The subject of this invention is an interferometer made on a multicore waveguide, particularly on waveguide, either fibrous or planar, the essence of which is to apply the core activation process, as disclosed below.

Measurement of geometric thickness of layers, carried out with the use of micrometric sets, requires a physical grasp of the entire layer to be assessed with a measuring instrument, which is difficult in the case of measurements of deformable elements or liquids. The use of this type of devices is also impossible when examining solutions or biological substances or when running biological tests, for instance when culturing and observing bacteria and viruses. In turn, optical thickness is referred to as the length of the optical path and is expressed by the product of the geometric layer thickness and its refraction coefficient. This meaning of optical thickness shall be applied hereafter.

Examinations of substances of this type (deformable, liquids, etc.) are usually carried out under the microscope, which is time-consuming and requires the use of expensive and non-universal measuring and observation instruments. Performance of In- situ examinations is also significantly hindered.

Generally speaking, optical thickness measurements can be carried out with the use of interferometers. Hence, the known methods of measuring the thickness of phase elements include ones with the use of interferometers, e.g. the Michelson interferometer or the Mach-Zehnder interferometer. Volumetric interferometers cannot however measure in-situ changes in optical thickness for relatively small layers of several to several hundred nanometers or single micrometers.

Various structures of waveguide interferometers are known in technology, particularly those based on optical fiber. Also known are measurement methods assuming their use.

The structure of an optical fiber interferometer assuming the tapering of optical fiber was described in article titled "Tapered fiber Mach-Zehnder Interferometer for Liquid Level Sensing", written by Hun-Pin Change and associates, published by PIERS Proceedings in 2013. The structure of the element is based on the use of a standard single-mode fiber and the execution of two non-adiabatic taperings on this fiber. The idea behind the operation of this interferometer is based on the measurement of interference of these modes after the second tapering. The interferometer is used to measure liquid levels. Multicore waveguides are not used in this solution.

Article titled "Simple all-microconstructed-optical-fiber interferometer built via fusion splitting", written by Joel Villatoro and associates, published by the Optics Express in 2007, presents a single-core photonic fiber interferometer concept, whereby the fiber is spliced in two places to enclose openings serving as couplers.

A review article titled "Recent Progress of In-Fiber Integrated Interferometers", written by Libo Yuan and published by PhotonicSensors in 2011, presents a concept for Mach-Zehnder and Michelson interferometer structures based on tapered double-core fibers. The Michelson interferometer in the proposed structure has a mirror on the entire fiber terminal's face surface. Passing through a tapering and reflected off the mirror, signals interfere.

The concept of a local tapering of double-core fibers is also known from article titled "Gemini Fiber for Interferometry and Sensing Applications" by E. Zetterlund and associated, published in the Journal of Sensors in 2009. According to this concept, no substances are applied on the cores of optical fibers (i.e. the fibers are not activated). The example presented in the article is characterized by equal-measuring arms.

The structure of a multicore fiber interferometer was also described in article titled "All-solid multi-core fiber-based multipath Mach-Zehnder interferometer for temperature sensing", written by Ming Tang and associates and published in Applied Physics B in 2013. The authors point to the sensor application of the interferometer, which can be particularly used to measure temperature. In this concept, the optical fiber is spliced with an SMF-28 fiber by connecting to the intra-core casing instead of the centers of particular cores. In this case, the authors point to the application of multibeam interference. In traditional interferometers, splices made in intra-core spaces serve as couplers here. Article titled "Multicore microstructured optical fiber for sensing applications", written by L. Sojka and associates, published in Optics Communications in 2015, presents a concept for a multibeam Mach-Zehnder interferometer, based on seven-core microstructured fiber. Splices made at both ends of the fiber serve as couplers. The fiber used has coupled cores, thanks to which the effect of external factors on intra-core power transfer can be truly examined. An idea for the structure of a multi-parameter sensor based on multicore fibers

(spatial multiplexing), and specifically on multicore fibers with heterogeneous cores, was presented in article titled "Spatial-Division Multiplexed Mach-Zehnder Interferometers in Heterogeneous Multicore Fiber for Multiparameter Measurement", written by Lin Gan and associates and published in the IEE Photonics Journal in 2016. According to the concept, a Mach-Zehnder interferometer is built on seven-core fiber (two taperings). All seven cores are activated at the input by a fan-in/fan-out element. At the end of the system, power is collected from all cores by a fan-in/fan-out element as well. By changing the parameters of the tapering, other interference images are collected at the output, using a detector. This concept is dedicated to temperature and strain measurements, and the authors claim cross- sensitivity can be eliminated.

In another example of sensor structure, as presented in description ref. US4653906, a device comprising multicore fibers is used to measure strain. In this solution, a double- core fiber is fixed to a strain-transferring structure. Strains change the value of crosstalk among cores, which signals the strain affecting the optical fiber. The above presented solutions based on interferometers made on multicore fibers are predominantly dedicated to strain and temperature measurements. They are however unsuitable for effective measurement of optical thickness of layers. The structures of their systems do not enable core activation either.

