Abstract
An optical coupling between optical components and, more particular, to an optical probe configured for optical testing of at least one micro-optical component, a method for producing an optical probe, and a method for optical testing of at least one micro-optical component. The optical probe includes a probe head, wherein an optical performance of the probe head is calibrated and wherein the probe head includes a testing circuit, wherein the testing circuit is fixed on a mechanical support; at least one micro-optical element, wherein the micro-optical element is a separate element with regard to the testing circuit and in mechanical contact with the testing circuit, wherein the micro-optical element is configured to optically couple light between the testing circuit and the micro-optical component, thereby being configured to determine an optical performance of the micro-optical component.
Claims
1. An optical probe configured for optical testing of at least one micro-optical component, comprising: a probe head, wherein an optical performance of the probe head is calibrated and wherein the probe head comprises a testing circuit, wherein the testing circuit is fixed on a mechanical support; and at least one micro-optical element, wherein the micro-optical element is a separate element with regard to the testing circuit and in mechanical contact with the testing circuit, wherein the micro-optical element is configured to optically couple light between the testing circuit and the micro-optical component, thereby being configured to determine an optical performance of the micro-optical component.
2. The optical probe of claim 1, wherein the micro-optical element comprises a photoresist produced on the testing circuit.
3. The optical probe of claim 1, wherein the testing circuit is coupled to a fiber array.
4. The optical probe of claim 3, wherein the testing circuit is configured to modify either a pitch or a mode-field diameter of the fiber array.
5. The optical probe of claim 1, wherein the testing circuit has at least one of: a mechanical functionality; an electrical functionality; an optical functionality, wherein the optical functionality is independent from the optical functionality of the micro-optical element.
6. The optical probe of claim 1, wherein the testing circuit comprises at least one of: a photodetector; a light source; an optical modulator; a spectrum analyzer; a power splitter; a polarization splitter, filter or stripper; a multiplexer.
7. The optical probe of claim 1, wherein a pitch of the testing circuit is 80 m or less.
8. The optical probe of claim 1, wherein a mode-field pitch of the micro-optical element varies 1000 nm or less.
9. The optical probe of claim 1, wherein a standard deviation of a variation of a mode-field diameter is 20% or less of an average mode-field.
10. The optical probe of claim 1, wherein the probe head is configured to function as an optical phase array.
11. A method for producing an optical probe configured for optical testing of at least one micro-optical component, the method comprising the following steps: (i) providing a probe head, wherein an optical performance of the probe head is calibrated and wherein the probe head comprises a testing circuit, wherein the testing circuit is fixed on a mechanical support; and (ii) producing at least one micro-optical element on the testing circuit by using a direct-write process, wherein the micro-optical element is being produced as a separate element with regard to the testing circuit and in mechanical contact with the testing circuit, wherein the micro-optical element is configured to optically couple light between the testing circuit and a micro-optical component, thereby being configured to determine an optical performance of the micro-optical component.
12. The method of claim 11, further comprising at least one of the following steps: (iii) detecting at least one marker within the testing circuit prior to step (ii); (iv) producing at least one marker configured for alignment during step (ii); (v) detecting the light being emitted from the testing circuit prior to step (ii); (vi) optically coupling the light into the testing circuit for detecting a coupling location prior to step (ii); (vii) fixing the testing circuit on a mechanical support prior to step (ii); (viii) applying an adhesion promoter on the testing circuit prior to step (ii); (ix) aligning the micro-optical element with respect to a fiber core comprised by the testing circuit to a variation of at least 1 m; (x) calibrating the optical performance of the optical probe prior to step (ii).
13. A method for optical testing of at least one micro-optical component, the method comprising the following steps: a) providing an optical probe, wherein the optical probe comprises a probe head and at least one micro-optical element, wherein an optical performance of the probe head is calibrated and wherein the probe head comprises a testing circuit, wherein the testing circuit is fixed on a mechanical support, and wherein the micro-optical element is a separate element with regard to the testing circuit and in mechanical contact with the testing circuit; and b) positioning the probe head in a manner that the micro-optical element optically couples light between the testing circuit and the micro-optical component; and c) determining an optical performance of the micro-optical component by measuring an optical signal being indicative for the optical performance of the micro-optical component.
