A Chirped Long Period Fiber Grating Sensor for Measuring Wind Pressure

Abstract

The present invention discloses a chirped long-period fiber grating sensor for measuring wind pressure, which is composed of a broadband light source, a filter, a sensing unit, a sensing unit fixing device, a spectrometer, and single-mode optical fibers used for connection. By limiting the broadband laser output by the broadband light source to a specific wavelength through the filter and then inputting it into the sensing unit, when the wind blows towards the sensing unit, it will bend, thereby driving the chirped long-period fiber grating embedded therein to deform. As a result, the chirped signal will be weakened, and the intensity of the transmission spectrum will also change accordingly, which can be used to detect the environmental wind pressure. At the same time, the transmission peak bandwidth of the sensing unit is very wide and has good stability, with good sensitivity and good application prospects.

Description

Technical Field

[0001] The present invention provides a chirped long-period fiber grating sensor for measuring wind pressure, belonging to the field of fiber optic sensing technology. Background Art

[0002] A chirped long-period fiber grating is a type of long-period fiber grating, which is a special long-period fiber grating with a period that continuously changes along the axial direction of the optical fiber; because its transmission spectrum has a very wide bandwidth, many wavelength band rejections can be achieved in the transmission spectrum, suitable for the characteristics of multi-wavelength filtering, and has special advantages in optical communication.

[0003] Currently, wind pressure is mainly measured by wind speed sensors, mainly including cup anemometers, propeller anemometers, hot-wire anemometers, and acoustic anemometers. A cup anemometer has three hemispherical empty cups fixed on a frame at 120° to each other and all facing the same direction. The entire frame and the cups are fixed on a freely rotating shaft. Under the action of the wind, the cups rotate around the shaft, and the rotation speed is proportional to the wind speed; a hot-wire anemometer consists of a metal wire heated by an electric current. According to the flowing air that cools it, the rate of heat dissipation of the metal wire is used to determine the magnitude of the wind speed; an acoustic anemometer measures the wind speed based on the characteristic that the wind speed component in the direction of sound wave propagation will increase the sound wave propagation speed. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a chirped long-period fiber grating sensor for measuring wind pressure. By limiting the broadband laser output by a broadband light source to a specific wavelength through a filter and then inputting it into the sensing unit, when the wind blows towards the sensing unit, it will bend, thereby driving the chirped long-period fiber grating embedded therein to deform. As a result, the chirped signal will be weakened, and the light intensity of the transmission spectrum will also change accordingly. It can be used to detect the environmental wind pressure. At the same time, the transmission peak bandwidth of the sensing unit is very wide and has good stability, with good sensitivity and good application prospects.

[0005] A chirped long-period fiber grating sensor for measuring wind pressure, characterized in that it consists of a broadband light source (1), a filter (2), a sensing unit (3), a sensing unit fixing device (4), a spectrometer (5), and a single-mode optical fiber (6) for connection; characterized in that: the sensing unit (3) consists of a chirped long-period fiber grating (31) and a PDMS film layer (32); the sensing unit (3) is a chirped long-period fiber grating (31) embedded in a cuboid-shaped PDMS film layer (32) in an arc shape, with a length of 2 cm and a height of 1 cm; the light output by the broadband light source (1) is transmitted by the single-mode optical fiber (6) to the filter (2) and then the optical signal is input into the sensing unit (3). When the wind blows towards the sensing unit (3), it will bend, thereby driving the chirped long-period fiber grating (31) embedded therein to deform, resulting in a decrease in the output light intensity. Subsequently, it is transmitted to the spectrometer (5) to analyze the change in the light intensity of the chirped optical signal transmission spectrum, thereby obtaining the magnitude of the wind pressure. At the same time, due to the broadband filtering ability of the chirped long-period fiber grating (31), the transmitted light intensity drifts at multiple wavelengths to form a mutual comparison, and the wind pressure can be measured more accurately.

[0006] Among them, the wavelength range of the broadband light source (1) is 1520 nm to 1570 nm.

[0007] Among them, the filter (2) is a band-pass filter.

[0008] Among them, the chirped long-period fiber grating (31) in the sensing unit (3) is a linear chirped long-period fiber grating, with a diameter of 100 μm, a length of 2 cm, a core refractive index of 1.45, and a refractive index modulation amplitude of 5×10 -5 and a chirp coefficient of 1×10 -8 nm / cm.

[0009] Among them, the thickness of the PDMS film layer (32) in the sensing unit (3) is 2 mm, the refractive index is 1.42, the Young's modulus is 800 kPa, and the Poisson's ratio is 0.49.

[0010] Among them, the sensing unit fixing device (4) needs to accurately fix the sensing unit (3) on the left and right sides thereof respectively.

[0011] The working principle of the present invention is: the transmission spectrum of the chirped long-period fiber grating has a close relationship with the magnitude of the pressure it receives. When the external force applied to the optical fiber changes, due to the elasto-optic effect, the refractive index of the optical fiber becomes:

[0012]

[0013] In the formula, n 0 is the initial refractive index of the optical fiber, and ν pν and Y represent the Poisson's ratio and Young's modulus of the optical fiber respectively, D represents the diameter of the optical fiber, l is the length of the part of the optical fiber subjected to external force, and p 11 and p 12 are both the photoelastic coefficients of the optical fiber, F is the magnitude of the force applied to the optical fiber. As the force applied to the optical fiber gradually increases, the refractive indices of the core and cladding of the optical fiber will gradually increase; after the optical fiber is subjected to external force, its refractive index will produce a periodic modulation along the axial direction of the optical fiber. The coupling efficiency expression between the core mode of the light transmitted in the optical fiber and the m-th order cladding mode LP 1m is:

[0014] l represents the length of the grating, and K g represents the coupling constant of the grating, where where is the detuning parameter. When δ is 0, the coupling rate at the resonant wavelength of the chirped long-period fiber grating is related to the force received by the optical fiber.

