Optical rotating transmitter having a free inside diameter

Translation of description of equivalent WO 03069392 A2

OPTICAL ROTATION ABOUT CARRIER WITH CLEAR DIAMETER

DESCRIPTION

p0003Technical field

p0004The invention relates to a device for transmitting optical signals between mutually rotatable units. Such devices are preferably used in CT scanners.

p0005State of the art

p0006For transmitting optical signals between against each of the rotatable units, in particular with a free internal diameter different devices are known. Basically herein to make the problem, a means for the transportation of light along the circumference of the device as well as suitable means for input and output coupling of light. For use in computer tomographs, such devices must have large free inner diameter of the order of 1 meter. The peripheral speed of rotation can be in the order of 20 m / s. Simultaneously with data rates above 1 gigabit per second (GBaud) should be possible.

p0007So is disclosed in US 4,109,997 an optical rotary joint, in which the transport of light along the perimeter by reflection on two opposite

p0008Surfaces (101, 1). For coupling or decoupling of light are optical fibers or glass fibers provided the bundling or focusing of the light beam by means of lenses. However, this device has a number of disadvantages. Thus, the optical transmission loss is relatively high early reflections at relatively steep angles due to multiple reflection. Thus, high transmission power in the optical transmitter are required. Furthermore, the manufacturing costs are relatively high due to the opposite mirrored surfaces. A broadband data transmission with period durations of the modulation signal, which are substantially less than the duration of the signal around the periphery of the device is not possible, since positions of the receiver close to the transmitter is a multi-path reception of signals occurs. So at the same time, signals are received over a short distance from the transmitter and simultaneously receive signals which have been reflected at least once around the perimeter of the device. The transit time difference uss be small compared with the period of the modulation signal. Therefore results in an inner diameter of about one meter and a term to the extent of about 10 nanoseconds. This can be realized for example in the transmission of digital signals bit periods of up to 50 nanoseconds, corresponding to a maximum transfer rate of 20 Mbaud.

p0009An improvement of the optical system is disclosed in US 4,525,025. Thus, a particularly suitable trench is shown therein for transmitting optical signals, in particular in Fig. 10. This consists only of a part and is therefore cost-effectively. However, in this patent no effective common solution to the problem of bandwidth limitation specified. In addition, the proposed coupling or decoupling of light by blunt fiber ends can only be realized with an extremely poor efficiency. Thus, this device is only suitable for small diameter.

p0010An improvement in the optical coupling or decoupling is disclosed in US 4,555,631. It takes place the coupling of optical signals in a mirrored cylinder by means of two mirrors. For coupling out an additional decoupling element, which is arranged at a fixed position in the trench, is provided. However, there is also a high attenuation of the optical transmission path, since the coupling mirror at high speeds of movement can not be brought as close to the mirrored cylinder in particular. Furthermore, because of the unavoidable fanning of the light beam on the planar mirror surface an additional deterioration of the efficiency. Furthermore, the mechanical design of the extraction element is particularly complex, thus prone to failure and expensive. Finally, the problem of bandwidth limitation is not solved. Thus, the light is guided in two ways in opposite directions from the coupling point for the output coupling, and finally evaluated jointly in a receiver. Here also the limitation that the period of the modulation signal substantially low ger than the duration of light around the perimeter of

p0011must be device. A device with a particularly high optical efficiency is described in US 4,934,783. Therein is a focus of the beam by a lens system. However, this system is very for expenditures dig, expensive suitable in manufacturing and only for small diameters. Furthermore, the bandwidth issue is not resolved here.

p0012In order to reduce the attenuation of the transmission path and to increase the transmittable bandwidth is proposed in US 6,104,849 a transmission in a plurality of truncated segments. By truncated segments results in a reduced attenuation. The maximum bandwidth is here inversely proportional to the length of the segments. Thus can be shorter

p0013Segments achieve a higher bandwidth. However, this requires a correspondingly higher number of optical transmitters or receivers to cover the full circumference is necessary. Thus, the system costs rise proportional to the bandwidth.

p0014In DE 195 43 386 Cl a device for wideband signal transmission is described which indeed allows a high bandwidth, but no Hinwei- se a transmission with high transmission quality are. It is the content of DE 195 43 386 Cl incorporated by reference in this document.

p0015In US Patent 4,962,986, an alternative device is described for the coupling of light. For light entry and coupling in light-conducting fibers is a coupling medium with a higher refractive index than the surroundings tion brought in direct contact with the fiber core. This deflection of the conveyed in the fiber light takes place in the coupling medium. This arrangement has the decisive disadvantage that the coupling medium must be directly related to the fiber core. Thus, this system can be used almost exclusively for the coupling to predetermined fixed positions. Such a system is hardly for arrangements in which the sender and receiver applicable move against each other, since the coupling medium must slide at high speed along the usually very thin and delicate fiber core.

