A fiber-optic micro-force sensor based on noon state and a demodulation method thereof

Abstract

The application belongs to the technical field of optical fiber sensing, and discloses an optical fiber micro-force sensor based on N00N state and a demodulation method. A N00N state light source outputs two path entangled lights, the two light beams first pass through a three-core optical fiber to enter a first port of an optical fiber ring and are output from a second port, and then propagate through the three-core optical fiber to enter a micro-force probe. One light beam is reflected at one end face of a fiber Fabry-Perot interferometer microcavity, and the other light beam is reflected at the other end face of the fiber Fabry-Perot interferometer microcavity. The reflected light propagates in the fiber core and produces interference, the interference light is incident from the second port and is output from a third port, and then enters a photoelectric detector through a fiber coupler to be subjected to coincidence counting. When a force-sensitive material is subjected to a micro-force, the length of the interferometer changes, and the intensity of the interference light changes. By measuring the coincidence count value, the micro-force change amount can be calculated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to a fiber-optic micro-force sensor based on N00N state and a demodulation method. BACKGROUND

[0002] Micro-force measurement refers to the technology for measuring extremely small forces, usually involving nanonewtons or even piconewtons. Micro-force measurement mainly includes optical and electromagnetic methods. The optical method mainly includes interferometers, atomic force microscopes, and optical tweezers. The electromagnetic method mainly includes piezoelectric elements and capacitive sensing. Micro-force measurement has broad application prospects, including measuring the mechanical properties of cells, protein folding, and the mechanical properties of nanomaterials.

[0003] N00N state is a quantum entangled state that has the ability to exceed the limit of shot noise and can theoretically reach the Heisenberg limit, and thus is used to measure small changes in physical quantities. N00N state can usually be prepared through spontaneous parametric conversion of a nonlinear crystal or spontaneous four-wave mixing effect in an optical fiber, and N=1 and 2 N00N states are usually used for sensing measurement. By inputting N00N state into an interferometer, the phase information of the N00N state can be obtained through particle number detection, and thus the change in the physical quantity can be calculated.

[0004] The Fabry-Perot interferometer is a high-precision optical device based on multi-beam interference, and the core is composed of two parallel high-reflectivity mirror surfaces forming an optical resonant cavity. The fiber-optic Fabry-Perot sensor has the advantages of simple structure, small size, high sensitivity, good stability, and immunity to electromagnetic interference, and thus is widely used in strain, temperature, pressure, and other measurement fields. The incident light beam produces interference in the Fabry-Perot interferometer, and when the cavity length changes, the interference light intensity also changes. By detecting the change in the interference light intensity, the change in the measured quantity can be derived.

[0005] Most existing micro-force measurement systems do not use quantum technology, and thus the detection limit and sensitivity are limited. An existing stress measurement device based on a fiber-optic Fabry-Perot interferometer uses an amplified spontaneous emission light source to generate interference light through the fiber-optic Fabry-Perot interferometer. The stress gauge acts on one end of the optical fiber to cause the interferometer to deform, and the change in the interference spectrum can be measured by a spectrometer to demodulate the size of the stress, with a resolution of 5 mN, which can meet the measurement of macroscopic micro-force. For microscopic micro-forces such as the interaction of cells and biological macromolecules, the fiber-optic sensor using ordinary light sources cannot be detected. Using quantum light sources and Fabry-Perot interferometers can be used to measure micro-forces through quantum state interference, which is of great significance for further improving the micro-force sensing limit. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide a fiber-optic micro-force sensor based on N00N state and a demodulation method.

