Absorption spectrum measuring device with light path adjusting function and light path adjusting method thereof

Abstract

The invention relates to a light path adjusting device, in particular to an absorption spectrum measuring device with a light path adjusting function and a light path adjusting method of the absorption spectrum measuring device, and aims to solve the technical problems that an optical axis is difficult to adjust, the efficiency is low, the structure is complicated and a plurality of parts exist when spatial light is coupled into an optical fiber in the conventional spectrum absorption measuring device. The absorption spectrum measurement device comprises a measurement absorption unit, a first optical fiber collimator, a second optical fiber collimator, a collimation unit, a multi-mode receiving optical fiber, a single-mode emergent optical fiber and a rear cover plate which are arranged in an area to be measured, the adjusting screw is arranged on the rear cover plate, the tail end of the adjusting screw abuts against the outer side face of the collimation tool, and the adjusting screw is used for adjusting the pitching angle of the collimation tool and the optical axis direction of the second optical fiber collimator, so that the second optical fiber collimator is coaxial with the first optical fiber collimator, and high coupling efficiency is achieved. The method is simple in adjusting process and suitable for external field implementation.

Description

Technical Field

[0001] The present invention relates to an optical path adjustment device, and particularly to an absorption spectrum measurement device with optical path adjustment and its optical path adjustment method. Background Art

[0002] Absorption spectroscopy technology can be used for on-line measurement of gas components, and has been increasingly applied to real-time detection and analysis of on-site environmental gases. In many application scenarios, in the face of harsh environments such as high temperature, strong shock, strong vibration, strong corrosion, and complex electromagnetic environments, in order to improve the survival ability of the probe, electronic devices such as lasers and photodetectors are usually placed in a relatively safe environment at the back end, and the detection probe is designed as an all-fiber structure. In this way, the laser emits from the output fiber, penetrates the gas to be measured, and then couples into the receiving fiber. However, there are problems of difficult optical axis adjustment and low coupling efficiency when spatial light couples into the fiber, which poses high requirements for the design of the probe. On the other hand, the harsh application environment requires the design of the detection probe to be as simple as possible to improve the reliability and operability of the system.

[0003] Chinese Patent CN218445111U discloses "a long optical path gas absorption cell with adjustable optical path", which can couple spatial light into the fiber through optical path adjustment. However, the structure of this absorption cell is relatively complex, with many components and high process requirements, and there is a risk of failure when applied in a harsh environment.

[0004] In summary, when the existing spectral absorption measurement devices and methods measure gas components, there are technical problems of difficult optical axis adjustment, low efficiency, complex structure, and many components when spatial light couples into the fiber. Summary of the Invention

[0005] The object of the present invention is to solve the technical problems of difficult optical axis adjustment, low efficiency, complex structure, and many components when spatial light couples into the fiber in the existing spectral absorption measurement device, and provides an absorption spectrum measurement device with optical path adjustment and its optical path adjustment method.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An absorption spectrum measurement device with optical path adjustment, characterized in that it includes a measurement absorption unit, a first fiber collimator, a second fiber collimator, a collimation unit, a multimode receiving fiber, a single-mode output fiber, and a rear cover plate arranged in the area to be measured;

[0008] The measuring absorption unit is a rectangular parallelepiped structure, and an airflow channel is arranged inside it. The two sides of the airflow channel are respectively arranged as a receiving end and a transmitting end, and the rear cover plate is arranged at the transmitting end; a first light-through hole is arranged at the end of the receiving end, and a step hole coaxial with the first light-through hole is arranged at the end of the transmitting end, and the large end of the step hole faces outward; the small end of the step hole is an arc-shaped groove, and a second light-through hole is coaxially arranged at the bottom of the arc-shaped groove; the large end of the step hole is a cylindrical hole, and an optical path adjustment area is formed between the step hole and the rear cover plate; the airflow channel is used for the flow of the gas to be measured;

[0009] The collimation unit includes a collimation tool and a plurality of adjustment screws; the collimation tool is nested in the optical path adjustment area, and a third light-through hole coaxial with the step hole is provided on the collimation tool, and the inner end of the collimation tool is adapted to the arc groove and rotatably connected to the arc groove;

