Interferometric sensor and its use in a device interférométriqqapteur-that.

An interferometric sensor dual, series or parallel, and its use in an interferometric optical device for, determining at one or more points one or more physical quantities, such as pressure and temperature, which can result on interferometric sensors β π term of optical path difference.

Industrial levels in all optical sensors are enormous and the arrival on the market of optical fibers industrially reliable for conducting light beams over long distances was contemplated embodiment of optical sensors industrial for responding has a number of requirements are particularly sensitive oil phase: measures to long distances, intrinsically safe, low volume,, immunity to electromagnetic interference and possibility of multiplexing.

Such a sensor has the advantage of allowing the accurate measurement of temperature and remote pressure especially in a hydrocarbon production well or geothermal.

A first goal is to provide an interferometric sensor wherein the spectra dual splined linked to variations in temperature and pressure are additive.

In a first embodiment, cc.e first aim is achieved in that the interferometric sensor comprises two interferometers - in parallel using light beams concentric, center and outer, from an optical fiber placed at the focus of a collimating lens, a first interferometer using the central beam comprised a deformable membrane whose beam centered comprises a deformable membrane whose deformation is pressure-sensitive and temperature which varies its position with respect to one of the faces of a glass wool faced ' parallel - / a second interferometer using the beam outside wherein

- the distance between two sides of glass strips parallel sided varies as a function of expansion different from each^- of the two blades_/ the. lens collimâtrice collects both beams of light toward an optical fiber.

- The first embodiment constitutes a sensor interferometer due to homogeneous parallel double-type " Perot Pèrraot ^ - V.^: - _

A second submanifold•can consist of a double sensor-parallel mixed. -^; ^

- - * c.^: with the second embodiment seHon " the first object is achieved by the cooking-that the sensor iftterferometric has two - interferometers in parallel using bundles - - concentric light, ' centered and outside from an optical fiber placed at the focus of a lens collimâtrice, the first interferometer using a central beam. comprises a deformable membrane whose. deformation is sentisble pressure and temperature which varies its position with respect to one of the faces of a first glass plate with parallel faces depending on these two, parameters, - - the second interferometer path: - ': ς the beam¹ exterior - is' consisting of a polarizer and a blade dual refractive ' whose birefringence varies as a function of temperature to create a spectra qiïi splined and is focused onto the optical fiber by the. lens' collimâtrice ' pdùr comstically recombine in adding up in splined with the spectrum of the central beam.

According to a third variant of the first - and fourth butyl double sensor can be homogeneous-parallel by association of two interferometers dual refractive or mixed parallel by associating a birefringent interferometer pressure sensitive and a Fabry-Perot interferometer responsive to temperature.

According to the third or fourth embodiment, this first object is achieved in that the interferometric sensor comprises two interferometers in parallel using beams of light outward from central concentric stored characteristics of an optical fiber located at the focus of a collimating lens, the first interferometer using the central beam includes a polarizer and a blade: dual refractive whose birefringence varies mainly depending on the pressure, the second interferometer in the beam path is outside, either of an interferometer wherein the distance between the sides of two blades. glass with parallel faces held by a cylindrical spacer varies with different expansion coefficients of each of these two blades, either. a second polarizer and a second blade dual refractive whose birefringence varies as a function of temperature to create a spectrum spline which is focused onto the optical fiber by the collimator lens to recombine in adding up in splined with the spectrum of the central beam.

A second object of the invention is to provide a dual interferometric sensor wherein the spectra fluted linked to changes in pressure and temperature can be multiplied.

As a: first variant, this second purpose " is achieved by the fact that the interferometric sensor comprises first and second interferometers in series using a single light beam from an optical fiber located at the focus of a collimating lens, the first interferometer being formed of a deformable membrane whose deformation is pressure-sensitive and temperature which varies its position with respect to one of the faces of a glass plate with parallel faces, based on these two parameters to obtain an optical path difference characteristic of the position of the membrane and creating a spectrum spline, the second interferometer positioned in the light path is composed of a polarizer, a blade dual refractive whose birefringence varies as a function of temperature to create, after being completed two CFSD Project to Vallêr and return, differential spline spectrum, the spectrum is the product resulting splined splined spectra of each of the interferometers, is focused onto the optical fiber by the collimating lens.

