Apparatus and method for measuring alignment errors of directional beam sources

Abstract

An apparatus for measuring alignment errors of a laser diode or other directional beam source (12) includes a holder (22) for the beam source (12) rotatably mounted about an axis of rotation (18) by a drive (18). The apparatus also includes a first spatially resolved radiation sensor (36), a beam splitter (26) that splits a beam (24) generated by the beam source (12) into a first partial beam (28) and a second partial beam (30), and focusing optics (32). The focusing optics is positioned in the radiation path of the first partial beam (28) and has a focal plane in which the first radiation sensor (36) is positioned. A second spatially resolved radiation sensor (38) is positioned in the radiation path of the second partial beam (30). The computing device (40) calculates the tilt (d) and lateral shift (α) of the beam (24) generated by the beam source (12) from a first position on the first radiation sensor (36) swept by the first partial beam (28) during rotation of the beam source (12), and from a second position on the second radiation sensor (38) swept by the second partial beam (30) during rotation of the beam source (12).

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for measuring alignment errors in laser diodes and similar directional beam sources. The alignment errors may be tilt and displacement in particular. [Background technology]

[0002] Laser diodes and similar directional beam sources are often secured, such as by adhesive bonding, to a mount that is then installed within the overall optical system. The outer surface of the mount is precision machined to allow the mount to be installed with the desired alignment within the overall optical system.

[0003] Alignment errors that adversely affect the functioning of an optical system can occur if the optical axis of a beam source is not precisely aligned with the mechanical axis of the mount during installation of the mount to said optical system. Therefore, it is known practice to adjust the beam source before it is adhesively bonded to the mount. However, this type of adjustment is complex and significantly increases the cost of the component.

[0004] WO 2019 / 224346 A2 discloses a method for rotating a mount together with an active beam source around a rotation axis and observing the circular movement of the radiation spot produced on a radiation sensor in two spaced apart planes. The alignment error can be estimated from the diameter of the circle of incident light detected by the radiation sensor. These planes are generated or defined by adjusting the back focal length of the light beam using a variable optical unit. If the measured alignment error is not within tolerance, the outer surface of the mount is post-machined, i.e., by turning, milling, or grinding (fine-tuning operation, also known as fine-tuning turning), so that the mechanical axis of the mount is finally aligned with the optical axis of the beam source.

[0005] The orientation of the optical axis of the beam source can only be measured sequentially with known methods, since the intensity in two planes must be detected successively. Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION The problem solved by the present invention is therefore to specify an apparatus and method for measuring alignment errors of a directional beam source, whereby the required measurement time can be reduced. [Means for solving the problem]

[0007] Regarding the apparatus, the problem is solved by an apparatus for measuring alignment errors of a directional beam source, the apparatus comprising: a mount for the beam source; a first spatially resolving radiation sensor; and a beam splitter configured to split a beam generated by the beam source into a first and a second component beam. The apparatus also comprises a focusing optics unit arranged in the beam path of the first component beam, the focusing optics unit having a focal plane on which the first radiation sensor is arranged. A second spatially resolving radiation sensor is arranged in the beam path of the second component beam. A drive of the apparatus is configured to effect relative movement about an axis of rotation between the first mount and the second other part of the apparatus. The computing means is configured to calculate tilt and lateral deviation of the beam generated by the beam source, using a first position on the first radiation sensor swept by the first component beam during rotation of the beam source relative to said other part of the apparatus, and using a second position on the second radiation sensor swept by the second component beam during rotation of the beam source relative to said other part of the apparatus.

[0008] The invention is based on the insight that the tilt and displacement of a beam generated by a beam source can be measured simultaneously and independently of one another if the beam is split into two component beams and the focal position of the first component beam is detected by a first radiation sensor during rotation of the mount about a central axis, whereas the second component beam is detected by a second radiation sensor but is not focused. By measuring the tilt and displacement simultaneously, the required measurement time can be significantly reduced.

[0009] Since the directional beam is nearly collimated, the angle can be converted to a position on the first radiation sensor by focusing the first component beam with a focusing optics unit. As a result, all beams incident on the focusing optics unit along the same direction of incidence are focused to the same point, whose position on the first radiation sensor is determined by the direction of incidence. Lateral displacement of the beam does not affect this part of the measurement, as it does not change the direction of incidence.