[0010] The first optical fiber collimator is arranged in the first light through hole, the inner end of which is opposite to the second light through hole, the outer end of which is connected to one end of the multimode receiving optical fiber, and the other end of the multimode receiving optical fiber is used to connect to the photoelectric detector;

[0011] The rear cover plate is provided with a fourth light-transmitting hole coaxial with the step hole;

[0012] The second optical fiber collimator passes through the fourth light hole and is connected to the collimation tooling, and the inner end passes through the third light hole and is opposite to the second light hole. One end of the single-mode output optical fiber is connected to the outer end of the second optical fiber collimator, and the other end is used to connect to the laser;

[0013] The adjusting screw is arranged on the rear cover plate, and its end abuts against the outer side surface of the collimating tooling, and is used to adjust the pitch angle of the collimating tooling and the optical axis direction of the second optical fiber collimator to make it coaxial with the first optical fiber collimator.

[0014] Furthermore, the collimation tooling includes a collimation disk adapted to the cylindrical hole and a spherical protrusion adapted to the arc-shaped groove; the spherical protrusion is arranged on a side wall of the collimation disk close to the second light-transmitting hole, and is rotatably connected to the arc-shaped groove; the third light-transmitting hole is coaxially arranged in the collimation disk and the spherical protrusion.

[0015] Furthermore, collimating lenses are respectively provided at the inner ends of the first optical fiber collimator and the second optical fiber collimator for collimating the laser; a gap is provided between the edge of the rear cover plate and the edge of the emitting end of the measuring absorption unit for glue injection and curing after the optical path adjustment is completed.

[0016] Furthermore, the outer ends of the first and second optical fiber collimators are both conical structures, and the inner ends are both cylindrical structures; the diameter of the collimating disc is smaller than the inner diameter of the cylindrical hole, and its inner edge is provided with a chamfered corner; the radius of the spherical protrusion is equal to the radius of the arc-shaped groove.

[0017] Furthermore, the materials of the measurement absorption unit, the collimation tooling, and the rear cover plate are all stainless steel; three threaded holes are evenly arranged along the circumference on the rear cover plate; there are three adjusting screws, which are respectively arranged in the three threaded holes.

[0018] Meanwhile, the present invention also provides an optical path adjustment method for the absorption spectrum measurement device with the above-mentioned optical path adjustment. The special feature lies in that it includes the following steps:

[0019] Connect the other ends of the multimode receiving optical fiber and the single-mode emitting optical fiber to the coupling detection device respectively; adjust the pitching angle of the collimation tooling and the optical axis direction of the second fiber collimator through the adjusting screws to perform laser coupling with the first fiber collimator. At the same time, use the coupling detection device to monitor the coupling efficiency of the laser in the multimode receiving optical fiber and the single-mode emitting optical fiber until the coupling efficiency ≥ -5dB, then complete the optical path adjustment of the absorption spectrum measurement device.

[0020] Furthermore, it also includes: after the optical path adjustment is completed, glue can be injected and cured through the gap between the edge of the rear cover plate and the emitting end edge of the measurement absorption unit.

[0021] Furthermore, before connecting the other ends of the multimode receiving optical fiber and the single-mode emitting optical fiber to the coupling detection device respectively, it also includes: calibrating the output laser power of the coupling detection device.

[0022] Furthermore, the coupling detection device is a Mini-OTDR.

[0023] The beneficial effects of the present invention:

[0024] 1. The absorption spectrum measurement device with optical path adjustment of the present invention can achieve a relatively high coupling efficiency through the collimation unit and the adjusting screws, which can reach more than -5dB. While for the existing spectrum absorption measurement devices and methods, when the coupling efficiency of measuring gas components exceeds -13dB, it can basically meet the use requirements.

[0025] 2. The absorption spectrum measurement device with optical path adjustment of the present invention has good coaxiality for the set first light passing hole, second light passing hole, and stepped hole, which can usually be achieved by rotary milling, with low requirements for the device, solving the problems of difficult optical path adjustment, low optical coupling efficiency, and high precision requirements for parts in the existing measurement devices; while ensuring the coupling efficiency, it reduces the requirements for processing precision.