This first variant of the~second purpose constitutes a double sensor mixed series. In one this second alternative. second goal, the dual sensor homogeneous series can be obtained by associating ' two Fabry-Perot interferometers.

the V, . In accordance with the second embodiment.., the second object is achieved w^{reverse speed} the. in that the interferometric sensor comprises a. first and second intefferometers in series using a, single light beam from an optical filter positioned at the focus of a collimating lens, the first interf erometer urié being formed of deformable membrane whose deformation is pressure-sensitive and temperature which varies its position with respect to one surface of a first glass plate with parallel faces depending on these two parameterized, so as to obtain an optical path difference characteristic of the membrane and creating a spectrum source is splined from there, the second interferometer wherein the distance between two sides, of two blades meeting place parallel faces varies with different expansion coefficients of each of cesdeux blades uses the beam exiting the first, the spectrum resulting spline being focused upon the optical fiber by the collimator lens..

In an alternative embodiment, a double sensor homogeneous series can be obtained by combination of two dual~interf erometers refracting in series and in an additional embodiment, a double sensor mixed series can be constructed by combining a birefringent interferometer pressure-sensitive and a Fabry-Perot interferometer "

In these third and fourth embodiments, the interferometric sensor comprises two interféroraètres in series using a single light beam from an optical fiber located at the focus of a collimating lens, the first interferometer being composed of a polarizer and a blade dual refractive whose birefringence varies mainly depending on the pressure, the second interferometer - ^ on the light path consists, either of an interferometer wherein the distance between two surfaces. two, glass slides. parallel sided held

by a cylindrical spacer varies. . of.

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coefficient... expansion, different, . of ., _ each of, these two blades, or a second polarizer and a second blade having two-refractive, birefringence. varies, depending on, temperature to create a trimmed - spectrum.

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interférc>3letric. ...■; - - EOPA; j. 1 .h.:;¹ : v-." U._has ._has; p-V.mm iJâ light beam emitted. by.. a. light source is. line. AI^{the R} a fiber optic delivery system. first. interferometer, 2.? n-|eficfW|^{the I 00} ^ W^ai1 !:;^the the Michelson principle. ; the incoming light beam Y is diyis ^ by a separator consisting of a semireflecting plate ., two-yote-beam one of which is reflected by a mirror. iF ^ th, . while .1 '. another. is reflected PUFs. - a movable mirror whose position varies; these two subbeams, ; PNA®^O reflection, at spntrocombinés. level, the, separator and jsystèmé .,, interfere for_O a give. stream. overall, which global flow has a spectrum having a number. of. splines in a, . strip

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pTC: R." the n. r:;vf of I- :: omèvr ' spectral Receive~confectioneries, given.. the position of these splines is characteristic of the difference D_C. optical paths followed by the partial beams corresponding to the two mirrors, which difference is related to the position of the movable mirror; this stream is fed by optical fiber to a second interferometer /, which plays the role of•measuring interferometer. Measuring interferometer also has two mirrors, of which, one is movable relative to the other, and a separator system consisting of a semireflecting plate which splits the light into two subbeams; these are directed toward the two mirrors on. which they reflect, and then recombined at the separator system.

The luminous intensity of the output stream from 1' measuring interferometer after recombination of the two subbeams, translates the degree of correlation between the optical responses of each of the interferometers for detection and measurement. In 1' measuring interferometer, the movable mirror is mechanically moved to detect the intensity maximum of the output stream, which most reflective of the equality of the two differences of optical paths, in the two interferometers. The position of the movable mirror of 1 'interferometer measurement corresponding to this maximum - can thus determine the optical path difference of 1' interféromètx * e of detection.

U.S. Patent U.S. 4,596 466 describes widely such an embodiment. Examples include raising a possibility of replacing the Michelson interferometer by interferometers of "Fabry-Perot", consisting of two partially transparent parallel mirrors placed between two lenses to - ends of two optical fibers.

