MXPA06003730A - Rugged fabry-perot pressure sensor - Google Patents

Abstract

A pressure sensor (100) and system for measuring pressure changes, especially in harsh environments, is described. The pressure sensor has a Fabry-Perot optical cavity formed within a tube (115) with a partial reflective mirror (130) provided by an end of an optical fiber (105) and a reflective mirror (135) provided by an end of a plug (120), with a gap (125) formed between. The pressure sensor may be disposed within a sensing chamber of a housing having an opening into the environment to be monitored. Alternatively, an isolator means may be used to isolate the sensor from the environment while communicating pressure changes to the sensing chamber. In another embodiment, the sensing chamber is filled with a compressible non-flowing material.

Description

REINFORCED PRESSURE SENSOR FABRY-PEROT Field of the Invention The present invention relates to pressure sensors that are robust enough to be used in extreme environments, such as an oil or gas well. More specifically, the invention relates to a pressure-reinforced sensor incorporating a Fabry-Perot optical cavity with an optical fiber in order to provide a pressure sensor with the ability to detect the pressure and the changes in temperature. The pressure through the analysis of "the light-reflected by the Fabry-Perot cavity." Background of the Invention There are many processes and environments or environments in which it is desirable to know the environmental pressure One of these processes or common environments It is during the exploration and extraction of hydrocarbons, such as oil, in which it is necessary to measure the pressure of the hydrocarbons in a reservoir.Another application is the measurement of the fluid pressure that is associated with pumps or natural conductors that transport these hydrocarbons from one location to another One way in which the fluid flow is detected perceives the pressure drop through a venturi, thus requiring the detour ection of the pressure difference on both sides of the venturi.

REF. 172073 Fluid pressures are commonly measured, for example, with a quartz crystal-based pressure measuring device, such as the Quartzdyne ™ QS Series High Pressure Laboratory Transducer from Quartzdyne Inc., of Salt Lake City, Utah . This pressure sensing device effects measurements of the change in the mechanical oscillation frequency associated with the elastic deformation of the quartz crystal in response to the applied pressure. Quartz is the medium of choice for these applications due to inherent long-term stability, as well as its minimal electrical current deviation and hysteresis properties. The change in frequency with temperature is also very predictable. In traditional form, the frequency change of the quartz crystal is measured and compared to a reference crystal which is the temperature compensated with the resulting data correlated and calibrated with a direct pressure measurement. Although the reliability of this quartz crystal is extremely high, the electronic devices required to measure the frequency change are subjected to faults, in particular, when the transducer and its associated electronic devices are subjected to high temperatures, such as the temperatures above 125 ° C. Pressure sensors with optical fibers and optical detection elements are very important for the remote detection where conventional manometers can not operate or where conventional manometers are not reliable enough. Certain techniques exist for pressure measurement using a Bragg diffraction grating. However, these techniques are complex, expensive or do not restrict the buckling or deformation of the optical fiber in the region of the diffraction grating. For example, a sensor based on a fiber optic diffraction grating is described in United States Patent Application Serial No. 08 / 925,598, entitled "High Sensitivity Fiber Optic Pressure Sensor for Use -in-Harsh Environment". In this example, an optical fiber is joined with a bellows capable of being compressed in a position along the fiber and with a rigid structure in a second position along the fiber with a grating. The Bragg diffraction is embedded within the fiber between the two fiber bonding positions, the fiber is joined in both positions, in order to place the diffraction grating in tension, as the bellows is compressed due to the external pressure change, the The voltage on the fiber diffraction grating is reduced, this changes the wavelength of the light reflected by the diffraction grating.This sensor requires a complex structure of bellows and does not restrict the deformation of the fiber in the region of the diffraction grating.

