DE19827125A1 - Generator for parallel collimated beams from fiber coupled laser diodes for laser Doppler measuring devices e.g. laser Doppler anemometers - Google Patents

Abstract

A fiber fixing arrangement (42-43) and a lens array (51-52) are in surface contact with one another in a plane of connection. Apparatus for generating parallel collimating beams from a fiber coupled laser diode which when superimposed in a volume for measurement by means of a transmitting optical device are suitable for illumination of the object in laser Doppler devices. A fiber fixing arrangement (4) and a lens array (5) are in surface contact with one another in a plane of connection (45). The fiber fixing arrangement is a plane parallel plate (42) and has at least two recesses (43) which are positioned in pairs symmetrically with respect to an optical axis predetermined by the transmitting optical device (71) in order to receive the transmitting fibers (31) provided by branching from the laser diode (1). The transmitting fibers are fixed orthogonally and rigidly in the plate in such a way that the end surfaces of the fibers coincide exactly with the plane of connection. The lens array consists of a plane parallel supporting plate (52) with collimating lenses (51) rigidly attached by cementing. The number of collimating lenses and the position thereof corresponds to the number and position of the supplied transmitting fibers in the fiber fixing arrangement. The parameters of the subsequent transmitting optical device and the optical path length through the supporting plate as far as the collimating lens is adapted by adjustment of the thickness of the supporting plate to the aperture of the transmitting fibers and the focal length of the transmitting optical device so that the laser narrowing of the beam (6) focused through the transmitting optical device coincide upon superimposition in the volume for measurement (8). An Independent claim is also given for a method of producing apparatus for generating parallel collimated beams from a fiber coupled laser diode.

Description

The invention relates to a device for generating parallel collimated Laser beam bundles that are provided from fiber-coupled laser diodes. Such precisely aligned and collimated laser beams can be adjusted preferably in laser Doppler devices as transmission beams for illuminating moving scattering particles used. The goodness of the collimation is A prerequisite for high measuring accuracy.

Since the introduction of the laser, laser Doppler measuring devices, such as laser Doppler anemometer (LDA), velocimeter (LDV), vibrometer and interferometer, purposefully developed as a measuring method for speed and length. Here are moving objects to be illuminated by a laser beam and by the Doppler effect evaluated frequency shift of the scattered light. Especially the so-called cross-beam principle has emerged as a laser Doppler measurement setup its relative insensitivity to misalignments. The measuring accuracy of such arrangements depends on the constancy of Wavelength also significantly depends on the curvature of the wavefronts from both transmit beams in the measuring volume. F. DURST describe this fact et al. in Appl. Opt. 18 (1979) 4, pp. 516-524, "Influence of Gaussian beam properties on laser Doppler signals ". It is therefore ideal - because of the flatness of the Wavefronts in the laser waist - an exact image of the laser waist of the focused transmission beams in the measuring volume. Becomes a gas laser as a light source used, its natural low divergence can be exploited to the two transmission beams generated via a beam splitter with a converging lens (Transmission lens) in the measurement volume.

With the development of laser diodes and their increasingly longer lifespan and power, these are increasingly used in laser Doppler devices. The great asymmetry of the laser diode radiation and the large opening angle (numerical aperture), however, lead to great difficulties in production of a Gaussian beam. Such a beam transformation is usually only with  complex multi-lens systems possible. That's why you go increasingly for the transmission of two transmission beams with polarization-maintaining Single-mode fibers, especially since fiber-coupled laser diodes are available, which Transform transmit beams into a Gaussian beam. This beam guidance enables at the same time a compact arrangement and a galvanic isolation of Electronics and optical probe.

In his essay "Applications of semiconductor components in laser Doppler anemometry, part II "(Laser Magazin 6/91, pp. 8-15) shows C. TROPEA optical arrangement in which the receiving lens has holes through which the Transmitting beam is passed unhindered. Larger usable Diameters of the receiving lens improve the scattered light signal. Every transmission fiber is cemented in a ferrule, this ferrule fiber arrangement with bevelled in order to reflect back into the fiber suppress. Because of the oblique light emission, this is required Arrangement a complex adjustment of the collimation optics to the Fiber outputs to collimate the two transmit beams exactly into the Show measurement volume and fix this state. Also the chosen one Application of two separate collimation lenses can be because of the high Adjustment requirements (in two 3 translational and 3 rotational degrees of freedom) insufficient stability and reproducibility of the adjusted state bring, so that in part considerable restrictions of the measuring accuracy must be included.

The invention has for its object a new way to Generation of parallel collimated beams from fiber-coupled laser diodes to find the high demands on the collimation state of Transmitting beams in laser Doppler arrangements are met and easily adjustable. The Invention is further directed to reproducible methods Manufacture of such a device for generating collimated Specify laser beam.  

According to the invention, the task in a device for generating parallel collimated beams from a fiber-coupled laser diode, which at Superposition in a measuring volume by means of a transmission optics are suitable for Object lighting in laser Doppler devices, solved in that a Fiber fixing device and a lens array in a connection plane are in contact with each other that the fiber fixing device is a plane-parallel plate and at least two recesses that are symmetrical in pairs with respect to one optical axis predetermined by the transmitting optics are arranged for recording which has transmission fibers provided by the laser diode by branching, the transmission fibers are so rigidly attached in the plate that the Fiber end faces exactly match the connection plane, and that the Lens array from a plane-parallel carrier plate with rigidly attached There are collimation lenses, the number of collimation lenses and their Position with the number and position of the transmitted fibers in the Fiber fixation device and the parameters of the following transmission optics in Agreement and the optical path length through the carrier plate to Collimation lens by adjusting the thickness of the support plate to the aperture of the Transmission fibers and the focal length of the transmission optics is adjusted so that the Laser waist of the beams focused by the transmission optics at the Overlap in the measurement volume coincide.

