CN116539155B - Spectral filter and spectrometer based on multistage resonant cavity structure - Google Patents

Abstract

The invention relates to the technical field of spectrum detection, and discloses a multistage resonant cavity structure-based spectrum filter and a spectrometer, which are configured in a computational spectrometer when in use, wherein the spectrum filter is provided with at least one path of optical channels, at least n+1 reflectors which are linearly arranged are arranged on one path of optical channels, N is equal to N, and N is more than or equal to 2; the reflector has a certain reflectivity, and the reflectivity is 5-50%; a resonant cavity is formed between two adjacent reflectors, and n+1 reflectors which are linearly arranged form an n-level resonant cavity; the cavity length of each resonant cavity is between 20 mu m and 2000 mu m, wherein the cavity lengths of at least two resonant cavities are different or the reflectivity of at least two reflectors is different, so that the n-level resonant cavities can generate transmission spectrums with high randomness in the frequency domain.

Description

Spectral filter and spectrometer based on multistage resonant cavity structure

Technical Field

The invention relates to the technical field of spectrum detection, in particular to a spectrum filter and a spectrometer based on a multi-stage resonant cavity structure.

Background

The spectrometer is used as a basic substance analysis device, and can effectively detect the physical and chemical components and properties of substances, so that the spectrometer is widely applied to the fields of material science, food safety, life health, environmental monitoring, aerospace and the like.

The traditional spectrum detection method is mainly a dispersion spectrometer based on a prism or a narrow-band filter and a Fourier transform spectrometer based on a Michelson interferometer.

The dispersive spectrometer obtains a complete input spectrum by decomposing the input spectrum with a broad spectrum into components in a frequency domain and detecting the components one by a detector array. The method has the advantages that the power of the input light beam is required to be decomposed in an equal proportion, so that a large amount of energy is consumed, the sensitivity and the responsivity of the detector array are required to be high, and along with the expansion of the detection range and the detection precision, the number of the detectors is increased in an equal proportion, so that the cost is increased.

The Fourier transform spectrometer encodes the information of the broad spectrum in the space domain by utilizing the interference spectrum of the interferometer under the condition of different optical path differences, so that the information of the whole input spectrum can be obtained by utilizing only one detector, and the power loss is avoided. However, the optical path difference adjustment of the interferometer often requires scanning of mechanical devices, resulting in a larger structure, longer detection time and higher cost. And the fourier operation process of this method requires a large consumption of computational power resources.

In recent years, a computational spectrometer has gained extensive attention in the academy and industry as a brand new spectrum detection method. The basic principle is that an input spectrum is led into a plurality of wide spectrum filter arrays calibrated in advance, and the light intensity of the filtered spectrum is detected by a corresponding number of photodetectors. And constructing a system of underdetermined equations by using the intensity information, and solving by using a correlation algorithm to obtain the information of the input spectrum. The method has the advantages that a larger number of pixel points of the spectrum in the frequency domain can be solved by using a smaller number of filters and photoelectric detector groups, so that the system volume, cost and computational complexity can be effectively reduced while the hyperspectral detection performance is obtained.

The core design difficulty of the computational spectrometer is the design of its broad spectrum filter array. From a mathematical point of view, to achieve an ideal spectral detection effect, such a filtering structure is required to fulfil the following two conditions: (1) The spectral response of each channel needs to have a small autocorrelation coefficient, thereby realizing high resolution; (2) The channels need to have smaller cross-correlation coefficients, so that the uncorrelation of spectrum sampling is ensured; the high-intensity random disturbance can be generated on the frequency domain, so that an effective underdetermined equation system can be constructed and solved when the computational spectrometer is used.

Disclosure of Invention

The present invention aims to solve one of the technical problems in the related art to a certain extent. To this end, the invention provides a spectral filter and a spectrometer based on a multi-stage resonant cavity structure, which can generate high-intensity random disturbance in the frequency domain based on the resonant cavity.