In known devices using such a measuring interferometer, the systems used to move and know the movement of the movable mirror are of two types.. in a first type of movement is known systems because in mechanically displaces the movable mirror of 1' measuring interferometer on a track ball or cross-roller. Also congestion problems, there are problems of friction, mechanical lash that cause an accuracy better than 0.1 microns is difficultly accessible. Gold, for small displacements of the mirror, for example 10 microns total amplitude, if we are to a large dynamic range, for example 10³ dots, it is necessary that the measuring sensitivity of the mirror position of 1' interferometer is better than 10"² micron.

In a second type of movement is unknown but systems is measured by laser interferometry thereof on a measuring interferometer, identical to 1' sensing interferometer. The sensitivity on the displacement measurement is based on the spectral properties of the laser can be significantly better than 0.1 microns, but the position of the fringes is known only relatively: the measurement requires continuous monitoring and without interruption possible from the position of the mirror corresponding to a zero optical path difference to the desired displacement.

In other known devices still, the determinations of the variation of the difference in optical paths of d_C. the sensing interferometer nene.se not using a measuring interferometer but performing 1 'spectral analysis of the stream coming from 1' sensing interferometer and by taking the Fourier transform. The spectral analysis provides the fringes and their phase and recover to the absolute value of d_C. . This approach requires a hardware for spectrophotometry for analyzing the spectrum spline, for example a grating monochromator, a diode array and software which the algorithms are known but heavy for the Fourier transform. On the other hand its sensitivity is not sufficient because of the attenuation that we are going to have in the long fiber length used, e.g. 6 km forward. and return, for a production well, the accuracy of these devices, which can reach. 10³ micron, is a function of the sampling performed on the spectrum, hence the resolution of the spectro photometer.

The invention, by retaining the principle of analysis using an interferometer measurement allows while retaining the advantages of prior devices

Anterior•, remove the drawbacks, including problems related to bulk and accuracy.

The device according to the invention avoids in particular the use of moving parts difficult to adjust and does not involve any piece heavy moving mechanical which increases the measurement time, eliminates the possibility of misoperation, obviates the problems of drift of the reference variables encountered on earlier apparatus with interferometric analysis, as well as the mechanical frictions that limit the sensitivity.

The proposed device is simple, robust, compact, does not create a problem of measurement reproducibility. In addition it enables continuous rapidly and reliably analyzed, with an accuracy equal, fluted mixed spectra corresponding to different optical path length differences of d_C. -|_ and d_c2 the lysis of more spectra from different detection interferometers having differences in optical paths adjacent but analyzed sequentially. The device therefore allows the analyzing information from sets of interferometric sensors characterized by d-optical path differences_C. different, each resulting in differing physical variables or not. The proposed device allows measurement of absolute differences of optical paths D._C. on 1' measuring interferometer.

This third object is achieved by the fact that the interferometric optical device for measuring physical quantities which may create multiple variations in optical path difference, comprising:

1 - (has) a transmitting device emitting a light flux to broad spectral band;

2 - (c.) a detector assembly comprising at^F. least one homogeneous or mixed double sensor consisting of two interferometers in, series or parallel, creating a composite of the splined spectrum; differences risers D._C. y and D ^;

vBE1 .3 PU assembly. (b}_; fiber .,, optical and: (3) couplers including a branch; (the X, the Y) -. to convey the luminous flux of the transmitter device (has) to the detector assembly (C.) and a connected^V. (a Y, Z) for, conveying by return reverse light the unparsed * reflected light by the detector assembly;

4 ™ - an analysis device for analyzing (D.) the information carried by the light flux from the sensor assembly and constructing a value, representative_; the measured physical, which analyzer comprises ':,

4a - measuring interféromëtre a two-wave comprising a collimator'd? inlet (10) illuminated by 1' - (Z-) end of the optical fiber, a reference mirror ml. (16) on which reflects a portion of the. collimated light flux provided by the double sensor; and a second mirror (12) m2 reflected off this other portion of said luminous flux; collimates, and for causing interference both streams reflected on the mirrors ml and m2 - and impart to the output luminous flux resulting ;.

