TWI585373B - Fiber grating sensing system for liquid - Google Patents

Description

Fiber Bragg Grating Liquid Sensing System

The present invention relates to a fiber grating sensing system, and more particularly to a fiber grating liquid sensing system having two or more sensing heads.

Compared with traditional electronic sensors, optical sensors have high sensitivity to subtle changes. With the rapid development of optical fiber communication, optical fiber sensing technology has also developed rapidly. The advantages of fiber sensing include high sensitivity, low attenuation rate, small size, corrosion resistance and electromagnetic interference, high temperature resistance, long life, etc. Therefore, the application of optical fiber to sense changes in strain, temperature, pressure, current, gas, etc. Developed.

The parameters of the liquid, such as liquid level, liquid temperature or refractive index, etc., can be measured using a fiber optic sensing system. The conventional fiber sensing system includes two optical fibers, each of which is combined with a sensor, and two different liquid parameters are obtained by matrix operation. This kind of parameter measurement using independent gratings and architectures for independent variables, the measurement of liquid parameter changes caused by complex changes in the real environment is indirect, and because of the need for two fibers, complex.

In addition, fiber Bragg gratings (FBGs) are now used as fiber optic sensors, such as short-period fiber gratings or long-period fiber gratings. Short-period fiber gratings, also known as reflective fiber gratings or Bragg fiber gratings, have a coupling direction and a opposite direction of propagation; long-period fiber gratings, also known as transmissive fiber gratings, have a coupling direction that is consistent with the direction of propagation. When the fiber grating is affected by the external environment, the effective refractive index and the grating period are changed, and the corresponding reflection center wavelength λ _B is drifted. Therefore, the split-wave multiplexing characteristics, coupling direction and mode propagation direction properties of the two are different.

Therefore, in order to produce a more efficient fiber grating sensing system, as a related industry needs, it is necessary to develop a new fiber grating sensing system, thereby improving the sensing efficiency of the fiber grating sensing system and reducing the sensor. manufacturing cost.

In order to solve the above problems, the present invention provides a fiber grating liquid sensing system, which combines a Bragg grating and a long-period grating double grating, and utilizes the characteristics of the split-wave multiplexing of the two and the characteristics of the coupling direction and the mode propagation direction. A plurality of liquid parameters are measured.

In order to solve the above problems, the present invention provides a fiber grating liquid sensing system. The Bragg fiber grating can be used for water level sensing, and the long period fiber grating can be used as a sensing refractive index or water temperature, so that the liquid level can be sensed simultaneously. Liquid temperature, or changes in liquid level and refractive index, can be applied to water quality, water temperature, refractive index and concentration assessment measurement applications.

In order to solve the foregoing problems, the present invention provides a fiber grating liquid sensing system. A single sensing architecture can simultaneously measure different liquid level, liquid temperature and liquid refractive index changes, and transmit signals measured by the sensing head to the light. An optical spectrum analyzer (OSA) analyzes and observes the changes in environmental parameters to improve the convenience of remote monitoring, save labor costs, and improve safety and reliability.

According to the foregoing, the present invention provides a fiber grating liquid sensing system, comprising: An optical fiber; a liquid characteristic sensing head disposed on the optical fiber; and a liquid level sensing head disposed on the optical fiber, wherein the liquid characteristic sensing head and the liquid level sensing head simultaneously measure a plurality of liquid liquids Parameters, the liquid parameters include a liquid level parameter sensed by the liquid level sensing head.

According to the above, a fiber grating liquid sensing system of the present invention comprises two sensing heads: a liquid property sensing head and a liquid level sensing head, which can simultaneously sense other liquids such as liquid level, liquid temperature or refractive index. parameter. Liquid characteristic sensing is realized by long-period fiber grating, liquid level sensing is realized by short-period fiber grating and designed as fiber laser light source, and broadband light source and fiber laser are integrated into the same optical path, and respectively sensed. The refractive index (or temperature) of the liquid and the depth of the liquid level enable a single fiber-optic configuration of the two sensing heads to achieve simultaneous sensing of a plurality of liquid parameters.