[0010] In contrast, the position at which the unfocused beam strikes the second radiation sensor depends on both the beam misalignment and tilt. Because the tilt is measured by the first radiation sensor, it can be easily removed by calculation from the measurement by the second radiation sensor, so that this second part of the measurement gives the lateral misalignment between the mechanical axis of the mount and the optical axis of the beam.

[0011] The alignment of the radiation sensors with respect to the rotation axis is not important during the two partial measurements, since only the diameter of the incident circle resulting in each case is evaluated. The position of the incident circle on each radiation sensor is not necessary for the calculation of tilt and displacement.

[0012] If the apparatus includes an imaging optical unit arranged in the beam path of the second component beam and configured to image the beam source onto the second radiation source, there is no need to calculate out the tilt when calculating the shift, since in that case the position at which the second component beam is incident on the second radiation sensor depends only on the shift and not on the tilt.

[0013] If such an imaging optical unit is provided, it can be configured to image the beam source onto the second radiation sensor in a demagnifying or enlarged manner. The decision to demagnify or enlarge depends, inter alia, on the radiation sensor and on the properties of the beam, such as its diameter and its intensity profile. A large beam cross-section can be useful for detecting small displacements, in which case the sensor area must be sufficiently large. When considering an intensity profile that deviates significantly from the shape of a Gaussian beam, optionally with secondary maxima, a large diameter can make it difficult to determine its position on the sensor, so demagnification can be advisable in such cases. The scale of the image generation is usually specified as fixed, but can also be variably adjustable.

[0014] Additionally or alternatively, the device may include an afocal optical unit, for example in the form of a Keplerian telescope, arranged in the beam path of the beam generated by the beam source, of the first component beam, or of the second component beam, with which the angle and / or diameter of the beam can be set.

[0015] Advantageously, the device comprises a beam deflection unit for deflecting the second component beam so that it runs at least approximately parallel to the first component beam. This allows the device to have a particularly compact mechanical configuration. For example, the beam deflection unit can be a deflection prism or a deflection mirror.

[0016] Preferably, only the mount in which the beam source is accommodated is rotated by the drive, however, it is also conceivable that the mount with the beam source remains stationary and the arrangement comprising the beam splitter, the focusing optics unit and the radiation sensor is rotated around an axis of rotation.

[0017] Once the tilt and misalignment are measured, the beam source can be aligned with respect to the axis of rotation so that any remaining residual alignment error is tolerable.

[0018] If the beam source and the mount are adhesively bonded to one another before the measurement is performed, the mount can be post-machined to change its mechanical axis. For this purpose, the apparatus includes a machining tool configured to machine the outer surface of the beam source mount so that the mechanical longitudinal axis of the mount extends parallel to the optical axis of the beam source. Such tools are known from conventional fine turning.

[0019] On the other hand, if measurements are performed before the beam source and mount are connected, the measurement results can be used to first optimally align the beam source and mount relative to each other, and only then can these components be bonded to each other. In this regard, a directional bonding process can be used. Here, a dispenser is used to first apply adhesive to the gap between the beam source and the mount before performing the measurement and final alignment. Preferably, in a prior step, the spatial orientation of the mount is first measured optically or tactilely. In doing so, the mount can be brought to the desired position, for example, relative to a rotation axis or any other mechanical reference. The beam source is then aligned with respect to the mount using the apparatus according to the present invention and an alignment chuck, hexapod, piezo actuator, or any other suitable alignment means. The alignment is performed until the tolerance specifications for translation and rotation are met. After the alignment process is complete, the adhesive is cured using a UV light source.

[0020] A method for measuring alignment errors of a directional beam source and solving the problems of the present invention includes the following steps: a) The beam source is inserted into the mount and relative rotation is caused about the axis of rotation. b) Simultaneously with step a), the beam generated by the beam source is split into a first component beam and a second component beam by a beam splitter. c) The focusing optics unit directs the first component beam onto a first spatially resolved radiation sensor located in the focal plane of the focusing optics unit. d) The second component beam is directed towards a second spatially resolving radiation sensor. e) The tilt and lateral shift of the beam generated by the beam source are calculated using a first position on the first radiation sensor swept by the first component beam during the relative rotation and a second position on the second radiation sensor swept by the second component beam during the relative rotation of the beam source.

