spectrometer

Abstract

A spectrometer is provided. The spectrometer may include: a tunable on-chip laser source configured to illuminate biological tissue with laser radiation; a photodetector configured to receive the laser radiation reflected from the biological tissue; and at least one processor. The tunable on-chip laser source may include: a semiconductor gain chip having a gain bandwidth for operating the tunable on-chip laser source within a predetermined wavelength range; and a plurality of resonant cavities connected between the semiconductor gain chip and the at least one processor and configured to perform both coarse high-speed measurements and fine measurements to measure the spectrum of the laser radiation reflected from the biological tissue.

Description

[0001] This application claims priority from Russian Patent Application No. 2019134249 filed in the Russian Intellectual Property Office on October 25, 2019, and Korean Patent Application No. 10-2020-0074450 filed in the Korean Intellectual Property Office on June 18, 2020, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0002] Apparatuses and methods consistent with example embodiments relate to measuring a spectrum from an object to obtain biological information of the object, and more particularly, to a spectrometer including a tunable on-chip laser and a spectrum measurement method using the spectrometer. Background Art

[0003] Optical devices used for spectroscopy purposes need to have features such as scanning of light wavelengths. This feature can be achieved by using narrow-bandwidth tunable light sources (such as lasers) or by using broadband light sources (such as light-emitting diodes (LEDs)) combined with optical filter systems. Both options mean a bulky overall structure of the light source system, resulting in a larger size of the entire spectrometer, which is difficult to fit into a wearable form factor. Form factor or size is a standard that defines the overall size of a technical product and describes a set of additional technical parameters of the product (for example, shape).

[0004] There are three problems at present.

[0005] The first problem is the lack of compactness of the spectrometer. Known spectrometers cannot be worn on the arm as a bracelet. Existing devices designed for this purpose are not compact.

[0006] The spectral resolution of commercial spectroscopic devices for wearable form factors does not exceed about 20 nm. Contemporary important tasks, such as non-invasive detection of blood glucose levels, require higher spectral resolutions that should be much smaller than several nanometers.

[0007] A second problem is the low spectral resolution of known spectrometers.

[0008] When determining blood glucose levels, the reflectance spectrum from the subject needs to be measured, which can be achieved with a set of narrowband light sources such as lasers or using broadband light sources such as light emitting diodes combined with an optical filter system, which implies a fairly large-scale design.

[0009] If a spectrum is measured using a set of narrowband sources, a set of points is obtained on the spectrum, and the distance between the points determines the resolution of the device. For existing devices, the resolution is not high enough, which does not meet the requirements for measuring parameters such as blood sugar.

[0010] The third problem is discrete wavelength scanning. In existing devices for tunable wavelengths, such scanning is performed discretely, ie, tuning is performed with a fixed step size within each time interval, and continuous and smooth wavelength scanning is not provided.

[0011] Broadband LED sources combined with individual optical filters or a set of narrowband lasers are used in existing spectroscopy setups to scan along the wavelength. These components are turned on and off in a predetermined sequence required for the measurement. Such setups do not allow for a continuous scan along the wavelength, which is important for achieving maximum measurement accuracy.

[0012] In the related art, LED-based coded source spectrometers include multiple LED light sources capable of exhibiting different wavelengths and bandwidths, arranged in any convenient manner relative to a detector module, with sample and reference light paths distinct from one another. The LED sources are switched in a coded pattern or a pattern corresponding to a Hadamard complement or modified Hadamard complement scheme. Discrete wavelength scanning and low spectral resolution are considered drawbacks of these spectrometers.

[0013] A large number of light-emitting diodes are used in spectrometers, and the number of these diodes determines the spectral resolution. If the spectral resolution needs to be improved, the number of light sources (i.e., the number of diodes) should be increased. However, because the size of the device is limited, the number of diodes cannot be increased indefinitely.

[0014] In the related art, a noninvasive glucose sensor noninvasively measures glucose concentration by measuring a plurality of absorption values ​​of the total amount of light passing through a sample using at least one emitter operating at corresponding multiple wavelengths and obtaining the glucose concentration from the absorption measurements.

[0015] The non-invasive glucose sensor is configured as a small device that is attached to a wrist, for example, and can be worn by a diabetic patient to generate continuous and non-invasive blood glucose level measurements. The sensor and sensing technology ensure the measurement of glucose, water, and albumin non-invasively and continuously. The sensor can be implemented as a low-power, small-size, and low-cost device. A vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser that can be configured as a tunable transmitter. In some embodiments, the transmitter can be used in a sensor for monitoring blood glucose levels. Typically, edge-emitting semiconductor lasers have low accuracy and are cheaper than VCSELs.