Therefore, the advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

10‧‧‧Fiber grating liquid sensing system

12‧‧‧ fiber

14‧‧‧Liquid property sensing head

16‧‧‧ Liquid level sensor head

18‧‧‧ Gain Media Parts (Figure 1A)

18‧‧‧Semiconductor Optical Amplifier (Figure 1B)

22‧‧‧Reflecting parts

24‧‧‧Dividing multiplex coupler

26‧‧‧ pump laser source

28‧‧‧Light spectrum analyzer

30‧‧‧ compartment

32‧‧‧ Container

34‧‧‧Liquid

40‧‧‧ Air

42‧‧‧Long-period fiber grating

44‧‧‧Viscos

46‧‧‧Mold

62‧‧‧Carbon fiber composite sheets

64‧‧‧Sense head

65‧‧‧ gap

66‧‧‧ Prague fiber grating

69‧‧‧Hydraulic

FIG. 1A is a schematic view showing the structure of a fiber grating liquid sensing system and a sample thereof according to the present invention.

FIG. 1B is a schematic view showing the structure of the fiber grating liquid sensing system and the sample thereof of the present invention.

2 is a schematic structural view of an embodiment of a liquid property sensing head of the present invention.

3 and 4 are respectively a schematic side perspective view and a front view of the structure of the embodiment of the liquid level sensing head of the present invention.

5A and 5B are schematic views showing the structure of the embodiment of the liquid level sensing head of the present invention, which is a perspective view of the side after the force is applied.

The invention is described in detail below. The preferred embodiment is merely illustrative and not intended to limit the invention, and FIG. 1A is a schematic diagram of the structure of the fiber grating liquid sensing system and its sample of the present invention.

Referring to FIG. 1A, the fiber grating liquid sensing system 10 of the present invention includes an optical fiber 12, a liquid property sensing head 14, a liquid level sensing head 16, a gain medium component 18, and a reflective component 22.

Still in the embodiment of the present invention as shown in FIG. 1A, in the fiber grating liquid sensing system 10, the sample to be measured is the liquid 34 in the container 32, and when measured, the liquid characteristic sensing head 14 is sensed in liquid level. The probe 16, the gain medium component 18, and the light reflecting component 22 can all be immersed in the liquid 34. Secondly, the fiber grating liquid sensing system 10 of the present invention is a plurality of liquid parameters that can be used to sense the liquid 34. The liquid parameters herein include liquid levels and other liquid characteristics such as temperature and refractive index, which will be described later.

As shown in FIG. 1A, the fiber grating liquid sensing system 10 may further include a Wavelength Division Multiplexing Coupler (WDM Coupler), a pump laser diode 26, and an optical spectrum analyzer 28 ( An optical spectrum analyzer (OSA) or associated detection instrument, wherein the split-wave multiplexer 24 is coupled to the optical fiber 12, the pump laser source 26, and the optical spectrum analyzer 28, respectively.

Continuing with the embodiment of the invention as shown in FIG. 1A, the liquid property sensing head 14 includes a sensing head that can measure the characteristics of the liquid 34, such as, but not limited to, liquid characteristics such as liquid temperature or liquid refractive index, and the like.

In addition, the gain medium component 18, the split multiplexer 24, and the pump laser source 26, as shown in Fig. 1B, can be simultaneously removed to replace the function with a semiconductor optical amplifier (SOA) 18.

2 is a schematic structural view of an embodiment of a liquid property sensing head of the present invention. Please Referring to Figures 1A and 2 above, in one embodiment, the liquid property sensing head 14 includes a long period fiber grating 42 that is sensitive to small changes in curvature due to long period fiber gratings, in order to avoid long period fiber gratings. The wavelength drift caused by the deformation of 42 affects the sensing result. In the present invention, the long-period fiber grating 42 is straightened, and the optical fiber 12 extending at both ends of the long-period fiber grating 42 is adhered to the mold 46 through the adhesive 44. While the mold 46 can be a flat-box shape, in addition to being secured by the adhesive 44, its materials and geometries provide strength to straighten the long-period fiber grating 42.