The V; 4Ja.!, " a photoelectric detector '(14) adapted to measure the intensity of the light output from 1' interferometer for measuring and providing a signal representative of said intensity; and

5 - a process assembly (th) of the signal from the photoelectric detector providing a value representative of the physical quantity,

is characterized in that the mirror m2 of 1 'measuring interferometer is, fixed on a micropositioner-meter (15) for moving the piezoelectric finely the mirror m2 and accurately measure a corresponding movement,, and that 1' processing assembly is connected both to the photoelectric detector but also at micropositioner " meter for driving, and determine the absolute position of the mirror m2, corresponding to the maximum light intensity received on the photoelectric detector and work out d-values_C. ^ and d_o2 necessary for the production of the desired physical or variables.

. . As an auxiliary feature the mirror ml of reference 1' measuring interferometer is provided with means for varying the optical path of a known value. This may be necessary to bring optical path differences and d_c2 in the moving range of the micropositioner-meter.

This offset can be obtained by interposition of transparent plates' to optical path difference known, in front of the mirrors fixed and mobile 1' measuring interferometer. A glass plate of thickness e, transparent in the spectral range of the light source, optical path difference creates a-d ≈=(n-L) th, where n is the index of refraction of the blade. Two blades, or two sets of. blades of respective thicknesses Ei and JE respectively disposed in front of the mirrors fixed and movable attracts an optical path difference d is a function of the difference of thickness e between these two blades or sets of blades. A stack of two or. more micropositioners to-meters may also perform this offset without changing over the measurement resolution.

In the interferometric optical device according to the invention the optical fibers used will work in light. white, it is to say with broadband spectra.

Flutes appear in the spectrum of a broadband source when certain wavelengths are turned off in this spectrum. These wavelengths correspond to destructive interference in an interferometer constituting the sensor which may be made by index variation in white light or polarized, or by variation of distance between two partially reflecting surfaces one reference, the other whose position is responsive to the physical quantity to be measured. The physical measured, pressure, temperature, force or displacement will then change in optical path difference: measuring displacement of a moving surface or optical path variation by birefringence. In these cases; .the optical path difference characterizing the; physical quantity to be measured at 1' interferometer sensor is d_C. 2Nd=where e is the difference in position between the stationary reflective surface reference and the position of the movable reflective surface subjected to the physical quantity to be measured or d_C. 2=(n-_Q the n -_I ) is greatly accelerated in the case where the sensitive element is a birefringent plate of thickness e twice passes.

The interferometer for measuring the stream analysis device from the sensor consists of a two-wave interferometer type Miehelson. by for example, having two mirrors one of which is moved by 'a piezoelectric ceramic constituting the micropositioner-meter using the inverse piezoelectric effect: in order to determine the difference in path length 1' measuring interferometer absolutely. In the head of the piezoelectric ceramic is integrated a displacement sensor working in a closed loop and allows to eliminate the phenomena of hysteresis, non-linearity and the influence of temperature.

Based on these advantages the invention finds a preferred application field in the measurement of the same physical variable, such as pressure, of dots. multiple (developed an optical sensor network. pressure) or the measurement of different physical quantities at the same point.

According to a preferred embodiment of the optical device for the interferometric measurement of a physical quantity termed main according to 1' disclosure, the dual sensor detection utilizes two interferometers of which one measures the physical quantity the other influence parameter necessary for correcting the main physical quantity.

Other features and advantages of the invention will appear more clearly upon reading the description hereinafter made reference to the accompanying drawings in which 9.ï

figure 1 - represents, a sectional view of a dual homogeneous parallel interferometric sensor according to the invention;

figure 2 - represents a sectional νμ℮ interferometric sensor of a dual mixed series according to the invention.

figure 3 - schematically shows the constitution of assembly of the device;

figure 4 represents. a concrete embodiment of the concentrator;

figure 5 - is the signal output by the photodetector that is the function correlated dfdf.inter ion of the interferometers of the sensor with a single interferometer and measurement in the case of a light source to a single LED in the vicinity of d_C. ;

figure 6 - is the signal output by the photodetector which is the cross-correlation function of the interferometers of the sensor and ' measure in the case of a light source to two different light emitting diodes;

figure 7 - represents one embodiment of a dual spectrum light source;

- figure 8 represents a variant of interferometric device multisensor switched light source;

- figure 9 represents an alternative device interférométrigue multisensor to light source and single analyzer?