p0016In Tamir, "Integrated Optics", Springer Verlag, Berlin, 1979, page 87, such a device is described. It is positioned therein serving for the coupling-out prism in the least possible distance through the fiber core. In order to achieve a reasonable coupling efficiency here has the distance between the prism and the fiber core in the order of the

p0017Light wavelength are. However, can only be achieved with small dimensions of the entire assembly with conventional high-precision bearings, these accuracies. So this system is currently, for example in computer tomography with a diameter of 1.5 meters and circumferential speeds up to 20 m / s can not be used.

p0018Summary of the Invention

p0019The invention is based on the object of a relatively inexpensive device for transmitting optical Signals between two units against each other to make rotatable such that a reliable transmission with low optical attenuation at large diameter, high mechanical movement speeds and high data rates is facilitated. Furthermore, the object of a particular embodiment of the invention to design the device so that signals are transmitted, the periods to the propagation time of light are small around the perimeter of the device.

p0020One inventive solution to this problem is defined in the independent claims. Further developments of the invention are the subject of the dependent claims.

p0021The inventive device comprises a light guide disposed along a circular path to a first unit. For simplicity, only one light guide will be described. Of course, multiple inventive arrangements, each having a light guide can be connected in parallel. connected to the light guide is at least one first light coupler for coupling in and coupling out of light into the light guide. connected to at least one of these first light coupler is at least one optical transmitter or receiver. Whether a transmitter or receiver to be connected to the optical fiber is determined by the desired transfer direction is right. Target light from the light guide to be transferred away, so is a transmitter to provide a receiver in the other case. For information transmission are the optical transmitter naturally modulated with a modulation signal.

p0022Furthermore, a second unit is provided which is mounted rotatable relative to the first unit. It is here assumed that a relative movement of the two units against each other and not to be taken rotating or stationary units with respect, as this is only a question of the reference to location. This second unit is at least one second

p0023associated light coupler which is opposite to the first moving with the rotation of the second unit in a predetermined path with respect to the light guide. At least one of these second light is equipped complementary to the first light with an optional optical transmitter or receiver.

p0024The invention provides that at least one second light coupler having an active position control unit. This position control unit comprises an actuator for precise positioning of the light coupler and a sensor for determining the position of the light coupler with respect to the light guide and a control unit for evaluating the sensor signals and the corresponding activation of the actuator. The position control of the optical coupler is in at least one axis, but preferably in two axes perpendicular to the tangent of the rotational movement. This is either the height of the light coupler through the optical fiber or the lateral distance between see light coupler and light guide at a constant

p0025Value held. This position control, it is now possible light at extremely shallow angles, ie einzukop- almost parallel to the tangent of the light guide PelN allow a quasi-parallel propagation of light to the mirror trench in the so-called "whispering gallery mode". Optionally, include the position control, a rotation or a tilt axis. Thus, in particular, a to the tangent the light guide parallel alignment of the coupled light beam an extremely large influence on the coupling loss. Even for the smallest deviation from the parallelism did the axes from the light guide and light coupler can cause an interruption of the signal when the light coupler having no means for the lateral reflection. In such a case is a scheme of parallelism particularly advantageous. such a position control is gelung especially for large diameters of the two mutually rotatable units, as they are implemented, for example in computer tomography equipment, necessary to compensate for mechanical tolerances and tolerances due to the mechanical movement. This position control can be a largely constant

p0026Path loss can be achieved. Alternatively, or in addition to this, even a regulation to a constant receive signal amplitude can be provided. Thus, for example, could be done with a first control circuit a lateral positioning of the center of the light guide. A second control loop would then make the height positioning in accordance with the received signal amplitude, with additional safeguards to avoid a collision between light coupler and light guide. Instead of an electric actuator, such as a magnetic or piezoelectric actuators' sector, other actuators, such as pneumatic or hydraulic actuators are also conceivable. Likewise, sensors or elements of the control loop can be configured as pneumatically or hydraulically in addition to electric performance.

p0027Another type of the invention provides means for hydrostatic or hydrodynamic bearing. Here, at least one second light coupler by means of a hydrostatic or hydrodynamic bearing against the optical fiber is positioned in one or two axes.

p0028Such a hydrostatic or hydrodynamic bearing is based on a thin film of gas or liquid film, preferably an air film between two flat surfaces. The film has a high rigidity, so that large force changes result in only minor changes in distance.

p0029In the case of a gas film, an inert gas such as nitrogen or, preferably, an inert gas is preferably used. The fumbildende material or gas is preferably transparent or non-absorbing at the wavelength used for the optical transmission. This causes the penetration of the medium into the optical fiber transmission no interference. Likewise, the medium can be specifically directed into the light guide, for example, this external

p0030Dirt kept clear or clean. Other suitable media are liquids that are passed at the operating temperature of the device in a gaseous state. This cooling system is also possible, particularly under difficult conditions.

p0031in the case of a hydrostatic bearing is preferably the supply of the bearing by means of a small pump or a compressed gas container. The medium is pressed here between the two plane bearing surfaces. Since in such camps due to the short distance and the high surface quality of the bearing surfaces only very small amounts of gas or air are consumed, such a power supply with inexpensive means can take place.

