CN217384137U

CN217384137U - Low-cost reproducible polarization-maintaining fiber end surface Michelson interference sensor

Info

Publication number: CN217384137U
Application number: CN202123378370.3U
Authority: CN
Inventors: 何赛灵; 吴胜楠; 吴迅
Original assignee: Taizhou Anqiling Intelligent Technology Co ltd
Current assignee: Taizhou Anqiling Intelligent Technology Co ltd
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2022-09-06
Anticipated expiration: 2031-12-30

Abstract

The utility model discloses a low-cost repeatedly producible polarization maintaining optical fiber end surface Michelson interference sensor, wherein a conducting optical fiber and a sensing optical fiber both adopt polarization maintaining optical fibers and are used for maintaining the polarization state of the optical fibers; the free end of the sensing optical fiber consists of a part of inclined end surface and a part of vertical end surface, the inclined end surface and the sensing optical fiber shaft form an angle of 45 degrees, and light of the fiber core is vertically emitted or light which is vertically emitted into the fiber core is coupled into the fiber core; the light reflected by the vertical end face part of the fiber core is transmitted reversely, and the light reflected by the inclined end face part of the fiber core enters the fiber core again after being reflected by the outer wall of the cladding and interferes with the light reflected by the vertical end face to form the end face Michelson interferometer. The sensor structure can be used for measuring temperature or transverse stress, has repeatability, eliminates the influence of environmental disturbance on the polarization state of transmitted light, and improves the stability of the structure; low cost, simple preparation and compact structure.

Description

Low-cost reproducible polarization-maintaining fiber end surface Michelson interference sensor

Technical Field

The utility model relates to an optical fiber sensing technical field especially relates to low-cost repeatedly producible's fiber end face michelson interferometer sensor.

Background

The optical fiber interference sensor, which is a typical representative of the optical fiber sensor, is a type of optical device which is currently most widely used in practical applications and has the most mature mechanism. The sensor has the advantages of large dynamic range, high sensitivity, good stability, electromagnetic interference resistance, suitability for extreme environments, capability of realizing long-distance multiplexing and the like, and has wide application scenes in the fields of electric power traffic, biochemistry, aerospace, astronomical meteorology, microorganism detection and the like.

The optical fiber interference type sensor has various types, including a Fabry-Perot interference (FPI) sensor, a Michelson Interference (MI) sensor, a Mach-Zehnder interference (MZI) sensor and a Sagnac interference sensor, and the preparation method comprises the following steps: the Fabry-Perot interference (FPI) sensor is prepared by collimating two optical fibers by a capillary tube or fixing a reflecting membrane by a sleeve outside the end face of the optical fibers at a certain distance, the Mach-Zehnder interference (MZI) sensor is prepared by staggered welding of the optical fibers, and the Sagnac interference sensor is prepared by a fusion method. Although the method for preparing the optical fiber interferometric sensor has low cost and high yield, the following problems exist: the repeatability is poor, the randomness of the preparation of the cutting and welding method is high, the consistency of the structural sizes of the optical fibers is difficult to ensure in batch production, the interference optical path difference of the optical fiber interferometer prepared each time is difficult to keep consistent, the sensors with almost consistent performance parameters are difficult to produce in batch, and the complicated calibration work needs to be carried out on different sensors. In addition, the structure with the damaged circular symmetry of part of the optical fiber has different responses to input light with different polarization states, and the stability of the output result is greatly reduced due to the polarization sensitivity of the structure. At present, the optical fiber interferometer sensors which can be produced in batches by accurately controlling the size only have the technologies of femtosecond laser processing, plasma beam etching and the like, but the processing technologies are generally high in cost and long in preparation period, so that the practicability of the optical fiber interferometer sensors is limited.

SUMMERY OF THE UTILITY MODEL

In order to overcome the defects of the prior art, the utility model aims at providing a polarization maintaining optical fiber end surface Michelson interference sensor which is low in cost and can be repeatedly produced.