In addition, in FIG. 2, the gain medium component 18 may be an Erbium-doped fiber amplifier (EDF amplifier) which is capable of incorporating a certain concentration of erbium ions (Er ³ ) in the core of the optical fiber 12. ⁺ ) is implemented and distributed throughout the fiber 12. The gain medium component 18 functions to generate a spontaneously amplified radiation from the light source to form a broad spectrum light source. The reflecting member 22 may be a mirror or a reflective coating layer on the end surface of the optical fiber 12, but the present invention is not limited to the above. Also shown in FIG. 2, the liquid level sensing head 16 includes a short period fiber grating that senses the level of the liquid 34 in the container 32.

3 and 4 are respectively a liquid level sensing head of the present invention, and a schematic side perspective view and a front view of the structure of the embodiment. The liquid level sensing head 16 includes a sensing head 64 composed of a closed hollow stainless steel cylinder, a carbon fiber reinforced plastic film (CFRP film) adhered to the notch 65 on the surface of the sensing head 64, and a paste. A Bragg fiber grating 66 on the carbon fiber composite sheet 62.

Still as shown in Figures 3 and 4, in one embodiment, the advantage of the sensing head 64 being of stainless steel is that it has a specific gravity greater than that of most liquids, and can overcome the buoyancy of most liquids to measure the depth of the liquid. In addition, the stainless steel material has strong anti-oxidation ability and is not easy to rust, and at the same time has corrosion resistance, and is suitable for long-term use in indoor and outdoor liquid level sensing head design. Secondly, The sensing head 64 is designed to pass through the hollow cylinder such that the hollow cylinder is covered with an air bladder. Further, the carbon fiber composite material sheet 62 has a size substantially the same as or slightly larger than the notch 65. Moreover, the carbon fiber composite sheet 62 can be designed with different thicknesses and stacking patterns for different load requirements, such as a two-layer structure of a single layer or two carbon fiber composite materials, preferably a single layer carbon fiber composite material, because of its performance. The linearity is preferred, but the invention is not limited thereto. Furthermore, the Bragg fiber grating 66 is designed as a fiber laser output to improve sensing sensitivity and peak light power.

FIG. 5A is a side perspective view showing the structure of the liquid level sensing head of the present invention. Referring to Figures 4 and 5A, the principle of sensing the liquid level is that since the carbon fiber composite sheet 62 has plasticity, the hydraulic pressure 69 increases as the depth of the liquid becomes deeper. At this time, the hydraulic pressure 69 causes the air bladder in the sensing head 64 to be reduced in compression volume, thereby causing the carbon fiber composite material sheet 62 to be deformed inward, and the period of the Bragg fiber grating 66 adhered to the carbon fiber composite material sheet 62 is due to the hydraulic pressure 69. The extrusion changes and causes the linear laser output wavelength to drift toward a short wavelength.

The operating principle of the present invention uses the "ideal gas equation" as follows: PV = nRT

P: air pressure

V: volume

n: moles

R: constant

T: absolute temperature

The volume (V) is inversely proportional to the pressure (P) when nRT is constant. Therefore, as shown in Fig. 5B, the optical fiber 12 is located at the bottom of the figure. When the water level of the liquid 34 is deeper, the hydraulic pressure will be larger, and the water pressure will press the Bragg fiber grating 66 through the spacer 30, so that the pressure of the air 40 is increased. . When Prague fiber optic light When the grid 66 is under pressure, the reflection (or penetration) of the spectrum changes, so that it can withstand several times or even 10 times the pressure. That is, due to the principle of "ideal gas equation", it is possible to reduce the barrier layer and even the compressed air layer to become the original 1/10 volume, and the structure shown in Fig. 5A can be used for less than 2 atmospheres. 40 is still difficult to compress the original volume to more than one-half.

Referring to FIG. 1 , according to the foregoing, the fiber grating liquid sensing system architecture of the present invention has an output spectrum of a fiber laser and a long period fiber grating penetrating a wide spectrum light source. The pump laser source 26 emits a beam of 1480 nm wavelength, which contains the bands of C-band and L-band. The split-wave multiplexer 24 directs the pump laser source 26 into the optical fiber 12, which produces forward and backward spontaneously amplified radiation through the gain medium component 18, and the forward spontaneously amplified radiation is reflected by the reflective component 22 The reflected, forward and backward spontaneously amplified radiation encounters a Bragg fiber grating of the liquid level sensing head 16 that reflects a particular wavelength. Except for the band of this particular wavelength, the remaining bands will penetrate the Bragg fiber grating of the liquid level sensing head 16 and become the broad spectrum source of the long period fiber grating of the liquid characteristic sensing head 14.

