WO2021123968A1

WO2021123968A1 - Optical fibre system

Info

Publication number: WO2021123968A1
Application number: PCT/IB2020/060984
Authority: WO
Inventors: Victor Hugo Aristizábal Tique; Jorge Alberto GÓMEZ LÓPEZ; Jairo Camilo QUIJANO PÉREZ; Francisco Javier VÉLEZ HOYOS
Original assignee: Politécnico Colombiano Jaime Isaza Cadavid; Universidad Cooperativa De Colombia
Priority date: 2019-12-20
Filing date: 2020-11-20
Publication date: 2021-06-24
Also published as: CO2019014494A1

Abstract

The present invention relates to an optical fibre system, which comprises: a structure comprising a first optical fibre segment (2) with two ends; a second MMF multimode optical fibre segment (3) with two ends; wherein the first end of the second MMF multimode optical fibre segment (3) is connected to the first end of the first optical fibre segment (2); the second MMF multimode optical fibre segment (3) has a disturbance region (8) that is exposed to a physical or chemical disturbance.

Description

FIBER OPTIC SYSTEM

Technical field of the invention

The present invention relates to fiber optic structures related to fiber optic sensors, fiber optic modulators, but is not limited to these applications and uses.

Description of the state of the art

In addition to communications, optical fibers and fiber optic structures have received a lot of interest, for example, as sensors for a large number of mechanical, electrical and chemical parameters, among others. This has led to the development of many new types of fiber and applications for use as fiber optic sensors.

Thus, in the state of the art fiber optic sensors are disclosed, such as those disclosed by documents US6144790 A, US4843233 A or the article “Specklegram in a grapefruit fiber and its response to external mechanical disturbance in a single-multiple-single mode fiber structure ”available online at https://www.ncbi.nlm.nih.gov/pubrned/180r7969·

Document US6144790 A discloses a fiber optic sensor comprising an optical source useful for detecting impact, vibration, temperature, pressure or other forces. The sensor comprises an optical fiber with one terminal connected to a light source and with the other terminal connected to a detector. The sensor has a measuring section, a particular embodiment of the invention comprises a light generated by an optical source that propagates through an optical fiber system such that a portion of the optical fiber is sensitive to external forces or disturbances that They affect the intensity of the light that propagates through the fiber optic system and the intensity of the light is received by a detector.

US6144790 A discloses that the speckle pattern changes according to disturbances of the sense fiber. Under the influence of an applied field, be it thermal, direct force or pressure, or other physical origin, the entire sensitive fiber, or parts thereof, or just a section of sensitive fiber, may undergo a deformation of an axial symmetry. Document US6144790 A discloses that it solves a sensitivity problem of fiber optic sensors used to measure variables such as pressure and force in which long lengths of sensitive fiber coupled to mechanical devices are required, the solution is made using a single-mode optical fiber that maintains polarization.

However, the sensor disclosed in document US6144790 A, is not manufactured taking into account parameters of the fiber core diameter in relation to a speckle pattern, therefore, the sensor does not take into account physical alterations on the fiber segment that allow metrological parameters of the sensor to be varied, such as the sensitivity, dynamic range and operating threshold of the sensor, so the sensor's operation is limited to static values of said metrological parameters and its sensitivity is limited.

The article "Specklegram in a grapefruit fiber and its response to external mechanical disturbance in a single -multiple -single mode fiber structuré" discloses a fiber sensor to measure mechanical disturbances in a structure SMS (for the acronym in English of Single Mode Fiber - Multi Mode Fiber - Single Mode Fiber) of fiber optic, which has an optical fiber MMF (Multi-Mode Optical Fiber) of stepped index from which is spliced an SMF fiber (for the acronym in English of Single -Mode Optical Fiber) at each of its ends that correspond to an input fiber and an output fiber, an irradiator (Faser He-Ne) connected to the other end of the input fiber and a photodetector connected to the other end of the output fiber.

The document of the article discloses that the sensitivity of the sensor could be improved by optimizing the diameter of the core of the output fiber by making it coincide with the size of the optical speckle pattern, since it functions as an aperture through which part of the fiber is captured. optical speckled pattern. However, it does not disclose information on a relationship of the parameters of the fibers that allow varying the sensitivity, dynamic range and operating threshold of the sensor.

Brief description of the invention

The present invention refers to an optical fiber structure, which comprises a first segment of Optical Fiber (2) with two ends; a second segment of MMF Multimode Fiber Optic (3) with two ends; where one end of the second segment Multimode Fiber Optic MMF (3) is connected to one of the ends of the first Fiber Optic segment (2); wherein said second segment has a disturbance region (8) in the cladding (3a) of the MMF Multimode Optical Fiber (3); and where the disturbance region (8) of the MMF Multimode Fiber Optic segment (3) is exposed to a physical or chemical disturbance.

In one embodiment of the invention, one of the ends of the first Optical Fiber segment (2) is connected to a photodetector (5) and at one end of the second MMF Multimode Optical Fiber segment (3) a coherent light emitter is connected (1).

In a further embodiment of the invention, one end of the first Fiber Optic segment (2) is connected to the second port of a three-port optical circulator (10); a coherent light emitter (1) is connected to the first port of the optical circulator (10); a photodetector (5) is connected to the third port of the optical circulator (10); and a reflective film (9) is arranged at the end of the second MMF Multimode Fiber Optic segment (3), which is not connected to the first Optical Fiber segment (2).

In a particular example of the invention, the first Optical Fiber segment (2) is Single-mode (SMF).

