUM>. The angle of acceptance <NUM> may be derived from a passband 33A of the first laterally variable bandpass optical filter 21A as follows.

In the geometry illustrated in the example implementation of <FIG>, the left marginal ray <NUM> may strike the first laterally variable bandpass optical filter 21A at a location x <NUM> -DΔx. Transmission wavelength λL at that location may be, according to Eq. (<NUM>), λL = λ<NUM>-DΔx. Since the left marginal ray <NUM> is at the reference wavelength λ<NUM>, the left marginal ray <NUM> may be attenuated depending on the width of the passband 33A of the first laterally variable bandpass optical filter 21A; for sake of this example, a <NUM> d B bandwidth is taken to be <NUM>DΔx. Thus, the left marginal ray <NUM> may be attenuated by 10dB. Similarly, the right marginal ray 311R may strike the first laterally variable bandpass optical filter 21A at a location x <NUM> +DΔx. Transmission wavelength λR at that location may be, according to Eq. (<NUM>), λR = λ<NUM> + DΔx. The right marginal ray 31R may also be attenuated by 10dB. All rays at the reference wavelength λ<NUM> within the acceptance angle <NUM> may be attenuated by a value smaller than <NUM> d B; and all rays at the reference wavelength λ<NUM> outside the acceptance angle <NUM> may be attenuated by a value larger than 10dB. The first laterally variable bandpass optical filter 21A may function as a spatial filter, effectively limiting the numerical aperture (NA) of incoming light to be separated in individual wavelengths by the second laterally variable bandpass optical filter 21B. This may result in reduction of the dependence of spectral selectivity of the optical assembly <NUM> in comparison with the corresponding dependence of the spectral selectivity of the single second laterally variable bandpass optical filter 21B on the degree of collimation of the signal light <NUM>. If the first laterally variable bandpass optical filter 21A were absent in the optical assembly <NUM>, the spectral selectivity of the optical assembly <NUM> would be much more dependent on the degree of collimation of the signal light <NUM>. Typically, the signal light <NUM> may result from scattering or luminescence of a sample, not shown, so that the signal light <NUM> is not collimated. The lack of collimation of the signal light <NUM> in the absence of the first laterally variable bandpass optical filter 21A would result in worsening of overall spectral selectivity unless a dedicated collimating element, such as a tapered light pipe, is used. Herein, the term "spectral selectivity" includes such parameters as passband width, stray light rejection, in-band and out-of-band blocking, etc..

For small angles θ, for example θ<<NUM>° <MAT> or <MAT>.

When the space between the first 21A and second 21B laterally variable bandpass optical filters is filled with a transparent medium having a refractive index n, Eq. (<NUM>) becomes <MAT>.

Eq. (<NUM>) may define an approximate relationship between the inter-filter distance L, the refractive index n of the inter-filter gap, a lateral distance Δx along the first direction <NUM>, corresponding to a bandwidth of the first laterally variable bandpass optical filter 21A, and the resulting acceptance half-angle θ. A more precise relationship may take into account the wavelength offset due to non-zero angle of incidence, which typically results in a blue shift (i.e. towards shorter wavelength) of the bandpass center wavelength λT. For instance, the right marginal ray 31R at the reference wavelength λ<NUM> striking the first laterally varying bandpass optical filter 21A at the position x<NUM> + Δx may be tilted by the angle θ, which shifts the transmission characteristic of the first laterally varying bandpass optical filter <NUM>1A to shorter wavelengths. If this wavelength dependence is to be accounted for, the shoulders of the passband 33A may shift to the left i.e. shorter wavelengths: <MAT> where neff represents an effective refractive index of the first laterally variable bandpass optical filter 21A.

Although in <FIG>, the first 21A and second 21B laterally variable bandpass filters have linearly variable bandpass center wavelengths λT as defined by Eq. (<NUM>) above, the center wavelengths λT of the first 21A and second 21B laterally variable bandpass optical filters may be monotonically non-linearly, for example parabolically or exponentially, increasing or decreasing in the first direction <NUM>. The bandpass center wavelengths λT dependence may also be non gradual, e.g., stepwise. The dependence of the bandpass center wavelength λT on the x coordinate along the first direction <NUM> of the first 21A and second 21B laterally variable filters may be identical, or may be different to enable optimizing or varying of the acceptance angle and/or wavelength response of the optical assembly <NUM>. In one embodiment, the bandpass center wavelengths λT of the first 21A and second 21B laterally variable bandpass optical filters may be aligned with each other, such that a line connecting positions corresponding to a same bandpass center wavelength λT of the first 21A and second 21B laterally variable bandpass optical filters forms an angle of less than <NUM> degrees with the normal <NUM> to the second laterally variable bandpass optical filter 21B. For non-zero angles with the normal <NUM>, the acceptance cone <NUM> may appear tilted. Thus, it may be possible to vary the acceptance cone <NUM> direction by offsetting the first 21A and second 21B laterally variable bandpass optical filters relative to each other in the first direction <NUM>. Furthermore, the angle may vary along the first direction (x-axis) <NUM>.