It was therefore the purpose of this invention to develop a waveguide interferometer, particularly an optical fiber interferometer, for measuring optical thickness and/or adsorption of thin layers. The use of waveguide interferometers opens technology to new possibilities, whereby interferometer tests are used in studies requiring significant miniaturization - such applications were not accessible for volumetric interferometers. Effective measurement with the use of the invention is possible thanks to the arm activation process, which is the essence of its operation. An additional advantage of the invention is that its concept, known from volumetric optics, is reinforced by the effect of interferometer imbalance. Another goal of the invention was to develop an interferometer structure, which would be also suitable for measuring other physical values, such as: temperature, elongation / expansion, strain, pressure, gas concentration and others. The changes of those values are further called the changes of environmental factor. An interferometer for measuring physical parameters, particularly changes in the geometric thickness of layers and/or the light refraction index in layers of varying optical thickness, according to the invention, works in a reflective configuration and contains a coupler connected to a light source and made on a waveguide, particularly on an optical fiber or planar waveguide, at least double-core, where the face of at least one core is activated, and least one core of the waveguide, particularly of an optical fiber, is connected directly or indirectly to a signal detector situated on the same side of the multicore waveguide as the light source.

Activation of at least one core is understood as a method / process, beneficially selected from among: - coating with at least one chemically active substance, to which another substance can connect,

coating with at least one chemically active substance, which can disconnect when exposed to environmental factors,

coating with at least one substance changing its parameters, particularly its thickness and/or its refractive index and/or absorption when exposed to environmental factors,

connecting a dielectric section using any known technique.

Activation by connecting at least one dielectric section to the face of at least a single core is understood as the case when the interferometer is preferably used to measure external factors, such as temperature, elongation / expansion, strain, pressure, affecting this connected dielectric section.

Coating the core with at least one active substance is understood as coating the surface of the fiber's face in the area, in which the core is situated, with this substance or its mixtures. In general terms, the activating substance changes its optical thickness and/or absorption by reacting with the environment. In particular, the active substance is a sorbent of chemical substances from the environment and/or a substance which swells / shrinks when exposed to external factors and/or a substance which binds chemical substances from the environment.

In a specific embodiment of the invention, each of the cores can be activated by means of one of the aforementioned methods, in particular each of the cores can be coated with a different substance. This beneficial embodiment can be used to measure the optical thickness of various substance layers with the use of a single interferometer according to the invention.

A coupler on the multicore waveguide, particularly on an optical fiber, is mademade by means of any known method, preferably by tapering and/or enclosing holes, if the structure of the waveguide includes holes. In particular, this method is analogous to the method described, among others, in patent description for invention application ref. P.411430. Enclosing holes without tapering is understood as a measure, by which holes are enclosed without applying an additional stretching force. Nonetheless, when enclosing holes without applying this additional stretching force, the crosswise dimensions of the waveguide, particularly the optical fiber, are decreased (tapering), since glass sinks above the holes.

A multicore waveguide used in the interferometer according to the invention is also understood as at least two optical fibers, at least single-core, set together, particularly in a capillary or its fixed on common substrate.

In a beneficial embodiment of the invention, the waveguide used in the structure of the interferometer is a polarization-preserving waveguide, particularly an optical fiber. In a beneficial embodiment of the invention, elements supporting the waveguide and forming the measuring system are also the polarization-preserving elements.

In a beneficial embodiment of the invention, apart from activating the core, at least one waveguide core has a different length to others. In particular, a dielectric section (particularly glass, particularly a waveguide) is connected to at least one of the waveguide's cores, particularly a multicore optical fiber, using any of the known methods. The connection is made by splicing, gluing or butt-coupling. The dielectric section connected facilitates the selective activation of a selected waveguide core. In this beneficial embodiment of the invention, imbalancing the interferometer results in optimizing the sensitivity of the interferometer to accommodate the expected changes in the optical parameters of activating substances. It is particularly possible to activate this arm of the interferometer, to which the dielectric section is connected, by coating the face of the connected dielectric section with an active substance. In another beneficial embodiment of the invention, one of the cores of the multicore waveguide can have different lengths to the remaining cores, either factory-made, or made by means of a different method. Preferably, the light source emits broad-spectrum light, and comprises particularly a supercontinuum light source, a halogen lamp or a super-luminescence lamp. Analogous effects can be obtained by using tunable lasers. In a beneficial embodiment, the detector is a spectrum analyzer or an optical spectrometer. When using tunable laser, the photodiode can be advantageously used as a detector.

In a beneficial embodiment of the invention, light is entered to the core or cores of a waveguide, preferably a multicore optical fiber, through an optical circulator, an optical coupler or a fan-in/fan-out device.

In another beneficial embodiment of the invention, signal from the light source travels the optical fiber to the first circulator port. The second circulator port is connected to one of the cores of the multicore waveguide, particularly a double-core fiber, and the third port - to the detector. In this beneficial embodiment, a superluminescence diode or a supercontinuum source serve as the light source, and the detector preferably comprises a spectrometer. The optical fiber is connected to the multicore optical fiber containing a coupler made with the use of any known method, particularly by tampering and/or enclosing holes, if the optical fiber used has holes. One of the cores of the multicore waveguide is activated at its output by connecting a dielectric section, an optical fiber in this instance, using any of the known methods, particularly by splicing, gluing or butt- coupling. The activated core beneficially differentiates the optical paths of the interferometer arms.