In the second segment of MMF Multimode Fiber Optic (3) there is a perturbation region (8) that is obtained by means of different methods as will be explained in detail later. For example, to achieve said region of disturbance (8) in the cladding (3a), also called cladding, of the MMF Multimode Optical Fiber segment (3) it is covered with an encapsulation (7) having an opening (A). In other embodiments of the invention, the coating (3a) can generate the disturbance region (8) by wearing away a part of the coating (3a).

Another way of generating the region of disturbance (8) is by means of a narrowing (also known as tapering technique) by fusion and stretching of a part or all of the cladding (3a) of the second segment of MMF Multimode Optical Fiber.

(3). It should be understood that the region of disturbance (8) must not necessarily consist of the modification of the cladding (3a) of the second segment of MMF Multimode Optical Fiber (3) (cladding), but that it may simply correspond to the exposure to a physical disturbance or chemistry directly from a zone or area of a part of the cladding (3a) of the second segment of MMF Multimode Optical Fiber (3).

Brief description of the figures

FIG. 1 illustrates a longitudinal section of the fiber optic structure of an embodiment of the invention.

FIG. 2 illustrates a longitudinal section of an embodiment of the fiber optic structure of the invention to which a reflective film (9) is added.

FIG. 3 illustrates a longitudinal section of an embodiment of the invention, the optical fiber structure of the invention to which is added a reflective film (9) and an encapsulation (7) with an opening (A) of length L.

FIG. 3A illustrates a reflective modality that implements the fiber optic structure of the invention to which is added a reflective film and an encapsulation (7) with an aperture (A) of length L.

FIG. 4 illustrates a longitudinal section of the fiber optic structure of the invention indicating the contact plane (B-B) between a first segment of Optical Fiber (2) and a second segment of MMF Multimode Optical Fiber (3).

FIG. 4A illustrates a modality that implements the fiber optic structure of the invention where a photodetector (5) is connected at one of the ends of the first Optical Fiber segment (2) and where at the end of the second MMF Multimode Fiber Optic segment ( 3) is connected to a coherent light emitter (1).

FIG. 4B illustrates an example of a grain (11) of a Speckle Pattern (12) also called an optical speckled pattern that is observed in a front view of the contact plane (BB) between the first Optical Fiber segment (2) and the second MMF Multimode Fiber Optic segment (3). FIG. 5 illustrates a cross section of the fiber optic structure of the invention indicating the contact plane (BB) between a first segment of Optical Fiber (2) and a second segment of MMF Multimode Optical Fiber (3) where the second segment of Fiber MMF Multimode Optics (3) is covered with an encapsulation (7) with an opening (A) forming a disturbance region (8).

FIG. 5A illustrates an embodiment that implements the fiber optic structure of the invention where the second segment of MMF Multimode Optical Fiber (3) is covered with an encapsulation (7) with an opening (A) forming a region of disturbance (8).

FIG. 5B illustrates an isometric section of the fiber optic structure of the invention indicating the contact plane (BB) between a first segment of Optical Fiber (2) and a second segment of MMF Multimode Optical Fiber (3) where the second segment of MMF Multimode Optical Fiber (3) is covered with an encapsulation (7) with an opening (A) forming a disturbance region (8).

FIG. 6 illustrates a cross section of the fiber optic structure of the invention where the region of disturbance is formed by melting and stretching tapering of part or all of the second fiber optic segment.

FIG. 7A illustrates a cross section of the second segment of MMF Multimode Optical Fiber (3), where the region of disturbance (8) obtained by coating with an encapsulation (7) with an opening (A).

FIG. 7B illustrates a cross section of the second segment of MMF Multimode Optical Fiber (3), with a region of disturbance (8) formed by wear, which is obtained by wear of a part of the cladding (3a) (cladding) and the cladding an encapsulation (7) with an opening (A).

FIG. 7C illustrates a cross section of the second segment of MMF Multimode Optical Fiber (3) with a region of disturbance (8), which is obtained by wear of a part of the cladding (3a) (cladding). FIG. 8 illustrates an example of voltage versus temperature response of a particular application of the invention implemented as a temperature sensor and with a 3 centimeter MMF fiber disturbance length.

FIG. 9 illustrates an example of voltage versus temperature response of a particular application of the invention used as a temperature sensor and with MMF fiber disturbance length of 4.5 centimeters.

FIG. 10 illustrates an example of voltage versus temperature response of a particular application of the invention used as a temperature sensor and with MMF fiber disturbance length of 8 centimeters.

FIG. 11 illustrates an example of voltage versus temperature response of a particular application of the invention used as a temperature sensor and with MMF fiber disturbance length of 12 centimeters.

Detailed description of the invention

Referring to FIG. 1, the present invention corresponds to an optical fiber structure, comprising:

- a first segment of Optical Fiber (2) with two ends;

- a second segment of MMF Multimode Fiber Optic (3) with two ends; where one end of the second MMF Multimode Fiber Optic segment (3) is connected to one of the ends of the first Optical Fiber segment (2); wherein said second segment has a disturbance region (8) in the cladding (3a) of the MMF Multimode Optical Fiber (3); and where the disturbance region (8) of the MMF Multimode Fiber Optic segment (3) is exposed to a physical or chemical disturbance. In the present invention, it should be understood that the disturbance region (8) of the MMF Multimode Fiber Optic segment (3) corresponds to an area of the second MMF Multimode Fiber Optic segment (3) which is exposed to a physical disturbance or chemistry. Likewise, it should be understood in the present invention that all optical fiber segments have a core and a cladding (3a), which is also called cladding.