In the fiber fixing device is advantageously in the middle between the transmission fibers and Another along the optical axis predetermined by the transmission optics Optical fiber as a receiving fiber for light transmission to a receiver provided, light scattered across the measurement objects in the measurement volume Transmission optics and an equivalent reception optics on the fiber end of the Receiving fiber is mapped. In this case, the receiving optics expediently Breakthroughs for the transmission of the transmitted beam.

The fiber fixing device and the lens array are in an advantageous design made from a uniform plane-parallel plate, the connection plane due to high-precision recesses on the one hand from the front of the plate for the Fiber fixation and on the other hand from the back of the plate for the lens frame is defined. The recesses for the lens frame are sufficient  reduced diameter up to the connection level, the Laser beams from the transmission fibers in the airspace of each Exit recess and be collimated by the collimation lens. To one To avoid complicated adjustment of the collimation lenses are preferred Ball lenses used.

In a further advantageous variant, the fiber fixing device and the Lens array rigidly with each other using a refractive index-adapted kit layer connected. With this design, the collimation lenses are the lens array preferably in the form of plano-convex lenses with their flat surface on the light path glued on the back surface of the carrier plate. To do this are both Fiber fixation device as well as the lens array for their cementing in the Appropriately ground and polished the connection level, thus in the Fiber fixing device all fiber ends are arranged exactly in one plane and in Lens array the optical path length of the composite of kit layer, carrier plate and Lens kit layer is adjustable up to the collimation lens.

It also proves to be advantageous if the fiber fixing device has a is a plane-parallel plate which is essentially divided in half along a straight line, has at least one of the partial plates along the separating surface of grooves arranged orthogonally to the plate surfaces and dimensioned so that the Fibers free of play during the subsequent joining and gluing of the partial panels are locked by the partial plates. Advantageous shapes of the grooves are rectangular, wedge-shaped or trapezoidal grooves.

When using the collimation device according to the invention in one Laser Doppler device (e.g. an anemometer), the transmission fibers are preferred decoupled from an integrated optical chip, the input of which fiber-coupled laser diode is fed and on which a branch as well as a Phase modulator for frequency shift between the two light waves Transmission fibers are present.

The object of the invention is achieved with a method for producing a Device for generating parallel collimated beams from one  fiber-coupled laser diode which, when superimposed in a measuring volume a transmission optics are suitable for object illumination in laser Doppler devices, solved in that the collimation device in two essential sub-processes, the manufacture of a fiber fixing device and a lens array, that tubular to produce the lens array in a plane-parallel plate Recesses are made to mount collimation lenses, the Positions and the depth of the recesses to the parameters of the used Transmission fibers and transmission optics can be adjusted so that those in parallel tube-shaped recesses entering laser beams over the The transmission optics are superimposed with their laser waists in the measuring volume become and through the uniform depth of the tubular recesses Surface of the plane-parallel plate is generated parallel connection plane that the contact surface to the fiber fixation device represents that for the manufacture of Fiber fixing device in a plane-parallel plate recesses for precise Fixing of transmission fibers coupled to the laser diode can be introduced a reproducible locking of the fiber end faces in the connection plane ensure, the positions of the recesses to the axes of the tubular recesses are aligned such that the axes of the Transmit fibers match the tube axes and the transmit fibers in each case the connection level open into the tubular recesses.

In a first advantageous embodiment of the method Fiber fixation device and lens array from a uniform plane-parallel plate manufactured, the recesses of the two components of different sides of the plane-parallel plate are introduced and in touch a virtual connection level. The recesses for receiving the Fibers are each preferably designed as double cylinders, one smaller cylinder diameter that touches the connection plane, only that Absorbs fiber core and compared to a larger cylinder diameter than Stop acts when inserting the fibers. To make the A so-called LIGA process can advantageously be used for recesses in which three - dimensional microstructures are created by a succession of  Lithography with synchrotron radiation (X-ray depth lithography), galvano molding and impression technique are made with plastics.

In a second advantageous process variant, fiber fixing device and Lens array made from two different plane-parallel plates, the two different plates with respect to the fiber axes and the axes of the tubular recesses are made to match each other, in the Connection plane aligned with each other and glued together.

