Optical fiber macro-bending coupling structure liquid level probe based on dark field detection

An optical fiber macrobending and dark field detection technology, applied in the field of liquid level probes, can solve the problems of poor robustness, low precision and poor stability, and achieve the effects of low power consumption, guaranteed stability and increased strength

Inactive Publication Date: 2014-12-17

ZHONGBEI UNIV

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AI-Extracted Technical Summary

Problems solved by technology

[0003] In order to solve the above problems, the present invention provides a liquid level probe with optical fiber macrobend coupling structure based on dark field detection, which solves the problems of poor stability...

Method used

After described active optical fiber 3 and passive optical fiber 2 are intertwined, overall bending forms macrobending coupling ring, and described high temperature resistant wire 4 is tightly wound on described macrobending coupling ring, and described active optical fiber 3, passive After the source optical fiber 2 and the high-temperature-resistant wire 4 pass through the plastic tube, they are fixed by filling silica gel with the fixing sleeve 1, which reduces unnecessary errors caused by the optical fiber being subjected to external stress changes.

As shown in Figure 3, described active optical fiber 3 and passive optical fiber 2 all adopt the plastic optical fiber of Mitsubishi SK-40, cladding is thin, and flexibility is good.

In sum, this embodiment utilizes the mode of two optical fiber twisted pair, has increased the stability of dark field coupling power and coupling structure and is the consistency of sensor; Utilize the mode of macrobending coupling to sense signal by The bright field is transferred to the dark field. Since the dark field signal is isolated from the light source path, the influence of the light source fluctuation is almost negligible, which greatly improves the system signal-to-noise ratio. At the same time, due to the macrobend dark field coupling, the ratio of the cladding mode in the passive fiber of the TMBCS is much higher than that of the active fiber, thereby further enhancing the CMFTIR effect, and the enhanced effect is remarkable. The sensor is directly affected by the change of the refractive index of the external medium, and the sensitivity of the sensor is improved.

Two optical fibers are made into a twisted-pair macrobending coupling structure (TMBCS), and the fingers lightly touch the TMBCS top, compared with straight optical fiber and single macrobend situation, the forward coupled end output normalized power of passive optical fiber It has dropped by 30%-40%, and the decline has been greatly improved. This is due to the use of macrobending dark field coupling, which makes the ratio of the cladding mode in the passive fiber of TMBCS much higher than that of the active fiber, thereby further enhancing the CMFTIR effect, and the enhanced effect is remarkable.

What liquid level probe adopted is the optical fiber macro-bending coupling structure, and the distortion of mod...

Abstract

The invention discloses an optical fiber macro-bending coupling structure liquid level probe based on dark field detection. The invention provides a liquid level sensing principle based on a cladding mode frustrated total internal reflection (CMFTIR) effect for the first time and successfully applies the principle. The distribution of a mould field in optical fibers is changed based on a macro-bending manner, the occupied ratio of cladding mode energy in the optical fibers is increased, and the CMFTIR effect is enhanced; meanwhile, a macro-bending radiation effect realizes the macro-bending coupling of the two optical fibers; a sensing signal is transmitted to a dark field through the macro-bending coupling manner, and the modulation depth of the coupling process is enhanced; meanwhile, the higher occupied ratio of the cladding mode energy is obtained in the passive optical fibers, and the CMFTIR effect is further enhanced; meanwhile, the stability of the coupling structure and the consistency of a sensor are guaranteed; the signal to noise ratio is effectively improved through detecting the signal of the dark field; the liquid level probe with low cost, low power consumption and high performance is realized, and the distinguishing degree is higher than 4dB.

Application Domain

Machines/enginesLevel indicators +1

Technology Topic

PhysicsSignal-to-noise ratio (imaging) +10

Image

Examples

Experimental program(1)

Example Embodiment

[0051] Example

[0052] CMFTIR effect enhancement experiment (finger touch)

[0053] A single straight optical fiber, one end connected to the led light source, one end to the optical power meter. Lightly touch the fiber with a finger, and the power measured by the power meter does not change, indicating that the CMFTIR effect is hardly observed in the intact straight fiber.