[0016] In this device, so-called "vixels" are used as light sources—light sources—with vertical resonators (i.e., vertical cavity lasers emitting from the surface). This device is not meant for wavelength scanning; several lasers are used, and their number determines the device's spectral resolution. Furthermore, using a large number of these lasers is a rather expensive solution.

[0017] In related technology, a tunable laser-based spectroscopic system is used to non-invasively measure body water content. One of the most important indicators of health is body water content, so spectroscopic systems help quantitatively control the body's hydration level and determine whether it is necessary to increase or decrease the amount of water in the body.

[0018] A system for assessing a bodily fluid metric includes a laser and a single detector, the laser configured and arranged to illuminate at least a portion of body tissue, the single detector being in optical communication with at least a portion of the body tissue. For example, the system may include a tunable laser and / or one or more fixed-wavelength lasers. In some embodiments, the system may include a sensor comprising a first optical fiber having a first end configured and arranged to be in optical communication with the laser and a second end configured and arranged to be in optical communication with a tissue sample, and a second optical fiber having a first end configured and arranged to be in optical communication with the detector and a second end configured and arranged to be in optical communication with the tissue sample. The system may also include a wavelength division multiplexer and / or an optical switch in optical communication with the laser and the first optical fiber. In some embodiments, the system may include a detector comprising a photodiode and / or an optical switch in optical communication with the second optical fiber. In some embodiments, the optical fibers (e.g., the first optical fiber and / or the second optical fiber) may include a beam splitter. In some embodiments, the sensor may be configured and arranged to be disposable or reusable. The sensor may include a collimator, a star beam splitter, and / or a beam expander in optical communication with the laser. In some embodiments, the system may not include a diffraction grating and / or a detector array.

[0019] Related art spectroscopy systems include bulky components or assemblies that are not suitable for wearable devices.

[0020] Another spectrometer in the related art includes: a tungsten lamp (as a first light source) that emits light having no peak wavelength in the wavelength range of visible light and having an amount of light that increases as the wavelength becomes longer; a violet LED (as a second light source) that emits light having a peak wavelength in the wavelength range of visible light; and a light mixer that mixes light from the respective light sources (i.e., the tungsten lamp and the violet LED); a light receiving unit (etalon) that receives the light mixed by the light mixer and transmits light having a specific wavelength contained in the received mixed light; and a measurement control unit that measures spectral characteristics of test target light that can pass through the etalon and measures spectral characteristics of light that has passed through the etalon based on the light received by the light receiving unit.

[0021] When using only a first light source that does not have a peak wavelength within the visible light wavelength range, as described above, the amount of light within a specific range within the visible light wavelength range can be significantly reduced. However, emitting a second light source that has a peak wavelength, particularly within a short wavelength range (the wavelength range where the amount of light from the first light source is reduced), can effectively compensate for the significant decrease in the amount of light within the short wavelength range. Therefore, the measurement accuracy of spectral characteristics within the wavelength range where the amount of light is reduced can be improved, which contributes to highly accurate measurement of spectral characteristics.

[0022] Discrete wavelength scanning and low spectral resolution should be considered as disadvantages of the spectrometer. Here, discrete wavelength tuning is performed. Smooth reconstruction is not performed. There is a specific step to determine the resolution, and the reconstruction is performed with minimal parts (i.e., discretely). Summary of the Invention

[0023] Example embodiments address at least the above problems and / or disadvantages and other disadvantages not described above. Also, example embodiments are not required to overcome the disadvantages described above, and may not overcome any of the problems described above.

[0024] One or more example embodiments provide spectral measurements with high spectral resolution and continuous wavelength tuning using a device compact enough to fit into a wearable form factor, while maintaining low levels of energy consumption, said goals being achieved by creating a spectrometer based on a tunable on-chip laser, which is maximally compact so that it can be arranged on an arm in the form of a bracelet, has high spectral resolution, and provides smoothly executed continuous wavelength sweeps.

[0025] The technical effect achieved by one or more example embodiments of the present disclosure is to ensure maximum compactness (i.e., a desirable wearable form factor) in order to provide higher performance, namely continuous wavelength scanning, higher measurement speed, high signal-to-noise ratio (due to the use of lasers), as well as high spectral resolution and the ability to perform both coarse and fine (if desired) spectral measurements simultaneously.

