WO1998035211A1 - Optical shutter, spectrometer and method for spectral analysis - Google Patents
Optical shutter, spectrometer and method for spectral analysis Download PDFInfo
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- WO1998035211A1 WO1998035211A1 PCT/IL1998/000059 IL9800059W WO9835211A1 WO 1998035211 A1 WO1998035211 A1 WO 1998035211A1 IL 9800059 W IL9800059 W IL 9800059W WO 9835211 A1 WO9835211 A1 WO 9835211A1
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- optical
- shutter
- attenuating
- wavelength
- zone
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
- G01J3/0213—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using attenuators
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
- G01J3/0232—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using shutters
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/04—Slit arrangements slit adjustment
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
- G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
- G01J3/51—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
- G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
- G01J3/501—Colorimeters using spectrally-selective light sources, e.g. LEDs
Definitions
- the present invention relates to an optical shutter suitable for spectrometers, a spectrometer comprising such an optical shutter and to a method for spectral analysis of light radiation making use of the spectrometer.
- US Patent 4,193,691 refers to a spectrometer which comprises a slit assembly manufactured in the form of a liquid ciystal cell.
- the electiOdes of the cell can be selectively actuated for producing a pattern of so-called “slits” (temporaiily transparent portions of the cell) which are arranged in a specific manner.
- Such a liquid ciystal cell with a selectively actuatable pattern of "slits” capable of switcliing between clear and opaque optical states has acquired the name optical shutter.
- the spectrometer described in US 4,193,691 comprises means for producing a spectrum of light under analysis, means for directing that spectrum on to the above-described slit assembly (where the slits have configurations appropriate to positions of specific spectral lines of interest in the spectrum), and also comprises detection means for detecting a portion of the spectrum which has passed the slit assembly at a specified time. The detected signal is then ttansmitted to so-called utilization means, i.e. the means by which the detected signal may be processed. It should be emphasized that the concept of the above-described device resides in obtaining the spectrum of the light under analysis prior to directing radiation to the slit assembly.
- the optical shutter array includes a plurality of optical shutter elements arranged in correspondence with the lines in the obtained spectrum and being made of a material (PLZT) characterized by the increased switching speed of the optical state.
- PZT material
- the spectrum producing means constitutes a diffractor by which an incident light beam is diffracted according to wavelengths.
- US patent 5,424,545 describes a method for non-invasive non-spectrophotometric infrared measurement of blood analyte concentrations.
- the method includes either illuminating a sample with a plurality of radiation beams each covering a distinct portion of the spectrum and partially overlapping one another, or detecting radiation reflected or transmitted by the sample using a plurality of broadband detectors having at least partially overlapping responses.
- the obtained signals are coded and analyzed by analogy to colorimetry and visual processing and can be converted into concentration measurements.
- the computational method is based on implementation of the idea of color perception for a quantitative substrate analysis, which renders the method complex and time consuming.
- a principal object of the invention is the provision of a new concept of a known spectrometer incorporating an optical shutter, allowing for the development of a variety of compact and inexpensive novel spectrometers and to a new design of the optical shutter per se suitable for them. It is another object of the invention to provide a method of spectral analysis using the inventive device.
- the conventional spectrum producing means may be replaced by an inexpensive device such as an attenuator comprising an assembly of attenuating zones having different wavelength-dependent attenuating characteristics, and being associated with switching segments (slits) of the optical shutter. Owing to such an exchange and, in accordance with the above-outlined idea, it becomes insignificant whether such a multi-zone attenuator is placed before or after the optical shutter, or is integrally combined therewith.
- an attenuating optical shutter for high speed spectral analysis of an optical radiation band so as to derive N wavelength-dependent portions thereof, said attenuating optical shutter incorporating: an optical shutter body including N shutter segments, each selectably switchable between a first substantially transparent and a second substantially opaque optical state, and a multi-zone attenuator comprising N optical attenuating zones each having a different predetermined wavelength-dependent attenuation characteristic; wherein each of the shutter segments is optically interconnected with a respective one of the N optical attenuating zones of the multi-zone attenuator thus forming N respective cells of the attenuating optical shutter.
- the N segments of the optical shutter are capable of being successively actuated so that at any given moment only one of the N segments is in its transparent state.
- each cell comprises one specific attenuation zone of the multi-zone attenuator optically intercon- nected to one corresponding segment of the shutter body.
