Waveguide interferometer

Abstract

A waveguide interferometer includes a multicore fiber used a multicore waveguide, where the multicore waveguide includes a coupler section formed by tapering a portion of the multicore waveguide so that one core though which a light source is fed is optically coupled to another core that is terminated differently that the core into which the source signal is provided. The terminations respond differently upon being exposed to an environmental condition or substance, and the difference in response to the environmental condition or substance results in a shift in interference of the light reflected back through the multicore waveguide, which is detected with a detector on the same side of the multicore waveguide as the light source.

Claims

1. A waveguide interferometer for measuring optical parameters, comprising: a light source configured to feed a light to a first core of a multicore waveguide at a first side of the multicore waveguide through a single core optical fiber that is coupled to the first core of the multicore waveguide, wherein the multicore waveguide is a multicore optical fiber and has at least the first core and a second core, where the first core has an output at a second side of the multicore waveguide, wherein a splitter is provided on the multicore waveguide, between the first side and the second side of the multicore waveguide, that splits the light from the light source between the first core and the second core, wherein the output of the first core is coated with at least one chemically active substance, and the first core is connected to a signal detector at the first side of the multicore waveguide through the single core optical fiber.

2. The waveguide interferometer according to claim 1, wherein the at least one chemically active substance is able to couple itself to another substance.

3. The waveguide interferometer of claim 1, wherein the at least one chemically active substance is able to detach from another substance when exposed to a selected environmental element.

4. The waveguide interferometer of claim 1, wherein the at least one chemically active substance changes one of thickness, absorption, or refractive index when exposed to a selected environmental element.

5. The waveguide interferometer of claim 1, wherein the multicore waveguide has more than two cores.

6. The waveguide interferometer of claim 1, wherein the first core of the multicore waveguide has a different length than the second core.

7. The waveguide interferometer of claim 1, wherein the first core of the multicore waveguide is extended at the second side of the multicore waveguide with at least one dielectric section selected from a group including: a glass pin, a waveguide, and an optical fiber.

8. The waveguide interferometer of claim 5, further comprising: a fan-in/fan-out element connected to the multicore waveguide at the first side of the multicore waveguide; and at least one additional detector, wherein the at least one additional detector and the light source are connected to the multicore waveguide through the fan-in/fan-out element.

9. The waveguide interferometer of claim 1, further comprising: a circulator having a first port connected to the light source, a third port connected to the signal detector, and a second port connected to the first core of the multicore waveguide through the single core optical fiber.

10. The waveguide interferometer of claim 1, wherein at least two of the cores are coated with different chemically active substances at the second side of the multicore waveguide.

11. The waveguide interferometer of claim 1 wherein the multicore waveguide is a polarization-maintaining waveguide.

12. The waveguide interferometer of claim 1, wherein the multicore waveguide is a multicore fiber and includes holes between the first core and the second core in a casing of the multicore fiber.

13. The waveguide interferometer of claim 1, wherein the splitter is a multicore fiber coupler provided on the multicore waveguide as an area having decreased crosswise dimension.

14. The waveguide interferometer of claim 1, wherein the splitter is a planar lightwave circuit splitter and the multicore waveguide is a planar lightwave circuit waveguide.

15. The waveguide interferometer of claim 1, wherein the chemically active substance comprises a substance selected of the group consisting of yttrium oxide, perfluorinated polymer, hydrolyzed collagen, polystyrene, and ethylcellulose.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and explain various principles and advantages all in accordance with the present invention.

(2) FIG. 1 shows a waveguide interferometer of a first example, in accordance with some embodiments;

(3) FIG. 2 shows a detail of a coupler for a waveguide interferometer, in accordance with some embodiments;

(4) FIG. 3 cross section view of a multi-core fiber for a waveguide interferometer, in accordance with some embodiments;

(5) FIG. 4 shows a waveguide interferometer of a further example, in accordance with some embodiments;

(6) FIG. 5 cross section view of a multi-core fiber for a waveguide interferometer, in accordance with some embodiments;

(7) FIG. 6 shows a waveguide interferometer of a further example, in accordance with some embodiments;