For a better overall throughput, it may be preferable to have a lateral distance Δx<NUM> along the first direction <NUM>, corresponding to a bandwidth of the first laterally variable bandpass optical filter 21A larger than a corresponding lateral distance Δx<NUM> along the first direction <NUM>, corresponding to a bandwidth of the second laterally variable bandpass optical filter 21B. In one embodiment, the first 21A and second 21B laterally variable bandpass optical filters each may have a 3dB passband no greater than <NUM>% of a corresponding bandpass center wavelength λT.

The first 21A and/or second 21B laterally variable bandpass optical filters may include a thin film layer stack including two, three, and more different materials, e.g., high-index and/or absorbing layers may be used to reduce overall thickness of each of the first 2IA and second 21B laterally variable bandpass optical filters. The first 21A and/or the second 21B laterally variable bandpass optical filters may include diffraction gratings e.g. sub-wavelength gratings, dichroic polymers, etc. An additional laterally variable bandpass optical filter may be provided in the optical path, the additional filter having a bandpass center wavelength varying in a coordinated fashion with the bandpass center wavelengths of the first 21A and second 21B laterally variable bandpass optical filters.

<FIG> and <FIG> are diagrams of an optical spectrometer assemblies <NUM> according to an example implementation described below. The optical spectrometer assembly <NUM> of <FIG> and <FIG> may include, for example, the optical assembly <NUM> of <FIG> and may further include an optical fiber <NUM> extending between its first 41A and second 41B ends for conducting the signal light <NUM> from the first end 41A to the second end 41B.

An optical conduit <NUM> may extend between its first 42A and second 42B surfaces. The first surface 42A may be optically coupled, i.e. via an air gap or by a direct physical contact, to the second end 41B of the optical fiber <NUM> for receiving the signal light <NUM> and conducting the signal light <NUM> in the optical conduit <NUM> from the first surface 42A to the second surface 42B. The second surface 42B may be optically coupled to the first laterally variable bandpass optical filter 21A for receiving the signal light <NUM> for propagation along the optical path <NUM>. A multi element sensor <NUM>, such as a photodetector array, may be optically coupled to the second laterally variable bandpass optical filter 21B. The sensor <NUM> may include photodetectors 43A disposed along the first direction <NUM> for wavelength selective detection of the signal light <NUM> propagated through the second laterally variable bandpass optical filter 21B.

In the exemplary embodiment shown in <FIG> and <FIG>, the optical conduit <NUM> may include a planar parallel slab of homogeneous transparent material, for example glass or an injection-molded transparent plastic material. The slab may have a plurality of extemal surfaces, for example the first 42A and second 42B surfaces, which may be flat or curved. The slab may be configured for unconstrained propagation of the signal light <NUM>, e.g. the slab may be continuous or hollow. The slab may be disposed generally parallel to the first direction <NUM>, and optionally mechanically coupled to the first laterally variable bandpass optical filter 21A.

A portion 23A of the signal light <NUM> may be reflected from the first laterally variable bandpass optical filter 21A. The portion 23A may include light at wavelengths other than the transmission wavelength at a particular reflection location of the first laterally variable bandpass optical filter 21A. To recycle the portion 23A, the optical conduit <NUM> may include a reflective wall or walls <NUM> for redirecting at least a portion of the reflected light portion 23A back to the first laterally variable bandpass optical filter 21A.

Turning to <FIG>, an optical spectrometer assembly <NUM> is shown according to an example implementation described below. The optical spectrometer assembly <NUM> of <FIG> may further include an elbowed optical conduit <NUM> instead of the straight optical conduit <NUM>. The elbowed optical conduit <NUM> may enable a more compact mechanical configuration. The elbowed optical conduit <NUM> may have the first surface 42A, the second surface 42B, and a third surface 42C, e.g. a flat or curved surface disposed in the optical path <NUM> between the first 42A and second 42B surfaces, for receiving the signal light <NUM> from the first surface 42A and reflecting the signal light <NUM> towards the second surface 42B. The third surface 42C may be optionally mirrored, or left uncoated when the refractive index of the elbowed optical conduit <NUM> is high enough for the signal light <NUM> to reflect by total internal reflection (TIR): n > <NUM>/sin(α), where n is the refractive index of the conduit <NUM>, and a is the angle of incidence of the signal light <NUM> on the third surface 42C. The straight optical conduit <NUM> or the elbowed optical conduit <NUM> may include multiple conduit branches coupled to multiple individual optical fibers, not shown.

