DE102008050847A1 - Optical path length modulator - Google Patents

Abstract

An optical path length modulator (28; 1218; 228; 328), which can be used in particular in an optical coherence tomograph (10), has an optical window (40; 140; 240; 340) from which light emerges during operation of the wavelength modulator and re-entering after covering a variable optical path length. A first reflective surface (52; 152; 252; 352) is stationary and is imaged onto the first reflective surface by optics (42; 142; 242; 342,362). A second reflective surface (45; 145; 245; 345) is planar and movable. According to the invention, the optical system (42, 142, 242, 342, 362) is designed in such a way that light incident on the second reflective surface (45, 145, 245, 345) is at least substantially collimated.

Description

BACKGROUND OF THE INVENTION

1. Field of the invention

• a) einem optischen Fenster, aus dem beim Betrieb des Weglängenmodulators Licht austritt und nach Zurücklegen einer veränderbaren optischen Weglänge wieder eintritt,
• b) einer ersten reflektierenden Fläche, die ortsfest angeordnet ist,
• c) einer Optik, die das optische Fester auf die erste reflektierende Fläche abbildet, und
• d) einer zweiten reflektierenden Fläche, die plan und bewegbar angeordnet ist.

The invention relates to an optical path length modulator, in particular for use in an optical coherence tomograph, comprising:

• a) an optical window from which light emerges during operation of the path length modulator and re-enters after traveling through a variable optical path length,
• b) a first reflecting surface, which is arranged stationary,
• c) an optic, which images the optical solid on the first reflective surface, and
• d) a second reflective surface which is arranged plane and movable.

Such a path length modulator is known from an article of N. Delachenal et al. entitled "Robust and rapid optical low-coherence reflectometer using a polygon mirror", Optics Communications 162 (1999), pages 195-199 ,

2. Description of the state of the technique

optical Path length modulators are devices with which variably change the optical path length of light leaves. In general, optical path length modulators Requires that the optical path length is fast and continuous (or at least quasi-continuous) change. Both Most optical path length modulators changes the optical path length is periodic, with the repetition frequencies can be several kilohertz.

requires For example, optical path length modulators are incorporated in optical coherence tomograph to the optical path length to tune in light guided in a reference arm.

By Use is known fiber optic path length modulators, in which an optical fiber wound on a hollow cylinder is whose diameter can be changed piezoelectrically. With an expansion of the hollow cylinder, there is an extension the optical fiber and, consequently, an extension the optical path length that the light in the optical fiber travels. The larger the path length stroke, the smaller the frequency with which the optical path length can be modulated, and vice versa. This can be done with these Path length modulators do not match the optical path length modulate with big strokes and high frequencies. Such path length modulators are marketed by the Company OPTIPHASE.

In most known optical path length modulators the optical path length is modulated by means of moving mirrors. Thus, in a confocal sensor, which is marketed by Siemens under the trade name SISCAN ^® C containing a retro-reflector that executes in parallel with the direction of incidence of an incident light beam high frequency vibrations.

A similar arrangement is from an article of N. Baksh, entitled "An autocorrelator-interferometer used to determine the pulse width of a pulsed laser used in two-photon endoscopy", Thesis MIT, June 25, cita-table URI: http://hdl.handle.net/ 1721.1 / 32882 known. In the path length modulator described there, the light is deflected by means of a rotationally offset retroreflector onto a fixed plane mirror and reflected back into itself.

From the DE 199 63 161 A1 is an optical path length modulator for a fiber optic coherence tomography known, having two mutually parallel plane mirror, which are arranged on a rotating turntable. The path length modulator further includes a collimator lens that collimates light exiting an exit window of an optical fiber and directs it to the rotating mirror assembly. The collimated light beam reflected by the mirror assembly strikes a stationary plane mirror which reflects the light beam back onto the mirror assembly. The reflected light from there is imaged by the collimator lens back onto the exit end of the optical fiber.

adversely in this known arrangement is that during a complete rotation of the mirror assembly relatively long Dead times occur. By this one understands times, with which the Light for whatever reason are not used can. For example, in the known path length modulator the light is not usable on the backs of the rotating Mirror is falling. Besides, even outside the dead times the intensity of the exit window the optical fiber coupled light subjected to strong fluctuations. traceable this must be due to unavoidable location inaccuracies or during the operation occurring vibrations of the Spiegelanordndung. comes there is slight tilting of the two rotating Plan mirror, so the incident on the fixed mirror light no longer reflected back exactly in itself. The The exit end of the optical fiber is then no longer exactly imaged itself, but oscillates with the vibration frequency of the mirror.

