DE19943387A1 - Method for producing an optical grating on an optical conductor and arrangement with such a grating and such a conductor - Google Patents

Abstract

Method for producing an optical Bragg grating (11), on an optical fiber (1), the fiber being fastened at two fastening points (21, 21) arranged at a distance (d) from one another and then the grating (11) being fastened on the Fiber is made between these attachment points, with the peculiarity that the fiber is permanently attached to the attachment points before the grid is made. An arrangement with such a grating and such a fiber is specified.

Description

According to the preamble of claim 1, the invention relates to a method for producing at least one optical git ters, in particular a Bragg grating, on an optical Conductor, the conductor being at least two at a distance fastened from each other and attached then the grid on the fixed ladder between them Attachment points is made.

In known methods of the type mentioned is the optical one Head of an optical fiber that is used during the manufacture of the git biased between the two attachment points and after making the grid on the fiber again is stretched.

An optical Bragg grating was first replaced by a standing one optical wave of radiation from an argon laser in an opti monomode fiber (see K.O. Hill. et al. "Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication ", Appl. Phys. Lett., Vol. 32, 1978, pp. 647-649). This creates relatively long fibers grids of about one meter in length, for example.

It was later proposed to have a Bragg grating in one Fiber by transverse UV radiation of an optical fiber to manufacture. A holographic process is used turns, by overlaying two UV rays an interference fringe pattern is generated with plane waves, with which the fiber is exposed.  

The generation of the two UV rays can be realized in various ways. The following arrangements have already been used:

• - an interferometer with divider mirror and three or more um steering mirrors (see G. Meltz, W. W. Morey, W. H. Glenn: "Formation of Bragg gratings in optical fibers by transverse holographic method ", Opt. Lett. 14 (15), 1989, p. 823);
• - a mirror (Lloyd mirror interferometer, see R. Kasyap et al. "All-fiber narrow-band reflection gratings at 1550 nm", Electron. Lett. 26 (12), 1990, p. 823 and / or B. Eggleton, P. A. Krug, L. Poladin: "Dispersion compensation by using Bragg grating filters with self induced chirp ", Tech. Digest. Opt. Fib. Co mm. Conf., OFC'94, 1994, p. 227);
• - a prism (Lloyd prism interferometer, see Q. Zhang et al. "Simple prism-based scheme for fabricating Bragg gratings in optical fibers ", Opt. Lett. 19 (23), 1994, pp. 2030-2032 and / or N.H. Rizvi, M.C. Gower: "Production of submicron period Bragg gratings in optical fibers using wavefront divi sion with a biprism and an excimer laser source ", Appl. Phys. Lett. 67 (6), 1995, pp. 739-741);
• - an interferometer with an optical diffraction beam splitter and two deflecting mirrors;
• - Total reflection in a quartz glass body (see R. Kashap et al. "A novel method of writing photo-induced chirped Bragg gratings in optical fibers ", Electron. Lett. 12, 1994, p. 994-997).

Another known method is to use egg ner phase mask for generating an interference fringe pattern sters (see K.O. Hill et al. "Bragg gratings fabricated in photosensitive optical fiber by UV exposure through a phase mask ", Appl. Phys. Lett. Vol. 62, 1993, pp. 1035-1037  and / or D. Z. Anderson et al. "Production of in-fiber gra tings using a diffractive optical element ", Electron. Lett., Vol. 29, 1993, pp. 566-568). The fiber becomes direct attached behind a phase mask made of quartz glass. On UV rays are sent through the phase mask. At a The UV radiation is diffracted by the lattice structure of the phase mask. A plus is created behind the grid structure of the phase mask first diffraction order and a minus first diffraction order. A superimposition of the two diffraction orders creates a UV interference fringe pattern. With this stripe pattern irradiated the fiber. Due to the photosensitivity of the Fiber is created in the irradiated areas of the fiber core a periodic increase in refractive index.

