CN212722598U - Spectrum measuring device and measuring system - Google Patents
Spectrum measuring device and measuring system Download PDFInfo
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- CN212722598U CN212722598U CN202020321615.5U CN202020321615U CN212722598U CN 212722598 U CN212722598 U CN 212722598U CN 202020321615 U CN202020321615 U CN 202020321615U CN 212722598 U CN212722598 U CN 212722598U
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Abstract
The utility model relates to an optical fiber sensing technical field, concretely relates to spectral measurement device and measurement system. The method comprises the following steps: the optical fiber module comprises an input optical fiber, a hollow optical fiber and an output optical fiber which are connected in sequence; and the hollow-core optical fiber is internally provided with preset gas, and the preset gas is used for absorbing input light so as to output a target spectrum from the output optical fiber. The hollow-core optical fiber filled with preset gas is connected through the input optical fiber, the hollow-core optical fiber is connected through the output optical fiber, when a light source enters the hollow-core optical fiber from the input optical fiber, light information in the light source and gas molecules in the preset gas carry out absorption reaction, the transmitted light information carries the information of the preset gas, the information is output through the output optical fiber and is reflected on a spectrum, and therefore reference basis can be provided for spectral measurement. And the gas absorption spectrum technology is utilized, so that the change of the spectrum position is avoided when the spectrum measurement is carried out, and the stability of the spectrum measurement result is ensured.
Description
Technical Field
The utility model relates to an optical fiber sensing technical field, concretely relates to spectral measurement device and measurement system.
Background
With the rapid development of optical communication technology, laser technology, and sensing technology, etalons for wavelength calibration thereof are being applied to these fields in large quantities. The Fabry-Perot etalon is the most common etalon and is an interferometer with high fineness mainly formed by two flat glass or quartz plates.
In the prior art, when the fabry-perot etalon is used for spectrum measurement, measurement errors are generated due to factors such as the structure and the environment of the fabry-perot etalon, and the measurement errors possibly cause inaccurate measurement results. For example, the etalon may change its interference optical path due to the influence of vibration, mechanical deformation, temperature variation, etc., resulting in wavelength shift, thereby directly affecting the accuracy of wavelength calibration. Or, the distance and reflectivity of the interference reflecting surface need to be precisely controlled in the process of manufacturing the etalon, so that the manufacturing cost is high. The etalon generates comb-shaped spectrum through the optical resonant cavity, and the spectrum generated through the optical resonant cavity is sensitive to factors such as external environment temperature, pressure and the like, so that the calibration result is seriously changed, and the stability of the measurement result is influenced.
SUMMERY OF THE UTILITY MODEL
In view of this, the embodiment of the present invention provides a spectrum measuring apparatus and a measuring system, so as to solve the problem that the etalon is limited by the material and the structure thereof, so that the calibration result is changed, and the stability of the measurement result is affected.
According to a first aspect, an embodiment of the present invention provides a spectral measurement apparatus, including: the optical fiber module comprises an input optical fiber, a hollow optical fiber and an output optical fiber which are connected in sequence; and the hollow-core optical fiber is internally provided with preset gas, and the preset gas is used for absorbing input light so as to output a target spectrum from the output optical fiber.
The hollow-core optical fiber filled with preset gas is connected through the input optical fiber, the hollow-core optical fiber is connected through the output optical fiber, when a light source enters the hollow-core optical fiber from the input optical fiber, light information in the light source and gas molecules in the preset gas carry out absorption reaction, the transmitted light information carries the information of the preset gas, and the reaction is output through the output optical fiber on a spectrum, so that a reference datum can be provided for spectral measurement. And the gas absorption spectrum technology is utilized, so that the change of the spectrum position is avoided when the spectrum measurement is carried out, and the stability of the spectrum measurement result is ensured.
With reference to the first aspect, in a first embodiment of the first aspect, the hollow-core optical fiber comprises:
a core and a cladding; wherein the cladding has a plurality of thin-walled capillaries, the thin-walled capillaries being axially parallel to the axial direction of the core.
Low-loss wide-passband transmission is achieved by antiresonance of the thin silica layer surrounding the core and by inhibiting coupling between the cladding structure and the core.
With reference to the first aspect, in a second embodiment of the first aspect, the output end diameter of the input optical fiber is the same as the diameter of the output end of the output optical fiber, and the hollow-core optical fiber diameter is the same as the diameters of the output end of the input optical fiber and the input end of the output optical fiber.