An improvement in this regard is achieved in a Weglängenmodulator, as he from the initially mentioned article of N. Delachenal entitled "Robust and rapid optical low-coherence reflectometer using a polygon mirror" is described. In this known path length modulator, an exit window of an optical fiber is imaged by a lens arranged behind it onto a plane reference mirror. In the light path between a rotating polygon scanner and a cuboid glass prism are arranged. The glass prism acts as a retroreflector and causes light reflected by the polygon scanner to be reflected back onto it, so that it always falls perpendicular to the reference mirror. If, due to vibrations of the polygon scanner, the focus of the light shifts on the reference mirror, the optical conjugation between the reference mirror and the exit window of the optical fiber caused by the lens causes the image of the exit window arising on the reference mirror to always be returned to the reference image Exit window is displayed.

It However, it has been shown that in this known path length modulator unwanted intensity fluctuations of weglängenmodulierten Light can occur.

SUMMARY OF THE INVENTION

task The invention is therefore a Weglängenmodulator the to improve the type mentioned above such that intensity fluctuations of the weglängenmodulierten light can be further reduced.

Solved This object is achieved in a path length modulator according to the The preamble of claim 1 by a design of the optics such that light striking the second reflective surface is at least substantially collimated.

The Invention is based on the finding that in the from the beginning mentioned article of N. Delachenal path length modulator the Intensity fluctuations are due to that the changing optical path length between the collimator lens and the fixed reference mirror the optical Conjugation disturbs, d. H. the exit window of the optical Fiber is generally not exactly, but only smeared on imaged the reference mirror. As a result of the regression through the collimator lens on the exit window becomes this image smeared even further, leaving a not negligible Proportion of light can not be coupled into the fiber core.

By the inventive design of optics in such a way that on the moving second reflective surface incident light is at least substantially collimated is ensured that path length changes the light does not affect the image, that on the stationary first reflecting surface arises. In the inventive Path length modulator can therefore indeed the image of the optical Window due to positional inaccuracies and vibrations itself moving second reflective surface at different locations arise on the first reflective surface, however This picture always has the same size and quality regardless of the respective path length modulation. As a result, that too has finally got into the optical window re-coupled light, except for possibly occurring Dead times, always a constant intensity.

at The optical window may be the light exit window an optical fiber or an integrated optical waveguide act. However, it is also possible to use an aperture (one-hole), as in particular in optical devices with free jet propagation Use finds.

The reflective surfaces can be formed as a mirror be who has a mirror support and an applied on it have reflective coating. In the reflective surfaces can but it is also the interfaces between optically act denser and optically thinner media, as they occur at prisms.

The Optics can be designed as a collimator in the light path between the optical window and the second reflective surface is arranged. Such a collimator has positive overall Refractive power and therefore contains at least one lens or a curved mirror with a collecting effect.

The optics can be designed particularly simply if a plurality of third planar reflective surfaces are provided, which direct the light reflected by the movably arranged second reflecting surface back onto the collimator, which focuses the light onto the first reflecting surface and thus the image of the optical window on the first reflective surface causes. In this illustration, the collimator will thus pass twice, so that one can ensure with one collimator, on the one hand, the collimation according to the invention and, on the other hand, the imaging of the optical window on the first reflecting surface. The image of the optical window formed on the fixed first reflecting surface is also imaged back onto the optical window in this embodiment of the invention. Thus, positional inaccuracies or vibrations of the movably arranged second reflecting surface can not affect the coupling of the light into the optical window even in this embodiment ken.

Preferably is then at least one of the third reflective surfaces stationarily arranged so as to be incident collimated Light reflected back in itself. This is on the one hand advantageous because in this way, that of the movably arranged second surface reflected light is reflected back in and thus the same way back to the collimator takes like his first passage through the collimator towards the movable second reflective surface. In addition, will by such a stationary third reflective surface Make sure the light is on it first first reflective surface meets, already twice from the movable second surface was reflected. To the reflection at the first reflecting surface follows the light this way a second time, but in the opposite direction. Overall, the light is thus between the exit and the Entry into the optical window a total of four times movable from the arranged second surface is reflected. This results a particularly long Weglängenhub.