The low-cost reproducible polarization-maintaining optical fiber end surface Michelson interference sensor is characterized by comprising a conducting optical fiber and a sensing optical fiber which are connected; the conducting optical fiber and the sensing optical fiber are polarization maintaining optical fibers and comprise a cladding and a fiber core; the free end of the sensing optical fiber consists of a part of 45-degree inclined end surface and a part of vertical end surface, the fiber core end surface of the sensing optical fiber also consists of an inclined part and a vertical part, and the fiber core end surface forms a beam splitter; the outer wall of the optical fiber cladding provides a reflecting surface; the inclined end face and the sensing optical fiber shaft form an angle of 45 degrees, and light of the fiber core is vertically emitted or light which is vertically emitted into the fiber core is coupled into the fiber core; the light reflected by the vertical end face part of the fiber core is transmitted reversely, and the light reflected by the inclined end face part of the fiber core enters the fiber core again after being reflected by the outer wall of the cladding and interferes with the light reflected by the vertical end face to form the end face Michelson interferometer.

The polarization maintaining optical fiber is in a non-circular symmetrical structure, has a double refraction effect, has a fast axis direction and a slow axis direction, can maintain the polarization state of transmitted light, and can ensure that polarization related devices have stable output. .

The inclined end face is parallel to the slow axis of the polarization maintaining fiber.

The interference optical path difference of the Michelson interferometer is determined by the drawing process of the optical fiber and is not influenced by the preparation process of the sensor.

The sensor employs wavelength demodulation and can be used to measure temperature and lateral pressure.

The side edge of the fiber core of the polarization-maintaining optical fiber can be chiseled into a hollow hole, light reflected by the inclined end surface of the fiber core penetrates through the hollow hole, and the sensor is used for measuring the refractive index of a medium in the hole.

The utility model has the advantages that:

the polarization maintaining optical fiber end surface Michelson interference sensor provided by the utility model can realize batch production, and the optical fiber Michelson sensor parameters produced each time can keep consistent height; the polarization sensitivity of the structure is considered, the influence of environmental disturbance on the polarization state of the transmitted light is eliminated, and the stability of the structure is greatly improved; the cost is low, the preparation process is simple, the yield is high, and the production period is short; the full optical fiber structure is more compact.

Drawings

Fig. 1 is a schematic diagram of a polarization maintaining fiber end surface michelson interferometer sensor according to an embodiment of the present invention, (a) a schematic diagram of a polarization maintaining fiber end surface, and (b) a schematic diagram of a cross-sectional optical path.

The optical fiber comprises 1-polarization maintaining optical fiber, 2-optical fiber core, 3-optical fiber cladding, 4-slow axis, 5-fast axis, 5-polarization maintaining optical fiber refractive index modulation region, 6-inclined end face part, 7-vertical end face part and 8-cladding side wall reflecting surface.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts all belong to the protection scope of the present invention.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or intervening elements may also be present.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Referring to fig. 1, in the present embodiment, a polarization maintaining fiber 1 is used as the sensing fiber. One end of the polarization maintaining optical fiber 1 is polished to form an inclined end surface 6 and a vertical end surface 7, the inclined angle of the inclined end surface 6 is 45 degrees, a part of light of the optical fiber core 2 can be vertically emitted into the optical fiber cladding 3 by rotating 90 degrees, the light is incident on the reflecting surface 8 of the cladding side wall of the optical fiber and is vertically reflected back to the inclined end surface, and then returns to the optical fiber core 2 and is transmitted back; the vertical end face 7 reflects a portion of the light from the fiber core 2 directly back to the transmission, thereby forming a michelson interferometer at the fiber end face.

In particular, light reflected by the perpendicular end face 7 of the optical fiber

Returning directly to the core 2 and transmitting back light reflected by the angled end face 6

Is normally incident on the cladding sidewall reflecting surfaces 8 and is reflected back to the angled end surfaces 6 and re-coupled into the core 2 and the core

Interference occurs, and the interference phase difference of the two beams can be expressed as:

wherein

Is the interference optical path difference of the two beams of light,

the size of the optical fiber is directly determined, and the optical fiber is not influenced by the processing technology;

the light of different polarization directions has different initial phase differences for the initial phase differences of the interfering light.

Further analysis, assuming that the sensing structure is made of a non-polarization-maintaining optical fiber, the s light and the p light reflected by the inclined end surface 6 have different phase differences when interfering, and when the s light and the p light are transmitted in the non-polarization-maintaining optical fiber (for example, a common standard single-mode optical fiber), the s light and the p light are coupled with each other, the coupling condition is random, and the interference spectrum is also unstable under the influence of the defects of the optical fiber and the external environment disturbances such as stress, bending, torsion, vibration and the like of the optical fiber.