Another example of a fiber diffraction grating pressure sensor is described in Xu,. G., et al., "Fiber grating pressure sensor with enhanced sensivity using a glass-bubble housing", Electronic Letters, 1996, Vol. 32, pp. 128-129. In this example, an optical fiber is secured through a cement cured by ultraviolet (UV) light in a glass bubble at the two ends of the fiber, with a diffraction grating formed in the fiber at a position located inside of the bubble. However, this sensor does not restrict or impede the optical fiber against the deformation - in the region - of the diffraction grating. It is also "known that a" pressure sensor based on a diffraction grating could be elaborated by placing a polarization that keeps the optical fiber in a capillarity tube that has rods or bars in it, and that measures the changes in the birefringence of the diffraction grating caused by changes in stress or transverse load on the fiber diffraction grating due to the transverse pressure forces acting on the capillary tube, as discussed in U.S. Patent No. 5, 841,131. However, 'this technique could be difficult and expensive to implement. Another limitation of the use of Bragg fiber diffraction gratings as integral parts of a pressure sensor is that the stress on the optical fiber of This sensor can not be very large without breaking the fiber. Consequently, this sensor could have a limited range of sensitivity. Attempts have been made to use Fabry-Perot optical cavity sensors for pressure measurement. Normally, sensors of this type are a function of a polished optical fiber as a reflector of the optical cavity and a flexible diaphragm as the other reflector of the cavity, and a separation between the two. As the pressure in this sensor increases, the diaphragm deforms, changing, the separation. A disadvantage of this construction is that the diaphragm, when flexed or deformed, does not remain perfectly flat as the pressure changes, because at least the periphery of the diaphragm is normally attached to the sensor housing to hold the diaphragm. This provides multiple reflective trajectories that distort the spectrum of light within the Fabry-Perot optical cavity, causing measurement errors. Other Fabry-Perot pressure sensors have been described using two optical fibers placed at the opposite ends of a glass splint, subsequently, they are joined in place with a desired spacing. The glass splint must be of sufficient strength and thickness to withstand high external pressures. If the fibers were attached to the inside of the splint along its total length, only the area of separation, commonly in the order of 100 microns, will be affected by the applied pressure, which provides very low sensitivity. Attempts to improve the sensitivity of these devices by bonding the fiber, only partially along its length, leave a portion of the adjacent fiber free with separation, which causes erroneous measurements due to the unbound portion. of the optical fiber that joins or slides in the splint as the -pressure .. Also, the unattached sections could move excessively "in response" to the vibrations, causing an increase in the measurement error What is needed and not available so far is a stabilization sensor of temperature and reinforcing, which is relatively inexpensive for pressure measurement in an extreme environment, such as, for example, a perforation, which overcomes the problems of electronic quartz gauges or sensors that incorporate the Bragg fiber diffraction gratings. This sensor would isolate the electronic devices and other equipment necessary to analyze the signals representing the pressure changes within the borehole of the extreme environment of the well.The present invention satisfies these and other needs.

SUMMARY OF THE INVENTION The present invention is incorporated, generally, into a pressure sensor formed by fabricating a Fabry-Perot optical cavity at the end of a length of the optical fiber. The sensor housing changes in its dimension in response to changes in pressure, thus changing the dimension of a gap forming an optical cavity between a partial mirror located at the far end of the optical fiber and a mirror formed on the distant end of a plug. Changes in the dimension of the separation affect the length of the optical path of the Fabry-Perot device, causing a detectable change in quality, such as the wavelength, frequency or intensity of the reflected light of Return of the fiber optic to the electronic devices configured to analyze the returned light. In one aspect, the present invention is incorporated into a device that senses the pressure of an environment, which comprises a capillarity having a proximal end and a distal end, and a bore extending therebetween, an optical fiber that has a proximal end and a distal end, the distal end is configured to partially reflect the light, the distal end is located within and extends through the capillarity bore to the distal end of the capillarity, a tube that has a proximal end and a distal end and a length, a stopper having a proximal end and a distal end, the distal end is configured to reflect light, and the distal end of the stopper is located in a hole at the distal end of the stopper. tube, wherein the optical fiber and the capillary are introduced into a hole in the proximal end of the tube at a selected distance, so that a gap is formed within the tube between the distal end of the optical fiber and the distal end of the stopper . In one aspect, the optical fiber is melted in the capillarity and the capillarity is melted in the tube, and the plug is melted in the tube. In another aspect, the capillarity, the tube and the plug could be formed from fused silica. In other aspects of the present invention, one or all of the capillarity, tube and cap could be configured from a suitable material other than fused silica, such as, for example, glass or Pyrex. In another aspect of the present invention, the separation is filled with air. Alternatively, the separation could be filled with a different gas from the air, or the separation could be evacuated to contain a reduced gas pressure, or a vacuum. In still another aspect of the present invention, the distal end of the plug is an optically polished mirror.