[0007] The technical scheme of the present application is as follows: a fiber micro-force sensor based on N00N state, comprising a N00N state source, an optical fiber, an optical fiber circulator, a micro-force probe, an optical fiber coupler and a photoelectric detector;

[0008] The optical fiber comprises a first optical fiber, a second optical fiber, a third optical fiber and a fourth optical fiber; the first optical fiber and the second optical fiber are both three-core optical fibers;

[0009] The N00N state source generates two path-entangled state lights, which are a first light beam and a second light beam respectively;

[0010] The first light beam generated by the N00N state source propagates through the core a in the first optical fiber, and the second light beam propagates through the core c in the first optical fiber; the first light beam and the second light beam are incident on the first port of the optical fiber circulator through the first optical fiber, and then enter the second optical fiber after being emitted from the second port of the optical fiber circulator; the first light beam propagates along the core a of the second optical fiber, and the second light beam propagates along the core c of the second optical fiber; the first light beam and the second light beam enter the micro-force probe after leaving the second optical fiber, and propagate along the waveguides in the micro-force probe;

[0011] The micro-force probe comprises a single-mode optical fiber, a waveguide a, a waveguide b, an optical fiber Fabry-Perot interferometer and a force-sensitive material; the cores of the waveguide a, the waveguide b and the single-mode optical fiber are located in the same plane, and the waveguide a and the waveguide b are located on both sides of the core; the waveguide a is not connected with the optical fiber Fabry-Perot interferometer, and the waveguide b is connected with the optical fiber Fabry-Perot interferometer; the force-sensitive material is located at one end of the optical fiber Fabry-Perot interferometer;

[0012] The first light beam propagates along the waveguide a, and the second light beam propagates along the waveguide b; the first light beam is reflected at the first end face of the optical fiber Fabry-Perot interferometer after being emitted from the waveguide a; the second light beam is reflected at the second end face of the optical fiber Fabry-Perot interferometer after being emitted from the waveguide b; after the two reflected lights are incident on the core of the single-mode optical fiber and interfere, the interference light propagates through the core b in the second optical fiber, is incident on the second port of the optical fiber circulator, is output from the third port of the optical fiber circulator, enters the optical fiber coupler along the third optical fiber, and is divided into two lights after being output from the optical fiber coupler, and enters the coincidence counter for coincidence counting by the photoelectric detector;

[0013] The micro-force acting on the force-sensitive material changes the cavity length of the optical fiber Fabry-Perot interferometer, causes the phase information of the interference light to change, and further changes the coincidence counting value; the micro-force to be measured is measured by demodulating the coincidence counting value.

[0014] The two path-entangled state lights are and wherein N is a positive integer; the N00N state source outputs more than 10000 N00N states per second.

[0015] The third optical fiber is a single-mode optical fiber.

[0016] The fourth optical fiber is a single-mode optical fiber.

[0017] The waveguide a and the waveguide b are obtained by etching a single-mode optical fiber by a femtosecond laser, and the medium is air; the starting points of the waveguide a and the waveguide b are both single-mode optical fiber cladding, and the arrangement angle of the waveguide a and the waveguide b ensures that the reflected light is shot into the core.

[0018] The fiber Fabry-Perot interferometer is a hollow optical fiber, the hollow optical fiber core medium is air, and the hollow optical fiber is fused with the single-mode optical fiber.

[0019] The initial cavity length of the fiber Fabry-Perot interferometer ensures that the reflected light of the first light beam and the reflected light of the second light beam have a 90-degree phase difference.

[0020] The fiber coupler is a single-mode optical fiber, and the splitting ratio is 50:50.

[0021] The coincidence counter counts the photons reaching the two photodetectors at the same time.

[0022] A demodulation method of a N00N state-based fiber micro-force sensor, when a micro-force acts on the force-sensitive material, the length of the fiber Fabry-Perot interferometer changes to

[0023] ;

[0024] The stiffness of the fiber Fabry-Perot interferometer is

[0025] The change of the interference phase caused by the change of the cavity length of the fiber Fabry-Perot interferometer is , and finally causes the change of the output N00N state;

[0026] According to the basic theory of the fiber Fabry-Perot interferometer, the relationship between the micro-force and the change of the interference phase is obtained:

[0027] ;

[0028] The wavelength of the N00N state is

[0029] For a two-photon N00N state, the probability distribution function of the output photon is

[0030] ;

[0031] The phase information of the N00N state is

[0032] The change amount of the output photon probability is,

[0033] ;

[0034] The reflectivity of the micro force probe is demodulated, and the reflectivity of the micro force probe is defined as,

[0035] ;

[0036] Wherein, The detected number of N00N states reflected by the fiber Fabry-Perot interferometer, The number of N00N states input to the fiber Fabry-Perot interferometer;

[0037] The change of the output photon probability causes the coincidence count of the photodetector to change , the corresponding reflectivity change is ;

[0038] Finally, the change amount of the cavity length of the fiber Fabry-Perot interferometer is,

[0039] ;

[0040] The measured micro force is,

[0041] .