[0026] According to one aspect of an exemplary embodiment, a spectrometer is provided, the spectrometer comprising: a tunable on-chip laser source configured to illuminate biological tissue with laser radiation; a photodetector configured to receive the laser radiation reflected from the biological tissue; and at least one processor. The tunable on-chip laser source may comprise: a semiconductor gain chip having a gain bandwidth for operating the tunable on-chip laser source within a predetermined wavelength range; and a plurality of resonant cavities connected between the semiconductor gain chip and the at least one processor and including a first resonant cavity and a second resonant cavity. Each of the plurality of resonant cavities may comprise: a waveguide and a plurality of tunable filters, wherein when the laser radiation is to be emitted into the biological tissue, the plurality of tunable filters generate light having different wavelengths depending on parameters of the plurality of tunable filters of each of the plurality of resonant cavities. The first resonant cavity may comprise a first tunable filter among the plurality of tunable filters, and the first resonant cavity may be configured to perform a coarse, high-speed measurement to measure a spectrum of the laser radiation reflected from the biological tissue when the biological tissue is illuminated by the laser radiation generated by the first tunable filter of the first resonant cavity. The second resonant cavity may include a second tunable filter among the plurality of tunable filters, and the second resonant cavity may be configured to perform fine measurement to measure a spectrum of the laser radiation reflected from the biological tissue when the biological tissue is illuminated by the laser radiation generated by the second tunable filter.

[0027] The waveguide of each of the plurality of resonant cavities may terminate in a Sagnac mirror that provides a feedback loop between each of the plurality of resonant cavities and a semiconductor gain chip.

[0028] The spectrometer may further include: a metal heating element located in the plurality of resonant cavities and configured to receive a voltage from an external source; and a thermo-optical control circuit configured to tune the wavelengths of the plurality of resonant cavities by applying a voltage to the metal heating element.

[0029] The spectrometer may further include a plurality of electro-optical control circuits configured to tune the wavelengths of the plurality of resonant cavities by applying an electric field to the plurality of resonant cavities to change the effective refractive index of the plurality of resonant cavities and the transmission spectrum of the laser radiation emitted from the spectrometer.

[0030] The spectrometer may further include a plurality of acousto-optic control circuits configured to tune wavelengths of the plurality of resonant cavities by exposing the plurality of resonant cavities to ultrasonic vibrations from an external source.

[0031] The semiconductor gain chip having a gain bandwidth for operating the tunable on-chip laser source within the predetermined wavelength range may be a first semiconductor gain chip having a first gain bandwidth for operating the tunable on-chip laser source within the predetermined wavelength range. The spectrometer may include an array of semiconductor gain chips having different gain bandwidths to provide scanning along an extended wavelength range wider than the predetermined wavelength range. The array of semiconductor gain chips having different gain bandwidths may include the first semiconductor gain chip having the first gain bandwidth.

[0032] The spectrometer may further include a modulator configured to control a gain bandwidth of the semiconductor gain chip.

[0033] The spectrometer may further include: a feedback control circuit and a wavelength calibration circuit, for performing real-time calibration on the wavelength of the spectrometer.

[0034] The spectrometer may further include a beam splitter configured to connect the semiconductor gain chip to the plurality of resonant cavities.

[0035] The first resonant cavity may include a first reflecting mirror paired with a first tunable filter, and the second resonant cavity may include a second reflecting mirror paired with a second tunable filter.

[0036] According to one aspect of another exemplary embodiment, a method for obtaining biological information using a spectrometer including a plurality of resonant cavities is provided. The plurality of resonant cavities may include a first resonant cavity and a second resonant cavity. The method may include: irradiating the biological tissue with first laser radiation generated by a first tunable filter of the first resonant cavity while the first resonant cavity performs a coarse, high-speed measurement to measure a spectrum of first laser radiation reflected from the biological tissue; irradiating the biological tissue with second laser radiation generated by a second tunable filter of the second resonant cavity while the second resonant cavity performs a fine, low-speed measurement to measure a spectrum of second laser radiation reflected from the biological tissue; and obtaining the biological information based on the coarse, high-speed measurement and the fine, low-speed measurement.

[0037] The method may further include tuning a wavelength of radiation in a waveguide of the first resonant cavity by thermo-optically tuning the wavelengths of the first and second tunable filters by heating the waveguide in the first resonant cavity.

[0038] The method may further include electro-optically tuning wavelengths of the first and second tunable filters by changing a refractive index of the waveguide by applying an external electric field to the waveguide of the first resonant cavity.

[0039] The method may further include acousto-optically tuning wavelengths of the first and second tunable optical filters by applying ultrasonic vibrations to the waveguide of the first resonant cavity to change an effective transmission spectrum of the waveguide of the first resonant cavity.

