CN111982859A - Refractive index sensor based on Mach-Zehnder structure and detection method thereof - Google Patents
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Abstract
The invention relates to a refractive index sensor based on a Mach-Zehnder structure and a detection method thereof, wherein the sensor comprises the Mach-Zehnder structure, a cladding layer with a certain length is stripped off from one interference arm to form a refractive index sensing area, and the refractive index sensing area is used for detecting liquid or gas; when liquid or gas to be detected is injected into the refractive index sensing area, the effective refractive index of the interference arm in the refractive index sensing area can be changed, so that the central wavelength of an output spectrum of the device is changed, the change of the effective refractive index and the change of the central wavelength are linear, and the central wavelength of the output spectrum is the wavelength corresponding to the maximum ratio of the output intensity to the input intensity. The refractive index sensor based on the Mach-Zehnder structure provided by the invention has the advantages of low manufacturing cost, simple preparation and firm structure, and the change of the central wavelength of the device and the change of the refractive index to be measured are in a linear relation, so that the ultra-large range and high sensitivity can be realized at the same time.
Description
Technical Field
The invention relates to a refractive index sensor based on a Mach-Zehnder structure and a detection method thereof, belonging to the technical field of refractive index measurement.
Background
The refractive index of a substance is an important physical quantity reflecting information inside the substance. The measurement of the refractive index of a substance has wide application in the fields of basic research, chemical analysis, environmental pollution assessment, medical diagnosis, food industry and the like. The method has important significance for accurately measuring the refractive indexes of some solids, liquids and gases in production and scientific research. For example: the interaction of biomolecules and the change in molecular structure caused by chemical reactions in solution produce small changes in refractive index, and the detection of such small changes is an important means for identifying viruses and different molecules. Especially, with the rapid development of national economy in China and the continuous increase of population, environmental pollution becomes a major problem seriously damaging the health of people, and more people begin to pay attention to the water pollution of toxic and harmful gases in the atmosphere, and organic matters and heavy metal ions in rivers, lakes and oceans. The fine detection of the concentration (refractive index) of toxic substances in the atmosphere and water has become a very urgent issue.
The following methods are commonly used to detect the concentration of substances in the atmosphere and water: abbe refractometer total reflection critical angle method, minimum deflection angle method using spectrometer, Michelson interferometer, atomic absorption method, spectrophotometry, atomic fluorescence spectroscopy, high performance liquid chromatography, and other techniques, but these techniques generally have low sensitivity and detection limit of 10-3～10-5To (c) to (d); some light paths are complex to adjust, the time of the measurement process is long, and real-time measurement is not facilitated; some detection ranges are small, one instrument is not enough under the condition of large detection range, and another instrument is needed; or large and expensive equipment is needed, the detection cost is high, and the popularization and the application are difficult.
The optical chip refractive index sensor has the characteristics of intrinsic insulation, electromagnetic interference resistance, high integration degree, high bandwidth, reusability, biochemical compatibility and the like, and is widely applied to the fields of biomolecule detection, environmental pollution control, chemical process control and the like. With the improvement of the requirement of refractive index measurement, the performances of the optical chip refractive index sensor, such as sensitivity, resolution, linearity and the like, need to be further improved.
The integrated optical waveguide sensor of mach-zehnder interferometer type generates phase modulation by using interferometry in order to obtain higher sensitivity and resolution, and particularly, the novel optical waveguide sensor based on mach-zehnder interferometer has many advantages such as low insertion loss, simple manufacturing method, compact structure, and low cost. Therefore, the optical waveguide sensor of the type is used for measuring various parameters, and the development prospect is quite wide. However, the conventional mach-zehnder type sensor is based on light intensity detection, the relation between the measured value and the light intensity is a sine-cosine curve, and a method generally adopted in practical use is to use only one section with better linearity, so that a certain contradiction still exists between the sensitivity and the measurement range, namely, the change of the light intensity caused by the refractive index variation is small under the condition of a large measurement range. And because the measuring method is not linear, great inconvenience is brought to factory calibration and later calibration.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the refractive index sensor based on the Mach-Zehnder structure, and the refractive index sensor has the advantages of low cost, high sensitivity, strong anti-interference performance, simple manufacture and firm structure.