Fas physical disturbances can be mechanical disturbances such as forces, pressures, temperature, among others, and chemical disturbances are considered any material or chemical substance that interacts with the disturbance region (8) in the coating (3a) of the second segment of MMF Multimode Fiber Optic (3).

Referring to FIG. 1, the first segment of Optical Fiber (2) has a core (2b) and a cladding (2a) and the second segment of MMF Multimode Optical Fiber (3), has a core (3b) and a cladding (3a).

The first segment of Optical Fiber (2) and second segment of MMF Multimode Optical Fiber (3) are connected for example by mechanical splices that for example is selected from the group formed by FC (for the acronym in English of Ferrule Connector), PC ( Physical Contact), APC UPC (Ultra Physical Contact), ST (Straight Tip), SC (Standard Connector), FC ( Lucent Connector), SMA (Sub Miniature A), MU (Miniature Unit), MTRJ (Mechanical Transfer-Registered Jack), MPO ( Multi-fiber Push-on), E2000 and combinations thereof or by means of splices that are selected for example from the group consisting of fusion splicing, mechanical splices such as splints with different polishes such as PC (for the acronym in English for Physical Contact), UPC n English for Ultra Physical Contact), APC (for the acronym in English of Angled Physical Contact).

Referring to FIG. 4 and FIG. 4A shows an embodiment of the invention in which there is a first Optical Fiber segment (2) with two ends; a second segment of MMF Multimode Optical Fiber (3) with two ends, in which a disturbance region (8) is generated in the cladding (3a) of the Multimode Optical Fiber MMF (3). As indicated above, the disturbance region (8) can be generated in different ways in such a way as to facilitate the exposure of the MMF fiber (3) to physical or chemical disturbances. Continuing with FIGS. 4 and 4A, the first end of the MMF Multimode Optical Fiber (3) is connected to one of the ends of the first Optical Fiber segment (2), where the first Optical Fiber segment (2) connects a photodetector (5) and where at the end of the second MMF Multimode Fiber Optic segment (3) a coherent light emitter (1) is connected.

The second segment of MMF Multimode Fiber Optic (3) is connected to a coherent light emitter (1), such as a laser source, so that when the light propagates through the second segment of MMF Multimode Fiber Optic (3) it is generates a modal interference pattern, in this case a Speckle Pattern (12) in the contact plane (B-B), which is the contact plane where the first Fiber Optic segment (2) and the second segment are connected Multimode Fiber Optic MMF (3). In the present invention, Speckle Pattern (12) (also called optical speckle pattern) should be understood as a pattern that is made up of a number of small spots or grains generated by optical intensity distributions, produced by mutual interference between coherent wavefronts that are subject to phase differences, or intensity fluctuations, or a product of random interference.

Referring to FIG. 4 the first Fiber Optic segment (2) generates a Speckle Pattern (12) in the contact plane (B-B). In the illustrated modality, the first segment of Optical Fiber (2) functions as a modal filter, where it takes part of the modes or the intensity of the coherent light that propagates through the Optical Fiber (2), which is in the plane where the grain (11) of the Speckle Pattern (12) is formed and is taken to a photodetector (5) which will respond to the power of the Speckle Pattern (12).

For the present invention, a modal filter will be understood as that system or device that is capable of taking at least one mode or a group of modes that come from an optical fiber, capturing a part of the power of the Speckle Pattern (12).

By changing the size of the area of the disturbance region (8), for example defined by the segment (L) along the axis of the second segment of MMF Multimode Optical Fiber (3), the value of the metrological parameters of the fiber optic structure. These metrological parameters are for example the sensitivity, the dynamic range or operating range and the detection threshold.

For the understanding of the present invention, sensitivity will be understood as the level of variation of the output variable of the fiber optic structure, in this case measured as the voltage, before changes in the variable to be measured, for example, temperature; that is, in how many millivolts the output signal changes for every ⁰ C that the temperature of the system to be measured varies.

The detection threshold is understood to be the minimum value of the variable to be measured from which the optical fiber structure begins to show variations above the noise level of its output signal.

Likewise, dynamic range (also called operating range) will be understood as the range of values of the variable to be measured in which the fiber optic structure responds continuously, above the noise levels of the output signal. This response may or may not be linear.

Each of these metrological parameters are affected by the region of disturbance (8), which in one embodiment of the invention is determined by the width of the aperture (A) and the length (L) of the region.

In the invention the perturbation region (8) has an area less than or equal to the area of the cladding (3a) of the second segment of the MMF Multimode Optical Fiber (3).

The region of disturbance (8) can be obtained in different ways, for example by referring to FIGS. 5, FIG. 5B and FIG, 7A in a particular example the perturbation region (8) can be obtained by coating with an encapsulation (7) with an opening (A) of the second segment of MMF Multimode Optical Fiber (3), said opening A can have various shapes for example circular shapes, regular or irregular shapes, or for example referring to FIG. 5B, the perturbation region (8) has a rectangular shape defined by the segment L along the axis of the fiber and a thickness A, which can be, for example, of the order of one to two millimeters of thickness A and length L it can for example reach up to 15 cm. In embodiments of the invention, the length L is in the range of 1 cm to 15 cm. In some examples of the invention, the MMF Multimode Optical Fiber (3) has a length less than or equal to 15 cm. The encapsulation coating (7) with an opening (A) isolates the coating (3a) of the MMF Multimode Optical Fiber segment (3) from a physical or chemical disturbance and allows only the MMF Multimode Optical Fiber segment (3) to be disturbed exposed at opening (A).