p0032Alternatively, can be effected by means of the by the movement of the two units to each other air flow caused in the case of a hydrodynamic bearing, the feed. In this case, the storage takes place by the flow (hydrodynamic paradox, Bernoulli effect). For this purpose, means for conducting the resulting by the movement of air flow between the bearing surfaces are preferably provided. In the simplest case, the air guide elements consist of a simple baffle, which deflects a portion of the air flow accordingly. Similarly, more complex configurations are conceivable, for example containing additional filter to free the airflow of larger or small but disturbing particles. Alternatively, arrangements can be selected, which, for example, for a large extent on the Movement speed gives independent air velocity. Thus, the independence of the air flow rate with an increasing moving speed by an element, which provides for increasing turbulence of the air, can be achieved. Such stock must naturally have runflat tires in case of low speeds. This can be achieved for example by additional combination with a hydrostatic design.

p0033It is particularly favorable combination of hydrodynamic and hydrostatic bearing in conjunction with an active position control. These can be used for example in the same axis for a particularly precise alignment or in a complementary manner in different axes. For example, also take the position control by controlling air flow and air pressure of a hydrodynamic or hydrostatic bearing see. This combination is obtained on the one hand a mechanical robust system that gets high-precision characteristics by an additional superposed control. This can in particular also tolerances in the spacing of the air bearing due to temperature and moisture fluctuations of the air, as well as variations in speed are compensated for.

p0034In a ^"further advantageous embodiment of the invention the sensor is designed as an optical sensor. He can, for example, to measure the size of an image of a light source, which in focus, the the optimal distance corresponds, has a minimum size, to be designed. Such methods are for example used for focusing in CD players.

p0035In a further advantageous embodiment of the invention, the sensor is alternatively equipped with a capacitive or inductive sensor. Here, the sensor is preferably designed as a differential sensor which evaluates the difference between two signals.

p0036A further advantageous embodiment of the invention provides that a reference track is parallel to the light guide provided. This reference track is the sensor for determining the exact position of the light guide and as a measurement signal for the control of a second light coupler.

p0037In a further advantageous embodiment of the invention, the actuator is designed as electromagnetic suspension of at least one second light coupler. Such electromagnetic- suspension carries and positions a light coupler in at least one, optionally also in two axes. Preference given to the coupling element is integrated in an electromagnetic suspension. This integration leads to an extremely compact assembly can be achieved. Furthermore, in this way the moving mass is very small so that a system with high speed is possible. Advantageously, is moved by the actuator only one movable component of the light coupler, so that for example, an existing fiber optic for Light supply must not be moved. This means that, for example, the whole light coupler can be moved in the form of a collimator and or even a single lens of the light coupler.

p0038In another advantageous embodiment of the invention, the light conductor is according to the invention divided into at least two segments, means being provided for optical isolation of the segments are provided with each other. An optical isolation can be done for example by absorbing materials between the segments, by deflection of light between the segments, such as by means of mirrors, gratings or scattering materials or also by a direction separation of the optical signals.

p0039In addition, the lengths of the segments as well as the directions of propagation of the light in the segments are dimensioned such that having only slight differences on the borders between any two segments in which the same signal is transmitted, the modulation signal in duration or phase. These differences should be small compared to a period of the modulation signal. Thus, the entire signal propagation time of the signal from the optical transmitter to the optical receiver at the boundaries of the segments in only minor differences. This is necessary to ensure a wide-band signal transmission. This interference-free transmission over the entire rotational range of 360 degrees is possible, the above-mentioned conditions for every need Junctions between two adjacent segments are true.

p0040Of course, can be transmitted simultaneously with a device according to the invention also a plurality of signals. It must be self-satisfied, only the above-mentioned condition for each of these signals. The relationship between different signals may be arbitrary.

p0041The insulation (absorber) between a plurality of segments can be implemented as a low reflectance output coupling. At this, for example, a monitor receiver for monitoring the transmission signal amplitude can be attached. Likewise, this isolation may be formed depending on the wavelength. Preferably, this is configured as a thin film.

p0042In a further advantageous embodiment of the invention, groups of in each case two adjacent

p0043Light guides are provided which are of equal length and have an opposite direction of light propagation. In the simplest case, the whole assembly, as described above, only one such group. but also can be arranged several such groups along the circumference. This may also have respectively different segment lengths, as long as both segments of a group have the same length. So may be provided, for example for reasons of design to simplify mounting different segment lengths. The subdivision into a plurality of segments also offers the advantage in part, that in each segment independently of the adjacent segments, data may be transmitted. This means that a correspondingly higher overall data rate can be realized. If an arrangement of four groups over the entire circumference is provided, for example, it can multiply the total data rate by simultaneous transmission of four signals.