[0040] A spectrometer according to example embodiments may provide the following advantages:

[0041] Simplify and miniaturize the entire optical scheme, where the gain chip is the largest component;

[0042] Simultaneously and independently scanning wavelengths λ1 and λ2 provides a high degree of flexibility in acquiring the spectrum of target biological tissue, wherein the scanning is performed by varying the transmittance of the tunable filter;

[0043] If several wavelengths are needed, fewer gain chips are used, thus reducing the power consumption and losses of the entire device;

[0044] Covering an extended wavelength range (e.g., 1500-1800 nm), which is important for blood glucose measurements;

[0045] It provides the possibility of realizing complex modulation of output power, which is important for communication systems;

[0046] Provides higher accuracy wavelength control due to real-time calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above and / or other aspects will become more apparent by describing certain example embodiments with reference to the accompanying drawings, in which:

[0048] Figure 1 is a diagram of a spectrometer according to an example embodiment;

[0049] Figure 2A is a top view of a gain chip positioned adjacent to a coin according to an example embodiment;

[0050] Figure 2B is a diagram of a tunable on-chip laser including a plurality of resonators according to example embodiments;

[0051] Figure 3 is a detailed scheme of a tunable on-chip laser including two resonators according to an example embodiment;

[0052] Figure 4 is a scheme of a tunable on-chip laser according to an example embodiment;

[0053] Figure 5 is a laser source spectrum of a tunable on-chip laser array based spectrometer according to example embodiments;

[0054] Figure 6is a scheme of a tunable on-chip laser including a thermo-optical resonator control unit according to example embodiments;

[0055] Figure 7 is a scheme of a tunable on-chip laser including an electro-optic / acousto-optic resonator control unit according to an example embodiment;

[0056] Figure 8 is a tunable on-chip laser array on a single base according to example embodiments;

[0057] Figure 9 is a scheme of a tunable on-chip laser including a real-time wavelength calibration unit for a spectrometer according to example embodiments;

[0058] Figure 10 is a sample reflectance spectrum obtained using a spectrometer having a laser source including a tunable on-chip laser array according to example embodiments;

[0059] Figure 11 is a rough, high-speed measured sample reflectance spectrum according to an example embodiment;

[0060] Figure 12 is a sample reflectance spectrum of a fine, low-speed measurement in a region of interest (B) according to an example embodiment. DETAILED DESCRIPTION

[0061] Example embodiments are described in more detail below with reference to the accompanying drawings.

[0062] In the following description, the same drawing reference numerals are used for the same elements even in different drawings. Matters defined in the description, such as detailed configuration and elements, are provided to assist in a comprehensive understanding of the example embodiments. However, it is apparent that the example embodiments can be practiced without those specifically defined matters. In addition, well-known functions or structures are not described in detail because they would obscure the description with unnecessary detail.

[0063] Expressions such as "at least one of," when following a list of elements, modify the entire list of elements without modifying the individual elements in the list. For example, the expression "at least one of a, b, and c" should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, all of a, b, and c, or any variation thereof.

[0064] Figure 1 A diagram illustrating a spectrometer according to example embodiments.

[0065] Figure 1The spectrometer 1 shown in FIG may include a laser source 2 configured to irradiate biological tissue 3 with laser radiation. The spectrometer 1 may include a photodetector 4 configured to receive radiation reflected from the biological tissue 3 and passed through an optical system 6 that provides collimation of the incident radiation and directs the incident radiation to the photodetector 4, as well as a control and photodetector data processing unit (e.g., a processor) 7.

[0066] Figure 2A shows a top view of a semiconductor gain chip 8 included in the spectrometer 1, Figure 2B Shown as Figure 1 Schematic diagram of a tunable on-chip laser with laser source 2 shown in FIG. The tunable on-chip laser may include a laser array and a semiconductor gain chip 8, which is combined with a photonic chip substrate (or base) 9 and a cooling system 11. The semiconductor gain chip 8 is connected to one or more resonant cavities 10. The resonant cavity 10 may also be referred to as a resonator (including the cavity therein).

[0067] Figure 3 A detailed scheme of a tunable on-chip laser comprising two resonant cavities 10A and 10B is shown. Figure 4 A scheme of a tunable on-chip laser comprising N resonant cavities 10A, 10B and 10N is shown, where N is an integer greater than 2. The semiconductor gain chip is characterized by its own gain bandwidth for operation of the tunable on-chip laser within a predetermined wavelength range, and is obtained by Figure 3 and Figure 4 10N. The waveguide 12 is connected to the waveguide 12 shown in FIG. The waveguide 12 is split by a beam splitter 13 and connected to one or more resonant cavities 10A, 10B, and 10N. The resonant cavities 10A, 10B, and 10N are connected to a control unit 18 and a power unit (e.g., a power supply) 19. The control unit 18 may include or correspond to the control and photodetector data processing unit 7, or may be provided independently of the control and photodetector data processing unit 7, and may have a circuit structure. The control unit 18 may also be referred to as a control circuit.

[0068] Each of the resonant cavities 10A, 10B, and 10N may include a waveguide 12 and a tunable filter. The resonant cavity 10A may include a tunable filter 14A and a reflector 15A, the resonant cavity 10B may include a tunable filter 14B and a reflector 15B, and the resonant cavity 10N may include a tunable filter 14N and a reflector 15N.