Leaving the second circulator port, the signal is directed through a single-core optical fiber to one of the cores of a multicore optical fiber, which contains a coupler. In the multicore fiber, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber cores. In one of the cores, the signal is reflected off the tip of the connected fiber, and the signal from the second core is reflected off the tip of the double-core fiber. Reflected light returns through the double-core fiber and the coupler mounted on it, and then reaches the detector through the circulator. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of parameters of the connected optical fiber, which can result from: elongation, strain, temperature change and other factors.

In another beneficial embodiment of the invention, signal from the light source travels the optical fiber to the first circulator port. The second circulator port is connected to one of the cores of the multicore fiber, particularly a double-core fiber, preferably with homogeneous cores. The reflected signal returns through the optical fiber to the second circulator port, and is sent to the optical fiber from the third circulator port to the detector. In this beneficial embodiment, a superluminescence diode or a supercontinuum source serve as the light source, and the detector preferably comprises a spectrometer. The optical fiber is connected to the multicore optical fiber containing a coupler made with the use of any known method, particularly by tampering and/or enclosing holes, if the optical fiber used has holes. One of the cores of the multicore fiber is activated at its output by applying a coating. A dielectric section, an optical fiber in this instance, is connected to the second core, using any of the known methods, particularly by splicing, gluing or butt-coupling. The connected section exposes the core, to which no substance is connected, thus differentiating the optical paths of the interferometer arms.

Leaving the second circulator port, the signal is directed through a single-core optical fiber to one of the cores of a multicore optical fiber, which contains a coupler. In the multicore fiber, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber cores. In one of the cores, the signal is reflected off the tip of the connected fiber, and the signal from the second core is reflected off the tip of the double-core fiber. Reflected light returns through the double-core fiber and the coupler mounted on it, and then reaches the detector through the circulator. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of parameters of the connected optical fiber, which can result from: elongation, strain, temperature change and other factors.

In another beneficial embodiment of the invention, signal from the light source travels the optical fiber to the first circulator port. The second circulator port is connected to one of the cores of the multicore fiber, particularly a double-core fiber, preferably with homogeneous cores. The reflected signal returns through the optical fiber to the second circulator port, and is sent to the optical fiber from the third circulator port to the detector. In this beneficial embodiment, a superluminescence diode or a supercontinuum source serve as the light source, and the detector preferably comprises a spectrometer. The optical fiber is connected to the multicore optical fiber containing a coupler made with the use of any known method, particularly by tampering and/or enclosing holes, if the optical fiber used has holes. One of the cores of the multicore fiber is activated at its output by applying a coating. A dielectric section, an optical fiber in this instance, is connected to the second core, using any of the known methods, particularly by splicing, gluing or butt-coupling. The connected section exposes the core, to which no substance is connected, thus differentiating the optical paths of the interferometer arms.

Leaving the second circulator port, the signal is directed through a single-core optical fiber to one of the cores of a multicore optical fiber, which contains a coupler. In the multicore fiber, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber cores. In one of the cores, the signal is reflected off the tip of the connected fiber, and the signal from the second core is reflected off the layer at its tip. Reflected light returns through the double-core fiber and the coupler mounted on it, and then reaches the detector through the circulator. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer.

In another beneficial embodiment of the invention, signal from the light source is directed to one of the cores of a multicore fiber, preferably three-core. In this beneficial embodiment, a supercontinuum source or two connected superluminescence diodes serve as the light source, which direct the light through a single-core input fiber, preferably to the central core of a multicore fiber, preferably a three-core. Detectors are connected to the remaining optical fiber cores through input fibers. A coupler is made on the multicore fiber, and two of the cores on the output are activated by applying initial layer thicknesses. To differentiate the optical paths of the interferometer arms, a dielectric section, preferably a glass pin, is connected to the third core using any of the known methods, particularly by splicing, gluing or butt-coupling. In the multicore fiber, signal is propagated in one of the cores until it reaches the coupler, which splits the signal among the fiber cores. The coupler is made using any of the known methods, particularly by tapering and/or enclosing holes, if the optical fiber used has holes. The diameters of the cores of the optical fiber are selected in a manner that thanks to the coupler made, for wavelength λΐ, light is propagated in the central core and in one of the external cores, and for wavelength XI, light is propagated in the central core an in the second of the external cores.

After passing through the coupler, the light is further propagated in particular cores and, reflecting off the measured layers and the connected fiber, returns on the path, through the multicore fiber, to the detectors. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer.

In another beneficial embodiment of the invention, signal from the light source is directed to one of the cores of a multicore fiber, preferably seven-core. A coupler is made on the multicore fiber. In this beneficial embodiment, a supercontinuum source or connected superluminescence diodes serve as the light source, which direct the light through a single-core input fiber, preferably to the central core of a multicore fiber, preferably a seven-core. Detectors are connected to the remaining optical fiber cores through input fibers. Detectors can be connected to each of the fibers or a single detector can be switched in between optical fibers, e.g. manually or with the use of an optical switch. To differentiate the optical paths of the interferometer arms, a dielectric section, preferably a glass pin, is connected to the third core using any of the known methods, particularly by splicing, gluing or butt-coupling. The remaining cores are activated at their outputs by applying initial layer thicknesses. In another beneficial embodiment of the invention, a different substance can be applied on each core. In the multicore fiber, signal is propagated in one of the cores until it reaches the coupler, which splits the signal among the fiber cores. The coupler is made using any of the known methods, particularly by tapering and/or enclosing holes, if the optical fiber used has holes. The diameters of the cores of the optical fiber are selected in a manner that thanks to the coupler made, particular wavelengths are propagated in the central core and in particular external cores.