[0026] 3. The absorption spectrum measurement device with optical path adjustment of the present invention uses three M4 stainless steel screws to achieve optical path adjustment. The adjustment process is relatively easy, which can effectively reduce the installation and adjustment difficulty, ensure the installation and adjustment precision, and can adjust the optical coupling efficiency to more than -5dB in a relatively short time, and even can reach a coupling efficiency of more than -2dB.

[0027] 4. The absorption spectrum measurement device with optical path adjustment according to the present invention has a collimating disc with a diameter smaller than the inner diameter of the cylindrical hole, and its inner edge is provided with a chamfer, which can ensure sufficient adjustment margin during the optical path adjustment process without interference; the radius of the spherical protrusion is equal to the radius of the arc-shaped groove, which can ensure a large contact area between the spherical protrusion and the arc-shaped groove, preventing wear during the adjustment process and ensuring no glue leakage during glue injection, and avoiding the laser passing through the second light passing hole being blocked.

[0028] 5. The absorption spectrum measurement device with optical path adjustment according to the present invention has a simple structure and is easy to implement, with high reliability and economy, and can adapt to relatively harsh application environments.

[0029] 6. The absorption spectrum measurement device with optical path adjustment according to the present invention, for different gases to be detected, the single-mode output optical fiber can be connected to a laser with a specific wavelength, and the multi-mode receiving optical fiber can be connected to a photodetector with a corresponding wavelength.

[0030] 7. The absorption spectrum measurement device with optical path adjustment according to the present invention, for different application scenarios, in addition to improving the coupling efficiency, can also enhance the signal by increasing the laser output power and adjusting the amplification circuit multiple, so that a strong enough signal can be detected when the coupling efficiency reaches -13 dB.

[0031] 8. The absorption spectrum measurement device with optical path adjustment according to the present invention, for gases with relatively special wavelengths corresponding to the absorption spectrum lines, when the output power of the laser is limited or the responsivity of the photodetector at this wavelength is relatively low, the coupling efficiency can reach more than -2 dB.

[0032] 9. The optical path adjustment method of the absorption spectrum measurement device with optical path adjustment according to the present invention has a relatively simple adjustment process, only requiring a Mini-OTDR or other loss measurement equipment, and is suitable for field implementation. Brief Description of the Drawings

[0033] Figure 1 is a schematic structural diagram of an embodiment of the absorption spectrum measurement device with optical path adjustment according to the present invention;

[0034] Figure 2 is a cross-sectional view of an embodiment of the absorption spectrum measurement device with optical path adjustment according to the present invention;

[0035] Figure 3 is an exploded view of an embodiment of the absorption spectrum measurement device with optical path adjustment according to the present invention;

[0036] Figure 4 is a schematic structural diagram of the absorption measurement unit in an embodiment of the absorption spectrum measurement device with optical path adjustment according to the present invention;

[0037] Figure 5It is a structural schematic diagram of the collimation tool in an embodiment of the absorption spectrum measuring device with optical path adjustment of the present invention.

[0038] Description of reference numerals:

[0039] 1-measurement absorption unit, 11-air flow channel, 12-first light hole, 13-second light hole, 14-step hole, 2-first fiber collimator, 21-multi-mode receiving fiber, 3-second fiber collimator, 31-single-mode output fiber, 4-collimation unit, 41-collimation disk, 42-spherical protrusion, 5-rear cover, 6-adjustment screw, 7-fastening screw. DETAILED DESCRIPTION

[0040] like Figure 1 , Figure 2 As shown, an absorption spectrum measuring device with optical path adjustment includes a measuring absorption unit 1 arranged in a measured area, a first optical fiber collimator 2, a second optical fiber collimator 3, a collimation unit 4, a multi-mode receiving optical fiber 21, a second optical fiber collimator 3, a single-mode emitting optical fiber 31 and a rear cover plate 5.

