Device and method for measuring alignment errors of a directed beam source
Patent Information
- Application Number
- EP2024704348
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-09
- Filing Date
- 2024-02-05
- Publication Date
- 2025-11-12
AI Technical Summary
Current methods for measuring alignment errors of laser diodes and similar directed beam sources are complex and time-consuming, requiring sequential measurement of the optical axis position, which increases costs and complexity.
A device with a beam splitter dividing the beam into two partial beams, one focused with focusing optics and the other unfocused, allowing simultaneous measurement of tilt and lateral offset using spatially resolving radiation sensors, significantly reducing measurement time.
Enables rapid and independent measurement of tilt and offset, reducing the overall measurement time and allowing for more efficient alignment of the beam source with the optical system.
Smart Images
Figure EP2024052724_15082024_PF_FP
Abstract
Description
[0001] Device and method for measuring alignment errors of a directed beam source
[0002] BACKGROUND OF THE INVENTION
[0003] 1. Field of the invention
[0004] The invention relates to a device and a method for measuring alignment errors of laser diodes and similar directed beam sources. These alignment errors can, in particular, be tilts or displacements.
[0005] 2. Description of the state of the art
[0006] Laser diodes and similar directed beam sources are often mounted in a mount by adhesive or similar means, which is then integrated into a higher-level optical system. The outer surface of the mount is precisely machined, allowing the mount to be installed in the higher-level optical system at the desired orientation.
[0007] If the optical axis of the beam source is not precisely aligned with the mechanical axis of the mount, alignment errors can occur when the mount is installed into the optical system, impairing the function of the optical system. Therefore, it is common practice to adjust the beam source before gluing it into the mount. However, this type of adjustment is complex and significantly increases the cost of the component.
[0008] From WO 2019 / 224346 A2, it is known to rotate the mount with the switched-on beam source around a rotation axis and to observe the circular movements of the radiation spot created in two spaced-apart planes on a radiation sensor. Alignment errors can be inferred from the diameters of the circles detected by the radiation sensor. The planes are generated or defined by adjusting the back focal length of the light beams using variable optics. If the measured alignment errors are intolerable, the outer surface of the mount is remachined by turning, milling, or grinding (so-called alignment machining, e.g., alignment turning) until the mechanical axis of the mount is aligned with the optical axis of the beam source.
[0009] With the known method, the position of the optical axis of the beam source can only be measured sequentially, since the intensity in both planes must be recorded successively.
[0010] SUMMARY OF THE INVENTION
[0011] The object of the invention is therefore to provide a device and a method for measuring alignment errors of directed beam sources, with which the required measuring time can be shortened.
[0012] With regard to the device, this object is achieved by a device for measuring alignment errors of a directed beam source, which device has 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 partial beam and a second partial beam. Furthermore, the device has focusing optics arranged in a radiation path of the first partial beam and having a focal plane in which the first radiation sensor is arranged. A second spatially resolving radiation sensor is arranged in a radiation path of the second partial beam. A drive of the device is configured to effect a relative movement about a rotational axis between the mount, on the one hand, and the remaining parts of the device, on the other hand.A computing device is configured to calculate a tilt and a lateral offset of the beam generated by the beam source from first locations swept over by the first partial beam during rotation of the beam source relative to the above-mentioned remaining parts of the device on the first radiation sensor, and from second locations swept over by the second partial beam during rotation of the beam source relative to the above-mentioned remaining parts of the device on the second radiation sensor. The invention is based on the finding that the tilt and offset of the beam generated by the beam source can be measured simultaneously and independently of one another if the beam is divided into two partial beams and the location of the focus of the first partial beam is detected with a first radiation sensor during rotation of the mount about a rotation axis.The second partial beam, however, is unfocused and detected by a second radiation sensor. The simultaneous measurement of tilt and offset allows for a significant reduction in the required measurement time.
[0013] Since the directed beam is largely collimated, focusing the first partial beam using the focusing optics translates angles into locations on the first radiation sensor. All rays that hit the focusing optics along the same direction of incidence are thus focused to the same point, whose position on the first radiation sensor is determined by the direction of incidence. A lateral offset of the beam does not change the direction of incidence and therefore does not affect this part of the measurement.