According to the invention, the object is furthermore in a method for production a device for generating parallel collimated beams from one fiber-coupled laser diode which, when superimposed in a measuring volume a transmission optics are suitable for object illumination in laser Doppler devices, solved in that the collimation device in two essential sub-processes, the manufacture of a fiber fixing device and a lens array, that plano-convex to manufacture the lens array on a plane-parallel carrier plate Collimation lenses are glued, their position and focal length to the Parameters of the incident beam and the subsequent transmission optics see above is adapted that from the collimation lenses collimated laser beams the transmitter optics in the measurement volume with their laser waist overlapped and the opposite of the glued-on collimation lenses Surface of the carrier plate as a connecting plane for connecting the lens array is used with the fiber fixing device, the setting for the Defined superposition of the laser beam in the measuring volume suitable optical thickness from carrier plate, collimation lens and intermediate Kit layer the said surface of the carrier plate is sanded flat until the necessary thickness is reached that in order to manufacture the fiber fixing device another plane-parallel plate through recesses for precise Fixation of transmission fibers coupled to the laser diode can be introduced an orthogonal locking of the transmission fibers with respect to the plate surface in the Ensure recesses, the positions of the recesses to the Axes of the collimation lenses are aligned such that the axes of the Transmitting fibers match those of the collimation lenses, the transmitting fibers  are inserted into the recesses and then glued, where the connection plane given by the back plate surface is pierced by the transmission fibers, and the protruding ends of the Transmitting fibers down to the rear panel surface as a connection level be ground that the fiber fixing device and the lens array with their plate surfaces defined as connection planes and are glued, the fiber axes with the axes of the collimation lenses in Be matched.

It proves to be when using light scattered back from objects Advantage, another in the middle between the recesses for the transmission fibers Make recess for receiving a receiving fiber.

There are different for all recesses in the fiber fixing device Possibilities of insertion into the plane-parallel plate are available.

On the one hand, the recesses can be made by laser drilling, these are expediently cylindrical or conical. At suitable choice of cylinder diameter (as a compromise between a more precise fit Fiber guidance and reliable introduction of the fiber with adhesive) is with the Adhesion of the fiber jacket also achieved strain relief. For certain Conditions of fiber stress show it as an advantage, the fiber core to be glued separately in the plane-parallel plate by using the recess as double cylinder, on the one hand the core diameter and on the other the Shell diameter of the fiber is adjusted, is executed. For gluing the fiber core is exposed at the fiber end.

In the conical case, the recesses are preferably large Diameter larger than the outside diameter of the transmission fibers and with their small diameter in the connection plane to the outer diameter adapted to the transmission fibers, the same as with a cylindrical recess Strain relief results and assembly is simplified. Should also here The small cone diameter is on the fiber core Adjust core diameter and strip the fiber end accordingly. Furthermore, this measure automatically centers the fibers reached.  

A particularly reliable and precise adjustment of the transmission fibers in the Fiber fixing device is done by dividing the plane-parallel plate used perpendicular to the surface of the plates, grooves are used to hold the fibers in at least one of the partitions and joining the partitions after the Place the fibers in the grooves. The grooves are advantageously wedge-shaped or Made trapezoidal and dimensioned so that when the Partial plates included the inserted fibers essentially without play and can also be glued.

The invention is based on the consideration that the adjustment and fixation of Fibers from fiber-coupled laser diodes with regard to the necessary Collimation lenses and a subsequent focusing optics only because of this simplified and reproducible if the number of necessary degrees of freedom of adjustment (for two transmission fibers: two three translational and three rotational degrees of freedom) is significantly reduced. According to the Invention - matched to the focusing optical system (transmission optics) and the Parameters of the fibers used - a composite system from a fiber fixer device and a lens array within narrow manufacturing tolerances proposed with the translational and rotational degrees of freedom of the fibers and the collimation lenses with each other as well as the fiber ends and the Collimation lenses to each other are omitted, so that only one degree of freedom of rotation and two degrees of translation freedom for the specific application (e.g. in one Laser Doppler anemometer) must be adjusted mechanically and optically. By simple manufacturing steps in which manufacturing tolerances are kept small or can be subsequently corrected (e.g. by face grinding) Production and adjustment of the collimation device according to the invention very high reproducibility achieved.

The device according to the invention enables the generation of parallel collimated Beams of fiber-coupled laser diodes that meet the high demands fulfill the collimation state of transmission beams in laser Doppler arrangements, and is easily adjustable. The invention further ensures  reproducible adjustment in the production of simple composite components for the coupling of optical fibers and collimation lenses.

The invention will be explained in more detail below on the basis of exemplary embodiments become. The drawings show:

Fig. 1 is an optical diagram of a cross-beam LDA according to the prior art

Fig. 2 shows an inventive optical diagram for the generation of collimated transmission beams with a composite of two plane-parallel plates to the fiber fixing and the arrangement of the collimating lens,

Fig. 3 shows an optical scheme according to the invention for generating collimated transmission beams with a uniform plane-parallel plate

Fig. 4 shows a complete optical diagram for the application of the device according to the invention in an LDA

Fig. 5 shows a variant of the Faserfixiereinrichtung with conical recesses for receiving four transmitting fibers and a receiving fiber,

Fig. 6 is a variant of the Faserfixiereinrichtung with cylindrical recesses for receiving two transmitting fibers and a receiving fiber,

Fig. 7 shows a variant for the design of the fiber fixing device from two partial plates with grooves for receiving the fibers.