In order to achieve the above object, the present invention adopts the following technical scheme in a first aspect:

the utility model provides a spectral filter based on multistage resonant cavity structure, its is disposed in computational type spectrometer when using, spectral filter has a light passageway at least, is equipped with n+1 linear arrangement's speculum on a light passageway of the said way at least, N epsilon N and N is greater than or equal to 2;

the mirror has a reflectivity of 5% to 50%;

a resonant cavity is formed between two adjacent reflectors, and n+1 reflectors which are linearly arranged form an n-level resonant cavity; the cavity length of each resonant cavity is between 20 μm and 2000 μm, wherein at least two resonant cavities have different cavity lengths and/or at least two reflectors have different reflectivities, so that n-level resonant cavities can generate transmission spectrums which are highly random in the frequency domain.

And a plurality of reflectors with different reflectivities or non-equidistant linear arrangement are utilized to form resonant cavities with different reflectivities or different cavity lengths, so that after input light enters the resonant cavities, a part of light is transmitted and a part of light is reflected when one reflector is encountered. In the course of the successive passes through the mirrors, these transmitted and reflected components interfere with one another, resulting in a nearly random transmission spectrum in the frequency domain at the output, so that an effective system of partial equations can be constructed and solved by the spectral filter when using a computational spectrometer.

It is further preferred in the present invention that the reflectivity of the mirror is between 10% and 20%.

It is further preferred in the present invention that n is 5 or 6 or 7 or 8.

The invention further preferably comprises an optical waveguide device on which a one-dimensional photonic crystal is provided to form the mirror.

Optionally, the optical reflection mirror comprises a plurality of substrates, wherein the surfaces of the substrates are covered with optical coating films with reflectivity, and the optical coating films form the reflection mirror.

Optionally, the optical fiber is included, and a bragg grating is arranged in the optical fiber to form the reflecting mirror.

In the present invention, it is further preferable that the optical fiber is a multi-core optical fiber, and a bragg grating is provided in each core to form the reflecting mirror.

It is further preferred in the present invention that the reflectivity of the mirror is between 10% and 20%.

The invention further preferably comprises at least M paths of optical channels, wherein each path of optical channel is provided with the n-level resonant cavity; in the M-way optical channel, the n-level resonant cavities on each way produce different transmission spectra by the difference in the setting of cavity lengths and/or mirror reflectivities.

The present invention also provides in a second aspect a spectrometer comprising a broad spectrum light source, a photodetector array, and a spectral filter as described in the first aspect: the wide-spectrum light source and the photoelectric detector array are respectively arranged at two ends of the spectrum filter, and the number of the photoelectric detectors in the photoelectric detector array is the same as that of the light channels in the spectrum filter. The spectrometer provided by the invention is similar to the above-mentioned spectrum filter in the process of reasoning beneficial effects, and will not be described here again.

Also, the present invention provides in a third aspect a spectrometer comprising a broad spectrum light source, a photodetector, and a spectral filter as described in the first aspect; the wide-spectrum light source and the photoelectric detector array are respectively arranged at two ends of the spectrum filter;

the spectrometer further comprises a microelectromechanical system; the mems includes an array of micro-actuators for moving mirrors in the propagation direction of the optical path and changing the spacing between the mirrors to form a tunable resonant cavity by the micro-actuators.

Further, the spectral filter has only one optical channel.

These features and advantages of the present invention will be disclosed in more detail in the following detailed description and the accompanying drawings. The best mode or means of the present invention will be described in detail with reference to the accompanying drawings, but is not limited to the technical scheme of the present invention. In addition, these features, elements, and components are shown in plural in each of the following and drawings, and are labeled with different symbols or numerals for convenience of description, but each denote a component of the same or similar construction or function.

Drawings

The invention is further described below with reference to the accompanying drawings:

fig. 1 is a schematic diagram of the spectral filter according to the present invention.

Fig. 2 is a graph of the transmission spectrum of a spectral filter based on a multi-stage resonator.

Fig. 3 is a schematic diagram of the structure of the spectral filter in an exemplary embodiment.

Fig. 4 is a schematic diagram of the structure of the spectral filter in an exemplary embodiment.