The same diameter is set, so that low loss during transmission is guaranteed, transmission quality is guaranteed, and spectral measurement in middle infrared and near infrared bands can be realized.
With reference to the first aspect, in a third implementation manner of the first aspect, the input optical fiber includes:
the first single-mode fiber and the first few-mode fiber are connected in sequence; one end of the first few-mode optical fiber is connected with one end of the first single-mode optical fiber, and the other end of the first few-mode optical fiber is connected with one end of the hollow-core optical fiber;
the output optical fiber includes:
the second few-mode optical fiber and the second single-mode optical fiber are connected in sequence; and one end of the second few-mode optical fiber is connected with the other end of the hollow-core optical fiber, and the other end of the second few-mode optical fiber is connected with one end of the second single-mode optical fiber.
With reference to the first aspect, in a fourth implementation manner of the first aspect, the few-mode fiber includes the first few-mode fiber and a second few-mode fiber, and the few-mode fiber is provided with a first end face and a second end face, the first end face of the few-mode fiber is connected to the hollow-core fiber, and the second end face of the few-mode fiber is connected to the single-mode fiber.
With reference to the first aspect, in a fifth embodiment of the first aspect, a first end face diameter of the few-mode optical fiber is the same as a hollow-core optical fiber diameter, and a second end face diameter of the few-mode optical fiber and the single-mode optical fiber diameter are matched with each other.
According to a second aspect, an embodiment of the present invention provides a measurement system, including: the light source, the tunable filter and the coupler are connected in sequence;
a first measuring branch connected with the coupler; the first measuring branch comprises at least one object to be measured, a circulator and a first detector; the circulator is respectively connected with the coupler and the first detector and is used for reflecting light emitted by the light source to the first detector after passing through the at least one object to be detected;
the second measuring branch is connected with the coupler; wherein the second measuring branch comprises the spectrum measuring device and the second detector of any one of the embodiments of the first aspect; the spectral measurement device is connected with the coupler, and the second detector is connected with an output optical fiber of the spectral measurement device.
The light source enters the first measuring branch and the second measuring branch through the tunable filter and the coupler, so that the function of calibrating the unknown wavelength is realized, and a reference is provided for determining the unknown wavelength.
Drawings
The features and advantages of the invention will be more clearly understood by reference to the accompanying drawings, which are schematic and should not be understood as imposing any limitation on the invention, in which:
fig. 1 is a structural diagram of a spectral measuring apparatus according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a hollow-core optical fiber according to an embodiment of the present invention;
fig. 3 is a schematic cross-sectional view of a hollow core optical fiber according to an embodiment of the present invention;
fig. 4 is a block diagram of an input optical fiber according to an embodiment of the present invention;
fig. 5 is a block diagram of an output optical fiber according to an embodiment of the present invention;
fig. 6 is a flow chart of a method of manufacturing a spectral measuring device according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a measurement system according to an embodiment of the present invention;
FIG. 8 shows an alternative embodiment CO of the present invention2A spectrum absorption intensity chart of the gas in a wave band of 1.53-1.549 mu m;
FIG. 9 shows an alternative embodiment CO of the present invention2A spectrum absorption intensity chart of the gas in a wave band of 2.045-2.08 μm;
FIG. 10 shows an alternative embodiment CO of the present invention2A spectrum absorption intensity chart of the gas in a wave band of 4.18-4.37 mu m;
fig. 11 is a comparison graph of the measured spectra of the detector 1 and the detector 2 modulated with the tunable filter according to an alternative embodiment of the present invention;
FIG. 12 is a graph of wavelength values for alternative embodiment wavelengths g, h, j, k, l, o, p, t, u of the present invention;
reference numerals
1-an input optical fiber; 2-hollow optical fiber; 3-an output fiber; 4-a light source; 5-gas molecules; 6-thin-walled capillary; 71-a first single mode optical fiber; 72-second single mode fiber 81-first few mode fiber; 82-a second few-mode fiber; 9-few-mode optical fiber melting, tapering and thinning ends; 10-few-mode optical fiber untapered end; 11-a tunable filter; 12-coupler, 13-circulator; 14-a spectral measuring device; 15-second detector, 16-first detector; 17-first FBG; 18-a second FBG; 19-a third FBG; 20-fourth FBG.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.