[0069] Each of the resonant cavities 10A, 10B, and 10N includes Figure 3, to ensure that the light generated by the laser source 2 (e.g., output 1, output 2, and output N) has different wavelengths λ1, λ2, ..., λn according to the parameters of the tunable filters 14A, 14B, and 14N included in the resonant cavities 10A, 10B, and 10N, respectively.

[0070] According to an example embodiment, the spectrometer 1 may include: Figure 3 The two resonant cavities 10A and 10B shown in FIG. 1 may include Figure 4 There are two or more resonant cavities 10A, 10B and 10N shown in FIG.

[0071] The tunable filter 14A of the resonant cavity 10A is configured to perform a rough, high-speed measurement of the reflection spectrum R(λ) of the target (e.g., biological tissue 3), where the reflection spectrum R(λ) is obtained by collecting light generated by the resonant cavity 10A and then reflected from the target. The tunable filter 14B of the resonant cavity 10B is configured to perform a fine, low-speed measurement of the reflection spectrum R(λ) of the target, where the reflection spectrum R(λ) is obtained by collecting light generated by the resonant cavity 10B and then reflected from the target.

[0072] The waveguide 12 of each resonant cavity 10A, 10B and 10N ends with a respective Sagnac mirror 15A, 15B and 15N, thereby providing a feedback loop between the resonant cavity 10A, 10B and 10N and the semiconductor gain chip 8 .

[0073] Beam splitter 13 divides the energy of semiconductor gain chip 8 into two or more resonant cavities 10A, 10B, and 10N. This achieves a major advantage in simplified manufacturing. Because resonant cavities 10A, 10B, and 10N are integrally fabricated using silicon-on-insulator (SOI) technology or silicon nitride-on-insulator (SiN) using photolithographic methods, this solution can be manufactured very simply on an industrial scale.

[0074] like Figure 3 、 Figure 4 and Figure 6 As shown in , the laser source 2 may include a metal heating element located on the surface of one or more tunable filters 14A, 14B and 14N as components of the resonant cavities 10A, 10B and 10N and configured to receive a voltage from a power unit (e.g., an external source) 19.

[0075] According to an example embodiment, Figure 3 and Figure 6 As shown, the control unit 18 of the spectrometer 1 may include a thermo-optical control unit (eg, a thermo-optical control circuit) for controlling a metal heating element, the metal heating element being configured to heat a resonant cavity (eg, Figure 3 The resonant cavity 10A, 10B or Figure 6 The wavelength of the resonant cavity A, resonant cavity B, and resonant cavity C in the embodiment of the present invention is tuned, wherein the wavelength tuning is performed by applying a voltage to the metal heating element.

[0076] According to another example embodiment, Figure 7 The spectrometer 1 shown in the figure includes an electro-optical control unit (e.g., an electro-optical control circuit) 20A according to the number of resonant cavities, and the electro-optical control unit 20A is configured to tune the wavelength of the resonant cavity by applying an electric field to the resonant cavity, wherein the change in the electric field changes the effective refractive index and transmission spectrum of the resonant cavity, thereby ensuring the tuning of the wavelength.

[0077] According to another example, Figure 7 The spectrometer 1 shown in the figure may include an acousto-optic control unit (e.g., an acousto-optic control circuit) 20B according to the number of resonant cavities, and the acousto-optic control unit 20B is configured to tune the wavelength of the resonant cavity, wherein the wavelength is tuned by exposing the resonator cavity to ultrasonic vibrations from an external source, wherein the parameters of the ultrasonic vibrations determine the transmission spectrum, which ensures the tuning of the wavelength.

[0078] According to another embodiment, Figure 8 The spectrometer 1 shown in FIG. 8 comprises an array of semiconductor gain chips 8 having different gain bandwidths to provide scanning along a wavelength within an extended wavelength range (eg, 1500-1800 nm).

[0079] In general, any semiconductor amplifier has its own gain bandwidth, and the laser cannot be operated outside this bandwidth. This bandwidth is limited. If it is necessary to measure the spectrum in a bandwidth exceeding the gain bandwidth of the semiconductor gain chip, another semiconductor gain chip with a different gain bandwidth should be used. By combining several tunable lasers, their bandwidths can be combined in a simple way (i.e., docking or attaching one to another) to ultimately cover the entire range, where each tunable laser is based on its own semiconductor gain chip with its own bandwidth.

[0080] According to another embodiment, Figure 9 The spectrometer 1 shown in FIG. 1 comprises a control unit 18 configured to control a resonant cavity and a modulation unit (or modulation module) 21 configured to control a gain bandwidth of a semiconductor gain chip.

[0081] According to another embodiment, Figure 9 The spectrometer 1 shown in FIG. 1 comprises a wavelength calibration unit 22 and a feedback control unit 23 for calibrating the wavelength of the spectrometer in real time.