Fig. 5 is a schematic diagram of the structure of the spectral filter in an exemplary embodiment.

Fig. 6 is a schematic diagram of the structure of the spectral filter in an exemplary embodiment.

Fig. 7 is a schematic diagram of a spectrometer in an exemplary embodiment.

Fig. 8 is a schematic diagram of a spectrometer in an exemplary embodiment.

Fig. 9 is a schematic diagram of a spectrometer in an exemplary embodiment.

Fig. 10 is a graph of spectral recovery effects of a computational spectrometer constructed using a 16-channel multi-stage resonator filter in an exemplary embodiment.

Wherein: 100. a spectral filter; 110. an optical waveguide device; 111. a Bragg grating; 120. an optical fiber; 121. a grating; 200. a photodetector array; 310. a micro-actuator.

Detailed Description

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The examples in the embodiments are intended to illustrate the present invention and are not to be construed as limiting the present invention.

Reference in the specification to "one embodiment" or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment itself can be included in at least one embodiment of the present patent disclosure. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

As shown in fig. 1, a schematic diagram of a spectral filter based on a multi-stage resonator structure according to the present invention is shown. The spectral filter based on the multi-stage resonant cavity structure is configured in a computational spectrometer when in use, and the spectral filter is provided with at least one path of optical channel, and the illustration of the path of optical channel is taken as an example.

At least n+1 reflecting mirrors which are linearly arranged are arranged on the light path, N is N and is more than or equal to 2. The arrangement direction is the propagation direction of the light path, the left side of the spectrum filter in the drawing is the input end of the spectrum, and the right side is the output end. The reflectors have a certain reflectivity, the reflectivity is 5-50%, and the reflectors with different reflectivities are preferably used for linear arrangement, so that the intensity of random disturbance of light in the propagation process is improved.

A resonant cavity is formed between two adjacent reflectors, and n+1 reflectors which are linearly arranged can form an n-level resonant cavity. The cavity length of each resonant cavity is between 20 mu m and 2000 mu m, wherein at least two resonant cavities are different in cavity length, so that the different cavity lengths are ensured as much as possible to achieve a better effect, and the intensity of random disturbance of light in the propagation process is improved.

After entering the cavity, a part of light is transmitted and a part of light is reflected by one reflecting mirror, and the transmission cursor is shown as E ⁺ The reflective cursor is E ^- . During the sequential passes through the mirrors, these transmitted and reflected components interfere with each other, ultimately producing a nearly random transmission spectrum in the frequency domain at the output. The factor influencing random disturbance is mainly three, and one is the number of reflectors, namely the number of resonant cavities; secondly, the difference between the reflectivity of all the reflectors; and thirdly, the difference between the cavity lengths of all the resonant cavities. The greater the number of mirrors, the greater the difference in reflectivity and cavity lengthThe larger the dissimilarity, the larger the random disturbance intensity of the outgoing spectrum at the output end.

Mathematically, the projection (i.e., transmission, i.e., refraction through a mirror) or reflection spectrum of such a resonant cavity structure can be described by a transmission matrix method:

，

wherein the method comprises the steps ofAnd->Representing the electric field intensity of the forward projection (transmission) propagation portion during propagation of light from the ith mirror to the (i+1) th mirror; />And->Representing the electric field intensity of the backward reflection propagation part in the process of light propagation from the ith reflecting mirror to the (i+1) th reflecting mirror; />The phase change caused by the optical path between the two reflectors, namely the cavity length of the resonant cavity, namely the distance between the two reflectors; />And->Respectively represent the firstiThe reflectivity and transmissivity of the individual mirrors; />Power loss for the mirror.

With this equation, the transmission spectrum of the multi-stage resonator can be represented by the cumulative multiplication of the matrix. Correlation calculations show that when the number of mirrors is 2, the resonator outputs a periodically varying transmission spectrum, whereas when the number of mirrors exceeds 3, the periodicity of the output spectrum can be effectively broken, resulting in a near random spectral disturbance.