p0044Advantageously, this is just the light guide is divided into a number of segments. By even number of segments, the arrangement because of the symmetry is particularly easy to implement. A particularly inexpensive embodiment is obtained with two segments. In order to achieve a constant running time at the segment boundaries with two segments, they must have an equal length and opposite directions of propagation of the light. In the case of two segments of the absorber at a position 180 degrees from the coupling point is arranged. This means in the case of light coupling into the first unit an offset by 180 degrees about the axis of rotation of the two units arranged absorber. In a light into the second unit (and transfer from there to the first unit) a tracked with the rotation of the second unit relative to the mirror trench absorber is used. These absorbers may, for example, by a position control or hydrostatic or hydrodynamic bearing, as this is described for the second light coupler, in a

p0045Target position are maintained. In a further advantageous embodiment of the invention, at least one second light coupler is provided which comprises a light-conducting fiber. The end of this fiber has a surface which serves for the lateral deflection of the guided light in the light-conducting fiber. By deflection at this surface, the light can then be deflected in an angle in which it can be further guided in the light guide. Due to the reciprocity of the optical system is of course with this embodiment, a coupling of guided into the light guide in the optical fiber possible. For further optimization of the fiber can be optionally adapted to the contour of the light guide. Thereby, a light coupling to the largest possible surface of the light guide occur. For light deflecting the surface can be designed on the basis of different refractive indices for deflection by total internal reflection, as it can also be mirrored or contain a diffraction grating.

p0046A further advantageous embodiment of the invention is that the light-conducting fiber is net arranged approximately perpendicular to the tangent of the light guide. Furthermore, the reflection angle of the emerging light advantageously almost tangentially runs al the light guide.

p0047Furthermore, the light-conducting fiber can be used simultaneously as an optical sensor. To this end, further surfaces for deflection of the sensor signals are preferably provided along the contour of the light guide hen. Through this integration, the number of required components can be reduced. Furthermore, the mechanical adjustment is simplified because the consuming precise adjustment of two components falls each other accordingly.

p0048In another embodiment, at least one further surface is designed such that can be selectively deflected or filtered wavelength with these sensor signals. This selectivity of the

p0049Wavelengths can be achieved in a simple manner a selection of the different directions.

p0050A further advantageous embodiment of the invention provides that at least is provided for coupling evanescent fields one second light coupler. By coupling of evanescent fields contactless coupling or decoupling in the optical fiber for short distances is possible.

p0051A second light coupler for coupling evanescent fields is preferably configured as a prism. Such a prism may then for coupling are guided over the optical fiber preferably at a distance of the order of half a wavelength, so a few micrometers or nanometers.

p0052In another embodiment of the invention the light guide has at least one boundary surface preferably having reflective properties. Through reflection on at least one such interface is a GE aimed guiding the light along the preferably circular contour of the light guide possible.

p0053Another embodiment of the invention, the light guide at least to a material having a specular surface. So it can be configured for example as a trench in a metal support with glossy machined surface. An editor with which one receives a reflective surface, for example, can be done with diamond tools.

p0054In a further embodiment of the invention, the light guide comprises at least a material having a mirror surface. Thus, so an additional Liehe layer with reflective properties to the light guide is applied. Such layers can be applied, for example, electroplating or by vapor deposition in a vacuum. Particularly suitable as a coating material is gold, since these are at a wavelength of 1.3 microns for which inexpensive optical components on the market, a very high reflection provides constant. Furthermore, this can be an extremely corrosion-resistant coating of the surface can be achieved.

p0055In an improved embodiment of the invention, the mirror surface is realized optionally by means of a reflective or reflective coated film. Such films are inexpensive manufactured adjustable and be applied in a simple manner in any medium, such as plastic or metal. Alternatively, either the Silvering the surface specular layer can be applied by electroplating or by vacuum coating. With such layers is particularly high reflectances can be achieved.

p0056A further advantageous embodiment of the invention is characterized in that the surface has a capable of generating interference multilayer system. This can be advantageously targeted wavelength-addicts reflection reach. So herewith, an inventive light guide can embellish such that he preferred the wavelengths used for signal transmission, but does not transmit a scattered light from the environment. Here can be especially in open light guides a particularly high ambient light suppression reach. Furthermore, can be reached in case of transfer of several channels with different wavelengths targeted wavelength-dependent reflection.

p0057Another embodiment of the invention provides that the surface has a protective layer. Such a protective layer can, for example, contamination or a chemical change, such as to prevent oxidation or at least slow down. This protective layer is advantageously formed such that it as little as possible interfere with the reflective properties of the underlying reflective layers, and for the light to be transmitted represents the smallest possible attenuation. A further advantageous embodiment of the invention provides that the light guide at least one side has an interface to air, in which a shaft is similar to a film wave or surface wave feasible. Such wave propagates in the boundary layer of the optical fiber to the surrounding medium and, by a coupler switched from outside or be coupled. Advantageously, a prism is used to coupling.

p0058In another embodiment of the invention an optical grating for coupling out light is mounted on the light guide. Such optical lattice are particularly simple and space-saving integration. With such a grating is simultaneously an insulation between the different segments realized, for example when it directs the light out at the boundaries of the light guide. Furthermore, these gratings can be designed wavelength selective, so that different wavelengths may be coupled at different locations. This can be a very small space, a multi-channel signal transmission in the wavelength division multiplexing realize.