If the collimator both collimation and optical imaging caused by multiple passage, the first are reflective Surface and the optical window at least substantially coplanar arranged because both are located in the focal plane of the collimator.

By a targeted misalignment can be achieved that the image of optical window on the first reflective surface at a greater distance from the optical window is produced.

better but it will be in general if the first reflective Surface in the immediate vicinity of the optical window is arranged. In particular, the shortest distance between the first reflective surface and the optical window smaller than the largest transverse extent of the optical Be window.

Thereby is the beam path before and after the reflection at the stationary first reflective surface virtually identical, which for a better coupling of the light into the optical window leads. The distance between the optical window and its Picture on the stationary first reflective surface must only be such that shifts of this image, such as in particular by vibrations of the second movably arranged reflecting surface can arise, not to lead, That light already enters the optical window before it once was reflected at the first reflecting surface.

A particularly simple realization of a first reflective surface in the immediate vicinity of the optical window, if the optical window, the light exit window of an optical Fiber is a light-conducting fiber core and a Fiber cladding has. The first reflective surface can then be formed by a reflective coating, the is applied on an end face of the fiber cladding. Such optical fibers are in the market in connection with others Uses available. The property that the coating is reflective, but rather results as a by-product other technological requirements and is used in these applications so far not exploited.

Becomes for example, the second reflective surface by 45 ° an optical axis of the collimator and along this Axis oscillating back and forth moves, so are none third reflective surfaces required to ensure that the optically collimated light on the first stationary reflective surface can fall. In this case, must between the moving second reflective surface and the stationary first reflective surface only another part of the optics can be arranged, which is the collimated light focused on the stationary first reflective surface and thereby generates an image of the optical window there. Indeed can be achieved with such linearly moveable mirrors no high repetition rates and only a relatively short path length produce.

at In a preferred embodiment, the second reflective Surface therefore arranged rotatable about a rotation axis. Just with rotating reflective surfaces can be high-frequency path length modulation with large Create path length strokes. When turning can it also involves a torsional vibration, in which the second reflective surface preferably periodically changes its direction of rotation.

A rotatably mounted second reflective surface can on a support structure which can be set in rotation about the axis of rotation, in particular a turntable be arranged. On a turntable or one other suitable support structure can then be several second reflecting surfaces on a circular line concentric with the axis of rotation Arrange. The resulting arrangement is preferably regular built in the sense that each two adjacent second reflective Include surfaces at the same angle. Of the optical path length modulator then generates at one revolution the support structure a periodic modulation of the optical path length.

If the path length modulator has a plurality of third reflective surfaces, then a plurality of groups, each comprising a second and at least one of the third reflective surfaces, may be disposed together on the support structure.

So For example, it is possible for each group to have a second one and a third reflective surface facing each other enclose an angle of 90 °. Every group then forms a plane retroreflector, d. H. a reflector, the light incident in its plane of symmetry is always offset in parallel reflected back.

In front Especially in the case of rotating retroreflectors it can be cheap when that is on the stationary third reflective surface incident light propagates along a first propagation direction, which includes an angle to a second propagation direction, along which the light is between the collimator and the second reflective surface propagates, the axis of rotation parallel to one defined by the first and second propagation directions Level passes. This way you can prevent that the collimator arranged the propagation of light between the movable second reflective surface and the stationary arranged obstructed third reflective surface.

Generated can be such a tilted arrangement of the propagation directions by an inclined arrangement of the second and / or third reflective Surfaces. Even easier this can be achieved if the rotation axis itself is different from 90 ° Includes angle to the second propagation direction.

at In another embodiment, each group has one second and a third reflective surface on each other enclose an angle of 45 °. Such Group forms a reflector that always deflects incident light by 90 °.

According to one Another embodiment, the optics one of the Collimator different partial optics with collection effect on. This partial optics is in the light path between the first reflective surface and the second reflecting surface and so on designed to be from the second reflective surface reflected light on the first reflective surface focused.

at This embodiment is the rotatably arranged second reflecting surface thus in the collimated beam path between the collimator and the sub-optics. Because the light between the Exit from and entry into the optical window only twice from the moving second reflective surface is reflected, the Weglängenhub is a little smaller. Therefore the dead times are very short, since in this arrangement no rotating Groups of two or more reflective surfaces are required, which direct the light in a very specific direction, z. B. parallel to the direction of incidence or perpendicular to reflect.

