EP2475965A1

EP2475965A1 - Optical fiber, method of preparation thereof and device

Info

Publication number: EP2475965A1
Application number: EP10757854A
Authority: EP
Inventors: Davide Iannuzzi; Grzegorz Gruca; Sven De Man
Original assignee: Vereniging voor Christelijik Hoger Onderwijs Wetenschappelijk Onderzoek en Patientenzorg
Current assignee: Vereniging voor Christelijik Hoger Onderwijs Wetenschappelijk Onderzoek en Patientenzorg
Priority date: 2009-09-08
Filing date: 2010-09-08
Publication date: 2012-07-18
Also published as: WO2011031142A1

Abstract

The invention provides an optical device, a method for the preparation thereof, and a device. The optical device, based on a ferrule top, is adapted for use on a distal end of an optical fiber, comprising a body provided with at least one receptacle for receiving an optical fiber, and at least one optical or mechanical element arranged in optical contact with an optical fiber received in the receptacle, and has the advantage of providing a faster and more flexible way of functional modification of optical fibers, for instance in sensor technology.

Description

Optical fiber, method of preparation thereof and device

FIELD OF THE INVENTION

The invention provides an optical device, a method for the preparation thereof, and a device.

BACKGROUND OF THE INVENTION

The shaping of the cleaved end of an optical fiber has been previously described, e.g., in the form of micromachined focusing elements (M. Sasaki et al., Direct photolithography on optical fiber endpjpn. J. Appl. Phys. 41 , 4350 -4355 (2002); P. N. Minh et al., Batch fabrication of microlens at the end of optical fiber using self- photolithography end etching techniquepOpt. Rev. 10, 150 -154 (2003); F. Schiappelli et al., Efficient fiber -to-waveguide coupling by a lens on the end of the optical fiber fabricated by focused ion beam millingpMicroelectroni c Eng. 73-74, 397-404 (2004); R. S. Taylor and C. Hnatovsky, Particle trapping in 3 -D using a single fiber probe with an annular light distributionp Optics Express 1 1 , 2775 -2782 (2003); C. Liberale et al., Hiniaturized all -fiber probe for three-dimensional optical trapping and manipulationp Nature Photonics 1 , 723-727 (2007).), optical antennas (E. J. Smithe, E. Cubucku, and F. Capasso, Optical properties of surface Plasmon resonances of coupled metallic nanorodspOptics Express 15, 7439 -7447 (2007).) or movable mechanical structures (fiber-top technology, D. lannuzzi et al., Monolithic fiber -top sensor for critical environment and standard applicationspAppl. Phys. Lett. 88, 053501 (2006).) . The possibility to shape the cleaved end of an optical fiber represents a fascinating opportunity for the development of new devices for a wide variety of applications, including photonics, optical trapping, biochemical sensing (D. lannuzzi et al., A fiber -top hydrogen sensorpSensors & Act. B121 , 706 -709 (2007).), and atomic force microscopy (D. lannuzzi et al., Fiber -top atomic force microscopep Rev. Sci. Instr. 77, 106105 (2006).). Unfortunately, the advantages offered by those instruments may be hampered by the large costs of production, which can be due to the fact that, at present, there are no known versatile fabrication procedures for batch manufacturing of arbitrary micromachined parts on the facet of optical fibers.

Fabrication of fiber-top devices usually requires high precision and resolution (often smaller than 1 pm) machining tools, which results in relatively high production costs. Optical fibers typically have a radius smaller than 100 pm, the area or section to be machined is therefore often in the range around 10000 pm², requiring very precise and accurate machining tools. Also, the need for precise machining may result in a relatively low machining speed.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to enable an easier and more flexible way to provide optical fibers with a functional device. It is another object of the invention to enable the easier and faster installation and/or replacement of optical and/or opto-mechanical devices dependent on optical fibers. It is yet another object of the invention to enable the production of optical and/or opto-mechanical device on optical fiber tops using less expensive tools and/or in a more reliable and faster way.

The invention provides an optical device, adapted for use on a distal end of an optical fiber, comprising a body provided with at least one receptacle for receiving an optical fiber, and at least one optical and/or mechanical element arranged in optical contact with an optical fiber received in the receptacle. Such optical devices have the advantage of providing a faster and more flexible way of functional modification of optical fibers, for instance in sensor technology. The optical device may be designed to host one or more optical fibers. This has the advantage that the optical device may be prepared separately from the optical fibers, allowing for a greater flexibility. Another advantage is that the optical device can be prepared after the optical fibers are put on the device, facilitating the alignment of the optical fibers with the optical and/or mechanical elements of the device. Yet another advantage is that the optical device may be prepared at a larger scale than devices made out of the distal end of an optical fiber. The optical device may be any type of optomechanical transducer, sensor or actuator.