[0042] The beneficial effects of the present application: through theoretical calculation, it can be concluded that the resolution of the fiber micro force sensor based on N00N state for micro force measurement can reach 0.477pN, which can meet the measurement of the bonding force (pN order of magnitude) existing in the process of T cell receptor and antigen binding, and can be applied to the research of micro biological interaction mechanism. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a structure schematic diagram of the fiber micro force sensor based on N00N state.

[0044] Figure 2 It is a micro force probe structure schematic diagram of the fiber micro force sensor based on N00N state.

[0045] Figure 3 It is a three-core fiber cross-section schematic diagram.

[0046] In the figure: 1-N00N state source; 101-first light beam; 102-second light beam; 103-interference light; 104-light; 2-first optical fiber; 3-optical fiber circulator; 301-first port; 302-second port; 303-third port; 4-second optical fiber; 401-core a; 402-core b; 403-core c; 5-micro force probe; 501-single mode optical fiber; 502-waveguide a; 503-waveguide b; 504-core; 505-fiber Fabry-Perot interferometer; 506-hollow optical fiber; 507-first end face; 508-second end face; 509-force sensitive material; 6-third optical fiber; 7-optical fiber coupler; 8-optoelectronic detector; 9-fourth optical fiber; 10-coincidence counter; 11-micro force. DETAILED DESCRIPTION

[0047] An optical fiber micro force sensor based on N00N state includes a N00N state source 1, an optical fiber, an optical fiber circulator 3, a micro force probe 5, an optical fiber coupler 7 and an optoelectronic detector 8.

[0048] The optical fiber includes a first optical fiber 2, a second optical fiber 4, a third optical fiber 6 and a fourth optical fiber 9; the first optical fiber 2 and the second optical fiber 4 are both three-core optical fibers; if a single mode optical fiber single-core transmission is used, the N00N state path entanglement characteristic disappears. The cores of the first optical fiber 2 and the second optical fiber 4 respectively include a core a 401, a core b 402 and a core c 403.

[0049] The N00N state source 1 generates two path entangled state lights, which are a first light beam 101 and a second light beam 102 respectively;

[0050] The first light beam 101 generated by the N00N state source 1 propagates through the core a 401 in the first optical fiber 2, and the second light beam 102 propagates through the core c 403 in the first optical fiber 2; the first light beam 101 and the second light beam 102 are incident to the first port 301 of the optical fiber circulator 3 through the first optical fiber 2, and then exit from the second port 302 of the optical fiber circulator 3 and enter the second optical fiber 4; the first light beam 101 propagates along the core a 401 of the second optical fiber 4, and the second light beam 102 propagates along the core c 403 of the second optical fiber 4; the first light beam 101 and the second light beam 102 enter the micro force probe 5 after leaving the second optical fiber 4 and propagate along the waveguides in the micro force probe 5;

[0051] Because the waveguide a 502, the waveguide b 503 and the core 504 of the micro force probe 5 are a total of 3 optical paths, the first optical fiber 2 needs to be provided with three cores, and because the positions of the waveguide a 502 and the waveguide b 503 are on both sides of the core 504, the first light beam 101 and the second light beam 102 pass through the two end cores.

[0052] The micro-force probe 5 comprises a single-mode optical fiber 501, a waveguide a 502, a waveguide b 503, a fiber Fabry-Perot interferometer 505 and a force-sensitive material 509; wherein the waveguide a 502, the waveguide b 503 and the core 504 of the single-mode optical fiber 501 are located in the same plane, and the waveguide a 502 and the waveguide b 503 are located on both sides of the core 504.