The invention also provides a detection method of the refractive index sensor based on the Mach-Zehnder structure.
The technical scheme of the invention is as follows:
a refractive index sensor based on a Mach-Zehnder structure comprises the Mach-Zehnder structure, wherein the Mach-Zehnder structure comprises an input beam splitter, two interference arms with different lengths and an output beam combiner, two output ends of the input beam splitter are respectively connected with one ends of the two interference arms, and the other ends of the two interference arms are respectively connected with two input ports of the output beam combiner; stripping off part of the cladding on one of the interference arms to form a refractive index sensing region, wherein the refractive index sensing region is used for detecting liquid or gas; when liquid or gas to be detected is injected into the refractive index sensing area, the effective refractive index of the interference arm in the refractive index sensing area can be changed, so that the central wavelength of an output spectrum of the device is changed, the change quantity of the effective refractive index of the interference arm in the refractive index sensing area and the change quantity of the central wavelength are linear, and the central wavelength of the output spectrum is the wavelength corresponding to the maximum ratio of the output intensity to the input intensity.
Preferably, according to the invention, the length of the lift-off is 1000 to 10 on the interference arm6And μm cladding to form a refractive index sensing region. The longer the waveguide length comprised by the refractive index sensing region, the higher the measurement sensitivity.
According to the invention, the length difference between the two interference arms is preferably 1 to 500 μm. The larger the length difference is, the smaller the perceived range is, and the detection effect is best in the range.
Preferably, according to the invention, both interference arms have a cross-sectional width of 1 to 10 μm and a cross-sectional thickness of 1 to 10 μm.
According to a preferred embodiment of the present invention, the interference arm includes a core layer and a cladding layer, and the cladding layer surrounds the outside of the core layer.
According to the present invention, it is preferable that the refractive index of the core layer is 1.45 to 1.51 and the refractive index of the clad layer is 1.40 to 1.45, and it is further preferable that the refractive index of the core layer is 1.4746 and the refractive index of the clad layer is 1.4448.
Preferably, according to the present invention, the input beam splitter is a Y-branch type or 1-to-2 type input beam splitter, and the output beam combiner is a Y-branch or 2-to-1 type output beam combiner. In the Y-branch type input beam splitter, light is input from a single waveguide portion of the Y-branch type, and light is output from two branches of the Y-branch type; in the Y-branch type output beam combiner, light is input from the Y-branch from two branches of the Y-branch type, and output from a single waveguide section.
The detection method of the refractive index sensor based on the Mach-Zehnder structure comprises the following steps:
(1) inputting wide-spectrum light into the refractive index sensor based on the Mach-Zehnder structure, and detecting the output spectrum of the refractive index sensor based on the Mach-Zehnder structure by using a spectrometer to obtain that the gas to be detected is air and the refractive index is n0At the center wavelength λ of the output spectrum of the corresponding device0；
(2) Placing the sensing region of refractive index into a known refractive index of n1In the liquid or gas, the wide-spectrum light is passed through a refractive index sensor based on a Mach-Zehnder structureThe spectrometer detects the output spectrum of the refractive index sensor to obtain the central wavelength lambda of the output spectrum of the device under the current liquid or gas1Thereby completing the calibration of the device;
(3) putting the refractive index sensing area into the refractive index n to be measured2The wide-spectrum light is input into the refractive index sensor in the liquid or the gas, the output spectrum of the refractive index sensor is detected by a spectrometer, and the central wavelength lambda of the output spectrum of the device under the corresponding refractive index of the liquid or the gas to be detected is obtained2(ii) a Calculating the refractive index n to be measured according to the formula (V)2The formula (V) is:
the invention provides a detection method of a refractive index sensor based on a Mach-Zehnder structure, which is based on the following principle:
the basic interference principle of the asymmetric Mach-Zehnder interferometer is obtained:
in the formula (I), neIs the effective refractive index, L, of the two interference arm waveguides1Is the length of the short interference arm, Ls+ L' is the length of the long interference arm, LsIs the length of the interference arm in the sensing region of refractive index, λ0The central wavelength of the output spectrum of the device when the diffraction order is M under the condition of not detecting gas or liquid; m is the number of diffraction orders, M is int (n.DELTA.L/lambda)0) Int (·) denotes rounding down a rounded real number, λ0When the refractive index sensing area does not detect gas or liquid, the device outputs the central wavelength of the spectrum; Δ L is the difference in length of the long and short interfering arms;
length L when detecting gas or liquidsThe effective refractive index change of the interference arm in the refractive index sensing region is Δ n, and the interference equation at this time is:
multiplying both sides of the two formulas by lambda0And λ3Then subtracting, and simplifying to obtain:
M(λ0-λ3)＝Δn·LS (III)
let Δ λ be λ0-λ3Formula (I) is obtained:
Δλ＝Δn·Ls/M (IV)
according to the formula (IV), the effective refractive index change quantity delta n of the interference arm in the refractive index sensing area is in a linear relation with the change quantity delta lambda of the central wavelength of the output spectrum; errors exist in the manufacturing and calculation processes of the optical device, and specific linear relations between the refractive index n applied to the refractive index sensing area and the change delta lambda of the central wavelength of the output spectrum are determined through the steps (1) and (2).