After passing through the coupler, the light is further propagated in particular cores and, reflecting off the measured layers and the connected glass pin, returns on the same path, through the multicore fiber, to the detectors. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer. In this case, a change of the optical thickness of the measured layer changes the position of the interference stripes.

In another beneficial embodiment of the invention, signal from the light source is directed through an optical fiber to the first circulator port. The second circulator port is connected by means of optical fibers to one of the cores of a multicore fiber, preferably a double-core. In this beneficial embodiment, a supercontinuum source or a superluminescence diode serve as the light source. The optical fiber is connected to a multicore fiber containing a coupler made using any of the known methods, particularly by tapering and/or enclosing holes, if the optical fiber used has holes. One of the cores of the multicore fiber is activated at its output by applying a layer. In the multicore fiber, signal is propagated in one of the cores, until it reaches a coupler which splits the signal among the fiber cores.

Leaving the second circulator port, the signal is directed through a single-core optical fiber to one of the cores of a multicore optical fiber, which contains a coupler. In the multicore fiber, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber cores. In one of the cores, the signal is reflected off the tip of the connected fiber, and the signal from the second core is reflected off the layer on its tip. Reflected light returns through the double-core fiber and the coupler mounted on it, and then reaches the detector through the circulator. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer. In this case, a change of the optical thickness of the measured layer changes the position of the interference stripes. In another beneficial embodiment of the invention, the planar waveguide technology based on PLC splitters (Planar Lightwave Circuit splitter) is applied. In this beneficial embodiment, an equal-power splitter is used for a specific wavelength and beneficial configuration of 2x2. Broad-spectrum light is used as the wave source. One of the outputs of the splitter is activated by applying initial layer thicknesses. The second splitter output is preferably factory extended or shortened and preferably hidden inside the splitter's housing to ensure the imbalance of the interferometer and stability of operation. From the light source, signal is directed through an optical fiber leading to the input splitter port. A detector is connected to the second input port through an input fiber. The detector preferably comprises an optical spectrum analyzer. Signal from the light source is divided by the PLC splitter and reflects off the layer and the tip of the extended arm, hidden in the housing. Reflecting off the tip and the layer, light returns on the same path, through the splitter. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer. In this case, a change of the optical thickness of the measured layer changes the position of the interference stripes. The invention can be particularly used as a sensor for measuring physical parameters, particularly optical thickness and/or layer absorption, which can be used to determine their increases.

The subject of the invention can be used for direct measurements of optical thickness and/or layer absorption, or, indirectly, for measuring other physical values, which affect these layers (temperature, humidity, gas concentration and others). Using the invention, it is possible to measure other parameters, such as strain/elongation, pressure or temperature. One of the advantages of the invention is the possibility of studying nanometer changes in the thickness of optical layers. An additional advantage of the invention is the possibility of increasing the sensitivity of the interferometer by imbalancing its arms.

The embodiments of the invention presented below do not limit its possible variants, which result from the essence of the invention, as described. In particular, the measured change of measured layer optical thickness and/or absorption cannot be caused by various external factors (temperature, elongation, pressure, shrinking, swelling, humidity, gas concentration, etc.). The method of causing a change in the optical thickness (thickness, refractive index) and/or absorption does not affect the physical operation principle of the invention, which is identical in all instances.

Particular embodiments of the invention were presented in a figure, in which:

Fig. 1 presents a beneficial embodiment of the invention in example 1, where the following elements are visible: light source 1, detector 2, optical fiber circulator 3, single- core input fibers 4, multicore fiber 6, coupler 7 made on a multicore fiber 6, single-core fiber section 8 of d in total length, connected to one of the cores of a multicore fiber 6.

Fig. 2 presents a close-up on a beneficial embodiment of the coupler 7, made by tapering a multicore fiber, where fiber 6 of initial diameter dl is tapered to diameter d2, whereas the proper tapering has the total length of c, and the transitional zones of the tapering - the falling and rising zone have total lengths of bl and b2. The length of the optical fiber outside the tapering equals, respectively, al and a2, counting from the light feed side and the side, on which the signal is reflected.

Fig. 3 presents the section of optical fiber 6, applicable to example 1, where microstructural elements - cores 9.1., 9.2 and holes 10 are lined at distances equaling Λ in casing 11.

Fig. 4 presents a beneficial embodiment of the invention in examples 2 and 6, where the following examples are possible: light source 1, detector 2, optical fiber circulator 3, single-core input fibers 4, activating layer applied on one of the cores 5, multicore fiber 6, coupler 7 made on the multicore fiber 6, single-core fiber section 8 of d in total length, connected to one of the cores of the multicore fiber 6.

Fig. 5 presents the section of optical fiber 6, applicable to example 2, where microstructural elements - cores 9.1., 9.2 and holes 10 are lined at distances equaling Λ in casing 11. Fig. 6 presents a beneficial embodiment of the invention in example 3, where the following elements are visible: light source 1, detector 2, single-core input fibers 4, activating layers 5.1 and 5.2 applied on two of the cores , multicore fiber 6, coupler 7 made on the multicore fiber 6, single-core fiber section 8 of d in total length, connected to one of the cores of the multicore fiber 6. Fig. 7 presents the section of optical fiber 6, applicable to example 3, where microstructural elements - cores 9.1., 9.2 and 9.3 and holes 10 are lined at distances equaling Λ in casing 11.