- figure 10 represents a device multianalysor.

figure 11 represents the cross-correlation function from Ε ¾=0 in the same conditions as those of Figure 5;

figure 12 represents the cross correlation function in the case of a double sensor D._lC and d_c2 and a light emitting diode.

The interferometric sensor dual called "sensor homogeneous parallel", in Figure 1, consists of a clamping ring (112) of hollow cylindrical shape wherein the threading (1120) at its end a cylindrical ring (11) forming a blind hole (114), the said bore is closed by a flat face (115) made of a membrane deformable metal depending on the pressure and the temperature at which is carried, a homogeneously, the whole sensor. This membrane is its perimeter over a spacer ring (12) of thickness (e2) and glass expansion coefficient (β - (1). On this ring (12) cylindrical spacer is adhered a plane-parallel plate made of a same glass expansion coefficient (#1) forming a plane-parallel plate (14), on the side facing the deformable membrane (115), is adhered a plane-parallel plate made of a same glass expansion coefficient TM (I), this blade (13) having a thickness (e3). A second parallel plate (17), includes a glass expansion coefficient (the O {2) is placed at a distance (e5) by a cylindrical spacer (15) made of glass having a same coefficient of expansion (^ 2)" in 1' (15) inside of the cylinder is a second cylinder (16) also hollow and having a thickness less than (AE) (e5). The internal diameter of said hollow cylinder (16) corresponds approximately to the outer diameter of the plane-parallel plate (13). This cylinder (16) consists in a first glass expansion coefficient (ε (I) and is adhered to the blade (14). On the second blade (17) is adhered a last strut (18) for mounting a collimator lens (19). On the edges of the collimator lens (19) also rests the base of a revolution part (110) which the vertex provides support for a light transmitting fiber (113) whose 1' end is placed in the focal point of the collimator lens. Finally a set of spring washers (111) with one end on the outer face of the part (110), on the other hand on the shoulder defining the central opening (1121) in the clamping ring (112) ., holds the different elements adhere together. An envelope (116) external to the clamping ring (112) which ensures the isolation of the sensor to the environment is sealed onto the diaphragm ring (11), for example by a weld seam (1160) and moreover ensures 1' seal, by a sealing ring (1161) on the cable (1130) which contains the optical fiber (113). To create the otherwise empty throughout the sensor provided the ports (120, 150 and 1122) (1162) of the outer casing (116) which is resealed once the vacuum created. Has outside (116) reign the pressure and temperature ' of the production well. In operation the sensor has its membrane (115) subjected to the pressure and temperature of the production well and under the action of these two parameters the diaphragm moves so as to vary the distance e equal to the difference in the thickness (e3) and (e2), of the respective blades (13) and (12). This distance (I) varies, the light beam passing through the first interferometer in the vicinity of the axis of symmetry of the sensor according to the path (has) sees its corrugations that can be varied with the movement of the membrane (115). By contrast the annular light beam passing through the second interferometer according to the path represented by arrow (d) through the contact gap (I ' j-separating " the element (16) of the element (17). Cettè. distance varies in accordance with temperature and due to differential expansion coefficients (çCL) and ($2) members respectively. Therefore, the light beam along the path B will be modified as a function of its corrugations. this variation. The light from the two interferometers is mixed with the input of the fiber (113) and. has corrugations of a representing distances and 2nd 2é ' traveled. The difference in path length of the first interferometer 2nd, by way of example, is of 300 microns and the 2nd ' of the second. interferometer 400 micron, .. 1/operating these■splines due to 2nd and 2nd ' taking into account. both variations in pressure and temperature will be performed by the circuit described later. In the embodiment. fig. related elements (12, 13, 14 and 16) are adhered between, them and the elements (15, 17) are also adhered between; them. The junction between the element (15) and the element (14) is not stuck so as to allow the different expansions occur.