(8) FIG. 7 shows a cross sectional view of a multi-core fiber optic cable for a waveguide interferometer, in accordance with some embodiments;

(9) FIG. 8 shows a waveguide interferometer of a further example, in accordance with some embodiments;

(10) FIG. 9 shows a cross sectional view of a multi-core fiber for use in a waveguide interferometer, in accordance with some embodiments;

(11) FIG. 10 is a waveguide interferometer of a further example, in accordance with some embodiments;

(12) FIG. 11 shows a cross sectional view of a multi-core fiber for use in a waveguide interferometer, in accordance with some embodiments;

(13) FIG. 12 shows a cross sectional view of an alternative multi-core fiber for use in a waveguide interferometer, such as that shown in FIG. 10, in accordance with some embodiments; and

(14) FIG. 13 shows a waveguide interferometer of a further example, in accordance with some embodiments.

DETAILED DESCRIPTION

(15) While the specification concludes with claims defining the features of the disclosure that are regarded as novel, it is believed that the disclosure will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. It is to be understood that the disclosed embodiments are merely exemplary of the disclosure, which can be embodied in various forms.

(16) FIG. 1 shows a waveguide interferometer 100 of a first example, in accordance with some embodiments. FIG. 3 shows a cross sectional view 300 of a double-core fiber 110 used in the waveguide interferometer 100.

Example 1

(17) A light source 102 is connected through a first optical fiber 104 to a first port C.1 of a circulator 106, and optical fiber 108 is connected to the second port C.2 of the circulator 106 and is further connected to a double-core fiber 110 with a coupler 112 formed in the double-core fiber 110. The face of one of the cores of the double-core fiber 110 is activated by splicing in a section of optical fiber 114 which is the second core of the double-core fiber 110, and the first core is connected to the core of optical fiber 108. A detector 116 is connected to the third port C.3 of the circulator 106 through an optical fiber 118.

(18) A signal from light source 102 travels down optical fiber 104 to the circulator 106 at port C.1. The second port C.2 is connected to the first core of the multi-core fiber 110 by means of optical fiber 108, and via the third port C.3 to the detector 116. A superluminescence diode can serve as the light source 102, and the detector 116 preferably comprises a spectrometer. One of the cores of the multicore fiber 110 is activated at its output by connecting an optical fiber 114 using any of the known methods, particularly by splicing. The activated core beneficially differentiates the optical paths of the interferometer arms. The first core of the double-core fiber 110 is blocked by a layer of substance 120.

(19) As shown in FIG. 3, the double-core optical fiber 110 comprises:

(20) two cores 302 and 304 made of SiO.sub.2 doped with GeO.sub.2 and being 8.2 m in total diameter, and doped with 3.5 molar % GeO.sub.2.

(21) A casing 308 having a 125 m diameter, made of non-doped SiO.sub.2 silica;

(22) seven air holes 306 being formed in a line between the cores 302, 304, each having a diameter of 7.2 m.

(23) The cores 302, 304 and the holes 306 are formed along a line, and their centers are located every 9 m (310).

(24) The length d in FIG. 1 of the tied-in optical fiber 114 section is 1 mm.

(25) The coupler 112 is shown in detail in FIG. 2, and is made as a tapering with hole. The parameters of the tapering are: b1=7 mm, c=10 mm, b2=8 mm. The fiber 110 is tapered in a manner such that waist region c has a diameter d2=0.3 (d1).

(26) Leaving the second port C.2 of the circulator 106, the signal is directed through a single-core optical fiber 108 to one of the cores of a multicore optical fiber 110, which contains the coupler 112. In the multicore fiber 110, the signal is propagated in one of the cores until reaching the coupler 112, which splits the signal between both cores of multicore fiber 110. In one of the cores, the signal is reflected off the distal tip of the connected fiber 114, and the signal from the second core is reflected off the tip of the double-core fiber 110 covered by substance 120. Reflected light returns through the double-core fiber 110 and the coupler 112 connected to it, and then reaches the detector 116 through the circulator 106. The detector 116 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 114. In this case, the measured change of position of interference stripes is approx. 5 nm for section 114 changing by approx. 1 . Thus, changes in length of core section 114 can be determined based on the interference pattern changes produced by the detector 116.