[0041] like Figure 4 As shown, the measuring absorption unit 1 is a rectangular parallelepiped structure, in which an airflow channel 11 is arranged inside, and the two sides of the airflow channel 11 are respectively arranged as a receiving end and a transmitting end, and the rear cover plate 5 is arranged at the transmitting end; a first light hole 12 is arranged at the end of the receiving end, and a step hole 14 coaxial with the first light hole 12 is arranged at the end of the transmitting end, and the large end of the step hole 14 faces outward; the small end of the step hole 14 is an arc-shaped groove, and a second light hole 13 is coaxially arranged at the bottom of the arc-shaped groove; the large end of the step hole 14 is a cylindrical hole, and an optical path adjustment area is formed between the step hole 14 and the rear cover plate 5; the airflow channel 11 is used for the flow of the gas to be measured, and different sizes can be set as needed. The collimation unit 4 includes a collimation tool and a plurality of adjustment screws 6; the collimation tool is nested in the optical path adjustment area, and a third light hole coaxial with the step hole 14 is arranged on it, and the inner end of the collimation tool is adapted to the arc-shaped groove and can be rotatably connected with the arc-shaped groove.

[0042] The first fiber collimator 2 is disposed in the first light passing hole 12, with its inner end opposite to the second light passing hole 13 and its outer end connected to one end of the multimode receiving fiber 21. The other end of the multimode receiving fiber 21 is connected to a photodetector through a connection. The rear cover plate 5 is connected to the outer edge of the emitting end of the measurement absorption unit 1 by 4 fastening screws 7, and is provided with a fourth light passing hole coaxial with the stepped hole 14. The second fiber collimator 3 passes through the fourth light passing hole and is connected to the collimation tooling. Its inner end passes through the third light passing hole and is opposite to the second light passing hole 13. One end of the single-mode emitting fiber 31 is connected to the outer end of the second fiber collimator 3, and the other end is used to connect to a laser. Collimation lenses are respectively provided at the inner ends of the first fiber collimator 2 and the second fiber collimator 3 for collimating the laser. The adjustment screw 6 is disposed on the rear cover plate 5, and its end abuts against the outer side surface of the collimation tooling for adjusting the pitching angle of the collimation tooling and the optical axis direction of the second fiber collimator 3 to make it coaxial with the first fiber collimator 2. A gap is provided between the edge of the rear cover plate 5 and the edge of the emitting end of the measurement absorption unit 1 for injecting glue and curing after the optical path adjustment is completed.

[0043] As Figure 5 shown, the collimation tooling includes a collimation disc 41 adapted to the cylindrical hole and a spherical protrusion 42 adapted to the arc-shaped groove. The diameter of the collimation disc 41 is 2 mm smaller than the inner diameter of the large-end cylindrical hole of the stepped hole 14 to ensure sufficient adjustment margin during the optical path adjustment without interference. A 3 mm rounded corner is provided at the inner edge of the collimation disc 41 to prevent interference during the optical path adjustment. The spherical protrusion 42 is disposed on the side wall of the collimation disc 41 close to the second light passing hole 13 and is rotatably connected to the arc-shaped groove. The purpose is that when the adjustment screw 6 is turned during the optical path adjustment, the spherical protrusion 42 can rotate accordingly. Preferably, the radius of the spherical protrusion 42 is equal to the radius of the arc-shaped groove to ensure a large contact surface between the spherical protrusion 42 and the arc-shaped groove, which can not only prevent wear during the adjustment process but also ensure no glue leakage during glue injection. The third light passing hole is coaxially disposed in the collimation disc 41 and the spherical protrusion 42.

[0044] As Figure 1 、 Figure 3 shown, the outer ends of both the first fiber collimator 2 and the second fiber collimator 3 are conical structures, and the inner ends are cylindrical structures. The first fiber collimator 2 is connected to the receiving end of the measurement absorption unit 1 through a flange, and the second fiber collimator 3 is connected to the collimation disc 41 through a flange. The materials of the measurement absorption unit 1, the collimation disc 41, the spherical protrusion 42, and the rear cover plate 5 are all stainless steel. Three threaded holes are evenly arranged along the circumference on the rear cover plate 5. There are three adjustment screws 6, which are respectively disposed in the three threaded holes. The coupling detection device is a Mini-OTDR.