In an alternate embodiment of the sensor, can be of the cylinder (16) to become attached to the blade (17). In

the second blade - this variant (17): and the second cylinder (16) will have the same coefficient of expansion (2), while the cylindrical spacer (15) will have a coefficient of expansion (" {1)

Figure 2 describes a second type of interferometer sensor dual called "blended sensor series" wherein there are the clamping ring (214) and the deformable membrane (21) with its side (215). The first interferometer of the sensor is also constituted by the engagement of the face (215) with the plane-parallel plate (23), the blade (24) and the brace (22), these elements behave in the same way as the elements with references (11/12, 13, 14). A second interferometer consisting 1' stacking a spacer (28), a polarizer (27), (28) of a spacer, a birefringent crystal (26) thickness (AE), e.g. lithium niobate (periodically poled linbo³ ) whose birefringence is temperature dependent. The second interferometer is splined a spectrum generator jetproof splines which vary as a function of temperature. This stack is contained in the hollow cylindrical spacer (25) and flanked by the firm iames with parallel faces (24) and adhered (29) and. Finally the sensor is terminated by a spacer (210) carrying a further one of a collimating lens (211) and a support (212) optical fiber, as in the previous embodiment. The sensor also includes spring washers (216) for pressing the assembly on the edges of the deformable membrane (21). The object elastic spacers (28) is to compensate for variations in thickness of the sum of the parts (.26) and (27) due to temperature variations by patch expansion (25). As in the first type of sensor, ports (220, 250, 2140, 1162) are arranged in the different, parts in order to allow the otherwise empty after mounting an outer shell (116) and assured sealing over the cable (1130) containing the optical fiber (213). In the case of the sensor the spectrum spline, created by the subsequent passage of the collimated light beam in the second interferometer, and then the first interferometer, and then after reflection again in the second interferometer, is focused by the collimating lens (211) on the optical fiber (213). Therefore the light beam exits the sensor has a spectrum consisting of the product spectra generated by each of the two fluted interféroæèfcres due to variations of pressure and temperature on the membrane (215) and temperature-modifying birefringence and 1' thickness (e6) of the blade (26).

The embodiment of Figure 1 consists of two interferometers Fafory-to-Perrot will in parallel called sensor homogeneous parallel.

The variant ' of Figure 2 consists of a interferometer Faory-to-Perrot will serially associated with an interferometer and faithfully-refractive light called blended sensor series.

Obviously there can be formed a sensor homogeneous series by associating in series, two interferometers dual refractive or yet another sensor homogeneous parallel by combining in parallel two interferometers dual refractive.

Similarly there can be formed a blended sensor in parallel in parallel a birefringent interferometer and a Fabry-Perot interferometer, 1' and faithfully-refractive interferometer act as first interferometer responsive to pressure or temperature-sensitive second interferometer.

The sensors above can be used in any measurement device interférométrigue and in particular with the device described below.

L⁷ assembly of the " - device consists, of a light-emitting device (has), system light flux (β), a detector assembly

(c.) composed of a double sensor, of a measuring system (D.) and a processing system (I), fig. 3.

The transmitting device (has) is constituted, as shown in Figure 3, a source, e.g. a light emitting diode (1), of which the luminous flux is focused onto the input of an optical fiber (s) of a transmission system (d), by means of a condenser (2). Preferably, may be used, in some embodiments, two diodes or a plurality of diodes broadband, the maximum of each SSC spectra coinciding with each minimum transmission attenuation of an optical fiber whose values are respectively about, 800, 1300 and 1500 nanometers. The source most advantageous is shown in Figure 7 and comprises a first spectrum centered at 800 nanometers and a second centered on 1300 nanometers. The broadband source is comprised of a first light emitting diode (71) that emits a first spectrum, a second light emitting diode (72) emitting in the second spectrum and a dichroic slide (73) steep face centered midway (1050 to nanometer) emission maxima of the two diodes. This blade (73) transmits the dichroic full-spectrum of the diode (72) whose spectrum is centered at 1300 nanometers and reflects the entire spectrum than (71) whose spectrum is centered at 800 nanometer. This idea of combining at least two light emitting diodes whose maxima are centered on the minimum attenuation of the fiber supports, as shown in Figure 6, greatly increase the difference between two maxima of the cross correlation function, a primary maximum (60) and (61) neighboring maxima (62) and the vicinity of the maximum (60) and allows much better sense margin against noise measurement; moreover the availability is better with two diodes with only one.