Example 2

(27) The second example utilizes a waveguide interferometer 400 and a double-core fiber 414 that has a cross section 500 as shown in FIG. 5.

(28) Referring now to FIG. 4, a light source 402 is connected through an optical fiber 404 to the first port C.1 of the circulator 406, and optical fiber 408 is connected to the second port C.2 of the circulator 406 and is also connected to a double-core fiber 414 that has a coupler 416 formed in the double-core fiber 414. A face of one of the cores of double-core fiber 414 is activated by coating 422, and a section of an optical fiber 418. A detector 412 is connected to the third port C.3 through an optical fiber 410.

(29) Signal from light source 402a super electroluminescence diodetravels the single-core optical fiber 404 to the circulator 406. The second port C.2 is connected to one of the cores of a double-core fiber 414 with homogeneous cores 502 and 504 by means of single-core optical fiber 408. The third port C.3 leads to a detector 412, which is a spectrum analyzer in the form of a spectrometer. Optical fiber 408 is connected to the double-core fiber 414 which contains the coupler 416 that is made by enclosing holes without additional tapering. One of the cores 502, 504 of the multicore fiber 414 is activated at its output by applying a layer of substance 422. A section of a single-core fiber 418 is connected to the second core 502 of the multicore fiber 414.

(30) The double-core optical fiber 414 comprises:

(31) two doped cores 502, 504 made of SiO.sub.2 doped with 3.5% Geo.sub.2 each having a diameter of 8.2 m, and the distance between cores 502, 504 is 126 m.

(32) a casing 508 having a diameter of 250 m, made of non-doped SiO.sub.2 silica;

(33) air holes 506 placed with the cores on nodes of a hexagonal lattice with a lattice constant 510 of 18 m, and the diameters of the holes are 0.8 of the lattice constant 510, or 14.4 m.

(34) The coupler 416 is made by enclosing holes at a length of 3 mm without additional tapering. The single-core fiber section 418 spliced to the double-core fiber is characterized with the same doping and core dimensions as cores 502 and 504 and is 50 m long.

(35) The substance used applied on the core 504 is a perfluorinated polymer solution with a refractive index of approx. 1.33. Substance 422 can be placed on the core 504 by immersing the fiber 414 in the perfluorinated polymer solution. Exposed to the effects of cooling media comprising carbon, chlorine and fluoride compounds, such as 1,1,2-Trichloro-1,2,2-trifluoroethane, the layer of substance 422 swells. In this configuration, the thickness of the substance 422 changes by approximately 10 nm, which corresponds to a stripe shift by approx. 2 nm.

(36) Leaving the second port C.1, the signal is directed through a single-core optical fiber 404 to the double-core optical fiber 414, which contains the coupler 416. In the double-core fiber 414, the signal is propagated in one of the cores until reaching the coupler 416, which splits it between the fiber cores 502, 504. In one of the cores, the signal is reflected off the tip of the connected fiber 418, and the signal from the second core is reflected off the subtance 522 on its tip. Reflected light returns through the double-core fiber 414 and the coupler 416 mounted on it, and then reaches the detector 412 through the circulator 406. The detector 412 displays interference stripes in a spectral band (wavelength), the shift and/or contrast of which depends on the change of optical thickness and/or 1 absorption of the substance 422.

Example 3

(37) A third example uses the waveguide interferometer 600 of FIG. 6, and a three core multi-core fiber, a cross section 700 of which is shown in FIG. 7. In FIG. 6 a source 602 is connected through an optical fiber 604 to the input of one of the cores of a three-core fiber 606, with a coupler 608 made on it, and a glass pin 618 is spliced to one of the cores, behind the coupler 608, and the remaining faces of three-core fiber 606 cores are activated by applying layers 620 and 622 of a substance. The cores of the three-core fiber 606 are connected to detectors 612, 614 by means of fibers 610, 616, respectively, on the side of the light source 602.