14. The method of claim 13, wherein the micro-optical element comprises a photoresist produced on the testing circuit.
15. The method of claim 14, further comprising at least one of the following steps: d) calibrating the optical performance of the probe head prior to performing step (b); e) modifying the optical signal by using an optical phase array; f) inserting at least one part of the micro-optical element into a trench comprised by the micro-optical component in a manner that the light is optically coupled between the testing circuit and the micro-optical component; g) matching a pitch of at least two micro-optical elements to a coupling location located at a surface of the micro-optical component by using the testing circuit.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0081] Further optional features and embodiments of the present invention are disclosed in more detail in the subsequent description of preferred embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be implemented in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. It is emphasized here that the scope of the invention is not restricted by the preferred embodiments. In the Figures:
[0082] FIGS. 1 to 7 each illustrates an exemplary embodiment of an optical probe configured for optical testing of a micro-optical component;
[0083] FIG. 8 illustrates an exemplary embodiment of a marker;
[0084] FIGS. 9A, 9B, 10A, 10B and 10C illustrate exemplary embodiments of a testing circuit;
[0085] FIGS. 11 and 12 each illustrates further exemplary embodiments of the optical probe configured for optical testing of a micro-optical component;
[0086] FIGS. 13A, 13B and 13C illustrate a facet view directed at a facet of a testing circuit;
[0087] FIGS. 14A and 14B illustrate projections of the exemplary embodiment of the optical probe of FIG. 2;
[0088] FIG. 15 illustrates a further exemplary embodiment of the optical probe configured for optical testing of micro-optical components;
[0089] FIG. 16 illustrates a method used for producing the probe head;
[0090] FIG. 17 illustrates a further exemplary embodiment of the optical probe configured for optical testing of a micro-optical component;
[0091] FIG. 18 illustrates experimental results obtained in a mode-field diameter statistics of 250 micro-optical elements; and
[0092] FIGS. 19 and 20 each illustrates a further exemplary embodiment of the probe head.
DETAILED DESCRIPTION
[0093] FIG. 1 illustrates an exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50. The optical probe 1 comprises a micro-optical element 20 configured for optically coupling light 3 between the micro-optical component 50 and a testing circuit 2 at coupling locations 51, 14, wherein the light 3 is transmitted through facets 103, 102, respectively. In the exemplary embodiment of FIG. 1, the micro-optical element 20 is configured to redirect the light 3 in a 90 angle 26. As an alternative (not depicted here), the angle 26 may be a different angle ranging from typically 0 to 100. Preferable values of the angle 26 may be 80 to 90, ensuring that a total internal reflection (TIR) of the reflecting surface 23 may not fail. If the angle 26 differs from 90 (e.g. being) 80, than the probe head 10 may be tilted 10 clockwise, as shown in FIG. 8. The light 3 may travel from the testing circuit 2 to the micro-optical component 50, from the micro-optical component 50 to the testing circuit 2, or simultaneously in both directions. The micro-optic component 50 is fixed on a mechanical support, such as a chuck 7, either permanently or by using vacuum tools. In some embodiments, an optical functionality of a functional element 56, being part of the micro-optical component 50, e.g. waveguide, laser or photodiode, which may be coupled to a waveguide 58, may be characterized, e.g. an optical transmission properties of the waveguide 58 or a spot size converter at the coupling location of the micro-optical component 50.
[0094] In the exemplary embodiment of FIG. 1, a lens 24 and a planar mirror as the reflecting surface 23 are used, causing the total internal reflection. As an alternative (not depicted here), a planar surface and a curved mirror or a combination thereof may be used. To ensure total internal reflection, the refractive index n of the micro-optical element 20 should be at least 1.53. The reflecting surface 23 may be a metal coated mirror, especially to avoid a failure of the total internal reflection. The testing circuit 2 comprises at least one waveguide 25, wherein the waveguide 25 is configured to guide light to a functional element 59, e.g. a photodetector, or a polarization sensitive splitter having two photodetectors configured for analyzing polarization. As an alternative (not depicted here), the functional element 59 can also be a light source. In other embodiments, the testing circuit 2 may optically couple light to a fiber array (FIG. 4) and, preferably, modify either a mode-field diameter (compared to an optical fiber 12) or a pitch of the waveguides (compared to a fiber array 11). This embodiment may, preferably, not comprise any functional element 59.
[0095] In the exemplary embodiment of FIG. 1, the testing circuit 2 is mounted here on a fixture 4 or directly on the translation stage 5. The part of the optical probe 1 which is movable with respect to the micro-optical component 50 is considered as the probe head 10. All components are, preferably, designed as being rather dynamic in motion, thus lightweight. The translation stage 5 can, preferably, be configured to control six degrees of freedom and may, preferably, be rather dynamic to allow fast testing of various micro-optical components 50. The testing circuit 2 may generate, receive, or generate and receive a signal configured for probing of an optical performance of the micro-optical component 50 or a part thereof, in particular of the functional element 56, the waveguide 58, or the coupling location 51. The optical performance may also comprise information about a quality of the facet 103, the coupling location 51 and, particularly about a spot-size converter within the waveguide 58. The light 3 may be used to align the probe heads 10 with respect to the micro-optical component 50. The testing circuit 2 may also be configured to generate a signal indicating a proximity, a distance, a collision with regard to at least one object, in particular the micro-optical component 50 or the mechanical support 7. The signal may, especially be generated by using a LiDAR device, a mechanical detection mechanism, an interferometric device, or a capacitive signal; however, using a different device or mechanism may also be feasible.