BRIEF DESCRIPTION OF THE DRAWINGS

Further Features and advantages of the invention will become apparent from the following Description of an embodiment with reference to the drawings. Show:

1 a schematic representation of a coherence tomograph with an optical path length modulator according to the invention according to a first embodiment;

2 a fragmentary perspective view of the in the 1 shown path length modulator;

3 a lateral meridional section through the in the 1 shown path length modulator;

4 a plan view of an exit window of an optical fiber with a surrounding, provided with a reflective coating fiber cladding;

5 schematically a fragmentary plan view of the path length modulator in five different rotational positions of the retroreflectors;

6 a schematic representation of a second embodiment of a path length modulator according to the invention;

7 a schematic representation of a third embodiment of a path length modulator according to the invention;

8th a schematic perspective view of a fourth embodiment of a Weglängenmodulators invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

First embodiment

The 1 shows a schematic representation of an optical coherence tomograph 10 for surveying a measurement object 11 is provided. The coherence tomograph 10 contains a light source 12 , which may be, for example, a superluminescent diode. That from the light source 12 generated light is using a collection lens 14 in a first optical fiber 16 coupled with an optical coupler 18 connected is. The coupler 18 directs a portion of the in the first optical fiber 16 guided light into a second optical fiber 20 , which together with end-mounted lenses 22 . 24 a measuring arm 26 of the coherence tomograph 10 forms. The remaining part of the first optical fiber 16 guided light is from the coupler 18 in a third optical fiber 26 coupled together with an optical path length modulator to be explained later 28 a reference arm 30 of the coherence tomograph 10 forms.

In the reference arm 30 the light is reflected, the optical path length traveled by means of the path length modulator 28 is changed. The in the reference arm 30 reflected light is transmitted through the coupler 18 in a third optical fiber 31 coupled and a detector 32 fed. There, the reference light from the reference arm overlaps 30 with measuring light, the measuring object 11 reflected, over the lenses 22 . 24 back to the second optical fiber 20 coupled in and over the coupler 18 also the detector 32 was forwarded. The optical path length modulation in the path length modulator 28 allows a scanner-like measurement of the DUT 10 along one through the lenses 22 . 24 fixed optical axis of the measuring arm 26 ,

As the coherence tomograph 10 so far, apart from the path length modulator 28 , is known, is dispensed with a more detailed description of structure and function.

The following is the path length modulator 28 closer with respect to the 2 and 3 described, wherein the 2 a perspective section of the path length modulator 28 and the 3 shows a lateral meridional section.

The path length modulator 28 has a turntable 34 on, around a rotation axis 36 is rotatably arranged. On the turntable 34 are on a concentric axis of rotation 36 extending circle line several designed for a flat beam path retroreflectors 38 arranged evenly distributed. In the illustrated embodiment, the retroreflectors 38 formed as prisms whose base has the shape of a right-angled and isosceles triangle.

Between a light exit window 40 the third optical fiber 26 and the turntable 34 is a collimator lens 42 arranged that from the light exit window 40 emergent divergent reference light collimated. As best in the lateral meridional section of the 3 is recognizable, this is the reference number 44 denotes collimated light directly, ie, without interfering with optical surfaces, on one of the retroreflectors 38 , There it is first on a reflective surface 45 and then on another reflective surface 47 reflected. How to best in the 1 can recognize the collimated reference light due to the two-fold reflection in the retroreflector 38 180 ° in the symmetry plane of the retroreflector 38 deflected and onto a fixed plane mirror 46 directed.

As from the lateral Meriodionalschnitt the 3 shows, the axis of rotation runs 36 of the turntable 34 not perpendicular to the propagation direction of the collimated light 44 , but this includes an angle α <90 °. This is also the retroreflectors 38 with the reflective surfaces 45 . 47 inclined to the propagation direction of the collimated light 44 arranged. Consequently, the direction of propagation of the retroreflector extends 38 reflected and with the reference number 48 designated light not parallel to the propagation direction of the light 44 but includes an angle not equal to 2 · α for this purpose. Only in one projection along the axis of rotation 38 Both propagation directions are parallel, as in the 1 is recognizable. There is the tilt of the axis of rotation 36 not shown for reasons of clarity. The inclination of the axis of rotation 36 Make sure the stationary plane mirror 46 outside the beam path of the collimated light 44 can be arranged.