In still another aspect, the distal end of the plug could have a coating in order to provide a relatively high optical reflectivity, which could be in some aspects, approximately 100%. The coating could be a metal coating, such as, for example, gold, silver and aluminum or another high reflectivity coating. In an alternative aspect, the far end of the optical fiber is a polished flat end. In another alternative aspect, the far end of the optical fiber is a curved surface. In yet another alternative aspect, the leading edge - of the fiber optic - is an exfoliated flat end. In yet another alternative aspect, the far end of the optical fiber has a coating in order to increase the reflectivity of the far end-of the optical fiber above the reflectivity of the glass with the air interface. In another aspect, the present invention also includes at least one periodic disturbance of the refractive index located in the optical fiber at a position proximate the distal end of the optical fiber to provide temperature compensation. In yet another aspect, the present invention is incorporated into a pressure sensor for use in extreme environments, which comprises a sensor assembly that includes: a capillarity having a proximal end and a distal end, and a bore extending therebetween, an optical fiber having a proximal end and a distal end, the distal end is configured to partially reflect the light, the far end is located within and extends through the capillary bore to the distal end thereof, a tube having a proximal end and a distal end and a length, and a stopper having a proximal end and a distal end, the The far end is configured to reflect the light, and the distal end of the plug is located in a hole at the distal end of the tube, where the optical fiber and capillarity are introduced into a hole in the proximal end of the tube at a distance selected, so that a separation is formed within the tube between the distal end of the optical fiber and the distal end of the stopper, a housing defining a detuning chamber. ection, the housing has a proximal end and a distal end, the distal end of the housing has a port formed therein, the sensor is mounted within the detection chamber, so that the proximal end of the optical fiber extends to through a pressure seal located on a wall of the housing forming a proximal end of the detection chamber. In another aspect, the detection chamber is filled with a filling material, which could be a non-flowing material susceptible to be compressed in some aspects of the invention. In yet another aspect, the present invention could include an isolation means mounted at the distal end of the housing and in communication with the interior of the detection chamber through the port. In one aspect, the detection chamber is filled with a fluid. In another aspect, the isolation means is a bellows or alternatively, the means of isolation is a structure sensitive to changes in pressure and capable of communicating these changes of pressure to the detection chamber. In still another aspect of the present invention, the invention is incorporated in a pressure detection system, which detects pressures, the system comprising: a light source; a bidirectional coupler is in optical communication with the light source, a pressure sensor that has a Fabry-Perot optical cavity, the pressure sensor is in optical communication with the bidirectional coupler, the bidirectional coupler provides a path or trajectory for the transmission of light from the light source to the pressure sensor and also provides a way for the transmission of reflected light by the Fabry-Perot optical cavity of the pressure sensor, and the analysis medium that is in optical communication with the bidirectional coupler for the study of the light reflected by the Fabry-Perot optical cavity in the pressure sensor with the object to determine the changes in pressure detected by the pressure sensor. In another aspect, the light source is a tunable laser. In still another aspect, the analyzing means is an optical power meter, or alternatively, the analyzing means is an optical spectrum analyzer. In still another aspect, the bidirectional coupler is a circulator or distributor. Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention. Brief Description of the Figures Figure 1 is a cross-sectional side illustration of an optical cavity of Fabry-Perot. Figure 2 is a schematic graph of reflectance versus frequency for an optical Fabry-Perot cavity. Figure 3 is a cross-sectional side view of a pressure according to an embodiment of the present invention. Figure 4 is a side view, partially in cross section, showing a pressure sensor according to the embodiment shown in Figure 3, which is located inside a housing for its deployment in an extreme environment. Figure 5 is a side view, partially in cross section, showing a pressure sensing system similar to that shown in Figure 4 using a bellows to isolate the pressure sensor from the environment being monitored. Figure 6 is a side view, partly in cross section, showing a pressure sensing system similar to that shown in Figure 4 which uses a filling material to isolate the pressure sensor from the surrounding environment. being monitored. Figure 7 is a schematic representation of a pressure detection system according to an embodiment of the present invention. Figure 8 is a schematic graph of the reflectance against the wavelength for the pressure sensor mode shown in Figure 3. Figure 9 is a schematic graph of a separation width versus the applied pressure for the mode of the Pressure sensor shown in Figure 3.