Therefore, an optical device according to the invention may be produced faster and using less expensive tools. The optical device also allows more flexibility, as it allows easier installation and replacement of the optical device. The receptacle may for instance be a hole, channel, or a number of cooperating clamp elements forming a receptacle, designed to hold an optical fibre in a predetermined position. Optionally, the optical fiber may be fixed in the receptacle, for instance by fixing means such as an adhesive, mechanical fixing means such as clamps or a narrow portion of the receptacle, or a combination thereof. The optical device according to the invention may be based on a cylindrical or rectangular body (other shapes are possible) having one or more channels, preferably along the longitudinal axis, which may act as a receptacle to fit one or more optical fibers. Such a body may be called a UerruleD

Preferably the receptacle is an elongate cavity or channel, having a diameter suitable to fit an optical fiber, optical fibers typically having a diameter in the range of 50 pm□ 500 pm, but other fibers with other diameters may be used. The hole/channel forming the receptacle in the ferrule may be not completely open on the facet.

The optical or mechanical element may be essentially two-dimensional, such as a grating, but preferably comprises a three-dimensional structure. It may be assembled from multiple parts, and different materials, and may comprise various mechanical parts, depending on the type of optical device. The optical or mechanical element may comprise for instance springs, membranes, hinges, rods, and combination of those parts. One optical device may have more than one optical and/or mechanical elements.

The ferrule may be of different materials, including, but not limited to, all kinds of glass, ceramics, metal and synthetic resins and plastics. The shape and dimensions of the ferrule and of the hole hosting the fiber may vary. In a preferred embodiment, the optical device has an essentially cylindrical shape, and the elongate cavity or channel is directed essentially parallel to the longitudinal axis of the cylindrical shape, but not necessarily coinciding with axis of the cylinder. The ferrule is preferably one monolithic block, but it can also be made out of parts that may be assembled at different stages of the fabrication procedure. The optical device may comprise multiple receptacles for receiving optical fibers, and/or receptacles suitable for holding multiple fibers. For instance one or more optical fibers may be used to shine light on a specific part of one or more optical or mechanical elements with the purpose, for example, of detecting the position of those elements or with the purpose of making spectroscopic or optical measurements in a specific point or region of space. One or more optical fibers may also be used, for example, to collect light from a specific point or region of space close or far away from the optical device.

It is preferred if the optical device is essentially monolithic. This makes for a very robust device. The surface of the monolithic device may be treated with for instance coating layers.

Preferably, the optical device is an optical sensor device. Examples of optical sensor devices include sensors for temperature, pressure, flow, vibrations, accelerations, material strain, magnetic field, electric field, atomic force microscope tip or selective chemical sensors, based on optical fiber and/or mechanical measuring principles known in the art. In a preferred embodiment, the optical element comprises an opto-mechanical element. Opto-mechanical elements are reliable and robust, and may be used under many different circumstances.

It is advantageous if the optical element is a cantilever element. Cantilever elements are elements that may vibrate or be bent under the influence of internal or external forces. The cantilever may have various shapes, depending on its intended purpose. The cantilever structure is preferably arranged at a distal end of the optical device, more preferably at a distal end of the optical device opposite to an entrance of the receptacle for receiving the optical fiber.

In a preferred embodiment, the cantilever element is provided with a tip. A tip is a protruding element, typically having a pointed shape. The tip may act as a sensor tip, for instance by mechanical interaction, of as an optical element for shining or collecting light at a predetermined position. The tip is preferably positioned near or at a distal end of the cantilever. Preferably, the sensor tip is designed for performing scanning probe microscopy, including, but not limited to, atomic force microscopy and scanning near field microscopy.

Light from the optical fiber may be reflected by a surface of the cantilever element in order to register its physical parameters, for instance its position or its vibration frequency. The cantilever may act for instance as a chemical sensor by coating the surface with a selectively binding material, for instance antibodies. By binding a selected analyte, the mass and therefore the vibration frequency of the cantilever will, which is detectable by a change in signal through the optical fiber. In another type, the cantilever may be made of or coated with a material sensitive to electrical and/or mechanical forces, offering another way for environmental influences to be detected through a change in the vibration frequency of the cantilever.