[0053] The first light beam 101 propagates along the waveguide a 502, and the second light beam 102 propagates along the waveguide b 503; the waveguide a 502 is not in communication with the fiber Fabry-Perot interferometer 505, and the waveguide b 503 is in communication with the fiber Fabry-Perot interferometer 505; when etching, the waveguide a 502 is not in communication with the fiber Fabry-Perot interferometer 505, and reflection is caused due to the difference in refractive index. After the first light beam 101 is emitted from the waveguide a 502, it is reflected at the first end face 507 of the fiber Fabry-Perot interferometer, and after the second light beam 102 is emitted from the waveguide b 503, it is reflected at the second end face 508 of the fiber Fabry-Perot interferometer. After the second light beam 102 is reflected at the second end face 508 of the fiber Fabry-Perot interferometer, it enters the core 504, and a part of it is also reflected at the first end face 507 of the fiber Fabry-Perot interferometer, and the interference generated at the first end face 507 of the fiber Fabry-Perot interferometer does not affect the coincidence counting. After the two reflected light beams enter the core 504 of the single-mode optical fiber 501 and generate interference, the interference light enters the core b 402 of the second optical fiber 4, is emitted from the second port 302 of the fiber optical circulator 3, is output from the third port 303 of the fiber optical circulator 3, enters the fiber coupler 7 along the third optical fiber 6, and is divided into two light beams 104 after being output from the fiber coupler 7 and entering the fourth optical fiber 9. The two light beams 104 are composed of a plurality of single photons, and the coincidence counter 10 is used for coincidence counting by the photodetector 8.

[0054] The micro-force 11 acts on the force-sensitive material 509 to change the cavity length of the fiber Fabry-Perot interferometer 505, causing the phase information of the interference light 103 to change, and further changing the coincidence counting value; the size of the micro-force to be measured is measured by demodulating the coincidence counting value.

[0055] The two-path entangled state light is and wherein is a positive integer; the N00N state source 1 outputs more than 10,000 N00N states per second.

[0056] The third optical fiber 6 is a single-mode optical fiber.

[0057] The fourth optical fiber 9 is a single-mode optical fiber.

[0058] The waveguide a502 and the waveguide b503 are obtained by etching a femtosecond laser in a single-mode optical fiber 501, and the medium is air; the starting point of both the waveguide a502 and the waveguide b503 is a single-mode optical fiber cladding, and the arrangement angle of the waveguide a502 and the waveguide b503 ensures that the reflected light is shot into the fiber core 504.

[0059] The fiber Fabry-Perot interferometer 505 is a hollow optical fiber 506, the hollow optical fiber 506 has an air core, and is fused to the single-mode optical fiber 501.

[0060] The initial cavity length of the fiber Fabry-Perot interferometer 505 ensures that the reflected light of the first light beam 101 and the reflected light of the second light beam 102 have a phase difference of 90 degrees.

[0061] The fiber coupler 7 is a single-mode optical fiber, and the splitting ratio is 50:50.

[0062] The coincidence counter 10 counts the photons that simultaneously arrive at the two photodetectors 8.

[0063] A demodulation method of a fiber micro-force sensor based on a N00N state, when a micro-force 11 acts on the force-sensitive material 509, the length of the fiber Fabry-Perot interferometer 505 changes to;

[0064] ;

[0065] The stiffness of the fiber Fabry-Perot interferometer 505 is;

[0066] The change of the cavity length of the fiber Fabry-Perot interferometer 505 causes the change of the interference phase to be , and finally causes the change of the output N00N state;

[0067] According to the basic theory of the fiber Fabry-Perot interferometer, the relationship between the micro-force and the change of the interference phase is obtained:

[0068] ;

[0069] The wavelength of the N00N state is;

[0070] For a two-photon N00N state, the probability distribution function of the output photons is,

[0071] ;

[0072] The phase information of the N00N state is;

[0073] The change amount of the output photon probability is obtained as,

[0074] ;

[0075] The reflectivity of the micro-force probe 5 is defined as,

[0076] ;

[0077] wherein, is the number of N00N states reflected by the fiber Fabry-Perot interferometer detected, is the number of N00N states input to the fiber Fabry-Perot interferometer;

[0078] The change of the output photon probability causes the coincidence count change of the photodetector 8 , the corresponding reflectivity change is ;

[0079] Finally, the change of the cavity length of the fiber Fabry-Perot interferometer is,

[0080] ;

[0081] The measured micro-force is,

[0082] .

