WO2007025834A1

WO2007025834A1 - Interferrometric measuring device

Info

Publication number: WO2007025834A1
Application number: PCT/EP2006/065007
Authority: WO
Inventors: Pawel Drabarek; Stefan Franz
Original assignee: Robert Bosch Gmbh
Priority date: 2005-09-01
Filing date: 2006-08-03
Publication date: 2007-03-08
Also published as: DE102005041491A1

Abstract

Interferrometric measuring device in a Mach-Zehnder arrangement comprising a light source and a beam splitter, which splits the coupled-in light beam from the light source into two partial beam paths, a deflection unit and a second deflection unit, which combine the partial beam paths in a second beam splitter, wherein the partial beam paths can interfere to different extents on account of adjustable path differences, and at least one light exit for forwarding the interference pattern for analysis by means of evaluation device, wherein the partial beam path is folded at one or a plurality of locations and the optical path length can be varied by a displaceable reflector arrangement in the deflection unit, wherein the path lengths in both partial beam paths can be set with an identical length. This arrangement enables an arbitrarily broad variation of the optical path differences in the interferometer without adversely influencing the polarization properties of the light.

Description

Interferometric measuring device

State of the art

Interferometric measuring device in Mach-Zehnder arrangement with a light source and a beam splitter which divides the coupled light beam of the light source into two partial beam paths, a deflection unit and a second deflection unit, which merge the partial beam paths in a second beam splitter, wherein the partial beam paths due to adjustable path differences in can interfere with different degrees, and at least one light exit for forwarding the interference pattern for analysis by means of an evaluation device.

In the known Mach-Zehnder interferometer, which is made up of components such as mirrors and beam splitter plates, the two partial beam paths form a parallelogram. Metrological path differences are achieved by refractive index changes. Thus, for example, a comparison of refractive index of liquids or precise pressure measurements of gases can be realized. The disadvantage here is that there is currently no way to change the optical path difference by changing the position of the components.

It was only through the combination of fiber-optic components, collimators and acousto-optic modulators that it became possible to geometrically change the optical path length in the two partial beam paths.

DE 102 44 553 B3 describes such an interferometric measuring device for detecting the shape, the roughness or the distance of the surface of a measurement object with a modulation interferometer, which is supplied with short-coherent radiation from a light source. This radiation is split in a first beam splitter into a first partial beam path guided via a first arm and a second partial beam path guided via a second arm. One partial beam path is compared to the other partial beam path by means of a modulation device in its light phase or light frequency and thereby passes through an unspecified delay line. Subsequently, the two partial beam paths are combined at a further beam splitter of the modulation interferometer.

DE 198 08 273 A1 also describes an interferometric measuring device for detecting the shape, the roughness or the distance of the surface of a measuring object, in which a Mach-Zehnder arrangement is used in one embodiment variant.

Other prior art interferometric measuring devices are constructed entirely of fiber-coupled elements. The optical path difference is set by a delay line (delay line), wherein the beam is coupled out of the optical fiber, reflected on a prism and coupled back into an optical fiber.

A disadvantage of these arrangements is that with fiber optic elements within the partial beam paths in the interferometer, the polarization properties of the light are adversely affected, which can lead to failure of the interferometer.

It is therefore an object of the invention to provide an interferometric measuring device ready, which does not have the above-mentioned disadvantages, but still allows an arbitrarily wide variation of the optical path differences.

Advantages of the invention

The object is achieved in that the partial beam path is folded at one or more locations and the optical path length can be varied by a displaceable reflector arrangement in the deflection unit, wherein the path lengths in both partial beam paths are set to be the same length. The folding allows the partial beam path to be guided into the displaceable reflector arrangement and back again. By moving the reflector arrangement, the optical path length of the partial beam path is changed. In this case, the actual change in the optical path length of the partial beam path and thus the path difference to the second partial beam beam path of the Mach-Zehnder arrangement is added to the change in the path of the displaceable reflector arrangement entering and leaving the path. the proportion of the partial beam path. The arrangement allows any geometric path differences between the partial beams to be set. Since no fiber-optic elements have to be used for this purpose, the polarization properties of the light are maintained, which is achieved in particular by the folding in both partial beam paths.

If the light beam is folded in the variable partial beam path in such a way that it runs parallel to itself over a partial section, the optical path length of the partial beam path can be varied by simply displacing the displaceable reflector arrangement along the axis of the light beam. Even if the position of the displaceable reflector arrangement is changed, the reflected beam impinges on the same location, for example of a subsequent deflecting mirror or of a subsequent beam splitter, so that its position does not have to be adjusted as a function of the setting of the displaceable reflector arrangement.