In a preferred embodiment, the receptacle for receiving an optical fiber is aligned to direct the optical fiber towards a reflecting surface of the cantilever structure. Thus, the optical fiber is aligned to irradiate a signal towards the reflecting surface and/or capture reflected signals from the cantilever. The reflecting surface could be the material of the cantilever itself, optionally suitable coatings could be applied to diminish intensity loss and filter the reflected light.

It is advantageous if the reflecting surface is provided by a reflecting filler material deposited in a recess of the cantilever structure. Thus a suitable reflecting material is applied which is more resistant to wear than a reflecting material applied in a thin layer to the top of the cantilever. The reflecting could for instance by applied by filling up a hole in the cantilever, optionally followed by polishing and/or coating in order to improve the reflecting surface.

Preferably, the reflecting surface is essentially perpendicular with respect to the direction of the optical fiber as induced by the receptacle. Thus, an optimal signal received by the optical fiber may be achieved. It is preferred if the receptacle has a tapered entrance. The tapered entrance is self- seeking and self-aligning, it is therefore easier to insert an optical fiber into the receptacle without need for special tools. Optionally, the tapered entrance is provided with anchoring means for fixing the position of the optical fiber in the receptacle. The invention further provides an optical device according to the invention wherein at least one optical fiber is arranged in a receptacle of the optical device in optical contact with the optical element. Now the optical fiber may be used to send an optical signal towards the optical element or receive optical signals generated by or reflected from the optical element. The fiber is preferably fixed in the receptacle, for instance by mechanical or chemical anchoring, such as clamps, and/or by a suitable adhesive

In a preferred embodiment, the optical fiber is fixed in the receptacle by an adhesive. Using an adhesive is an easy and reliable way to fix the optical fiber in the receptacle. Suitable adhesives include UV-curable glues. The adhesive may be combined with other fixing means, for instance mechanical fixing by the friction of a tight fit.

The invention also provides a method for preparing an optical device according to the invention, comprising the steps of providing a body, machining of the body to provide at least one receptacle for receiving at least one optical fiber, machining of the body to provide at least one optical and/or mechanical element, positioned to be in optical contact with an optical fiber received in the receptacle, and optionally arranging an optical fiber in the receptacle in optical contact with the optical element. The applying of the optical fiber may be done before or after the machining of the body to produce an optical element. Part of one or more fibers may be also used as optical and/or mechanical elements or as parts of optical and/or mechanical elements. The carving procedure of the optical element can be partially or entirely achieved with different tools, including, but not limited to, mechanical milling, lapping, polishing, laser ablation, focused ion beam milling, ion etching, chemical etching, embossing, molding, and imprinting. For some applications, the devices may be cleaned or polished at different stages of the fabrication process. For some applications, the devices or some of their parts may be coated with proper materials. If more than one fiber is used, the mechanical machining procedure may be partially or entirely performed before or after only part of or all of the fibers have been inserted or glued into the receptacle. Instead of carving the facet of the ferruled fiber, one may deposit and pattern alternate layers of sacrificial and structural materials, following, for example, the same principles and methods used in the fabrication of conventional silicon-based MicroElectroMechanical Systems. The sacrificial layers may then be removed via, for example, etching procedures.

Preferably, the receptacle is a channel through the body, wherein at least part of the channel is filled with a filler material. This technique makes it easier to produce the optical device, as at the pm scale it is easier to make a channel through a ferrule or other body, and later on selectively patch the channel. It is more difficult, although still possible to those skilled in the art, to directly make a hole of predetermined depth with a closed end, as it is more difficult to reliably remove waste material from a one-exit hole. In a preferred embodiment, the optical element comprises a cantilever structure, wherein part of the channel is arranged through the cantilever structure in a direction essentially perpendicular to a cantilever element of the cantilever structure, and wherein the part of the channel extending through the cantilever structure is filled with a reflecting filler material to provide a reflecting surface optically in line with the channel.

The invention will now be further elucidated by the following non-limiting examples. BACK GROUND INFORMATION

In 2005, one of the inventors (Davide lannuzzi) and his collaborators have introduced a new approach for the development of miniaturized all-optical sensors and actuators. Those devices, called fiber-top micromachined devices, are obtained, for instance, by carving the cleaved end of an optical fiber in the form of mechanical parts that, upon external stimuli, bend or move. Using the light coupled into the fiber from the opposite side, one can then detect, for example with interferometric techniques, tiny displacements of the mechanical parts, giving one the opportunity to implement, among others, temperature sensors, mechanical transducers , biochemical sensors and probes for atomic force microscopy.