Preferably, according to the invention, the broad spectrum light output spectrum has a spectral width of 40 nm.
The invention has the beneficial effects that:
1. the refractive index sensor provided by the invention is specially designed on a Mach-Zehnder interferometer, the cladding of one interference arm is stripped, the waveguide core layer of the interference arm is communicated with the outside air/liquid, the change of the refractive index of the outside substance causes the change of the interference effect, and the outside refractive index can be calculated, and the interference arm can be increased to dozens of centimeters, so that the high sensitivity is realized, and the highest sensitivity can detect 10-6Is changed.
2. The refractive index sensor based on the Mach-Zehnder structure provided by the invention has the advantages of low manufacturing cost, simple preparation and firm structure, and the change quantity of the central wavelength of the device and the change quantity of the refractive index to be measured are in a linear relation, so that the ultra-large range and high sensitivity can be realized simultaneously, and the range for measuring the change of the refractive index can be as high as 0.01.
3. The refractive index sensor based on the Mach-Zehnder structure is a semiconductor optical waveguide-based device which is compact in structure and small in size.
Drawings
Fig. 1 is a schematic structural diagram of a refractive index sensor based on a mach-zehnder structure provided in embodiment 1;
FIG. 2 is a cross-sectional view of a short interference arm without a refractive index sensing region in example 1;
FIG. 3 is a cross-sectional view of an interference arm provided with a refractive index sensing region in example 1;
1. the device comprises an input beam splitter, 2, a long interference arm, 3, a short interference arm, 4, a refractive index sensing area, 5, an output beam combiner, 6, a cladding, 7, a core layer, 8 and liquid or gas to be detected.
Detailed Description
The invention is further described below, but not limited thereto, with reference to the following examples and the accompanying drawings.
Example 1
A refractive index sensor based on a Mach-Zehnder structure is disclosed, as shown in figure 1, the sensor comprises a wide-spectrum light source, a Mach-Zehnder structure and a spectrometer, wherein the Mach-Zehnder structure comprises an input beam splitter 1, two interference arms with different lengths and an output beam combiner 5, two output ends of the input beam splitter 1 are respectively connected with one ends of the two interference arms, and the other ends of the two interference arms are respectively connected with two input ports of the output beam combiner 5; stripping off a part of the coating 6 on one of the interference arms to form a refractive index sensing region 4, wherein the refractive index sensing region 4 is used for detecting liquid or gas; when the liquid or gas 8 to be measured is injected into the refractive index sensing region 4, the effective refractive index of the interference arm in the refractive index sensing region 4 is changed, and further the central wavelength of the output spectrum of the device is changed, and the change amount of the effective refractive index of the interference arm in the refractive index sensing region 4 and the change amount of the central wavelength are linear, and the central wavelength of the output spectrum is the wavelength corresponding to the maximum ratio of the output intensity to the input intensity.
The two interference arms with different lengths are respectively a long interference arm 2 and a short interference arm 3, and a refractive index sensing region 4 is arranged on the long interference arm 2; the cross-sectional structure of the short interference arm 3 without the refractive index sensing region 4 is shown in fig. 2.