The plane mirror 46 is approximately perpendicular to the propagation direction of the of the retroreflector 38 reflected light 48 arranged so that this light is reflected back into itself and the light paths described above in reverse order back to the light exit window 40 the third optical fiber 26 travels. With exactly vertical orientation of the fixed plane mirror 46 to the propagation direction of the of the retroreflector 38 reflected light 48 would due to the identical beam path before and after the reflection on the stationary plane mirror 46 the exit window 40 the third optical fiber 26 through the collimator, twice penetrated by the light 42 imaged on itself. The rotation of the retroreflector 38 around the axis of rotation 36 can be neglected because of the many orders of magnitude higher speed of the light.

However, adjustment tolerances and vibrations of the retroreflector can not be neglected 38 due to its rotational movement about the axis of rotation 36 , The vibrations actually lead to slight displacements of the axis of rotation 36 so that from the retroreflector 38 reflected light 48 under certain circumstances no longer exactly perpendicular to the fixed plane mirror 46 thence. That reflected there Then light would take a slightly different path back towards the collimator 42 , As a result, the image of the exit window would become 40 no longer centered on the exit window without additional measures 40 arise, but more or less decentered this. For temporally varying misalignments, as caused by vibrations of the retroreflector 38 occur during its rotation, these decentrations would be with the vibrations of the retroreflector 38 correlated. The consequence of decentering the image of the optical exit window 40 are a deteriorated coupling of the reference light in the third optical fiber 26 , which translates into intensity fluctuation of the reference arm 30 led light makes noticeable.

In the path length modulator according to the invention 28 is therefore the stationary plane mirror 46 adjusted so that regardless of constant or time-dependent misalignments of optical elements in the beam path the image of the exit window 40 clearly offset from the exit window 40 arises. In the 4 showing a top view of the end of the third optical fiber 26 are through the fiber core of the third optical fiber 26 formed light exit window 40 and a fiber cladding surrounding the fiber core 50 recognizable. The face of the fiber mantle 50 is provided with a reflective coating having an at least substantially planar reflective surface 52 in the immediate vicinity of the exit window 40 forms. The reflective surface 52 is in the same plane as the exit window 40 and thus also in the focal plane of the collimator 42 ,

The picture of the exit window 40 arises in the inventive alignment of the stationary plane mirror 46 on the reflective surface 52 of the fiber jacket 50 , The resulting image at a given time is in the 4 shown as a gray background area and with 40 ' designated. This picture 40 ' migrates due to vibrations of the turntable 34 over the reflective coating 52 away, as with dotted circles 40 '' indicated for different times. In general, the area over which the picture passes 40 ' the exit window 40 wanders back and forth, be spatially limited, as in the 4 through a dashed circle 54 is indicated. That's why it can be enough for the function, only for the circle 54 To provide enclosed area with a reflective coating.

Alternatively, it is of course possible, a reflective surface 54 outside the third optical fiber 26 to arrange and z. B. as an additional stationary mirror to realize. The further, however, the picture 40 ' from the optical axis of the collimator 42 is removed, the worse is generally the image through the collimator 42 , If a picture smeared by aberrations relatively strong 40 ' then again through the collimator 42 on the exit window 40 is pictured, there is a risk that only a portion of the light in the third optical fiber 26 can be coupled.

As already briefly indicated above, the picture becomes 40 ' the exit window 40 now exactly on the exit window 40 through the collimator 42 displayed. That of the area 52 reflected light re-enters through the collimator 42 through, is at the retroreflector 38 reflected, at the fixed plane mirror 46 thrown back in and meets again on a retroreflector 38 , From there, the light returns to the collimator 42 and from this exactly on the exit window 40 focused.