Sometimes, fabrication of fiber-top devices requires high resolution (for example, smaller than 1 pm) machining tools, which, for some applications, result in high costs of production. The reason for which high resolution is needed is often related to the fact that the optical fibers used for fiber-top technology have typically a radius smaller than 100 pm. The area that can be machined is thus typically limited to ~ 10.000 pm2. Since the space is limited, it is then necessary to have a very precise and accurate machining tool. In many applications, however, larger devices would accomplish similar functions of the smaller ones. Therefore, if one had a larger area to fabricate fiber-top devices, one could think to scale up the design and fabricate larger devices with similar functions as the smaller ones. In this case, the requirements on the precision and the accuracy of the machining tool could be less severe, and one could thus use less expensive tools that might adapt better to low cost series production. The presence of surface roughness may reduce the optical signal that is used to detect, for example, the movement of the mechanical parts. It is thus desirable to find a way to fabricate ferrule- top devices using an approach that relies on cost-effective cutting tools but still guarantees very low surface roughness (e.g., optically flat surfaces) of the machined parts. SUMMARY OF EXEMPLARY EMBODIMENTS

It is possible to provide an exemplary embodiment of a process and system which can allow one to fabricate ferrule-top devices according to the invention where at least part of the areas of the machined surfaces may be, for example, optically smooth or anyway smoother than what can be obtained with some of the other fabrication methods reported so far or that might be disclosed in the future.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figs. IA-IE show exemplary steps of an exemplary embodiment of a fabrication procedure for an exemplary ferrule-top micromachined device according to the invention.

Fig. 2 is an exemplary optical microscope image of one of the exemplary ferrule top micromachined devices which has been fabricated in accordance with the exemplary

procedures shown in Figs. 1A-IE;

Fig. 3 is a schematic drawing of an experiment performed to demonstrate a principle of producing the exemplary ferrule-top micromachined device illustrated shown in Fig. 2 in accordance with the exemplary embodiments of the invention;

Fig. 4 is a diagram of an exemplary embodiment of a system according to the present disclosure in which an opposite end of the fiber (e.g., an end opposite to the ferrule) is coupled to an exemplary optical fiber interferometer readout system; and

Fig. 5 is a graph shows an output signal of the exemplary readout system as illustrated in Fig. 4, which was observed during linear forward and backward movements of a needle.

Figure 6A-F shows a method of preparing a device according to the invention.

Figure 7A-F show an alternative method of preparation.

Figures 8A-3F show yet another alternative method of preparing a device according to the invention.

Figures 9A-4F show yet another method of preparing a device according to the invention.

Figures 10A-5F show yet another method of preparing a device according to the invention.

Figures 1 1A-6F show yet another method of preparing a device according to the invention.

Figure 12 shows an alternative design of a ferrule top according to the invention. An optical device such as a cantilever device may be simply prepared by machining a ferrule top (with or without an inserted optical fibre). However, also more advanced methods are possible, as will be discussed in the following non-limiting examples.

Figs. 1.4-1 E show an exemplary flow of an exemplary embodiment of a fabrication of a ferrule-top micromachined device according to the present disclosure. For example, as shown on Figs. 1A and IB, a single mode optical fiber 102 (with, e.g., a diameter of 125 m), can be inserted into a glass ferrule 101 (with, e.g., a diameter of 1 .8 mm) that can have a central hole 103 to host the fiber (with, e.g., a diameter of 127 pm). The fiber can then be glued to the ferrule (see Fig. 1 C) to obtain a ferruled fiber 104. If needed; the facet of the ferruled fiber can be polished after gluing (not illustrated in Figs. 1 .4-IE). The top of the ferruled fiber can then be machined, for example, as shown in Figs. ID and 1 F in the form of a suspended rectangular mechanical beam 105. In this example, the mechanical beam can be fabricated along one of the diameters of the ferrule and its width may be larger than the diameter of the fiber. In this way, the light coupled into the fiber from the opposite end impinges on the mechanical beam. Using well known interferometric techniques, one can then detect deflections of the mechanical beam in response to external forces.