The infrared absorption spectrum is a molecular absorption spectrum. When a sample is illuminated with infrared light of continuously varying frequency, the molecules absorb radiation of certain frequencies and a net change in dipole moment is induced by their vibrational or rotational movement, resulting in a transition of the molecular vibrational and rotational energy levels from the ground state to the excited state and a reduction in the intensity of transmitted light corresponding to the absorption region. And recording the relation curve of the percent transmittance of the infrared light and the wave number or wavelength to obtain the infrared spectrum, thereby realizing the spectral measurement. The utility model discloses optional embodiment will use well/near infrared light to describe as the light source, through the embodiment of the utility model provides a spectral measurement device how to carry out spectral measurement.
The embodiment of the utility model provides a spectral measurement device also can be an etalon, as shown in fig. 1-3, this spectral measurement device has the light of the wavelength of continuous distribution and jumps to each excited state through the gaseous molecule 5 absorption that is in ground state and low excited state to form the dark line according to the wavelength range and constitute the spectrum. And the spectral measurement device/etalon is less influenced by factors such as temperature and stress variation, and the like, and the manufacturing cost is low. According to the absorption characteristic of the gas molecules 5, the working waveband of the spectral measuring device/etalon covers the wavelength interval of near infrared and middle infrared, which is 1.0-5.0 μm.
As shown in fig. 1, an embodiment of the present invention provides a spectrum measuring apparatus, including: the optical fiber comprises an input optical fiber 1, a hollow optical fiber 2 and an output optical fiber 3 which are connected in sequence; the hollow-core optical fiber 2 is internally provided with preset gas, and the preset gas is used for absorbing input light so as to output a target spectrum from the output optical fiber 3.
The light source 4 enters the hollow-core optical fiber 2 from the input optical fiber 1, is output through the output optical fiber 3, transmits the optical information subjected to absorption reaction to the spectral analysis equipment, and analyzes and measures the optical information transmitted to the spectral analysis equipment. The input optical fiber 1 and the output optical fiber 3 can be fluoride optical fibers, and the characteristics of high doping concentration and high intensity of the fluoride optical fibers are utilized to realize high stability of spectral measurement and low loss of optical information transmission. The characteristics that the performance of the hollow-core optical fiber 2 is not limited by the material characteristics of the fiber core are utilized, so that the influence of the material characteristics of the optical fiber on the optical properties and the optical fiber performance is greatly reduced.
The light information emitted by the light source 4 enters the hollow-core optical fiber 2 and generates an absorption reaction with the filled preset gas, and then the target spectrum is obtained through the output of the output optical fiber 3, wherein the output target spectrum information comprises a specific spectrum line sequence corresponding to the absorption of the gas molecules 5. And the wavelength value corresponding to each spectral sequence is determined by the type of the gas molecule 5. Therefore, a set of wavelength sequences is preset as a reference for spectral measurement, and spectral information is measured/calibrated.
Because the output spectrum information can be the rule that the light intensity is attenuated along with the penetration distance after the preset gas is mixed with the hollow-core optical fiber 2, the wavelength information of the preset gas can be obtained from the rule, and the wavelength of the preset gas or the concentration of the preset gas can be determined according to the obtained wavelength information.
The hollow-core optical fiber 2 is connected at both ends to the input optical fiber 1 and the output optical fiber 3, preferably by fusion splicing using an optical fiber fusion splicer, but may be bonded or mechanically connected to reduce loss of optical information during transmission.
The input end of the input optical fiber 1 is used for inputting the light source 4, the output end of the input optical fiber 1 is connected with the input end of the hollow optical fiber 2, the output end of the hollow optical fiber 2 is connected with the input end of the output optical fiber 3, when the light information in the light source 4 enters the hollow optical fiber 2 from the input optical fiber 1, photons in the light information collide with gas molecules in preset gas and then carry out absorption reaction, the light information transmitted by the light source 4 carries the preset gas information and is output to spectral analysis equipment through the output optical fiber 3, and therefore the preset gas can be analyzed and measured through spectra and reference can be provided. And when utilizing gas absorption spectroscopy technique, can also guarantee when carrying out spectral measurement, avoid the spectral position to change, guarantee spectral measurement result's stability.
Alternatively, the light source 4 may be mid-infrared or near-infrared light.