An implementation of the invention to be realized with a few components can be realized in that the beam folding in the variable partial beam path in the deflection unit is carried out by means of a rigid deflection mirror and the displaceable reflector arrangement. With this arrangement, the parallelism of the incoming and outgoing in the reflector array light beam can be achieved. In this case, the deflection unit is preferably arranged in a corner of the parallelogram of the Mach-Zehnder interferometer, since either the incident portion of the light beam can pass directly into the displaceable reflector arrangement without further optical aids or, if the rigid deflection mirror inserted into the incident part of the partial beam path is, the reflected portion of the light beam directly to the beam splitter, in which the two partial beam paths are brought to interference, can pass.

In a preferred embodiment, the displaceable reflector arrangement has a triple prism, which is held in a triple prism version, and a linear drive. The triple prism ensures that the light beam reflected by the displaceable reflector arrangement runs parallel to the incident light beam. Angular or guide errors of the linear guide have no influence on the parallelism. With the linear drive, the displaceable reflector assembly can be moved exactly in the beam direction. - A -

In a specific embodiment, the linear drive of the displaceable reflector arrangement has a threaded spindle and a servomotor. By the servo motor, the desired path difference between the partial beam paths can be adjusted by means of a corresponding electronic control. The adjustment can be done manually or, for example, in automatic interferometer operation, by a corresponding control unit in dependence on the measurement result or a predetermined measurement routine. Through the threaded spindle, the motor rotation is converted into a linear movement. In this case, the propulsion of each motor rotation can be specified by the pitch of the threaded spindle and so a very feinstufϊge adjustment of the displacement of the reflector assembly can be achieved.

In a variant of the interferometric measuring device, the deflecting unit may have a rigid deflecting mirror and a reflector arrangement in the second partial beam path. The two partial beams thus go through the same optical components, which can be achieved an exact balance of the arms.

It is particularly advantageous if the reflector arrangement of the deflection unit is designed as a hollow triple mirror. The hollow triple mirror ensures that the light beam emerging from the reflector arrangement is reflected parallel to the incoming light beam, whereby mounting tolerances are compensated.

If the light coupling into the interferometric measuring device by means of a light-guiding fiber and a collimator, so that a particularly compact measuring device can be realized. Furthermore, this allows a quick change of the light source to adapt to the measurement task.

If the light emission from the interferometric measuring device is carried out by means of a collimator and a light-guiding fiber, the measurement and the evaluation can take place in a separate detector or in a separate evaluation unit. This achieves high flexibility.

In further embodiment variants, the deflection unit can have one or more auxiliary mirrors and / or prisms for coupling into and / or for decoupling from the displaceable reflector. have reflector arrangement. It is thus possible that the displaceable reflector arrangement does not have to be arranged in the corners of the beam parallelogram typical for Mach-Zehnder interferometers. Rather, it can be introduced into a straight section of the partial beam path, wherein, for example, an auxiliary mirror directs the incident beam to the displaceable reflector arrangement, and a further auxiliary mirror reflects the emergent beam back into the original axis of the partial beam path. The overhead of required components may be useful if, for example, in large desired path changes an arrangement in the corner of the parallelogram for reasons of space is not possible. The arrangement can also be used if the displaceable reflector unit is provided in a corner of the parallelogram, but for structural reasons, for example, the displacement can not take place parallel to the incoming or outgoing beam. By suitable deflection of the partial beam, the propagation direction and thus the displacement direction of the displaceable reflector unit can be carried out, for example, at an angle of 45 ° to the incident direction of the partial beam.

For certain measuring tasks, it may be advantageous if beam folding and the variation of the optical path length can be carried out by means of displaceable reflector arrangements in both partial beam paths.

An inexpensive interferometer structure with a reduced number of components can be achieved by causing the partial beam path in one of the light exits to interfere with the non-reflected portion of the beam entrance from the light source. For this purpose, the displaceable reflector arrangement can be arranged directly behind a first beam splitter and the reflected light beam in a second beam splitter, which is arranged in the extension of the optical axis between the light source and the first beam splitter, brought to interference. The non-varied partial beam passes through the first beam splitter and impinges directly on the second beam splitter.

While retaining the advantage of the two freely accessible jet outlets, the beam path can be folded like a Michelson interferometer. The interferometer offers the possibility of setting large differences in the path between the partial beam paths. The displaceable reflector unit can be constructed equal to the described reflector units. drawing

The invention will be explained in more detail below with reference to an exemplary embodiment shown in the figures. Show it:

Figure 1 is a schematic representation of a Mach-Zehnder interferometer according to the

State of the art,

FIG. 2 is a schematic representation of an embodiment variant of a machine

Zehnder interferometer in an inventive embodiment,

FIG. 3 is a schematic representation of an embodiment variant of a machine

Zehnder interferometer with optical fiber coupling,

FIG. 4 is a sectional view of a machine according to the invention.