Referring to <FIG>, an optical spectrometer assembly <NUM> is shown according to an example implementation described below. The optical spectrometer assembly <NUM> of <FIG> may include an optical probe <NUM> optically coupled to the first end 41A of the optical fiber <NUM>, for collecting the signal light <NUM> emanating from a fluid or granular sample <NUM> when the sample <NUM> is illuminated with illuminating light <NUM>, and for coupling the signal light <NUM> to the first end 41A of the optical fiber <NUM>. In the example implementation shown in <FIG>, the fluid or granular sample <NUM> is held in a cuvette <NUM> having a transparent window <NUM> at the bottom for transmitting through the illuminating light <NUM>. For instance, the signal light <NUM> may represent transmitted illuminating light <NUM>, or scattered illuminating light <NUM>, or luminescence, such as fluorescence or phosphorescence.

Still referring to <FIG>, the optical probe <NUM> may include a relay lightpipe <NUM> extending between its first 59A and second 59B ends. The first end 59A, herein termed "distal" end, that is the farthest from the optical fiber <NUM>, may be configured for contacting or inserting into the sample <NUM>, thereby collecting the signal light <NUM> emanating from the sample <NUM>, and the second end 59B, herein termed "proximal" end, that is, the closest to the optical fiber <NUM>, may be configured for optical and mechanical coupling to the first end 411A of the optical fiber <NUM>. The relay lightpipe <NUM> of the optical probe <NUM> may be configured for unconstrained propagation of the signal light <NUM> in bulk of the relay lightpipe from the first 59A to the second 59B end. For instance, the relay lightpipe <NUM> may be made of glass or a rigid transparent, chemically inert plastic, so that it can be inserted through a fluid or granular overlayer <NUM> down to the sample <NUM>. The relay lightpipe <NUM> may also be made hollow, with mirrored internal walls.

In the example implementation shown in <FIG>, the first (distal) end 59A of the relay lightpipe <NUM> may include a slanted optical surface <NUM>, which may cause the sample <NUM> flowing in a direction <NUM> to exert a pressure onto the slanted optical surface <NUM>, which may facilitate the collection of the signal light <NUM>, especially for granular samples <NUM> or samples <NUM> including a fluid suspension of a solid material.

It is to be understood that the relay lightpipe <NUM> is only one possible embodiment of the optical probe <NUM>. Other embodiments of the optical probe <NUM> may include an irradiance probe, a reflection / backscatter probe, a transmission cuvette, an oxygen probe, a fluorescence or phosphorescence probe, etc. The optical fiber <NUM> may include a bifurcated fiber including a branch for delivering the illuminating light <NUM> to the transmission cuvette, for example.

Referring now to <FIG> and <FIG>, an example implementation of a flow spectrometer optical assembly <NUM> may include a light source <NUM> for providing the illuminating light <NUM>, an elongated optical cuvette <NUM> extending generally parallel to the first direction <NUM> (<FIG>), the optical assembly <NUM> of <FIG>, and the sensor <NUM>.

The elongated optical cuvette <NUM> may include an inlet 63A for receiving the sample <NUM> in fluid form, a substantially transparent sidewall <NUM> defining a cavity <NUM> in fluid communication with the inlet 63A, for receiving and containing the sample <NUM> while transmitting the illuminating light <NUM> through the sidewall <NUM> for illuminating the sample <NUM> received in the cavity <NUM>. Upon illumination, the sample <NUM> received by the cavity <NUM> emits the signal light <NUM>. The transparent sidewall <NUM> may be configured for transmitting the signal light <NUM> through the transparent sidewall <NUM> for optical coupling the signal light <NUM> to the first laterally variable bandpass optical filter 21A for propagation along the optical path <NUM>. The elongated optical cuvette <NUM> may further include an outlet 63B in fluid communication with the cavity <NUM>, for outputting the sample <NUM> illuminated with the illuminated light <NUM>.

The sensor <NUM> may be optically coupled to the second laterally variable bandpass optical filter 21B. The photodetectors 43A of the sensor <NUM> may be disposed along the first direction <NUM> for wavelength selective detection of the signal light <NUM> propagated through the second laterally variable bandpass optical filter 21B. For a more uniform illumination of the sample <NUM> in the cavity <NUM>, the light source <NUM> may be elongated as shown in <FIG>, extending generally parallel to the first direction <NUM>. For example, an incandescent lamp having a tungsten spiral extending along the first direction <NUM> may be used. The wall <NUM> of the elongated optical cuvette <NUM> may function as a lens facilitating refracting or focusing the illuminating light <NUM> onto the cavity <NUM> containing the sample <NUM>, and/or facilitating refracting or focusing the signal light <NUM> onto the sensor <NUM> (<FIG>).