To better elaborate the invention, FIG. 1 shows a prior art scheme for a fiber-optic laser Doppler anemometer (LDA) according to the cross-beam principle using the light backscattered from moving objects. The optical fiber 3 emanating from a fiber-coupled laser diode 1 is guided into a light splitter and modulator module 2 , which divides the light into two transmission fibers 31 and generates a frequency difference between the two transmission fibers 31 . The transmission fibers 31 are polarization-maintaining monomode fibers of any length, so that the following elements can be combined in a handy probe head. The ends of the transmission fibers 31 are gripped in so-called ferrules 41 for their highly precise adjustment. To avoid back reflections on the fiber end face, each ferrule is beveled at the end, resulting in the beam path shown (exaggerated) in the enlarged circular section. The diverging beam of rays is refracted at the oblique fiber end surface and therefore leaves the transmission fiber 31 at the marked angle to the fiber axis. Consequently, the axis of the collimation optics 51 is also arranged slightly inclined for the generation of a collimated transmission beam bundle 61 and makes the adjustment of the entire free beam optics considerably more difficult. The compact optics unit consisting of the transmission optics 71 and the reception optics 72 having the same parameters only improves this little. The receiving optics 72 , which should be larger than the distance between the transmission beams 31 in order to receive as much scattered light as possible, have openings for the transmission of the transmission beams 31 not being influenced. This results in very strict requirements for the collimation state of the transmission beams 31 and the adjustment of the transmission beam bundles in the measurement volume 8 , the point of intersection of the beams in the cross-beam principle named afterwards. Due to the large number of individual adjustments required (ferrules 41 with axis tilt to collimating lenses 51 and to the transmitting and receiving optics 71 and 72 ) and the number of degrees of freedom of each individual element (3 degrees of translation and 3 degrees of rotation), these requirements make the adjustment very complex and prone to failure and hardly reproducible.

In the case of the backscatter principle which is mostly used and shown in FIG. 1, an intensity modulation is generated in the measurement volume 8 by scattering on moving object particles. Via the transmission optics 71 and the reception optics 72 , this temporal intensity curve is imaged as focused scattered light 62 onto the reception fiber 32 , which is likewise held by a ferrule 41 . By means of the reception fiber 32 , a multimode fiber, the receiver 9 , which often contains an avalange photodiode (APD), is subjected to the intensity-modulated scattered light and an evaluation unit for evaluating Doppler frequency shifts for determining Doppler frequency and derived variables such as speed or length of the movement , causes.

In contrast, the invention - with the same basic structure (cross-beam principle) of any laser Doppler measuring device - is specifically aimed at simplifying the critical adjustment between the ends of the transmission fibers 31 and the collimation lenses 51 and reducing the number of degrees of freedom of adjustment.

The basic structure of a device according to the invention for generating parallel collimated beams consists - as shown in FIG. 2 - of a fiber fixing device 4 and a lens array 5 which are rigidly connected to one another in a connection plane 45 . The special feature of the fiber fixing device 4 is that a plane-parallel plate 42 is provided for all the transmission fibers 31 , into which orthogonally penetrating recesses 43 are made true to size in accordance with the geometric-optical imaging conditions of the transmission optics 71 and the dimensions of the transmission fibers 31 . The transmission fibers 31 are fixed orthogonally in the plane-parallel plate 42 in such a way that the end faces of the transmission fibers 31 are flush with the rear surface of the plate, which also represents the connecting plane 45 to the fiber array 5 . In manufacturing terms, this adjustment state is first exactly achieved by inserting and gluing the transmission fibers 31 with a protrusion of the fiber ends and then by grinding the transmission fibers 31 down to the surface of the plate 42 .

The lens array 5 contains the transmission fibers 31 in the fiber array 4 with respect to the number and spacing associated collimation lenses 51 and in this variant consists of a plane-parallel support plate 52 made of optical glass (preferably quartz glass) to which the collimation lenses 51 are glued. The collimation lenses 51 are plano-convex lenses, preferably hemispherical lenses, which form an optical bond with the carrier plate 52 by means of a kit layer 53 . This composite has the refractive indices of the carrier plate 52 , lens kit layer 53 and collimation lenses 51 matched to the refractive index of the transmission fibers 31 . A kit layer 54 , through which the lens array 5 is rigidly connected to the fiber fixing device 4 , also has a refractive index matched to the refractive index of the transmission fibers 31 , so that back reflections on the fiber end faces are largely avoided.

An essential function in the lens array 5 is the optical thickness of the carrier plate 52 together with the adjacent kit layers, the lens cement layer 53 and the kit layer 54 , because this sets the spacing ratios of the collimation lenses 51 to the ends of the transmission fibers 31 .

Deviations from the calculated thickness of the support plate 52 and lens kit layer 53 , which arise due to manufacturing tolerances of the lens kit layer 53 , are eliminated during the manufacture of the lens array 5 by subsequent surface grinding of the surface of the support plate 52 opposite the collimation lenses 51 . When cementing the fiber fixing device 4 and the lens array 5 , only one degree of rotational freedom and two degrees of translational freedom are to be adjusted in the connection plane 45 , this adjustment process being carried out once and the achieved state then being maintained in a stable manner. The adjustment is carried out by feeding light into the transmission fibers 31 and checking the collimation state of the parallel transmission beam bundle 61 or - as explained more specifically below in FIGS. 5 and 6 - checking the state of the laser waist in the measurement volume 8 , which is focused via the transmission optics 71 , taking into account a reception fiber 32 , transmission optics 71 and reception optics 72 as a complete adjustment of the transmission and reception channel within a process.