The system light flux (d) is constituted by a subassembly comprising optical fibers 3 (the X, the Y, Z-) and a coupler (a T). The coupler it removes the light flux from the forward, from the source of X to Y as well as of the luminous flux from the dual sensor to Z. The length of each of the fibers can be any.

The assembly includes a sensor (C.) (4) twice, one of the two types described previously>illuminated by Y. It consists of a lens (7) goIlimâtrice and two interferometers in "series" or "parallel" (5) and (6). The interferometer (5) is responsive to temperature and the other interferometer (6) is pressure-sensitive and temperature (semi-reflecting plate and membrane (13, 115 fig. 1 or 23, fig. 2 215).

The collimating lens (7) receives the light from the optical fiber therein and direct it towards the interferometers. By returning reverse it focuses the light flux derived from interferometers to 1' fiber entrance therein.

The luminous flux has a spectrum fluted composite which is the sum for the sensor parallel, or product for the sensor series, fluted spectra due to each of the interferometers are sensitive to temperature and to. the pressure and temperature.

The luminous flux carried by the fiber (a Z) enters the package (D.) interferometer analysis, passes through a collimating lens (10) and (11) a separator system, which divides it into two subbeams réléchi which one is by a mirror (16) ml of the reference, while the other is reflected by a movable mirror (12) m2 bound micropositonnor-meter (15) piezoelectric, and subjected to the displacement to be measured.

The light fluxes reflected by each of the two mirrors ml and m2 will interfere at the separator system (11). The light flux passes through a condenser (13) and illuminates a photoelectric detector (14). The micropositioner-meter (15) as well as the photoelectric detector (14) are connected to a processing device and control (I).

The relative positions of the two mirrors ml and m2 will define an optical path difference measurement

as going can be changed by moving the the micropositionor-meter (15) by an electronic control system the movable mirror m2. The luminous flux incident on the photoelectric detector passes through a series of maxima, represented in Figure 5, increasingly larger as as the distance of the "main maximum" (50). (50) main this maximum imply the equality of the two differences of optical paths D._C. in each of the interferometers and Djj (4) sensor on the one hand and measuring (11, 12, 16) on the other hand. A second maxima occurs in the cross correlation function for Σ ¾ ≈ 0, fig. 11.

'Lit directly by the source, 1' measuring interferometer would transmit light flux having the spectrum spline would be characteristic of the optical path difference of 1' measuring interferometer. Back illuminated a light flux having a splined spectrum associated with a difference in optical path D._C. , . 1 'interferometer' measurement will transmit output a stream whose intensity fader the level of correlation between the spectra fluted optical path differences associated with Djj and d_C. . Gold the interferometric sensor (4) has a dual spectrum fluted composite which is the sum of two spectra fluted due to two interferometers (5) and (6) in 1st when a sensor * "parallel" or the product spectra fluted due to two interferometers (5) and (6) "in the case of a sensor" series ". The intensity of the output stream collected on the photodetector 'thus has three maxima main, one of which corresponds to a difference in path length zero 1' measuring interferometer conveying the fact that there is not destructive interference and that all energy which enters 1 'interferometer spring, and the other correspond to path differences on 1' measuring interferometer equal in absolute value than the double sensor:%=or DC_^ 2₎ the I fig. 12.^O (i) corresponds to c ' market unlike the first interferometer (5), fig. 3 d-St._C. , fPG~than the second interferometer (6) ., fig. 3. These two path differences allow, by computation, know the true pressure and temperature, - for example in the production well.

To enable measurement in the case where the path differences D._C. ^ and d_c2 are away from L^/ another is arranged, for the zero of décalex * 1 'interferometer measuring low value known, a blade set low difference known optical paths that can be disposed in front of the mirrors mid or m2 of 1' measuring interferometer. In the case of a substantial discrepancy in one blade (17, fig. 3) is disposed in front of the mirror per ml, or a single blade (18) is disposed in front of the mirror m2.