[0045] The present invention also provides an optical path adjustment method based on the above absorption spectrum measurement device with optical path adjustment, including the following steps:

[0046] 1. Place the absorption spectrum measurement device with optical path adjustment in the air;

[0047] 2. Calibrate the output laser power of the coupling detection device, and then connect the other ends of the multimode receiving optical fiber 21 and the single-mode output optical fiber 31 to the coupling detection device respectively; use the adjustment screw 6 to adjust the pitching angle of the collimation tooling and the optical axis direction of the second fiber collimator 3 to perform laser coupling with the first fiber collimator 2. At the same time, use the coupling detection device to monitor the laser coupling efficiency in the multimode receiving optical fiber 21 and the single-mode output optical fiber 31 until the coupling efficiency ≥ -5 dB, then complete the optical path adjustment of the absorption spectrum measurement device;

[0048] 2.1. Calibrate the output laser power of the Mini-OTDR;

[0049] The specific method for calibrating the output laser power of the Mini-OTDR is to connect one end of an optical fiber with FC connectors at both ends to the OTDR&LS interface of the Mini-OTDR, and insert the other end into the OPM interface of the Mini-OTDR. Turn on the Mini-OTDR, select "Loss Test", select "Wavelength" as 1310 nm, click "Start", and click "Reference" after the reading is stable to complete the calibration of the output laser power of the Mini-OTDR;

[0050] 2.2. Connect the other ends of the multimode receiving optical fiber 21 and the single-mode output optical fiber 31 to the coupling detection device respectively; turn on the Mini-OTDR, use the adjustment screw 6 to adjust the pitching angle of the collimation tooling and the optical axis direction of the second fiber collimator 3 to perform laser coupling with the first fiber collimator 2. At the same time, use the Mini-OTDR to monitor the laser coupling efficiency in the multimode receiving optical fiber 21 and the single-mode output optical fiber 31 until the coupling efficiency ≥ -5 dB, then complete the optical path adjustment of the absorption spectrum measurement device;

[0051] 3. After the optical path adjustment is completed, glue can be injected and cured through the gap between the edge of the rear cover plate 5 and the emission end edge of the measurement absorption unit 1.

[0052] The optical path adjustment method for absorption spectrum measurement of the present invention. For different gases to be detected, the single-mode output optical fiber 31 can be connected to a laser with a specific wavelength, and the multi-mode receiving optical fiber 21 can be connected to a photodetector with the corresponding wavelength. For different application scenarios, in addition to improving the coupling efficiency, the signal can also be enhanced by increasing the laser output power and adjusting the amplification circuit multiple, so that a strong enough signal can be detected when the coupling efficiency reaches -13 dB. However, for some gases, the wavelengths corresponding to their absorption lines are relatively special, the output power of the laser is limited, or the responsivity of the photodetector at this wavelength is relatively low. In this case, it is necessary to further improve the laser coupling efficiency.

Claims

1. An absorption spectrum measurement device with optical path adjustment, characterized in that: It comprises a measurement absorption unit (1) arranged in a region to be measured, a first optical fiber collimator (2), a second optical fiber collimator (3), a collimation unit (4), a multi-mode receiving optical fiber (21), a single-mode emitting optical fiber (31), and a rear cover plate (5); The measuring absorption unit (1) is a rectangular parallelepiped structure, and an airflow channel (11) is arranged inside the unit. The two sides of the airflow channel (11) are respectively arranged as a receiving end and a transmitting end, and the rear cover plate (5) is arranged at the transmitting end; the receiving end is provided with a first light-through hole (12), and the transmitting end is provided with a step hole (14) coaxial with the first light-through hole (12), and the large end of the step hole (14) faces outward; the small end of the step hole (14) is an arc-shaped groove, and the bottom of the arc-shaped groove is coaxially provided with a second light-through hole (13); the large end of the step hole (14) is a cylindrical hole, and an optical path adjustment area is formed between the step hole (14) and the rear cover plate (5); the airflow channel (11) is used for the flow of the gas to be measured; The collimation unit (4) comprises a collimation tool and a plurality of adjustment screws (6); the collimation tool is nested in the optical path adjustment area, and is provided with a third light-transmitting hole coaxial with the step hole (14); the inner end of the collimation tool is adapted to the arc-shaped groove and is rotatably connected to the arc-shaped groove; The first optical fiber collimator (2) is arranged in the first light through hole (12), the inner end of which is opposite to the second light through hole (13), the outer end of which is connected to one end of the multimode receiving optical fiber (21), and the other end of the multimode receiving optical fiber (21) is used to be connected to the photoelectric detector; The rear cover plate (5) is provided with a fourth light-transmitting hole coaxial with the step hole (14); The second optical fiber collimator (3) passes through the fourth light-through hole and is connected to the collimation tooling, and the inner end passes through the third light-through hole and is opposite to the second light-through hole (13); one end of the single-mode output optical fiber (31) is connected to the outer end of the second optical fiber collimator (3), and the other end is used to connect to the laser; The adjusting screw (6) is arranged on the rear cover plate (5), and its end is in contact with the outer side surface of the collimating tool, and is used to adjust the pitch angle of the collimating tool and the optical axis direction of the second optical fiber collimator (3) so that it is coaxial with the first optical fiber collimator (2).