Specifically, when each mirror is reflective to satisfy its reflectivity of between about 5% and 50%, and the spacing between each two mirrors (i.e., each cavity length) is between tens to thousands of microns, the resulting spectral perturbation is ideal in both the range of fluctuation and the rate of fluctuation. As the number of resonant cavities increases, the disturbance density increases.

As shown in fig. 2, a transmission spectrum graph of a spectral filter implementing a five-level resonator structure based on an integrated optical waveguide device is shown, wherein the reflectivity of a single mirror is between 10% and 20%, and the cavity length is between 50 and 200 microns. From the figure, the transmission spectrum of the spectral filter has very high random disturbance.

How to construct a spectral filter of a multi-stage resonator structure and a spectrometer using the same will be described in detail below in conjunction with mirrors of different structures.

Example 1:

as shown in fig. 3, a multi-stage resonator structure based spectral filter 100 is shown implemented on an integrated optical platform using an optical waveguide device 110. In this embodiment, only one optical channel is taken as an example for explanation, multiple optical channels can be adopted according to actual needs, and an optical waveguide device based on a multi-stage resonant cavity structure is arranged on each optical channel.

Specifically, partial reflection of light is achieved by etching a segment of the bragg grating 111 region over the optical waveguide device 110 (structure) of silicon/silicon nitride/InP or the like. The Bragg grating is a periodic structure, and a periodic refractive index change is added into an optical waveguide (device) in an etching mode and the like to realize the reflection of specific intensity of light with specific wavelength, wherein specific reflection intensity, central wavelength of reflection and the like can be effectively controlled through parameters such as period length, period number, refractive index difference and the like of the grating. Based on this approach, as described above, the reflectivity of each segment of the bragg grating region (formed mirror) can be set in the range of about 10% to 20%, and the spacing (i.e., cavity length) between each two mirrors can be controlled to be between several tens to several hundreds of micrometers to achieve a good effect of random spectral perturbation.

It should be noted that, in addition to the above solution, one skilled in the art may also implement partial reflection of light through a one-dimensional nano Liang Guangzi crystal structure (mirror), as an alternative to etching the bragg grating. A one-dimensional photonic crystal (nano-beam) structure is also a structure with periodic refractive index variation, and the basic principle is that a forbidden band is formed based on the modulation of a photonic band gap (photonic band gap), so that light with a specific wavelength is reflected by a specific reflectivity, and the specific reflectivity can be effectively modulated by parameters of the nano-beam structure (such as the geometric parameters and the period length of the crystal of the nano-beam structure). Similarly, based on this approach, as described above, the reflectivity of each photonic crystal mirror can be set in the range of about 10% to 20%, while the spacing (i.e., cavity length) between each two mirrors is controlled to be between several tens to several hundreds of micrometers to achieve a good effect of random spectral perturbation.

It should be noted that, as shown in fig. 4, in an exemplary embodiment, a similar resonant cavity structure may be formed in the photosensitive optical fiber 120, and the manufacturing method is similar to that of a conventional fiber bragg grating, the photosensitive optical fiber may generate refractive index change under the irradiation of UV light, the period and the duty ratio of the grating 121 are designed, the grating 121 with the required reflectivity/transmissivity may be obtained, and a plurality of gratings 121 may be cascaded to obtain a complex response spectrum.

As shown in fig. 5, if the spectral filter needs multiple optical path channels, in addition to the single-channel photosensitive optical fiber, multiple optical fibers with special response spectrums can be designed, and in the multiple optical path channels, n-level resonant cavities on each path are different to generate different transmission spectrums. The multiple optical fibers can be fabricated in the same structure by direct drawing of the multi-core preform, fastening the multiple optical fibers together, known as multi-core optical fibers. One end of the multi-core optical fiber is used for entering a spectrum to be detected, and the other end of the multi-core optical fiber is connected with the photoelectric detector array and used for detecting spectrum signals, and finally, an intensity information recovery spectrum is obtained.

Example 2:

as shown in fig. 6, another spectral filter based on a multi-level resonator structure is shown that implements the multi-level optical resonator structure on a free-space optical platform using an optical coating method.