Another method of making a grid on egg ner fiber is a selective exposure of the fiber (see K. O. Hill et al. "Efficient mode conversion in telecommunicati on fiber using externally written gratings ", Electron. Lett. 26 (16), 1990, p. 1270 and / or B. Malo et al. "Point by point fabrication of micro-Bragg gratings in photosensitive fiber using single excimer laser pulse refractive index modes fication techniques ", Electron. Lett. Vol. 29, 1993, p. 1668-1669). It is important that the fiber during the relative long time to inscribe the grid in the fiber no changes to their mechanical condition is required experiences.

A general overview of the ver driving is, for example, K. O. Hill et al. "Fiber Bragg Gra Technology Fundamentals and Overview ", Journal of Lightwave Technology, Vol. 15, No. 8, August 1997, pp. 1263-1276 refer to.

From B. Malo et al. "Apodised in-fiber Bragg grating reflec tors photoimprinted using a phase mask ", Electron. Lett., Vol. 31, 1995, pp. 223-224 and / or J. Albert et al. "Apodization of the spectral response of fiber Bragg gratings using a phase mask with variable diffraction efficiency ",  Electron. Lett., Vol. 31, 1995, pp. 222-223 it is known Fiber grating with precisely defined requirements for the spec to produce central properties by apodization, where here, too, the fiber is first clamped and after the on writing the grid into the fiber is stretched out again.

The object of the invention is to show how on an op an optical grating, ins especially a Bragg grating that can be made exactly defined and constant lattice constant has.

This object is achieved by the Merk specified in claim 1 times solved.

According to this solution, the optical conductor is in front of the manufacturer the grid at the attachment points Stigt, in contrast to the known methods in which egg ne fiber before the production or registration of the Git Clamped more or less during the registration process preloaded and after the git was registered Ters is stretched again so that the fiber does not last is fixed, but only temporarily attached.

The invention is based on the finding that previously used clamping and subsequent unclamping of the Fiber after making the lattice on the fiber mechani tensions that existed during this manufacturing process become free again, or that new mechanical tensions by handling the fiber after unclamping the. These mechanical stresses lead to changes in the Lattice constants or period in the lattice and thus for change change in the reflection or transmission spectrum. Mechani tensions that only work in parts of the grid and consequently affect only parts of the lattice structure drastically change the spectral course and thus the Question the usability of the grid in question.  

Even with a grid with precisely defined requirements the spectral properties, for example with a through Apodization produced grid or a particularly long Fiber mesh, play unwanted partial changes in the Lattice constants play a major role. Such unwanted parti Changes can also occur in this case be called that in the manufacture of such a Git ters the fiber first clamped and after production the grid is stretched out again.

In the method according to the invention, it is advantageous the stability of the lattice constants and all other para meters of the grid after the grid is made on the guaranteed optical conductor.

When the method according to the invention is carried out, the optical conductors during the manufacture of the grating between the attachment points free of tension, at another off is the optical conductor during the manufacture of the Grid stretched between the attachment points.

The invention also provides an advantageous arrangement with a carrier body, an optical conductor and an opti grid, in particular a Bragg grid, the conductor being at least two apart other arranged attachment points on the support body attached and the grid on the attached conductor between these attachment points is formed, and thereby is marked that the conductor at the attachment point ten is permanently attached to the support body and the Git ter a after the permanent attachment of the conductor on the Carrier body is made grid.

The invention is described in the following description of the drawings explained in more detail by way of example. Show it:  

FIG. 1a to 1d an output stage, two intermediate stages and a final stage of an embodiment of he inventive method,

FIGS. 2a and 2b in side view and top view of a Bragg grating sensor manufactured by the inventive method for measuring a temperature,

Fig. 3 is a plan view of a Bragg grating sensor manufactured with the method according to the invention for measuring acceleration and

Fig. 4 shows a side view of a temperature-stable Bragg reference grid manufactured using the method according to the invention.

The figures are schematic and not to scale.