Fig. 3 shows the same basic structure of the collimation arrangement according to the invention of fiber fixation device 4 and lens array 5 , in which case the fiber fixation device 4 in addition to the recesses 43 for the transmission fibers 31, a further recess 43 for receiving a reception fiber 32 , which is centered between the transmission fibers 31 is positioned in the same plane (drawing plane). There are also recesses in the lens array 5 , which are provided as tubular recesses 55 for mounting the collimation lenses 51 . This variant can be produced in a suitable manner, ie with sufficient accuracy, for example using the so-called LIGA process. The LIGA process is a special process for the production of microstructures by the processes lithography with synchrotron radiation (X-ray depth lithography), electroforming and plastic molding. Fiber fixation device 4 and lens array 5 can be manufactured as separate plane-parallel plates in this way within particularly narrow tolerance limits. However, it is also advantageous, as shown in FIG. 3, to produce a uniform, plane-parallel plate by molding the recesses 43 and 55 by means of two different molding tools, which face each other and touch in the connecting plane 45 . As can be further seen 3 to Fig., The recesses 43 for the transmitting fibers 31 and the receiving fiber 32 are each made in two different diameters, so that after a defined exposure of the fiber cores 33 is provided for transmitting and receiving fibers 31 and 32, a stop, which positions the fiber ends exactly in the connection plane. The collimation lenses 51 , preferably in the form of spherical lenses, are likewise reliably positioned within the tubular recesses 55 by means of corresponding stops and, like the transmitting and receiving fibers 31 and 32 , are locked by gluing. In order to image the backscattered light from the moving object particles as weakly as possible onto the receiving fiber 32 , a suitable recess is expediently provided for the scattered light 62 focused by the transmitting and receiving optics 71 and 72 (not shown in FIG. 3).

In FIG. 4 is a collimation assembly according to the invention in the optical scheme is applied a fiber optic laser Doppler anemometer (LDA). The light from a fiber-coupled laser diode 1 is directed to an integrated optical chip (IOC) 21 for division into two transmission beams 31 and generation of a frequency shift. The IOC 21 contains a Y-branch 22 and an electro-optical phase modulator 23 , which is represented by its electrodes. The transmission fibers 31 leaving the IOC 21 are polarization-maintaining monomode fibers and their ends are glued into the recesses 43 of the plane-parallel plate 42 of the fiber fixing device 4 . Via the rigidly coupled carrier plate 52 with the collimation lenses 51 cemented thereon as a lens array 5 , parallel, collimated transmission beam bundles 61 are generated, which pass through a receiving lens 72 that has openings and are unaffected and are focused by means of a transmission optics 71 with their laser waists into the measurement volume 8 . An interference fringe pattern is generated in the measurement volume 8 as a result of the frequency difference between the two transmission beams 31 generated in the phase modulator 23 . When traversing the measuring volume 8 , moving object particles scatter the laser light falling on them intensity-modulated due to the stripe pattern. Via the system of transmitting optics 71 and receiving optics 72 , which are optically equivalent, part of the scattered light (backscattered light in this case) is imaged as focused scattered light 62 onto the receiving fiber 32 glued in the middle between the transmitting fibers 31 in the plate 42 . The receiving fiber 32 forwards the modulated light to the receiver 9 , which is preferably an avalange photodiode (APD), which is followed by a customary evaluation of the Doppler frequency and calculation of the derived variables, such as speeds and path lengths, of the moving objects.

Fig. 5 shows in the upper part of a plan view of the Faserfixiereinrichtung 4, which in this example is a circular plane-parallel plate 42 with a receiving fiber 32 and four transmitting fibers 31. The symmetrical arrangement of two pairs of transmission fibers 31 selected here results on the one hand in higher thermal stability and on the other hand enables the measurement of particle movements with movement components in two coordinate directions in the measurement volume 8 . Various materials, such as glass, glass ceramics and certain types of steel, can be used as materials for the plate 42 , provided that their linear expansion coefficients are matched to those of the lens array 5 and the transmission and reception fibers 31 and 32 .

In the lower part of FIG. 5, a section along the line AA of the top view is shown. The recesses 43 have a conical shape. In order to achieve a simpler and precise centering of all fibers 3 , the small diameter of the conical recess 43 on the surface of the plate 42 , which forms the connection plane 45 with the lens array 5, is matched to the diameter of the fiber cores 33 of the transmission fibers 31 and reception fiber 32 and the large diameter larger than the outside diameter of the transmitting and receiving fibers 31 and 32 , which then have to be stripped at the fiber end. The ends of all fiber cores 33 are flush with the connection plane 45 . The manufacturing process can be made straightforward if the outer diameter of the fibers 3 in the conical recesses 43 lies approximately in the middle of the plate 42 . In this case, the transmitting and receiving fibers 31 and 32 center themselves when they are introduced into the conical recesses 43 with adhesive. The dimension of the exposed fiber core 33 is of no importance, since the fiber core 33 can penetrate the surface of the plate 42 , which forms the connection plane 45 to the lens array 5 , as far as desired if this excess is ground off after the fibers 3 have been glued.

FIG. 6 shows the fiber fixing device 4 in the same way (in plan view and as a section) as in FIG. 5. The fiber fixing device 4 is in turn a circular, plane-parallel plate 42 , into which two transmission fibers 31 and a reception fiber 32 positioned in the middle between them have a diameter line (section plane BB). As the sectional illustration BB shows, the recesses 43 for all fibers 3 are cylindrical here and are produced in the plate 42 with sufficient accuracy in terms of production technology, preferably by laser drilling. The fibers 3 are then inserted and glued through the recesses 43 so that they penetrate the surface of the plate 42 which serves as the connecting plane 45 . After the adhesive has hardened, the ends of the transmitting and receiving fibers 31 and 32 are brought into exact alignment with the connecting plane 45 by surface grinding.

