A water body scattering, rayleigh scattering and brillouin scattering measurement technique based on add-drop type filter

Abstract

Based on the Add-Drop filter type filter water Mie scattering, Rayleigh scattering and Brillouin scattering measurement technology, the corresponding implementation by narrow linewidth laser, laser frequency stabilization system, optical transmission system, optical receiving system, cascaded Add-Drop filter, multi-channel photoelectric detection system, data acquisition and processing system. With Add-Drop filter as narrow band optical filter, can separate water Mie scattering, water molecular Rayleigh scattering and water Brillouin scattering, so as to directly measure the water Mie scattering, Rayleigh scattering and Brillouin scattering intensity, and obtain the corresponding high precision parameters.

Description

TECHNICAL FIELD

[0001] The present application relates to a water Mie scattering, Rayleigh scattering and Brillouin scattering measurement technology and implementation method based on an Add-Drop filter, and more particularly to a water Mie scattering, Rayleigh scattering and Brillouin scattering measurement technology using an Add-Drop filter as a narrowband optical filter. BACKGROUND

[0002] When laser is incident on water, it will undergo Mie scattering with suspended particles in water, Rayleigh scattering with water molecules, and Brillouin scattering with phonons in water. Mie scattering and Rayleigh scattering are elastic scattering, and the spectral width of Mie scattering of particles in water is basically the same as the line width of incident laser; the spectral width of Rayleigh scattering of water molecules is about 1 GHz. Water Brillouin scattering includes two parts: Stokes Brillouin scattering and anti-Stokes Brillouin scattering. Within the temperature range of 0-40℃ and the salinity range of 35‰ (seawater salinity), Stokes Brillouin scattering and anti-Stokes Brillouin scattering are located on both sides of the excitation wavelength within the range of ±6.5GHz to ±8.5GHz, and the spectral width is about 0.4GHz to 2GHz.

[0003] According to the spectral characteristics of the three kinds of scattering, a laser with a line width smaller than the spectral width of Rayleigh scattering is used as a light source, and a narrowband optical filter is used to separate the Mie scattering, Rayleigh scattering and Brillouin scattering of water in the spectrum. In the water Mie scattering, Rayleigh scattering and Brillouin scattering measurement technology, the currently used narrowband optical filters include Fabry-Pérot interferometer, molecular (atomic) filter, etc.

[0004] An Add-Drop filter is composed of three parts: a Bus waveguide, a Dropping waveguide, and a coupling unit between the Bus waveguide and the Dropping waveguide. Light is input from the input port of the Bus waveguide, and most of the light is output from the output port of the Bus waveguide with almost no attenuation. When the wavelength of light meets the resonant wavelength of the coupling unit, the light of this wavelength is coupled from the Bus waveguide to the Dropping waveguide and output from the forward or backward port of the Dropping waveguide. Therefore, the output of the Bus waveguide is equivalent to an optical band-stop filter, and the output of the Dropping waveguide is equivalent to an optical band-pass filter.

[0005] The Add-Drop filter is currently mainly applied in the fields of optical communication, biosensors, etc. SUMMARY

[0006] The application aims to provide a water Raman scattering, Rayleigh scattering and Brillouin scattering measurement technology based on an Add-Drop filter as a narrow-band optical filter.

[0007] The application comprises a narrow-line-width laser, a laser frequency stabilization system, an optical transmitting system, an optical receiving system, cascaded Add-Drop filters, a multi-channel photoelectric detection system, a data acquisition and processing system.

[0008] The cascaded Add-Drop filters are divided into three groups, corresponding to water Raman scattering and Rayleigh scattering, water Stokes Brillouin scattering and water anti-Stokes Brillouin scattering.

[0009] The output wavelength of the narrow-line-width laser is locked by the laser frequency stabilization system, the locked wavelength is selected in the group of Add-Drop filters corresponding to water Raman scattering and Rayleigh scattering, and is located at the peak wavelength of the optical band-pass filter of the Add-Drop filter in the middle of the spectral characteristics of the group.