That from the light exit window 40 Exiting light is thus before it returns to the light emission window 40 enters, once at the fixed plane mirror 46 , once at the on the fiber coat 50 applied reflective coating 52 and a second time at the fixed plane mirror 46 reflected. In between, the light passes through the collimator four times in total 42 as well as the retroreflector 38 , By passing four times through the retroreflector, the Weglängenhub, resulting from the movement of the retroreflector 38 results, also quadrupled. The illustration of the exit window 40 on the stationary reflective coating 52 of the fiber jacket 50 results in that despite the relatively long light path adjustment errors and vibrations of the turntable 34 the coupling of the light into the exit window 40 do not interfere.

The 5 schematically shows a fragmentary plan view of the path length modulator 28 in five different rotational positions of one of the retroreflectors 38 , For clarity, only one of the retroreflectors is shown and the inclination of the axis of rotation 36 not shown.

As indicated by an arrow in the left partial representation, it is assumed that the retroreflector 38 himself with the turntable 34 counterclockwise about the axis of rotation 36 rotates. In the various partial representations is clearly visible, like a ray of light after reflection at the retroreflector 38 parallel to the fixed plane mirror 46 directed and reflected back into it (apart from the targeted misalignment described in detail above). The optical path, the light between the outlet from the Kolli mator 42 and the reflection on the fixed plane mirror 46 depends on the rotational position of the turntable 34 as from the various partial representations of 5 becomes clear. Since the light in the way the whole way shown in the partial representations travels four times, a long Weglängenhub is achieved.

In the embodiment described above, the through the coating on the fiber cladding 50 formed reflective surface 52 a first reflecting surface on which the exit window 40 is shown. A second reflective surface, which is arranged planar and movable, is defined by the reflective surface 45 of the retroreflector 38 formed by the collimator 42 collimated light hits first. The other area 47 of the retroreflector 38 as well as the fixed plane mirror 46 Make up third reflective surfaces that make sure of that from the second reflective surface 45 reflected light back to the collimator 42 is directed.

Second embodiment

A similar arrangement of reflective surfaces as in the in the 1 to 5 embodiment shown is in which in the 6 shown embodiment provided. Identical or corresponding parts are designated by reference numerals increased by 100.

In contrast to the embodiment described above are in the in the 6 shown wavelength modulator 128 on the turntable 134 no in-plane retroreflectors, in which the reflective surfaces form an angle of 90 °, but arrangements of two at an angle of 45 ° to each other aligned plane mirrors 145 . 147 intended. The two plane mirrors 145 . 147 can of course be replaced by a pentaprism.

Due to the angle of 45 ° between the two plane mirrors 145 . 147 this will be on the plane mirror 145 incident collimated light after further reflection on the other plane mirror 147 deflected by a total of 90 ° and on the stationary plane mirror 146 directed. Due to this lateral deflection by 90 °, it is the path length modulator 128 not required, the axis of rotation 36 tilted to arrange.

Compared to in-plane retroreflectors 38 After a rotation angle of 20 °, a dead time is created, while the collimated light is created 44 from a group of plane mirrors 145 . 147 to the next changes. Furthermore, with the same size of achievable Weglängenhub is only about half as large as in the basis of 1 to 6 explained path length modulator 28 ,

But the construction is easier because of the tilting of the axis of rotation 136 can be waived. The arrangement of reflective surfaces 145 . 147 on the turntable 134 It is also very easy to create with the help of eight individual double-sided mirrored plates, each of which encloses an angle of 45 ° between them and on the axis of rotation 136 of the turntable 134 to meet.

Third embodiment

The 7 shows a section of an optical path length modulator according to a further embodiment in a schematic representation. The same or corresponding parts are designated by reference numerals increased by 200.

In contrast to the two embodiments described above are here on the turntable 234 no prisms or groups comprising several mirrors, but only individual plane mirrors 245 arranged. The rotating plane mirror 245 , respectively, the collimated light 244 is exposed, the light reflects toward a stationary retroreflector acting in a plane of symmetry 260 , This reflects the light offset parallel to the respective rotating plane mirror 245 back. From there, the light is perpendicular to the stationary plane mirror 246 directed, which reflects the light back into itself. Also in this embodiment, the exit window 240 on the near the exit window 240 located reflective surface 252 displayed. This image is then returned to the exit window 240 displayed. The stationary retroreflector 260 thus ensures a result similar to the beam path, as in the in the 1 to 5 shown path length modulator 28 is achieved.

The stationary retroreflector 260 and the fixed plane mirror 246 are in a direction perpendicular to the plane of the drawing 7 arranged in a manner one above the other, as is similar for the fixed plane mirror 46 in the 3 is shown. This can also be achieved by tilting the axis of rotation around the turntable 234 can be turned.