In the example implementation shown in <FIG> and <FIG>, the cavity <NUM> has a slab portion 65A extending parallel to the first direction <NUM>, e.g. a planar parallel slab. This may enable the liquid sample <NUM> to be thin in the cavity <NUM>, for example thinner than <NUM>, or thinner than <NUM> if the light source <NUM> has a high optical power, for instance when the light source <NUM> includes, or is coupled to, a laser source. Small thickness may be useful for obtaining absorption spectra of aqueous solutions dominated by vibrational frequencies of water.

Turning to <FIG> and <FIG>, an example implementation of a flow spectrometer optical assembly <NUM> is shown. The flow spectrometer optical assembly <NUM> of <FIG> and <FIG> includes a flow cuvette <NUM> having an inlet 73A, an outlet 73B, a transparent sidewall <NUM> defining a cavity <NUM> having a cylindrical portion 75A having an optical axis 75B, extending substantially parallel to the first direction <NUM>. The cylindrical portion 75A of the cavity <NUM> allows for a larger volume of the sample <NUM> to be held therein, which may be more suitable for obtaining absorption spectra of organic solutions. Specific applications may require other path lengths. Similarly to the flow spectrometer optical assembly <NUM> of <FIG> and <FIG>, the transparent sidewall <NUM> of the flow spectrometer optical assembly <NUM> of <FIG> and <FIG> may function as a lens facilitating refracting the illuminating light <NUM> onto the cavity <NUM> containing the sample <NUM> and/or facilitating focusing the signal light <NUM> onto the sensor <NUM> (<FIG>).

In one embodiment, the sensor <NUM> may include a 2D array of photodetectors, including multiple rows of the photodetectors 43A. Preferably, each such row may extend parallel to the first direction <NUM>. The 2D array of photodetectors may be used to simultaneously obtain spectra of the signal light <NUM> in different wavelength ranges.

In an example implementation, the first 21A or second 21B laterally variable bandpass optical filters, or both 21A and 21B laterally variable bandpass optical filters of the optical assembly <NUM> (<FIG>) may be segmented. <FIG> are diagrams of schematic plan views of optical assemblies according to example implementations described below. Referring specifically to <FIG>, first 221A and second 221B segmented laterally variable bandpass optical filters of an optical assembly 80A may each include an array 85A of bandpass optical filter segments e.g. 81A, 82A, 83A, 84A for the first segmented laterally variable bandpass optical filter 221A, arranged side by side in the first direction <NUM>; and an array 85B of bandpass optical filter segments 81B, 82B, 83B, 84B for the second segmented laterally variable bandpass optical filter 221B, arranged side by side in the first direction <NUM>.

Each bandpass optical filter segment 81A-84A of the first segmented laterally variable bandpass optical filter 221A may have a laterally invariable, i.e. constant, transmission center wavelength λT different from a transmission center wavelength λT of an immediate neighboring bandpass optical filter segment 81A-84A. For example, the transmission center wavelength λT of the second bandpass optical filter segment 82A may be different from the transmission center wavelength λT of the first bandpass optical filter segment 81A and the third bandpass optical filter segment 83A, and so on. The same rule may hold for the second segmented laterally variable bandpass optical filter 221B: each bandpass optical filter segment 81B, 82B, 8AB, 84B of the second segmented laterally variable bandpass optical filter 221B may have a laterally invariable, i.e. constant, transmission center wavelength λT different from a transmission center wavelength λT of an immediate neighboring bandpass optical filter segment 81B-84B. As a result, the bandpass center wavelengths of the first 221A and second 221B segmented laterally variable bandpass optical filters may laterally vary stepwise from segment to segment, and/or non-monotonically from segment to segment.

As illustrated by arrows <NUM> in <FIG>, the transmission center wavelengths AT of the bandpass optical filter segments 81A, 81B, 81C, and 81D of the first 221A and second 221B segmented laterally variable bandpass optical filters may be mutually coordinated. By way of a non-limiting example, the transmission center wavelengths λT may be equal to each other: the transmission center wavelength λT of the first bandpass optical filter segment 81A may be equal to the transmission center wavelength λT of the first second bandpass optical filter segment 81B, and so on. The transmission bandwidths of the corresponding bandpass optical filter segments of the first 221A and second 221B segmented laterally variable bandpass optical filters may be equal to each other, e.g. no greater than <NUM>%, and more preferably no greater than <NUM>% of the corresponding transmission center wavelengths λT of the bandpass optical filter segments 81A- 84A. For a better overall throughput of the optical assembly 80A, transmission bandwidths of the bandpass optical filter segments 81A- 84A of the first segmented laterally variable bandpass optical filter 221A may be greater than transmission bandwidths of the corresponding bandpass optical filter segments 81B- 84B of the second segmented laterally variable bandpass optical filter 221B. By way of an illustrative, non-limiting example, the transmission bandwidths of the bandpass optical filter segments 81A- 84A of the first segmented laterally variable bandpass optical filter 221A may be no greater than <NUM>% of the corresponding transmission center wavelengths λT of the bandpass optical filter segments 81A- 84A, while the transmission bandwidths of the bandpass optical filter segments 81B- 84B of the second segmented laterally variable bandpass optical filter 221B may be no greater than <NUM>% of the corresponding transmission center wavelengths λT of the bandpass optical filter segments 81B- 84B.