[0082] A method of measuring reflected radiation from a biological object by using a spectrometer includes the following operations.

[0083] Due to its compact size, the spectrometer can be fixed on the patient's arm. The biological tissue is irradiated with laser radiation generated by two or more resonators 10A, 10B and 10N, wherein the tunable filter 14A of the resonator 10A is configured such that when the laser radiation is generated by the resonator 10A, the tunable filter 14A of the resonator 10B is configured such that when the laser radiation is generated by the resonator 10N, the tunable filter 14A of the resonator 10A is configured such that when the laser radiation is generated by the resonator 10A, the tunable filter 14A of the resonator 10A is configured such that when the laser radiation is generated by the resonator 10N, the tunable filter 14A of the resonator 10A is configured such that when the laser radiation is generated by the resonator 10A, the tunable filter 14A of Figure 3 When the light generated by the resonant cavity 10A shown in FIG. 1 illuminates a target, as shown in FIG. Figure 10 As shown in FIG, a rough high-speed measurement of the reflection spectrum R(λ) of a target (eg, biological tissue) is performed.

[0084] The method may include modifying the resonant cavity 10 (see FIG. 1 ) by changing the resonant cavity 10 (see FIG. 1 ) within the tunable filter 14A of one or more resonant cavities 10A, 10B, and 10N. Figure 3 ) by tuning the wavelength of the source using the transmittance of the tunable filter 14A to generate light, to perform a rough and high-speed measurement of the reflection spectrum R(λ) of the target.

[0085] The resulting reflectance spectrum R(λ) is then analyzed and the region of interest for identifying artifacts is determined. Figure 11 As shown in , the region of interest may be, for example, a portion of the spectrum of the source containing a peak (rectangle indicated by dashed lines).

[0086] Furthermore, during the generation of radiation by the other resonator 10B using the tunable filter 14B, a fine low-speed measurement of the reflection spectrum of the target in the region of interest is performed.

[0087] Tuning the wavelength of the radiation in the waveguides of the resonant cavity is performed by thermo-optical tuning of the wavelength of the tunable optical filters A and B by heating the waveguides in the resonant cavity, wherein the wavelength of the source is changed from a smaller value to a larger value, wherein the filtering capability is determined by the refractive index of the material from which the waveguides are made.

[0088] According to another embodiment, electro-optical tuning of the wavelength of the tunable optical filters A and B is performed by changing the refractive index of the waveguide of the resonator by applying an external electric field to the waveguide, wherein the wavelength is changed from a smaller value to a larger value and the filtering capability is determined by the refractive index of the material from which the waveguide is made.

[0089] According to another embodiment, the transmission spectrum of the waveguide of the resonant cavity is changed by applying ultrasonic vibrations to the waveguide, and the wavelength of the waveguide is acousto-optically tuned by performing acousto-optic tuning on the wavelength of tunable filters A and B, wherein the wavelength is changed from a smaller value to a larger value and the filtering capability is determined by the refractive index of the material from which the waveguide is made.

[0090] Two micro-resonators 16A and 16B ( Figure 3) performs fine tuning along the wavelength.

[0091] This effect manifests itself as a significant increase in the resonator tuning range due to the cascaded arrangement of two microresonators 16A and 16B having different transmitted radiation spectra.

[0092] If the distance between the transmission peaks of the first microresonator (and therefore, the tuning range of the wavelength of the transmitted optical radiation) is defined as FSR1, and the distance between the transmission peaks of the second microresonator is defined as FSR2, then the tuning range Δ of the resonant cavity composed of the two microresonators is determined according to Expression 1, and the tuning range Δ can significantly exceed the values ​​of FSR1 and FSR2.

[0093]

[0094] As mentioned above, if it is necessary to measure the spectrum in a bandwidth exceeding the gain band of the semiconductor gain chip, another semiconductor gain chip with a different gain bandwidth is used. By combining several tunable lasers, each based on its own semiconductor gain chip with its own bandwidth, their bands can be simply combined (i.e., docked or attached to another) to ultimately cover the entire range.

[0095] Figure 5 A specific reference spectrum based on a tunable laser array is shown.

[0096] Initially, the emission spectrum is a narrow bandwidth covering the range from 1500 to 1800 nm. This range is determined according to the research object. If a biological object (e.g., the glucose content in human tissue) is to be measured, it is necessary to measure the spectrum within this range. Therefore, it is not possible to perform such a measurement using a semiconductor gain chip covering approximately 50 nm. This would require the use of several semiconductor amplifiers.

[0097] Figure 10 The reflection spectrum from the object is shown as a result of using a tunable laser array. As a result, a curve is obtained, where each point on the curve corresponds to the reflection spectrum of the wavelength from the object.