[0021] Exemplary embodiments of the invention are explained in detail below with reference to the drawings, in which: [Brief explanation of the drawings]

[0022] [Figure 1a] 1 shows a schematic diagram of a device according to the invention according to a first exemplary embodiment, where it is implied that the optical axis of the beam extends coaxially with the axis of rotation. [Figure 1b] 2 shows a top view of a first radiation sensor and the focal spot generated therein; [Figure 1c] 10 shows a top view of a second radiation sensor and the light spot generated therein; [Figure 2] 1a-1c show diagrams corresponding to those of FIGS. 1a-1c, but with a laterally offset beam generated by a laser diode. [Figure 3] 1a-1c when the light beam generated by the laser diode is tilted. [Figure 4] The diagram based on Figures 1a to 1c shows a device according to a second exemplary embodiment. [Figure 5] In the diagram based on FIG. 1a, an apparatus according to a third exemplary embodiment is shown. DETAILED DESCRIPTION OF THE INVENTION

[0023] First Exemplary Embodiment FIG. 1 shows schematically an apparatus, designated 10, for measuring alignment errors of a laser diode 12 according to a first exemplary embodiment of the present invention.

[0024] The apparatus includes an alignment chuck 14, which can be rotated by a drive 16 about an axis of rotation 18, as indicated by arrow 20 in Figure 1. In another exemplary embodiment, the alignment chuck 14 is rotated by a spindle (not shown here) rather than directly by the drive 16.

[0025] The alignment chuck 14 carries a mount 22 to which the laser diode 12 is fixed, for example, by adhesive bonding or screwing. The beam 24 produced by the laser diode is directional, which is equivalent to being collimated. As a result, the deviation of the beam 24 in the direction of propagation is so small that, in beam optics terms, it can be viewed as a bundle of parallel individual light rays.

[0026] The beam 24 is split by a beam splitter 26 into a first component beam 28 and a second component beam 30. In this case, the splitting ratio may be, for example, 50:50.

[0027] A focusing optics unit 32 is arranged in the beam path of the first component beam 28; in Figure 1a, the focusing optics unit is shown with only one lens, but it may also consist of several lenses and / or other optical elements. The focusing optics unit 32 is suitably positioned, for example centered, with respect to the rotation axis 18 and focuses the first component beam 28 to a focal point 34 in the plane of a first radiation sensor 36. The first radiation sensor 36 measures the incident radiation intensity in a spatially resolved manner and may be designed, for example, as a CCD camera or as a PSD sensor.

[0028] The second component beam 30 is not focused but is incident directly on a second radiation sensor 38 which is preferably configured similarly to the first radiation sensor 36 .

[0029] Data lines connect the drive 16 and the two radiation sensors 36, 38 to computing means, represented by a PC 40 in FIG. 1a.

[0030] 1a implies that the optical axis of beam 24 is precisely aligned with the mechanical axis of mount 22, which is defined by the cylindrical outer surface of mount 22, which itself extends coaxially with rotation axis 18. Centering of the outer surface of mount 22 relative to rotation axis 18 can be easily ensured by some kind of "balancing."

[0031] Here, rotation of mount 22 about longitudinal axis 18 has no effect on beam 24. As a result, focal point 34 of first component beam 28 remains on axis of rotation 18, as shown in the top view of first radiation sensor 36 in Figure 1b. In this case, axis of rotation 18 is at the intersection of two intersecting lines, which are drawn only to assist with orientation.

[0032] A stationary radiation spot 44 is also produced on the second radiation sensor 38 (see FIG. 1c), said radiation spot having a diameter larger than the focal point 34 of the first component beam 28 because it is unfocused.

[0033] 2a shows the situation when laser diode 12 is laterally displaced in mount 22 by an absolute value d, which causes beam 24 to be correspondingly displaced relative to rotation axis 18. As a result of this lateral displacement, the optical axis of beam 24 rotates as alignment chuck 14 rotates about rotation axis 24, but remains parallel to it.

[0034] This does not affect the first component beam 28, since it still extends parallel to the axis of rotation 18. As can be seen by comparing Figures 2b and 1b, the position of the focal point 34 does not change as a result of the lateral displacement.