Only the multi-level cavity structure on one optical path is shown. Specifically, a reflector with partial reflectivity and partial transmissivity is realized by coating a specific coating material (such as oxide, fluoride, silicon and the like formed by dielectric material coating) on the surface of a substrate material (such as optical glass or quartz glass), wherein the specific reflectivity and transmissivity of the reflector can be effectively controlled by adjusting the thickness, material composition ratio and the like of the coating.

The multi-stage resonator filter proposed in this patent can be realized by preparing a plurality of such coated mirrors and arranging them between each other according to different intervals (i.e., cavity lengths). Also, to achieve a good perturbation effect, the reflectivity of each coated mirror may be set between about 10% and 20%, while the spacing between each two mirrors (i.e., each cavity length) may be between tens to hundreds of microns.

The mirror here is a plating film provided on the surface of the substrate. The substrate is glass, which can be several tens of microns thick, and the spectrum passes through the glass substrate with little effect, so the cavity length here actually includes the glass thickness and spacing.

Example 3:

as shown in fig. 7, a chip-scale computational spectrometer is shown that includes a broad spectrum light source, a spectral filter 100 based on a multi-stage resonant cavity structure, and a photodetector array 200. The broad spectrum light source is located at the input of the spectral filter and the photodetector array 200 is located at the output of the spectral filter 100.

The spectrum filter is an integrated optical platform, and adopts the multi-stage resonant cavity structure proposed in the embodiment 1, which is different in that multiple optical channels are adopted, and an optical waveguide device 110 of the multi-stage resonant cavity structure is arranged on each optical channel.

The input light is led into the integrated optical chip through a port coupler or a grating coupler and the like, is split into a plurality of input light, is led into multi-stage resonant cavities of different light paths on the spectrum filter, and is finally measured by an on-chip or off-chip photoelectric detector array. Because the transmission response of each resonant cavity filter is different, the input spectrum can be reversely deduced through the reading of the photoelectric detector, so that the aim of spectrum detection is fulfilled. The unknown sample to be detected may be placed between the multi-cavity structure and the light source, or between the multi-cavity structure and the photodetector, only the manner in which the sample is placed between the multi-cavity structure and the light source is shown.

Example 4:

as shown in fig. 8, another computational spectrometer is shown that includes a plurality of broad spectrum light sources, a spectral filter based on a multi-stage resonant cavity structure, and a photodetector array. The wide-spectrum light source is positioned at the input end of the spectrum filter, and the photoelectric detector array is positioned at the output end of the spectrum filter.

The spectrum filter is based on the multi-stage resonant cavity structure proposed in the embodiment 2 in free space, and is different in that multiple paths of optical channels are adopted, and each path of optical channel is provided with the multi-stage resonant cavity structure, and accordingly, the number of wide-spectrum light sources and the number of photodetectors in the photodetector array are the same as the number of paths of optical channels.

It should be noted that the multiple broad spectrum light sources in this embodiment use the same light source and enter the multiple resonant cavities in parallel. The filtered light intensity is also detected by the photodetector array, thereby back-pushing the input spectrum. Likewise, the unknown sample being probed may be placed between the multi-chamber structure and the light source or between the multi-chamber structure and the photodetector, only the manner in which the sample is placed between the multi-chamber structure and the light source being shown in the figures.

Furthermore, instead of using a plurality of broad spectrum light sources as described above, embodiments using only a single broad spectrum light source may be used as an alternative, which will not be described in detail herein.

Example 5:

as shown in fig. 9, another computational spectrometer is shown, and the spectrometer described in this embodiment is different from the spectrometer described in embodiment 4 in that the spectral filter in this embodiment uses only one optical channel, and correspondingly only one broad spectrum light source and photodetector are provided. The spectrometer in this embodiment also includes a microelectromechanical system. The mems includes an array of micro-actuators for moving mirrors in a propagation direction of an optical path and changing a pitch between the mirrors to form an adjustable cavity by the micro-actuators. At least one of the micro-actuators is equal to the number of the reflecting mirrors in the spectrum filter at most, and in order to achieve the maximum adjustment number, in this embodiment, the other reflecting mirrors are fixed on the corresponding micro-actuators one by one except that one reflecting mirror is used as the origin of the reference coordinates and no micro-actuator is configured. The micro-actuator, in operation, moves with the mirror fixed thereto in a direction along the optical path to adjust the cavity length of the resonant cavity. By adjusting different cavity lengths, the spectrometer with multiple optical channels can be realized by measuring for multiple times.