[0098] The solid line shows the spectrum of the source, and the dashed line shows the reflected spectrum of the object (e.g., from biological tissue). Thus, a very coarse spectrum is obtained (i.e., the number of wavelengths corresponds to the number of points, which is a broken line). This curve may not be very informative at the initial stage, but it allows future estimation of times and regions of interest that are important for more accurate and refined measurements.

[0099] The function of the resonant cavity is as follows:

[0100] The resonant cavity provides feedback (i.e., a portion of the radiation traveling along the waveguide is sent back for amplification);

[0101] The resonant cavity provides filtering of the radiation.

[0102] In theory, any optical filter or other kind of filter can achieve this function.

[0103] When radiation with two different wavelengths λ1 and λ2 is generated simultaneously, the configuration of the spectrometer according to this exemplary embodiment allows for a significant reduction in the size of the entire circuit, as the largest component is a semiconductor gain chip, which is much smaller than a coin. When two different wavelengths are obtained at the output of the resonant cavity using a single gain chip, the circuit is half the size of a circuit using two semiconductor gain chips, also providing two different wavelengths. However, the energy of a single semiconductor gain chip cannot be shared indefinitely.

[0104] Furthermore, such a scheme according to example embodiments makes it feasible to implement a spectrum measurement method by simultaneously tuning two different wavelengths through the use of a predetermined algorithm.

[0105] Thus, selective spectral measurement is performed. The two spectral measurement modes (i.e., coarse and fine) are directly related to the use of two wavelengths obtained from a single semiconductor gain chip. Since two wavelengths are generated, coarse measurements can be performed for one wavelength and fine measurements can be performed for the second wavelength.

[0106] This is performed as follows. Initially, wavelength tuning is performed using a filter and a resonant cavity based on the Vernier effect, meaning the source wavelength is changed from shorter to longer at the maximum permissible speed. However, the higher the speed, the lower the resolution and the lower the noise signal. In this case, a rough reflectance spectrum from the object is obtained. This rough reflectance spectrum is a fluctuating object and, since the measurement is performed very quickly, can be noisy. In this case, relatively little energy is detected at each moment.

[0107] After a rough measurement of the spectrum has been performed, the resulting curve is analyzed in order to refine very important regions of interest.

[0108] When measuring glucose, the spectrum itself isn't as informative as specific parts of it. This is especially true when using spectra to determine relative changes in glucose, or any chemical. That is, relative spectral measurements can be very important. In such cases, it's necessary to analyze certain parts of the spectrum (i.e., how those parts change).

[0109] For example, Figure 12As shown in , the next step is to perform a fine measurement of the region of interest. To this end, the fine measurement mode using the second wavelength is used. That is, the parameters of the second resonant cavity are changed in such a way that the wavelength tuning is performed at a low speed only in the region of interest, not over the entire region.

[0110] First, a portion of the spectrum that is a region of interest is determined by performing a high-speed scan using a single filter, and a low-speed scan is performed using a second wavelength.

[0111] The advantages of using two wavelengths are as follows. The filtering capacity of an optical filter is determined by the temperature dependence of the effective refractive index of the material from which it is made. Tuning is performed by heating these resonant cavities. Heating is an inertial process; heating special metal contacts is much easier than cooling them, especially in wearable devices that do not include special active cooling systems. Since there are two independent filter banks with two radiation sources, it is possible to heat one resonant cavity, perform coarse tuning, and then fine tune by heating the second resonant cavity. There is no need to cool the first resonant cavity and wait for a certain period of time for it to cool sufficiently before performing tuning again. In this way, the efficiency and performance of the entire device are improved. The main advantage is that using two sources does not require cooling each source separately, and by heating the first and second sources alternately, using the first and then the second, a double scan can be performed.

[0112] In the second case, tuning of the microresonator can be achieved not only by changing the temperature (i.e., by heating) but also by using various electro-optic effects. In the case where various materials (other than ordinary silicon) (e.g., lithium niobate) with significant electro-optic effects are used to fabricate the microresonator (i.e., by changing the effective refractive index according to the applied external electromagnetic field), it is possible to change the applied electromagnetic field instead of the temperature.

[0113] In the case of using the wavelength calibration unit 22, the operation is as follows.

[0114] Each of the radiation sources generates light that enters calibration unit 22. Calibration unit 22 determines whether the generated wavelength corresponds to a wavelength embedded in the control algorithm of resonant cavity 10A, 10B or 10N. Tuning is performed assuming a specific relationship between the control signal and the wavelength of the resulting radiation.

[0115] However, this dependence is subject to external interference. If the external interference is temperature, there may be an effect associated with additional heating of the entire substrate to which the gain chip is mounted. The wavelength may differ from the desired wavelength (i.e., there may be a difference between the actual wavelength and the desired wavelength). To compensate for this effect, an additional wavelength calibration module is used in conjunction with the feedback module of the semiconductor gain chip's power supply.