[0035] In contrast, on the second radiation sensor 38, a lateral deviation of the beam optical axis relative to the rotation axis 18 is discernible in that the light spot 44 no longer lies at its centre but undergoes a rotational movement around the rotation axis 18 (a 90° bend), which can be seen in Figure 2c. The centre of the light spot 44 represents an incidence circle 46, half of whose diameter corresponds to the lateral deviation d. The intensity distribution recorded by the second radiation sensor 38 during the rotation of the alignment chuck 14 is evaluated by the computing means 40, which allows the diameter of the incidence circle 46 to be determined.

[0036] 3a shows the situation when the optical axis of beam 24 is tilted by an angle α with respect to the axis of rotation 18. During rotation of alignment chuck 14, focal point 34 describes an entrance circle 48, the diameter D of which is related to the focal length f of focusing optics unit 32 and the tilt angle α by the following relationship: α ≒ D / 2 f

[0037] In the case of tilt, the light spot 44 appearing on the second radiation sensor 38 also describes the circle of incidence, as shown in Figure 3c. Again, the tilt angle α can be derived from the diameter of the circle of incidence 50.

[0038] In general, the lateral shift shown in Figure 2a and the beam tilt shown in Figure 3a do not occur separately but together, but even then the tilt can only be determined by evaluating the circle of incidence 48 described on the first radiation sensor 36 by the focal point 34 of the first component beam 28.

[0039] In this case, the displacement of the light spot 44 caused by the shift and tilt is superimposed on the second radiation sensor 38. Since the tilt angle α is known with high precision from measurements of the first component beam 28, its effect on the circle of incidence 46 of the light spot 44 can be calculated out. In this way, the lateral displacement d can be calculated based on the position on the second radiation sensor 38 swept by the light spot 44 during rotation.

[0040] Second Exemplary Embodiment 4 shows an option that makes it unnecessary to calculate out the movement component caused by the tilt if an imaging optics unit 52, which is arranged centrally with respect to the (curved) rotation axis 18 and is shown here only by a lens, is introduced into the beam path of the second component beam 30. The imaging optics unit 52 is designed in such a way that the laser diode 12 with its light exit window is imaged onto the second radiation sensor 38. In this way, the tilt of the beam 24 does not have any effect on the position of the light spot 44 on the second radiation sensor 38.

[0041] In the absence of a lateral offset, the light spot 44 lies on the rotation axis 18. In the case of an offset d≠0, the light spot 44 follows a circular orbit around the curved rotation axis 18, from which the lateral offset d can be derived when the image generation scale of the image generation optics unit 52 is taken into account.

[0042] Other variants An afocal optical unit, e.g., a telescope, can be additionally provided in the above-described exemplary embodiment, which can be used to adjust the beam angle and beam diameter of the bundle of rays emitted from the beam source 12. In this case, the afocal optical unit can be arranged, for example, between the beam source 12 and the beam splitter 26 in the beam path of the beam 24, and can thereby influence the beam angle and beam diameter of both component beams 28, 30.

[0043] 3a shows an afocal optics unit, designated as 54, which is shown using hatched lenses and is shown in the beam path of second component beam 30. Afocal optics unit 54 is designed to be able to expand second component beam 30 to form a second component beam 30' of larger beam diameter, as shown using dotted lines.

[0044] After the measurement is made, the beam source 12 can be aligned with respect to the rotation axis 18. If the beam source 12 is already adhesively bonded or otherwise connected to the mount 22 during the measurement, fine turning using a machining tool such as that shown at 56 in Figure 3a is the obvious choice.

[0045] Another alignment option is shown in Figure 4a. If the beam source 12 is accommodated loosely, i.e., not fixedly, in the mount 22 during the measurement, the beam source 12 can still be aligned in the mount 22 after the measurement. For this purpose, the orientation of the mount 22 is initially measured optically or tactilely using a distance sensor 58, and adhesive is injected into the gap between the mount 22 and the beam source 12 using a dispenser 60. After alignment, the adhesive is cured, for example by irradiation with UV light from a UV lamp 62.

[0046] Third Exemplary Embodiment Another exemplary embodiment of the device according to the invention is shown in Fig. 5. In this exemplary embodiment, a deflecting prism 70 is arranged in the beam path of the second component beam 30. The deflecting prism 70 ensures that the component beam 30 is deflected such that it extends approximately parallel to the first component beam 28 downstream of the deflecting prism 70. For this purpose, the deflecting prism 70 deflects the component beam 30 by an angle of, for example, 85° to 95°, preferably by an angle of 90°. Such parallel beam paths of the component beams 28, 30 enable the entire device 10 to have a particularly compact mechanical configuration.