2. The absorption spectrum measuring device with optical path adjustment according to claim 1, characterized in that: The alignment tool comprises an alignment disk (41) matched with the cylindrical hole and a spherical protrusion (42) matched with the arc-shaped groove; The spherical protrusion (42) is arranged on a side wall of the collimating disk (41) close to the second light-through hole (13), and is rotatably connected to the arc-shaped groove; The third light-through hole is coaxially arranged in the collimating disk (41) and the spherical protrusion (42).

3. The absorption spectrum measuring device with optical path adjustment according to claim 2, characterized in that: The inner ends of the first optical fiber collimator (2) and the second optical fiber collimator (3) are respectively provided with collimating lenses for collimating laser light; A gap is provided between the edge of the rear cover plate (5) and the edge of the emission end of the measurement absorption unit (1), which is used for glue injection and curing after the optical path adjustment is completed.

4. The absorption spectrum measuring device with optical path adjustment according to claim 3, wherein: The outer ends of the first fiber collimator (2) and the second fiber collimator (3) are both conical structures, and the inner ends are both cylindrical structures; The diameter of the collimation disc (41) is smaller than the inner diameter of the cylindrical hole, and its inner edge is provided with a chamfer; The radius of the spherical protrusion (42) is equal to the radius of the arc-shaped groove.

5. The absorption spectrum measuring device with optical path adjustment according to claim 4, wherein: The materials of the measurement absorption unit (1), the collimation tooling and the rear cover plate (5) are all stainless steel; Three threaded holes are evenly arranged along the circumference on the rear cover plate (5); There are three adjustment screws (6), which are respectively arranged in the three threaded holes.

6. A method for adjusting the optical path of an absorption spectrum measuring device with optical path adjustment according to any one of claims 1 to 5, characterized in that, It includes the following steps: Connect the other ends of the multimode receiving optical fiber (21) and the single-mode emitting optical fiber (31) to the coupling detection device respectively; adjust the pitch angle of the collimation tooling and the optical axis direction of the second fiber collimator (3) through the adjustment screw (6) to perform laser coupling with the first fiber collimator (2), and at the same time use the coupling detection device to monitor the coupling efficiency of the laser in the multimode receiving optical fiber (21) and the single-mode emitting optical fiber (31). When the coupling efficiency is ≥ -5 dB, complete the optical path adjustment of the absorption spectrum measuring device.

7. The optical path adjustment method of an absorption spectrum measurement device with optical path adjustment according to claim 6, characterized in that, It further includes: After the optical path adjustment is completed, glue can be injected and cured through the gap between the edge of the rear cover plate (5) and the emission end edge of the measurement absorption unit (1).

8. The optical path adjustment method of an absorption spectrum measurement device with optical path adjustment according to claim 7, characterized in that Before connecting the other ends of the multimode receiving optical fiber (21) and the single-mode emitting optical fiber (31) to the coupling detection device respectively, it further includes: Calibrate the output laser power of the coupling detection device.

9. The optical path adjustment method of the absorption spectrum measuring device with optical path adjustment according to claim 8, wherein: The coupling detection device is a Mini-OTDR.

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