Turning to <FIG>, an optical assembly 80B according to an example implementation, may be a two-dimensional (2D) segmented optical filter assembly. The first 221A and second 221B segmented laterally variable bandpass optical filters of the optical assembly 80B may each include 2D arrays of the bandpass optical filter segments 81A-84A and 81B-84B. By way of illustration, the first segmented laterally variable bandpass optical filter 221A may include four one-dimensional arrays 85A, 86A, 87A, 88A arranged side by side in the second direction <NUM>' and combined into a two-dimensional array, each such one-dimensional array 85A-88A including the bandpass optical filter segments 81A-84A having transmission center wavelengths λT unique to the entire two-dimensional array and arranged side by side in the first direction <NUM>. Similarly, the second segmented laterally variable bandpass optical filter 221B may include one-dimensional arrays 85B, 86B, 87B, 88B arranged side by side in the second direction <NUM>' and combined into a two-dimensional array, each such one-dimensional array 85B-88B including the bandpass optical filter segments 81B-84B having a unique transmission center wavelength λT and arranged side by side in the first direction <NUM>. The transmission center wavelengths λT of the bandpass optical filter segments 81A-84A and 81B- 84B of the first 221A and second 221B segmented laterally variable bandpass optical filters may be mutually coordinated along the first direction <NUM> and along a second direction <NUM>' perpendicular to the first direction <NUM> and transversal to the optical path <NUM> (not shown in <FIG>). In one embodiment, a black grid <NUM> separating neighboring bandpass optical filter segments 81A-84A or 81B-84B of at least one of the first 221A and second 221B segmented laterally variable bandpass optical filters may be provided for suppressing light leakage between neighboring bandpass optical filter segments 81A-84A or 81B-84B.

According to one aspect of the disclosure, the transmission center wavelengths λT of neighboring bandpass optical filter segments 81A-84A and 81B-84B for each array 85A-88A and 85B-88B need not be successive, that is, need not be disposed in an increasing or decreasing order. The stepwise laterally variable bandpass center wavelength of the first 221A or second 221B segmented laterally variable bandpass optical filters needs not be monotonically increasing or decreasing. In fact, it may be preferable to "scramble" the transmission center wavelength λT, so neighboring bandpass optical filter segments 81A-84A and 81B-84B for each array 85A-88A and 85B-88B differ in the transmission center wavelength λT by a magnitude larger than a "typical" wavelength increment of the transmission center wavelength λT. By way of a non limiting example, referring to <FIG>, transmission center wavelengths λT of neighboring bandpass optical filter segments 81A-84A and 81B-84B of a segmented filter 80C are shown (in nanometers) for each array 85A-88A. In <FIG>, the top left segment 81A of the top row 88A has the transmission center wavelength λT = <NUM>, while its immediate neighbor to the right 82A has the transmission center wavelength λT = <NUM>, and its immediate neighbor below 87A has the transmission center wavelength λT= <NUM>. The transmission center wavelengths λT of the bandpass optical filter segments 81A-84A and 81B-84B of the first 221A and second 221B segmented laterally variable bandpass optical filters may be spread across a wavelength range with a constant or variable wavelength step such that the transmission center wavelengths λT of the neighboring bandpass optical filter segments 81A-84A and 81B-84B of the first 221A and second 221B segmented laterally variable bandpass optical filters differ at least by an integer multiple of the constant or variable wavelength step. For instance, if the wavelength step is <NUM>, that is, the transmission center wavelength λT of the bandpass optical filter segments 81A- 84A and/or 81B-84B includes the values of <NUM>; <NUM>; <NUM>; and so on, the transmission center wavelengths λT of the neighboring bandpass optical filter segments 81A-84A and 81B- 84B of the first 221A and second 221B segmented laterally variable bandpass optical filters may differ at least by <NUM> = <NUM>*<NUM>, that is, five times the wavelength step. For example, the minimum difference between the transmission center wavelengths λT of the neighboring bandpass optical filter segments in each individual array 85A-88A, that is, in horizontal direction in <FIG>, is between the leftmost bottom bandpass optical filter segments 81A (<NUM>) and 82A (<NUM>) in the bottom array 85A. All the other differences in each individual array 85A- 88A in <FIG>, that is, in horizontal direction, are larger. The differences in vertical direction may be somewhat smaller in this example, e.g. at least <NUM> = <NUM>*<NUM>, that is, three times the wavelength step. Thus, the differences in the transmission center wavelengths λT of the horizontal or vertical optical filter segments 81A-84A and/or 81B-84B may be at least three times the wavelength step. The wavelength step may be variable i.e. the transmission center wavelength λT of the optical filter segments 81A-84A and/or 81B-84B may include, for example, the values of <NUM>; <NUM>; <NUM>; <NUM>; and so on. The total number of the optical filter segments 81A-84A and/or 81B-84B may of course vary. The bandpass optical filter segments 81A-84A of the first 221A or second 221B segmented laterally variable bandpass optical filters may include a colored glass, an absorptive pigment, or a dye, for absorption of light at wavelengths other than wavelengths of corresponding passbands of the bandpass optical filter segments 81A-84A.