- each cell comprises one specific attenuation zone of the multi-zone attenuator optically intercon- nected to one corresponding segment of the shutter body.
- each of the N segments of the optical shutter may be switched from the first to the second state and vice versa at a different pre-selected frequency.
- each optical radiation portion passing through a particular segment of the optical shutter is modulated at a frequency associated with this particular segment. It is known to those skilled in the art that frequency modulation renders a signal noise resistant, and that the higher the modulation frequency, the greater the signal-to-noise ratio.
- each of the optical attenuating zones of the multi-zone attenuator may constitute a bandpass filter which allows passage therethrough of a narrow sub-band of optical radiation having predetermined wavelengths, while rejecting (i.e. absorbing or scattering) radiation of other wavelengths.
- the multi-zone attenuator functions as an assembly of bandpass filters.
- the optical attenuating zones may have other, more complex wavelength-dependent attenuating characteristics and the only requirement which is to be met for the inventive device is that all the different attenuating zones must have different but known attenuating characteristics for all wavelengths of interest.
- the attenuating shutter may comprise the two above-mentioned components (i.e. the multi-segment optical shutter body and the multi-zone attenuator) applied to one another in that a pattern of N segments of the optical shutter body substantially coincides with a pattern of N optical attenuation zones of the multi-zone attenuator.
- Such an embodiment of the attenuating shutter may be manufactured by arranging the N zones of the multi-zone attenuator and the N segments of the optical shutter in predetermined identical geometrical shapes, applying the multi-zone attenuator on to the optical shutter and affixing (for example, by gluing) one to the other so, that respective zones and segments coincide.
- mutual positions of the optical shutter body and the multi-zone attenuator are such that each of the N segments of the optical shutter body lie on one and the same optical path with the corresponding optical attenuation zone of the multi-zone attenuator, while being spaced therefrom.
- the N segments of the optical shutter body may be respectively interconnected to the N respective optical attenuation zones of the multi-zone attenuator by means of at least N optical fibers .
- such attenuating shutters may be irradiated either from the side of the shutter body or from the side of the multi-zone attenuator.
- the multi-zone attenuator may either precede the optical shutter along the direction of the optical beam or follow the optical shutter.
- the multi-zone attenuator receives the optical radiation band and simultaneously transmits N wavelength-dependent portions thereof on to the appropriate N segments of the optical shutter body, which body controllably transmits therethrough the obtained wavelength-dependent portions.
- the optical shutter may transmit these portions successively, i.e. one by one through the N segments, respectively.
- each of the optical segments may switch on and off with its own frequency, so that the optical portions produced by the shutter will outgo therefrom substantially simultaneously, being modulated each by its particular frequency.
- said optical shutter receives the optical radiation band and allows for controllable passing of optical portions thereof through the N segments of the shutter's body; the optical portions pass either successively or simultaneously (by applying a particular frequency modulation to each of them); the optical portions outgoing from the N segments of the optical shutter pass through the corresponding N wavelength-dependent attenuation zones of the multi-zone attenuator, thus turning into N wavelength-dependent optical portions of the optical band.
- the attenuating shutter may be manufactured as an integral body constituting the optical shutter combined with the multi-zone attenuator and, where the N segments which are capable of selectively switching between the first and the second optical states, also serve as N optical attenuating zones having different predetermined wavelength-dependent attenuation characteristics.
- the optical shutter body may be manufactured from a ferroelectric liquid crystal, having a high switching speed.
- a liquid crystal cell comprises N zones each having its own predetermined wavelength-dependent attenuating characteristics, which are selectively actuatable in a manner enabling each of the zones to switch between the first (relatively transparent) and the second (relatively opaque) optical states.
- the optical shutter body is used not for switching between positions of optical portions of a preliminarily obtained spectrum (as it is arranged in the prior art), but for controllable passing of the initial radiation through a pre-arranged assembly of attenuating zones of the multi-zone attenuator.
- the attenuating shutter structure according to the invention enables the attenuating zones (and the corresponding segments of the optical shutter body) to be designed according to any desired configuration.
- the novel attenuating shutter will be indispensable in applications where it is impossible to amplify an initial light signal but, to the contrary, there is a need to thoroughly collect this initial light signal from a ready-to-access region.
- the optical radiation band may be initially restricted so as to include only characteristic wavelength ranges, and the attenuating shutter may have a restricted number of cells for processing the spectral lines.