The structure of the present invention can simultaneously sense the liquid level and liquid parameters other than the liquid level, such as liquid temperature or refractive index, when measuring a sample liquid. It can be applied to the field and place of water quality monitoring, and the application field can be as far as the remote turbidity monitoring of the water quality of the water tower in commercial or residential places such as buildings, or the sensing temperature or concentration as small as the milk brewing of the baby, so the use is very Wide range to meet the needs of different industries.

The above is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention; all other equivalent changes or modifications which are not departing from the spirit of the present invention should be included in the following. Within the scope of the patent application.

10‧‧‧Fiber grating liquid sensing system

12‧‧‧ fiber

14‧‧‧Liquid property sensing head

16‧‧‧ Liquid level sensor head

18‧‧‧ Gain media parts

22‧‧‧Reflecting parts

24‧‧‧Dividing multiplex coupler

26‧‧‧ pump laser source

28‧‧‧Light spectrum analyzer

32‧‧‧ Container

34‧‧‧Liquid

Claims (13)

A fiber grating liquid sensing system includes at least: an optical fiber; a liquid characteristic sensing head disposed on the optical fiber; and a liquid level sensing head disposed on the optical fiber, wherein the liquid characteristic sensing head and the The liquid level sensing head simultaneously measures a plurality of liquid parameters of the liquid, the plurality of liquid parameters including a liquid level parameter sensed by the liquid level sensing head, wherein the liquid level sensing head comprises a closed hollow cylinder A sensing head, a carbon fiber composite sheet adhered to one of the closed hollow cylindrical surfaces, and a Bragg fiber grating fixed to the carbon fiber composite sheet. The fiber grating liquid sensing system of claim 1, wherein the liquid property sensing head comprises a long period fiber grating and a mold for fixing the long period fiber grating. The fiber grating liquid sensing system of claim 1, wherein the closed hollow cylinder is made of a stainless steel material. The fiber grating liquid sensing system of claim 1, wherein the liquid parameter comprises a liquid temperature or a liquid refractive index sensed by the liquid property sensing head. The fiber grating liquid sensing system according to the first to fourth aspects of the patent application scope further includes a split-wave multiplex coupler for connecting the fiber. The fiber grating liquid sensing system of claim 5, further comprising a pump laser source coupled to the split multiplex coupler. The fiber grating liquid sensing system of claim 1 to 4, wherein the fiber further comprises a gain medium component. The fiber grating liquid sensing system of claim 7, wherein the gain medium component comprises erbium ions doped in the fiber. The fiber grating head sensing system according to any one of claims 1 to 4, further comprising a reflecting member disposed at a mirror end of the fiber or at the end of the fiber A reflective coating of the inner surface. A fiber grating liquid sensing system includes at least: an optical fiber; a liquid characteristic sensing head disposed on the optical fiber; and a liquid level sensing head disposed on the optical fiber, wherein the liquid level sensing head includes a closed a sensing head formed by a hollow cylinder, a carbon fiber composite material sheet adhered to a surface of the closed hollow cylinder, and a Bragg fiber grating fixed on the carbon fiber composite material sheet, wherein the closed hollow cylinder is The stainless steel material is prepared, wherein the liquid property sensing head and the liquid level sensing head simultaneously measure a plurality of liquid parameters of the liquid, the plurality of liquid parameters including a liquid level parameter sensed by the liquid level sensing head. The fiber grating liquid sensing system of claim 10, wherein the liquid property sensing head comprises a long period fiber grating and a mold for fixing the long period fiber grating. The fiber grating liquid sensing system of claim 10, wherein the liquid parameter comprises a liquid temperature or a liquid refractive index sensed by the liquid property sensing head. The fiber grating liquid sensing system described in claims 10 to 12 further includes a semiconductor optical amplifier (SOA) to connect the fibers.