CN112485225A

CN112485225A - Optical fiber probe based on laser interference

Info

Publication number: CN112485225A
Application number: CN201910868560.1A
Authority: CN
Inventors: 杨炳雄; 李雷
Original assignee: Dalian Actech Microwave Photoelectron Engneering Research Co ltd; Nanjing University of Aeronautics and Astronautics
Current assignee: Dalian Actech Microwave Photoelectron Engneering Research Co ltd; Nanjing University of Aeronautics and Astronautics
Priority date: 2019-09-12
Filing date: 2019-09-12
Publication date: 2021-03-12

Abstract

The invention discloses a fiber probe based on laser interference, which comprises: the optical fiber branching device, the external incident light source is divided into at least 2 bundles through the optical fiber branching device 1, and the bundles enter the gas detection loop and the reference loop; in said gas detection circuit and reference circuit; the detection loop at least comprises a transmitting collimator, a receiving collimator and an open gas detection area positioned between the two collimators; the reference loop at least comprises a transmitting collimator, a receiving collimator and an open reference area positioned between the transmitting collimator and the receiving collimator. The passive probe structure of full optical fiber is realized through the optical fiber branching unit, meanwhile, the noise interference of the optical fiber structure is removed by dividing the difference between the reference loop and the detection loop, and the difference result is the wide variable quantity of a gas detection area, namely the refractive index change of a medium in the area, and is converted into the concentration change through calibration.

Description

Optical fiber probe based on laser interference

Technical Field

The invention relates to a fiber probe based on laser interference. Relates to a patent classification number: g physical G01 measurement; test G01N test or analysis of the refractive index of the material G01N21/00 by optical means, i.e. by infrared, visible or ultraviolet light, of a system G01N21/41 in which the incident light of the material G01N21/17 changes according to the properties of the material tested, by means of determination of the chemical or physical properties of the material; affecting the properties of the phase, such as the optical path length.

Background

The core function of the interference probe is to split and converge incident light to obtain interference light, and the interference light is output through an optical fiber. Through a special structural design, laser beam splitting, interference and convergence are completed in an optical fiber system and integrated into a gas detection probe, so that passive gas detection is realized.

The scattered light emitted by the light source reaches the plane mirror through the light beam focused by the condenser, wherein a part of the light beam is reflected by the plane mirror, the air passing through the air chamber reaches the refraction prism, the refraction prism refracts the light beam back to the air chamber at the other side, then returns to the plane mirror and refracts the light beam to the reflecting film at the rear surface, and the light beam is reflected to the prism through the reflecting film and then enters the telescope system through deflection. The other part of the light beam is reflected by a reflecting film on the rear surface of the plane mirror after being refracted and incident on the plane mirror, methane passing through the gas chamber is reflected by the refraction prism and then returns to the plane mirror through the methane chamber, and the methane and the part of the light beam enter the reflection prism after being reflected by the plane mirror and enter the telescope system through deflection. As a result of the optical path difference, interference fringes are generated on the focal plane of the objective lens, and can be observed through the eyepiece. When the methanic chamber and the air chamber are both filled with the same gas, the position of the interference fringes does not move, but when methane is pumped into the methanic chamber, the interference fringes move a distance relative to the original position due to the change of the medium through which the light beam passes. By measuring this displacement, the content of methane in the air can be known.

In the prior art, as shown in the following table, a relatively common lithium niobate (LiNbO3) is that a phase modulator changes a crystal refractive index by applying an electric field to a lithium niobate crystal, and further changes a phase of a crystal laser, so that a phase cancellation state of interference light changes accordingly, and finally light intensity modulation is realized, and the phase modulator is particularly suitable for high-speed optical communication modulation. The present design can eliminate the current sweep of the laser if a phase modulator is used, thus circumventing the limitation of the laser wavelength sweep range. However, because the lithium niobate crystal needs to apply an external electric field, the optical fiber probe is inevitably subjected to a charging operation.