Detailed Description of the Invention The present invention is illustrated by way of example in the accompanying drawings, and generally comprises a pressure sensor located at the end of an optical fiber that is configured to be deployed below the bore of a Well to measure pressure changes inside the borehole. In general, the pressure sensor of the present invention includes a Fabry-Perot optical cavity mounted at the end of the optical fiber. As will be discussed in more detail below, light is transmitted down the optical fiber until it reaches the Fabry-Perot optical cavity. In the Fabry-Perot optical cavity, a portion of the light is reflected, forming an interference within the optical cavity. As the pressure changes are transmitted to the optical cavity, the interference within the optical cavity also changes. These changes can be detected from the light that is reflected by the optical cavity back to the optical fiber. Using appropriate electronic devices and optical components to analyze and convert the changes in the returned light into digital signals representative of the pressure changes, the digital signals can then be analyzed and visualized or stored for further study. In addition, reports, - alerts or other signals could be generated in response to the analyzed pressure signals to inform the well operators of the conditions within the borehole that could require their attention. In general, a Fabry-Perot optical cavity or double mirror optical cavity, which is known in the art, comprises at least two mirrors, which are separated from each other by a certain distance. For ease of understanding, a Fabry-Perot optical cavity or double-mirror optical cavity will be referred to as a Fabry-Perot optical cavity for ease of description, however, in no way should this description be interpreted as "limiting for the invention". When the light is incident on the optical cavity of Fabry-Perot, optical interference is presented.As a result of optical interference, at certain optical resonance frequencies that correspond to the interference fringes, approximately 100% of the light is transmitted through the optical cavity of Fabry-Perot, and no amount of light is reflected, On the contrary, at other frequencies, approximately 100% of the light is reflected by the Fabry-Perot optical cavity, and no amount of the light is transmitted through the optical cavity of Fabry-Perot.The positions of the optical resonance frequencies are sensitive to and are a function of a optical path length between the mirrors in the Optical cavity of Fabry-Perot. In addition, the path or optical path between the mirrors is a function of the pressure on the Fabry-Perot optical cavity. Therefore, by evaluating the interferences, the condition of the pressure can be determined quickly. The conditions of pressure on the object are determined through a remote optical interrogation of the light. As described hereafter, using the reflected light that comes from the mirrors in the cavity Fabry-Perot optics, several conditions can be determined _ - __ in__the _obj.eto, such as the_ temperature and pressure conditions. Next, a brief description of the Fabry-Perot optical cavity will be provided with reference to the Figure 1. The Fabry-Perot 1 optical cavity, as illustrated in Figure 1, comprises at least two mirrors 11 and 12. At least two mirrors 11 and 12 are reflective, at least partially. In the optical cavity of Fabry-Perot 1, at least two mirrors 11 and 12 are separated from each other through of a space 10 having a distance d "The space 10 at least between two mirrors 11 and 12 defines a refractive index n8, which is different from the refractive index nm of at least two mirrors 11 and 12. When a beam of light 3, also known as wave light, is incident on the optical cavity of Fabry-Perot 1, the reflection and transmission of the light wave 3 occurs in a first interface 14, which is defined as the interface between the first mirror 11 and the space 10. A component 4 of the light wave 3 is reflected off the optical cavity of Fabry-Perot 1, and assuming normal reflection conditions, does not interact additionally with the Fabry-Perot 1 optical cavity. A transmitted component of the light wave 13 that comes from the light wave 3 passes through the space 10 until it hits or impinges with the second interface 15 on the mirror 12. A reflected component 33 of the transmitted light wave 13 is then reflected by the interface 15. A transmitted component 23 of the transmitted light wave 13 is sent through of the mirror 12, and assuming normal reflection conditions, does not interact additionally with the Fabry-Perot optical cavity 1. The reflected component 33 of the transmitted light wave 13 remains in the space 10 at least between the two mirrors 11 and 12, and is directed back to the interface 14. The reflected component 33 of the transmitted light wave 13 is once again reflected and transmitted at the interface 14, as discussed above with reference to the interface 15. The reflection and transmission of the light wave components will continue, as discussed previously and illustrated in Figure 1, with a component of the reflected light wave component that is being transmitted and a component of the reflected light wave that is being reflected one more time