[0054] A single optical fiber forms a macrobend ring structure, one end is connected to an LED light source, and one end is connected to an optical power meter. When a finger touches the top of the bent part of the optical fiber, the normalized power measured by the power meter drops by about 5%, indicating that the CMFTIR effect has increased to a certain extent. This is because the macrobending of the optical fiber causes the change of the internal mode field of the optical fiber, and relatively more cladding modes are generated in the bent optical fiber, and the light touch of the finger causes more cladding modes to radiate out, which causes a decrease in optical power. Although the CMFTIR effect is enhanced at this time, the effect is not obvious.

[0055] Two optical fibers are made into a twisted pair macrobend coupling structure (TMBCS), and the tip of the TMBCS is touched with a finger. Compared with the straight fiber and a single macrobend, the output normalized power of the passive fiber's forward coupling end is reduced by 30 %-40%, the decline is greatly improved. This is due to the use of macrobend dark field coupling, which makes the proportion of cladding modes in the passive fiber of TMBCS much higher than that of the active fiber, thereby further enhancing the CMFTIR effect and the enhancement effect is significant.

[0056] In summary, the twisted-pair macrobend coupling structure can greatly enhance the CMFTIR effect, significantly improve the sensitivity of the sensor, and improve the measurement accuracy.

[0057] Dark field detection greatly improves the signal-to-noise ratio, measurement accuracy and range;

[0058] Due to the temperature drift of the laser or LED light source, the optical power sensor is susceptible to fluctuations in the power of the light source. The usual sensor design requires a temperature compensation circuit, combined with signal processing methods such as reference optical path differential and related operations. The use of lock-in amplifiers to achieve correlation operations to extract weak signals increases system complexity and cost, while also reducing response speed.

[0059] However, the present invention uses the twisted pair macrobend coupling structure to transfer the sensing signal to the dark field through macrobend coupling to realize dark field signal detection. Since the dark field signal is isolated from the light source path, it is less affected by the fluctuation of the light source and has natural characteristics. The advantage of sex to noise ratio. Such as Figure 5 As shown, without any signal processing, the signal-to-noise ratio of the original sensor signal directly obtained by the power meter can reach more than 7dB during the "initial bath", and the signal-to-noise ratio remains above 4dB when the probe is wet.

[0060] In summary, this implementation uses two optical fiber twisted pairs to increase the dark field coupling power and the stability of the coupling structure, that is, the consistency of the sensor; the macro-bend coupling method is used to transfer the sensing signal from the bright field To the dark field, since the dark field signal is isolated from the light source path, the influence of the light source fluctuation is almost negligible, which greatly improves the system signal-to-noise ratio. At the same time, due to the macrobending dark field coupling, the proportion of cladding modes in the passive fiber of TMBCS is much higher than that in the active fiber, thereby further enhancing the CMFTIR effect, and the enhancement effect is significant. The sensor is directly affected by the change of the refractive index of the external medium, and the sensitivity of the sensor is improved.

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Classification and recommendation of technical efficacy words

Enhanced CMFTIR effect

Dark field detection based optical-fiber macrobending coupling structure liquid-level probe

ActiveCN104198014AEnhanced CMFTIR effectGreat modulation depth

Owner:ZHONGBEI UNIV

Optical fiber macro-bending coupling structure liquid level probe based on dark field detection

An optical fiber macrobending and dark field detection technology, applied in the field of liquid level probes, can solve the problems of poor robustness, low precision and poor stability, and achieve the effects of low power consumption, guaranteed stability and increased strength

AI-Extracted Technical Summary

Problems solved by technology

Method used

Abstract

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Examples

Example Embodiment

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Description & Claims & Application Information

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Dark field detection based optical-fiber macrobending coupling structure liquid-level probe