The encapsulated coating (7) can be made with different materials such as plastics, epoxy resin, polyuria, ceramic, glass, among other materials. The coating of the encapsulation (7) has among other functions, that of isolating the cladding (3a) (cladding) of the MMF Multimode Optical Fiber (3) from physical or chemical disturbances of the coated part of the second segment of MMF Multimode Optical Fiber ( 3).

Thus, for example, in particular applications of the invention such as, for example, as a temperature sensor, the encapsulation (7) with an opening (A) functions as a thermal insulator allowing only the area exposed by the opening to be thermally disturbed ( TO).

In a particular embodiment of the invention, the region of disturbance (8) can be obtained by coating with an encapsulation (7) around the coating (3a), where said encapsulation (7) has an opening (A). Said opening can be covered with a material that allows, among other effects, to change the refractive index of the region of disturbance (8). Examples of such materials are polyvinyl alcohol; tetraethyl orthosilicate doped porous silica matrix membranes; Eriochromocyanin R, among other materials.

The materials lining the aperture (A) can also be magnetostrictive, or piezoelectric so that a magnetic or electrical disturbance becomes a mechanical disturbance in the disturbance region (8).

In another particular example and referring to FIGS. 7C the disturbance region (8) can be obtained by wear of a part of the cladding (3a) (cladding) of the second segment of MMF Multimode Optical Fiber (3), covering it with an encapsulation (7). In a further embodiment, and referring to FIG. 7B, the region of disturbance (8) can be obtained by wear of a part of the cladding (3a) (cladding) of the second segment of MMF Multimode Optical Fiber (3).

In a fourth non-illustrated example, the region of disturbance (8) is obtained as the area of exposure to a physical or chemical disturbance directly from an area of the cladding (3a) (cladding) of the second segment of MMF Multimode Optical Fiber

(3).

In another embodiment of the invention, the perturbation region (8) is formed by a narrowing (tapering) by fusion and stretching of a part or all of the second segment of MMF Multimode Optical Fiber (3).

Fa region of disturbance (8) can generate an evanescent field and the change in the Speckle Pattern (12) can be related to said evanescent field, which occurs at the external border of the region of disturbance (8) in the coating. (3a).

The material that is around the worn fiber produces a modification of the Speckle Pattern (12) that will be registered by the first Optical Fiber segment (2) and that corresponds to a change in the optical power that reaches the photodetector ( 5) and on the photodetector output voltage. The intensity of the change in power will depend on how strong the change is in the optical properties associated with the presence of the external environment.

Thus, changes in the exterior will affect the refractive index for the evanescent field that propagates, and this will be reflected by means of changes in the Speckle Pattern (12) registered by the photodetector.

Referring to FIG. 2 the fiber optic structure, comprises: a first segment of Optical Fiber (2), with two ends, a second segment of MMF Multimode Optical Fiber (3), with a disturbance region (8) in the cladding (3a), and with two ends, one end of the second MMF Multimode Fiber Optic segment (3) is connected to one of the ends of the first Optical Fiber segment (2) and where a reflective film (9) is added that is arranged in the second extreme, of the second segment of MMF Multimode Fiber Optic (3) said reflective film (9) is a reflective element such as a mirror, first surface, a polished surface such as a fine polishing type PC (for its acronym in English Phisical contact): where the level of return is around -40dB, UPC also called UltraPC Polishing , where the pickup level is further reduced than the PC by around -55dB. o APC APC (Angled Physical Contact): where the reflection is reduced to around -70dB or a shiny layer, such as silver deposited by sputtering (sputtering) or dip-coating (dip coating) ) deposited on the end of the second segment of MMF Multimode Optical Fiber (3).

With this embodiment of the invention, the fiber optic structure and the reflective film (9) and referring to FIG. 3A a second embodiment of the invention is made where the first segment of Optical Fiber (2) at its end is connected to the second port of the optical circulator (10); a coherent light emitter (1) is connected to the first port of the optical circulator (10); a photodetector (5) is connected to the third port of the optical circulator (10).

In an unillustrated example of the invention, the reflective film (9) is not in contact with the second segment of MMF Multimode Optical Fiber (3) but is approached by means of an optical line of sight of the light that leaves the second segment of MMF Multimode Fiber Optic (3) and returns the light to the same second segment of MMF Multimode Fiber Optic (3) through reflection.

In another example and referring to FIG. 3 the fiber optic structure comprising: a first segment of Optical Fiber (2), with two ends, a second segment of MMF Multimode Optical Fiber (3), with a disturbance region (8) in the cladding (3a) , and with two ends, in which the first end is connected to the second end of the first Optical Fiber segment (2); and where a reflective film (9) arranged at the second end of the second segment of MMF Multimode Optical Fiber (3) is added, said reflective film (9) is a reflective element such as a mirror, a polished surface or a glossy layer deposited on the end of the second segment of MMF Multimode Optical Fiber (3) and the perturbation region (8) can be obtained by coating with an encapsulation (7) with an opening (A) of the second MMF Multimode Optical Fiber segment ( 3), and an embodiment of the invention is made where one end of the first Fiber segment Optics (2) is connected to the second port of the optical circulator (10); a coherent light emitter (1) is connected to the first port of the optical circulator (10); and in the third port of the optical circulator (10) a photodetector (5) is connected.