(38) A signal from light source 602 is directed to one of the cores of the three-core fiber 606. A supercontinuum source serves as the light source 602 and transmits light through the single-core input fiber 604 to the central core of the three-core fiber 606. Detectors 612, 614 are connected to the remaining cores of the fiber 606 by means of input fibers 610, 616. The coupler 608 is formed on the three-core fiber 606, and two of the cores are activated at their outputs by applying initial layer thicknesses 620 and 622. A glass pin section 618 is spliced to the third of the cores. Signal in the multicore fiber 606 is propagated in one of the cores until it reaches the coupler 608, which splits the signal among the three fiber cores.

(39) The coupler 608 is made by enclosing holes in optical fiber 606 without additional tapering.

(40) The optical fiber 606, as shown in cross section view 700 of FIG. 7, comprises:

(41) three cores 702, 704 and 706 made of SiO.sub.2 doped with GeO.sub.2: the central core 702 can have a diameter of about 8.2 m in total diameter is doped with 3.5 molar % GeO.sub.2, the side core 704 has can have a diameter of about 6.1 m and can be doped with 4.5 molar % GeO.sub.2, the side-core 706 can have a diameter of about 6.24 m and can be doped with 4.5 molar % GeO.sub.2, a casing 710 can have a diameter of about 125 m, and can be made of non-doped SiO.sub.2 silica;

(42) two air holes 708 between the cores, of 10 m in total diameter.

(43) The cores 702, 704, 706 and the holes 708 are lined together, and their centers are spanned 712 every 20 m.

(44) The coupler 608 is made by enclosing holes at the length of 5 mm without additional tapering beyond the coupler 608. These diameters of the fiber are selected so that light at a wavelength of 1.57 m is propagated in the central core 702 and one of the external cores 706, and lights at wavelength of 1.45 m propagates in the central core 702 and in the second of the external cores 704. Thus, the central core 702 gets two different wavelengths of light, and the outer cores 704, 706 each get one wavelength of light. The glass pin section 618 is spliced to the three-core fiber 606 is 80 m long and is made of silica.

(45) The substance 620 applied on the core 704 is Yttrium oxide, characterized by small porosity and a refractive index of approx. 1.8. Substance 620 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.

(46) At the same time, the substance 622 applied on the core 706 is perfluorinated polymer with a refractive index of approx. 1.33. Substance 622 can be placed on the core 706 by immersing the fiber in the polymer solution. Exposed to the effects of cooling media comprising carbon, chlorine and fluoride compounds, such as 1,1,2-Trichloro-1,2,2-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 608, it is propagated in particular cores and, reflecting off the measured layers 620 and 622 and the connected fiber 618, returns on the same path through the multicore fiber 606 to the detectors 612, 614.

(47) The detectors 612, 614 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 620 and 622.

Example 4

(48) Referring to FIGS. 8 and 9, a light source 802 is connected through an optical fiber segment 804 to the input of one of the cores of a seven-core fiber 806 through a fan-in/fan-out element 808, and a coupler 810 is made on the seven-core fiber, and a glass pin 812 is spliced to the face of central core 902, and the faces of the external cores of the seven-core fiber 806 are activated by applying layers 814, and the cores of the seven-core fiber 806 are connected to detectors 816 on the side of the light source by means of fibers segments 804, after having passed through a fan-in/fan-out multiplexer element 808.

(49) Signals from the light source 802 are directed to one of the cores of the seven-core fiber 806. A supercontinuum source serves as the light source 802, which directs the light through a corresponding one of the single-core input fiber segments 804 to the central core 902 of a multicore fiber 806. Detectors 816 are connected to the remaining optical fiber cores 904-914 through respective corresponding input fiber segments 804. Detectors 816 can be connected to each of the fibers 904-914, or a single detector can be switched in between optical fibers 904-914, e.g. manually or with the use of an optical switch. The coupler 810 is made on the seven-core fiber 806, and the external cores 904-914 are activated at their outputs by applying initial layer of substance 814 at a prescribed thicknesses. A glass pin section 812 is spliced to the central core 902. In the seven-core fiber 806, a signal is propagated in one of the cores until it reaches the coupler 810, which splits the signal among the fiber cores 902-914.

