ES2206043A1 - Interrogation device for photonic transducer has detector array located at specific distance that is smaller than focal length of diffraction grating in tilted diffraction grating optical waveguide - Google Patents

Abstract

The interrogation device has a tilted diffraction grating optical waveguide with an optical guide in which a short period or uniform or non-uniform period diffraction grating is provided. A detector array is located at a specific distance that is smaller than the focal length of diffraction grating in tilted diffraction grating optical waveguide. The tilted diffraction grating optical waveguide generates radiated field whose spatial position and shape depends on the wavelength and optical power of light.

Description

Transducer Interrogation Device photonics based on the measurement of the near field of a network of inclined diffraction in optical waveguide.

Object of the invention

The invention belongs to the field of demodulation of information from transducers photonics that encode it in wavelength (such as Short Period Optical Diffraction Networks (R.D.O.P.C.)), in the intensity of the light reflected / transmitted by them (the so-called intensity sensors), and, in certain cases, of those who encode it in phase (such as cavities of Fábry-Perot of high purity).

State of the art

Photonic transducers are finding more and more different application niches. So, for example, the based on R.D.O.P.C. they are increasingly spread in areas of as much impact as civil engineering or aeronautics (although not exclusively in them) in an attempt to get the maximum possible information on the behavior and health of structures With this information you can activate the measures opportune conducive to repair and / or improve the behavior of that structure under supervision. The reason that motivates this, each growing, use of photonic transducers and that, little by little, goes displacing more traditional technologies you have to look for it in the advantages inherent in this type of technology. Among other are the small size and low weight of the elements sensors and that, among other things, allows you to enter them in the inside the structures without hardly disturbing them. Another advantage fundamental of this type of technologies is that they allow the creation of multipoint measurement systems with a single fiber channel optics. Thus several photonic transducers can be arranged along the same optical fiber without interfering with each other. Thanks to all these advantages it is possible to obtain a valuable information that with other types of transducers would be very difficult. The fact that they are totally dielectric elements It also provides not very important advantages, since example, enable the use of this technology in environments electromagnetically hostile But all these advantages do not they would justify the use of this technology if it were not available schemes that allow to extract the information encoded by the optical transducers with technical characteristics (stability, resolution, etc.) comparable if not higher than those With traditional systems. Focusing the discussion on R.D.O.P.C.-based transducers, as they are currently are receiving more attention, it should be said that throughout the last decade many have been the interrogation schemes of this type of transducers collected in the literature specialized. The techniques used have been very varied [1] going from the use of interferometers [2,3], through filters wavelength dependent [4,5], tunable filters [6.7], tunable lasers [8], etc. They all offer features good enough to be able to, in principle, allow real use of photonic transducers based on diffraction networks, but a more detailed study reveals that the vast majority of them have large Difficulties to be employed in the field. These difficulties they can be of economic nature, of little robustness or to specify Very controlled conditions for proper operation. The above statements are supported by the shortage of commercial interrogation units that exist in the market.

The interrogation device object of this patent solves the previous difficulties presenting a simple, compact and robust interrogation scheme that does suitable to be used in the field. The system is able to obtain simultaneous information of several multiplexed transducers spectrally that they are located remotely in several points of a structure and distributed along the same channel of optical fiber. The principle of operation is based on capacity presented by the R.D.O.P.C. inclined to extract light from the guide of optical wave and redirect it outside of it in a determined direction dependent on the wavelength. Is property has been widely collected in the literature and has been Subject of several prior patents (US4749248 [9], EP0438759 [10], EP0435194 [11], EP0435201 [12]).

The authors know the existence of the patent US5982962 [13] as well as the works included in [14,15] that, using the same components that are used in the invention object of this patent although arranged in a very different way and based on a different operating principle (capacity than the R.D.O.P.C. inclined and non-uniform period have extract light from the fiber optic core and focus on one point which varies with the wavelength), they propose the possible construction of a system that could eventually be used to the interrogation of the same type of transducers as here It has been spoken although with inferior benefits. Do not However, the present invention offers two fundamental aspects and Innovative regarding the state of the art today: architecture of the system and principle of operation (field measurement close to the non-focused light extracted from the fiber core optical by an R.D.O.P.C. inclined and non-uniform period as well as the dependence that the direction of propagation and the position of the maximum of this field present with the wavelength. Other differential feature of the device is that it uses the fingerprints that cover modes print on the radiated field to improve your resolution).