The second embodiment of the invention works by reflection, where the light from the coherent light emitter (1) enters through the second MMF Multimode Fiber Optic segment (3), propagating through the second MMF Multimode Optical Fiber segment (3), and then a reflection is generated in the reflective film (9). The reflected light is returned and re-enters again through the contact plane (BB), where the Speckle Pattern (12) is generated between the first Optical Fiber segment (2) and the second MMF Multimode Fiber Optic segment ( 3), which reaches the photodetector (5) through an optical circulator (10). The first Fiber Optic segment (2) takes part of the power from the Speckle Pattern (12) formed in the contact plane (B-B).

For all the embodiments of the invention, the power capture of the Speckle Pattern (12) formed in the contact plane (BB) is associated with the diameter of the core (2b) of the first Optical Fiber segment (2) and of the core (3b ) of the second MMF Multimode Fiber Optic segment (3). The light that comes from the second MMF Multimode Fiber Optic segment (3) will be coupled to a greater or lesser extent in the first Fiber Optic segment (2) depending on the dimensions of the first Fiber Optic segment (2) and the second segment of MMF Multimode Fiber Optic (3).

Referring to FIG. 4B, each grain (11) of the Speckle Pattern (12) carries an amount of optical power. If the size of the core (2b) of the first Fiber Optic segment (2) is very similar to the average grain size (11) of the Speckle Pattern (12), it is equivalent to capturing the power of the grain (11) of the Speckle Pattern Speckle (12) and bring said power to the photodetector (5).

Referring to FIG. 4, when a Speckle Pattern (12) is generated in the contact plane (BB) between a first Optical Fiber segment (2) and a second MMF Multimode Optical Fiber segment (3), the grains (11) of the Pattern of Speckle (12), also called spots, have a statistical size and correspond to a statistical distribution, with an average grain size (11) of the Speckle Pattern (12). The first Fiber Optic segment (2) functions as a power filter, so that as the size of the core (2b) of the first Fiber Optic segment (2) changes compared to the average grain size (11 ) of the Speckle Pattern (12) the following situations may occur:

If the diameter of the core (2b) of the first Optical Fiber segment (2) is very small compared to the statistical average grain size (11) of the Speckle Pattern (12), in this case if disturbances occur on the Speckle Pattern , the first Fiber Optic segment (2), when behaving as a power filter, it would not adequately capture the power of the Speckle Pattern disturbances (12).

Similarly, if the diameter of the core (2b) of the first Optical Fiber segment (2) is very small compared to the statistical average grain size (11) of the Speckle Pattern (12), the optical power of many grains (11) of the Speckle Pattern (12) would pass through the first segment of Optical Fiber (2), for example, in proportion 5 or 6 times the order of magnitude of the size of the grain (11), so that when there is a disturbance of the Speckle Pattern (12), the photodetector (5) would not adequately capture the changes in power associated with the Speckle Pattern disturbances (12).

Now, when the first Optical Fiber segment (2) has a core diameter (2b) approximately equal to the statistical average grain size (11) of the Speckle Pattern (12), then when there is a disturbance on that Speckle Pattern (12) the power of one of the grains (11) of the Speckle Pattern (12) passes through the first Optical Fiber segment (2) as well as the power of the Speckle Pattern (12) disturbances that will be recorded by the photodetector (5).

Thus, for all the embodiments of the invention it is preferable that the core diameter (2b) of the first Optical Fiber segment (2) and the average grain diameter (11) of the Speckle Pattern (12), which is generated in the contact plane (BB) between the first segment of Optical Fiber (2) and the second segment of MMF Multimode Optical Fiber (3); When the second segment of MMF Multimode Fiber Optic (3) is irradiated by its second end with light from the coherent light emitter (1), comply with the following condition: 0.5 1.8

where L

(D _s ) = - -jy: is the average grain size (11) of the Speckle Pattern (12); d. is the diameter of the core (2b) of the first Optical Fiber segment (2); AN: the numerical aperture of the second MMF fiber optic segment (3); yl: the wavelength of the coherent light source (1).

The ratio of: the core diameters (2b) of the first Fiber Optic segment (2), the numerical aperture (3b) of the second MMF Multimode Fiber Optic segment (3); and the wavelength of the coherent light source (1), the average grain size (11) of the Speckle Pattern (12) allows calibrating the assemblies and modalities of the invention by organizing the relationships of the elements and metrological parameters such as previously described by means of test disturbances and corresponding voltage or power measurements in a photodetector (5) obtaining a direct response that correlates, for example, the change of a variable of interest with the voltage or power in the photodetector (5) corresponding to the optical power of a grain (11) of average size of the Speckle Pattern (12).

The foregoing without the need to use spectral measurements, or signal post-processing method, or without the need to use CCD devices or Charge-Coupled Devices in the measurement as used by other measurement devices and specklegram-based sensors. This makes the invention in its application as a sensor very compact as it does not need complex or expensive processing hardware or measurement devices and the measurement or detection of the variable of interest can be carried out, for example, using a photodetector (5) connectorized photodiode, that is, with connectors for mechanical fiber splicing

However, for all the modalities the invention is also possible to perform spectral analysis at the output of the photodetector (5), and at the end of the fiber segment (3) opposite the first end of the second MMF Multimode Fiber Optic segment (3) that is connected to the second end of the first Fiber Optic segment (2), an electronic image acquisition system with CCD devices (Charge - Coupled Device), CMOS (Complementary Metal-Oxide-Semiconductor), or equivalent. The images obtained by the electronic image acquisition system are transferred and stored in a computer system, where correlation calculations can be developed between the image captured without disturbance (Speckle Pattern (12) undisturbed) and the captured image that is generated. after performing a disturbance on the disturbance region (8). These results can be displayed on a display device such as a screen, or a video player, or video beam. For all the modalities of the invention the photodetector (5) is selected from the group consisting of: light detector, photodiode, PIN photodiode, avalanche photodiode, phototransistor, photoresistor, photocathode, phototube, photovalve, photomultiplier, CCD, CMOS sensor, cell photoelectric, photoelectrochemical cell, photocell, connectorized photodetector, connectorized photodiode and combinations thereof.