In Fig. 2, exemplary optical microscope images of one of the exemplary ferrule top micromachined devices which have been fabricated are shown. For example, the ferruled fiber (made out of glass and, e.g., with the same or similar dimensions as the fiber shown in Figs. 1A-IE) can be used. The mechanical carving can be performed thereon using a ps-laser ablation. The exemplary dimensions of the mechanical beam in such example can be, but certainly not limited to: length - 1 .6 mm, width = 200 pm, thickness = 50 pm. In Fig. 3, a schematic diagram and illustration is shown of an experiment performed to demonstrate an exemplary principle of the exemplary ferrule-top micromachined device 131 as illustrated in Fig. 2.

Fig. 4 shows an exemplary embodiment of an optical fiber interferometer readout system in which the opposite end of the fiber (i.e., the end opposite to the ferrule) is coupled thereto. A sharp needle can then be inserted repetitively in and out of contact with the hanging end of the mechanical beam to distort the optical signal reflected by t he beam, which is detectable as an altered output signal. Fig. 5 shows a graph of an exemplary output signal of the optical fiber interferometer readout system of Fig. 4 observed during linear forward and backward movements of the needle. For example, the sinusoidal signal that can be observed when the needle is in contact with the device demonstrates that the device operates appropriately. In the example described herein above, the exemplary fabrication of an exemplary ferrule-top straight mechanical beam or cantilever has been discussed. It should be understood that this design is only an example. For example, similar exemplary processes can be used to fabricate other kinds of mechanical parts, such as, but not limited to, springs, membranes, hinges, rods, etc. In addition, the exemplary ferrule can be composed of different materials with respect to that used in the exemplary sample, including, but not limited to, various types of glass, metal, plastic, etc. The ferrule does not have to be necessarily a monolithic piece, and can be fabricated by assembling more then one part. The shape and dimensions of the ferrule and of the hole hosting the fiber may vary. The position of the hole in the ferrule may also vary. The ferrule can have more than one hole to host more than one fiber on the same device. Some of the holes of the ferrule may not be completely open on the facet. For some applications, ferrule-top devices can be cleaned at different stages of the fabrication process, and/or the ferrule- top devices or some of their parts can be coated with proper materials. Further, the mechanical machining procedure can be partially or entirely performed before inserting or gluing the fiber into the hole. If more than one fiber is used, the mechanical machining procedure can be partially or entirely performed before or after only part of or all of the fibers have been inserted or glued into the hole. The optical fiber(s) may vary in dimensions, materials, and optical properties. The exemplary carving procedure can be partially or entirely achieved with different tools, including, but not limited to, mechanical milling, lapping, polishing, laser ablation, focused ion beam milling, ion etching, chemical etching, embossing, molding, imprinting. Fibers inserted in a ferrule device do not necessarily have to be glued to the ferrule. For example, the fibers may be mechanically anchored via different methods, which can even allow for certain movement of the fibers with respect to the exemplary ferrule. Instead of carving the facet of the ferruled fiber: it is possible to deposit and pattern alternate layers of sacrificial and structural materials, following, for example, the same principles and methods used in the fabrication of conventional silicon-based MicroElectroMechanical Systems, as described in G. T. A. Kovacs, "Micromachined transducers sourcebook" (McGraw-Hill, New York, 1998). The sacrificial layers can then be removed via etching procedures.

Fig. 6 shows a flow diagram of an exemplary embodiment of the fabrication of a ferrule- top micromachined device according to the present invention. The figure shows a ferrule 1 (for instance, a pierced cylinder made out of glass with an outer diameter of 1 .8 mm and an inner diameter of 127 pm) that can be carved, using any cutting tool (such as, but not limited to, laser ablation, chemical or physical etching, molding, embossing, grinding, polishing, sawing, milling, focused ion beam, et cetera) in the form of a mechanical device. The ferrule in figure 1 is shown in a top view and as a cross section.

Further figures only show the cross section.

Figure 6A shows a basic ferrule top 1 provided with a fiber-guiding, tapered entrance 2 leading to a channel 3, suitable to take up an optical fibre.