For the cases the design of the Faserfixiereinrichtung 4 shown in FIGS. 5 and 6 with introduction of the receiving fiber 32 between the transmitting fibers 31 in addition to the actual positioning advantages of the fibers 3 is additionally possible a uniform adjustment of the transmit beam 61 to the image of the focused scattered light 62nd The collimated transmit beams are focused with their laser waists in the measuring volume 8 61 and at the same time the receiving fiber 32 during the adjustment and cementing of Faserfixiereinrichtung 4 and lens array 5 used as a light input and displayed, the fiber end of the receive fiber 32 to the same point in the measurement volume. 8 The adjustment state is observed, optimized and held on a monitor until it is finally fixed when the kit layer 54 has hardened.

FIG. 7 shows a further top view of the plane-parallel plate 42 of the fiber fixing device 4 , which in turn holds two transmitting fibers 31 and one receiving fiber 32 in a defined manner. The peculiarity in this example lies in the special type of manufacture of the plate 42 , which in this case consists of two partial plates 47 . Although both partial plates 47 can in principle consist of different materials, since they have no optical function, a uniform plate 42 is preferably divided along a plane orthogonal to the plate surfaces. Grooves 48 are introduced into one of the separating surfaces created in accordance with the optical requirements described above, into which the transmission fibers 31 are inserted at the same distance on both sides from the reception fiber 32 . The grooves 48 are wedge-shaped in this example. They can also have a trapezoidal or rectangular cross section. In any case, they are to be introduced so deeply into the separating surface that the fibers 3 protrude from the separating surface by the same amount, even with different thicknesses of the transmitting and receiving fibers 31 and 32 . When gluing to the other partial plate 47 , all fibers 3 are thereby locked without play and orthogonally. The plate adhesive 49 only serves to fix the locked state. However, the diameters of the transmission and reception fibers 31 and 32 are too different, so that the deviation from the uniform plane of the transmission and reception fibers 31 and 32 is not due to the losses to be expected when the focused scattered light 62 is picked up (see FIG. 4) more can be tolerated, 47 grooves 48 are expediently introduced into both partial plates.

After the partial plates 47 have been glued, the entire plate 42 , in particular for flattening the fiber ends of the transmitting and receiving fibers 31 and 32 , is flattened and in turn obtains the necessary correspondence between the fiber ends and the connecting plane 45 for coupling to the lens array 5 .

With the method of producing defined ratios of the fiber ends of the transmission fibers 31 and the reception fiber 32 according to the invention, there is a further advantage for the already simplified optical adjustment process (only two degrees of translational freedom and one degree of rotational freedom). In this case, the combination of fiber fixation device 4 and lens array 5 is most easily realized when gluing through the kit layer 54 along the connection plane 45 (see FIGS. 2 and 4) by feeding light into the receiving fiber 32 . By positioning a sufficiently well reflecting or scattering (stationary) object in the measurement volume 8 , the focusing state of the returning beams 6, which are focused by the collimation lenses 51 on the ends of the transmission fibers 31 , is then optimized during the cementing process. This provides a sufficiently precise, reproducible and particularly simple method for producing a collimation arrangement.

Reference list

1

Laser diode (fiber coupled)

2nd

Light divider and modulator module

21

IOC (integrated optical chip)

22

Y-branch

23

Phase modulator

3rd

Fibers

31

Transmission fibers

32

Receiving fiber

33

Fiber core

4th

Fiber fixation device

41

Ferrule

42

(plane-parallel) plate

43

Recess

44

Laser drilling

45

Connection level

46

Fiber bonding

47

Partial plate

48

Grooves

49

Panel bonding

5

Lens array

51

Collimation lenses

52

Carrier plate

53

Lentil kit layer

54

Kit layer

55

tubular recess

6

Bundle of rays

61

Transmitting beam

62

focused stray light

71

Transmission optics

72

Receiving optics

8th

Measuring volume

9

receiver

Claims (27)

1. A device for generating parallel collimated beams from a fiber-coupled laser diode, which are suitable for superimposition in a measurement volume by means of a transmitter optics for object lighting in laser Doppler devices, characterized in that

• 1. a fiber fixing device ( 4 ) and a lens array ( 5 ) are in flat contact with one another in a connection plane ( 45 ),
• 2. the fiber fixing device ( 4 ) is a plane-parallel plate ( 42 ) and at least two recesses ( 43 ), which are arranged in pairs symmetrically with respect to an optical axis predetermined by the transmitting optics ( 71 ), for receiving the laser diode ( 1 ) by branching provided transmission fibers ( 31 ), the transmission fibers ( 31 ) being fixed orthogonally and rigidly in the plate ( 42 ) such that the fiber end faces exactly match the connection plane ( 45 ), and
• 3. The lens array ( 5 ) consists of a plane-parallel support plate ( 52 ) with collimation lenses ( 51 ) rigidly attached by cementing, the number of collimation lenses ( 51 ) and their position with the number and position of the transmitted fibers ( 31 ) in the fiber fixing device ( 4 ) and the parameters of the following transmission optics ( 71 ) are in agreement and the optical path length through the carrier plate ( 52 ) to the collimation lens ( 51 ) by adjusting the thickness of the carrier plate ( 52 ) to the aperture of the transmission fibers ( 31 ) and the The focal length of the transmitting optics ( 71 ) is adapted such that the laser waists of the beams ( 6 ) focused by the transmitting optics ( 71 ) coincide when they are superimposed in the measuring volume ( 8 ).