[0116] The wavelengths are compared and a signal is received indicating the difference between the actual wavelength and the desired wavelength. A feedback signal is generated and the power to the semiconductor gain chip is changed to reduce the signal and change the desired wavelength.

[0117] Spectrometers including tunable on-chip lasers are used as wearable health care sensors that mainly perform: non-invasive blood glucose measurement; non-invasive blood oxygen level and blood pressure value measurement; non-invasive subcutaneous fat level measurement; non-invasive skin condition assessment; non-invasive skin moisturization level assessment; food quality assessment; drug quality control; measurement of clothing stains required for smart washing machines; and bottled water quality assessment.

[0118] The foregoing exemplary embodiments are merely exemplary and are not to be construed as limiting. The present teachings can be readily applied to other types of devices. Furthermore, the description of the exemplary embodiments is intended to be illustrative rather than limiting the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.

Claims

1. A spectrometer comprising: a tunable on-chip laser source configured to irradiate biological tissue with laser radiation; a photodetector configured to receive laser radiation reflected from the biological tissue; and at least one processor, Among them, the tunable on-chip laser sources include: a semiconductor gain chip having a gain bandwidth for operating a tunable on-chip laser source within a predetermined wavelength range; a plurality of resonant cavities connected between the semiconductor gain chip and the at least one processor and comprising a first resonant cavity and a second resonant cavity; Each of the plurality of resonant cavities comprises: a waveguide and a tunable filter, wherein when laser radiation is to be emitted into biological tissue, the tunable filters of the plurality of resonant cavities generate light having different wavelengths according to parameters of the tunable filters of the plurality of resonant cavities, wherein the first resonant cavity comprises a first tunable filter, and the first resonant cavity is configured to, in a first spectral measurement mode, perform a coarse measurement of a spectrum of laser radiation reflected from biological tissue when the biological tissue is illuminated by laser radiation generated by the first tunable filter of the first resonant cavity, wherein the second resonant cavity includes a second tunable filter, and the second resonant cavity is configured to: in a second spectral measurement mode subsequent to the first spectral measurement mode, when the biological tissue is irradiated with laser radiation generated by the second tunable filter, perform fine measurement of a spectrum of laser radiation reflected from the biological tissue in a region of interest, wherein the region of interest is a portion of the spectrum obtained by performing the coarse measurement and containing a sharp peak, The speed of the fine measurement is lower than the speed of the coarse measurement.

2. The spectrometer according to claim 1, wherein The waveguide of each of the plurality of resonant cavities ends with a Sagnac mirror that provides a feedback loop between each of the plurality of resonant cavities and a semiconductor gain chip.

3. The spectrometer according to claim 1 or 2, further comprising: a metal heating element positioned within the plurality of resonant cavities and configured to receive a voltage from an external source; and The thermo-optical control circuit is configured to tune the wavelengths of the plurality of resonant cavities by applying a voltage to the metal heating element.

4. The spectrometer according to claim 1 or 2, further comprising: A plurality of electro-optical control circuits are configured to tune the wavelengths of the plurality of resonant cavities by applying an electric field to the plurality of resonant cavities to change the effective refractive index of the plurality of resonant cavities and the transmission spectrum of the laser radiation emitted from the spectrometer.

5. The spectrometer according to claim 1 or 2, further comprising: A plurality of acousto-optic control circuits are configured to tune the wavelengths of the plurality of resonant cavities by exposing the plurality of resonant cavities to ultrasonic vibrations from an external source.

6. The spectrometer according to claim 1, wherein The semiconductor gain chip having a gain bandwidth for operating the tunable on-chip laser source in the predetermined wavelength range is a first semiconductor gain chip having a first gain bandwidth for operating the tunable on-chip laser source in the predetermined wavelength range, wherein the spectrometer comprises an array of semiconductor gain chips having different gain bandwidths to provide scanning of wavelengths along an extended wavelength range wider than the predetermined wavelength range, and The semiconductor gain chip array with different gain bandwidths includes a first semiconductor gain chip with a first gain bandwidth.

7. The spectrometer according to claim 1, further comprising: A modulator is configured to control a gain bandwidth of the semiconductor gain chip.

8. The spectrometer according to claim 1, further comprising: The feedback control circuit and the wavelength calibration circuit are used to calibrate the wavelength of the spectrometer in real time.

9. The spectrometer according to claim 1, further comprising: A beam splitter is configured to connect the semiconductor gain chip to the plurality of resonant cavities.

10. The spectrometer according to claim 1, wherein The first resonant cavity includes a first reflecting mirror paired with a first tunable filter, and the second resonant cavity includes a second reflecting mirror paired with a second tunable filter.

Images