As in this embodiment, a lot of plane mirror 245 on the turntable 234 can be arranged, it is particularly suitable for applications in which high repetition rates are required with not too long Weglängenhub.

Also in this embodiment, the reflective surface formed by the coating on the fiber cladding 252 a first reflecting surface on which the exit window 240 is shown. A second reflecting surface, which is arranged plane and movable, is rotated by the rotating plane mirror 245 formed by the collimator 242 collimated light hits. The at the reflective surfaces of the retroreflector 260 Fixed third third reflective surfaces, which ensure that the light reflected from the second reflective surface back to the collimator form 242 is directed.

Fourth embodiment

The 8th shows in a perspective view essential parts of a Weglängenmodulators 328 according to a fourth embodiment. Similar to the one in the 7 shown path length modulator 228 are there on the turntable 34 several plane mirrors 345 arranged. In the 8th is just one of these plane mirrors 345 shown in different rotational positions. By tilting the axis of rotation or an equally acting inclined position of the plane mirror 345 on the turntable is achieved in this embodiment, that the spread of the rotating plane mirror 345 reflected light 348 not by the collimator consisting of two convergent lenses 342 is impaired.

In contrast to the embodiments described above is between the rotating plane mirror 345 and the fixed plane mirror 352 another collecting lens 362 arranged the incident collimated light 348 on the fixed plane mirror 352 focused. The picture of the exit window 340 thus arises directly on the fixed plane mirror 352 , Deformations, such as those caused by vibrations of the rotating plane mirror 345 caused in this embodiment do not lead to fluctuations in the return window in the exit window 340 coupled intensity, because of the optical conjugation between the exit window 340 and the fixed plane mirror 352 It is always ensured that when moving the plane mirror 345 over the stationary plane mirror 46 wandering image of the exit window 340 is reproduced exactly on this back.

In this embodiment, since the light is only twice from the rotating plane mirror 345 is reflected, the Weglängenhub is smaller than in the embodiments described above. For this, the dead times between the individual modulation cycles are very short.

Because of the rotating mirror 245 is located in the collimated beam path, which remains through the collimator 342 and the condenser lens 362 caused optical image unaffected by the position of each of the collimated light 344 exposed plane mirror 245 ,

In this embodiment, the stationary plane mirror provides 352 a first reflecting surface on which the exit window 340 is shown. A second reflecting surface, which is arranged plane and movable, is rotated by the rotating plane mirror 345 formed by the collimator 342 collimated light 344 meets.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 19963161 A1 [0008]

Cited non-patent literature

• - N. Delachenal et al. entitled "Robust and rapid optical low-coherence reflectometer using a polygon mirror", Optics Communications 162 (1999), pages 195-199 [0002]
• - N. Baksh, entitled "An autocorrelator-interferometer used to determine the pulse width of a pulsed laser used in two-photon endoscopy", Thesis MIT, June 25, cita-table URI: http://hdl.handle.net /1721.1/32882 [0007]
• N. Delachenal entitled "Robust and rapid optical low-coherence reflectometer using a polygon mirror" [0010]

Claims (19)