- the optical radiation band may be chosen to comprise wavelengths in the near infrared range, for example those which may be produced by light emitting diodes (LEDs).
- the attenuating shutter may therefore comprise only cells active in this specific wavelengths range.
- a spectrometer for spectral analysis of a band of optical radiation, comprising the attenuating shutter according to any of the embodiments described herein before.
- the spectrometer comprises: an optical detector for receiving said optical radiation and producing an analog signal, an analog-to-digital (A/D) converter coupled to an output of the optical detector for converting the analog signal to an equivalent digital signal, a computing means coupled to the A/D converter for processing the digital signals so as to derive the desired spectral data; and a controller means for controlling activation of said attenuating shutter and for controlling other components of the spectrometer.
- A/D analog-to-digital
- the attenuating shutter may be activated, for example, according to any of the two above-described principles (schedules). More particularly, the N zones of the optical shutter body of the attenuating shutter may be activated successively so that at each specific timing only one zone is in its first (transparent) state.
- the optical detector of the spectrometer is controlled synchronously for successively detecting light intensities of the N wavelength-dependent portions of the optical radiation outgoing from the attenuating shutter.
- the A/D converter block is adapted for synchronous receiving of electric signals from the optical detector and for transmitting thereof in the digital form to the computer means for processing.
- the optical shutter body of the attenuating shutter may be controlled so as to activate each of the N optical zones thereof with a pre-selected frequency, thus applying a pre-selected frequency modulation to the optical radiation portion passing through a particular cell of the attenuating shutter and thereby allowing for simultaneous passage of the N optical radiation portions through said shutter in real time.
- the spectrometer may be equipped with N drivers having different frequencies for controlling the attenuating shutter; the detector, in turn, may be linked to an electronic circuitry capable of separating the detected integral signal into N constituent signals.
- the electronic circuitry is designed for deriving N constituent signals from the integral detected signal, according to their carrier frequencies, and converting each of said N constituent signals into digital form for further processing by the computer means.
- the main components of the spectrometer may be arranged in the following exemplary and non-limiting configurations.
- the attenuating shutter is adapted for receiving the band of optical radiation from a sample to be investigated, the optical detector being arranged to follow the attenuating shutter along the optical beam direction.
- the detector may be coupled to the attenuating shutter directly or via a collecting lens.
- the optical detector is placed after the attenuating shutter along the optical beam direction in such a manner that a sample to be investigated can be positioned between the attenuating shutter and the optical detector; the attenuating shutter being subjected to direct illumination by the band of optical radiation.
- the spectrometer may be additionally equipped with a light source.
- the light source may be placed before the attenuating shutter, to enable the introduction of the sample to be investigated between the light source and the shutter.
- the light source may be placed before the attenuating shutter for direct illumination thereof (while the sample to be investigated is accommodated between the attenuating shutter and the detector).
- Such an embodiment provides for more accurate measurements than placing the object before the attenuating shutter, since it allows for more precise calibration of the attenuating shutter owing to the known optical composition of the initial radiation band.
- the light source may comprise one or more light emitting diodes (LEDs).
- LEDs light emitting diodes
- components in the spectrometer may be arranged in yet a different way. For example, if the spectral analysis is performed for the radiation portion reflected from an object, and not for that transmitted through the object, configuration of the spectrometer must be modified slightly for illuminating samples so as to ensure the collecting of the reflected radiation.
- a novel method of spectral analysis of an optical radiation band involves a reverse approach, and comprises the following steps: (a) providing the above-described novel attenuating shutter comprising N cells, each having its own preliminarily defined wavelength-dependent attenuation characteristics; (b) illuminating said attenuating shutter with said optical radiation band; (c) actuating said attenuating shutter in a controlled manner for obtaining N wavelength-dependent portions of said optical radiation band; (d) providing N measurements of intensity of the obtained N respective wavelength-dependent portions of said band; and (e) calculating the spectral function of said optical radiation band based on the obtained N measurements of intensity and the preliminarily defined wavelength-dependent attenuation characteristics.
- the novel method can also be used for determining spectral function of a sample.
- the optical radiation band may constitute radiation acquired from the sample, more particularly, either the radiation transmitted through the sample or the radiation reflected therefrom.
- the sample must be illuminated by an initial optical radiation band with a known optical composition, the sample being considered a radiation absorbing and/or scattering optical environment.
- the method of determining spectral function of a sample comprises the following steps:
- the plurality of wavelength-dependent attenuation ratios for each of the N optical attenuation zones of the attenuation can be obtained experimentally by a manufacturer, during a calibration procedure.