Zehnder,

FIG. 5 is a schematic representation of an embodiment variant of a machine

Zehnder interferometers with auxiliary mirrors,

6 shows a schematic representation of a further embodiment of a

Mach-Zehnder interferometers with auxiliary mirrors,

Figure 7 shows a schematic representation of a Mach-Zehnder interferometer with a reduced number of deflecting mirrors

FIG. 8 is a schematic representation of another variant of a Mach-Zehnder

Interferometers with reduced number of deflecting mirrors.

Description of the embodiments

Figure 1 shows a schematic representation of a Mach-Zehnder interferometer according to the prior art. As main components, this arrangement includes a light source 10 and a beam splitter 20 which divides the coupled light beam of the light source 10 into two partial beam paths 21, 22. In a deflection unit 30 and a second deflection unit 40, which in the simplest case may each be a plane mirror, the partial beam paths 21, 22 merge in a second beam splitter 50, wherein the partial beam paths 21, 22 may interfere due to gear differences. The thus modulated light can be analyzed at one or both light exits 60 of the interferometer arrangement or for be decoupled from further use. The analysis is preferably carried out in a detector.

The embodiment of a Mach-Zehnder interferometer shown schematically in FIG. 2 shows an interferometric measuring device 1 in an inventive embodiment.

In the example shown, the deflecting unit 30 is constructed from a rigid deflecting mirror 31 and a displaceable reflector unit 32 in comparison to the arrangement shown in FIG. The optical path is folded in the partial beam path 21 in such a way that the displacement of the displaceable reflector unit 32 does not change the direction of the beams during the displacement. Only the path length is varied. In the exemplary embodiment shown, the deflection unit 40 is also constructed in the partial beam path 22 from a rigid deflection mirror 41 and a stationary reflector unit 42.

In certain cases, it may be necessary for such variable beam folding to be used in both partial beam paths. This makes it possible to make the optical path in both partial beam paths of the same length. It is particularly appropriate to replace the deflecting units 30, 40 at the corners of the known Mach-Zehnder interferometer by such arrangements.

The advantage of this arrangement is that the difficult-to-control polarization influence of fiber-optic components within the partial beam paths 21, 22, which are usually used for modulation, is avoided and, at the same time, the state of the interferometer adjustment is more easily adjustable.

FIG. 3 is a schematic representation of an embodiment variant of a Mach-Zehnder interferometer in which the light coupling into the interferometric measuring device 1 is carried out by means of a light-guiding fiber 11 and a collimator 12 in contrast to the variant shown in FIG. The light extraction from the Mach-Zehnder arrangement of the interferometric measuring device 1 takes place at the two light exits 60 in the example shown by means of a collimator 61 and a light-guiding fiber 62. Within the Mach-Zehnder interferometer, the first beam splitter 20 is designed as a beam splitter cube. The one partial beam path 21 initially strikes the displaceable reflector unit 32, which has a triple prism 32.1, which is held in a triple prism version 32.2, which is guided in a linear bearing. The triple prism 32.1 has three reflector surfaces, which are arranged orthogonal to each other and therefore reflect the light beam exactly in the same direction back.

The displacement takes place by means of a linear drive 32.3 parallel to the axis of the partial beam path 21. In the example shown, the linear drive 32.2 of the displaceable reflector assembly 32 of a threaded spindle 32.4 and a servomotor 32.5 constructed.

In the example shown, the deflecting unit 40 has a rigid deflection mirror 41 and a likewise fixed reflector arrangement 42, which is designed as a hollow triple mirror. Similar to the triple prism 32.1, the reflective surfaces are also arranged orthogonally here and can reflect the light back exactly in the same direction.

4 shows a sectional view of an enlarged according to the invention Mach-Zehnder arrangement is shown. The interferometric measuring device 1 is designed as a solid block of metal or glass ceramic, are incorporated in the channels in which the partial beam paths 21, 22 extend. In specially provided recesses are the optical components, such as beam splitters 20, 50, deflecting units 30, 40 with the individual components, such as rigid deflecting mirrors 31, 41 as the displaceable reflector assembly 32 in the variable partial beam path 21 and the fixed reflector assembly 42 in the partial beam path 22 of the extended Mach-Zehnder arrangement introduced. If necessary, as shown, additional optical components 70 may be incorporated into the device.

The light is coupled from a light source 10, not shown here, by means of a light-guiding fiber 11 and passes through a collimator 12. The light beam splits in the beam splitter 20 into the two partial beam paths 21, 22 and, in the example shown, passes through another optical component 70 first encounters the rigid deflecting mirror 31 of the deflecting unit 30 and is guided in the displaceable reflector assembly 32, which is designed as a triple prism 32.1. This reflects the light exactly in the same Direction back toward the second beam splitter 50, which is designed as a beam splitter plate. In the other branch of the interferometer arrangement of the partial beam path 22 is passed after passing through an optical device 70 in the direction of the reflector assembly 42 of the deflection unit 40, which is designed as a solid triple mirror. After reflection, the partial beam path 22 is reflected at the rigid deflection mirror 41 in the direction of the second beam splitter 50 and can there interfere with the partial beam path 21. At the two light exits 60 beam couplings 63 are arranged for the light-guiding fibers 62.