In one embodiment, the first 221A or second 221B segmented laterally variable bandpass optical filters may have a segmented portion and a continuously varying portion. For instance, referring to <FIG>, an upstream filter 321A of an optical assembly 80D <NUM> a continuously varying AT filter, and a downstream filter 321B of the optical assembly 80D includes a continuously varying portion 21B' and a segmented portion 21B". Similarly to the optical assembly <NUM> of <FIG>, the bandpass center wavelengths of these upstream 321A and downstream 321B filters of the optical assembly 80D of <FIG> may vary in a mutually coordinated fashion along the first direction <NUM> and/or along the second direction <NUM>'.

Turning to <FIG> with further reference to <FIG> and <FIG>, an optical spectrometer assembly <NUM> may include a sensor <NUM> optically coupled to the second laterally variable bandpass optical filter 21B of the optical assembly <NUM> of <FIG> or the second segmented laterally variable bandpass optical filter 221B of the optical assembly 80A of <FIG>. The sensor <NUM> may have a one-dimensional array of photodetectors 93A disposed along the first direction <NUM> separated by boundaries 93B between the individual photodetectors 93A. Thus, the photodetectors 93A may be disposed for wavelength selective detection of the signal light <NUM> propagated through the second segmented laterally variable bandpass optical filter 221B. For embodiments including the optical assembly 80A of <FIG>, the sensor <NUM> may have one photodetector corresponding to each segment 81B-84B. In the example implementation shown in <FIG>, the black grid <NUM> may be disposed between neighboring bandpass optical filter segments 81B-82B, 82B-83B, and 83B-84B of the second segmented laterally variable bandpass optical filter 221B and along the boundaries 93B between the photodetectors 93A. In one embodiment, the black grid <NUM> may extend between the first 221A and second 221B segmented laterally variable bandpass optical filters, as shown.

Referring to <FIG>, an optical spectrometer assembly 100A according to an example implementation may include a sensor <NUM> optically coupled to the second segmented laterally variable bandpass optical filter 221B of the optical assembly 80B of <FIG> or the optical assembly 80D of <FIG>. The sensor <NUM> may have a two-dimensional array of photodetectors 103A optically coupled to the second segmented laterally variable bandpass optical filter 221B and having the photodetectors 103A disposed along the first direction <NUM> and the second direction <NUM>', for wavelength selective detection of the signal light <NUM> propagated through the second segmented laterally variable bandpass optical filter 221B.

Turning to <FIG>, an optical spectrometer assembly 100B according to an example implementation may include a plurality of sensors <NUM>, <NUM>, <NUM>, <NUM> disposed side by side along the second direction <NUM>' and optically coupled to the second segmented laterally variable bandpass optical filter 221B of the optical assembly 80B of <FIG> or the optical assembly 80D of <FIG>. Each of the sensors <NUM>-<NUM> may include a photodetector array extending along the first direction <NUM>. For instance, the first sensor <NUM> may include an array of photodetectors 105A extending along the first direction <NUM>; the second sensor <NUM> may include an array of photodetectors 106A extending along the first direction <NUM>; the third sensor <NUM> may include an array of photodetectors 107A extending along the first direction <NUM>; and the fourth sensor <NUM> may include an array of photodetectors 108A extending along the first direction <NUM>. The sensors <NUM>-<NUM> may be spaced apart along the second direction <NUM>', or may be joined. Each sensor <NUM>-<NUM> may be optically coupled to the second segmented laterally variable bandpass optical filter 221B. Each sensor <NUM>-<NUM> may have a corresponding operational wavelength range, and a corresponding plurality of the bandpass optical filter segments 85B-88B optically coupled to the sensor <NUM>-<NUM>. By way of a non-limiting example, silicon (Si) based sensor arrays may be used in a visible - near infrared range of wavelengths between <NUM> and <NUM>, and indium gallium arsenide (InGaAs) based sensor arrays may be used in an infrared range of wavelengths between <NUM> and <NUM>.