[0096] As further illustrated in FIG. 1, the translation stage 5 is mounted to a mechanical support 6. The chuck 7 is a mounting device, on which the micro-optical component 50 may be temporarily or permanently fixed. Preferably, a wafer chuck having vacuum holes, wherein the micro-optical component 50 may be part of the wafer 60 may be used. Herein, the chuck 7 may be translated with respect to the optical probe 1.
[0097] FIG. 2 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical components 50, 50b, 50c. As schematically depicted in FIG. 2, the micro-optical component 50 is comprised here by a wafer 60. The wafer 60 may, in general, have a size of 6 inch, preferably of 8 inch, in particular of 12 inch or more, and may comprise at least 1000 micro-optical components, whereof the micro-optical components 50, 50b, 50c are, exemplarily, shown in FIG. 2. Measuring optical signals that may be indicative for the optical performance of the micro-optical components 50, 50b can be performed in a trench 55, which may comprise dicing lanes for wafer singulation or may have been etched for a purpose of wafer level testing. Alternatively or in addition, V-Grooves for fiber alignment etched into the wafer 60 may be used for the optical testing. The chuck 7 and/or the translation stage 5 may be moved to sequentially scan at least a portion of the micro-optical components 50, 50b within the wafer 60.
[0098] FIG. 3 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. As schematically depicted in FIG. 3, a second probe 1b is, additionally, used here for the optical testing of a second coupling location 52 of the micro-optical component 50. This exemplary embodiment is configured for optically testing micro-optical component 50 having two or more coupling location 51, 52. The probe heads 10, 16 can be individually aligned to the micro-optical component 50. This exemplary embodiment can, especially, be used for micro-optical components 50 having two or more coupling location 51, 52 that may, preferably, be tested simultaneously. By way of example, such a micro-optical component 50 may be selected from a distributed feedback (DFB) laser, where no facet is reflecting but both facets (also a rear facet) are transmitting, or an amplifier, such as a semiconductor optical amplifier (SOA) or a gain material (such as erbium) doped integrated photonic chip. In a similar arrangement, at least one further micro-optical component 50, such as at least one of a micro-lens, an isolator, or a beam splitter cube, may be tested.
[0099] FIG. 4 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. As schematically depicted in FIG. 4, the testing circuit 2 is optically coupled here to a fiber array 11 at a second coupling location 14b of the testing circuit 2. This exemplary embodiment may be configured for a pitch conversion from the pitch of the fiber array 11 of typically 80 m or 127 m or 250 m to a pitch below 80 m, e.g. 25 m. In addition to the pitch conversion, the testing circuit 2 may, further, be configured for re-shaping a mode. Herein, the testing circuit 2 may be based on a platform, preferably selected from ioNext, SiN, Triplex, Si rich glass, a photonic platform as produced in a lamination process, an ion diffusion platform, a platform structured in polymer or inscribed in glass. This embodiment may, particularly, be favorable for testing narrow pitches of less than 80 m.
[0100] FIG. 5 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. As schematically depicted in FIG. 5, the testing circuit 2 is in mechanical contact with an electrical circuit 30. In particular, the testing circuit 2 may be a part of the electrical circuit 30, or the electrical circuit may be a part of the testing circuit 2, e.g. in that the testing circuit 2 may comprise at least one electrical functionality. This exemplary embodiment has a distance sensor 31 comprised by the electrical circuit 30, which in configured for measuring a distance 32 to the wafer 60. The distance sensor 31 may, alternatively or in addition, be configured of measuring a depth or a presence of the trench 55. The distance sensor 31 may, preferably, be selected from a capacitive sensor, an inductive sensor, or an optical sensor. In a further embodiment (not depicted here), the distance sensor 31 may be comprised by the testing circuit 2 without an electrical circuit 30, e.g. by generating a distance sensor signal to measure the distance 32 via an additional waveguide 25.
[0101] FIG. 6 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. As schematically depicted in FIG. 6, the optical probe 1 is configured for optically testing of a grating coupler 105, which emits in an angle 26, which may, typically, be 95 to 115, often 100. Herein, the refractive surface 24 may be implemented in a manner that it may deflect light in a 10 angle from a surface normal to match the light emission 3 with the grating coupler 105, particularly to achieve a high optical coupling to the micro-optical component 50. In addition, the angle 26 can be fine-adjusted by the translation stage 5. In a further embodiment, the refractive surface 24 may be an optical lens emitting in a direction along the waveguide 25, while the complete probe head 10 may be tilted by an angle 26 minus 90, typically between 0 and 20, preferably 10, see FIG. 8. Such a kind of tilting may, preferably, implemented by using a part 4b of the fixture and the micro-optical element 20, fine-adjusted by using the translation stage 5.