[0010] The frequency-stabilized laser is transmitted into the measured water body by the optical transmitting system, the water echo is received by the optical receiving system and coupled into the cascaded Add-Drop filters. The output of the cascaded Add-Drop filters is converted into an electrical signal by the multi-channel photoelectric detection system and introduced into the data acquisition and processing system.

[0011] The models of water Raman scattering and Rayleigh scattering, Stokes Brillouin scattering and anti-Stokes Brillouin scattering are accurately known, the corresponding signals are filtered out by the three groups of cascaded Add-Drop filters, and the parameters of water Raman scattering, water Rayleigh scattering and water Brillouin scattering can be calculated.

[0012] The line width of the narrow-line-width laser is less than the spectral width of the Add-Drop filter. The free spectral range of the Add-Drop filter is greater than the spectral interval between water Stokes Brillouin scattering and anti-Stokes Brillouin scattering. The spectral interval between the adjacent two Add-Drop filters in each group of cascaded Add-Drop filters is less than the spectral width of water Rayleigh scattering and the spectral width of water Brillouin scattering. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed by the embodiments are briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application.

[0014] Figure 1The Add-Drop filter structure of the present application

[0015] Figure 2 The Add-Drop filter spectrum characteristic diagram of the present application

[0016] Figure 3 The water Raman scattering, Rayleigh scattering and Brillouin scattering measurement system structure based on the Add-Drop filter of the present application

[0017] Figure 4 The spectrum of the cascaded Add-Drop filter and the water Raman scattering, Rayleigh scattering and Brillouin scattering spectrum of the present application

[0018] Figure 5 The water Raman scattering, Rayleigh scattering and Brillouin scattering spectrum filtered by the Add-Drop filter of the present application

[0019] In the figure: 1. Bus waveguide of the Add-Drop filter, 2. Dropping waveguide of the Add-Drop filter, 3. Coupling unit of the Add-Drop filter, 4. Input port of the Bus waveguide, 5. Output port of the Bus waveguide, 6. Backward output port of the Dropping waveguide, 7. Forward output port of the Dropping waveguide, 8. Bandpass spectrum output by the backward or forward output port of the Dropping waveguide of the Add-Drop filter, 9. Band-stop spectrum output by the output port of the Bus waveguide of the Add-Drop filter, 10. Spectrum width (full width at half maximum) of the Add-Drop filter, 11. Free spectral range of the Add-Drop filter, 12. Narrow linewidth laser, 13. Laser frequency stabilization system, 14. Optical transmitting system, 15. Optical receiving system, 16. Cascaded Add-Drop filter, 17. Multi-channel photoelectric detection system, 18. Data acquisition and processing system, 19. Bandpass spectrum of the cascaded Add-Drop filter, 20. Laser wavelength locking point, 21. Water Raman scattering, 22. Water Rayleigh scattering, 23. Water Stokes Brillouin scattering, 24. Water anti Stokes Brillouin scattering, 25. Spectral interval between adjacent two Add-Drop filters in each group of cascaded Add-Drop filters, 26. λ L Water Raman scattering and water Rayleigh scattering signals filtered at 26, 27. Water Rayleigh scattering filtered, 28. Water Stokes Brillouin scattering signal filtered, 29. Water anti Stokes Brillouin scattering signal filtered. DETAILED DESCRIPTION

[0020] The application aims to provide a water Raman scattering, Rayleigh scattering and Brillouin scattering measurement technology and implementation method based on an Add-Drop filter, so as to solve the technical problems in the related field. In order to make the technical problems and technical solutions of the application clearer, the application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application.