each time a component of the reflected light wave is at interface 14 or 15. The optical interference in the optical cavity of Fabry-Perot happens as a result of the continuous reflection and transmission of light waves. The total reflectivity (R) of a Fabry-Perot optical cavity is a function, in the simplest case, of the reflectivity (r) of each mirror, the distance (d) between the mirrors, the refractive index (n) of a medium between the mirrors, and the angle of incidence (?) of a wave of light that comes from an energy source. Consequently, the total reflectivity (R) of an optical cavity of Fabry-Perot is determined by: Equation 1: R where, v is a frequency, F is the fineness of the Fabry-Perot optical cavity (which will be described later), and ax is a separation between the interference peaks ax. The fineness F is, in the simplest case of the Fabry-Perot optical cavity comprising two mirrors that have the same reflectivity, a measurement of the characteristics total reflectivity of the Fabry-Perot optical cavity. The fineness F is determined according to Equation (2) in terms of the mirror reflectivity (r): Equation 2: r - Í (2) 1 - r The interference of light waves happens as a result of the combined reflection and transmission of light waves. A separation between the interference peaks 0 ax of the light waves originates from the continuous reflection of a wave of light in the Fabry-Perot optical cavity. The separation ax between the interference peaks of the light waves in the Fabry-Perot optical cavity can be written in terms of the speed of light c. The 5 vax separation of the interference peaks is determined according to: = c _ Equation 3: ** 2nd - Cos? (3) A common intensity of reflection, or reflectivity, 0 against the frequency profile for the Fabry-Perot optical cavity, determined from Equations (l) - (3), is plotted in Figure 2. In Figure 2, there are some series of minimum reflectivity, which are separated through the vax separation between the 'peaks' of' 5 interference. One position of each minimum vm is directly related to a gap vax between the interference peaks, and can be determined from Equation (4): Equation 4: V | H = m vax (4) where m is an integer. A frequency width vc of a minimum peak in Figure 2 is expressed in terms of fineness F and separation vax. The frequency width vc of a minimum peak is approximately given by: Equation 5: v ° = WflX ^ As can be seen from equations (3) and (4), the position of each minimum is a function of a refractive index (n) and the distance (d) between the mirrors in the optical cavity of Fabry-Perot. Consequently, this change in position of each minimum is related to a change in the optical length parameters. This change of position of each minimum? Vm is determined in this way in accordance with: Equation 6 (6) A change in the minimum frequencies of reflectance? Vm, for example, due to pressure changes? P, is then determined by: Equation 7: (7) wherein the relative magnitudes of the terms 5 are a function of the particular details of the configuration of the Fabry-Perot optical cavity. Figure 3 depicts an embodiment of a pressure sensor 100 utilizing a Fabry-Perot optical cavity in accordance with the principles of the present invention. He pressure sensor 100 is mounted on the end of the fiber _. optical 105. The end of the optical fiber 105 is melted within a capillary 110, which in turn is fused into the bore of a tube 115. The plug 120 is inserted into the end of the tube 115 opposite the end of the tube 115 where the end of the optical fiber 105 is inserted. The plug 120 is dimensioned, so that, when the plug 120 is inserted into the end of the tube 115, a gap 125 is formed between a plug end 120 and the end of the optical fiber 105. The inserted end of the optical fiber 105 is a polished or exfoliated planar end to form a partially reflective mirror 130 at the end of the optical fiber 105.

The fiber end could also be curved to form a partially curved reflective mirror. The end of mirror 130 could also be coated with a coating optical, or could not be coated with an optical coating, depending on the design requirements of the pressure sensor. Suitable coatings include various coatings that are known to those skilled in the art to control reflectivity or other optical properties. The inserted end of plug 120 could be polished or exfoliated, or otherwise formed in order to provide a mirror 135 having a very high reflectivity, preferably close to a reflectance of 100%. The cap 120 is fused within the tube 115. The tube 115, the capillarity 110 and the cap 120 could be configured from fused silica or other suitable glass material. The spacing 125 could be filled with air, or alternatively, the spacing 125 could be evacuated to a low pressure, so that the spacing 125 could be conceived or intended to contain a vacuum. Alternatively, the separation 125 could be filled with a different gas from the air, depending on the design requirements of the device. Because the optical fiber 105 is melted in the capillary 110, and the capillary 110 is fused in the tube 115, and the plug 120 is fused in the tube 115, the gas or vacuum contained within the separation 125 should not be capable to escape from separation, and therefore, it must be maintained within the separation 125.