[0014] The location where the unfocused beam hits the second radiation sensor, however, depends on both the offset and the tilt of the beam. Since the tilt is measured by the first radiation sensor, it can be easily eliminated when measuring with the second radiation sensor, so that this second part of the measurement provides the lateral offset between the mechanical axis of the mount and the optical axis of the beam.
[0015] For both partial measurements, the orientation of the radiation sensors relative to the rotation axis is irrelevant, as only the diameter of the resulting impact circle is evaluated. The position of the impact circle on the respective radiation sensor is not required for calculating the tilt and offset.
[0016] If the device contains an imaging optics which is arranged in the beam path of the second
[0017] partial beam and is designed to image the beam source onto the second radiation sensor, the tilt does not have to be taken into account when calculating the offset because the location at which the second partial beam strikes the second radiation sensor then depends only on the offset and not on the tilt.
[0018] If such imaging optics are provided, they can be set up to image the beam source onto the second radiation sensor either in a reduced or enlarged size. Whether a reduction or an enlargement is chosen depends, among other things, on the radiation sensor used and on the properties of the beam, e.g. its diameter and intensity profile. A large beam cross-section can be helpful for detecting small displacements, but the sensor area must be sufficiently large. In the case of an intensity profile that deviates greatly from a Gaussian shape and may have secondary maxima, it can be difficult to clearly determine its position on the sensor for large diameters, so a reduction in size can be useful in such a case. The imaging scale is normally fixed, but can also be variably adjustable.
[0019] Additionally or alternatively, the device may include an afocal lens, e.g., in the form of a Keppler telescope, arranged in the beam path of the beam generated by the beam source, the first partial beam, or the second partial beam. The afocal lens can be used to adjust the angles and / or diameters of the beams.
[0020] It is advantageous if the device has a beam deflection unit that deflects the second partial beam such that the deflected second partial beam runs at least approximately parallel to the first partial beam. This enables a particularly compact mechanical design of the device. The beam deflection unit can be, for example, a deflection prism or a deflection mirror.
[0021] It is preferred if the drive only rotates the mount with the beam source housed therein. However, it is also possible for the mount and the beam source to remain stationary, and instead an assembly comprising the beam splitter, focusing optics, and radiation sensors to be rotated around the rotation axis. After measuring the tilt and offset, the beam source can be aligned to the rotation axis in such a way that the remaining alignment errors are tolerable.
[0022] If the beam source and the mount are already bonded before the measurement is performed, the mount can be remachined to change its mechanical axis. For this purpose, the device has a cutting tool designed to machine an outer surface of the beam source mount such that a mechanical longitudinal axis of the mount runs parallel to the optical axis of the beam source. Such tools are familiar from conventional alignment turning.
[0023] If, however, the measurement is carried out 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 one another and only then to glue them together. A directional bonding process can be used for this. Before the measurement and final alignment, an adhesive is first applied to the space between the beam source and the mount using a dispenser. Preferably, the spatial position of the mount is first measured optically or tactilely in a preceding step. The mount can be brought into a desired position, e.g. relative to the axis of rotation or another mechanical reference. The beam source is then aligned relative to the mount using the device according to the invention and an alignment chuck, hexapod, a piezo actuator or another suitable alignment device.Alignment is continued until the specified translational and rotational tolerances are met. After alignment is complete, the adhesive is cured using a UV light source.
[0024] A method according to the invention for measuring alignment errors of a directed beam source comprises the following steps: a) the beam source is inserted into a mount and a relative rotation about a rotation axis is generated; b) simultaneously with step a), a beam generated by the beam source is split by a beam splitter into a first partial beam and a second partial beam; c) the first partial beam is directed via focusing optics onto a first spatially resolving radiation sensor arranged in a focal plane of the focusing optics; d) the second partial beam is directed onto a second spatially resolving radiation sensor;e) a tilt and a lateral offset of the beam generated by the beam source are calculated from first locations swept over by the first partial beam during the relative rotation on the first radiation sensor and from second locations swept over by the second partial beam during the relative rotation of the beam source on the second radiation sensor;
[0025] BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In the following, exemplary embodiments of the invention are explained in more detail with reference to the drawings. In these drawings:
[0027] Figure 1 is a schematic representation of a device according to the invention according to a first embodiment, assuming that the optical axis of the beam is coaxial with the axis of rotation;
[0028] Figure 1 b is a plan view of the first radiation sensor and the focal point generated there;
[0029] Figure 1 c shows a plan view of the second radiation sensor and the light spot generated there;
[0030] Figures 2a to 2c show representations corresponding to Figures 1a to 1c for the case where the beam generated by the laser diode is laterally offset;
[0031] Figures 3a to 3c show the device shown in Figures 1a to 1c for the case where the light beam generated by the laser diode is tilted; Figures 4a to 4c show a device according to a second embodiment in representations similar to Figures 1a to 1c; and
[0032] Figure 5 shows a device according to a third embodiment in a representation similar to Figure 1a.