[0021] The Add-Drop filter structure of the application is shown in Figure 1 The Add-Drop filter spectrum characteristic diagram is shown in Figure 2

[0022] The Add-Drop filter is composed of three parts: the Bus waveguide (1) of the Add-Drop filter, the Dropping waveguide (2) of the Add-Drop filter, and the coupling unit (3) of the Add-Drop filter between the Bus waveguide and the Dropping waveguide. Light is input from the Bus waveguide input port (4), and most of the light is output from the Bus waveguide output port (5) with almost no attenuation. When the wavelength of light meets the resonance wavelength of the coupling unit (3) of the Add-Drop filter, the light of the wavelength is coupled from the Bus waveguide (1) of the Add-Drop filter to the Dropping waveguide (2) of the Add-Drop filter, and is output from the Dropping waveguide backward output port (6) or the Dropping waveguide forward output port (7). Therefore, the Dropping waveguide backward output port (6) or the Dropping waveguide forward output port (7) is equivalent to an optical bandpass filter, and the corresponding spectrum characteristic is (8); the Bus waveguide output port (5) is equivalent to an optical bandstop filter, and the corresponding spectrum characteristic is (9). The spectrum width (full width at half maximum) (10) of the corresponding Add-Drop filter of (8) and (9), and the free spectral range (11) of the corresponding Add-Drop filter.

[0023] The Add-Drop filter structure of the application is shown in Figure 3 The Add-Drop filter spectrum characteristic diagram is shown in

[0024] ​The narrow line width laser (12) is used as the light source, and the laser wavelength is locked by the laser frequency stabilization system (13). The frequency-locked laser enters the measured water body through the optical emission system (14). The laser echo of the water body is received by the optical receiving system (15) and introduced into the cascaded Add-Drop type filter optical frequency discriminator (16). The output of the cascaded Add-Drop type filter (16) is detected by the multi-channel photoelectric detection system (17) and introduced into the data acquisition and processing system (18).

[0025] The spectrum of the cascaded Add-Drop type filter and the water body Mie scattering, Rayleigh scattering and Brillouin scattering spectrum are as shown in the figure. Figure 4

[0026] The cascaded Add-Drop type filter is divided into three groups: corresponding to the water Mie scattering (21) and the water Rayleigh scattering (22) with the wavelength λ L as the center; the water Stokes Brillouin scattering (23) with the wavelength λ N as the center; and the water anti Stokes Brillouin scattering (24) with the wavelength λ M as the center. λ N and λ M are located at about 7.5GHz on both sides of λ L .

[0027] The cascaded Add-Drop type filter is to connect the output port (5) of the Bus waveguide of the previous Add-Drop type filter to the input port (4) of the Bus waveguide of the next Add-Drop type filter, and the backward output port (6) of the Dropping waveguide or the forward output port (7) of the Dropping waveguide is used as the output of the current stage.

[0028] The laser wavelength is locked at the laser wavelength locking point (20) in Figure 4 , which corresponds to the Add-Drop type filter with the wavelength λ L . The center wavelengths of the water Mie scattering (21) and the water Rayleigh scattering (22) are also λ L . The present application requires that the line width of the narrow line width laser (12) is less than the spectral width (full width at half maximum) (10) based on the Add-Drop type filter, and the free spectral range (11) of the Add-Drop type filter is greater than the wavelength interval between the water Stokes Brillouin scattering (23) and the anti Stokes Brillouin scattering (24). The spectral interval (25) of the adjacent two Add-Drop type filters in each group of cascaded Add-Drop type filters is less than the spectral width of the water Rayleigh scattering and the spectral width of the water Brillouin scattering.