In figure 6B, the top part of the ferrule has been shaped into an essentially rectangular beam 4. In figure 6C, selective removal of the ferrule material yields the cantilever 5, spanning the diameter of the ferrule. The cantilever 5 still has an aperture marked an After that, an optical fiber 6 (for example, a single mode optical fiber with a diameter of 125 pm) may be inserted into the ferrule (Fig. 6D) and may be fixed (Fig. 6E) by an adhesive 7 or expanding cement. Optionally, the hole acin the cantilever 5 may be at least partially filled up in order to provide a reflecting surface opposite to the optical fibre (fig 6F). The hole may for instance be fit with a premade cover or filled with a curable material, Fig. 6E, detail a). For instance, one may put a droplet of UV curable glue or of another suitable material in the hole and cure it. In this way, a smoother reflecting surface may be produced than by direct cutting, allowing for a more sensitive and precise sensor. Using, among others, standard interferometric techniques, one can then detect deflections of the mechanical beam/cantilever in response to external forces.

Fig. 7 shows one possible exemplary alternative fabrication method, where the fiber is put in the ferrule before the ferrule is carved. Figure 7A shows a ferrule top 1 1 comparable to the ferrule 1 shown in figure 1A. The ferrule 1 1 is provided with a fiber- guiding entrance 12 and a channel 13 passing through the ferrule. In figure 7B, an optical fiber 14 is inserted into the channel 13. The fiber is fixed in the ferrule by adding an adhesive or cement 15 into the entrance 12 of the channel 13, as shown in figure 7C. In figure 7D, an essentially rectangular bar 16 is shaped out of the top part of the ferrule, comparable to the bar in figure 7B. The rectangular bar 16 is subsequently machined into a cantilever element 17 as shown in figure 7E. The remaining hole or aperture in the cantilever element is filled up with a suitable material 18, for instance a premade element or a curable material, as described for the method according to figure 6A-6F. Fig. 8 shows yet another possible exemplary alternative fabrication method, wherein glue or another curable material to cover the hole in the ferrule is put before the ferrule is carved. Thus, the steps are comparable to the methods of figure 1 and 2, but in a different order. Figure 8A shows a ferrule top 21 comparable to the ferrule 1 shown in figure 6A and ferrule 1 1 in figure 7A. The ferrule 21 is provided with a fiber-guiding entrance 22 and a channel 23 passing through the ferrule. In figure 8B, exit of the channel 23 is filled up with a suitable material 24, for instance a premade element or a curable material, as described for the method according to figure 1 A-1 F. In figure 8C, an essentially rectangular bar 25 is shaped out of the top part of the ferrule. The rectangular bar 25 is subsequently machined into a cantilever element 26 as shown in figure 8D. An optical fiber 27 is inserted into the channel 23 (fig. 8E), and fixed in the ferrule by adding an adhesive or cement 28 into the entrance 22 of the channel 23, as shown in figure 8F. Fig. 9 shows another possible exemplary alternative fabrication method, where both the fiber and the glue to cover the hole in the ferrule are applied before the ferrule is carved or otherwise machined. Figure 9A shows a ferrule top 31 comparable to the ferrules shown in figures 1 -3. The ferrule 31 is provided with a fiber-guiding entrance 32 and a channel 33 passing through the ferrule. In figure 9B, exit of the channel 33 is filled up with a suitable material 34, for instance a premade element or a curable material. In figure 9C, an optical fiber 35 is inserted into the channel 33. An essentially rectangular bar 36 is shaped out of the top part of the ferrule (fig. 9D), and the optical fiber 35 is fixed in the ferrule by adding an adhesive or cement 37 into the entrance 32 of the channel 33, as shown in figure 9D. The rectangular bar 35 is subsequently machined into a cantilever element 36 as shown in figure 9F.

Fig. 10 shows another possible exemplary alternative fabrication method, where another piece of fiber is used to cover the hole in the ferrule. Figure 10A shows a symmetrical ferrule 41 having tapered entrances 42 at opposite sides, connected by a channel 43. A first optical fiber 44 and a second optical fiber 45 are inserted into the channel 43, wherein a separation between the fibers is kept at a predetermined position (fig. 10B). The fibers are then fixed in their positions by a fixing material 46 (fig. 10C). Subsequently, the top part and lower part of the ferrule are separated by regular cutting techniques, also cutting part of the first fiber 44, covering the top exit of the channel 43 (fig. 10D). The separated first fiber part 44 remains in place through tight fitting friction, optionally reinforced by glue. Subsequently, the top part of the ferrule is machined into a bas shape 47 and eventually a cantilever structure 48 as shown in figures 10E and 10F).