The transmission center wavelengths λT of the pluralities of the bandpass optical filter segments 85B-88B (and, accordingly, 85A-88A) may be selected to be within the operational wavelength ranges of the corresponding photodetector arrays <NUM>-<NUM>. In this way, a multi-spectral optical spectrometer assembly may be constructed. It is further noted that the segmented filter configurations of the optical assemblies 80A-80D of <FIG>, and the sensor configurations of <FIG>, <FIG> may also be used, for example, in the optical spectrometer assemblies <NUM> of <FIG>, <NUM> of <FIG> and <FIG>, and <NUM> of <FIG> and <FIG>.

Referring to <FIG>, a circular polarizer <NUM> according to an example implementation may be disposed in the optical path <NUM> between the first 221A and second 221B laterally variable bandpass optical filters, for suppressing light <NUM>' reflected from the second laterally variable bandpass optical filter 221B. The circular polarizer <NUM> polarizes the incoming light <NUM> to be in clockwise circular polarization, for example. The reflected light <NUM>' will be counterclockwise polarized due to reversal of the direction of propagation. The reflected light <NUM>' may be suppressed by the circular polarizer <NUM>, i.e., an absorbing circular polarizer which removes the energy of the reflected light <NUM>'. The circular polarizer <NUM> may also be disposed between the first 21A and second 21B laterally variable bandpass optical filters of the optical assembly <NUM> of <FIG>, to suppress light reflected from the second laterally variable bandpass optical filter 21B.

Turning now to <FIG> and <FIG>, an imaging optical assembly <NUM> according to an example implantation, may include, for example, the optical assembly 80B of <FIG> and an objective lens <NUM> optically coupled to an optional diffuser <NUM> optically coupled to the first segmented laterally variable bandpass optical filter 221A for forming an image <NUM> A of an object <NUM> on the diffuser <NUM> or directly on the first segmented laterally variable bandpass optical filter 221A. The first 221A and second 221B segmented laterally variable bandpass optical filters may each have the respective invariable bandpass optical filter segments 81A- 84A, 81B-84B (only the segments 81A-84A of the first segmented laterally variable bandpass optical filter 221A are shown for brevity) grouped into "compound pixels" <NUM>, each compound pixel <NUM> including a pre-defined set of laterally invariable bandpass optical filter segments 81A- 84A, 81B-84B having pre-defined transmission center wavelengths AT common to each compound pixel. This configuration may be similar to one employed in color CMOS sensors used for digital photography, only the number of the filters segments 81A-84A may be at least <NUM>, or even at least <NUM>. Such configurations may enable multi-spectral imaging of the object <NUM>.

The sensor <NUM> (<FIG>) may be optically coupled to the second segmented laterally variable bandpass optical filter 221B (<FIG>, <FIG>). The sensor <NUM> may include photodetectors 103A disposed along the first direction <NUM> and the second direction <NUM>', for wavelength selective detection of the signal light <NUM> propagated through the first segmented laterally variable bandpass optical filter 221A and the second segmented laterally variable bandpass optical filter 221B. The diffuser <NUM>, when used, may spread the image 123A formed by the objective lens <NUM> on the first segmented laterally variable bandpass optical filter 221A. The objective lens <NUM> may be replaced with another image-forming optical element such as a concave mirror, for example. The 2D sensor <NUM> may be replaced with the 1D sensor <NUM> of <FIG> or with the plurality of sensors <NUM>-<NUM> of <FIG>.

Referring to <FIG>, a method <NUM> of making an optical spectrometer assembly of the disclosure may include a step <NUM> of providing the first laterally variable bandpass optical filter 21A and a second laterally variable bandpass optical filter 21B. In a step <NUM>, the second laterally variable bandpass optical filter 21B may be fixed at the distance L from the first laterally variable bandpass optical filter 21A in the optical path <NUM> downstream of the first laterally variable bandpass optical filter 21A. Finally in a step <NUM>, the sensor <NUM> may be optically coupled to the second laterally variable bandpass optical filter 21B. As explained above, the sensor <NUM> may include the photodetectors 43A disposed along the first direction <NUM> for wavelength selective detection of the signal light <NUM> propagated along the optical path <NUM> through the second laterally variable bandpass optical filter 21B.