(50) The coupler 810 is made by means of enclosing holes 920 in optical fiber 806 without additional tapering beyond the coupler 810. The diameters of the cores 902-914 of the optical fiber 806 are selected such that particular selected wavelengths are propagated in the central core 902 and in particular external cores 904-914.

(51) The optical fiber comprises:

(52) seven cores 902-914 made of SiO.sub.2 doped with GeO.sub.2:

(53) central core 902 has a diameter of 8.2 m, and is doped with 3.5 molar % GeO.sub.2, external core 904 has a diameter of 6.24 m, and is doped with 4.5 molar % GeO.sub.2, external core 906 has a diameter of 6.1 m, and is doped with 4.5 molar % GeO.sub.2, external core 908 has a diameter of 5.96 m, and is doped with 4.5 molar % GeO.sub.2, external core 910 has a diameter of 5.82 m, and is doped with 4.5 molar % GeO.sub.2, external core 912 has a diameter of 5.86 m, and is doped with 4.5 molar % GeO.sub.2, external core 914 has a diameter of 5.54 m, and is doped with 4.5 molar % GeO.sub.2, a casing 916 has a diameter of 300 m and is made of non-doped SiO.sub.2 silica; air holes 920 between the cores, have a diamer of 10 m.

(54) The cores 902-914 are placed on nodes of a hexagonal lattice with a lattice constant 918 of =20 m. The coupler 810 is made by enclosing holes at the length of 10 mm without additional tapering beyond the coupler 810. The diameters of the fiber are selected for light propagation as follows:

(55) wavelengths of approx. 1.57 m propagate in the core couple of cores 902, 904,

(56) wavelengths of approx. 1.45 m propagate in the core couple of cores 902, 906,

(57) wavelengths of approx. 1.35 m propagate in the core couple of cores 902, 908,

(58) wavelengths of approx. 1.25 m propagate in the core couple of cores 902, 910,

(59) wavelengths of approx. 1.15 m propagate in the core couple of cores 902, 912,

(60) wavelengths of approx. 1.05 m propagate in the core couple of cores 902, 914.

(61) The glass pin section 812 is 100 m long and is made of silica.

(62) The substance 814 applied is hydrolyzed collagen with a refractive index of 1. Substance 814 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 810, the light is further propagated in particular cores and, reflecting off the measured layers 814 and the connected fiber 812, returns on the same path, through the multicore fiber 806, to the detectors 816. The detector 816 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 814. In this case, a change of the optical thickness of the measured layer changes the position of the interference stripes.

Example 5

(63) Referring now to FIGS. 10-11, a source 1 is connected through a polarization-preserving optical fiber 4 to the first polarization-preserving circulator port C.1, 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.

(64) Signal from light source 1 travels optical fiber 4 to the first circulator 3 port C.1. 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.

(65) 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.

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

(67) The optical fiber comprises:

(68) two cores 9.1 and 9.2 made of SiO.sub.2 doped with 3.5 molar % GeO.sub.2 of 8.2 m in total diameters,

(69) a casing 11 of d1=125 m in total diameter, made of non-doped SiO.sub.2 silica;

(70) an air hole between the cores of 15 m in total diameters.

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

(72) The coupler 7 is made as a tapering with hole enclosing. The parameters of the tapering are: b1=b2=5 mm, c=5 mm. The fiber is tapered in a manner that d2=0.6.Math.d1.

(73) 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

(74) Referring to FIGS. 10-11, a source 1002 is connected through an optical fiber 1004 to a circulator 1006 at a first circulator port C.1, and an optical fiber 1008 connected to the second port C.2 is also connected to a double-core fiber 1010 with a coupler 1012 made on it, and the face of one of the cores 1102 of double-core fiber 1010 is activated by coating with an active substance 1018. A detector 1016 is connected to the third circulator port C.3 through an optical fiber 1014.

(75) Signal from light source 1002 travels in optical fiber 1004 to the first circulator port C.1. The second circulator port C.2 is connected to one of the cores of a double-core fiber 1010 by means of optical fibers 1008. A superluminescence diode serves as the light source 1002.