p0059Another aspect of the invention provides a Fresnel for light outcoupling the light guide. Such structures are particularly cost-effectively in modern molding techniques.

p0060In a further advantageous embodiment of the

p0061Invention are optional optical transmitter and optical receiver at the same time designed as a light coupler det. For example, a photodiode can be directly integrated into either the first or second unit for receiving optical instead of an optical coupler having a downstream optical receiver. Thus it combines the functional characteristics of optical receiver and light coupler. Also, for example, be integrated to emit light selectively in the first or second unit, a laser diode or LED. For this combines the functional characteristics of the photo couplers and optical transmitter.

p0062A further embodiment of the invention provides a light guide, consisting of a fiber with a mirrored surface coating. Such a fiber, which is provided on the outside, for example with gold or an interference-capable multi-layer coating is subsequently applied or glued to a prefabricated trench or another carrier. Thus, the reflection properties are no longer determined by the grave surface, but due to the extremely smooth surface of the fiber. Thereby, the manufacturing cost can be substantially reduced since fibers are inexpensive to produce and at the same time the cost of machining of the most large first unit is reduced.

p0063In another embodiment of the invention, the light guide comprises a on the outside or inside of glossy coated tube. Such tubes can be as well as the previously described fiber used and offers the same advantages. A further advantageous embodiment of the invention comprises a light guide with collecting properties in at least one plane. This allows an expansion of the light beam is reduced or the light beam will be further concentrated.

p0064A further advantageous embodiment of the invention for the simultaneous transmission of multiple channels can be used by being provided for transmitting different optical wavelengths. By wavelength-selective transmission of signals and wavelength-selective reception of the signals to be clearly separated.

p0065A particularly advantageous embodiment of the wavelength-selective transmission of multiple channels arises, especially when a plurality of first light couplers are arranged at different positions of the light guide. Advantageously, the means of isolation shall be provided depending on the wavelength at respective positions. As much advantageously the second light are respectively disposed at different positions of the second unit. This arrangement at different positions simplifies the mechanical attachment of light couplers and reduces the expenditure on the optical components.

p0066Further advantageously, at least one means for optical isolation is wavelength selective trained det. Preferably, a plurality of means for optical isolation are wavelength-selective and arranged at both locations corresponding to the segment boundaries for each wavelength. This configuration allows, for example, wavelength-dependent different segmentations or different arrangements of the segment boundaries, as is required in the arrangement of light couplers at different positions.

p0067Another advantageous embodiment of the invention provides that polarized light is transmitted in the light guide. Measurements have shown that many fiber optic light of a specific polarization transmitted with especially low attenuation. It is particularly advantageous, for example, a transfer of

p0068Light having a polarization to a metal surface, as this is used for example in a mirrored trench as a light guide vertically. Preference is given to the polarized light produced by a polarized light source (14). Likewise, polarization filters can be provided in the optical path, however. This can for example be integrated into a light coupler.

p0069In a further advantageous embodiment of the

p0070Invention is provided at least one polarization-sensitive receiver. Optionally, a receiver, a polarization filter can be connected upstream. Used to Sign lausSendung an unpolarized light source is used, as the light propagates dependent on the polarization with different attenuation and often with different maturities. Through a polarization selective receiver a certain polarization can now be selected with a defined maturity or a defined damping. This results in a largely POSITION sunabhängige amplitude and the lowest signal distortion.

p0071A further advantageous embodiment ^• of the invention provides that a plurality of optical transmitters (14) are provided for emitting polarized light and at the same time a plurality of polarization-selective optical receiver (15) are provided for receiving polarized light. Several groups are formed of optical transmitters and receivers, each of which is adjusted to each other in the polarization that a signal transmission within the group takes place, but no signals to receivers are transferred from other groups. This can be on different polarizations a plurality of channels transmitted simultaneously.

p0072In another embodiment of the invention, the signal transmission is carried out by means of modulation of polarization. For this purpose, at least one optical transmitter (14) is provided, which emits preferably polarized light. Furthermore, at least one means for modulating the polarization of the transmitter is optionally provided in the transmitter itself or in the optical path between transmitter and receiver. For evaluation of the polarization modulation is an optical

p0073Receivers provided, which has means to a polarization change in an amplitude modulation implement. This may be for example a simple polarization filter.

p0074According to the invention the embodiments of dependent claims and the following also as independent inventions to improve optical transmission paths according to the preamble of claim 1 can be used. This is especially true for referring back to the patent claim 1 or 2 claims before.