Fig. 8 presents a beneficial embodiment of the invention in example 4, where the following elements are visible: light source 1, detector 2, single-core input fibers 4 connected to multicore fiber 6 through a fan-in/fan-out element 12, activating layer 5 applied on two of the cores, multicore fiber 6, coupler 7 made on a multicore fiber 6, section of single-core fiber 8 of d in total length, connected to one of the cores of the multicore fiber 6.

Fig. 9 presents the section of optical fiber 6, applicable to example 4, where microstructural elements - cores 9.1., 9.2, 9.3, 9.4, 9.5, 9.6, 9.7 and holes 10 are placed on the nodes of a hexagonal lattice at distances equaling Λ in casing 11.

Fig. 10 presents a beneficial embodiment of the invention in example 4, where the following elements are visible: light source 1, detector 2,polarization-preserving fiber circulator 3, polarization-preserving single-core input fibers 4, activating layer 5 applied on two of the cores, multicore fiber 6, coupler 7 made on a multicore fiber 6.

Fig. 11 presents the section of optical fiber 6, applicable to example 5, where microstructural elements - cores 9.1., 9.2 and holes 10 are lined at distances equaling Λ in casing 11.

Fig. 12 presents the section of optical fiber 6, applicable to example 6, where cores 9.1, 9.2 are lined at distances equaling Λ in casing 11.

Fig. 13 presents a beneficial embodiment of the invention from example 7, where the following elements are visible: light source 1, detector 2, PLC splitter 13 with two output arms 13.1 and 13.2, which is placed in a housing 14 and activating layer 5 applied on the tip of one of the arms. Example 1

A source 1 is connected through an optical fiber 4 to the first circulator 3 port C.l, and optical fibers 4 connected to the second port C.2 are also connected to a double-core fiber 6 with a coupler 7 made on it, and the face of one of the cores of double-core fiber 6 is activated by splicing in a section of an optical fiber 8. A detector is connected to the third circulator 3 port C.3 through an optical fiber 4.

Signal from light source 1 travels optical fiber 4 to the first circulator 3 port C.l. The second circulator 3 port C.2 is connected to one of the cores of a multicore fiber 6 by means of optical fibers 4, and the third port C.3 - to a detector 2. A superluminescence diode serves as the light source 1, and the detector preferably comprises a spectrometer. One of the cores of the multicore fiber 6 is activated at its output by connecting an optical fiber 8 using any of the known methods, particularly by splicing. The activated core beneficially differentiates the optical paths of the interferometer arms.

The optical fiber comprises: - two cores 9.1 and 9.2 made of S1O2 doped with Ge0 ₂ of 8.2 μιη in total diameters, doped with 3.5 molar % GeC .

A casing 11 of dl=125 μιη in total diameter, made of non-doped S1O2 silica;

seven air holes between the cores, of 7.2 μιη in total diameter.

The core and the holes are lined together, and their centers are spanned every Λ = 9 μη-ι.

The length of the tied-in optical fiber 8 section is 1 mm.

The coupler 7 is made as a tapering with hole enclosing. The parameters of the tapering are: bl=7mm, c=10 mm, b2=8 mm. The fiber is tapered in a manner that d2 = 0.3 · dl. Leaving the second circulator 3 port C.2, the signal is directed through a single-core optical fiber 4 to one of the cores of a multicore optical fiber 6, which contains the coupler 7. In the multicore fiber 6, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber 6 cores. In one of the cores, the signal is reflected off the tip of the connected fiber 8, and the signal from the second core is reflected off the tip of the double-core fiber. Reflected light returns through the double- core fiber 6 and the coupler 7 mounted on it, and then reaches the detector 2 through the circulator 3. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of parameters of the connected optical fiber 8. In this case, the measured change of position of interference stripes is approx. 5 nm for section 8 elongation by approx. 1 με.

Example 2

A source 1 is connected through an optical fiber 4 to the first circulator 3 port C.l, and optical fibers 4 connected to the second port C.2 are also connected to a double-core fiber 6 with a coupler 7 made on it, and the face of one of the cores of double-core fiber 6 is activated by coating 5, and a section of an optical fiber 8. A detector is connected to the third circulator 3 port C.3 through an optical fiber 4.

Signal from light source 1 - a super electroluminescence diode - travels the single- core optical fiber 4 to the circulator 3. The second circulator 3 port C.2 is connected to one of the cores of a double-core fiber 6 with homogeneous cores 9.1 and 9.2 by means of single-core optical fibers 4. The third port C.3 leads to a detector 2 - a spectrum analyzer in the form of a spectrometer. Optical fiber 4 is connected to the double-core fiber 6 which contains the coupler 7 made by enclosing holes without additional tapering. One of the cores of the multicore fiber 6 is activated at its output by applying a layer 5. A section of a single-core fiber 8 is connected to the second core 9.1 of the multicore fiber 6.