The polarization maintaining fiber 1 has a high birefringence effect, which is explained in detail by the fact that the fiber has different refractive indexes for light with the polarization direction along the fast axis 5 and light with the polarization direction along the slow axis 4, and the polarized light along the fast axis 5 and the slow axis 4 are not coupled with each other when the light is transmitted in the polarization maintaining fiber 1.

Based on the fresnel reflection law, the phase jump edges of the light with different polarization directions after being reflected by the inclined end surface 6 are different, so that the inclined end surface 6 is parallel to the slow axis 4 of the polarization-maintaining fiber 1 during preparation, that is, the polarization direction of the p light component (the polarization direction is parallel to the reflection surface) is parallel to the slow axis 4 when the light is reflected by the inclined end surface 6, and the polarization direction of the s light component (the polarization direction is perpendicular to the reflection surface) is parallel to the fast axis 5, so that when the interference occurs, the interference of the p light and the s light is independent and cannot be coupled with each other, the transmission of the polarization state cannot be influenced by the environmental disturbance, and the structure has stable output response.

Because the optical path difference of the interference light is only influenced by the size and the refractive index of the optical fiber, the sensor prepared each time can have the same parameters, and the method has the advantage of repeatable production.

The sensor may be used to measure temperature or lateral stress, in particular, changes in temperature or lateral stress that alter the lateral dimensions of the fibre and the refractive index of the fibre cladding 3, whereby changes in temperature or stress can be judged by drift of the interference spectrum.

The low-cost reproducible polarization maintaining optical fiber end surface Michelson interference sensor provided by the embodiment can be manufactured by the following preparation method:

1) after the polarization maintaining fiber 1 is cut flat, the polarization maintaining fiber is placed into a microscope for observation, and the directions of the fast axis 4 and the slow axis 5 are determined.

) And (3) after the polarization maintaining optical fiber 1 is clamped, putting the polishing machine on the polarization maintaining optical fiber to ensure that the included angle between the flattened end surface and the abrasive paper is about 45 degrees, and the slow shaft 5 is parallel to the polishing plane, and starting the polishing machine.

) And (3) directly observing the inclined end face 6 of the polarization maintaining optical fiber 1 through a microscope, observing whether an interference spectrum exists in the reflection spectrum, judging whether the inclined end face 6 has an inclined angle of 45 degrees and whether a boundary line between the inclined end face 6 and the vertical end face 7 just passes through the fiber core 2, and if not, adjusting the included angle between the polarization maintaining optical fiber 1 and the abrasive paper, and repeating the steps until the interference spectrum appears.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. The low-cost reproducible polarization maintaining optical fiber end surface Michelson interference sensor is characterized by comprising a conducting optical fiber and a sensing optical fiber which are connected;

the conducting optical fiber and the sensing optical fiber are polarization maintaining optical fibers and comprise a cladding and a fiber core;

the free end of the sensing optical fiber consists of a part of 45-degree inclined end surface and a part of vertical end surface, the fiber core end surface of the sensing optical fiber also consists of an inclined part and a vertical part, and the fiber core end surface forms a beam splitter; the outer wall of the optical fiber cladding provides a reflecting surface; the inclined end face and the sensing optical fiber shaft form an angle of 45 degrees, and light of the fiber core is vertically emitted or light which is vertically emitted into the fiber core is coupled into the fiber core; the light reflected by the vertical end face part of the fiber core is transmitted reversely, and the light reflected by the inclined end face part of the fiber core enters the fiber core again after being reflected by the outer wall of the cladding and interferes with the light reflected by the vertical end face to form the end face Michelson interferometer.

2. The fiber-optic endface michelson interferometer sensor of claim 1, wherein the polarization maintaining fiber is non-circularly symmetric, having a birefringence effect, and having a fast axis direction and a slow axis direction.

3. The fiber-optic endface michelson interferometer sensor of claim 1, wherein the angled endface is parallel to the polarization maintaining fiber slow axis.

4. The fiber-optic endface michelson interferometer sensor of claim 1, wherein the sensor employs wavelength demodulation.

5. The fiber-optic endface michelson interferometer sensor of claim 1, wherein after the side of the core of the polarization maintaining fiber is drilled into an open hole, light reflected from the angled endface of the core will pass through the open hole.