[0047] Otherwise, the device 10 shown in Figure 5 corresponds to the device 10 shown in Figure 1a and already described, and therefore can be understood without further explanation at this point.

[0048] It should be understood that the deflecting prism 70 can be incorporated into each of the exemplary embodiments described above. Instead of the deflecting prism 70, a deflecting mirror or any other reflective optical element can also be used to deflect the component beams 30.

Claims

1. An apparatus for measuring alignment errors of a directional beam source (12), comprising: a mount (22) for said beam source (12); a first spatially resolving radiation sensor (36); a beam splitter (26) configured to split the beam (24) generated by the beam source (12) into a first component beam (28) and a second component beam (30); a focusing optics unit (32) arranged in the beam path of the first component beam (28) and having a focal plane in which the first radiation sensor (36) is arranged; a second spatially resolved radiation sensor (38) positioned in the beam path of the second component beam (30); a drive (16) configured to provide relative movement between firstly said mount (22) and secondly said other parts of said device about an axis of rotation (18); - computing means (40) configured to calculate the tilt (α) and lateral displacement (d) of the beam (24) generated by the beam source (12), using a first position swept by the first component beam (28) on the first radiation sensor (36) during a rotation of the beam source (12) relative to the other part of the apparatus, and using a second position swept by the second component beam (30) on the second radiation sensor (38) during a rotation of the beam source (12) relative to the other part of the apparatus; An apparatus comprising:

2. 2. The apparatus of claim 1, further comprising an imaging optical unit (52) arranged in the beam path of the second component beam (30) and configured to image the beam source (12) onto the second radiation sensor (38).

3. 3. The apparatus of claim 2, wherein the imaging optics unit (52) is configured to image the beam source onto the second radiation sensor (38) in a demagnifying or magnifying manner.

4. An apparatus according to any one of claims 1 to 3, wherein the mount (22) is supported by an alignment chuck (14) with which the mount (22) can be aligned.

5. 5. The apparatus according to claim 1, further comprising an afocal optical system unit (54) arranged in the beam path of the beam (24), the first component beam (28), or the second component beam (30) generated by the beam source.

6. 6. The apparatus according to claim 1, further comprising a beam deflection unit (70) for deflecting the second component beam (30) so that the deflected second component beam (30) travels at least approximately parallel to the first component beam (28).

7. A method for measuring alignment errors of a directional beam source (12), comprising the steps of: a) inserting the beam source (12) into a mount (22) and causing relative rotation about an axis of rotation (18); b) simultaneously with step a), splitting the beam (24) generated by the beam source (12) into a first component beam (28) and a second component beam (30) by a beam splitter (26); c) directing said first component beam (28) by a focusing optical unit (32) onto a first spatially resolved radiation sensor (36) arranged in a focal plane of said focusing optical unit (32); d) directing said second component beam (30) towards a second spatially resolved radiation sensor (38); e) calculating the tilt (α) and lateral displacement (d) of the beam (24) generated by the beam source (12) using a first position on the first radiation sensor (36) swept by the first component beam (28) during the relative rotation and a second position on the second radiation sensor (38) swept by the second component beam (30) during the relative rotation of the beam source (12); A method comprising:

8. 8. The method of claim 7, wherein the beam source (12) is imaged onto the second radiation sensor (38).

9. 9. The method of claim 8, wherein the beam source (12) is imaged demagnified or magnified onto the second radiation sensor (38).

10. 10. The method according to claim 7, wherein the angle and beam diameter of the beam (24), of the first component beam (28) and / or of the second component beam (30) generated by the beam source are set using an afocal optical unit (54).

11. The method according to any one of claims 7 to 10, wherein the beam source (12) is aligned with respect to the axis of rotation (18) after step d).

12. 12. The method of claim 11, wherein the beam source (12) is rigidly connected to the mount (22) before steps a) to d), and the alignment with respect to the rotation axis (18) is achieved by machining an outer surface of the mount (22) with a tool.

13. 12. The method of claim 11, wherein the beam source (12) is loosely inserted into the mount (22), and the alignment with the rotation axis (18) is achieved by applying an adhesive, then bringing the beam source (12) to a desired position with respect to the mount (22) using an alignment chuck, hexapod, or any other alignment means, and then allowing the adhesive to cure.

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