[0083] When , the measured micro-force is,

[0084] .

[0085] Further, the waveguide a 502 and the waveguide b 503 are etched in the single-mode optical fiber 501 by a femtosecond laser, and the medium in the waveguide a 502 and the waveguide b 503 is air. The starting points of the two waveguides are both the cladding of the single-mode optical fiber, and the angles of the two waveguides are configured to make the reflected light enter the core 504.

[0086] Further, the force-sensitive material 509 has a reflectivity of more than 95%.

[0087] The coincidence counter 10 counts the photons that reach the two photodetectors 8 at the same time.

[0088] The demodulation method is given by the function relationship between the micro-force and the number of photon coincidence counts.

[0089] When the minimum number of N00N states that can be detected by the N00N state-based fiber micro-force sensor is 1, the wavelength of the photons is , , , The minimum micro-force value that can be measured is The theoretical measurement limit exceeds the limit of existing atomic force microscopes .

[0090] The application will be further described in combination with specific examples.

[0091] The binding force exists in the process of T cell receptor and antigen binding, the size of the force is in the order of pN, and the ordinary optical fiber sensor cannot be used for measurement. A N00N state with N=2 is selected as a N00N state source 1 and input to the first optical fiber 2. The surface of the force sensitive material 509 of the micro force probe 5 is modified with an antigen, and is placed in a T cell solution. When the receptor and the antigen are combined, the binding force The combination and separation process causes the change of the cavity length of the fiber Fabry-Perot interferometer 505, and then affects the phase information of the first light beam 101 and the second light beam 102, so that the coincidence count value changes.

[0092] The change amount of the coincidence count when the receptor combines and separates is recorded According to the demodulation scheme, the minimum binding force that can be measured in theory is , which can meet the detection requirements of the process of T cell receptor and antigen binding.

Claims

1. A fiber-optic micro-force sensor based on N00N states, characterized in that, The fiber micro-force sensor based on N00N state comprises a N00N state source (1), a fiber, a fiber circulator (3), a micro-force probe (5), a fiber coupler (7) and a photoelectric detector (8); The fiber comprises a first fiber (2), a second fiber (4), a third fiber (6) and a fourth fiber (9); the first fiber (2) and the second fiber (4) are both three-core fibers; The N00N state source (1) generates two path entangled state lights, which are a first light beam (101) and a second light beam (102); The first light beam (101) generated by the N00N state source (1) propagates through a fiber core a (401) in the first fiber (2), and the second light beam (102) propagates through a fiber core c (403) in the first fiber (2); the first light beam (101) and the second light beam (102) are incident to a first port (301) of the fiber circulator (3) through the first fiber (2), and are emitted from a second port (302) of the fiber circulator (3) to enter the second fiber (4); the first light beam (101) propagates along a fiber core a (401) of the second fiber (4), and the second light beam (102) propagates along a fiber core c (403) of the second fiber (4); the first light beam (101) and the second light beam (102) enter the micro-force probe (5) after leaving the second fiber (4) and propagate along respective waveguides in the micro-force probe (5); The micro-force probe (5) comprises a single-mode fiber (501), a waveguide a (502), a waveguide b (503), a fiber Fabry-Perot interferometer (505) and a force-sensitive material (509); wherein the waveguide a (502), the waveguide b (503) and a fiber core (504) of the single-mode fiber (501) are located in the same plane, and the waveguide a (502) and the waveguide b (503) are located on both sides of the fiber core (504); the waveguide a (502) is not connected with the fiber Fabry-Perot interferometer (505), and the waveguide b (503) is connected with the fiber Fabry-Perot interferometer (505); the force-sensitive material (509) is located at one end of the fiber Fabry-Perot interferometer (505); The first light beam (101) propagates along the waveguide a (502), and the second light beam (102) propagates along the waveguide b (503); the first light beam (101) is reflected at a first end face (507) of the fiber Fabry-Perot interferometer after being emitted from the waveguide a (502); the second light beam (102) is reflected at a second end face (508) of the fiber Fabry-Perot interferometer after being emitted from the waveguide b (503); after the two reflected lights are incident to the fiber core (504) of the single-mode fiber (501) and interfere, interference light is formed to propagate in a fiber core b (402) of the second fiber (4), is incident to the second port (302) of the fiber circulator (3) and is output from a third port (303) of the fiber circulator (3), enters the fiber coupler (7) along the third fiber (6); after the interference light is output from the fiber coupler (7), the interference light is divided into two light beams (104) to enter two fourth fibers (9) respectively, and is input into a coincidence counter (10) by the photoelectric detector (8) for coincidence counting; The micro force (11) acts on the force sensitive material (509) to change the cavity length of the fiber Fabry-Perot interferometer (505), causing the phase information of the interference light (103) to change, and then changing the coincidence count value; the micro force size is measured by demodulating the coincidence count value.