- Such calibration may constitute an additional preliminary step which is to be performed before the above method.
- the calibration may be performed by illuminating the attenuating shutter with a known spectrum of optical radiation through a medium having known optical properties (such as air).
- the N attenuation characteristics preliminarily defined either by a manufacturer or by a customer are then used for computerized calculations of the sought-for spectral function according to the inventive method.
- the above-described method may be accomplished in a number of versions, depending on a manner of the shutter cells' actuation (either successive or simultaneous with frequency modulation), and a pre-selected mathematical way of determining the spectral function (e.g., calculation of the spectral intensities point-by-point, restoration of the spectrum using methods of approximation, etc).
- the spectral function is determined in respect of M wavelengths of interest; said wavelength-dependent attenuation characteristics of each particular cell of the attenuating shutter being composed of M preliminarily defined wavelength-dependent attenuation ratios of the corresponding zone of the multi-zone attenuator, thereby M*N of said ratios are preliminarily defined; the spectral function of said optical radiation band is calculated based on the obtained N measurements of intensity and the preliminarily defined M*N wavelength-dependent attenuation ratios where M is not greater thanN.
- the spectral function of the optical band under examination (i.e. its light intensity distribution) may be built based on data of elementary spectral intensity of each specific wavelength of the M predetermined spectral lines of interest in this band.
- the spectral function (being the distribution of intensities of the M wavelengths) can be calculated using the following system of equations:
- N the number of attenuation zones in the attenuating shutter, which may be obtained therefrom; j - a running number of an attenuating zone in the shutter,
- M the quantity of spectral lines (corresponding to specific wavelengths) which is chosen for spectral analysis, M ⁇ N; i - a running number of a spectral line (1 ⁇ i ⁇ M); ⁇ i - a wavelength corresponding to a specific spectral line i;
- a - intensity of a specific spectral line (in case of examining a sample - a discrete value of its spectral function at a specific spectral line); ⁇ j( ⁇ i)- an attenuation ratio of the attenuation zone in the attenuating shutter regarding the wavelength ⁇ -
- the ratio ⁇ j( ⁇ i) may be represented as follows:
- ⁇ j i exp (- ⁇ dj) where: ⁇ - a coefficient which is inherent in the material of the attenuation zone j and is constant for the wavelength ⁇ i; dj - the thickness of the attenuation zone j.
- Alj Ai ⁇ j( ⁇ ) + A 2 ⁇ j( ⁇ 2) + ⁇ Ai ⁇ j( ⁇ i) + ... A M ⁇ PJ(1M)
- the accuracy of the obtained function depends on the complexity of the device.
- M ⁇ N the number of optical channels of the attenuating shutter
- the attenuating shutter divides the incoming radiation into a large number of optical portions according to the number of the cells, it inevitably leads to the essential decrease in power of each of the obtained portions and thereby directly affects sensitivity of the device.
- the attenuating shutter with a large number of cells would bring up, according to the above-described method, a system of equations having the corresponding large complexity.
- the inventors have suggested to calculate the sought-for spectral function by mathematically approximating thereof by an unknown function, applying a procedure of error minimization and further restoring the spectral function.
- the inventive method may be used for defining concentration of a predetermined substance in a sample under examination.
- the sample or the attenuating shutter may be irradiated by an electromagnetic radiation band having the wavelength composition being not only known, but initially restricted to wavelengths which are characteristic of the spectral function of said substance.
- the above method may be used for invasive or non-invasive determining of the hemoglobin or glucose concentration in blood.
- the optical composition of the restricted radiation may be chosen from the near infrared range, for example the light produced by LEDs.
- Fig. 1 is a schematic cross-sectional view of one embodiment of the attenuating shutter according to the invention.
- Fig. 2 is a schematic cross-sectional view of another embodiment of the attenuating shutter according to the invention.
- Figs. 3 and 4 are schematic cross-sectional views of embodiments which may be designed based on the attenuating shutter shown either in Fig. 1, or in Fig. 2.
- Fig. 5 is a schematic cross-sectional view of yet another embodiment of the attenuating shutter where the optical shutter body integrally incorporates a multi-zone attenuator.
- Fig. 6 is a schematic perspective view of the attenuating shutter having a different pattern of the attenuating zones and the shutter segments.