According to the output stage indicated in FIG. 1a of the method according to the invention, an optical conductor 1 is applied to a carrier body 2 shown in FIGS . 1a to 1d in each case in a side view and at two fastening points 21 , 21 which in the direction of a defined longitudinal axis 10 of the Conductor 1 are arranged at a distance d from one another, permanently attached to the carrier body 2 , so that the first intermediate stage of the method according to the invention indicated in FIG. 1b has arisen.

On the conductor 1 fastened in this way, an optical grating 11 (see FIG. 1d) is produced between the two fastening points 21 , 21 . For example, any of the methods described in the prior art can be used for this purpose.

For example, Fig of the photosensitive Lei, according. 1c ter 1 with a skillful through a phase mask 3 Strah lenbündel 4, for example from UV light, exposed. The opti cal as a plane wave 41 incident on the mask 3 4 radiation is diffracted at a grating structure 31 of the phase mask. 3 Behind the grating structure 31 of the phase mask 3 there is a plus first diffraction order 32 and a minus first diffraction order 33 , each of which defines an interference fringe and which together form an interference fringe pattern 35 . With this striped pattern 35 , the conductor 1 between the fastening points 21 , 21 is exposed in such a way that the interference strips defined by the diffraction orders 32 and 33 interfere in the direction of the longitudinal axis 10 of the conductor 1 pe periodically. Due to the photosensitivity of the conductor 1 , there is an increase in refractive index in each exposing interference strip.

After this exposure of the conductor 1 , the final stage of the method according to the invention shown in FIG. 1d was formed, in which the optical grating 11 is formed between the two fastening points 21 , 21 of the carrier body 2 on the conductor 1 , which in the direction of the longitudinal axis 10 of the conductor 1 is defined periodically successive local refractive index increases 110 .

A particular advantage of the described use of the phase mask 3 is that the phase mask 3 can be applied directly to the carrier body 2 and not, as previously, the conductor 1 in the form of the glass fiber has to be brought into position at a distance from the phase mask 3 . This procedure advantageously also ensures a very precise position of a Bragg wavelength and the other parameters of the grating 11 , for example a spectral width, a degree of reflection, etc., of the grating 11 . These parameters ter, since the grid 11 is already fixed by a support body 2 , advantageously no longer be set subsequently during installation.

In this way, two or more optical gratings 11 can be produced on the conductor 1 between the two fastening points 21 , 21 , at the same time and / or chronologically in succession and / or spatially separated from one another and / or superimposed on one another.

The attachment of the conductor 1 on the support body 2 at the two attachment points 21 , 21 remains after the position of the one or more grids 11 and is not solved.

The optical conductor 1 is already permanently attached to the carrier body 2 before the production of one or more optical grids 11 and not only subsequently.

The optical conductor 1 to be fastened on the carrier body 2 preferably does not yet have an optical grating, although on this conductor 1 there may already be at least one grating 11 that is different from a grating 11 that is to be produced, but then does not have the advantageous properties of the grating 11 .

The optical conductor 1 is preferably an optical glass fiber, for example a single-mode or multimode fiber and / or a core-cladding glass fiber. The conductor 1 can also be an optical waveguide integrated on a substrate. The optical conductor 1 is preferably elongated in the direction of the longitudinal axis 10 .

The optical conductor 1 can be held between the two fastening points 21 , 21 so that it is tension-free during the manufacture of a grating 11 between the fastening points 21 . The conductor 1 preferably hangs freely between the fastening points 21 , 21 and the grid 11 is produced in the freely hanging conductor 1 .

It is also useful if the optical conductor 1 during the manufacture of the grating 11 between the two fastening points 21 , 21 is stretched. Such a pretension is useful because it keeps the conductor 1 stretched even when it is mechanically relieved.

The carrier body 2 can be designed only for fastening the conductor 1 , but also for realizing certain functions.