2. The N00N state based fiber optic micro-force sensor of claim 1, wherein, The two beams of path-entangled state light are respectively and Wherein is a positive integer; the N00N state source (1) outputs more than 10,000 N00N states per second.

3. The N00N state based fiber optic micro-force sensor of claim 1, wherein, The third optical fiber (6) is a single-mode optical fiber.

4. The N00N state based fiber optic micro-force sensor of claim 1, wherein, The fourth optical fiber (9) is a single-mode optical fiber.

5. The N00N state based fiber optic micro-force sensor according to claim 1, wherein, The waveguide a (502) and the waveguide b (503) are obtained by etching a femtosecond laser in a single-mode optical fiber (501), and the medium is air; the starting points of the waveguide a (502) and the waveguide b (503) are both single-mode optical fiber cladding, and the arrangement angle of the waveguide a (502) and the waveguide b (503) ensures that the reflected light is shot into the fiber core (504).

6. The N00N state based fiber optic micro-force sensor according to claim 1, wherein, The fiber Fabry-Perot interferometer (505) is a hollow optical fiber, and the hollow optical fiber core medium is air, which is fused with the single-mode optical fiber (501).

7. The N00N state based fiber optic micro-force sensor according to claim 1, wherein, The initial cavity length of the fiber Fabry-Perot interferometer (505) ensures that the reflected light of the first light beam (101) and the reflected light of the second light beam (102) have a 90-degree phase difference. 8.The N00N state based fiber optic micro-force sensor according to claim 1, wherein, The fiber coupler (7) is a single-mode optical fiber, and the splitting ratio is 50:

50. 9.The N00N state based fiber optic micro-force sensor according to claim 1, wherein, The coincidence counter (10) counts the photons reaching the two photodetectors (8) at the same time.

10. A demodulation method of the fiber-optic micro-force sensor based on N00N states according to any one of claims 1-9, characterized in that, When the micro force (11) When acting on the force sensitive material (509), the length of the fiber Fabry-Perot interferometer (505) changes ； stiffness of the fiber optic Fabry-Perot interferometer (505); The cavity length change of the fiber Fabry-Perot interferometer (505) causes the interference phase change to be and finally causes the change of the output N00N state; According to the basic theory of the fiber Fabry-Perot interferometer, the relationship between the micro force and the change of the interference phase is obtained: ； Wavelength for N00N state; For a two-photon N00N state, the probability distribution function of the output photon is, ； Phase information for N00N state; The change of the output photon probability is, ； The reflectivity of the micro force probe (5) is used for demodulation, and the reflectivity of the micro force probe (5) is defined as, ； wherein, N0 is the number of N00N states detected by the fiber Fabry-Perot interferometer, N0 is the number of N00N states input to the fiber Fabry-Perot interferometer; Changes in the probability of output photons cause the photodetector (8) coincidence count to change The corresponding reflectivity change is ; Finally, the cavity length change of the fiber Fabry-Perot interferometer is obtained, ； The measured micro force size is 。

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