2. Device according to claim 1, characterized in that in the fiber fixing device ( 4 ) centrally between the transmission fibers ( 31 ) and along the optical axis given by the transmission optics ( 71 ) a further optical fiber ( 3 ) as a receiving fiber ( 32 ) for light transmission the receiver ( 9 ) is provided, light scattered on measurement objects in the measurement volume ( 8 ) being imaged onto the fiber end of the reception fiber ( 32 ) via the transmission optics ( 71 ) and an equivalent reception optics ( 72 ). 3. Device according to claim 2, characterized in that the receiving optics ( 72 ) has openings for the passage of the transmitting beam ( 6 ). 4. Device according to claim 1, characterized in that the fiber fixing device ( 4 ) and the lens array ( 5 ) are made of a uniform plane-parallel plate, the connecting plane ( 45 ) through highly accurate recesses ( 43 ; 55 ) on the one hand from the plate front for Fiber fixation and on the other hand is defined by the back of the plate for the lens frame. 5. Device according to claim 4, characterized in that the recesses for the lens frame as a tubular recess ( 55 ) up to the connection plane ( 45 ), the laser beams ( 6 ) from the transmission fibers ( 31 ) divergent into the respective tubular recess ( 55 ) emerge and are collimated by the collimation lens ( 51 ). 6. Device according to claim 5, characterized in that the collimation lenses ( 51 ) are spherical lenses. 7. Device according to claim 1, characterized in that the fiber fixing device ( 4 ) by means of a refractive index-adapted kit layer ( 54 ) is rigidly connected to the lens array ( 5 ). 8. Device according to claim 7, characterized in that the collimation lenses ( 51 ) are glued in the form of plano-convex lenses with their flat surface on the back surface of the carrier plate ( 52 ) in the light path. 9. Device according to claim 7, characterized in that both the fiber fixing device ( 4 ) and the lens array ( 5 ) are ground and polished for their cementing in the connection plane ( 45 ), with all fiber ends exactly in the fiber fixing device ( 4 ) are arranged in one plane and the optical path length of the composite of kit layer ( 54 ), carrier plate ( 52 ) and lens kit layer ( 53 ) to the collimation lens ( 51 ) can be adjusted in the lens array ( 5 ). 10. The device according to claim 7, characterized in that the fiber fixing device ( 4 ) is a plane-parallel plate ( 42 ) which is substantially halved along a straight line, and at least one of the partial plates ( 47 ) in the separating surface grooves ( 48 ) which are arranged orthogonally to the plate surfaces and are dimensioned such that the fibers ( 31 ; 32 ) are locked without play by the partial plates ( 47 ) during the subsequent joining and gluing of the partial plates ( 47 ). 11. The device according to claim 10, characterized in that the grooves ( 48 ) in the separating surface are rectangular grooves ( 48 ). 12. The device according to claim 10, characterized in that the grooves ( 48 ) in the separating surface are wedge-shaped grooves ( 48 ). 13. The device according to claim 10, characterized in that the grooves ( 48 ) in the separating surface are trapezoidal grooves ( 48 ). 14. The device according to claim 3 and 8, characterized in that the transmission fibers ( 31 ) from an integrated optical chip ( 21 ) are coupled, the input of which is fed by the fiber-coupled laser diode ( 1 ) and on which a branching device ( 22 ) and a phase modulator ( 23 ) for frequency shift between the two light waves of the transmission fibers ( 31 ) are present. 15. A method for producing a device for generating parallel collimated beams from a fiber-coupled laser diode, which are suitable for superimposition in a measurement volume by means of a transmitter optics for object lighting in laser Doppler devices, characterized in that

• 1. the collimation device is produced in two essential sub-processes, the manufacture of a fiber fixing device ( 4 ) and a lens array ( 5 ),
• 2. to produce the lens array ( 5 ), tubular recesses ( 55 ) for mounting collimation lenses ( 51 ) are made in a plane-parallel carrier plate ( 52 ), the positions and the depth of the tubular recesses ( 55 ) depending on the parameters of the transmission fibers used ( 31 ) and transmission optics ( 71 ) are adapted so that the laser beam bundles ( 6 ) entering the parallel tubular recesses ( 55 ) are superimposed on the transmission optics ( 71 ) with their laser waists in the measurement volume ( 8 ) and by the uniform depth the tubular recesses ( 55 ) a connection plane ( 45 ) parallel to the surface of the plane-parallel support plate ( 52 ) is generated, which represents the contact surface to the fiber fixing device ( 4 ),
• 3. for the manufacture of the fiber fixing device ( 4 ) in a plane-parallel plate ( 42 ) recesses ( 43 ) for exact fixing of the transmission fibers ( 31 ) coupled to the laser diode ( 1 ) are introduced, which reproducibly locking the fiber end faces in the connection plane ( 45 ) ensure, the positions of the recesses ( 43 ) to the axes of the tubular recesses ( 55 ) are aligned such that the axes of the transmission fibers ( 31 ) coincide with the axes of the tubular recesses ( 55 ) and the transmission fibers ( 31 ) in each case The connecting plane ( 45 ) opens into the tubular recesses ( 55 ).