Figure 6 represents the cross-correlation function between one of the interferometers of the sensor and 1' measuring interferometer when the light from, the source is constituted by the sum of the spectra of two LEDs whose spectra. are respectively centered on 800 and 1300 nanometers with a spectrum width of about 100 nanometers. With this configuration, the maximum (60) will be more easily determined since the contrast between the main peak (60) and (61) the sidelobes (62) and will be sharper.

The use of a detection system in series in the same sensor on a single fiber, with waveform analysis using an absolute measuring system movement, combined with use of a set of parallel plate for returning the operation differences within the movement range of the measuring system, with the widening of the spectrum of the source using a plurality of transmission windows of the optical fibers to improve detection and protection against noise measurement, results in a pressure range of 200 bar and temperature of 150 degrees C, at a measurement point to about 3 km, in a hydrocarbon production well, measurement accuracy min to optimize both the level and the contrast of the signal delivered by the ' photodetector,, above are reflection coefficients of the parallel blades interferometers double sensor between 0.4 and 0.95. Advantageously, the reflection coefficient will be between 0.4 and 0.7.

According to another embodiment of the above item, shown in Figure 8, the 'interferometric optical device for the measurement of physical quantities is a device having multiple transmitter whose emission source may be comprised of a plurality of sources (81 - 1 to 81 n) selected either by a processing device and switching (89) for illuminating one by one the connected (82 - 1 to 82 H-a) die ii' pier assembly optical transmission. Le. optical device also includes a pier assembly couplers (83 - 1 'to 83 n) constituting with the fibers' optical (82', 84, 86) n transmission systems; (b.) identical to that described in the preferred form, a set^! of " the n *¹ detectors composed of sensors (85) for each measurements, a measuring system (38) and system (89) processing and switching of light sources connected by n bonds (810) (81) sources. There is not in this aspect of addressing means and the fluxes reflected by each upon sensors measure are combined prior to entry of 1' interféromette " of^; measure by means of a hub (87) shown schematically on the figured.

The ends of the n fibers (86 - 1 to 8' 6 - hr *) to the system output of optical waveguides are combined into a circular beam of a diameter such that it does contain such fibers. These 'fibers are then bonded and the surface normal, ' to their axed is erected, polished and appressed to a concentrator (87). The concentrator '(87) has an input face (870) whose web' diameter is greater than the diameter of the *' beam n fiferès (86 - 1 to 86 n). The concentrator (87) is formed by drawing a glass rod to obtain a tapered fiber and low angle. If the angle is not too large, can be obtained at the end (871) having the smallest diameter a luminous flux which is adjacent to the input stream, fig. 4.

This stream is sequentially the flux emitted by each of the sources.

A processing system (89) linked to the photodetector 1 '(88) measuring interferometer identical to 1'-assembly referenced (9) Figure 3 provides, from variation measurements of optical paths D._C. j and D_c2 corresponding to the maximum correlation, the measured physical parameters in each of the sensors.

Another embodiment, shown in Figure 9, is comprised of an instrumentation system (96) multi sensor connected to a single interferometer analysis (98) by a switching device of the measurement channels from the sensors. The system is supplied by a light source (91) connected by an optical fiber to a coupler (92) (93) joined to a switch (94) of optical channels driven by a linkage (910) from the processing circuit and control (99). Each of these channels (95 - 1 to 95 n) constituted by an optical fiber is connected to a respective sensor (96 - 1 to 96 n). The coupler (93) transmits the switched line to the fiber (97) connected to the system (98) analyzing or measuring identical to that referenced (9) in Figure 3. In the two exemplary embodiments described above, the n spectra fluted composite from each of one dual sensors are selectively illuminated sequentially analyzed one after the other by the processing system (89) or (99).

Another variation may include, as shown in Figure 10, coupling a plurality of measuring devices (102) as previously described star to the output of a spark gap (103), each of the measurement devices (102) being coamartabls■to D.^{the R} improve ià '■- - availability of 1' set *•"•

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