Alternatively, as shown in fig. 1-3, the hollow-core optical fiber 2 comprises: a core and a cladding; wherein, the cladding has a plurality of thin-walled capillaries 6, and the thin-walled capillaries 6 are axially parallel to the axial direction of the fiber core. Low-loss wide-passband transmission is achieved by antiresonance of the thin silica layer surrounding the core and by inhibiting coupling between the cladding structure and the core. Furthermore, the transmission spectral range of the hollow-core fiber 2 covers 0.6 μm to 5.0. mu.m.
Optionally, the diameter of the output end of the input optical fiber 1 is the same as that of the output end of the output optical fiber 3, the diameter of the hollow optical fiber 2 is the same as that of the output end of the input optical fiber 1 and that of the input end of the output optical fiber 3, and the same diameter is set, so that low loss during transmission is guaranteed, transmission quality is guaranteed, and spectral measurement in mid-infrared and near-infrared can be realized.
Optionally, as shown in fig. 1 to 5, when the infrared light is measured in use, the input optical fiber 1, the hollow-core optical fiber 2, the output optical fiber 3, and the spectrum detection device are connected in sequence, and the output optical information is subjected to spectrum analysis. When the near infrared light is used for measurement, although the input optical fiber 1, the hollow-core optical fiber 2, the output optical fiber 3 and the spectrum detection equipment are connected in sequence, the input optical fiber 1 can also be a first single-mode optical fiber 71 and a first few-mode optical fiber 81 which are connected in sequence; one end of the first few-mode fiber 81 is connected with one end of the first single-mode fiber 71, and the other end of the first few-mode fiber 81 is connected with the input end of the hollow-core fiber 2; the output fiber 3 can be a second few-mode fiber 82 and a second single-mode fiber 72 which are connected in sequence; one end of the second few-mode optical fiber 82 is connected with the output end of the hollow-core optical fiber 2, and the other end of the second few-mode optical fiber 82 is connected with one end of the second single-mode optical fiber 72. Furthermore, the first single-mode fiber 71 and the second single-mode fiber 72 both belong to single-mode fibers, and the first few-mode fiber 81 and the second few-mode fiber 82 both belong to few-mode fibers. The first single mode fiber 71 and the second single mode fiber 72 are made of the same material and have the same intercepting length, and the first few-mode fiber 81 and the second few-mode fiber 82 are made of the same material and have the same intercepting length, so that low loss of optical information during transmission is ensured.
Optionally, when the infrared light is used for measurement, the few-mode optical fiber includes a first few-mode optical fiber 71 and a second few-mode optical fiber 72, where the few-mode optical fiber is provided with a first end face and a second end face, the first end face of the few-mode optical fiber is connected to the hollow-core optical fiber 2, and the second end face of the few-mode optical fiber is connected to the single-mode optical fiber. The diameter of the first end face of the few-mode optical fiber is the same as that of the hollow-core optical fiber 2, and the diameter of the second end face of the few-mode optical fiber is matched with that of the single-mode optical fiber.
Wherein the diameter of the first end face and the diameter of the second end face can be set to different diameters, for example: a truncated cone shape may be formed between the first end surface and the second end surface. The diameter of the first end face is the same as that of the hollow-core optical fiber 2, and the diameter of the second end face is matched with the single-mode optical fiber, so that loss of optical information in the transmission process can be reduced, and the transmission quality of the optical information is guaranteed.
Optionally, the preset gas is: CO 22、NO2、C2H2And a predetermined gas is connected to the input optical fiber 1 and the output optical fiber 3 by being pre-filled in the hollow-core optical fiber 2. This ensures to the maximum extent that the predetermined gas of the hollow-core optical fibre 2 is filled with the optical information transmitted by the light source 4The system is characterized by comprising a gas pre-filling device, a light spectrum measuring device and a light spectrum measuring device, wherein the light spectrum measuring device is used for measuring the light spectrum of different gases, and the light spectrum measuring device is used for measuring the light spectrum of different gases.