As shown in fig. 3, a cross-sectional structure diagram of the long interference arm 2 of the refractive index sensing region 4 is set, and the liquid to be measured is injected into the refractive index sensing region 4 of the long interference arm 2.
In this embodiment, the total length of the Mach-Zehnder structure of the optical waveguide chip is 30mm, the length of the long interference arm 2 is 22144 μm, the length of the short interference arm 3 is 22000 μm, and the length difference between the two interference arms is 144 μm.
In this embodiment, the long interference arm 2 is provided with a refractive index sensing region 4, and a region indicated by a dashed line in fig. 1 is the refractive index sensing region 4. The length of the interference arm in the refractive index sensing zone 4 is 1000 μm.
The dimensions of the cross-section of the long 2 and short 3 interference arms are 4 μmx4 μm.
The cladding layer 6 is low refractive index silica, and the refractive index of the low refractive index silica is 1.4448, and the core layer 7 is high refractive index silica, and the refractive index of the high refractive index silica is 1.4746.
The center wavelength of the device was 1.55 μm.
When the liquid or gas 8 to be measured is injected into the refractive index sensing area 4, the effective refractive index of the interference arm in the refractive index sensing area 4 is changed, so that the central wavelength of the output spectrum of the device is changed, the change of the effective refractive index and the change of the central wavelength are linear, and the central wavelength of the output spectrum is the wavelength corresponding to the maximum ratio of the output intensity to the input intensity.
The refractive index sensor provided by the embodiment can sense 10 of liquid or gas 8 to be measured-6The refractive index changes.
Example 2
The detection method of the refractive index sensor based on the mach-zehnder structure provided in embodiment 1 includes the steps of:
(1) inputting the wide-spectrum light into a refractive index sensor based on a Mach-Zehnder structure, and detecting the output spectrum of the refractive index sensor based on the Mach-Zehnder structure by using a spectrometer to obtain that the gas to be detected is air and the refractive index is n0At the center wavelength λ of the output spectrum of the corresponding device0；
In this example, the spectral width of the broad spectrum light was 40 nm. The output spectrum of the refractive index sensor is measured by a spectrometer or a wavelength demodulator.
(2) Placing the refractive index sensing region 4 into a known refractive index n1The wide-spectrum light passes through a refractive index sensor based on a Mach-Zehnder structure in the liquid or the gas, the output spectrum of the refractive index sensor is detected through a spectrometer, and the central wavelength lambda of the output spectrum of the device under the current liquid or the gas is obtained1Thereby completing the calibration of the device;
(3) placing the refractive index sensing region 4 into the refractive index n to be measured2The wide-spectrum light is input into the refractive index sensor in the liquid or the gas, the output spectrum of the refractive index sensor is detected by the spectrometer, and the central wavelength lambda of the output spectrum of the device under the refractive index corresponding to the liquid or the gas 8 to be detected is obtained2(ii) a Calculating the refractive index n to be measured according to the formula (V)2The formula (V) is:
the invention provides a detection method of a refractive index sensor based on a Mach-Zehnder structure, which is based on the following principle:
the basic interference principle of the asymmetric Mach-Zehnder interferometer is obtained:
in the formula (I), neIs the effective refractive index, L, of the two interference arm waveguides1Is the length of the short interference arm 3, Ls+ L' is the length of the long interference arm 2, LsIs the length of the interference arm in the refractive index sensing zone 4, lambda0The central wavelength of the output spectrum of the device when the diffraction order is M under the condition of not detecting gas or liquid; m is the number of diffraction orders, M is int (n.DELTA.L/lambda)0) Int (·) denotes rounding down a rounded real number, λ0When the refractive index sensing area 4 does not detect gas or liquid, the device outputs the central wavelength of the spectrum; Δ L is the difference in length between the long interference arm 2 and the short interference arm 3;
when detecting qiLength L in the case of body or liquidsHas an effective refractive index change Δ n of the interference arm in the refractive index sensing region 4, at which the center wavelength λ of the obtained output spectrum is3The interference equation at this time is:
multiplying both sides of the two formulas by lambda0And λ3Then subtracting, and simplifying to obtain:
M(λ0-λ3)＝Δn·LS (III)
let Δ λ be λ0-λ3Formula (I) is obtained:
Δλ＝Δn·Ls/M (IV)；
from the formula (IV), the effective refractive index change Δ n of the interference arm in the refractive index sensing region 4 has a linear relationship with the change Δ λ of the central wavelength of the output spectrum; errors exist in the manufacturing and calculation processes of the optical device, and specific linear relations between the refractive index n applied to the refractive index sensing region 4 and the change delta lambda of the central wavelength of the output spectrum are determined through the steps (1) and (2).