The partial mirror 130, the spacing 125 and the mirror 135 act as an optical resonator. Due to the arrangement of the partial mirror 130 and the mirror 135, an interference occurs within the separation 125. This interference changes as a function of the changes in the dimensions of the separation 125 that originate from the pressure changes on the outside of the pressure sensor 100. The sensor of the present invention differs from a classical Fabry-Perot optical cavity in that the light that is emitted from the end of the inserted end of the optical fiber 105- through the partial reflection mirror 130 it is divergent in a certain way. This divergence originates in a limited number of interference light rays within the separation 125, resulting in a slight attenuation of the light reflected by the mirror 135. This light attenuation could be overcome by ensuring that the reflectivity of the mirror 135 is larger than the reflectivity of the partial mirror 130. FIGS. 4-6 represent various embodiments of a pressure sensor 150 of the present invention shown 'unfolded within a protection housing 155. In Figure 4, the pressure sensor 150, constructed as described. with reference to Figure 3, it is enclosed within the housing 155. The housing 155 could be a stainless steel pipe, a pipe or a glass pipe, or another arrangement having walls that form a detection chamber 160. A port 165 is located at the distal end 167 of the housing 155 to expose the interior of the detection chamber 160 to the pressure of the environment to be monitored. The pressure sensor 150 is bonded to the optical fiber 152, which extends through a high pressure seal 170 at the distal end of the detection chamber 160. The Bragg fiber diffraction gratings 175 could be formed in Optical fiber 152 in order to provide a means for temperature compensation, such as__es - good. -known by those skilled in the art. This temperature compensation means is useful to provide a correction of the changes in the dimensions of the separation 125 of the pressure sensor 150 that affect the performance or operation of the Fabry-Perot optical cavity, which are artifacts of temperature changes that are not related to the pressure changes inside the perforation. In this embodiment, the pressure sensor is enclosed in a housing formed of a rigid metal or other suitable material that is capable of withstanding the desired operating pressure. As the pressure increases, the fluid / gas - which comes from the surrounding environment enters the detection chamber 160 through the port 165, whereby, the pressure in the sensor 150 is increased, changing the separation 125 (Figure 3). While this embodiment is useful, exposure to extreme environments could degrade the sensor 150. Figure 5 depicts an alternative embodiment of the pressure sensing system of Figure 4. In this embodiment, the interior of the detection chamber 160 is insulated of the environment in which the sensor is deployed by mounting an insulator, such as a bellows 180, in port 165. The sensing chamber 160 could be filled with a fluid 162 in order to provide the transfer of the changes. pressure in the environment towards the sensor 150. For example when the pressure "of the environment is increased, the bellows 180 is compressed, increasing the pressure of the fluid inside the detection chamber 160, which in turn increases the pressure in the sensor 150, changing the dimensions of the separation 125 (Figure 3) of the sensor 150. The process is reversed when the environmental pressure decreases, causing the bellows 180 to expand. or 162 must be carefully chosen to ensure compatibility with the pressure sensor components. In addition, the fill fluid selected for use must have a coefficient of thermal expansion that will not cause an over extension of the bellows beyond their mechanical limits. In addition, any amount of air trapped inside the detection and assembly chamber The bellows will be compressed or decompressed depending on the change in pressure, causing the error in the detection of the pressure. In this way, removal of all of the air or other gases from the chamber 160 is advantageous before the chamber 160 is filled with the fluid 162. Figure 6 represents another embodiment of the present invention, wherein the port 165 of the housing 155 it remains open to the environment, although the detection chamber 160 is filled with a non-flowing filler material 169, such as, for example, grease, gel, rubber without hardening, and the like. The filler material 1.69 should remain compliant and elastic according to the conditions experienced in the operating environment, and should connect the changes in the ambient pressure with the pressure sensor 150, so that the dimensions of separation 125 (Figure 3) of sensor 150 changes in response to changes in pressure in the environment. The use of a non-flowing material 169 for filling the detection chamber 160 is advantageous because the relatively delicate bellows is not required, the filling material 169 will not escape from the detection chamber, and the filling material 169 also acts to hold and stabilizing the sensor 150 within the detection chamber 160, which could be useful to protect the sensor 150 from damage due to handling shock, softening molding or other events that They happen during the deployment of the sensor. Figure 7 represents an embodiment of a system that includes the pressure sensor of the present invention and the apparatus and electronic devices that convert the information contained within the reflected light of the