As shown in fig. 1-6, the embodiment of the present invention provides a method for preparing a spectrum measuring apparatus, which is suitable for measuring a mid-infrared band or a near-infrared band, and specifically includes:
s1, providing an input optical fiber 1, an output optical fiber 3 and a hollow-core optical fiber 2;
when measuring mid-infrared light, the input fiber 1/output fiber 3 uses a traditional fluoride fiber, and when measuring near-infrared light, the structure of the input fiber 1/output fiber 3 needs to be processed, and the specific original input fiber is replaced by a first single-mode fiber 71 and a first few-mode fiber 81; and the first few-mode fiber 81 needs to be melted so that one end of the fiber is tapered (tapered), and two ends of the first few-mode fiber 81 are respectively adapted to one end of the first single-mode fiber 71 and one end of the hollow-core fiber 2.
And the original output fiber 3 is replaced by a second single mode fiber 72 and a second few mode fiber 82; and performing optical fiber melting on the second few-mode optical fiber 82 to make one end of the optical fiber become thin after tapering treatment, so that two ends of the second few-mode optical fiber 82 are respectively matched with the other end of the hollow-core optical fiber 2 and one end of the second single-mode optical fiber 72. The input optical fiber 1/output optical fiber 3 is prepared by fusion welding of the fused tapered few-mode optical fiber and the single-mode optical fiber, and the input optical fiber 1/output optical fiber 3 is formed by combining the few-mode optical fiber and the single-mode optical fiber, so that the optical fiber coupling loss can be reduced.
S2, vacuumizing the hollow optical fiber 2 and filling preset gas; and the filling gas may be CO2、NO2、C2H2Any one or more of them mixed.
And S3, connecting the two ends of the hollow-core optical fiber 2 filled with the preset gas with the input optical fiber 1 and the output optical fiber 3 respectively.
Through connecting input optical fiber 1, hollow optic fibre 2 and output optical fiber 3 in order, wherein be provided with in the hollow optic fibre 2 and predetermine gas, input light source 4 gets into from input optical fiber 1, when passing through hollow optic fibre 2, utilizes spectral absorption characteristic, makes it carry out absorption reaction through the light information of output optical fiber 3 and predetermine gas to can provide benchmark/reference for spectral measurement. And through the gas absorption spectrum technology, the temperature stability is very good, the influence of stress change is small, the characteristic wavelength drift is not easy to generate, the measurement accuracy is higher, and the manufacturing cost is low. The hollow optical fiber 2 is used as an absorption pool, the fiber core of the hollow optical fiber 2 is large, the amount of gas contained is large, the effective absorption rate of gas molecules 5 in unit volume is improved, and the device also has the characteristics of high absorption spectrum intensity, small device volume and wide spectrum application range.
Furthermore, the utility model discloses can also be compromise near infrared band and mid infrared band gas absorption spectrum's etalon, this etalon has spectral range wide, receives temperature and stress variation to influence little advantage.
Alternative embodiments
A spectral measuring device, which may also be an etalon. Compare in current Fabry-Perot etalon, the utility model provides a spectral measurement device has higher stability and lower cost of manufacture. And simultaneously, the utility model discloses can compromise the gas absorption spectral measurement of near-infrared wave band and mid-infrared wave band.
As shown in fig. 1 to 5, the spectral measuring apparatus includes an input optical fiber 1, a hollow-core optical fiber 2, and an output optical fiber 3. The hollow-core optical fiber 2 is a node-free anti-resonant hollow-core optical fiber 2. CO in the hollow optical fiber 22、NO2、C2H2The single and mixed filling gas is respectively welded with the input optical fiber 1 and the output optical fiber 3 at two ends. After input light is incident on the hollow-core optical fiber 2 from the input optical fiber 1, the output spectral information output from the output optical fiber 3 contains a specific spectral line sequence corresponding to the absorption of the gas molecules 5 due to the characteristic absorption of the gas molecules 5. And the wavelength value of each spectral sequence is determined by the type of gas molecule 5. Therefore, a group of wavelength sequences are used as the reference of the spectral measurement, and the function of calibrating the spectral measurement is realized.
The spectral range of the hollow-core optical fiber 2 covers 0.6-5.0 μm, and the absorption spectrum line of the gas molecules 5 exists in near-infrared and mid-infrared bands. And correspondingly preparing the spectrum measuring device in different spectrum working sections according to the absorption characteristics of the optical fiber.
Specifically, in a mid-infrared band of 2.0 to 5.0 μm, the input optical fiber 1 and the output optical fiber 3 of the spectrum measuring apparatus are fluoride optical fibers; in a near-infrared band of 1.0-2.0 microns, an input optical fiber 1 and an output optical fiber 3 of the spectral measurement device adopt a mode adaptation method, a few-mode optical fiber thinned by melting tapering and a single-mode optical fiber are welded to prepare the input and output optical fiber 3, and the optical fiber coupling loss is reduced.