Fig. 1 1 shows another possible exemplary alternative fabrication method, where the ferrule is machined and then an optical fiber is introduced in the ferrule. In this exemplary method, the fiber may be previously modified in such a way that one part of it (part a of the figure) can be dissolved in a suitable solvent. Figure 1 1A shows a ferrule top 31 comparable to the ferrules shown in figures 1 -4. The ferrule 51 is provided with a fiber-guiding entrance 52 and a channel 53 passing through the ferrule. The top of the ferrule is machined into a cantilever element 54, leaving a hole 55 in the cantilever surface opposite the exit of the channel 53. Subsequently, an optical fiber 56 is inserted into the ferrule, passing both through the channel 53 and the hole 55 in the cantilever 54 (figure 1 1 C). The fiber 56 is separated while fixed in the ferrule, cutting at the position §n in figure 1 1 C just under the surface of the cantilever directed towards the exit of the channel 53. As shown in figure 1 1 D, this leaves a fiber part 57 as a plug element for the hole 55 in the cantilever structure.

Figure 12 shows a device according to the invention, which can be produced by modification of any of the methods shown above. A ferrule 61 is provided with a first channel and a second channel, wherein a first optical fiber 62 and a second optical fiber 63 are inserted. The top of the ferrule 61 is provided with a cantilever element 64, which has a sensor tip 65. Holes 66, 67 in the cantilever element 64 are filled up with suitable reflecting materials, for instance UV curable filler material or optical fibre parts. The two optical fibres serve a dual monitoring purpose. The first optical fiber 62, aligned with a distal end of the cantilever, is designed to illuminate or collect light on a sample for, for example, Raman spectroscopy, Scanning Near Field Optical Microscopy, or Forster resonance energy transfer. The second optical fiber 63 is designed to detect the displacement of the optical fiber due to external forces exerted on the sensor tip 65.

In the examples reported above, we have described the fabrication of an exemplary ferrule-top straight mechanical beam. This design represents only an example.

Similarly, the methods of fabrications described above represent only a limited list of exemplary methods.

The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention. In addition, to the extent that the prior art knowledge has not been explicitly incorporated by reference herein above, it is explicitly being incorporated herein in its entirety. All publications referenced herein above are incorporated herein by reference in their entireties.

Claims

1. Optical device, adapted for use on a distal end of an optical fiber, comprising a body provided with at least one receptacle for receiving an optical fiber, and at least one optical or mechanical element arranged in optical contact with an optical fiber received in the receptacle.

2. Optical device according to claim 1 , wherein the optical device is essentially monolithic.

3. Optical device according to claim 1 or 2, wherein the optical or mechanical device is an optical-mechanical, optical or mechanical sensor device.

4. Optical device according to any of the preceding claims, wherein the optical or mechanical element comprises a three-dimensional structure.

5. Optical device according to claim 3, wherein the optical element comprises an optomechanical element.

6. Optical device according to any of the preceding claims, wherein the optical element comprises a cantilever element.

7. Optical device according to claim 6, wherein the cantilever element is provided with a tip.

8. Optical device according to claim 6 or 7, wherein the receptacle for receiving an optical fiber is arranged to direct the optical fiber towards a reflecting surface of the cantilever element.

9. Optical device according to claim 8, wherein the reflecting surface is essentially perpendicular with respect to the direction of the optical fiber as induced by the receptacle.

10. Optical device according to any of the preceding claims, wherein the receptacle has a tapered entrance.

1 1 . Optical device according to any of the preceding claims, wherein at least one optical fiber is arranged in a receptacle of the optical or mechanical device in optical contact with the optical element.

12. Optical device according to claim 1 1 , wherein the optical fiber is fixed in the receptacle by an adhesive.

13. Method for preparing an optical device according to any of the preceding claims, comprising the steps of

- Providing a body,

- machining of the body to provide at least one receptacle for receiving an optical fiber,

- machining of the body to provide at least one optical element, positioned to be in optical contact with an optical fiber received in the receptacle, and - optionally arranging an optical fiber in the receptacle in optical contact with the optical element.

14. Method according to claim 13, wherein

the receptacle comprises a channel through the body, wherein at least part of the channel is filled with a filler material.

15. Method according to claim 14, wherein the optical element comprises a cantilever structure, wherein part of the channel is arranged through the cantilever structure in a direction essentially perpendicular to a cantilever element of the cantilever structure, and

wherein the part of the channel extending through the cantilever structure is filled with a reflecting filler material to provide a reflecting surface optically in line with the channel.