sensor into digital signals representative of the detected changes in pressure and that have the ability to be analyzed to determine pressure changes within the environment that is being monitored. The laser light that comes from a tunable laser or a broadband source 205, is thrown to the optical fiber 210 through a bidirectional coupler and later, through the optical fiber 220 towards the pressure sensor 225. The light reflected by the Fabry-Perot optical cavity in the pressure sensor 225, (see Figure 3) is transmitted back through the optical fiber 220 and the bidirectional coupler 215 in the optical fiber 230 to the optical power meter 235 The system depicted in Figure 7 could take the form of several alternative embodiments without departing from the spirit of the present invention. For example, a circulator could also be used instead of the bidirectional coupler. A broadband optical source could be used in place of the tunable laser, and an optical spectrum analyzer could be used in place of the optical power to analyze the signal information contained in the reflected light of the sensor 225. These alternatives could be incorporated into the system in any combination. Figure 8 depicts a graph of the intensity of the light reflected by the Fabry-Perot optical cavity of the pressure sensor of the present invention as a wavelength function. It is apparent from this graph that changes in the spectrum could be analyzed to determine the dependence of the spectral changes observed-as-an-f-junction of the changes in the dimensions of the separator T25 (Figure 3) of the sensor "Pressure as a function of changes in the pressure of the environment in which the pressure sensor is deployed As can be seen from Figure 8, the wavelengths of the edge notches, or minima, of the Wavelengths are determined with ease, and these wavelengths meet the resonance conditions for waves in a resonance structure, so that the width of the separation 125 (Figure 3) could be calculated according to: Mx? "Equation 8: Gap = --- (8) where M is an integer number and? M is the wavelength of the M notch.

Normally, at least two notch wavelengths are used to calculate the dimension of the spacing 125. Because the dimensions of the spacing 125 change as a function of the pressure exerted on the sensor 100 (FIG. 3) a spacing could be generated. search table, which contains a matrix of values that represent the dependence of the separation dimension as a function of pressure. Figure 9 illustrates that dependence for a mode of the pressure sensor of the present invention, showing as the width of the separation 125 changes as an element, of the pressure applied in the - • pressure sensor 100 (Figure i) t-A suitable processor programmed with an appropriate software, or a wired circuit card, or an embedded processor, could be used to analyze the signals coming from the pressure sensor according to this Search table stored in suitable memory media that can be accessed through the processor in order to determine the value of the pressure change experienced by the pressure sensor. The various embodiments of the present invention are advantageous in that they provide a reinforced pressure sensor that has the ability to operate in extreme environments, which avoids the problems associated with prior art sensors. For example, unlike Fabry-Perot sensors that use a diaphragm as a Optical cavity mirror, the reflective surfaces of the present invention remain substantially parallel according to all except the most extreme pressure changes. Furthermore, the fusion of the fiber optic ends within a capillarity and subsequently the fusion of the capillarity inside a tube allows an increase in the sensitivity of the pressure without increasing the sensitivity of the optical cavity to the vibration or the adhesion effects. / sliding experienced with the prior art devices. While various particular forms of the invention have been illustrated and described, it will be apparent that various modifications may be made without departing from the spirit and scope of the invention. It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (33)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A device that senses the pressure of an environment, characterized in that it comprises: a capillarity having a proximal end and a distal end, and a bore extending therebetween, __ an optical fiber having a proximal end and a distal end, the distal end is configured to partially reflect the light, the distal end is located within and extends through the capillarity bore to the distal end of the capillarity, a tube having a proximal end and a distal end and a length, a cap having a proximal end and a distal end, the distal end is configured to reflect light, and the distal end of the cap is located in a hole at the distal end of the tube, where the optical fiber and capillarity are introduced in a hole in the proximal end of the tube at a selected distance, so that a separation within the tube between the distal end of the optical fiber and the distal end of the stopper. The device according to claim 1, characterized in that the optical fiber is melted in the capillarity, and the capillarity is melted in the tube, and the plug is fused in the tube. 3. The device according to claim 1, characterized in that the capillarity is formed from fused silica. 4. The device according to claim 1, characterized in that the tube is formed from fused silica. - - - - - 5. The device according to claim 1, characterized in that the plug is formed from fused silica. 