Example 7:

the present embodiment provides a computational spectrometer that employs a 16-channel multi-stage resonator filter.

As shown in fig. 10, fig. 10 is a graph of the spectral recovery effect of a computational spectrometer constructed using a 16-channel multi-stage resonator filter. It can be seen that the recovered spectrum is highly coincident with the actual input spectrum, indicating a high degree of accuracy in its spectral detection. Specifically, in this example, the bandwidth is up to 120nm, and the accuracy is up to 0.5nm, i.e., over the wavelength range 1480nm-1600nm measured, there are > 240 spectral pixels.

The above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that the present invention includes but is not limited to the accompanying drawings and the description of the above specific embodiment. Any modifications which do not depart from the functional and structural principles of the present invention are intended to be included within the scope of the appended claims.

Claims (12)

1. A spectral filter based on a multistage resonant cavity structure, which in use is configured in a computational spectrometer, the spectral filter having at least one optical channel, characterized in that: at least n+1 reflecting mirrors which are linearly arranged are arranged on one path of light channel, N is equal to N and is more than or equal to 2;

the mirror has a reflectivity of 5% to 50%;

a resonant cavity is formed between two adjacent reflectors, and n+1 reflectors which are linearly arranged form an n-level resonant cavity; the cavity length of each resonant cavity is between 20 and 2000 mu m;

wherein at least two of the resonators have different cavity lengths and/or at least two of the reflectors have different reflectivities, such that the n-level resonators produce a transmission spectrum that is highly random in the frequency domain.

2. The spectral filter of claim 1, wherein n is 5 or 6 or 7 or 8.

3. The spectral filter of claim 1, comprising an optical waveguide device on which bragg gratings are etched to form the mirror.

4. The spectral filter of claim 1, comprising an optical waveguide device having a one-dimensional photonic crystal disposed thereon to form the mirror.

5. The spectral filter of claim 1, comprising a plurality of substrates, wherein the surfaces of the substrates are covered with an optical coating having a reflectivity, the optical coating comprising the mirror.

6. The spectral filter of claim 1, comprising an optical fiber in which a bragg grating is disposed to form the mirror.

7. The spectral filter of claim 6, wherein the optical fibers are multicore optical fibers, each having a bragg grating disposed therein to form the mirror.

8. The spectral filter of claim 1, wherein the reflectivity of the mirror is between 10% and 20%.

9. The spectral filter of any of claims 1-6, having at least M optical channels, each optical channel having the n-stage resonator disposed thereon;

in the M-way optical channel, the n-level resonant cavities on each way produce different transmission spectra by the difference in the setting of cavity lengths and/or mirror reflectivities.

10. A spectrometer comprising a broad spectrum light source, a photodetector array, and the spectral filter of any one of claims 1-8: the photoelectric detector array is characterized in that the wide-spectrum light source and the photoelectric detector array are respectively arranged at two ends of the spectrum filter, and the number of the photoelectric detectors in the photoelectric detector array is the same as that of the light channels in the spectrum filter.

11. A spectrometer comprising a broad spectrum light source, a photodetector, and a spectral filter as claimed in claim 5; the wide-spectrum light source and the photoelectric detector are respectively arranged at two ends of the spectrum filter;

the spectrometer further comprises a microelectromechanical system; the mems includes an array of micro-actuators for moving mirrors in the propagation direction of the optical path and changing the spacing between the mirrors to form a tunable resonant cavity by the micro-actuators.

12. The spectrometer of claim 11, wherein the spectral filter has only one optical channel.