[0033] DESCRIPTION OF PREFERRED EMBODIMENTS
[0034] First embodiment
[0035] Figure 1 schematically shows a device, designated overall by 10, for measuring alignment errors of a laser diode 12 according to a first embodiment of the invention.
[0036] The device comprises an adjusting chuck 14, which can be rotated about a rotational axis 18 by means of a drive 16, as indicated in Figure 1 by an arrow 20. In other embodiments, the adjusting chuck 14 is not rotated directly by the drive 16, but rather via a spindle (not shown).
[0037] The alignment chuck 14 carries a mount 22 into which the laser diode 12 is mounted, e.g., glued or screwed. The beam 24 generated by the laser diode is directed, or, what is equivalent, collimated. As a result, the beam 24 diverges so slightly in the direction of propagation that, in ray optics, it can be imagined as a bundle of parallel individual beams.
[0038] The beam 24 is split by a beam splitter 26 into a first partial beam 28 and a second partial beam 30. The splitting ratio can be, for example, 50:50.
[0039] Arranged in the radiation path of the first partial beam 28 is a focusing optic 32, which is indicated in Figure 1a by only a single lens, but can also consist of multiple lenses and / or other optical elements. The focusing optic 32 is suitably positioned, e.g., centered, with respect to the axis of rotation 18 and focuses the first partial beam 28 into a focal point 34 located in the plane of a first radiation sensor 36. The first radiation sensor 36 measures the radiation intensity incident thereon with spatial resolution and can be designed, for example, as a CCD camera or a PSD sensor.
[0040] The second partial beam 30 is not focused, but falls directly onto a second radiation sensor 38, which is preferably constructed in the same way as the first radiation sensor 36.
[0041] The drive 16 and the two radiation sensors 36, 38 are connected via data lines to a computing device, which is indicated in Figure 1a by a PC 40.
[0042] In Figure 1a, it is assumed that the optical axis of beam 24 is exactly aligned with the mechanical axis of mount 22, which is defined by the cylindrical outer surface of mount 22 and, in turn, is coaxial with the rotation axis 18. Centering of the axis defined by the outer surface of mount 22 with respect to the rotation axis 18 can be easily ensured by a type of "balancing."
[0043] If the mount 22 rotates along the longitudinal axis 18, this has no effect on the beam 24. The focal point 34 of the first partial beam 28 thus remains on the axis of rotation 18, as shown in the top view of the first radiation sensor 36 in Figure 1b. The axis of rotation 18 lies at the intersection point of the two crossed lines drawn only for better orientation.
[0044] A stationary radiation spot 44 is also created on the second radiation sensor 38 (see Figure 1c), the diameter of which is larger than the focal point 34 of the first partial beam 28 due to the lack of focusing.
[0045] Figure 2a shows the situation when the laser diode 12 is laterally offset in the mount 22 by an amount d. The beam 24 is then also offset accordingly from the rotation axis 18. As a result of this lateral offset, the optical axis of the beam 24 rotates around the rotation axis 24 when the alignment chuck 14 rotates, but remains parallel to it. This has no effect on the first partial beam 28, since it continues to run parallel to the rotation axis 18. As a comparison of Figures 2b and 1b shows, the focal point 34 does not change its position as a result of the lateral offset.
[0046] On the second radiation sensor 38, however, the lateral offset of the optical beam axis relative to the rotation axis 18 is detectable in that the light spot 44 is no longer centered, but rather rotates around the rotation axis 18 (angled by 90°), as can be seen in Figure 2c. The center of the light spot 44 describes a striking circle 46, half the diameter of which corresponds to the lateral offset d. The intensity distributions recorded by the second radiation sensor 38 during the rotation of the adjustment chuck 14 are evaluated by the computing device 40 to determine the diameter of the striking circle 46.