Bibliography

[one]

J.M. López-Higuera, editor, "Handbook of optical fiber sensing technology ". John Wiley & Sons, pp. 800 (2002).

[two]

AD Kersey , TA Berkoff and WW Morey , "High resolution fiber-grating based strain sensor with interferometric wavelength shift detection", Electronics Letters , 28, pp. 236-238 ( 1992 ).

[3]

MD Todd , GA Johnson and CC Chang , "Passive, light intensity-independent interferometric method for fiber Bragg grating interrogation", Electronics Letters , 35, pp. 1970-1971 ( 1999 ).

[4]

MA Davies and AD Kersey , "All-fiber Bragg grating strain sensor demodulation technique using a wavelength division coupler" Electronics Letters , 30, pp. 75-77 ( 1994 ).

[5]

T. Coroy and RM Measures , "Active wavelength demodulation of a Bragg grating fiber optic strain sensor using a quantum well electroabsorption filtering detector", Electronics Letters , 32, pp. 1811-1812 ( 1996 ).

[6]

AD Kersey , TA Berkoff and WW Morey , "Multiplexed fiber Bragg grating strain sensor system with a Fabry-Pérot wavelength filter", Optics Letters , 18, pp. 1370-1372 ( 1993 ).

[7]

MG Xu , H. Geiger and JP Dakin , "Modeling and performance analysis of a fiber Bragg grating interrogation system using an acousto-optic tunable filter", Journal of Lightwave Technology , 14, pp. 391-396 ( 1996 ).

[8]

LA Ferreira , EV Diatzikis , JL Santos and F. Farahi , "Demodulation of fiber Bragg grating sensors based on dynamic tuning of a multimode laser diode", Applied Optics , 38, pp. 4751-4759 ( 1999 ).

[9]

U.S. Patent 4749248, "Device for tapping radiation from, or injecting radiation into, single made optical fiber, and communication system comprising same ", White et al., Jun 7, 1988.

[10]

European Patent 0438759, "Optical waveguide embedded light redirecting Bragg grating arrangement ", Glenn et al., Aug. 27, 1991.

[eleven]

European Patent 0435201, "Optical waveguide embedded light redirecting and focusing Bragg grating arrangement ", Morey et al., Oct. 29 1991

[12]

European Patent 0435194, "Multi-core opticalwaveguide Bragg grating light redirecting arrangement ", Morey et al., May 21 1991

[13]

U.S. Patent 5982962, "Fiber-Integrated Microlenses and Optical Fiber FBG Couplers, Spectrometers, and Multiplexers Comprised Thereof ", Koops et al., Nov. 9, 1999.

[14]

CK Madsen , J. Wagener , TA Strasser , D. Muehlner , MA Milbrodt , EJ Laskowski and J. DeMarco , "Planar Waveguide Optical Spectrum Analyzer Using a UV-Induced Grating", J. Selected Topics in Quantum Electronics , vol. 4, n ° 6, pp. 925-929 ( 1998 ).

[fifteen]

J. Wagener , TA Strasser , J. Pedrazzani , J. DeMarco and D. DiGiovanni , "Fiber Grating Optical Spectrum Analyze Tap", ECOC'97, Conference Publication No. 448, pp. 65-68 ( 1997 ).

Description of the invention

The interrogation system, as you can see in figure 2, it consists of:

- An R.D.O.P.C. inclined

- An array of detectors

- Electronic processing unit

The R.D.O.P.C. inclined is inscribed in a guide optical wave located above a detector array at a Small distance from it. You also have to add a unit electronics for processing, demodulation and conditioning of the signal as well as for the control of the detector array.

On this basic scheme it will be necessary to carry out small modifications to adapt it to the particularities concrete of the type of photonic transducer desired question. Thus, for example, and without loss of generality, for the case sensors based on R.D.O.P.C. should be added to the scheme basic a broadband light source and a coupler or circulator optical.

The innovative working principle of Interrogator is based on the ability of the R.D.O.P.C. inclined to extract light from the optical waveguide and redirect it outside of it at a specific address dependent on the wavelength This way it will form, in the vicinity of the R.D.O.P.C. inclined, a radiated field (of approximately the same length as the inclined network) that will move towards the right or left parallel to the optical waveguide depending on its wavelength. Moreover, the shape of this Radiated field will also be modified with wavelength because the cover modes print a print on the amplitude thereof that is dependent on this parameter. East effect can be enhanced if an R.D.O.P.C. from non-uniform period since the movement of the near field caused by the variation of the exit direction with the wavelength will be added to the offset, dependent of this same parameter, along the network length of the point of maximum light extraction. Thus, using these characteristics, if an array of detectors is placed in the proximity of one of these R.D.O.P.C. inclined and parallel to she will capture a different image depending on the length of wave of light that propagates through the optical waveguide. Likewise the captured image will have greater or lesser intensity depending on the power of light that was propagated by the waveguide. This way you can extract information from transducers that the encode in the wavelength, in the light intensity or, in certain cases, in phase.