[0102] FIG. 7 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. As schematically depicted in FIG. 7, the testing circuit 2 is or comprises a light source or a light source array, particularly selected from a laser, a laser bar, an optical amplifier (SOA), or a superluminescent light emitting diode (SLED). While the testing circuit 2 may be operated, the coupling performance may be measured by using the functional element 56, which may be an optical device, especially a photodiode. As an alternative (not depicted here), the optical coupling may be measured by using a further optical element, preferably an optical fiber coupled to the micro-optical component 50, the second probe head 6, a grating coupling coupled to the waveguide 58 and a camera. The facet 103 may, further, be equipped with an optical lens. The testing circuit 2 may be fixed by a vacuum gripper to the mechanical support 4 or permanently, e.g. by using an adhesive or an adhesion promoter.
[0103] FIG. 8 illustrates an exemplary embodiment of the 3D-printed marker 21. The marker 21 may, preferably, be produced in the same printing process as the micro-optical element 20 and may be well aligned, particularly at least to 10 m, preferably to 5 m, especially to 1 m, to both the micro-optical element 20 and the coupling location 14. The marker 21 may be visible in a field of view of a top-view camera 33, which may for configured to provide a simplified alignment of the probe head 10 to the micro-optical component 50, especially the wafer 60, and to the trench 55. To avoid a blocking of a vision of the top-view camera 33 on the marker 21, the mechanical fixture 4 has a part 4b which is configured to fix the testing circuit 2 at a certain angle. The angle may, preferably, be 5 to 15 compared to a surface normal. To avoid mechanical contact of the testing circuit 2 with the surface of the wafer 60, the exemplary testing circuit 2 as shown in FIG. 8 comprises a chamfer 18. A region of the chamfer 18 is indicated here by a dashed line. Without the chamfer 18, a mechanical contact could occur at position assumed by the chamfer 18, which would destroy at least a portion of the micro-optical component 50, especially the wafer 60. Furthermore, the micro-optical element 20 is arranged here in a manner that the light 3 is emitted horizontally to the surface of the micro-optical component 50, especially of the wafer 60. This arrangement can be achieved by tilting the reflecting surface 23.
[0104] FIGS. 9A and 9B illustrate exemplary embodiments of the testing circuit 2 connected to a fiber array 11. As schematically depicted in FIGS. 9A and 9B, the testing circuit 2 is configured to translate a pitch 28 at the facet of the testing circuit 2 of typically 80 m or 127 m or 250 m to a pitch 27 of the coupling location of the testing circuit 2 being typically below 80 m. For this purpose, a plurality of optical fibers 12 is connected to the single micro-optical element 20. However, in some embodiments, the pitch 27 may be 80 m or more. This may, particularly, be favorable if: [0105] an extremely constant pitch may be needed, as the accuracy of the pitch 27 is better than the accuracy of the pitch 28, wherein, in this case, the coupling loss at the second coupling location 14b of the testing circuit 2 may be calibrated; [0106] an irregular pitch may be desired, e.g. a first pitch of 127 m alternating with a second pitch of 350 m; or [0107] at least one additional functionality within the testing circuit 2 may be desired, such as a polarization splitting.
In this embodiment, the pitch may also be 80 m or less.
[0108] Herein, the waveguides 25 as well as the fiber cores 13 may be polarization maintaining. Further, the width 29a may range from 2 m to 10 mm, preferably being 2 mm or less. In the exemplary embodiment of FIG. 9A each individual waveguide 25 is coupled to a separate channel in the micro-optical element 20, while in the exemplary embodiment of FIG. 9B more than one waveguide 25e is concurrently coupled into a single channel and coupled to a single element 20e in the micro-optical element 20. Further, multiplexing may be implemented by connecting several micro-optical elements 20 to a single optical fiber 12b.
[0109] FIGS. 10A, 10B and 10C illustrate further exemplary embodiments of the testing circuit 2. In the exemplary embodiment of FIG. 10A, a polarization splitter 40 is configured to split light of orthogonal E-vectors into two polarization channels 41, 42, which are coupled to the two optical fibers 12. The waveguide 25b is configured here it a manner that it does not change a polarization between a facet 102 of the testing circuit 2 and the polarization splitter 40. This advantage can, in particular, be achieved by a straight, birefringing or short waveguide. Further, the micro-optical element 20 is configured here it a manner that not to change a polarization between a facet 103 of the micro-optical component 50 and the facet 102 of the testing circuit 2. This advantage can, in particular, be achieved by providing the micro-optical element 20 as an optical lens without reflecting surfaces or by ensuring that light may be impinging on reflecting surfaces 23 in a manner that there no alteration of phase or intensity between different polarization components may occur, which may be the case for light of which the E-field is either in the reflection plane or perpendicular to the reflection plane. The reflection plane is a plane defined by incoming and reflected light at a planar surface. Alternatively, the alteration of the polarization of a reflective surface may be accounted for numerically, especially by using Fresnel equation, a calibration or a training measurement. In a further embodiment, the complete Mller Matrix can be determined by measuring both phase and intensity of the two polarization channels 41, 42. Further, the polarization of at least a portion of light within two polarization channels 41, 42 may be rotated by 90 and interfered at a detector with each other.