Because single mode fibers and few mode fibers cannot conduct mid-infrared light, when measuring mid-infrared bands, the manufacturing of the spectrum measuring device needs to include the following steps:
the method comprises the following steps: the fluoride optical fibers with the same core diameter and cladding diameter as those of the hollow-core optical fiber 2 are used as the input optical fiber 1 and the output optical fiber 3. The two ends of the input fluoride optical fiber and the hollow optical fiber 2 are cut flat by a cutter.
Step two: cutting 1m long hollow optical fiber 2, placing in a sealing device, vacuumizing, and filling CO2、NO2、C2H2A single or mixed gas of (1). Then the hollow-core optical fiber 2 is rapidly taken out and two ends of the hollow-core optical fiber 2 are respectively welded with the input fluoride optical fiber and the output fluoride optical fiber.
When the near-infrared band is measured, the manufacturing of the spectrum measuring device comprises the following steps:
the method comprises the following steps: replacing the connecting structure of the single-mode optical fiber and the few-mode optical fiber with an input optical fiber 1 and an output optical fiber 3; wherein, both ends of the single mode fiber and the few-mode fiber are cut flat by a cutter, then the few-mode fiber is fused and tapered on an oxyhydrogen mixed type fiber tapering machine, and tapering is stopped when the minimum diameter of the fiber core in the tapered area reaches 8-12 mu m. And then cutting the fiber core along the minimum diameter of the tapered area by a cutting knife to obtain a smooth fiber end surface with the fiber core of 8-12 mu m and the cladding of 100-120 mu m, and welding the thinned end and one end of the cut single-mode fiber by a welding machine to obtain the input fiber 1 and the output fiber 3 which are suitable for the near infrared band.
Step two: cutting 1m long hollow optical fiber 2, placing in a sealing device, vacuumizing, and filling CO2、NO2、C2H2A single or mixed gas of (1). And then the hollow optical fiber 2 is rapidly taken out, and two ends of the hollow optical fiber 2 are respectively welded with the other ends of the few-mode optical fibers in the input optical fiber 1 and the output optical fiber 3.
The embodiment has the advantages that:
1. the embodiment is based on the gas absorption spectrum technology, has very good temperature stability, is less influenced by stress change, is not easy to generate characteristic wavelength drift, has higher measurement accuracy and is low in manufacturing cost;
2. in the embodiment, the hollow-core optical fiber 2 is used as the absorption cell, and the adopted hollow-core optical fiber 2 has a large fiber core, a large amount of contained gas, high effective absorption rate of gas molecules 5 in unit volume, high absorption spectrum intensity and small device volume.
3. The embodiment gives consideration to both the near-infrared band and the mid-infrared band, and has a wider spectrum application range.
The embodiment of the utility model provides a measurement system, as shown in FIG. 7, include: a light source 4, a tunable filter 11, and a coupler 12 connected in this order; wherein, the light source 4 includes: the tunable filter 11 is preferably a tunable optical filter, and may be a flat-top, ultra-high-selectivity and narrow-bandwidth tunable filter 11. The coupler 12 may be a directional coupler 12 or a coupler 12 equipped according to experimental requirements.
A first measuring branch connected with the coupler 12; the first measuring branch comprises at least a target to be measured, a circulator 13 and a first detector 16; the circulator 13 is respectively connected with the coupler 12 and the first detector 16, and is configured to reflect light emitted by the light source 4 to the first detector 16 after passing through at least one object to be detected;
a second measuring branch connected with the coupler 12; wherein the second measuring branch comprises a spectral measuring device 14 and a second detector 15; the spectral measuring device 14 is connected to the coupler 12, and the second detector 15 is connected to the output fiber 3 of the spectral measuring device 14. The light source 4 enters the first measuring branch and the second measuring branch through the tunable filter 11 and the coupler 12, so that the function of calibrating the unknown wavelength is realized, and a reference is provided for determining the unknown wavelength.