For the understanding of the present invention, it is generally understood that a connectorized element is one that includes at one end a connector for mechanical splicing to optical fiber.

EXAMPLE 1

With reference to FIG. 2, FIG. 3 and 3A, the optical fiber structure comprising: A first segment of Optical Fiber (2) of 1 m in length, with a core diameter (2b) of 9 pm and a numerical aperture (AN) of 0.13, the first segment of Optical Fiber (2) with two ends, a second segment of MMF Multimode Optical Fiber (3) of 15 cm in length, with a core diameter (3b) of 50 pm and an aperture numerical value of 0.22, where the second MMF Multimode Fiber Optic segment (3) includes a disturbance region (8), and with two ends, where one end of the second MMF Multimode Fiber Optic segment (3) is connected to one of the ends of the first Fiber Optic segment (2) by fusion splicing and where a reflective silver film (9) deposited by sputtering (sputtering) is added and arranged at the second end of the second segment of MMF Multimode Optical Fiber (3. The second segment of MMF Multimode Fiber Optic (3) has a region of disturbance (8) obtained by coating the MMF Multimode Optical Fiber (3) with an encapsulation (7) with an opening (A).

An embodiment of the invention is made where one end of the first Fiber Optic segment (2) is connected to the second port of the optical circulator (10) by means of a mechanical connection type FC / PC (Ferrule Connector / Physical Contact) - other alternatives of mechanical connection is through connectors type ST (Straight Tip), SC (Standard Connector), LC (Lucent Connector), MU (Miniature Unit), MTRJ (Mechanical Transfer Registered Jack), E2000 connector or any type of mechanical fiber optic connector- . In the first port of the optical circulator (10) a coherent light emitter (1) is connected, which is a fiber-connectorized laser source, with emission wavelengths at 1310, 1490 and 1550 nm, and using the wavelength of 1550 nm. In the third port of the optical circulator (10) a photodetector (5) connectorized to fiber is connected, which is a photodetector of point optical power (5) type photodiode with response in the range of wavelengths from 800 to 1700nm.

The laser source ensures that the second segment of MMF Multimode Fiber Optic (3) works in a multimodal regime. There is a relationship of 0.8 between the core diameter (2b) of the first Optical Fiber segment (2) and the average grain diameter (11) of the Speckle Pattern (12) that is generated in the contact plane (BB) between the first Fiber Optic segment (2) and the second MMF Multimode Fiber Optic segment (3) when it is irradiated with coherent light from the coherent light emitter (1).

The second segment of MMF Multimode Fiber Optic (3) has a disturbance region (8) obtained by coating with an encapsulation (7) with an aperture (A), MMF Multimode Optical Fiber (3), where the aperture (A) It is rectangular and runs along the length of the second MMF Multimode Fiber Optic segment (3) exposing the opening (A) in the second MMF Multimode Fiber Optic segment (3). The longitudinal dimension L of the opening (A) is selected from 1 cm, 3 cm, 4.5 cm, 8 cm and 12 cm and the transverse dimension of this area is between 1 mm and 3 mm. The region of disturbance (8) is brought into contact or approaches a body whose temperature is to be measured. The output of the photodetector (5), which is a punctual optical power photodetector (5) type photodiode connectorized to fiber with response in the wavelength range of 800 to 1700nm, is connected to a voltage meter that allows characterization of the response of the assembly of this example when a certain temperature is applied; On the other hand, said temperature is also measured with a standard temperature sensor such as a thermocouple, an RTD sensor (Resistance Temperature Detector), a thermistor or a combination of the above, and in this way obtain the calibration curve of the assembly of this example. With the calibration curves, a sensitivity, dynamic range and threshold analysis of the present invention can be carried out, in the same way as illustrated in Example 2. The way to obtain the calibration curves is known to a person who is moderately versed in matter and the way to obtain said curves will be described in Example 2.

EXAMPLE 2

Referring to FIG. 4 and FIG. 4A, in a first embodiment of the invention there is a first segment of Singlemode Fiber Optic (2) of 1 m in length, with a core diameter (2b) of 9 pm and a numerical aperture of 0.13, and the first segment of Fiber Optic (2) has two ends; a second segment of MMF Multimode Fiber Optic (3) 15 cm long, with a diameter of 50 pm and a numerical aperture of 0.22, with a region of disturbance (8), and with two ends, where one end of the second segment Multimode Fiber Optic MMF (3) is connected to one of the ends of the first Fiber Optic segment (2) Single-mode by fusion splicing; The first segment of Optical Fiber (2) Singlemode at its first end is connected by mechanical connection type FC / PC to a photodetector (5) which is a point photodetector (5) connectorized to fiber with response in the 800 wavelength range at 1700nm, additionally a coherent light emitter (1) which for this example is a fiber optic connectorized laser source with 1550 nm emission wavelengths. Said emitter is a coherent light emitter (1) that is connected by means of a mechanical connection type SC / APC (Square connector or standard connector / Angled phisical contact) to the second end of the second segment of MMF Multimode Fiber Optic (3 ).