[0047] Figure 3a shows the conditions when the optical axis of the beam 24 is tilted by an angle a relative to the rotation axis 18. During the rotation of the adjusting chuck 14, the focal point 34 describes a circle 48 whose diameter D is related to the focal length f of the focusing optics 32 and the tilt angle a by the relationship a ~ D / 2-f.
[0048] In the event of a tilt, the light spot 44 created on the second radiation sensor 38 also describes a circle of impact, as shown in Figure 3c. Here, too, the tilt angle α can be derived from the diameter of the circle of impact 50.
[0049] In general, the lateral offset illustrated in Figure 2a and the tilt of the beam illustrated in Figure 3a do not occur separately, but together. However, the tilt is also determined exclusively by evaluating the beat circle 48 described by the focal point 34 of the first partial beam 28 on the first radiation sensor 36. On the second radiation sensor 38, the movements of the light spot 44 caused by the offset and the tilt are then superimposed. Since the tilt angle α is known with high accuracy from the measurement of the first partial beam 28, its effect on the beat circle 46 of the light spot 44 can be subtracted. In this way, the lateral offset d can be calculated based on the locations that the light spot 44 sweeps over on the second radiation sensor 38 during rotation.
[0050] Second embodiment
[0051] Figure 4 shows one way in which the calculation of the movement component caused by the tilt can be omitted by inserting an imaging optic 52, indicated here only by a lens, into the beam path of the second partial beam 30. The imaging optic 52 is arranged centered relative to the (angled) rotation axis 18. The imaging optic 52 is designed such that the laser diode 12 is imaged with its light exit window onto the second radiation sensor 38. In this way, a tilt of the beam 24 no longer influences the location of the light spot 44 on the second radiation sensor 38.
[0052] If there is no lateral offset, the light spot 44 rests on the angled axis of rotation 18. If there is an offset d 0, the light spot 44 describes a circular path around the angled axis of rotation 18, from which the lateral offset d can be derived taking into account the imaging scale of the imaging optics 52.
[0053] Other variants
[0054] In the embodiments described above, an afocal optic, e.g. a telescope, can also be provided. This allows the beam angle and beam diameter of the beam bundle emanating from the beam source 12 to be adjusted. The afocal optic can be arranged, for example, in the beam path of the beam 24 between the beam source 12 and the beam splitter 26, whereby the beam angle and beam diameter of both partial beams 28, 30 can be influenced. Figure 3a shows an afocal optic, designated 54 and indicated by dashed lenses, which is indicated in the beam path of the second partial beam 30. The afocal optic 54 is designed such that the second partial beam 30 is expanded into a second partial beam 30', indicated by dotted lines, with a larger beam diameter.
[0055] After the measurement has been completed, the beam source 12 can be aligned relative to the rotation axis 18. If the beam source 12 was already firmly glued or otherwise connected to the mount 22 during the measurement, an adjustment rotation using a cutting tool is recommended, as indicated at 56 in Figure 3a.
[0056] Another alignment option is illustrated in Figure 4a. If the beam source 12 was still loosely, i.e., not firmly, mounted in the mount 22 during the measurement, the beam source 12 can be aligned in the mount 22 after the measurement. For this purpose, the position of the mount 22 is first measured optically or tactilely using a distance sensor 58, and an adhesive is applied to the gap between the mount 22 and the beam source 12 using a dispenser 60. After alignment, the adhesive is cured, e.g., by irradiation with UV light from an ultrasonic lamp 62.
[0057] Third embodiment
[0058] A further embodiment of a device according to the invention is shown in Figure 5. In this embodiment, a deflecting prism 70 is located in the beam path of the second partial beam 30. The deflecting prism 70 ensures that the partial beam 30 is deflected such that it runs approximately parallel to the first partial beam 28 behind the deflecting prism 70. For this purpose, the partial beam 30 is deflected by the deflecting prism 70, for example, by an angle between 85° and 95°, preferably by an angle of 90°. Such a parallel beam path of the partial beams 28, 30 allows for a particularly compact mechanical design of the entire device 10.