Wherein the coupler 12 is used for measuring the proportional distribution of the light beam; the number of the targets to be detected is at least 2, and the circulator 13 is configured to receive FBG reflected light power reflected by an FBG (Fiber Bragg Grating), and send the FBG reflected light power to the first detector 16 for detection. The second measurement branch is connected with the second detector 15 for measurement by using the spectrum measurement device 14, and since the wavelength value corresponding to each spectrum sequence is determined by the type of the gas molecule 5, the target to be measured can be measured and calibrated by comparing the measurement result of the first detector 16 with the measurement result of the second detector 16. And because the system utilizes the gas absorption spectrum technology, the system has very good temperature stability, is less influenced by stress change, is not easy to generate characteristic wavelength drift, has higher measurement accuracy and low manufacturing cost.
The embodiment of the utility model provides a pair of measurement system's measuring method, include:
acquiring a first detection result of the first detector 16 and a second detection result of the second detector 15; and comparing the first detection result with the second detection result to obtain the central wavelength of at least one target to be detected.
The position and the number of the wavelength to be measured are determined by using the first detection result, and the second detection result is compared, so that the position of the first detection result corresponding to the second detection result can be determined, and then the detection result of the first detector 16 can be the reflected light power of the FBG to be measured according to the second detection result, and the detection result of the second detector 15 can be the light power change curve, because the first detector 16 and the second detector 15 pass through the same tunable filter 10, both have the same wavelength information. By comparing the two spectra, the wavelength range and other spectral information of the object detected in the first detector 16 can be determined and can be used as a reference for measuring and calibrating the object. Thereby improving the accuracy of detection and improving the stability of the measuring system. The wavelength to be measured provides a reference, so that the wavelength to be measured is determined.
Alternative embodiments
A measuring system is shown in figures 1-11 and comprises an input optical fiber 1 which is a node-free anti-resonance hollow-core optical fiber, specifically, as shown in figures 1-3, the anti-resonance hollow-core optical fiber is of a single-loop and node-free structure, an optical fiber cladding adopts a layer of 8 thin-wall capillaries 6, and low-loss wide-passband transmission is realized through anti-resonance of a quartz thin layer around the fiber core and inhibition coupling between the cladding structure and the fiber core. The light transmission spectrum range of the hollow-core optical fiber 2 is 1.0-5.0 μm. CO in the hollow optical fiber 22、NO2、C2H2The single and mixed fill gas is fused at both ends to the input and output fibers 1 and 3, respectively. Light emitted by the light source 4 is input through the input optical fiber 1, and generates a spectrum absorption effect with filling gas in the hollow optical fiber 2, and the spectrum is output through the output optical fiber 3 and is detected by the detector.
When the intermediate infrared band of 2-5 microns is detected, the input optical fiber 1 and the output optical fiber 3 of the measuring system both adopt fluoride optical fibers, and the typical component (mass fraction) in the fluoride optical fiber is 53 percent ZrF4，20％BaF2，4％LaF3，3％AlF3And 20% NaF (ZBLAN), wherein the phonon energy is 550cm & lt-1 & gt, and the light with the wavelength of 2-5 mu m can realize low-loss transmission.
When detecting a near-infrared band of 1.0-2.0 μm, in order to reduce the coupling loss of the input and output optical fibers 3, the input optical fiber 1 and the output optical fiber 3 of the measurement system adopt a mode adaptation method, wherein the mode adaptation method is a matching mode of optical fiber core diameters among single-mode optical fibers, few-mode optical fibers and hollow-core optical fibers 2. Because the single mode fiber core is small (about 10um), and the few-mode fiber and the hollow-core fiber 2 core are about 25um, the direct fusion splicing of the fibers will result in the mismatch of the core diameters and the generation of large optical loss. Therefore, one end of the few-mode optical fiber is matched with the diameter of the core of the hollow-core optical fiber 2 in a tapering mode, and the other end of the few-mode optical fiber is directly matched with the core of the single-mode optical fiber. Thereby achieving the effect of mode adaptation.
As shown in fig. 4-5, the input optical fiber 1 or the output optical fiber 3 suitable for the measurement system is obtained by fusing the few-mode optical fiber fusion taper end 9 with one end of a single-mode optical fiber. The non-tapered end 10 of the few-mode optical fiber is welded with the hollow-core optical fiber 2.