[0029] Figure 4 ​The middle Add-Drop type filter filters out the water Raman scattering and water Rayleigh scattering signals (26) at wavelength λ L The corresponding Add-Drop type filter can filter out the water Rayleigh scattering (27) at wavelength λ L-2 The corresponding Add-Drop type filter can filter out the water Stokes Brillouin scattering signals (28) at wavelength λ L-1 The corresponding Add-Drop type filter can filter out the water anti Stokes Brillouin scattering signals (29) at wavelength λ L+1 The corresponding Add-Drop type filter can filter out the water Raman scattering and water Rayleigh scattering signals (26) at wavelength λ L+2 The corresponding Add-Drop type filter can filter out the water Rayleigh scattering (27) at wavelength λ N-2 The corresponding Add-Drop type filter can filter out the water Stokes Brillouin scattering signals (28) at wavelength λ N-1 The corresponding Add-Drop type filter can filter out the water anti Stokes Brillouin scattering signals (29) at wavelength λ N The corresponding Add-Drop type filter can filter out the water Raman scattering and water Rayleigh scattering signals (26) at wavelength λ N+1 The corresponding Add-Drop type filter can filter out the water Rayleigh scattering (27) at wavelength λ N+2 The corresponding Add-Drop type filter can filter out the water Stokes Brillouin scattering signals (28) at wavelength λ M-2 The corresponding Add-Drop type filter can filter out the water anti Stokes Brillouin scattering signals (29) at wavelength λ M-1 The corresponding Add-Drop type filter can filter out the water Raman scattering and water Rayleigh scattering signals (26) at wavelength λ M The corresponding Add-Drop type filter can filter out the water Rayleigh scattering (27) at wavelength λ M+1 The corresponding Add-Drop type filter can filter out the water Stokes Brillouin scattering signals (28) at wavelength λ M+2 The corresponding Add-Drop type filter can filter out the water anti Stokes Brillouin scattering signals (29) at wavelength λ

[0030] Because the bandpass spectral characteristics (8) of the Add-Drop type filter are accurately known, and the models of the water Raman scattering, water Rayleigh scattering, water Stokes Brillouin scattering and water anti Stokes Brillouin scattering are accurately known, the parameters of the water Raman scattering, water Rayleigh scattering and water Brillouin scattering can be calculated by comprehensively considering the signal intensities of (26), (27), (28) and (29). Figure 5

[0031] In summary, Figure 3 The water Raman scattering, water Rayleigh scattering and water Brillouin scattering measurement technology based on the Add-Drop type filter can directly measure the water elastic scattering and Brillouin scattering, and obtain corresponding high-precision parameters.

[0032] It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art.​

Claims

1. A water body measurement technique based on Add-Drop filter type for measuring Mie scattering, Rayleigh scattering and Brillouin scattering, characterized in that: The system is composed of a narrow line width laser, a laser frequency stabilization system, an optical transmitting system, an optical receiving system, a cascaded Add-Drop filter, a multi-channel photoelectric detection system, a data acquisition and processing system; the cascaded Add-Drop filter is divided into three groups, which correspond to water Mie scattering and Rayleigh scattering, water Stokes Brillouin scattering, and water anti Stokes Brillouin scattering respectively; The output wavelength of the narrow line width laser is locked by the laser frequency stabilization system, and the locked wavelength is selected in the group of Add-Drop filters corresponding to water Mie scattering and Rayleigh scattering, and is located at the peak wavelength of the optical band pass filter of the Add-Drop filter in the middle of the spectral characteristics of the group; The frequency stabilized laser is transmitted into the measured water body by the optical transmitting system, and the water echo is received by the optical receiving system and coupled into the cascaded Add-Drop filter; the output of the cascaded Add-Drop filter is converted into an electrical signal by the multi-channel photoelectric detection system, and is introduced into the data acquisition and processing system; The models of water Mie scattering and Rayleigh scattering, Stokes Brillouin scattering and anti Stokes Brillouin scattering are accurately known, and the corresponding signals filtered by the three groups of cascaded Add-Drop filters can be used to calculate the parameters of water Mie scattering, water Rayleigh scattering and water Brillouin scattering.

2. The water backscattering, Rayleigh scattering and Brillouin scattering measurement technique based on Add-Drop filter according to claim 1, characterized in that: The line width of the narrow line width laser is less than the spectral width of the Add-Drop filter.

3. The water backscattering, Rayleigh scattering and Brillouin scattering measurement technique based on Add-Drop filter according to claim 1, characterized in that: The free spectral range of the Add-Drop filter is greater than the spectral interval between water Stokes Brillouin scattering and anti Stokes Brillouin scattering.

4. The water backscattering, Rayleigh scattering and Brillouin scattering measurement technique based on Add-Drop filter according to claim 1, characterized in that: The spectral interval between the adjacent two Add-Drop filters in each group of cascaded Add-Drop filters is less than the spectral width of water Rayleigh scattering and the spectral width of water Brillouin scattering.

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