The optical fiber comprises: two doped cores 9.1 and 9.2 made of S1O2 doped with 3,5% Ge0 ₂ of 8.2 μιη in total diameters, the distance between cores is 126 μιη

a casing 11 of dl=250 μιη in total diameter, made of non-doped S1O2 silica;

- air holes 10 placed with the cores on nodes of a hexagonal lattice with a lattice constant of Λ = 18 μιη, whereas d/Λ = 0,8, i.e. the diameters of the holes are 0,8 · Λ.

The coupler 7 is made by enclosing holes at the length of 3mm without additional tapering. The single-core fiber section 8 spliced to the double-core fiber is characterized with the same doping and core dimensions as cores 9.1 and 9.2 and is 50 μιη long.

The substance used applied on the core 9.2 is perfluorinated polymer with a refractive index of approx. 1.33. Substance 5 can be placed on the core 9.2 by immersing the fiber in the polymer solution. Exposed to the effects of cooling media comprising carbon, chlorine and fluoride compounds, such as l,l,2-Trichloro-l,2,2-trifluoroethane, the layer swells. In this configuration, the thickness of the substance changes by approx. 10 nm, which corresponds to a stripe shift by approx. 2 nm.

Leaving the second circulator 3 port C.l, the signal is directed through a single-core optical fiber 4 to the double-core optical fiber 6, which contains the coupler 7. In the double- core fiber 6, the signal is propagated in one of the cores until reaching the coupler 7, which splits it between the fiber cores. In one of the cores, the signal is reflected off the tip of the connected fiber 8, and the signal from the second core is reflected off the layer 5 on its tip. Reflected light returns through the double-core fiber 6 and the coupler 7 mounted on it, and then reaches the detector 2 through the circulator 3. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or layer 5 absorption.

Example 3

A source 1 is connected through an optical fiber 4 to the input of one of the cores of a three-core fiber 6, with a coupler 7 made on it, and a glass pin is spliced to one of the cores, behind the coupler, and the remaining faces of three-core fiber 6 cores are activated by applying layers 5.1 and 5.2, and the cores of the three-core fiber 6 are connected to detectors 4 by means of fibers 4 on the side of the light source.

Signal from light source 1 is directed to one of the cores of the three-core fiber 6. A supercontinuum source serves as the light source 1 and enters light through the single-core input fiber 4 to the central core of the three-core fiber. Detectors are connected to the remaining cores of the fiber 6 by means of input fibers 4. A coupler 7 is made on the three- core fiber 6, and two of the cores are activated at their outputs by applying initial layer thicknesses 5.1 and 5.2. A glass pin section 8 is spliced to the third of the cores. Signal in the multicore fiber 6 is propagated in one of the cores until it reaches the coupler 7, which splits the signal among the three fiber cores. The coupler 7 is made by enclosing holes in optical fiber 6 without additional tapering.

The optical fiber comprises: three cores 9.1, 9.2 and 9.3 made of S1O2 doped with GeC : the central core 9.1 of 8.2 μιη in total diameter is doped with 3.5 molar % GeC , the side core 9.2 of 6.1 μιη in total diameter is doped with 4.5 molar % GeC , the side-core 9.3 of 6.24 μιη in total diameter is doped with 4.5 molar % GeC ,

a casing 11 of dl=125 μιη in total diameter, made of non-doped S1O2 silica;

seven air holes between the cores, of 10 μιη in total diameter.

The cores 9 and the holes 10 are lined together, and their centers are spanned every Λ = 20 μη-ι. The coupler 7 is made by enclosing holes at the length of 5 mm without additional tapering. The diameters of the fiber are selected in a manner that thanks to the coupler made, at wavelength of 1.57 μιη, light propagated in the central core 9.1 and one of the external cores 9.3, and at wavelength of 1.45 μιη, light propagates in the central core 9.1 and in the second of the external cores 9.2. The glass pin section 8 spliced to the three-core fiber 6 is 80 μιη long and is made of silica.

The substance 5.1 applied on the core 9.2 is Yttrium oxide, characterized by small porosity and a refractive index of approx. 1.8. Substance 5.1 can be obtained with the use of high-power laser pulses shot at the Yttrium oxide in a manner that its vapors settle on the fiber. A layer made in this manner can serve as a hydrochloric acid flooding sensor. When exposed to the effects of hydrochloric acid, the thickness of the layer changes by approx. 50 nm, which causes a shift of the stripes by approx. 5 nm.

At the same time, the substance applied on the core 9.2 is perfluorinated polymer with a refractive index of approx. 1.33. Substance 5 can be placed on the core 9.2 by immersing the fiber in the polymer solution. Exposed to the effects of cooling media comprising carbon, chlorine and fluoride compounds, such as l, l,2-Trichloro-l,2,2- trifluoroethane, the layer swells. In this configuration, the thickness of the substance changes by approx. 10 nm, which corresponds to a stripe shift by approx. 2 nm. After the light has passed through the coupler 7, it is propagated in particular cores and, reflecting off the measured layers 5.1 and 5.2 and the connected fiber 8, returns on the same path through the multicore fiber 6 to the detectors 2.