If the carrier body 2 is used only for fastening the conductor 1 , it can be simple, for example in one piece. If, on the other hand, it has certain other functions to perform, for example functions of a Bragg grating sensor, the carrier body 2 can be of a more complicated, in particular composite, structure. So z. B. mechanical levers, actuators or elements with characteristic thermal expansion coefficient for temperature compensation may be part of the carrier body 2 Trä.

A particular advantage of the method according to the invention is that the conductor 1 can be connected to the carrier body 2 without special attention to conductor voltage, room temperature and later desired grid parameters of the grid 11 , for example by gluing, soldering, collapsing, etc. With a conductor 1 in the form of a quartz glass fiber, for example, a temperature necessary for attaching the conductor 1 to the support body can be up to 800 ° C., while a grid 11 to be produced after this attachment is degraded from approximately 150 ° C. and even destroyed at higher temperatures. After the conductor 1 has been fastened to the carrier body 2 at a higher temperature, it is only necessary to wait until the temperature of the conductor 1 has dropped below the temperature at which the grid 11 to be produced is degraded or deformed.

The method according to the invention can advantageously be used generally Bragg grating sensors for measuring one realize physical quantity, including, for example, a Sensor for measuring a temperature, an acceleration, a force, an electric current, an electric Voltage, an electric field, a magnetic field  des etc. as well as, for example, a stable Bragg grating as optical wavelength reference, an exact Bragg grating for an application in telecommunications and / or an opti Long period grating (LPG) and realize its applications.

In FIGS. 2a and 2b, in side view and plan view of a manufactured with the inventive method at play exemplary Bragg grating sensor for measuring a temperature, in the Fig. 3 in plan view of a manufactured with the inventive method Bragg grating sensor for Measurement of an acceleration and in Fig. 4 in side view shows a temperature-stable Bragg grating produced by the method according to the invention as an optical wavelength reference Darge.

Each of the two sensors and the temperature-stable Bragg grating each have an arrangement with a support body 2 , with an elongated optical conductor 1 and with a Bragg grating 11 , the conductor 1 having two fastening points 21 arranged at a distance d from one another, 21 attached to the support body 2 and the grid 11 is formed on the fixed conductor 1 between the attachment points 21 , 21 , with the particularity that the conductor 1 is permanently attached to the support body 2 at the attachment points 21 , 21 and the grid 11 a after the permanent attachment of the conductor 1 on the support body 2 is manufactured grid.

In the sensor according to FIGS. 2a and 2b, the carrier body 2 is preferably in one piece and consists, for example, of quartz glass. The conductor 1 is, for example, a glass fiber which is permanently attached to the body 2 between the two fastening points 21 , 21, preferably under a prestress, and in the Bragg grating 11 is formed between the two fastening points 21 , 21 . Between the two fastening points 21 , 21 , the fiber 1 hangs freely. For this purpose, the carrier body 2 has on its side facing the glass fiber 1 a recess 20 which is bridged by the fiber 1 . A temperature-dependent change in the refractive index and expansion of the fiber 1 lead to a measurable shift in the Bragg wavelength of the grating 11 with the temperature. The expansion of the fiber 1 with the temperature can be reinforced by a suitable material of the carrier body 2 who is selected.

The arrangement of the sensor according to FIG. 3 differs from that of the sensor according to FIGS. 2a and 2b essentially only by the presence of an inert mass M. Otherwise the sensor according to FIG. 3 is structurally compatible with the sensor according to FIGS. 2a and 2b match, and parts that are the same in both sen sensors are denoted in Fig. 3 with the same reference numerals as in Figs. 2a and 2b.

In the sensor of FIG. 3, the mass M is connected to the fiber 1 and exerts an expanding and / or contracting force on the Bragg grating 11 formed on the fiber 1 when the carrier body 2 is moved accelerated.