Optical path length modulator, in particular for use in an optical coherence tomograph ( 10 ), comprising: a) an optical window ( 40 ; 140 ; 240 ; 340 ), from which during operation of the path length modulator ( 28 ; 128 ; 228 ; 328 ) Light emerges and re-enters after covering a variable optical path length, b) a first reflecting surface ( 52 ; 152 ; 252 ; 352 ), which is arranged stationary, c) an optic ( 42 ; 142 ; 242 ; 342 . 362 ), which images the optical solid onto the first reflective surface, and d) a second reflective surface (FIG. 45 ; 145 ; 245 ; 345 ), which is arranged plane and movable, characterized in that the optics ( 42 ; 142 ; 242 ; 342 . 362 ) is designed such that on the second reflective surface ( 45 ; 145 ; 245 ; 345 ) incident light is at least substantially collimated. Path length modulator according to claim 1, characterized in that the optics is a collimator ( 42 ; 142 ; 242 ; 342 ) located in the light path between the optical window and the second reflecting surface (FIG. 45 ; 145 ; 245 ; 345 ) is arranged. Path length modulator according to claim 2, characterized in that a plurality of third planar reflecting surfaces ( 46 . 47 ; 146 . 147 ; 246 . 260 ) provided by the second reflecting surface ( 45 ; 145 ; 245 ) reflected light back to the collimator ( 42 ; 142 ; 242 ), which focuses the light onto the first reflecting surface ( 52 ; 152 ; 252 ). Path length modulator according to claim 3, characterized in that at least one of the third reflecting surfaces ( 46 ; 146 ; 246 . 260 ) is fixed so as to reflect incident collimated light back into itself. Path length modulator according to one of claims 3 or 4, characterized in that the first reflecting surface ( 52 ; 152 ; 252 ) and the optical window ( 40 ; 140 ; 240 ) are arranged at least substantially coplanar. Path length modulator according to one of the preceding claims, that the first reflective surface ( 52 ; 152 ; 252 ) in the immediate vicinity of the optical window ( 40 ; 140 ; 240 ) is arranged. (due to maladjustment and vibrations only small deviations occur) Path length modulator according to claim 6, characterized in that the shortest distance between the first reflecting surface ( 52 ; 152 ; 252 ) and the optical window ( 40 ; 140 ; 240 ) is smaller than the largest transverse extent of the optical window. Path length modulator according to one of the preceding claims, characterized in that the optical window ( 40 ; 140 ; 240 ) the light exit window of an optical fiber ( 26 ) having a light guiding fiber core and a fiber cladding ( 50 ), and that the first reflective surface ( 52 ; 152 ; 252 ) is formed by a reflective coating, which on an end face of the fiber cladding ( 50 ) is applied. Path length modulator according to one of the preceding claims, characterized in that the second reflecting surface ( 45 ; 145 ; 245 ; 345 ) about a rotation axis ( 36 ; 136 ) is rotatably arranged. Path length modulator according to claim 9, characterized in that the second reflecting surface ( 45 ; 145 ; 245 ; 345 ) on one about the axis of rotation ( 36 ; 136 ) rotatable support structure, in particular a turntable ( 34 ; 134 ; 234 ) is arranged. Path length modulator according to claim 9 or 10, characterized in that a plurality of second reflective surfaces ( 45 ; 145 ; 245 ; 345 ) on one to the axis of rotation ( 36 ; 136 ) are arranged concentric circle. Path length modulator according to claim 11, characterized in that each two adjacent second reflective surfaces ( 45 ; 145 ; 245 ; 345 ) include the same angle. Path length modulator according to claim 3 and any one of claims 10 to 12, characterized in that a plurality of groups each having a second ( 45 ; 145 ) and at least one of the third ( 47 ; 147 ) reflective surfaces, together on the support structure ( 34 ; 134 ) are arranged. Path length modulator according to claim 13, characterized in that each group has a second ( 45 ) and a third reflective surface ( 47 ), which enclose an angle of 90 ° with each other. Path-length modulator according to claim 4 and claim 14, characterized in that the force applied to the stationary third reflecting surface ( 47 ) incident light along a first propagation direction ( 48 ) extending at an angle to a second propagation direction ( 44 ), along which the light between the collimator ( 42 ) and the second reflective surface ( 45 ) and that the axis of rotation ( 36 ) parallel to one extends through the first and second propagation direction defined plane. Path length modulator according to claim 15, characterized in that the axis of rotation ( 36 ) an angle different from 90 ° (α) to the second propagation direction ( 44 ). Path length modulator according to claim 12, characterized in that each group has a second ( 145 ) and a third reflective surface ( 147 ), which enclose an angle of 45 ° to each other. Path length modulator according to claim 2, characterized in that the optics ( 342 . 362 ) one of the collimator ( 342 ) different partial optics ( 362 ) having collecting action, which in the light path between the first reflective surface ( 352 ) and the second reflective surface ( 345 ) and is designed so that they from the second reflective surface ( 345 ) reflected light on the first reflective surface ( 352 ) focused. Optical coherence tomograph comprising: a) a light source ( 12 ), b) a light divider ( 18 ), c) a detector ( 32 ), d) a measuring arm ( 26 ) and e) a reference arm ( 30 ) in which an optical path length modulator ( 28 ; 128 ; 228 ; 328 ) is arranged according to one of the preceding claims.