The interrogation block object of the invention also allows simultaneous information from one or several transducers The interrogator may be part of a system of multipoint measure, as seen in Figure 1, which It consists of three or four distinct parts (depending on if the transducers work in reflection or in transmission), the first of them (zone A) is composed of the unit optoelectronics consisting of interrogation block (3), and in function of transducer type to interrogate, light sources (1_ {1}) and light routing elements (2). The second part (zone B), is formed by a fiber optic channel (4). The third part (zone C) is the multipoint system of composite measure of the different transducers (5_ {a} a 5_ {N}) arranged along the fiber optic channel. And by last, the fourth part (zone D), which will exist or not depending on the types of transducers that make up the multipoint system, It will be formed by a light source (1_ {2}). So it looks like in a complete multipoint measurement system in addition to the block of interrogation and optical transducers are also necessary other elements such as light sources (1_ {1} or 1_ {2}), light addressing elements (2), and a fiber channel optic (4) that communicates the optoelectronic unit that composes the zone A with the fiber region that contains the different transducers (5_ {1} to 5_ {N}). These are arranged along  of the same fiber optic channel and will be interrogated in a manner simultaneous by the interrogation block object of this invention. Thus the overall operation of the system is as follows: the light source emits light towards the transducers, these in function of the external parameter they measure will modify any of the characteristics of the light (for example presenting greater or lesser attenuation to the passage of light and / or selecting specific parts spectrum) coding the information in this way. After this modified light is directed towards the interrogation block where the information concerning the parameters will be extracted measured by transducers. To enable spot measurements far removed from the optoelectronic unit the use of a fiber optic channel (4) between it and the transducers Finally, thanks to both the channel (4) and the  sensors are made of dielectric material can operate in electromagnetically hostile zones.

In the interrogation block, the light (2) is directs towards an inclined diffraction network and, in the most case general, of non-uniform period (it being understood that the structures of uniform period are a particular case of this). In each of the successive refractive index changes that make up the network (dark ovals of the drawing) a fraction of the light will be ejected incident outside the optical waveguide in a given band of wavelengths and in a specific direction. Is Output direction depends on the wavelength. Likewise, except for inclined networks of uniform period, the point at along the length of the network in which a maximum of ejected light also varies depending on the wavelength. By On the other hand, the so-called cover modes print on this outgoing radiation a characteristic footprint in the form of very abrupt variations in the amplitude that also depends on the wavelength This way it will be formed in the Surroundings of the waveguide an outgoing light radiation (4) of approximately the same physical dimensions as the R.D.O.P.C. inclined that generated it and whose spatial position and shape will change With the wavelength. In addition the intensity of this radiation It will depend on the optical power of the light that generated it. Is radiation will be captured by an array of detectors (5) located at a small distance d from the waveguide forming this way An image that will be captured. For the above explained is You can see that the characteristics of this image will depend on The wavelength / s of light / s as well as its intensity. A Once captured, the image must be conveniently processed by a specific algorithmic to extract simultaneously the information of the different transducers.

The distance d is not especially critical but yes it must be small compared to the focal length (7), typically this distance will be around millimeters so that the near field condition is met. Light also It can also influence the R.D.O.P.C. inclined by any of its extremes (which does not happen if what is wanted is to focus the light at point 7), the only difference would be that, following the agreements established in Figure 2, if the light affected the right would have to place the array of detectors in the part upper instead of lower.

The interrogation block thus constituted has been chosen to achieve the following advantages and / or benefits:

one.

Measure Simultaneous multi-photon transducers spectrally.

two.

Obtaining high performance in terms of spectral interrogation range with respect to other proposed systems.

3.

Benefits comparable, and in some cases superior, to other schemes proposed and those of traditional techniques.

Four.

Capacity of obtain information encoded in wavelength, amplitude or in phase

5.

Construction is simple by not being subject to severe physical restrictions (for example distance of the detector array from the network inclined) for the correct operation of the unit.