(76) Leaving the second circulator port C.2, the signal is directed through a single-core optical fiber 1008 to one of the cores of a multicore optical fiber 1006, which contains the coupler 1012. In the multicore fiber 1010, the signal is propagated in one of the cores until reaching the coupler 1012, which splits the signal between both cores of the fiber 1010. In one of the cores, the signal is reflected off the tip of the connected fiber 1020, and the signal from the second core is reflected off the layer 1018 at that tip. Reflected light returns through the double-core fiber 1010 and the coupler 1012 formed on it, and then reaches the detector 1016 through the circulator 1006. The detector 1016 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 1018. In this case, a change of the optical thickness of the measured layer 1018 changes the position of the interference stripes.

(77) The coupler 1012 is made using any of the known methods, in particular by tapering the fiber 1010.

(78) The optical fiber 1010 comprises:

(79) two cores 1102 and 1104 made of SiO.sub.2 doped with 3.5 molar % GeO.sub.2, and have a diameter of 8.2 m;

(80) a casing 1106 having a diameter of 125 m that is made of non-doped SiO.sub.2 silica;

(81) The cores 1102, 1104 are lined together, and their centers are spanned 1110 every =25 m.

(82) The coupler 1012 is made as a tapering, such as that shown in FIG. 2. The parameters of the tapering are: b1=b2=5 mm, c=5 mm. The fiber 1010 is tapered in a manner that d2= that of d1.

(83) The section of the single-core fiber 1020 spliced to the double-core fiber is characterized by the same doping and core dimensions as cores 1102 and 1104 and is 75 m long.

(84) The fiber 1020 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 1020 in a solution containing allylamine polyhydrochloride, a polymer layer 2 nm thick and with a refractive index of approx. 1.5 is connected to the fiber 1020. Connecting a 2 nm layer causes a 0.5 nm shift of the stripes produced by the detector 1016. The sensor is used to detect allylamine polyhydrochloride.

Example 7

(85) In a beneficial embodiment of the invention, the planar waveguide technology based on PLC splitters (Planar Lightwave Circuit splitter) is applied. Referring to FIGS. 12-13, using an optical fiber 1304, a source 1302 is connected to a PLC splitter 1312. One of the outputs of the splitter 13.1 is activated by applying initial layer 1314 of material at a known thickness, and the second splitter output 13.2 is extended by 40 m and hidden inside the splitter's housing 1312 to ensure the imbalance of the interferometer and stability of operation. The return arm of the splitter 1312 is connected to a decoder 1308 by means of an optical fiber 1306.

(86) From the light source 1302, signal is directed through an optical fiber 1304 leading to the splitter 1312 at the splitter's input port. A detector 13108 is connected to the second input port through an input fiber 1306. The detector 1308 preferably comprises an optical spectrum analyzer. Signal from the light source is divided by the PLC splitter 1312 and reflects off the layer 1314 and the tip of the extended arm (e.g. 13.2), hidden in the housing. Reflecting off the tip 13.2 and the layer 1314, light returns on the same path, through the splitter 1312. The detector 1308 displays interference stripes in a spectral band (wavelength), and the shift and/or contrast of which depends on the change of optical thickness and/or the absorption of the layer 1314. In this case, a change of the optical thickness of the measured layer 1314 changes the position of the interference stripes.

(87) In this beneficial embodiment, an equal-power splitter 1310 is used for a 1500 nm wavelength and a 22 configuration. A tungsten bulb with a light color corresponding to a black body of 1900 K is used as the light source 1302.

(88) Signal from the light source 1302 is directed through the input fiber 1304 to the input splitter port. Detector 1308 is connected to the second input splitter port by means of an input fiber 1306. The detector 1308 is an optical spectrum analyzer. From the light source 1302, the signal is split in the PLC splitter 1312 and is then reflected off the layer 1314 and off the tip of the extended arm hidden in the housing 13.2. Reflecting off the tip 13.2 and the layer 1314, light returns on the same path through the splitter 1312. The detector 1308 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 1314. In this case, a change of the optical thickness of the measured layer 1314 changes the position of the interference stripes.

(89) The substance 1314 applied on the output port is ethylcellulose with a refractive index of approx. 1.4. Substance 1314 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.