Claims (9)
1. The refractive index sensor based on the Mach-Zehnder structure is characterized by comprising the Mach-Zehnder structure, wherein the Mach-Zehnder structure comprises an input beam splitter, two interference arms with different lengths and an output beam combiner, two output ends of the input beam splitter are respectively connected with one ends of the two interference arms, and the other ends of the two interference arms are respectively connected with two input ports of the output beam combiner; stripping off part of the cladding on one of the interference arms to form a refractive index sensing region, wherein the refractive index sensing region is used for detecting liquid or gas; when liquid or gas to be detected is injected into the refractive index sensing area, the effective refractive index of the interference arm in the refractive index sensing area can be changed, so that the central wavelength of an output spectrum of the device is changed, the change quantity of the effective refractive index of the interference arm in the refractive index sensing area and the change quantity of the central wavelength are linear, and the central wavelength of the output spectrum is the wavelength corresponding to the maximum ratio of the output intensity to the input intensity.
2. The mach-zehnder structure-based refractive index sensor of claim 1, wherein the length of the strip off the interference arm is in the range of 1000 to 106And μm cladding to form a refractive index sensing region.
3. The refractive index sensor based on a Mach-Zehnder structure according to claim 1, characterized in that the length difference between the two interference arms is 1-500 μm.
4. The refractive index sensor based on Mach-Zehnder structure according to claim 1, characterized in that the cross-sectional width of both interference arms is 1-10 μm and the cross-sectional thickness is 1-10 μm.
5. A mach-zehnder structure-based refractive index sensor in accordance with claim 1, wherein said interference arm comprises a core layer and a cladding layer, said cladding layer surrounding an outer side of said core layer.
6. The refractive index sensor according to claim 1, wherein the refractive index of the core layer is 1.45-1.51, and the refractive index of the cladding layer is 1.40-1.45.
7. The refractive index sensor based on the Mach-Zehnder structure of claim 1, characterized in that the input beam splitter is a Y-branch or 1-branch 2-type input beam splitter and the output beam combiner is a Y-branch or 2-in-1 type output beam combiner.
8. A Mach-Zehnder structure-based refractive index sensor sensing method according to any one of claims 1-7, comprising the steps of:
(1) inputting broad spectrum light into the Mach-Zehnder based structureAnd detecting the output spectrum of the refractive index sensor based on the Mach-Zehnder structure by using a spectrometer to obtain that the gas to be detected is air and the refractive index is n0At the center wavelength λ of the output spectrum of the corresponding device0；
(2) Placing the sensing region of refractive index into a known refractive index of n1The wide-spectrum light passes through a refractive index sensor based on a Mach-Zehnder structure in the liquid or the gas, the output spectrum of the refractive index sensor is detected through a spectrometer, and the central wavelength lambda of the output spectrum of the device under the current liquid or the gas is obtained1Thereby completing the calibration of the device;
(3) putting the refractive index sensing area into the refractive index n to be measured2The wide-spectrum light is input into the refractive index sensor in the liquid or the gas, the output spectrum of the refractive index sensor is detected by a spectrometer, and the central wavelength lambda of the output spectrum of the device under the corresponding refractive index of the liquid or the gas to be detected is obtained2(ii) a Calculating the refractive index n to be measured according to the formula (V)2The formula (V) is:
9. a mach-zehnder structure-based refractive index sensor detection method according to claim 8, characterized in that a spectral width of a broad spectrum optical output spectrum is 40 nm.
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| CN114485743A (en) * | 2022-01-14 | 2022-05-13 | 中央民族大学 | Asymmetric Mach-Zehnder interference structure optical waveguide polymer sensor |
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