The linear displacement of the displaceable reflector arrangement 32 takes place by means of a linear drive 32.3. The triple prism 32.1 is held in a triple prism socket 32.2, which is guided linearly in a corresponding recess. The triple prism version is rigidly connected to an actuator of the linear drive 32.3.

FIGS. 5 and 6 show a schematic representation of variants of a Mach-Zehnder interferometer in which the deflection unit 30 has one or more auxiliary mirrors 33, 34 and / or prisms for coupling in and / or decoupling from the displaceable reflector arrangement 32.

Figures 7 and 8 show a schematic representation of a respective Mach-Zehnder arrangement with a reduced number of deflecting mirrors. In the variants shown, the partial beam path 21 in one of the light exits 60 with the non-reflected portion of the beam entrance from the light source 10 can be made to interfere.

The convolution can also lead to an interferometer arrangement which resembles a Michelson interferometer. Maintaining the advantage of the two freely accessible jet outlets 60 in the Mach-Zehnder arrangement, the beam path is folded.

With the illustrated embodiments, the known Mach-Zehnder arrangement can be adapted in an interferometric measuring device in a wide range of the respective measurement task. Only relatively simple optical components are required. In this case, the variation of the optical path differences in the partial beam paths, depending on the measurement task, is possible in a wide range without negatively influencing the polarization properties of the light.

Claims

claims

1. Interferometric measuring device (1) in Mach-Zehnder arrangement with a light source (10) and a beam splitter (20) which divides the coupled light beam of the light source (10) into two partial beam paths (21, 22), a deflection unit (30) and a second deflection unit (40), which merge the partial beam paths (21, 22) in a second beam splitter (50), wherein the partial beam paths (21, 22) can interfere to varying degrees due to adjustable gait differences, and at least one light exit (60). for forwarding the interference image for analysis by means of an evaluation device, characterized in that the partial beam path (21) is folded at one or more locations and the optical path length by a displaceable reflector assembly (32) in the deflection unit (30) is variable, wherein the path lengths in Both partial beam paths (21, 22) are the same length adjustable.

2. Interferometric measuring device (1) according to claim 1, characterized in that in the variable partial beam path (21) of the light beam is folded such that it runs parallel to itself over a partial distance.

3. Interferometric measuring device (1) according to one of claims 1 or 2, characterized in that the beam folding in the variable part of the beam path (21) in the deflection unit (30) by means of a rigid deflecting mirror (31) and the displaceable reflector assembly (32) is executed ,

4. Interferometric measuring device (1) according to one of claims 1 to 3, characterized in that the displaceable reflector arrangement (32) has a triple prism (32.1), which is held in a triple Prisma (32.2), and a linear drive (32.3).

5. Interferometric measuring device (1) according to one of claims 1 to 4, characterized in that the linear drive (32.3) of the displaceable reflector arrangement (32) has a threaded spindle (32.4) and a servomotor (32.5).

6. Interferometric measuring device (1) according to one of claims 1 to 5, characterized in that the deflection unit (40) has a rigid deflection mirror (41) and a reflector arrangement (42).

7. Interferometric measuring device (1) according to one of claims 1 to 6, characterized in that the reflector arrangement (41) of the deflection unit (40) is designed as Hohltripel- mirror.

8. Interferometric measuring device (1) according to one of claims 1 to 7, characterized in that the light coupling into the interferometric measuring device (1) by means of a light-guiding fiber (11) and a collimator (12) is executed.

9. Interferometric measuring device (1) according to one of claims 1 to 8, characterized in that the light exit (60) from the interferometric measuring device (1) by means of a collimator (61) and a light-guiding fiber (62) is executed.

10. Interferometric measuring device (1) according to one of claims 1 to 9, characterized in that the deflecting unit (30) one or more auxiliary mirrors (33, 34) and / or prisms for coupling in and / or out of the displaceable reflector assembly ( 32).

11. Interferometric measuring device (1) according to one of claims 1 to 10, characterized in that a beam folding and the variation of the optical path length by means of displaceable reflector arrangements in both partial beam paths (21, 22) is feasible.

12. Interferometric measuring device (1) according to one of claims 1 to 11, characterized in that the partial beam path (21) in one of the light exits (60) with the unreflected portion of the beam entrance from the light source (10) is brought to interference.

13. Interferometric measuring device (1) according to one of claims 1 to 12, characterized in that the beam path is folded similar to a Michelson interferometer.