Disclosure of Invention

Aiming at the technical problems, the invention provides a fiber probe based on laser interference, which comprises:

the optical fiber branching device, the external incident light source is divided into at least 2 bundles through the optical fiber branching device 1, and the bundles enter the gas detection loop and the reference loop;

in said gas detection circuit and reference circuit;

the detection loop at least comprises a transmitting collimator, a receiving collimator and an open gas detection area positioned between the two collimators;

the reference loop at least comprises a transmitting collimator, a receiving collimator and an open type reference area positioned between the transmitting collimator and the receiving collimator.

As a preferred embodiment of the method of the present invention,

the detection loop is also provided with a loop optical fiber splitter which divides the input optical fiber into a detection optical fiber and a contrast optical fiber;

the detection optical fiber is connected with a transmitting collimator, the transmitting collimator irradiates the open gas detection area, and the open gas detection area is received by a receiving collimator and then transmitted to a tail end optical fiber splitter of the detection loop through a receiving optical fiber;

the loop fiber splitter is connected with the tail end fiber splitter through a contrast fiber.

As a preferred embodiment of the method of the present invention,

the reference loop is also provided with a loop optical fiber splitter which divides an input optical fiber into a reference optical fiber and a contrast optical fiber;

the reference optical fiber is connected with a transmitting collimator, the transmitting collimator irradiates the open reference area, and the reference area is received by a receiving collimator and then transmitted to a tail end optical fiber splitter of the reference loop through the optical fiber;

the loop optical fiber splitter in the reference loop

Further, as a preferred embodiment,

the open type gas detection area and the open type reference area are gas chambers.

A gas detection apparatus comprising:

the tail ends of the gas detection circuit and the reference circuit are respectively provided with a photodiode and a processing unit connected with the photodiode;

and the processing unit receives the loop waveform/optical path variable quantity of the open type detection area and the open type reference area, namely the refractive index change of the medium in the two areas, obtained by the photodiode, and calibrates and calculates to obtain the concentration of the current detection gas.

By adopting the technical scheme, the optical fiber probe and the gas detection device based on laser interference disclosed by the invention realize an all-fiber passive probe structure through the optical fiber branching unit, simultaneously remove the noise interference of the optical fiber structure by dividing the difference between the reference loop and the detection loop, and convert the difference result into the wide variation of a gas detection area, namely the refractive index variation of a medium in the area into the concentration variation through calibration. The whole structure can detect the specific gas concentration and can also be compatible with the detection of the fiber bragg grating temperature and the water molecule detection. The whole structure is simple, the size of the parts is small, and the weight is light.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is a schematic diagram of the probe structure of the present invention

FIG. 2 is a structural view of a probe according to the present invention

Detailed Description

In order to make the objects, technical solutions and technical effects of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and the detailed description. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. The embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

Example 1

As shown in fig. 1-2, a fiber-optic probe based on laser interference mainly includes:

a host laser,

The laser light emitted by the main laser is split into two beams through the optical fiber splitter 1, and the two beams enter the gas detection loop and the reference loop respectively.

And the tail ends of the gas detection loop and the reference loop are respectively provided with a host photodiode 1 and a host photodiode 2 which respectively receive the waveforms of the detection loop and the reference loop and calculate interference waveforms. The processing unit analyzes the waveform of the photocurrent received by the photodiode, namely the loop waveform, and obtains the light path variation.

In a preferred embodiment, changes in the shape, length, stress, etc. of the probe outer sheath fiber do not affect the interference optical path, enabling engineering applications.

As shown in fig. 1:

as a preferred embodiment, the detection circuit comprises: optical fiber splitter 2, external optical fiber 1, transmitting collimator 1, receiving collimator 1, optical fiber 2, optical fiber splitter 4, and optical fiber 3.

The reference loop comprises: the device comprises an optical fiber splitter 3, an optical fiber 4, a transmitting collimator 2, a receiving collimator 2, an optical fiber 5, an optical fiber splitter 5 and an optical fiber 6; the optical path difference L1 of the detection circuit is determined by the lengths of the optical fibers 1, 2, and 3 and the detection region length La. The optical path difference L2 of the reference loop is determined by the lengths of the optical fibers 4, 5, and 6 and the reference region length Lb.