- Fig. 7 is a schematic block diagram of a spectrometer comprising the attenuating shutter according to the invention.
- Fig. 8 is a schematic diagram illustrating one embodiment of a spectrometer for performing spectral analysis of radiation transmitted through a sample with the aid of the attenuating shutter according to the invention.
- Fig. 9 is a diagram showing another embodiment of a spectrometer with the inventive attenuating shutter for performing a method of spectral analysis differing from that shown in Fig. 8.
- Fig. 10 illustrates a block diagram of a spectrometer where N cells of the attenuating shutter are switched on and off in a successive manner.
- Fig. 11 illustrates a block-diagram of another embodiment of the spectrometer, where each of the N cells of the attenuating shutter is controlled separately at a particular frequency.
- Fig. 1 illustrates a novel attenuating shutter 10 according to a first embodiment, comprising a combination of a conventional optical shutter S formed on a liquid crystal body, and a multi-zone attenuator F which, for example, constitutes an array-like filter assembly.
- the attenuating shutter 10 is suitable for spectral analysis of an optical radiation band, i.e. for use in spectrometers for defining light intensities of a number (for example M) of specific wavelengths of interest. These wavelengths of interest are called spectral lines.
- the optical shutter S comprises N segments S 2 ,...SJ...SN, each being selectably switchable between a first (essentially transparent) and a second (essentially opaque) optical state.
- the multi-zone attenuator F includes N optical attenuating zones (filters) Fi, F 2 ,... Fj... FN, each being characterized by its wavelength-dependent characteristics, i.e. by a plurality M of light attenuation ratios ⁇ j( ⁇ i) inherent in the material of the segment and constant for each wavelength ⁇ i from the mentioned M values of the wavelengths of interest.
- the optical shutter S precedes the multi-zone attenuator F along the direction of the light beam, and each segment Sj is optically interconnected to a corresponding attenuating zone Fj.
- an optical radiation band having intensity I enters the body of the optical shutter S and is successively passed through each of its segments Sj one at a time, so that the attenuation array F successively receives one optical portion I INTERMED IA TE of the band which, however, has the same spectral composition as the initial band.
- the optical portion IIN TE R MEDIATE enters a particular attenuation zone Fj, it is transferred in this zone to a particular wavelength-dependent optical portion having intensity ⁇ lj.
- the attenuating shutter 10 upon receiving at its inlet an optical band having intensity I, produces at its outlet N successive wavelength-dependent optical portions having intensities ⁇ li,
- Fig. 2 illustrates an attenuating shutter 20 according to an alternative embodiment which has identical components to the attenuating shutter 10 shown in Fig. 1 but arranged differently.
- the shutter S follows the multi-zone attenuator F along the direction of the optical beam.
- the incoming optical band having intensity I is simultaneously attenuated by each of N attenuation zones of the attenuator F so that all these zones Fi to F N produce simultaneously N wavelength-dependent optical portions having light intensities from ⁇ li to ⁇ I N , respectively
- the optical shutter S successively transmits through its body the obtained wavelength-dependent optical portions by means of successive actuation of the segments Fi to FN, each of which receives only a particular optical portion from a corresponding attenuating zone of the multi-zone attenuator F.
- the result obtained at the outlet of the attenuating shutter 20 is identical to that obtained from the shutter 10.
- Fig. 3 illustrates a mode of optical interconnection which may be established between the shutter S and the multi-zone attenuator F. Contrary to the configurations shown in Fig. 1 and in Fig. 2, where the shutter and the attenuator are spaced from one another, Fig.3 illustrates an arrangement where the shutter S and the attenuator F are tight-fitting or even glued to one another. The order of the components S and F along the direction of the optic beam is irrelevant.
- Fig. 4 shows another way of providing optical connection between the shutter S and the attenuator F. It can be seen that the components are interconnected by optical fibers, so that each segment Sj of the optical shutter S is coupled to a corresponding attenuating zone Fj of the attenuator F by at least one optic fiber Lj.
- Fig. 5 is a generalized illustration of a third embodiment 30 of the attenuating shutter F/S constituting the optical shutter and the multi-zone attenuator integrally combined with one another in one body, such as a liquid crystal body.
- the optical shutter 30 may constitute, for example, a liquid 5 crystal cell comprising N zones, which are selectively actuatable in a manner enabling each zone to switch between the first (relatively transparent) and the second (substantially opaque) optical state; however, each of these zones in its relatively transparent state has its own predetermined wavelength-dependent attenuating characteristics (i.e. will differently l o attenuate light radiation of different wavelengths) .