Turning to <FIG>, a method <NUM> of making the optical spectrometer assembly <NUM> of <FIG> may include a step <NUM> of providing the optical probe <NUM> for collecting the signal light <NUM> emanating from the sample <NUM> when the sample <NUM> is illuminated with the illuminating light <NUM>. In a step <NUM>, the first end 41A of the optical fiber <NUM> may be optically coupled to the probe <NUM> for receiving the signal light <NUM> collected by the optical probe <NUM> and propagating the signal light <NUM> in the optical fiber <NUM> towards its second end 41B. In a next step <NUM>, the first surface 42A of the optical conduit <NUM> may be optically coupled to the second end 41B of the optical fiber <NUM> for receiving the signal light <NUM> propagated to the second end 41B of the optical fiber <NUM> for propagating in the optical conduit <NUM> towards its second surface 42B. In a next step <NUM>, the first laterally variable bandpass optical filter 21A may be optically coupled to the second surface 42B of the optical conduit <NUM> for receiving the signal light <NUM> propagated in the optical conduit <NUM>.

In a following step <NUM>, the second laterally variable bandpass optical filter 21B may be fixed at the distance L from the first laterally variable bandpass optical filter 21A in the optical path <NUM> of the signal light <NUM> downstream of the first laterally variable bandpass optical filter 21A. Finally in a step <NUM>, the sensor <NUM> may be optically coupled to the second laterally variable bandpass optical filter 21B. A one-dimensional or two-dimensional detector array may be used in place of the sensor <NUM>.

Referring to <FIG>, a method <NUM> of making the optical spectrometer assembly <NUM> may include a step <NUM> of providing the light source <NUM> for providing the illuminating light <NUM>. In a step <NUM>, the optical cuvette <NUM> may be provided. In a step <NUM>, the first 21A and second 21B laterally variable bandpass optical filters may be provided. In a step <NUM>, the second laterally variable bandpass optical filter 21B may be fixed at the distance L from the first laterally variable bandpass optical filter 21A in the optical path of the signal light <NUM> downstream of the first laterally variable bandpass optical filter 21A. In a step <NUM>, the first laterally variable bandpass optical filter 21A may be optically coupled to the transparent sidewall <NUM> for receiving the signal light <NUM>. Finally in a step <NUM>, the sensor <NUM> may be optically coupled to the second laterally variable bandpass optical filter 21B. A one-dimensional or two-dimensional detector array may be used in place of the sensor <NUM>. In the methods <NUM>, <NUM>, and <NUM>, segmented laterally variable bandpass optical filters 221A and 221B may be used instead of the laterally variable bandpass optical filters 21A and 21B.

An optical filter and spectrometer may involve the processing of input data and the generation of output data. This input data processing and output data generation may be implemented in hardware and/or software. For example, specific electronic components may be employed in a processor, module, or similar related circuitry for implementing the functions associated with providing an optical filter and/or a spectrometer in accordance with the various example implementations described above. Alternatively, one or more processors operating in accordance with instructions may implement the functions associated with the exemplary implementations described above. Such instructions may be stored on one or more processor readable storage media (e.g., a magnetic disk or other storage medium), or be transmitted to one or more processors via one or more signals embodied in one or more carrier waves.

Claim 1:
A flow spectrometer optical assembly (<NUM>) comprising:
a light source (<NUM>) configured to provide illuminating light (<NUM>);
an elongated optical cuvette (<NUM>) comprising a cavity (<NUM>) extending generally parallel to a first direction (<NUM>) and being configured to receive and contain a sample (<NUM>) while transmitting the illuminating light through the cavity, an inlet (63A) configured to receive the sample (<NUM>) in fluid form, wherein the cavity (<NUM>) is in fluid communication with the inlet (63A), and the cavity (<NUM>) is defined by a substantially transparent sidewall (<NUM>);
an optical assembly (<NUM>) including a first laterally variable bandpass optical filter (21A) optically coupled to the transparent sidewall (<NUM>); and
a sensor (<NUM>) comprising photodetectors disposed along the first direction (<NUM>) and being optically coupled to the optical filter, configured to selectively detect signal light (<NUM>) propagated through the optical filter,
wherein the signal light (<NUM>) is emitted by the sample (<NUM> in the cavity (<NUM>) when illuminated with illuminating light (<NUM>) characterised in that the cavity of the cuvette has along an axis (75B) extending parallel to the first direction (<NUM>) cylindrical portion (75A) that allows for a larger volume of sample (<NUM>) to be held therein, and wherein the optical assembly (<NUM>) includes an optically coupled second laterally variable bandpass optical filter (21B) having a bandpass center wavelength varying in a mutually co-ordinated fashion with the first laterally variable bandpass optical filter (21A) along the first direction (<NUM>).