The fiber optic connectorized laser source with emission wavelengths 1550 nm ensures that the second segment of MMF Multimode Fiber Optic (3) works in multimodal regimen. The relationship is 0.8 between the core diameter (2b) of the first Optical Fiber segment (2) and the average grain diameter (11) of the Speckle Pattern (12) that is generated in the contact plane (BB) between the first segment of Optical Fiber (2) and second segment of MMF Multimode Optical Fiber (3) when it is irradiated with coherent light from the coherent light emitter (1).

The second segment of MMF Multimode Optical Fiber (3) has a disturbance region (8) obtained by coating the cladding (3a) of the MMF Multimode Optical Fiber (3) with an encapsulation (7) with an opening (A), where the aperture (A) is rectangular along the length of the second MMF Multimode Fiber Optic segment (3) exposing the second MMF Multimode Optical Fiber segment (3) in the aperture (A). The longitudinal dimension L of the opening (A) is selected from 1cm, 3cm, 4.5cm, 8cm and 12cm and the transverse dimension of this area is between 1mm and 3mm. The region of disturbance (8) is brought into contact or approaches a body whose temperature is to be measured.

The output of the photodetector (5) which is a point optical power photodetector (5) type photodiode connectorized to fiber with response in the range of wavelengths from 800 to 1700 nm is connected to a voltage meter that allows the characterization of the Response of the assembly of this example when the disturbance region (8) is brought into contact or approaches a body whose temperature is to be measured, on the other hand said temperature is also measured with a standard temperature sensor such as a thermocouple, an RTD (Resistance Temperature Detector) sensor, a thermistor or a combination of the above, in order to obtain the mounting calibration curve of this example. With the calibration curves, a sensitivity, dynamic range and threshold analysis of the present invention can be performed as presented below.

Referring to FIG. 8 the response of the structure of the invention with the assembly of example 2 and where the disturbance length of the second segment of MMF Multimode Optical Fiber (3) is 3 cm provides an average sensitivity of 1.4mV / ° C, a dynamic range from 87 ° C to 152 ° C, the threshold temperature is 87 ° C, the average trend is 97% linear, and the linear response equation that linearizes the response curve using least squares is y = 0.0014x + 2.0406 with R ² = 0.9792 where lay corresponds to the voltage response of the photodetector (5) and x corresponds to the disturbance temperature of the disturbance region (8) of the segment of MMF Multimode Fiber Optic (3)

Referring to FIG. 9 the response of the structure of the invention with the assembly of example 2 and where the disturbance length of the second segment of MMF Multimode Optical Fiber (3) is 4.5 cm provides an average sensitivity of 5.4mV / ° C, a dynamic range from 72 ° C to 132 ° C, the threshold temperature is 72 ° C, the average trend is 97% linear, and the linear response equation that linearizes the response curve using least squares is: y = 0.0054x + 1 , 7844 with R ² = 0.9719 where lay corresponds to the voltage response of the photodetector (5) and x corresponds to the disturbance temperature of the disturbance region (8) of the MMF Multimode Fiber Optic segment (3) .

Referring to FIG. 10 the response of the structure of the invention with the assembly of example 2 and where the disturbance length of the second segment of MMF Multimode Optical Fiber (3) is 8 cm provides an average sensitivity of 7.7mV / ° C, a dynamic range from 46 ° C to 104 ° C, the threshold temperature is 46 ° C, the average trend is 96% linear, and the linear response equation that linearizes the response curve using least squares is: y = 0.0077x + 1 , 8577 with R ² = 0.9623 where lay corresponds to the voltage response of the photodetector (5) and x corresponds to the disturbance temperature of the disturbance region (8) of the MMF Multimode Fiber Optic segment (3) .

Referring to FIG. 11 the response of the structure of the invention with the assembly of example 2 and where the disturbance length of the second segment of MMF Multimode Optical Fiber (3) is 12 cm provides an average sensitivity of 9.4mV / ° C, a dynamic range from 26 ° C to 79 ° C, the threshold temperature is 26 ° C, the average trend is 97% linear, and the linear response equation that linearizes the response curve using least squares is: y = 0.0094x + 1 .9073 with R ² = 0.9709 where the corresponds to the voltage response of the photodetector (5) and the x corresponds to the disturbance temperature of the disturbance region (8) of the MMF Multimode Fiber Optic segment (3).

EXAMPLE 3

In a first embodiment of the invention there is a first segment of Optical Fiber

(2) Singlemode 1 m long, with a core diameter (2b) of 9 pm and a numerical aperture of 0.13, the first Fiber Optic segment (2) has two ends; a second segment of MMF Multimode Fiber Optic (3) 15 cm long, with a diameter of 50 um and a numerical aperture of 0.22, with a perturbation region (8), and with two ends, where one end of the second segment Fiber Optic Multimode MMF

(3) is connected to one of the ends of the first Optical Fiber segment (2) Singlemode by fusion splicing; The first segment of Optical Fiber (2) Singlemode at its first end is connected by means of a mechanical connection type FC / PC to a photodetector (5) which is a point photodetector connectorized to fiber with response in the range of wavelengths from 800 to 1700nm, additionally a coherent light emitter

(1) which for this example is a fiber optic connectorized laser source with emission wavelengths 1550 nm. Said emitter is a coherent light emitter (1) that is connected by means of a mechanical connection type SC / APC (for its acronym in English Square connector or standard connector / Angled phisical contact) to the end of the second segment of MMF Multimode Fiber Optic (3) .

The fiber optic connectorized laser source with emission wavelengths 1550 nm ensures that the second segment of MMF Multimode Fiber Optic (3) operates in a multimodal regime. The relationship is 0.8 between the core diameter (2b) of the first Optical Fiber segment (2) and the average diameter of grains (11) of the Speckle Pattern (12) that is generated in the contact plane (BB) between the first Fiber Optic segment

(2) and second segment of MMF Multimode Fiber Optic (3) when it is irradiated with coherent light from the coherent light emitter (1).