The detectors display interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or absorption of layers 5.1 and 5.2. Example 4

A source 1 is connected through an optical fiber 4 to the input of one of the cores of a seven-core fiber 6 through a fan-in/fan-out element, and a coupler 7 is made on the seven-core fiber, and a glass pin is spliced to the face of central core 9.1, and the faces of the external cores of the seven-core fiber 6 are activated by applying layers 5, and the cores of the seven-core fiber 6 are connected to detectors 2 on the side of the light source by means of fibers 4, after having passed through a fan-in/fan-out element 12. Signal from the light source is directed to one of the cores of the seven-core fiber 6. A supercontinuum source serves as the light source, which directs the light through a single- core input fiber 4 to the central core of a multicore fiber 6. Detectors 2 are connected to the remaining optical fiber cores through input fibers 4. Detectors 2 can be connected to each of the fibers or a single detector can be switched in between optical fibers, e.g. manually or with the use of an optical switch. The coupler 7 is made on the seven-core fiber 6, and the external cores are are activated at their outputs by applying initial layer 5 thicknesses. A glass pin section 8 is spliced to the central core 9.1. In the seven-core fiber 9.1, signal is propagated in one of the cores until it reaches the coupler, which splits the signal among the fiber cores.

The coupler is made by means of enclosing holes in optical fiber 6 without additional tapering. The diameters of the cores of the optical fiber are selected in a manner that thanks to the coupler made, particular wavelengths are propagated in the central core and in particular external cores. The optical fiber comprises:

- seven cores 9.1, 9.2, 9.3, 9.4, 9.5, 9.6 and 9.7 made of Si0 ₂ doped with Ge0 ₂ : central core 9.1 of 8.2 μιη, doped with 3.5 molar % GeC ,

external core 9.2 of 6.24 μιη, doped with 4.5 molar % GeC ,

external core 9.3 of 6.1 μιη, doped with 4.5 molar % GeC ,

external core 9.4 of 5.96 μιη, doped with 4.5 molar % GeC ,

external core 9.5 of 5.82 μιη, doped with 4.5 molar % GeC ,

external core 9.6 of 5.86 μιη, doped with 4.5 molar % GeC ,

external core 9.7 of 5.54 μιη, doped with 4.5 molar % GeC , - a casing 11 of dl=300 μιη in total diameter, made of non-doped S1O2 silica;

air holes between the cores, of 10 μιη in total diameter.

The cores are placed on nodes of a hexagonal lattice with a lattice constant of Λ =

20 μη-ι.

The coupler 7 is made by enclosing holes at the length of 10 mm without additional tapering. The diameters of the fiber are selected in a manner that thanks to the coupler made: wavelengths of approx. 1.57 μιη propagate in the 9.1 and 9.2 core couple, wavelengths of approx. 1.45 μιη propagate in the 9.1 and 9.3 core couple, wavelengths of approx. 1.35 μιη propagate in the 9.1 and 9.4 core couple, wavelengths of approx. 1.25 μιη propagate in the 9.1 and 9.5 core couple, - wavelengths of approx. 1.15 μιη propagate in the 9.1 and 9.6 core couple,

wavelengths of approx. 1.05 μιη propagate in the 9.1 and 9.7 core couple.

The glass pin section 8 is 100 μηη long and is made of silica.

The substance 5 applied is hydrolyzed collagen with a refractive index of 1. Substance 5 is applied by immersing the fiber in a 1% water solution of hydrolyzed collagen and drying it. This configuration is used to measure humidity, as collagen swells when exposed to cold water and airborne humidity. Immersed in water at 20°C, collagen swells, changing its thickness from 100 nm to 200 nm, and causing stripes to shift by approx. 2 nm. After passing through the coupler 7, the light is further propagated in particular cores and, reflecting off the measured layers 5 and the connected fiber 8, returns on the same path, through the multicore fiber 6, to the detectors 2. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the measured layers 5. In this case, a change of the optical thickness of the measured layer changes the position of the interference stripes. Example 5

A source 1 is connected through a polarization-preserving optical fiber 4 to the first polarization-preserving circulator port C.l, and polarization-preserving optical fibers 4 connected to the second port C.2 are also connected to a double-core fiber 6 with a coupler 7 made on it, and the face of one of the cores of double-core fiber 6 is activated applying a layer 5. A detector is connected to the third circulator 3 port C.3 through an optical fiber 4.

Signal from light source 1 travels optical fiber 4 to the first circulator 3 port C. l. The circulator 3 is a polarization-preserving circulator. The second circulator 3 port C.2 is connected to one of the cores of a double-core fiber 6 by means of polarization-preserving optical fibers 4. A superluminescence diode serves as the light source 1. Leaving the second circulator 3 port C.2, the signal is directed through a polarization-preserving single-core optical fiber 4 to one of the cores of a multicore optical fiber 6, which contains the coupler 7. In the multicore fiber 6, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber 6 cores. In one of the cores, the signal is reflected off the tip of the connected fiber 6, and the signal from the second core is reflected off the layer 5 at its tip. Reflected light returns through the double-core fiber 6 and the coupler 7 mounted on it, and then reaches the detector 2 through the circulator 3. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer 5. In this case, a change of the optical thickness of the measured layer 5 changes the position of the interference stripes.

The coupler is made using any of the known methods, in particular by tapering and enclosing holes.

The optical fiber comprises: - two cores 9.1 and 9.2 made of S1O2 doped with 3,5 molar % Ge0 ₂ of 8.2 μιη in total diameters,

a casing 11 of dl=125 μιη in total diameter, made of non-doped S1O2 silica;

an air hole between the cores of 15 μιη in total diameters.