DESCRIPTION OF THE DRAWINGS

p0076The invention is described below, without restricting the general inventive idea, by exemplary embodiments with reference to the drawings.

p0077Fig. 1 shows a general schematic view of an inventive device.

p0078Fig. 2 shows schematically a device according to the invention in plan view.

p0079Fig. 3 illustrates the problem of the bandwidth control according to the prior art.

p0080Fig. 4 schematically shows the transmission of optical signals from the first unit to the second unit.

p0081Fig. Figure 5 schematically shows the transmission of optical signals from the second unit to the first unit.

p0082FIGS. 6, 7 and 8 show a capacitive position sensor.

p0083FIGS. 9 and 10 show the second light coupler, which are integrated in an actuator.

p0084Fig. 11 shows an optical position sensor.

p0085Fig. Figure 12 shows a second light coupler with integrated optical position sensor. Fig. 13 shows the second light coupler shown in FIG. 12 to illustrate in perspective view.

p0086Fig. 14 schematically shows the light on or coupling into the light guide by means of a second light coupler.

p0087Fig. Figure 15 shows the schematic structure of the control and integration of a second light coupler with integrated optical position sensor.

p0088Fig. 16 shows a light guide with a reflective coating.

p0089Fig. 17 shows a light guide of a coated fiber.

p0090Fig. 18 shows the basic structure of a coupler grid.

p0091Fig. 19 shows a signal coupling nelstruktur means of a Fresnel.

p0092Fig. 20 shows a device for coupling a surface wave.

p0093Fig. 21 shows a device with integrated active and passive position control. Fig. 1 shows in schematic form an apparatus according to the invention in section. Therein are illustrated as discs with a central bore, which are mounted rotatably about the axis of rotation (6), both the first unit (1) and the second unit (2). The light guide (3) is here exemplified as on the inside supply-mirrored trench shown. It extends around the entire circumference of the first unit. In engagement with the trench is a second light coupler (5) provided at the second unit (2) is arranged. This

p0094Light coupler taps the guided in the light guide and directs it with a light-conducting fiber (7) on. For exact alignment of optical fiber and the second light coupler in an axis a hydrodynamic bearing and an electrodynamic position control is provided. The hydrodynamic bearing is based on a thin film of air, which will be formed by the movement of the two units against each other between the first bearing surface (21) and the second bearing surface (20). To support such as additional means are provided for guiding air. Furthermore, the device advantageously runflat tires, which also provide a certain guidance at low speeds without sufficient air film, such as occur for example in an acceleration or braking phase has. Furthermore, a sensor (9) for determining the distance between the two units is provided for precise positioning. This sensor senses the distance from a reference track (11) from which the present

p0095Example identical to the first bearing surface (21). The output signals of the sensor by means of a Control unit (10) further processed and the actuator (8) for precise regulation of the position of the second light coupler supplied.

p0096Fig. 2 shows in schematic form an apparatus according to the invention in plan view. A first unit (1) serves to receive a ring-shaped light guide (3). This light guide is for example a mirrored on the inside ditch. A second unit (2) rotates relative to the first unit to the

p0097Axis of rotation (6). The second unit includes a second light coupler (5). The operation will now be presented separately for both directions of transmission of the first unit to the second unit and from the second unit to the first unit.

p0098Transmission from the first unit to the second unit: light from a transmitter not shown is based on the modulation signal in phase by means of the two first light coupler (4a, 4b) is fed into the light conductor (3). The light from the first light coupler (4a) passes on the right side of the figure to the absorber (13). Simultaneously, the light of the first light coupler (4b) running on the left side to the absorber (13). The absorber is disposed symmetrically in relation to the coupling point of the first photo coupler, so that the light paths (32) on both sides are the same length. The tap of the light is performed using a second light coupler (5) which is mounted rotatably about the axis of rotation (6) along the path of the light conductor (3) and the tapped light supplying an optical receiver. In order to simplify the optical receiver is also not shown. In Fig. 3 the problem of bandwidth limitation is shown on the prior art from US 6,104,849. Thus, here, light from a second unit (2) extending around the rotational axis (6) rotates is transmitted to a first unit (1). The light emission takes place by means of the second light coupler (5a, 5b, 5c, 5d, 5e). The light emitted from these light couplers light is transmitted into the light guide (3) to said first light coupler (4) in the case of engagement. The problematic limiting case occurs when, for example, in a counter-clockwise rotation, the second light coupler (5a) just comes out of the light guide and the second light coupler (5b) enters the light guide. Since all second light are in phase fed from a light source, the light of the second optical coupler (5a) (4) occurs in this limit the shortest route to the first light on. The light of the other second light coupler (5b) has but a path length of the whole optical fiber segment (3) to cover and thus enters delayed in the first light on. For example, in a CT scanner with a free inner diameter of the light guide comprises a quarter of the circumference, so this represents about a path length of 0.8 meters. The delay of a propagating speed of light optical wave corresponds to 2.6 nanoseconds. Now, if signals are transmitted with much shorter pulse durations, this leads to the double reception of the signals or in a superposition of the signals to distortions and falsifications. A useful data transfer is only possible if digital signals a bit width is substantially larger than this period. In this example, data with a bit width of greater than 10 nanoseconds, ie a data rate of 100 Mbit / s would thus transferable. In the other, corresponding to the prior art, cited above, embodiments of the optical fiber around the entire circumference is usually arranged, and usually only one second light coupler is provided so that the time difference is determined by the circumference of the device. For very small devices with just a few centimeters in diameter, the bandwidth limit is often not significant.