6.

Compact scheme and robust that makes it suitable for field use.

7.

It is possible to use eventually the device as an optical spectrometer of limited resolution.

Description of the drawings

Figure 1: Shows a block diagram of a multipoint measurement system. The blocks inside the different regions (A, B, C, and D) that are bordered by dashed lines are optional and will be used or not depending on the nature of the transducers employed. This way it looks that the system requires a light source (1_ {1} or 1_ {2}) which can be located in such a way that it makes the transducers work in reflection (zone A) or in transmission (zone D). In case you have the light source located in zone A also the presence of an element that is capable of routing will be required  the light emitted to the photonic transducers (5) and from these to interrogation block (3). This element (2) can be a directional collector, a circulator or any other element that perform an analogous function. Zone B of the system comprises a fiber optic channel (4) that allows remote operation. And by Finally, zone C is that of multipoint measurement, where several transducers (5_ {1} to 5_ {N}) conveniently arranged along the same fiber channel.

Figure 2: It basically shows the block of interrogation object of this invention. It is composed of one optical waveguide, represented in the figure by an optical fiber (1) through which light is propagated (2) in the direction of an R.D.O.P.C. inclined (3). This has been represented as a period not uniform because this is the general case that encompasses the networks of uniform period. The light (2) incident on the inclined network (3) is ejected out of the fiber (4) in a certain direction and captured by a matrix of detectors (5) arranged parallel to the R.D.O.P.C. inclined (3) at a distance d that meets the near field condition. To complete the block of interrogation must incorporate an electronic unit (6) to the signal processing as well as for the control of the matrix of detectors Finally, point (7) represents the focus of the R.D.O.P.C. inclined (3) for the wavelength of light (2) employee. This point would go away to infinity in the case of use inclined networks of uniform period.

An embodiment of the invention

Although it is considered that the above has sufficiently described the invention, as a whole, as to that its realization can be deduced, in what follows, and not excluding other possibilities of realization, a way of carrying out the invention.

It starts from an optical waveguide in which have registered an R.D.O.P.C. inclined at a sufficient angle as to allow to extract light from the guide. Preferably this network will have a non-uniform period (of linear variation) for enhance the displacement effect of the maximum extraction of light with wavelength. This, together with the effect of variation of the direction of light output with its wavelength, will cause a very noticeable increase in the spectral resolution of the device. On the other hand, the greater the linear variation of the smallest period may be the distance d at which the waveguide with respect to the array of detectors for a spectral resolution given. In this way if a R.D.O.P.C. inclined of uniform period the distance d would have to be older, thus incurring a device less compact. On the other hand the network registration method inclined in the waveguide may be any of the employ the use, read holographic method, phase mask, etc.

On the other hand it is also necessary to have of an array of detectors, such as a CCD, an array Linear of detectors type PIN, APD or similar, or any other device that is capable of capturing light along a line.

In principle the physical dimensions of the network inclined should be equal to or less than those of the matrix of detectors, although this is not an indispensable condition either. I know fix the optical waveguide that contains the network inclined to the array of detectors being careful to direct them the side of the guide through which the light will come out. The guide fix from wave to matrix can be chemical (by glue by example), mechanic, or any other type that confers robustness and reliability.

The array of detectors must be incorporated an electronic unit for its control and image capture from the inclined network. Finally this unit will connect to another signal processing in which the images will be treated captured with a specific algorithmic to extract simultaneously the information encoded by each of the transducers

The materials, shape, size and configuration of the elements will be susceptible to variation, as long as this does not imply an alteration of the essence of the invention.

Claims (3)

1. Transducer interrogation device photonics based on the measurement of the near field of a network of inclined diffraction in optical waveguide composed of a guide optics, within which a diffraction network of short inclined period of uniform or non-uniform period, and by a detector array located at a distance d (much smaller than the focal length of the diffraction network if this is non-uniform period) of the optical waveguide. 2. Transducer interrogation device photonics based on the measurement of the near field of a network of inclined diffraction in optical waveguide, which according to the claim 1, generates a radiated field whose spatial position and shape depends on the wavelength and optical power of the light. 3. Interrogation device of photonic transducers based on the measurement of the near field of an inclined diffraction network in optical waveguide, which according to the preceding claims, is characterized in that by means of an electronic processing of the images captured by the matrix of Detectors and using a specific algorithmic, is able to obtain simultaneous information from one or several transducers.