[0110] In the exemplary embodiment of FIG. 10B, light of the two polarization channels 41, 42 is coupled to the functional element 59, which may especially be a waveguide integrated photodiode. Optionally, the polarization of the light may be rotated by 90 or by a different angle prior to coupling into a fiber or a functional element 59, especially a photodetector.
[0111] In the exemplary embodiment of FIG. 10C, light is coupled to the functional elements 59. Herein, the functional elements 59 are configured for testing properties of the micro-optical component 50 either by transmitting or receiving or by receiving and transmitting light at the same time. In particular, the functional elements 59 may be selected from at least one of a photodiode, especially PIN, PN, or APD; a waveguide integrated photodiode; an IQ-receiver; a beam combiner; an optical modulator; a light source, especially a laser or an SLED; an amplifier, especially an SOA; an IQ modulator; an intensity modulator; a polarization splitter; a polarization stripper; a polarization filter, especially a rating coupler; or a polarization rotator. Herein, the waveguides 25 may be single-mode or multimode. Further, the waveguides 25 may be arranged at an angle #0 to the facet 102 of the testing circuit 2, in particular to reduce reflections. Further, the micro-optical element 20 may have only angled surfaces with respect to the light propagation, in particular to avoid back-reflections, see FIG. 11. The functional elements 59, in particular the IQ receiver or the beam combiner, may be used to measure the phase of two light beams relative to each other and may be used as feedback signal to trim the waveguide 58.
[0112] FIG. 11 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. Herein, the waveguides 25c, 58b are configured not to be normal to the surfaces of the facets 102, 103, respectively. The refractive surface 24 of the micro-optical element 20 deflects the light 3 in a manner that it may couple well between the waveguides 25c, 58b. For this purpose, the refractive surface 24 of the micro-optical element 20 may have no optically effective surfaces which are perpendicular to the beam propagation direction of the light 3. This embodiment may be favorable, particularly since it may suppress back-reflection due to the angled surfaces. In a further embodiment (not depicted here), it may be favorable that the reflecting surface 23 may also have no surfaces perpendicular to the propagation direction of the light 3. In a still further embodiment (not depicted here), an optical isolator and/or an additional anti-reflective coating may be used on at least one of the facets 102, 103 or on the refractive surface 24 of the micro-optical element 20.
[0113] FIG. 12 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical components 50, 50b, 50c. As schematically depicted in FIG. 12, the testing circuit 2 has a large number of coupling locations 14. Herein, several or all coupling locations 14 are equipped with one or more micro-optical elements 20. Each coupling location 14 may be selected from a grating coupler, a photodetector, an adiabatic taper, an etched facet, an etched facet in an angle of 30 to 120 with respect to the surface normal of the facet 102, or a VCSEL array. In case of a coupling location 14 emitting light or receiving light being predominantly perpendicular to the facet 102 only to a small extent, the micro-optical element 20 may be or comprise a refractive surface 24 that may be shaped in a manner as schematically shown in FIG. 6 that the light 3 being perpendicular to the facet 102 may be received to a large extent. As an alternative, the probe head 10 may be designed to have a minimum or a maximum alteration of sensitivity with respect to the amount of the light 3 coupled into the coupling location 14 by either using a high-NA lens or a low-NA lens as the refractive surface 24, wherein NA denotes a numerical aperture. This embodiment can be used for measuring a spatial and/or angular distribution of the light 3. The light 3 may be either come from the micro-optical component 50, then the coupling location 14 may receive the light 3, or the light 3 may be transmitted into the micro-optical component 50, then the coupling location 14 may emit the light 3. The probe head 10 may function as a Shack-Hartmann sensor, in particular by measuring at least one of a propagation direction or an intensity of the light 3. During a measurement, the probe head 10 may be moved according to a programmed pattern for sub-sampling, in particular by measuring the light 3 at more locations than micro-optical element 20 are present. In a preferred embodiment, at least a region 19 may be removed, especially by thinning, etching, or milling, for fitting the probe head 10 into smaller trenches 55. As an alternative, a thin testing circuit 2 having a thickness 19b, preferably of 730 m or less, more preferred of 100 m or less, over the complete component or at least in the region 19. In further preferred embodiment, a thin substrate, especially prepared by using a direct bandgap semiconductor, may be used.
[0114] FIGS. 13A, 13B and 13C illustrate a facet view directed at the facet 102 of a testing circuit 2. As schematically depicted in FIG. 13A, each micro-optical element 20 has a preferable diameter 110a. As schematically depicted in FIG. 13B, each micro-optical element 20 has a diameter 110b, wherein adjacent micro-optical elements 20 are intersecting. As schematically depicted in FIG. 13C, each micro-optical element 20 has a diameter 110b, wherein adjacent micro-optical elements 20 are separated by leaving a gap 111. The gap 111 may be advantageous for mechanically decoupling the adjacent micro-optical elements 20 which is preferable for a higher reliability of the probe head 10.