p0099In FIG. 4, the transmission of optical signals from the first unit is represented schematically to the second unit. An optical transmitter (14) generates modulated optical signals, which are transmitted, for example by means of a light-conducting fiber (7) to the first unit (1). From there, the coupling to the second unit (2) which transmits the optical signals by means of a further light-conducting fiber (7) to the optical receiver (15) for evaluation.

p0100Fig. 5 shows, similarly in the opposite direction to before and previous figure, the transmission of optical signals from the second unit to the first unit.

p0101In FIG. 6, a capacitive sensor for determining the position of the second light coupler (5) relative to the light conductor (3) is exemplified. There are a first capacitive sensor surface (22) and a second capacitive sensor surface (23) on the second Lichtkopp- ler or attached to an associated with this part. In this embodiment, the light guide or has an area located under the light guide, such as the support of the light guide be configured to be electrically conductive. To determine the position of the second light coupler with respect to the light conductors, the capacitance between the first capacitive sensor surface and the light guide and between the second capacitive sensor surface and the light guide are determined and evaluated. Such capacitive

p0102Sensor can also be configured independently of the light guide and second light. To determine the position in a plane can have only one capacitive sensor surface. Also, run the preferably configured in a U or V-shaped trench, which is used exclusively for position determination. Preferably, this trench on two mutually perpendicular surfaces.

p0103Fig. 7 shows a particularly advantageous embodiment of a capacitive sensor, wherein an additional capacitative reference surface (24) is provided. Since usually the opposite the second light, movable light guides is contactable not for electrical measurements, now the additional capacitive reference surface can be used as reference.

p0104Fig. 8 shows an electrical equivalent circuit diagram of the capacitances of the first capacitive sensor surface (22) of the second capacitive sensor surface (23) and the capacitive reference surface (24) to the light guide (3). Since the optical fiber is not directly contacted, carried the measurement for determining a first position between the first contact point (25) and the reference contact point (27). The measurement to determine a second position between the second contact point (26) and the reference contact point (27). To obtain the largest possible measurement signal by the capacitive reference surface (24) is capacitance formed as large as possible. The center position in the guide can be easily by evaluating the differences in capacitance of the contact points (25, 26) determine the reference point of contact (27). The absolute value of the capacity is a measure of the absolute height above the grave centers.

p0105Fig. 9 shows a particularly advantageous embodiment of an integrated in an actuator second light coupler. The path of the light (32) from the optical system for beam guidance bzw.- molding (30), for example a collimator, through the mirror (31) in the direction of the light guide is not shown here. Of course, the light path run in the opposite direction. The mirror (31) is attached to an armature (33). The guide or storage takes place by the magnetic field of a permanent magnet (34) and a coil (35). The embodiment shown here offers the advantage of mechanical decoupling of a light guide or a light source or a receiver on the side facing away from the light guide of the collimator. can be used to achieve a very substantial reduction in coupling loss, however, applied in place of the collimator and a mirror waveguide. This configuration is also less sensitive to dirt. In Fig. 10, a further embodiment of an integrated in an actuator photocoupler is given. The configuration is similar to that of Fig. 9. However, at least one yoke (36) for guiding the at least one coil (35a, 35b) the generated magnetic field is provided.

p0106In Fig. 11, an optical position sensor is illustrated. Such a position sensor advantageously passes as well as a second light coupler (5) is in close contact with the light guide (3). It comprises an optical waveguide (40), which is fed from a light source not shown with light at least one wavelength. According to the approach of a first sensor area (43) and a second sensor area (44) at the respective boundaries of the light guide, the light is reflected more or less strong. The evaluation of the intensity of the reflected light is effected in a non-illustrated sensor unit, which performs a wavelength-selective evaluation in cases of multiple wavelengths. For example, to operate a first sensor area (43) having a first wavelength, while a second sensor area (44) is operated at a second wavelength. For this purpose, preferably mounted on the exit surfaces wavelength-selective filters. In addition to the evaluation of the intensity, the arrangement can be designed such that in accordance with the distance changes the polarization of the reflected light. The sensor is in Fig. 11 once in a side view and below it in a plan view shown provides. This sensor could also be used rotated 90 degrees as light couplers. In this case, a first sensor area (43) a first coupling surface (41) and a second coupling surface (44) of a second sensor area (42) would correspond to.

p0107Fig. Figure 12 shows a second light coupler, which is combined with a position sensor in one unit. Here, in addition to the drawings previously illustrated arrangement a first coupling surface (41) and a second

p0108Coupling surface (42) to activate or outcoupling of light provided for information transmission in the light guide. Advantageously, the first coupling surface, and the second coupling surface are arranged diametrically opposite to light in both directions of the light guide on or decouple.

p0109Fig. 13 shows the second light coupler shown in FIG. 12 to illustrate in perspective view.