- Fig. 6 is a three-dimensional view of another, disc-like embodiment 40 of the attenuating shutter, where the attenuating zones ⁇ to Fj 2 and the corresponding shutter segments Si to S] 2 are congruent and mutually overlapping. It will be appreciated that many other configurations of the 1 5 attenuating shutter, its attenuating zones Fj and the shutter segments S j may be employed , i.e. that the invention is not limited to the patterns illustrated in the above described drawings.
- Fig. 7 illustrates a block diagram of a spectrometer 45 comprising an attenuating optical shutter designated generally as 50 according to any one of 20 the above-described embodiments.
- the attenuating shutter 50 is in optical communication with a regular optical detector 52 via an optional lens 51.
- the detector is further connected to a computer 54 via an analog-to-digital converter 53.
- the computer 54 serves both for processing the information received from the converter 53, and for the synchronized control of all the 25 components of the spectrometer.
- Fig. 8 illustrates one possible schematic embodiment 55 of a spectrometer comprising an attenuating shutter 60 according to the invention for performing spectral analysis of a sample 56.
- the sample 56 is a finger which can be accommodated in a housing 57 of the device between a light source (or a plurality of light sources) 58 and the shutter 60.
- the light source 58 may comprise one or more light emitting diodes (LED) which illuminate(s) the finger 56 by a radiation band in the range from 920 to 1050 nm. Radiation transmitted through the finger's tissue forms a working optical radiation band which is collected by a collecting lens 59 and directed on to the attenuating shutter 60.
- LED light emitting diodes
- Optical segments of the attenuating shutter 60 are controlled in a predetermined manner as will be described below with reference to Figs 10 and 11.
- An outgoing optical signal produced by the attenuating shutter 60 is fed to an optical detector 61. Electrical signals created by the detector 61 in response to the received optical signals are further digitized and processed (not shown). Data obtained by the spectrometer 55 is used for calculating the sought-for spectrum of the sample (in this example - of the blood-perfused tissue of the finger). The obtained spectrum may then be used for determining concentration of a substance, such as glucose or hemoglobin, in the blood.
- a substance such as glucose or hemoglobin
- Fig. 9 illustrates schematically another embodiment of the spectrometer generally marked 65 which performs a modified method of spectral analysis of a sample.
- An attenuating shutter 62 is illuminated by an initial radiation band from a light source 63 via a collecting lens 64.
- the received initial radiation band is rearranged by the confrollably actuated shutter 62 into N wavelength-dependent optical portions, which are collected by a lens 69 and directed on to a sample 66 which is to be placed between the shutter and an optical detector 67.
- the sample is shown as a finger of an individual. Radiation which has been transmitted through the finger is acquired by the optical detector 67 and converted into electrical signals, which are further processed.
- the embodiment depicted in this particular figure has larger outer dimensions than that of Fig.
- the detectors 61 and 67 may be arranged so as to perceive radiation that is reflected by the sample, and not the radiation transmitted therethrough.
- computing means should be provided with an appropriate data base and equations for calculating the sought-for spectral function based on the reflectance measurements.
- Fig. 10 shows schematically a spectrometer 70 comprising a light source 71 having a plurality of light emitters each irradiating at a specific wavelength, an attenuating shutter 72 with N cells (a cell being an optical segment and attenuating zone), and an optical detector coupled to an amplifier and generally marked 73, which are all connected to a central processing unit (CPU) 74.
- the CPU 74 stores the initial data in a CPU memory (not shown) and performs both the control of the mentioned components of the spectrometer, and the processing of measurements received from the detector.
- the light source 71 is operated by a driver 75 coupled to the CPU 74 via an input-output port 76.
- the optical detector 73 is coupled to the CPU 74 via an analog-to-digital port 80.
- Cells of the attenuating shutter 72 (more exactly, the optical segments thereof) are controlled by an actuator unit 77 which is activated by the CPU 74 through an input-output port 78 and a digital-to-analog port 79.
- the actuator unit 77 comprises an amplifier 81 linked to a multiplexer 82 which, in turn, is connected to an assembly 83 of N amplifiers.
- the spectrometer 70 is controlled in the following way.
- CPU causes the port 79 to produce an analogous electric signal (for example, in the form of a voltage pulse) which is amplified by the amplifier 81 and fed to the multiplexer 82.