[0115] FIG. 14A illustrates the further exemplary embodiment of the optical probe 1 in a projection direction along +z according to FIG. 2. Dashed lines indicate part of elements of the drawing that are not visible since they are covered by another element. As schematically depicted in FIG. 14A, the micro-optical component 50 comprises waveguides 58, each having a pitch 28b. In a preferred embodiment, the pitch 28b may be 30 m or less. Providing a probe having a pitch 27 that may match pitch 28b would, however, lead to rather small micro-optical element 20, leading to a short working distance 34 or to poor coupling between the coupling locations 14, 51 due to the rather too small micro-optical elements 20. Instead of coupling opposing coupling locations 14, 51, a plurality of coupling locations 14 couple with, preferably, at least one waveguide 58c at a coupling location 51b in the embodiment of FIG. 14A. This arrangement can be achieved by interfering light originating from the plurality of coupling locations 14, wherein the light has a phase that is adjusted in a manner that the light constructively interferes at the coupling location 51b such that the mode-field generated at the coupling location 51b, preferably, corresponds to the mode field that couples best into the coupling location 51b. The mode-field coupling best into the coupling location 51b is the mode-field that corresponds to the coupling location 51b as much as possible in intensity distribution and phase distribution. To generate such a mode-field the phase and amplitude of the light emitted by the coupling locations 14 is adjusted in a manner that a concentric wave-front is generated in the center of the coupling location 51b. Additionally, the coupling sites 14 that are further away from the coupling location 51b may be reduced in intensity to generate an appropriate mode-field size. This principle as used in the embodiment of FIG. 14A can be referred to as optical phase array. The appropriate phase may be adjusted by cascade phase shifters within the testing circuit 2. The phase shifters may be operated by changing the refractive index controlling the phase and/or intensity of the light, especially by using at least one of heat, a current injection into a semiconductor junction, a piezo electric element, a voltage applied to a material that changes its refractive index upon an electric field, or a silicon-organic hybrid modulator. The optical phase array is configured for addressing the plurality of the coupling locations 51b without mechanical movement. It is also possible to determine the mode-field distribution at the coupling locations 51b by alternating the mode-field distribution in a manner that the coupling may be maximal or by adjusting the light 3 to an appropriate test light distribution, in particular a very small or large mode-field, or a mode-field that may be scanned along the facet 103 while the coupling of the light 3 may be monitored, such that the mode-field at the coupling locations 51b can be determined, especially by using a deconvolution. The micro-optical elements 20 may be further configured for enabling light propagating, preferably from every coupling location 14 to every coupling location 51. This can, particularly, be achieved by designing individual micro-optical elements 20 having a high NA in the drawing plane of FIG. 14A. In summary, by using the exemplary embodiment of the optical probe 1 according to FIG. 14A it is possible to probe a large number of coupling locations 14, in particular more than 100, having a small pitch, especially of 30 m or less, in a fast time, preferably within 100 ms or less per connection, by using a large working distance, especially of 30 m or more, under adjustment of the incident angle in the drawing plane of FIG. 14A. Alternatively or in addition, a plurality of mode-fields may be generated, in particular for allowing to probe components having a highly irregular pitch 28b or for using a single probe head 10 for probing various different micro-optical components 50.
[0116] FIG. 14B illustrates the further exemplary embodiment of the optical probe 1 in an observation projection direction along +x according to FIGS. 14A and 14B. Herein, each refractive surface 24 of the coupling locations 14 are elongated along the waveguide 25 in a manner that the light can be well-focused in the out-of-plane direction of FIG. 14B. Preferably, the each coupling location 14 is as high as a distance of the simultaneously emitting elements in FIGS. 14A and 14B, or such that each refractive surface 24 is at least capturing 50%, preferably 90% of an emission of the light distribution emitted by the coupling location 51 in an out-of-plane direction according to FIG. 14B.
[0117] FIG. 15 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical components 50, 50b, 50c. As schematically depicted in FIG. 15, the testing circuit 2 has a position sensitive device 14c. In combination with the refractive surface 24, the position sensitive device 14c can detect the tilt angle of a facet 103b, dashed line, and can distinguish the tilt angle of the facet 103b from a straight facet 103. This procedure can identify facets that are not perpendicular, which is a common fabrication deviation. The optical probe 1 is configured to detect the tilted facet 103b by detecting light propagating along a center ray 3d. For this purpose, the position sensitive device 14c may, preferably, be located in or close to a Fourier plane of the center ray 3d, which causes the center of the light distribution to be displaced on the position sensitive device 14c depending on an orientation of the tilted facet 103b. In an alternative embodiment (not depicted here), the position sensitive device 14c may be located in the image plane for imaging the coupling location 51.