p0110In Fig. 14 the principle of light and coupling light deflection is shown. So is deflected led light in a second light (5) for optical coupling selectively in different directions of the light guide (3). The deflection is preferably carried out by refraction. It can be coupled in this way both light into the light guide and is coupled out. The drawn rays do not correspond exactly to the physical optical path, however, give the signal transport schematically right again. In FIG. 15 structure and integration of a second light coupler is illustrated schematically with integrated optical position sensor. A second light coupler (5) is movable and arranged variable in its height by a corresponding control of the coil (35). The beam guide (32) of light from the light guide (3) by means of a second light coupler (5) in an optical system (30) for beam guidance and beam shaping. This system, the light, for example, in a light-conducting fiber forward (7). but also can be arranged readily beam-forming system at this point already a light-conducting fiber. Of course, even light is transmitted in the reverse direction. To determine the exact position of a Positionssensor- transmitter / receiver (47) of light deflected by a located in the beam path wavelength-selective mirror (45) toward the second light coupler (5) and by means of this in the light guide for position determination, as previously describes coupled. The reflected depending on the position light (46) is again transmitted through the second light coupler and the wavelength selective mirrors back to Positionssensor- transmitter / receiver (47) for evaluation. This can now be made of the light intensity, the position of the second

p0111determine light coupler and output a corresponding measurement signal to the control unit for controlling the coil (35) of the actuator. Instead of a wavelength-selective mirror can also, however with higher damping, a commercial Schliffkoppler be used. In this case, may also optionally include a shaft conductor are used for signal feed and signal coupling.

p0112In Fig. 16, a light guide (3) is shown with a reflective coating. The light guide consists in this case of a groove which is introduced into the first unit (1). The surface of this groove is provided with a reflective coating (53).

p0113In Fig. 17, a light guide is shown, which was prepared from a coated tube. A reflective coated tube (50) is in a corresponding groove in a first unit (1) by means of adhesive (52). In order to obtain a grave-shaped, open light guide, this on the final contour (51) is reworked. Alternatively, the processing can also be performed before gluing. As this tube also a particular coated fiber can be used.

p0114In Fig. 18 the basic structure of a lattice is illustrated coupler. In this embodiment, the light guide (3) along the circumference around the axis of rotation (6) has a recess in the form of an arc segment on. In this recess there is optically transparent material (61) which carries an optical grating (60). Light beams (32), which are incident on the grating within that arc segment deflected by the grating and to the outside by means of a first lens (62) and a second lens (63) on the entrance opening of a light-conducting fiber (7) focused. Of course, other lens arrangements can be realized. Since the individual light beams are incident, although at different positions, but all the same angle on the grating, a uniform lattice constant can be used over the entire bend segment. So can be produced, which corresponds to a divergent wave which has its origin on the axis of rotation (6) a diffraction order. This point for all extracted signals represent the focal point. It is imaged by the two lenses on the end of the light conducting fiber (7). The device is particularly sensitive to dust and other pollution, as the essential components of the optical system, the two lenses and the light-conducting fiber can be placed in a protected area. Furthermore, the light guide itself by the inserted optical grating no holes or undercuts, on which dirt can accumulate.

p0115In Fig. 19 a signal coupling is represented by means of a Fresnel nelstruktur (64). Of a first unit (1) associated with the light conductor (3) fed in the vicinity of a first light coupler (4) has a stepped structure to the beam deflection of the second by a

p0116Light coupler (5) emitted beam towards a first light coupler.

p0117Fig. 20 shows an embodiment of the invention for coupling a film wave or surface wave. The light guide (3) is here exemplified as a fiber whose core is ground. is to couple a short distance above the surface of the light guide is ground a prism (5) is guided. In this prism in the present example (not shown), coupled light from above. For exact alignment, a hydrodynamic bearing is provided comprising a first bearing surface (21) and a second bearing surface (20). Corresponding bearing elements can be provided to a stabilization in the direction of a second axis and perpendicular thereto. As a bearing surface and the light conductor itself can be used.

p0118Fig. 21 shows a further embodiment of the invention wherein a hydrodynamic bearing is complemented by an active position control is provided. One of the first bearing surfaces (21) serves as a reference track (11) for the sensor (9).

LIST OF REFERENCE NUMBERS

p01201 First session

p01212 Second unit 3 light guide

p01224 first light coupler

p01235 Second light coupler

p01246 rotational axis of rotation between the first and second unit 7 light-transmitting fiber

p01258 actuator

p01269 sensor

p012710 control unit

p012811 reference track 12 means of hydrostatic or hydrodynamic bearing

p012913 absorber

p013014 Optical Transmitter

p013115 Optical Receiver 20 second bearing surface

p013221 first bearing surface

p013322 first capacitive sensor face

p013423 second capacitive sensor face

p013524 capacitive reference face 25 first contact point

p013626 second contact point 27 Reference point of contact

p013730 optical system for beam guidance and beam shaping

p013831 levels 32 Beam

p013933 anchor

p014034 permanent magnet Coil yoke optical waveguide first coupling face second coupling surface first sensor surface second sensor surface wavelength-selective mirror light beam position sensor position sensor transmitter / receiver first light path of second light path coated tube reworked tube adhesive reflective coating grating optical transparent material first lens second lens Fresnel