6. The device according to claim 1, characterized in that the separation is filled with gas. The device according to claim 1, characterized in that the separation contains a vacuum. 8. The device according to claim 6, characterized in that the gas is air. The device according to claim 1, characterized in that the far end The cap is an optically polished mirror. The device according to claim 1, characterized in that the distal end of the plug has a coating that provides a relatively high optical reflectivity. The device according to claim 1, characterized in that the reflectivity of the distal end of the plug is approximately 100%. The device according to claim 10, characterized in that the coating is a coating of metal or another high-reflectivity coating.- 13. The device according to claim 12, characterized in that the metal coating is selected from of the group consisting of gold, silver and aluminum. The device according to claim 1, characterized in that the distal end of the optical fiber is flat and polished. 15. The device according to claim 1, characterized in that the distal end of the optical fiber is a curved surface. 16. The device according to claim 1, characterized in that the distal end of the optical fiber has a coating to increase the reflectivity of the far end of the optical fiber above the reflectivity of a glass at an air interface. The device according to claim 1, characterized in that the optical fiber is a single mode fiber. 18. The device according to claim 1, characterized in that the optical fiber has a core and a coating layer. 19. The device according to claim 1, further characterized in that it comprises at least one periodic disturbance of the refractive index located in the optical fiber at a position proximate to the distal end of the optical fiber that provides a temperature compensation. 20. A pressure sensor for use in extreme environments, characterized in that it comprises: a detection assembly including: a capillarity having a proximal end and a distal end, and a bore extending therebetween, an optical fiber having a proximal end and a distal end, the far end is configured to partially reflect the light, the far end is located inside and extends through the capillarity bore to the far end of it; a tube having a proximal end and a distal end and a length, and a stopper having a proximal end and a distal end, the distal end is configured to reflect light, and the distal end of the stopper is located in an aperture in the distal end of the tube, wherein the optical fiber and capillarity are introduced into a hole in the proximal end of the tube at a selected distance, so that a gap is formed within the tube between the distal end of the optical fiber and the remote end of the plug, a housing defining a detection chamber, the housing has a proximal end and a distal end, the distal end of the housing has a port formed therein, the sensor is mounted within the detection chamber, so that the proximal end of the optical fiber extends through a pressure seal located in a wall of the housing forming a proximal end of the chamber of tection 21. The device according to claim 20, characterized in that the detection chamber is filled with a filling material. 2

2. The device according to claim 21, characterized in that the material of Filler is a non-flowing material that can be compressed. The device according to claim 20, further characterized in that it comprises an isolation means mounted at the distal end of the housing and in communication with the interior of the detection chamber through the port. 24. The device according to claim 23, characterized in that the detection chamber is filled with a fluid. 25. The device according to claim 23, characterized in that the isolation means is a bellows. 26. The device according to claim 23, characterized in that the isolation means is a structure sensitive to changes in pressure and capable of communicating these pressure changes to the detection chamber. 27. A pressure sensing system that senses pressures, characterized in that it comprises: a light source; a bidirectional coupler that is in optical communication with the light source; a pressure sensor that has an optical cavity of Fabry-Perot, the pressure sensor is in optical communication with bidirectional coupler, bidirectional coupler provides a path or path for the transmission of light from the light source to the pressure sensor and also provides a way for the transmission of light reflected by the Fabry-Perot optical cavity of the pressure sensor; and the analysis medium that is in optical communication with the bidirectional coupler for the study of the light reflected by the Fabry-Perot optical cavity in the pressure sensor in order to determine the changes in the pressure detected by the sensor. Pressure. 28. The system according to claim 27, characterized in that the light source is a tuneable laser. 29. The system in accordance with the claim 27, characterized in that the analysis means is an optical power meter. 30. The system according to claim 27, characterized in that the means of. Analysis is an optical spectrum analyzer. 31. The system according to claim 27, characterized in that the bidirectional coupler is a circulator. 32. The system according to claim 27, characterized in that the optical communication between the Light source, bidirectional coupler, pressure sensor and analysis medium is provided by the optical fiber. 3

3. The device according to claim 1, characterized in that the distal end of the optical fiber is an exfoliated planar end.