[0118] FIG. 16 illustrates a method for producing the probe head 10. An objective lens 201 generates a laser beam 202 configured for curing a photoresist 200. As an alternative, the solubility of the photoresist 200 may be changed by the irradiation of the laser beam 202. By scanning the laser beam 202 in three dimensions, the structures 20b constituting a micro-optical element are produced. For aligning a further structure 20c constituting a further micro-optical element to the coupling location 14, light 15 may be coupled into the testing circuit 2. The light 15 is chosen in a manner that it may be transmitted by the waveguides 25. The lithography system 210 has a detector configured to detect the position of light 15 exciting the testing circuit 2 through coupling locations 14. The detector may be a CCD camera, or a confocal detector. Alternatively, the laser beam 202 may be coupled to the probe head 10 through the coupling locations 14 and is detected at the fiber core 13 or by a detector within the testing circuit 2 coupled to the probe head 10. As a further alternative, a feature within the testing circuit 2, especially the waveguide 25 or the marker 21 (not depicted here), may be used for the alignment. For this purpose, light of the laser beam 202 coupling into the waveguides 25 and being reflected at a feature within waveguide 25, such as the facet 104 or at the fiber core 13, may be detected.
[0119] FIG. 17 illustrates a further exemplary embodiment of the optical probe 1 configured for the optical testing of the micro-optical component 50. As schematically depicted in FIG. 17, the micro-optical element 20 has a mechanical support 8 configured for providing a certain distance, especially 5 m to 250 m, between the refractive surface 24 and the facet 102. Instead of using a mechanical support 8 in form of pillars, the micro-optical element 20 may also be attached to the fixture 4 for the testing circuit 2, in this case, the fixture 4 may, preferably, be arranged in a manner that it is not flush with the facet 102 but protrudes from the facet 102. The refractive surface 24b, here implemented as an optical lens, can reduce a divergence of then light 3 to avoid failure of total internal reflection at the region 9. Additionally, the angle 26 may exceed 90 to mitigate failure of the total internal reflection. Alternatively or in addition to the refractive surface 24b, the testing circuit 2 may have at least one optical 3D-printed element, preferably an on-chip mode-field converter, configured to reduce the divergence of the light 3, which is fabricated close to facet 102. This embodiment according to FIG. 17 may be favorable, if the divergent light 3e emitted or collected by the pitch at the facet 103b may be more divergent than light emitted by a standard single mode fiber, such as the single mode fiber 28.
[0120] FIG. 18 illustrates experimental results obtained in a mode-field diameter statistics of 250 micro-optical elements 20, which were implemented as optical lenses. Herein, a mode-field diameter w is normalized to a design mode field w.sub.0. A relative mode-field diameter of e.g. 1.04 would imply a mode-field that is 4% larger than designed, e.g. w=10.4 m instead of w0=10 m. Hereby, a standard deviation of 2% could be achieved.
[0121] FIG. 19 illustrates a further exemplary embodiment, in which the probe head 10 comprises a probe-card made out of a printed circuit board (PCB), a wafer, or a planar light wave circuit (PLC) comprising both electrical cantilevers 411 and electrical transmission line 412 as well as a micro-electrical mechanical system (MEMS) actuator 420 having an optical waveguide. Preferably, a hole or a via 401 may allow aligning the probe head 10 to the micro-optical component 50 by observing a fiducial 402. By using the probe card which comprises optical, electrical and mechanical functionalities, the electrical cantilever 411 can, in an initial contact step, be aligned with the electrical contact pad 410 of the wafer 60. After the contact step, the micro-optical element 20 can be aligned by using the MEMS actuator 420 to couple the light 3. In particular, the MEMS actuator 420 can move the micro-optical element 20 by at least 1 m, preferably by at least 10 m, especially by at least 25 m or more. In other embodiments, a plurality of cantilevers 411 and a plurality of micro-optical elements 20, in some embodiments at least 1000, may be present. The PLC may further comprise optical switches, optical splitters, or optical detectors. The PLC may be connected to the optical probe 1 either electrically or by using the fiber array 11. The optical probe 1 may, additionally, comprise the distance sensor 31, which is configured to measure the distance 32 between the distance sensor 31 and a surface of the wafer 60. The distance sensor 31 may, preferably be selected from at least one of an optical sensor or a capacitive sensor.
[0122] FIG. 20 illustrates a further exemplary embodiment, in which the probe head 10 is configured to test a functionality of a beam-shaping element 430, in particular an emission direction. For this purpose, the MEMS actuator 420 may be configured to provide at least one of a rotation or a translation of the micro-optical element 20. In this embodiment, the micro-optical element 20 is configured to redirect the light 3 to an angle that allows coupling it into the grating coupler 105. The reflecting surface 23 is also configured to redirect the light from the waveguide 25 towards the surface of the wafer 60.