- the multiplexer addresses the amplified voltage pulse to a particular amplifier selected from N amplifiers of the assembly 83, and therefrom - to a specific cell of the attenuating shutter 72.
- this selected optical segment will open (i.e. become transparent) while the other segments will remain closed.
- one measurement is taken, i.e.
- Fig. 11 is a block diagram of a spectrometer 85 suitable for illustrating an alternative principle for controlling the attenuating shutter. In Fig. 11 like elements to those of Fig. 10 have been given like reference numerals.
- the spectrometer comprises a light source 71, an attenuating shutter 72 with N cells, an optical detector 73 coupled to an amplifier, and a CPU 74 similar to those shown in Fig. 10.
- the light source 71 is activated by the emitters' driver 75 controlled from the CPU via the input-output port 76.
- the attenuating shutter 72 is controlled as follows.
- An input-output port 86 of the CPU 74 activates an assembly 87 comprising N drivers operating at different frequencies.
- Each of the drivers independently controls a certain respective cell of the attenuating shutter 72 causing it to switch on and off at a particular frequency, thus applying a specific frequency modulation to the wavelength-dependent optical portion which is being transmitted through the particular cell.
- more than one cell of the shutter 72 may be opened at a specific time.
- the optical detector 73 receives from the attenuating shutter 72 all the N differently modulated wavelength-dependent optical portions simultaneously.
- the detector 73 is coupled to a set 88 comprising N so-called “lock-in” amplifiers which, in turn, are connected to corresponding channels of an N-bit analog-to-digital converter (A/D) 89.
- A/D analog-to-digital converter
- Each of the lock-in amplifiers selects from the "mixed" signal obtained from the detector only one signal according to its particular pre-selected carrier frequency and, after removing the carrier (i.e. upon demodulation of the signal), transmits the signal to a corresponding channel of the A/D converter 89.
- N separated electrical signals are simultaneously digitized and stored in the CPU memory for further processing.
- the described embodiment 85 of the spectrometer is advantageous in comparison to that of Fig. 10, since all the N measurements are effected simultaneously, which may be especially important for measurements in vivo. However, from the point of view of hardware such an embodiment is slightly more complex.
- the spectral function of an optical band (or of an object) under investigation may be restored either point-by-point (by using the described equations (1)), or by applying a particular mathematical approximation to the N measurements of light intensity obtained according to the method.
- lj is intensity of light detected at the outlet of the attenuating shutter when th only the j optical segment thereof is open;
- jo is intensity of light detected at the outlet of the attenuating shutter when all the optical segments thereof are closed; It is assumed that the following requirements are satisfied: there is a linear dependence between the measured energy and the light intensity, including the case when the whole attenuating shutter is closed; the light passing through any optical segment of the shutter passes completely through the corresponding attenuating zone of the filter and is completely sensed by the detector; there are no additional light sources except for a defined source; - the spectrum of the defined source is within the following wavelength interval: ⁇ min ⁇ ⁇ ⁇ max in the above interval all segments of the optical shutter are neutral, i.e. react identically to any wavelength.
- Al j is intensity of the f h optical portion detected by the detector, in other words - intensity allowed by the/ attenuating zone.
- the measurement Alj may be represented by an integral equation (3):
- J( ⁇ ) is a source spectrum which must be known
- ⁇ pj(7) is the transmitting spectrum of the J attenuating zone which must be known or obtained by calibration
- A( ⁇ ) is the sample's spectrum (i.e. its spectral intensity function) which is to be reconstructed.
- the unknown of the above equation is the function ⁇ (7) representing the transmitting spectrum of the j cell of the attenuating shutter and which can thus be readily obtained.
- the attenuating shutter can be utilized for measurements of the spectral function of a real sample. According to equations (1) or (3), the measurements will result in obtaining M values of the light intensity received from the real sample for each of the M wavelengths of interest.
- the full spectral intensity function of the sample can be restored by applying a method of mathematical approximation using the above-mentioned M obtained measurements of light intensity.
- a method of polynomial approximation is one of the effective ways for reconstructing so called “smooth" spectral intensity functions that are widespread in the class of biological objects.
- Lk( ⁇ ) is a LaGrange polynomial of the power k on the interval ( ⁇ min, ⁇ max); xu are unknown parameters of expansion of the spectral function of the sample, in terms of the LaGrange polynomials.