Using filling gas as CO2For example, referring to FIGS. 8-9, the present measurement system is filled with CO2The corresponding absorption spectrum detected from the single mode fiber 7 is in the wave bands of 1.53-1.549 μm and 2.04-2.08 μm. As also shown in FIG. 10, the present measurement system was filled with CO2The corresponding absorption spectrum detected from the output optical fiber 3 is in a wave band of 4.18-4.37 μm, and the function of wavelength correction of the corresponding spectrum interval is realized by taking the spectrum absorption lines with uniform intervals as the reference of the spectrum wavelength.
Alternative embodiments
7-12, a measurement system based on gas absorption spectroscopy; the light emitted by the broadband light source 4 is filtered by the tunable filter 11 and then is divided into two beams with 90% and 10% of the ratio by the coupler 12. The light beam with the proportion of 90% is reflected by four first FBGs 17, second FBGs 18, third FBGs 19 and fourth FBGs 20 which have different central wavelengths and are connected in series to form FBGs, and then reaches the first detector 16 after passing through the circulator 13 for detection. With the time-varying modulation of the tunable filter 11, the first detector 16 receives the time-varying FBG reflected light power. As shown in fig. 7-10. Meanwhile, when 10% of the light beam passes through the hollow-core optical fiber 2 in the spectrum measuring device 14, the light beam is in contact with CO in the hollow-core optical fiber 22The spectral absorption reaction occurs, and the change curve of the optical power output by the second detector 15 is obtained along with the modulation effect of the tunable filter 11 with time points, as shown in fig. 11. Since the light received by the first detector 16 and the second detector 15 comes from the same tunable filter 11, both have the same wavelength information. Two spectra were compared, the central wavelength λ of the four series FBGs in FIG. 111、λ2、λ3、λ4Are respectively provided withA spectral line can be found in fig. 11 at a corresponding position. Referring to fig. 11, the wavelength values of the waves g, h, j, k, l, o, p, t, u are shown in fig. 12. The central wavelengths of the reflection spectra of the FBGs to be measured are respectively lambda through comparison and calculation of the two1＝1.5415μm、λ2＝1.5429μm、λ3＝1.5450μm、λ41.5469 μm, so as to calibrate the spectrum of the device under test FBG.
Claims (6)
1. A spectral measuring device, comprising:
the optical fiber module comprises an input optical fiber, a hollow optical fiber and an output optical fiber which are connected in sequence;
the input optical fiber includes: the first single-mode fiber and the first few-mode fiber are connected in sequence; one end of the first few-mode optical fiber is connected with one end of the first single-mode optical fiber, and the other end of the first few-mode optical fiber is connected with one end of the hollow-core optical fiber;
the output optical fiber includes: the second few-mode optical fiber and the second single-mode optical fiber are connected in sequence; one end of the second few-mode optical fiber is connected with the other end of the hollow-core optical fiber, and the other end of the second few-mode optical fiber is connected with one end of the second single-mode optical fiber;
and the hollow-core optical fiber is internally provided with preset gas, and the preset gas is used for absorbing input light so as to output a target spectrum from the output optical fiber.
2. The apparatus of claim 1, wherein the hollow-core optical fiber comprises:
a core and a cladding; wherein the cladding has a plurality of thin-walled capillaries, the thin-walled capillaries being axially parallel to the axial direction of the core.
3. The apparatus of claim 1 or 2, wherein the diameters of the input optical fiber, the hollow-core optical fiber, and the output optical fiber are the same.
4. The apparatus of claim 1, wherein the few-mode fiber comprises the first few-mode fiber and the second few-mode fiber, and the few-mode fiber is provided with a first end face and a second end face, the first end face of the few-mode fiber is connected with a hollow-core fiber, and the second end face of the few-mode fiber is connected with a single-mode fiber.
5. The apparatus of claim 4, wherein the first end face diameter of the few-mode fiber is the same as the diameter of the hollow-core fiber, and wherein the second end face diameter of the few-mode fiber is matched to the diameter of the single-mode fiber.
6. A measurement system, comprising:
the light source, the tunable filter and the coupler are connected in sequence;
a first measuring branch connected with the coupler; the first measuring branch comprises at least one object to be measured, a circulator and a first detector; the circulator is respectively connected with the coupler and the first detector and is used for reflecting light emitted by the light source to the first detector after passing through the at least one object to be detected;
the second measuring branch is connected with the coupler; wherein the second measuring branch comprises the spectral measuring device of any of claims 1-2 or 4-5 and a second detector; the spectral measurement device is connected with the coupler, and the second detector is connected with an output optical fiber of the spectral measurement device.
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