The core and the holes are lined together, and their centers are spanned every Λ = 15 μιη. The double-core fiber 6 is a polarization-preserving fiber.

The coupler 7 is made as a tapering with hole enclosing. The parameters of the tapering are: bl=b2=5 mm, c=5mm. The fiber is tapered in a manner that d2 = 0.6 · dl.

The substance 5 applied is polystyrene with a refractive index of approx. 1.5. Substance 5 is applied on the fiber by immersing the fiber in a 1% solution of methylene chloride and drying it. The layer swells when exposed to acetone, which is why the sensor can be used as acetone sensor. Immersed in room-temperature acetone, the layer increases its thickness by approx. 900 nm and causes the stripes to shift by approx. 120 nm.

Example 6

A source 1 is connected through an optical fiber 4 to the first circulator port C.l, and an optical fiber 4 connected to the second port C.2 is also connected to a double-core fiber 6 with a coupler 7 made on it, and the face of one of the cores 9.1 of double-core fiber 6 is activated by coating with an active substance. A detector is connected to the third circulator 3 port C.3 through an optical fiber 4.

Signal from light source 1 travels optical fiber 4 to the first circulator 3 port C.l. The second circulator 3 port C.2 is connected to one of the cores of a double-core fiber 6 by means of optical fibers 4. A superluminescence diode serves as the light source 1.

Leaving the second circulator 3 port C.2, the signal is directed through a single-core optical fiber 4 to one of the cores of a multicore optical fiber 6, which contains the coupler 7. In the multicore fiber 6, the signal is propagated in one of the cores until reaching the coupler, which splits it preferably between both fiber 6 cores. In one of the cores, the signal is reflected off the tip of the connected fiber 8, and the signal from the second core is reflected off the layer 5 at its tip. Reflected light returns through the double-core fiber 6 and the coupler 7 mounted on it, and then reaches the detector 2 through the circulator 3. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer 5. In this case, a change of the optical thickness of the measured layer 5 changes the position of the interference stripes.

The coupler is made using any of the known methods, in particular by tapering.

The optical fiber comprises: two cores 9.1 and 9.2 made of S1O2 doped with 3,5 molar % GeC of 8.2 μιη in total diameters,

a casing 11 of dl=125 μιη in total diameter, made of non-doped S1O2 silica;

The cores are lined together, and their centers are spanned every Λ = 25 μιη.

The coupler 7 is made as a tapering. The parameters of the tapering are: bl=b2=5 mm, c=5mm. The fiber is tapered in a manner that d2 = 0.5 · dl.

The section of the single-core fiber 8 spliced to the double-core fiber is characterized by the same doping and core dimensions as cores 9.1 and 9.2 and is 75 μιη long. The fiber is prepared by immersing in a solution containing sulfuric acid and 30% perhydrol in a 3:1 ratio for an hour. A surface prepared in this manner is active and, after placing the fiber in a solution containing allylamine poly hydrochloride, a polymer layer 2 nm thick and with a refractive index of approx. 1.5 is connected to the fiber. Connecting a 2 nm layer causes a 0.5 nm shift of the stripes. The sensor is used to detect allylamine poly hydrochloride.

Example 7

In a beneficial embodiment of the invention, the planar waveguide technology based on PLC splitters (Planar Lightwave Circuit splitter) is applied. Using an optical fiber 4, a source 1 is connected to a PLC splitter 14. One of the outputs of the splitter 13.1 is activated by applying initial layer 5 thicknesses, and the second splitter output 13.2 is factory by 40 μιη and hidden inside the splitter's housing 14 to ensure the imbalance of the interferometer and stability of operation. The return arm of the splitter is connected to a decoder 2 by means of an optical fiber 4. From the light source, signal is directed through an optical fiber leading to the splitter's input port. A detector is connected to the second input port through an input fiber. The detector preferably comprises an optical spectrum analyzer. Signal from the light source is divided by the PLC splitter and reflects off the layer and the tip of the extended arm, hidden in the housing. Reflecting off the tip and the layer, light returns on the same path, through the splitter. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer. In this case, a change of the optical thickness of the measured layer changes the position of the interference stripes.

In this beneficial embodiment, an equal-power splitter 13 is used for a 1500nm wavelength and a 2x2 configuration. A tungsten bulb with a light color corresponding to a black body of 1900 K is used as the light source.

Signal from the light source 1 is directed through the input fiber 1 to the input splitter port. Detector 2 is connected to the second input splitter port by means of an input fiber 4. The detector is an optical spectrum analyzer. From the light source 1, the signal is split in the PLC splitter and is then reflected off the layer 5 and off the tip of the extended arm hidden in the housing 13.2. Reflecting off the tip 13.2 and the layer 5, light returns on the same path through the splitter 13. The detector displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer 5. In this case, a change of the optical thickness of the measured layer 5 changes the position of the interference stripes. The substance 3 applied on the output port is ethylcellulose with a refractive index of approx. 1.4. Substance 3 is applied on the port by immersing the double-core fiber in a 0.5% solution of butyl acetate, extracting it and drying. An optical fiber coated in this manner reacts to ethanol vapors, which cause it to swell. An approx. 50 nm change in the thickness of the layer causes the stripes to shift by approx. 10 nm.