The detailed structure is shown in figure 2:

in the figure, an optical fiber 1A corresponds to the external optical fiber 1 in the above-described figure, and the optical fiber 1A, a splitter-encapsulating steel tube 2A (corresponding to the optical fiber splitter 2), an optical fiber 3A, and an optical fiber 11A form the above-described optical fiber splitter 1, and divide laser light incident from an external light source into 2 paths.

The optical fiber 7A, the splitter packaging steel tube 8A, the optical fiber 9A and the optical fiber 17A form the splitters 4 and 5.

Two collimating lenses of the

collimating lenses

4A and 6A are respectively fixed at two ends of the reference air chamber 5A; the collimating lens 12A and the collimating lens 16A are respectively fixed at two ends of the detection air chamber 14A; the packaging steel pipes and the 2 air chambers of the splitter are fixed to the probe shell 19A through the 4 hoops, so that all the optical fibers and the steel pipes are suspended in the grooves in the probe platform and then are fixed in the grooves in an adhesive pouring mode.

In order to improve the detection accuracy, the difference between La and Lb should be as large as possible, and La is now 10cm and Lb is 0.1 em.

The photodiode receives the waveforms of the detection loop and the reference loop respectively, the ideal interference waveform is a sine wave, and the frequency w is in direct proportion to the optical path difference L and the scanning current range I of the laser;

the phase difference θ is proportional to the amount of change from L1 to L2. In order to calculate the phase difference θ, the two rows of sine waves should have the same frequency, so the lengths of the optical fibers 3 and 6 should be adjusted so that the initial state L1 ≈ L2. The interference waveforms are: u1 ═ asirnt, U2 ═ Bsin (wt + θ)

And (3) calculating a phase difference:

ΔU＝Asinwt-Bsin(wt+θ)

＝Asinwt-B(sinwt*cosθ+coswt*sinθ)

＝sinwt*(A-B*cosθ)-B*coswt*sinθ

U3＝ΔU*U1＝(sinwt*(A-B*cosθ)-B*coswt*sinθ)

*Asinwt＝A*(A-B*cosθ)*sinwt*sinwt-A*B*coswt*sinwt*sinθ

＝A*(A-B*cosθ)*1/2*(1-cos2wt)-A*B*1/2*sin2wt*sinθ

filtering to obtain direct current

U4＝A*(A-B*cosθ)*1/2

The gas concentration was calculated by calibrating U4.

In a preferred embodiment, the probe measures a standard gas concentration of 1000ppm, and measures U4a to 500 mv; it is also known that U4b is 0 when the concentration of gas in air is 0. And determining a calibration standard according to the two points, wherein the real-time concentration P of the gas is U4 × 1000/(U4a-U4b) unit ppm.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A fiber optic probe based on laser interference, comprising:

the reference loop at least comprises a transmitting collimator, a receiving collimator and an open reference area positioned between the transmitting collimator and the receiving collimator.

2. The laser interference based fiber optic probe of claim 1, further characterized by:

the detection optical fiber is connected with a transmitting collimator, the transmitting collimator irradiates the open gas detection area, and the open gas detection area is received by a receiving collimator and then transmitted to a tail end optical fiber branching unit of the detection loop through a receiving optical fiber;

3. The laser interference based fiber optic probe of claim 1, further characterized by: the reference loop is also provided with a loop optical fiber splitter which divides the input optical fiber into a reference optical fiber and a contrast optical fiber;

the reference optical fiber is connected with a transmitting collimator, the transmitting collimator irradiates the open reference area, and the reference area is received by a receiving collimator and then transmitted to a tail end optical fiber splitter of a reference loop through an optical fiber;

and the loop optical fiber splitter in the reference loop.

4. The laser interference based fiber optic probe of claims 2 or 3, further characterized by:

5. A gas detection apparatus comprising the laser interference based fiber optic probe of claim 2 or 3, characterized by comprising:

and the processing unit receives the loop waveform/optical path variation of the open type detection area and the open type reference area, namely the medium refractive index variation in the two areas, obtained by the photodiode, and calibrates and calculates to obtain the concentration of the current detection gas.