16. The method according to claim 15, characterized in that the fiber fixing device ( 4 ) and lens array ( 5 ) are produced as a uniform plane-parallel plate, the recesses ( 43 ; 55 ) of the two components being introduced from different sides of the plane-parallel plate and in touch a virtual connection level ( 45 ). 17. The method according to claim 16, characterized in that the recesses ( 43 ) for receiving the fibers ( 31 ; 32 ) are each designed as a double cylinder, a smaller cylinder diameter which touches the connecting plane ( 45 ), only the fiber core ( 33 ) and acts as a stop when inserting the fibers ( 31 ; 32 ) compared to the larger cylinder diameter. 18. The method according to claim 16, characterized in that a so-called LIGA method is used to produce the recesses ( 43 ; 55 ). 19. The method according to claim 15, characterized in that the fiber fixing device ( 4 ) and lens array ( 5 ) from two different plane-parallel plates ( 42 ; 52 ) are made, the two different plates ( 42 ; 52 ) with respect to the axes of the fibers ( 31 ) and the tubular recesses ( 55 ) in the connection plane ( 45 ) are aligned with one another and glued together. 20. A method for producing a device for generating parallel collimated beams from a fiber-coupled laser diode, which are suitable for superimposition in a measurement volume by means of a transmitter optics for object lighting in laser Doppler devices, characterized in that

• 1. the collimation device is produced in two essential sub-processes, the manufacture of a fiber fixing device ( 4 ) and a lens array ( 5 ),
• 2. for manufacturing the lens array ( 5 )
  • 1. on a plane-parallel support plate ( 52 ) plano-convex collimation lenses ( 51 ) are glued, the position and focal length of which are adapted to the parameters of the incident beam ( 6 ) and the subsequent transmission optics ( 71 ) so that the collimation lenses ( 51 ) collimate Laser beams ( 61 ) are superimposed with their laser waists in the measurement volume ( 8 ) via the transmitting optics ( 71 ),
  • 2. the surface of the carrier plate ( 52 ) opposite the glued-on collimation lenses ( 51 ) is used as a connecting plane ( 45 ) for connecting the lens array ( 5 ) to the fiber fixing device ( 4 ), the laser beam ( 6 ) being set for the defined superimposition in the measuring volume ( 8 ) of suitable optical thickness consisting of carrier plate ( 52 ), collimation lens ( 51 ) and intermediate kit layer ( 53 ), said surface of the plate is ground flat until the necessary thickness of the carrier plate ( 52 ) is reached,
• 3. for the production of the fiber fixing device ( 4 )
  • 1. In a further plane-parallel plate ( 42 ) through recesses ( 43 ) for high-precision fixing of the transmission fibers ( 31 ) coupled to the laser diode ( 1 ) are introduced, which orthogonal locking of the transmission fibers ( 31 ) with respect to the plate surface in the recesses ( 43 ) ensure, the positions of the recesses ( 43 ) being aligned with the axes of the collimation lenses ( 51 ) such that the axes of the transmission fibers ( 31 ) match those of the collimation lenses ( 51 ),
  • 2. the transmission fibers ( 31 ) are each pushed into the recesses ( 43 ), the connection plane ( 45 ) predetermined by the rear plate surface being pierced by the transmission fibers ( 31 ), and then glued, and
  • 3. the ends of the transmission fibers ( 31 ) penetrating the rear plate surface are ground down to the level of the plate surface as connection plane ( 45 ),
• 4. the fiber fixing device ( 4 ) and the lens array ( 5 ) are brought into contact and glued to the plate surfaces defined for the connection plane ( 45 ), the axes of the fibers ( 3 ) being brought into line with those of the collimation lenses ( 51 ).

21. The method according to claim 20, characterized in that a further recess ( 43 ) for receiving a reception fiber ( 32 ) is introduced centrally between the recesses ( 43 ) for the transmission fibers ( 31 ). 22. The method according to claim 20 or 21, characterized in that the recesses ( 43 ) in the fiber fixing device ( 4 ) are made by introducing a laser bore ( 44 ). 23. The method according to claim 22, characterized in that the recesses ( 43 ) in the fiber fixing device ( 4 ) are cylindrical. 24. The method according to claim 22, characterized in that the recesses ( 43 ) in the fiber fixing device ( 4 ) are made conical. 25. The method according to claim 24, characterized in that the conical recesses ( 43 ) of the fiber fixing device ( 4 ) with its large diameter larger than the outer diameter of the fibers ( 31 ; 32 ) and with its small diameter in the connecting plane ( 45 ) the diameter of the fiber cores ( 33 ) can be adjusted, the sheath of the fibers ( 31 ; 32 ) serving as a centering aid and strain relief after the subsequent gluing. 26. The method according to claim 20 or 21, characterized in that the recesses ( 43 ) in the fiber fixing device ( 4 ) through

• 1. dividing the plane-parallel plate ( 42 ) used perpendicular to the plate surfaces into two partial plates ( 47 ),
• 2. Introduction of grooves ( 48 ) for receiving the fibers ( 3 ) in at least one of the parting surfaces of the partial plates ( 47 ) and
• 3. assembling the partial plates ( 47 ) after inserting the fibers ( 3 ) into the grooves ( 48 ),

be generated. 27. The method according to claim 26, characterized in that the grooves ( 48 ) are made wedge-shaped or trapezoidal and dimensioned such that when the partial plates ( 47 ) are joined together, the inserted fibers ( 3 ) are enclosed essentially without play and additionally glued.