[0015] The beneficial effects of the present invention are: a chirped long-period fiber grating (3) in which the change in wind pressure is linearly related to the light intensity of the transmission spectrum is proposed as a sensing unit, and this sensor is also particularly sensitive to changes in external wind pressure; a new method that is relatively simple to build, reliable, and highly sensitive is provided for wind pressure detection. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the characteristic device of a chirped long-period fiber grating sensor for measuring wind pressure according to the present invention.

[0017] Figure 2 is a schematic diagram of the structure of the sensing unit of the present invention.

[0018] Figure 3 is a schematic diagram of the structure of the sensing unit under wind-pressure bending according to the present invention. Detailed Embodiments

[0019] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0020] See the appendix Figure 1, A chirped long-period fiber grating sensor for measuring wind pressure, characterized in that: it is composed of a broadband light source (1), a filter (2), a sensing unit (3), a sensing unit fixing device (4), a spectrometer (5), and a single-mode optical fiber (6) used for connection; characterized in that: the sensing unit (3) is composed of a chirped long-period fiber grating (31) and a PDMS film layer (32); the sensing unit (3) is a chirped long-period fiber grating (31) embedded in a cuboid-shaped PDMS film layer (32) in an arc shape, with a length of 2 cm and a height of 1 cm; the output light of the broadband light source (1) is transmitted by the single-mode optical fiber (6) to the filter (2) and then the optical signal is input into the sensing unit (3). When the wind blows towards the sensing unit (3), it will bend, thereby driving the chirped long-period fiber grating (31) embedded therein to deform, resulting in a decrease in the output light intensity. Subsequently, it is transmitted to the spectrometer (5) to analyze the change in the light intensity of the transmitted spectrum of the chirped optical signal, thereby obtaining the magnitude of the wind pressure. At the same time, due to the broadband filtering ability of the chirped long-period fiber grating (31), the transmitted light intensity drifts at multiple wavelengths to form a mutual comparison, and the wind pressure can be measured more accurately.

Claims

1. A chirped long-period fiber grating sensor for measuring wind pressure, characterized in that: It is composed of a broadband light source (1), a filter (2), a sensing unit (3), a sensing unit fixing device (4), a spectrometer (5), and a single-mode optical fiber (6) used for connection; characterized in that: the sensing unit (3) is composed of a chirped long-period fiber grating (31) and a PDMS film layer (32); the sensing unit (3) is a chirped long-period fiber grating (31) embedded in a cuboid-shaped PDMS film layer (32) in an arc shape, with a length of 2 cm and a height of 1 cm; The working principle of the chirped long-period fiber grating sensor for measuring wind pressure is: the transmission spectrum of the chirped long-period fiber grating has a close relationship with the magnitude of the pressure it receives. When the external force applied to the optical fiber changes, due to the elasto-optic effect, as the force on the optical fiber gradually increases, the refractive indices of the core and cladding of the optical fiber will gradually increase, and the refractive index of the optical fiber will be periodically modulated along the optical fiber axis, resulting in a change in the light intensity of the transmission spectrum; The output light of the broadband light source (1) is transmitted by the single-mode optical fiber (6) to the filter (2), and then the optical signal is input into the sensing unit (3). When the wind blows towards the sensing unit (3), the PDMS film layer (32) will bend, thereby driving the chirped long-period fiber grating (31) embedded therein to deform, resulting in a decrease in the output light intensity. Subsequently, it is transmitted to the spectrometer (5) to analyze the change in the light intensity of the chirped optical signal transmission spectrum, thereby obtaining the magnitude of the wind pressure. At the same time, due to the broadband filtering ability of the chirped long-period fiber grating (31), the transmitted light intensity drifts at multiple wavelengths to form a mutual comparison, enabling more accurate measurement of the wind pressure; The wavelength range of the broadband light source (1) is 1520 nm to 1570 nm; the filter (2) is a band-pass filter.

2. The chirped long-period fiber grating sensor for measuring wind pressure according to claim 1, characterized in that: The chirped long-period fiber grating (31) in the sensing unit (3) is a linear chirped long-period fiber grating, with a diameter of 100 μm, a length of 2 cm, a core refractive index of 1.45, and a refractive index modulation amplitude of 5×10 -5 , and a chirp coefficient of 1×10 -8 nm / cm.

3. The chirped long-period fiber grating sensor for measuring wind pressure according to claim 1, characterized in that: The thickness of the PDMS film layer (32) in the sensing unit (3) is 2 mm, the refractive index is 1.42, the Young's modulus is 800 kPa, and the Poisson's ratio is 0.

49.

4. The chirped long-period fiber grating sensor for measuring wind pressure according to claim 1, characterized in that: The sensing unit fixing device (4) needs to accurately fix the sensing unit (3) on its left and right sides respectively.

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