[0059] Otherwise, the device 10 shown in Figure 5 corresponds to the device 10 shown in Figure 1a and already explained above, so a repeated description is omitted here. It is understood that the deflection prism 70 can be used in any of the embodiments described above. Instead of a deflection prism 70, a deflection mirror or another reflective optical element can also be used to deflect the partial beam 30.
Claims
PATENT CLAIMS 1. Device for measuring alignment errors of a directed beam source (12), comprising: a mount (22) for the beam source (12), a first spatially resolving radiation sensor (36), a beam splitter (26) configured to split a beam (24) generated by the beam source (12) into a first partial beam (28) and a second partial beam (30), focusing optics (32) arranged in a radiation path of the first partial beam (28) and having a focal plane in which the first radiation sensor (36) is arranged, a second spatially resolving radiation sensor (38) arranged in a radiation path of the second partial beam (30), a drive (16) configured to effect a relative movement about an axis of rotation (18) between the mount (22) on the one hand and the above-mentioned remaining parts of the device on the other hand, a computing device (40) configured to places,which are swept over by the first partial beam (28) during a rotation of the beam source (12) relative to the above-mentioned remaining parts of the device on the first radiation sensor (36), and from second locations which are swept over by the second partial beam (30) during the rotation of the beam source (12) relative to the above-mentioned remaining parts of the device on the second radiation sensor (38), to calculate a tilt (oc) and a lateral offset (d) of the beam (24) generated by the beam source (12).
2. Device according to claim 1, with an imaging optics (52) which is arranged in the beam path of the second partial beam (30) and is designed to image the beam source (12) onto the second radiation sensor (38).
3. Device according to claim 2, wherein the imaging optics (52) are configured to image the radiation source onto the second radiation sensor (38) either in a reduced or enlarged size.
4. Device according to one of the preceding claims, wherein the socket (22) is carried by an adjusting chuck (14) with the aid of which the socket (22) can be aligned.
5. Device according to one of the preceding claims, with an afocal optic (54) which is arranged in the beam path of the beam (24) generated by the beam source, the first partial beam (28) or the second partial beam (30).
6. Device according to one of the preceding claims, with a beam deflection unit (70) which deflects the second partial beam (30) such that the deflected second partial beam (30) runs at least approximately parallel to the first partial beam (28).
7. A method for measuring alignment errors of a directed beam source (12), comprising the following steps: a) the beam source (12) is inserted into a mount (22) and a relative rotation about an axis of rotation (18) is generated; b) simultaneously with step a), a beam (24) generated by the beam source (12) is split by a beam splitter (26) into a first partial beam (28) and a second partial beam (30); c) the first partial beam (28) is directed via focusing optics (32) onto a first spatially resolving radiation sensor (36) which is arranged in a focal plane of the focusing optics (32); d) the second partial beam (30) is directed onto a second spatially resolving radiation sensor (38); e) a tilt (oc) and a lateral offset (d) of the beam (24) generated by the beam source (12) are calculated from first locations swept over by the first partial beam (28) during the relative rotation on the first radiation sensor (36) and from second locations swept over by the second partial beam (30) during the relative rotation of the beam source (12) on the second radiation sensor (38).
8. The method according to claim 7, wherein the radiation source (12) is imaged onto the second radiation sensor (38).
9. The method according to claim 8, wherein the radiation source (12) is imaged onto the second radiation sensor (38) in a reduced or enlarged manner.
10. Method according to one of claims 7 to 9, wherein the angles and the beam diameter of the beam (24) generated by the beam source, the first partial beam (28) and / or the second partial beam (30) are adjusted by means of an afocal optic (54).
11. Method according to one of claims 7 to 10, wherein after step d) the beam source (12) is aligned relative to the axis of rotation (18).
12. The method according to claim 11, wherein the beam source (12) is fixedly connected to the mount (22) prior to steps a) to d) and the alignment relative to the axis of rotation (18) is carried out by means of a tool by machining an outer surface of the mount (22).
13. The method according to claim 11, wherein the beam source (12) is loosely inserted into the mount (22) and the alignment relative to the axis of rotation (18) is carried out by, after adding an adhesive, bringing the beam source (12) into a desired position relative to the mount (22) using an adjusting chuck, a hexapod or another adjusting device and then curing the adhesive.