LIST OF REFERENCE SIGNS
[0123] 1, 1b Optical probe [0124] 2 Testing circuit [0125] 3 Light coupled between testing circuit and micro-optical component [0126] 3b Light coupled between grating coupler and micro-optical component [0127] 3c Phase front of light coupled between testing circuit and micro-optical component [0128] 3d Beam path in case of facet [0129] 3e Divergent light emitted or collected by pitch at facet [0130] 4 Fixture for testing circuit [0131] 4b Part of fixture for testing circuit configured for mounting testing circuit at an angle compared to being directly mounted on the surface [0132] 4c Surface, being part of the fixture for testing circuit essentially vertical to the surface of wafer [0133] 5 Translation stage, typically 6 degrees of freedom [0134] 6 Mechanical support, carrier [0135] 7 Mechanical support for micro-optical component and wafer, chuck [0136] 8 Mechanical support, being part of micro-optical element [0137] 9 Region in which total internal reflection may fail without refractive surface reducing divergence of light coupled between testing circuit and micro-optical component [0138] 10 Probe head [0139] 11 Fiber array [0140] 12 Optical fiber [0141] 12b Optical fiber [0142] 13 Fiber core [0143] 14 Coupling location of testing circuit [0144] 14b Second coupling location of testing circuit [0145] 14c Position sensitive device, such as a PSD, CCD, CMOS or image sensor [0146] 15 Light coupled into probe head [0147] 16 Second probe head [0148] 18 Chamfer in testing circuit [0149] 19 Thinned, etched, milled or thin region in testing circuit [0150] 19b Resulting thickness of testing circuit after removal of thinned region in testing circuit [0151] 20 Micro-optical element [0152] 20b Micro-optical element just fabricated [0153] 20c Micro-optical element being fabricated [0154] 20d Micro-optical element being behind testing circuit from the observation direction [0155] 20e Single element of micro-optical element [0156] 21 (3D-printed) marker [0157] 23 Reflecting surface e.g. a total-internal reflection mirror [0158] 24 Refractive surface (optical lens) [0159] 24b Refractive surface reducing divergence of light coupled between testing circuit and micro-optical component [0160] 25 Optical waveguide, being part of testing circuit [0161] 25b Optical waveguide configured to preserve polarization, e.g. by being short, straight or birefringing or a combination thereof [0162] 25c Angled waveguide, not being normal to facet of testing circuit configured for attaching micro-optical element [0163] 25e Optical waveguide, being part of testing circuit [0164] 26, 26b Angle [0165] 27 Pitch of coupling location of testing circuit at facet of testing circuit [0166] 28 Pitch at facet of testing circuit which facet is configured for attaching micro-optical component [0167] 28b Pitch at facet of micro-optical component [0168] 29a Width of testing circuit, may extend over testing circuit or only extends over a region configured for being inserted in trench etched into wafer or cavity [0169] 29b Thickness of light coupled between testing circuit and micro-optical component, may extend over testing circuit or only extends over a region intended to be inserted in trench etched into wafer or a cavity [0170] 30 Electrical circuit [0171] 31 Distance sensor [0172] 32 Distance between distance sensor and surface of wafer [0173] 33 Top-view camera [0174] 34 Free working distance [0175] 35 Vacuum tool or permanent fixture [0176] 40 Polarization Splitter [0177] 41 Polarization channel TM [0178] 42 Polarization channel TE [0179] 50 Micro-optical component [0180] 50b,c Further micro-optical component, there may be thousands per wafer [0181] 51, 52 Coupling location of micro-optical component [0182] 51b Coupling location of micro-optical component being currently addressed [0183] 55 Trench etched into wafer [0184] 56 Functional element, being part of micro-optical component, e.g. waveguide, laser or photodiode [0185] 57 Bottom of deep etch [0186] 58 Waveguide, being part of micro-optical component [0187] 58b Angled waveguide not normal to tilted facet of micro-optical component [0188] 58c Waveguide being currently addressed by light coupled between testing circuit and micro-optical component, i.e. light currently coupled from waveguide to probe head, or vice versa [0189] 59 Functional element part of testing circuit, e.g. photodetector or light source [0190] 60 Wafer [0191] 102 Facet of testing circuit configured for attaching micro-optical element [0192] 103 Facet of micro-optical component [0193] 103b Tilted facet of micro-optical component [0194] 104 Facet of testing circuit which facet is configured for attaching micro-optical component [0195] 105 Grating coupler [0196] 110a Diameter of a micro-optical element, being smaller or equal than pitch of coupling location of testing circuit at facet of testing circuit [0197] 110b Diameter of a micro-optical element, being larger than pitch of coupling location of testing circuit at facet of testing circuit [0198] 111 Gap between micro-optical elements having diameter 110b [0199] 200 (Liquid) photoresist [0200] 201 Objective lens for fabrication of micro-optical elements [0201] 202 Laser beam of objective lens [0202] 210 Lithography system [0203] 401 Hole or via, configured to allow observing fiducial in arrow direction [0204] 402 Fiducial, part of micro-optical component [0205] 410 Electrical contact pad, part of micro-optical component [0206] 411 Electrical cantilever, part of probe head [0207] 412 Electrical transmission line, part of probe head [0208] 420 MEMS actuator comprising a waveguide, part of probe head [0209] 421 Movement direction of MEMS actuator [0210] 423 Direction of rotation provided by MEMS actuator [0211] 430 Beam-shaping element
[0212] While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.