In the arrangement of the temperature-stable Bragg grating according to FIG. 4, the carrier body 2 is not made in one piece, but rather is assembled. The composite carrier body 2 has a substrate body 2 'and two subcarrier bodies 2 ", 2 " fastened to the substrate body by 2 ' and separated by an intermediate space 22 '. On the two subcarrier bodies 2 ", 2 ", for example, also consisting of a fiber optic conductor 1 at the two fastening points 21 , 21 so that a fastening point 21 on a subcarrier body 2 "and the other fastening point 21 on the other subcarrier body 2 "be finds that the conductor 1 bridges the gap 22 ', and that the grid 11 formed on the conductor 1 is arranged over the inter mediate space 22 '.

The two subcarrier bodies 2 ", 2 " are attached to the substrate body 2 'in such a way that a section 20 ', 20 'of each subcarrier body 2 ", 2 " bordering on the intermediate space 22 ' is not connected to the substrate body 2 'and itself can expand and / or contract freely when the temperature changes relative to the substrate body 2 '.

The material of the substrate body 2 'and the material of the subcarrier bodies 2 ", 2 " are matched to one another such that the space 22 ' between the subcarrier bodies 2 ", 2 " due to a temperature-related expansion and / or contraction of the sections 20 ", 20 "of the two subcarrier bodies 2 ", 2 "is narrowed and / or expanded. For example, be the subcarrier body 2 ", 2 " made of a material with a coefficient of thermal expansion α <0 and the sub strate body 2 'of a material with a smaller than this coefficient α smaller, preferably vanishingly low thermal expansion coefficient.

A narrowing of the intermediate space 22 'caused by a temperature change counteracts an expansion of the conductor 1 and thus the grid 11 caused by this temperature change. A widening of the intermediate space 22 'caused by a change in temperature counteracts a contraction of the conductor 1 and thus the lattice 11 caused by this change in temperature.

The material of the substrate body 2 ', the material of the two Subträgerkörper 2 ", 2" and the material of the conductor 1 are preferably matched so that the induced by a temperature change narrowing of the gap 22' that caused by this change of temperature expansion of the Lei ters 1 and thus the lattice 11 essentially just lifts up and the expansion of the intermediate space 22 'caused by a temperature change essentially abolishes the contraction of the conductor 1 and thus the lattice 11 caused by this temperature change.

This is the case, for example, if the material of the sub carrier body 2 ", 2 " and the material of the conductor 1 have essentially the same coefficient of thermal expansion α <0 and if the coefficient of thermal expansion of the material of the substrate body 2 'is relative to this coefficient α is negligible.

Claims (4)

1. A method for producing at least one optical lattice ( 11 ), in particular a Bragg grating, on an optical conductor ( 1 ), the conductor ( 1 ) at least at two spaced apart (d) fastening points th ( 21st , 21 ) and then the grid ( 11 ) on the fixed conductor ( 1 ) be made between these fastening points ( 21 , 21 ), characterized in that the conductor ( 1 ) before the production of the grid ( 11 ) at the fastening points ( 21 , 21 ) is permanently attached. 2. The method according to claim 1, characterized in that the optical conductor ( 1 ) during the manufacture of the grating ( 11 ) between the fastening points ( 21 , 21 ) is voltage-free. 3. The method according to claim 1, characterized in that the optical conductor ( 1 ) is stretched between the fastening points ( 21 , 21 ) during the manufacture of the grating ( 11 ). 4. Arrangement with
no support body ( 2 ),
an elongated optical conductor ( 1 ) and
an optical grating ( 11 ), in particular a Bragg grating, wherein
the conductor ( 1 ) is fastened to the support body ( 2 ) at least in the case of two fastening points ( 21 , 21 ) arranged at a distance (d) from one another and
the grid ( 11 ) is formed on the fixed conductor ( 1 ) between these fastening points ( 21 , 21 ), characterized in that
the conductor ( 1 ) at the attachment points ( 21 , 21 ) is permanently attached to the support body ( 2 ) and
the grid ( 11 ) is a grid produced after the conductor ( 1 ) has been permanently fastened to the carrier body ( 2 ).