- the unknown parameters X k are to be found. These parameters can be determined by minimizing the measurement deviation (MD) using a so-called method of "minimal squares" (Equation (6)):
- Alj - (already defined) is a measured value of intensity of the light passed through the / cell of the attenuating shutter; Alj is represented by the above-mentioned equation (3); ij - is an approximated value of intensity of the light passed through the j cell of the attenuating shutter.
- P is the number of parameters X k which must be not more than the number of cells in the attenuating shutter, i.e. NP, and jk is a construction matrix depending on the type of approximation, which in our case looks as shown in formula (8) below.
- Readings of ajk can be obtained from equation (8) and substituted to the equation (7). It can be seen from equation (7) that approximation i) is a linear function of unknown parameters Xk , thus they can be defined by applying any procedure for minimization of total measurement deviation.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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AU58766/98A AU5876698A (en) | 1997-02-07 | 1998-02-06 | Optical shutter, spectrometer and method for spectral analysis |
IL13103398A IL131033A0 (en) | 1997-02-07 | 1998-02-06 | Optical shutter spectrometer and method for spectral analysis |
US09/370,131 US6191860B1 (en) | 1998-02-06 | 1999-08-06 | Optical shutter, spectrometer and method for spectral analysis |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
IL12017697A IL120176A (en) | 1997-02-07 | 1997-02-07 | Optical shutter for spectral analysis a spectrometer with said optical shutter and a method of spectral analysis |
IL120176 | 1997-02-07 |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US09/370,131 Continuation US6191860B1 (en) | 1998-02-06 | 1999-08-06 | Optical shutter, spectrometer and method for spectral analysis |
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WO1998035211A1 true WO1998035211A1 (en) | 1998-08-13 |
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Family Applications (1)
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PCT/IL1998/000059 WO1998035211A1 (en) | 1997-02-07 | 1998-02-06 | Optical shutter, spectrometer and method for spectral analysis |
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AU (1) | AU5876698A (en) |
IL (1) | IL120176A (en) |
WO (1) | WO1998035211A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2002027285A1 (en) * | 2000-09-28 | 2002-04-04 | Plain Sight Systems, Inc. | System and method for encoded spatio-spectral information processing |
US7219086B2 (en) | 1999-04-09 | 2007-05-15 | Plain Sight Systems, Inc. | System and method for hyper-spectral analysis |
US7652765B1 (en) | 2004-03-06 | 2010-01-26 | Plain Sight Systems, Inc. | Hyper-spectral imaging methods and devices |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5166755A (en) * | 1990-05-23 | 1992-11-24 | Nahum Gat | Spectrometer apparatus |
US5457530A (en) * | 1993-08-27 | 1995-10-10 | Minolta Co., Ltd. | Spectrometer provided with an optical shutter |
US5553613A (en) * | 1994-08-17 | 1996-09-10 | Pfizer Inc. | Non invasive blood analyte sensor |
-
1997
- 1997-02-07 IL IL12017697A patent/IL120176A/en not_active IP Right Cessation
-
1998
- 1998-02-06 WO PCT/IL1998/000059 patent/WO1998035211A1/en active Application Filing
- 1998-02-06 AU AU58766/98A patent/AU5876698A/en not_active Abandoned
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5166755A (en) * | 1990-05-23 | 1992-11-24 | Nahum Gat | Spectrometer apparatus |
US5457530A (en) * | 1993-08-27 | 1995-10-10 | Minolta Co., Ltd. | Spectrometer provided with an optical shutter |
US5553613A (en) * | 1994-08-17 | 1996-09-10 | Pfizer Inc. | Non invasive blood analyte sensor |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6859275B2 (en) * | 1999-04-09 | 2005-02-22 | Plain Sight Systems, Inc. | System and method for encoded spatio-spectral information processing |
US7219086B2 (en) | 1999-04-09 | 2007-05-15 | Plain Sight Systems, Inc. | System and method for hyper-spectral analysis |
WO2002027285A1 (en) * | 2000-09-28 | 2002-04-04 | Plain Sight Systems, Inc. | System and method for encoded spatio-spectral information processing |
US7652765B1 (en) | 2004-03-06 | 2010-01-26 | Plain Sight Systems, Inc. | Hyper-spectral imaging methods and devices |
Also Published As
Publication number | Publication date |
---|---|
AU5876698A (en) | 1998-08-26 |
IL120176A (en) | 2000-01-31 |
IL120176A0 (en) | 1997-06-10 |
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