Referring to FIG. 7C, the second MMF Multimode Fiber Optic segment

(3) has a disturbance region (8) that is obtained by wear of a part of the cladding (3a) (cladding) where for the worn area the longitudinal dimension of is selected between 1 cm, 3 cm, 4.5 cm, 8 cm and 12 cm and the transverse dimension is select between 1mm and 3mm. The region of disturbance (8) is brought into contact with substances that are changing their chemical composition, such as, for example, a percentage by volume of propyl alcohol in distilled water. The output of the optical power photodetector (5) is connected to a voltage meter that allows the characterization of the response of the assembly of example 3 when the percentage by volume of propyl alcohol in distilled water is changed, to obtain the calibration curve of the system proposed in this invention. With this calibration curve, sensitivity, dynamic range and threshold analysis can be performed, in the same way as illustrated in Example 2. The present invention is not limited to the modalities described and illustrated, as it will be evident to a skilled person. In the art, there are variations and possible modifications that do not depart from the spirit of the invention, likewise the applications of the invention are illustrated for measurements of variables and applications as a sensor, but the invention could be used in other applications such as modulators. optical fiber where the modulation of light signals is carried out by means of physical or chemical disturbance disturbance region (8) in the cladding (3a) of the second segment of MMF Multimode Optical Fiber (3).

Claims

1. A fiber optic structure, comprising:

- a first segment of Optical Fiber (2) with two ends;

- a second segment of MMF Multimode Fiber Optic (3) with two ends; where one end of the second MMF Multimode Fiber Optic segment (3) is connected to one of the ends of the first Optical Fiber segment (2); wherein said second segment has a disturbance region (8) in the cladding (3a) of the MMF Multimode Optical Fiber (3); and where the disturbance region (8) of the MMF Multimode Fiber Optic segment (3) is exposed to a physical or chemical disturbance.

2. The fiber optic structure of Claim 1, wherein the other end of the first Fiber Optic segment (2) is connected to a photodetector (5); and where the other end of the second MMF Multimode Fiber Optic segment (3) is connected to a coherent light emitter (1).

3. The fiber optic structure of Claim 1, wherein the first Fiber Optic segment (2) at its other end is connected to the second port of a three-port optical circulator (10); a coherent light emitter (1) is connected to the first port of the optical circulator (10); a photodetector (5) is connected to the third port of the optical circulator (10); and a reflective film (9) is arranged at the other end of the second segment of MMF Multimode Optical Fiber (3).

4. The fiber optic structure of any of the preceding Claims, wherein in the contact plane (BB) between the first fiber optic segment (2) and the second MMF Multimode Fiber Optic segment (3), a Speckle Pattern (12) with an average grain size (11) from Speckle Pattern (12); and where the core diameter (2b) of the first Optical Fiber segment (2), the numerical aperture (AN) of the second MMF multimode optical fiber segment (3) and the wavelength of the coherent light (1), respond to the relationship: (D _s )

0.5 <£ 1.8 d where: l

(D _s ) = - -jy: is the average grain size (11) of the Speckle Pattern (12), d. is the diameter of the core (2b) of the first Fiber Optic segment (2),

A.N: the numerical aperture of the second MMF fiber optic segment (3), l: the wavelength of the coherent light source (1).

5. The fiber optic structure of Claim 1, wherein the first Fiber Optic segment (2) is a Single Mode Fiber Optic (SMF) segment.

6. The fiber optic structure of Claim 1, wherein the second MMF Multimode Fiber Optic segment (3) has a length less than or equal to 15 cm.

7. The fiber optic structure of Claim 1, wherein the second MMF Multimode Optical Fiber segment (3) is covered with an encapsulation (7) with an aperture (A) forming the disturbance region (8) defined by the segment (L) and where said region of disturbance (8) allows metrological parameters to be varied.

8. The fiber optic structure of Claim 7, wherein the package (7) with an opening (A) is rectangular and has a length L less than the second segment of MMF Multimode Optical Fiber (3) forming the disturbance region (8 )

9. The fiber optic structure of Claim 1, wherein the second segment of MMF Multimode Optical Fiber (3) presents a narrowing of the cladding (3a) (cladding) forming the disturbance region (8).

10. The fiber optic structure of Claim 1, wherein the second segment of MMF Multimode Optical Fiber (3) presents a wear of the cladding (3a) of the second MMF Multimode Optical Fiber (3) parallel to the axis of the fiber, forming the region of disturbance (8).

The fiber optic structure of Claim 1, wherein the first Optical Fiber segment (2) and the first end of the second MMF Multimode Optical Fiber segment (3) are connected by fusion splicing.

12. The fiber optic structure of Claim 1, wherein the first segment of Optical Fiber (2) and the second segment of MMF Multimode Optical Fiber (3) are connected by mechanical splices that are selected from the group consisting of FC, PC, APC, ST, SC, LC, MU, MTRJ, E2000, and combinations thereof.

13. The fiber optic structure of Claims 2 and 3, where the photodetector (5) is selected from the group consisting of light detector, photodiode, PIN photodiode, avalanche photodiode, phototransistor, photoresistor, photocathode, phototube, photovalve, photomultiplier , CCD, CMOS sensor, photoelectric cell, photoelectrochemical cell, photocell, connectorized photodetector, connectorized photodiode and combinations thereof.